draft-ietf-dhc-dhcpv6-stateless-02.txt   draft-ietf-dhc-dhcpv6-stateless-03.txt 
Network Working Group R. Droms Network Working Group R. Droms
Internet-Draft Cisco Systems Internet-Draft Cisco Systems
Expires: May 25, 2004 November 25, 2003 Expires: June 20, 2004 December 21, 2003
A Guide to Implementing Stateless DHCPv6 Service A Guide to Implementing Stateless DHCPv6 Service
draft-ietf-dhc-dhcpv6-stateless-02.txt draft-ietf-dhc-dhcpv6-stateless-03.txt
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
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Abstract Abstract
Stateless DHCPv6 service is used by nodes to obtain configuration Stateless DHCPv6 service is used by nodes to obtain configuration
information such as the addresses of DNS recursive name servers that information such as the addresses of DNS recursive name servers
does not require the maintenance of any dynamic state for individual that does not require the maintenance of any dynamic state for
clients. A node that uses stateless DHCP must have obtained its IPv6 individual clients. A node that uses stateless DHCP must have
addresses through some other mechanism, typically stateless address obtained its IPv6 addresses through some other mechanism,
autoconfiguration. This document is a guide to the protocol messages typically stateless address autoconfiguration. This document is a
and options that must be implemented to provide stateless DHCPv6 guide to the protocol messages and options that must be
service. implemented to provide stateless DHCPv6 service.
1. Introduction 1. Introduction
Nodes that have obtained IPv6 addresses through some other
Nodes that have obtained IPv6 addresses through some other mechanism mechanism such as stateless address autoconfiguration [6] or
such as stateless address autoconfiguration [6] or manual manual configuration can use stateless DHCPv6 to obtain other
configuration can use stateless DHCPv6 to obtain other configuration configuration information such as a list of DNS recursive name
information such as a list of DNS recursive name servers or SIP servers or SIP servers. A stateless DHCPv6 server provides only
servers. A stateless DHCPv6 server provides only configuration configuration information to nodes and does not perform any
information to nodes and does not perform any address assignment. address assignment. Such a server is called "stateless" because
Such a server is called "stateless" because it need not maintain any it need not maintain any dynamic state for individual clients.
dynamic state for individual clients.
While the DHCPv6 specification [1] defines more than 10 protocol While the DHCPv6 specification [1] defines more than 10 protocol
messages and 20 options, only a subset of those messages and options messages and 20 options, only a subset of those messages and
are required for stateless DHCPv6 service. This document gives options are required for stateless DHCPv6 service. This document
guidelines about which messages and options are required for gives guidelines about which messages and options are required for
stateless DHCPv6 service. The intended use of the document is to stateless DHCPv6 service. The intended use of the document is to
guide the efficient and complete implementation of clients and guide the efficient and complete implementation of clients and
servers that use stateless DHCPv6 service. servers that use stateless DHCPv6 service.
The operation of relay agents is the same for stateless and stateful The operation of relay agents is the same for stateless and
DHCPv6 service. The operation of relay agents is described in the stateful DHCPv6 service. The operation of relay agents is
DHCPv6 specification. described in the DHCPv6 specification.
Section 4 of this document lists the sections of the DHCPv6 document Section 4 of this document lists the sections of the DHCPv6
that an implementor should read for an overview of the DHCPv6 document that an implementor should read for an overview of the
specification and the basic requirements of a DHCPv6 service. Section DHCPv6 specification and the basic requirements of a DHCPv6
5 lists the specific messages and options that are specifically service. Section 5 lists the specific messages and options that
required for stateless DHCPv6 service. Section 6 describes how are specifically required for stateless DHCPv6 service. Section 6
stateless and stateful DHCPv6 servers interact to provide service to describes how stateless and stateful DHCPv6 servers interact to
clients that require address assignment and clients that require only provide service to clients that require address assignment and
stateless service. clients that require only stateless service.
2. Terminology 2. Terminology
Throughout this document, "DHCP" refers to DHCP for IPv6. Throughout this document, "DHCP" refers to DHCP for IPv6.
This document uses the terminology defined in RFC2460 [2], the DHCP This document uses the terminology defined in RFC2460 [2], the
specification [1] and the DHCP DNS configuration options DHCP specification [1] and the DHCP DNS configuration options
specification [3]. specification [3].
"Stateless DHCP" refers to the use of DHCP to provide configuration "Stateless DHCP" refers to the use of DHCP to provide
information to clients that does not require the server to maintain configuration information to clients that does not require the
dynamic state about the DHCP clients. server to maintain dynamic state about the DHCP clients.
3. Overview 3. Overview
This document assumes that a node using stateless DHCP configuration This document assumes that a node using stateless DHCP
is not using DHCP for address assignment, and that a node has configuration is not using DHCP for address assignment, and that a
determined at least a link-local address as described in section 5.3 node has determined at least a link-local address as described in
of RFC2461 [4] section 5.3 of RFC2461 [4].
To obtain configuration parameters through stateless DHCP, a node To obtain configuration parameters through stateless DHCP, a node
uses the DHCP Information-request message. DHCP servers respond to uses the DHCP Information-request message. DHCP servers respond to
the node's message with a Reply message that carries configuration the node's message with a Reply message that carries configuration
parameters for the node. The Reply message from the server can carry parameters for the node. The Reply message from the server can
configuration information such as a list of DNS recursive name carry configuration information such as a list of DNS recursive
servers [3] and SIP servers [5]. name servers [3] and SIP servers [5].
This document does not apply to the function of DHCPv6 relay agents This document does not apply to the function of DHCPv6 relay
as described in RFC 3315. A network element can provide both DHCPv6 agents as described in RFC 3315. A network element can provide
server and DHCPv6 relay service. For example, a network element can both DHCPv6 server and DHCPv6 relay service. For example, a
provide stateless DHCPv6 service to hosts requesting stateless DHCP network element can provide stateless DHCPv6 service to hosts
service, while relaying messages from hosts requesting address requesting stateless DHCP service, while relaying messages from
assignment through DHCPv6 to another DHCPv6 server. hosts requesting address assignment through DHCPv6 to another
DHCPv6 server.
4. Basic Requirements for Implementation of DHCP 4. Basic Requirements for Implementation of DHCP
Several sections of the DHCP specification provide background Several sections of the DHCP specification provide background
information or define parts of the specification that are common to information or define parts of the specification that are common
all implementations: to all implementations:
1-4: give an introduction to DHCPv6 and an overview of DHCP message 1-4: give an introduction to DHCPv6 and an overview of DHCP
flows message flows
5: defines constants used throughout the protocol specification 5: defines constants used throughout the protocol
specification
6, 7: illustrates the format of DHCP messages 6, 7: illustrates the format of DHCP messages
8: describes the representation of Domain Names 8: describes the representation of Domain Names
9: defines the "DHCP unique identifier" (DUID) 9: defines the "DHCP unique identifier" (DUID)
13-16: describe DHCP message transmission, retransmission and 13-16: describe DHCP message transmission, retransmission and
validation validation
21: describes authentication for DHCP 21: describes authentication for DHCP
5. Implementation of Stateless DHCP 5. Implementation of Stateless DHCP
The client indicates that it is requesting configuration information The client indicates that it is requesting configuration
by sending an Information-request message that includes an Option information by sending an Information-request message that
Request option specifying the options that it wishes to receive from includes an Option Request option specifying the options that it
the DHCP server. For example, if the client is attempting to obtain wishes to receive from the DHCP server. For example, if the
a list of DNS recursive name servers, it identifier the DNS Recursive client is attempting to obtain a list of DNS recursive name
Name Server option in the Information-request message. The server servers, it identifies the DNS Recursive Name Server option in the
determines the appropriate configuration parameters for the client Information-request message. The server determines the appropriate
based on its configuration policies and responds with a Reply message configuration parameters for the client based on its configuration
containing the requested parameters. In this example, the server policies and responds with a Reply message containing the
would respond with DNS configuration parameters. requested parameters. In this example, the server would respond
with DNS configuration parameters.
A node uses the Client Identifier option to identify itself to a
server, because the server administrator may want to customize the
server's response to each node, based on the node's identity.
Whenever a client may have moved to a new link, the configuration
parameters obtained for the interfaces on that link may no longer be
appropriate for the link to which the client is attached. Examples
of times when a client may have moved to a new link include:
o The client reboots.
o The client is physically connected to a wired connection.
o The client returns from sleep mode. As described in section 18.1.5 of RFC 3315, a node may include a
Client Identifier option in the Information-request message to
identify itself to a server, because the server administrator may
want to customize the server's response to each node, based on the
node's identity.
o The client using a wireless technology changes access points. RFC 3315 does not define any mechanisms through which the time at
which a host uses an Information-request message to obtain updated
configuration parameters can be controlled. The dhc WG has
undertaken the development of such a mechanism or mechanisms which
will be published as Standards-track RFC(s).
In any situation when a client may have moved to a new link, the RFC 3315 also does not provide any guidance about when a host
client initiates an Information-request/Reply message exchange. might use an Information-request message to obtain updated
configuration parameters when the host has moved to a new link.
The dhc WG is reviewing a related document, "Detection of Network
Attachment (DNA) in IPv4" [8], which describes how a host using
IPv4 can determine when to use DHCPv4. Either the dhc WG or a WG
formed from the dna BOF will undertake development of a similar
document for IPv6.
5.1 Messages Required for Stateless DHCP Service 5.1 Messages Required for Stateless DHCP Service
Clients and servers implement the following messages for stateless Clients and servers implement the following messages for stateless
DHCP service; the section numbers in this list refer to the DHCPv6 DHCP service; the section numbers in this list refer to the DHCPv6
specification: specification:
Information-request: sent by a DHCP client to a server to request Information-request: sent by a DHCP client to a server to request
configuration parameters (sections 18.1.5 and 18.2.5) configuration parameters (sections 18.1.5 and 18.2.5)
Reply: sent by a DHCP server to a client containing Reply: sent by a DHCP server to a client containing
configuration parameters (sections 18.2.6 and 18.2.8) configuration parameters (sections 18.2.6 and 18.2.8)
In addition, servers and relay agents implement the following In addition, servers and relay agents implement the following
messages for stateless DHCP service; the section numbers in this list messages for stateless DHCP service; the section numbers in this
refer to the DHCPv6 specification: list refer to the DHCPv6 specification:
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 Relay-forward: Sent by a DHCP relay agent to carry the client
the relay agent (section 15.14) 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 5.2 Options Required for Stateless DHCP Service
Clients and servers implement the following options for stateless Clients and servers implement the following options for stateless
DHCP service; the section numbers in this list refer to the DHCPv6 DHCP service; the section numbers in this list refer to the DHCPv6
specification: specification:
Option Request: specifies the configuration information that the Option Request: specifies the configuration information that
client is requesting from the server (section 22.7) the client is requesting from the server (section 22.7)
Status Code: used to indicate completion status or other status Status Code: used to indicate completion status or other
information (section 22.13) status information (section 22.13)
Server Identifier: used to identify the server responding to a client Server Identifier: used to identify the server responding to a
request (section 22.3) client request (section 22.3)
Servers and relay agents implement the following options for Servers and relay agents implement the following options for
stateless DHCP service; the section numbers in this list refer to the stateless DHCP service; the section numbers in this list refer to
DHCPv6 specification: the DHCPv6 specification:
Client message: Sent by a DHCP relay agent in a Relay-forward message Client message: Sent by a DHCP relay agent in a Relay-forward
to carry the client message to a server (section 20) message to carry the client message to a server (section 20)
Server message: Sent by a DHCP server in a Relay-reply message to Server message: Sent by a DHCP server in a Relay-reply message to
carry a response message to the relay agent (section 20) carry a response message to the relay agent (section 20)
Interface-ID: Sent by the DHCP relay agent and returned by the Interface-ID: Sent by the DHCP relay agent and returned by the
server to identify the interface to use to forward a message to server to identify the interface to use to forward a message to
the client (section 22.18) the client (section 22.18)
5.3 Options Used for Configuration Information 5.3 Options Used for Configuration Information
Clients and servers use the following options to pass configuration Clients and servers use the following options to pass
information to clients; note that other options for configuration configuration information to clients; note that other options for
information may be specified in future Internet Standards: configuration information may be specified in future Internet
Standards:
DNS Recursive Name Servers: specifies the DNS recursive name servers
[7] the client uses for name resolution; see "DNS Configuration
options for DHCPv6" [3]
DNS search list: specifies the domain names to be searched DNS Recursive Name Servers: specifies the DNS recursive name
during name resolution; see "DNS Configuration options for DHCPv6" servers [7] the client uses for name resolution; see "DNS
[3] Configuration options for DHCPv6" [3]
SIP Servers: specifies the SIP servers the client uses DNS search list: specifies the domain names to be
to obtain a list of domain names of IPv6 addresses that can be searched during name resolution; see "DNS Configuration options
mapped to one or more SIP outbound proxy servers [5] for DHCPv6" [3]
SIP Servers: specifies the SIP servers the client
uses to obtain a list of domain names of IPv6 addresses that
can be mapped to one or more SIP outbound proxy servers [5]
5.4 Other Options Used in Stateless DHCP 5.4 Other Options Used in Stateless DHCP
Clients and servers may implement the following options for stateless Clients and servers may implement the following options for
DHCP service; the section numbers in this list refer to the DHCPv6 stateless DHCP service; the section numbers in this list refer to
specification: the DHCPv6 specification:
Preference: Sent by a DHCP server to indicate the preference Preference: Sent by a DHCP server to indicate the preference
level for the server (section 22.8) level for the server (section 22.8)
Elapsed time: Sent by a DHCP client to indicate the time since the Elapsed time: Sent by a DHCP client to indicate the time since
client began the DHCP configuration process (section 22.9) the client began the DHCP configuration process (section 22.9)
User Class: Sent by a DHCP client to give additional information User Class: Sent by a DHCP client to give additional
to the server for selecting configuration parameters for the information to the server for selecting configuration
client (section 22.15) parameters for the client (section 22.15)
Vendor Class: Sent by a DHCP client to give additional information Vendor Class: Sent by a DHCP client to give additional
about the client vendor and hardware to the server for selecting information about the client vendor and hardware to the server
configuration parameters for the client (section 22.16) for selecting configuration parameters for the client (section
22.16)
Vendor-specific Information: Used to pass information to clients in Vendor-specific Information: Used to pass information to clients
options defined by vendors (section 22.17) in options defined by vendors (section 22.17)
Client Identifier: Sent by a DHCP client to identify itself (section Client Identifier: Sent by a DHCP client to identify itself
22.2). Clients are not required to send this option; servers send (section 22.2). Clients are not required to send this option;
the option back if included in a message from a client servers send the option back if included in a message from a
client
Authentication: Used to provide authentication of DHCP messages Authentication: Used to provide authentication of DHCP messages
(section 21) (section 21)
6. Interaction with DHCP for Address Assignment 6. Interaction with DHCP for Address Assignment
In some networks, there may be both clients that are using stateless In some networks, there may be both clients that are using
address autoconfiguration and DHCP for DNS configuration and clients stateless address autoconfiguration and DHCP for DNS configuration
that are using DHCP for stateful address configuration. Depending on and clients that are using DHCP for stateful address
the deployment and configuration of relay agents, DHCP servers that configuration. Depending on the deployment and configuration of
are intended only for stateless configuration may receive messages relay agents, DHCP servers that are intended only for stateless
from clients that are performing stateful address configuration. configuration may receive messages from clients that are
performing stateful address configuration.
A DHCP server that is only able to provide stateless configuration A DHCP server that is only able to provide stateless configuration
information through an Information-request/Reply message exchange information through an Information-request/Reply message exchange
discards any other DHCP messages it receives. Specifically, the discards any other DHCP messages it receives. Specifically, the
server discards any messages other than Information-Request or server discards any messages other than Information-Request or
Relay-forward it receives, and the server does not participate in any Relay-forward it receives, and the server does not participate in
stateful address configuration messages exchanges. If there are any stateful address configuration messages exchanges. If there
other DHCP servers that are configured to provide stateful address are other DHCP servers that are configured to provide stateful
assignment, one of those servers will provide the address assignment. address assignment, one of those servers will provide the address
assignment.
7. Security Considerations 7. Security Considerations
Stateless DHCPv6 service is a proper subset of the DHCPv6 service Stateless DHCPv6 service is a proper subset of the DHCPv6 service
described in the DHCPv6 specification, RFC 3315. Therefore, stateless described in the DHCPv6 specification, RFC 3315. Therefore,
DHCPv6 service introduces no additional security considerations stateless DHCPv6 service introduces no additional security
beyond those discussed in sections 21, 22.11 and 23 of the DHCPv6 considerations beyond those discussed in sections 21, 22.11 and 23
specification. of the DHCPv6 specification.
Configuration information provided to a node through stateless DHCPv6 Configuration information provided to a node through stateless
service may be used to mount spoofing, man-in-the-middle, DHCPv6 service may be used to mount spoofing, man-in-the-middle,
denial-of-service and other attacks. These attacks are described in denial-of-service and other attacks. These attacks are described
more detail in the specifications for each of the options that carry in more detail in the specifications for each of the options that
configuration information. Authenticated DHCPv6, as described in carry configuration information. Authenticated DHCPv6, as
sections 21 and 22.11 of the DHCPv6 specification, can be used to described in sections 21 and 22.11 of the DHCPv6 specification,
avoid attacks mounted through the stateless DHCPv6 service. can be used to avoid attacks mounted through the stateless DHCPv6
service.
8. Acknowledgments 8. Acknowledgments
Jim Bound, Ted Lemon and Bernie Volz reviewed this document and Jim Bound, Ted Lemon and Bernie Volz reviewed this document and
contributed editorial suggestions. Thanks to Peter Barany, Tim contributed editorial suggestions. Thanks to Peter Barany, Tim
Chown, Christian Huitema, Tatuya Jinmei, Ted Lemon, Pekka Savola and Chown, Christian Huitema, Tatuya Jinmei, Ted Lemon, Pekka Savola
Juha Wiljakka for their review and comments. and Juha Wiljakka for their review and comments.
Normative References Normative References
[1] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M. [1] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M.
Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", Carney, "Dynamic Host Configuration Protocol for IPv6
RFC 3315, July 2003. (DHCPv6)", RFC 3315, July 2003.
[2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6
Specification", RFC 2460, December 1998. (IPv6) Specification", RFC 2460, December 1998.
Informative References Informative References
[3] Droms, R., "DNS Configuration Options for DHCPv6", [3] Droms, R., "DNS Configuration options for Dynamic Host
draft-ietf-dhc-dhcpv6-opt-dnsconfig-04 (work in progress), Configuration Protocol for IPv6 (DHCPv6)", RFC 3646, December
August 2003. 2003.
[4] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for [4] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
IP Version 6 (IPv6)", RFC 2461, December 1998. for IP Version 6 (IPv6)", RFC 2461, December 1998.
[5] Schulzrinne, H. and B. Volz, "Dynamic Host Configuration [5] Schulzrinne, H. and B. Volz, "Dynamic Host Configuration
Protocol (DHCPv6) Options for Session Initiation Protocol (SIP) Protocol (DHCPv6) Options for Session Initiation Protocol
Servers", RFC 3319, July 2003. (SIP) Servers", RFC 3319, July 2003.
[6] Thomson, S. and T. Narten, "IPv6 Stateless Address [6] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998. Autoconfiguration", RFC 2462, December 1998.
[7] Mockapetris, P., "Domain names - concepts and facilities", STD [7] Mockapetris, P., "Domain names - concepts and facilities",
13, RFC 1034, November 1987. STD 13, RFC 1034, November 1987.
[8] Aboba, B., "Detection of Network Attachment (DNA) in IPv4",
draft-ietf-dhc-dna-ipv4-04 (work in progress), October 2003.
Author's Address Author's Address
Ralph Droms Ralph Droms
Cisco Systems Cisco Systems
1414 Massachusetts Avenue 1414 Massachusetts Avenue
Boxborough, MA 01719 Boxborough, MA 01719
USA USA
Phone: +1 978 497 4733 Phone: +1 978 497 4733
EMail: rdroms@cisco.com EMail: rdroms@cisco.com
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