draft-ietf-dhc-dhcpv6-stateless-00.txt   draft-ietf-dhc-dhcpv6-stateless-01.txt 
Network Working Group R. Droms Network Working Group R. Droms
Internet-Draft Cisco Systems Internet-Draft Cisco Systems
Expires: October 5, 2003 April 6, 2003 Expires: April 5, 2004 October 6, 2003
A Guide to Implementing Stateless DHCPv6 Service A Guide to Implementing Stateless DHCPv6 Service
draft-ietf-dhc-dhcpv6-stateless-00.txt draft-ietf-dhc-dhcpv6-stateless-01.txt
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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 information such as the addresses of DNS recursive name servers that
that does not require the maintenance of any dynamic state for does not require the maintenance of any dynamic state for individual
individual clients. A node that uses stateless DHCP must have clients. A node that uses stateless DHCP must have obtained its IPv6
obtained its IPv6 addresses through some other mechanism, addresses through some other mechanism, typically stateless address
typically stateless address autoconfiguration. This document is a autoconfiguration. This document is a guide to the protocol messages
guide to the protocol messages and options that must be and options that must be implemented to provide stateless DHCPv6
implemented to provide stateless DHCPv6 service. 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 can use stateless DHCPv6 to obtain other configuration such as stateless address autoconfiguration [6] or manual
information such as a list of DNS recursive name servers or NTP configuration can use stateless DHCPv6 to obtain other configuration
information such as a list of DNS recursive name servers or SIP
servers. A stateless DHCPv6 server provides only configuration servers. A stateless DHCPv6 server provides only configuration
information to nodes and does not perform any address assignment. information to nodes and does not perform any address assignment.
Such a server is called "stateless" because it need not maintain Such a server is called "stateless" because it need not maintain any
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 messages and 20 options, only a subset of those messages and options
options are required for stateless DHCPv6 service. This document are required for stateless DHCPv6 service. This document gives
gives guidelines about which messages and options are required for 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 The operation of relay agents is the same for stateless and stateful
stateful DHCPv6 service. The operation of relay agents is DHCPv6 service. The operation of relay agents is described in the
described in the DHCPv6 specification. DHCPv6 specification.
Section 4 of this document lists the sections of the DHCPv6 Section 4 of this document lists the sections of the DHCPv6 document
document that an implementor should read for an overview of the that an implementor should read for an overview of the DHCPv6
DHCPv6 specification and the basic requirements of a DHCPv6 specification and the basic requirements of a DHCPv6 service. Section
service. Section 5 lists the specific messages and options that 5 lists the specific messages and options that are specifically
are specifically required for stateless DHCPv6 service. Section 6 required for stateless DHCPv6 service. Section 6 describes how
describes how stateless and stateful DHCPv6 servers interact to stateless and stateful DHCPv6 servers interact to provide service to
provide service to clients that require address assignment and clients that require address assignment and clients that require only
clients that require only stateless service. 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 This document uses the terminology defined in RFC2460 [2], the DHCP
DHCP specification, the DHCP DNS configuration options specification [1] and the DHCP DNS configuration options
specification [3] and the DHCP NTP configuration options specification [3].
specification [4].
"Stateless DHCP" refers to the use of DHCP to provide "Stateless DHCP" refers to the use of DHCP to provide configuration
configuration information to clients that does not require the information to clients that does not require the server to maintain
server to maintain dynamic state about the DHCP clients. dynamic state about the DHCP clients.
3. Overview 3. Overview
This document assumes that a node using stateless DHCP This document assumes that a node using stateless DHCP configuration
configuration is not using DHCP for address assignment, and that a is not using DHCP for address assignment, and that a node has
node has determined at least a link-local address as described in determined at least a link-local address as described in section 5.3
section 5.3 of RFC2461 [5] of RFC2461 [5]
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 uses the DHCP Information-request message. DHCP servers respond to
to the node's message with a Reply message that carries the DNS the node's message with a Reply message that carries the DNS
configuration parameters. The Reply message from the server can configuration parameters. The Reply message from the server can
carry configuration information such as a list of DNS recursive carry configuration information such as a list of DNS recursive name
name servers and NTP servers. servers and SIP servers.
4. Basic Requirements for Implementation of DHCP 4. Basic Requirements for Implementation of DHCP
Several sections of the DHCP specification [1] provide background Several sections of the DHCP specification provide background
information or define parts of the specification that are common information or define parts of the specification that are common to
to all implementations: all implementations:
1-4: give an introduction to DHCPv6 and an overview of DHCP 1-4: give an introduction to DHCPv6 and an overview of DHCP message
message flows flows
5: defines constants used throughout the protocol 5: defines constants used throughout the protocol specification
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) optionally used 9: defines the "DHCP unique identifier" (DUID) optionally used to
to identify DHCP participants identify DHCP participants
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 The client indicates that it is requesting configuration information
information by sending an Information-request message that by sending an Information-request message that includes an Option
includes an Option Request option specifying the options that it Request option specifying the options that it wishes to receive from
wishes to receive from the DHCP server. For example, if the the DHCP server. For example, if the client is attempting to obtain
client is attempting to obtain DNS configuration information, it DNS configuration information, it includes either or both of the DNS
includes either or both of the DNS configuration options in the configuration options in the Information-request message. The server
Information-request message. The server determines the determines the appropriate configuration parameters for the client
appropriate configuration parameters for the client based on its based on its configuration policies and responds with a Reply message
configuration policies and responds with a Reply message
containing the requested parameters. In this example, the server containing the requested parameters. In this example, the server
would respond with DNS configuration parameters. would respond with DNS configuration parameters.
A node uses the DUID option to identify itself to a server, A node uses the Client Identifier option to identify itself to a
because the server administrator may want to customize the server, because the server administrator may want to customize the
server's response to each node, based on the node's identity. server's response to each node, based on the node's identity.
5.1 Messages required for stateless DHCP 5.1 Messages required for stateless DHCP
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 DNS
DNS 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 the
the DNS configuration parameters (sections 18.2.6 and 18.2.8) DNS 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: messages for stateless DHCP service:
Relay-forward: Sent by a DHCP relay agent to carry the client Relay-forward: Sent by a DHCP relay agent to carry the client message
message to a server (section 15.13) to a server (section 15.13)
Relay-reply: Sent by a DHCP server to carry a response message Relay-reply: Sent by a DHCP server to carry a response message to
to the relay agent (section 15.14) 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 the
client is requesting from the server (section 22.7) 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 status
information (section 22.13) information (section 22.13)
Server Identifier: used to identify the server responding to a 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 stateless DHCP service; the section numbers in this list refer to the
the DHCPv6 specification: DHCPv6 specification:
Client message: Sent by a DHCP relay agent in a Relay-forward Client message: Sent by a DHCP relay agent in a Relay-forward message
message to carry the client message to a server (section 20) 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 Clients and servers use the following options to pass configuration
configuration information to clients: information to clients; note that other options for configuration
information may be specified in future Internet Standards:
DNS Recursive Name Servers: specifies the DNS recursive name DNS Recursive Name Servers: specifies the DNS recursive name servers
servers [6] the client uses for name resolution; see "DNS [7] the client uses for name resolution; see "DNS Configuration
Configuration options for DHCPv6" options for DHCPv6" [3]
DNS search list: specifies the domain names to be DNS search list: specifies the domain names to be searched
searched during name resolution; see "DNS Configuration options during name resolution; see "DNS Configuration options for DHCPv6"
for DHCPv6" [3]
NTP Servers: specifies the NTP servers the client SIP Servers: specifies the SIP servers the client uses
uses for synchronizing its clock; see "Time Configuration to obtain a list of domain names of IPv6 addresses that can be
Options for DHCPv6" mapped to one or more SIP outbound proxy servers [4]
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 Clients and servers may implement the following options for stateless
stateless DHCP service; the section numbers in this list refer to DHCP service; the section numbers in this list refer to the DHCPv6
the DHCPv6 specification [1]: specification, RFC 3315>:
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 Elapsed time: Sent by a DHCP client to indicate the time since the
the client began the DHCP configuration process (section 22.9) client began the DHCP configuration process (section 22.9)
User Class: Sent by a DHCP client to give additional User Class: Sent by a DHCP client to give additional information
information to the server for selecting configuration to the server for selecting configuration parameters for the
parameters for the client (section 22.15) client (section 22.15)
Vendor Class: Sent by a DHCP client to give additional Vendor Class: Sent by a DHCP client to give additional information
information about the client vendor and hardware to the server about the client vendor and hardware to the server for selecting
for selecting configuration parameters for the client (section configuration parameters for the client (section 22.16)
22.16)
Vendor-specific Information: Sent by a DHCP server to pass Vendor-specific Information: Used to pass information to clients in
information to clients in options defined by vendors (section options defined by vendors (section 22.17)
22.17) Client Identifier: Sent by a DHCP client to identify itself (section
Client DUID: Sent by a DHCP client to identify itself (section 22.2). Clients are not required to send this option; servers send
22.2). Clients are not required to send this option; servers the option back if included in a message fro ma client
never send this option
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 In some networks, there may be both clients that are using stateless
stateless address autoconfiguration [7] and DHCP for DNS address autoconfiguration and DHCP for DNS configuration and clients
configuration and clients that are using DHCP for stateful address that are using DHCP for stateful address configuration. Depending on
configuration. Depending on the deployment and configuration of the deployment and configuration of relay agents, DHCP servers that
relay agents, DHCP servers that are intended only for stateless are intended only for stateless configuration may receive messages
configuration may receive messages from clients that are from clients that are performing stateful address configuration.
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 Relay-forward it receives, and the server does not participate in any
any stateful address configuration messages exchanges. If there stateful address configuration messages exchanges. If there are
are other DHCP servers that are configured to provide stateful other DHCP servers that are configured to provide stateful address
address assignment, one of those servers will provide the address assignment, one of those servers will provide the address assignment.
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 [1]. Therefore, stateless described in the DHCPv6 specification, RFC 3315. Therefore, stateless
DHCPv6 service introduces no additional security considerations DHCPv6 service introduces no additional security considerations
beyond those discussed in sections 21, 22.11 and 23 of the DHCPv6 beyond those discussed in sections 21, 22.11 and 23 of the DHCPv6
specification. specification.
Configuration information provided to a node through stateless Configuration information provided to a node through stateless DHCPv6
DHCPv6 service may be used to mount spoofing, man-in-the-middle, service may be used to mount spoofing, man-in-the-middle,
denial-of-service and other attacks. These attacks are described denial-of-service and other attacks. These attacks are described in
in more detail in the specifications for each of the options that more detail in the specifications for each of the options that carry
carry configuration information. Authenticated DHCPv6, as configuration information. Authenticated DHCPv6, as described in
described in sections 21 and 22.11 of the DHCPv6 specification, sections 21 and 22.11 of the DHCPv6 specification, can be used to
can be used to avoid attacks mounted through the stateless DHCPv6 avoid attacks mounted through the stateless DHCPv6 service.
service.
Usually, a node using stateless DHCPv6 service will have
configured its interfaces with IPv6 addresses through stateless
address autoconfiguration. A node that has configured an
appropriate IPv6 address can use IPsec [8] to authenticate and
secure DHCPv6 messages exchanged between the node and the DHCPv6
server.
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 Pekka Savola and contributed editorial suggestions. Thanks to Peter Barany, Christian
Christian Huitema for their review and comments. Huitema and Pekka Savola for their review and comments.
Normative References Normative References
[1] Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and [1] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M.
R. Droms (ed.), "Dynamic Host Configuration Protocol for IPv6 Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
(DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress), RFC 3315, July 2003.
October 2002.
[2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
(IPv6) Specification", RFC 2460, December 1998. Specification", RFC 2460, December 1998.
[3] Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and [3] Droms, R., "DNS Configuration Options for DHCPv6",
R. Droms, "DNS Configuration options for DHCPv6", draft-ietf- draft-ietf-dhc-dhcpv6-opt-dnsconfig-04 (work in progress),
dhc-dhcpv6-opt-dnsconfig-01 (work in progress), October 2002. August 2003.
[4] Vijayabhaskar, A., "Time Configuration Options for DHCPv6", [4] Schulzrinne, H. and B. Volz, "Dynamic Host Configuration
draft-ietf-dhc-dhcpv6-opt-timeconfig-00 (work in progress), Protocol (DHCPv6) Options for Session Initiation Protocol (SIP)
February 2002. Servers", RFC 3319, July 2003.
Informative References Informative References
[5] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery [5] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for
for IP Version 6 (IPv6)", RFC 2461, December 1998. IP Version 6 (IPv6)", RFC 2461, December 1998.
[6] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[7] 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.
[8] Kent, S. and R. Atkinson, "Security Architecture for the [7] Mockapetris, P., "Domain names - concepts and facilities", STD
Internet Protocol", RFC 2401, November 1998. 13, RFC 1034, November 1987.
Author's Address Author's Address
Ralph Droms Ralph Droms
Cisco Systems Cisco Systems
300 Apollo Drive 1414 Massachusetts Avenue
Chelmsford, MA 01824 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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