draft-ietf-dhc-dhcpv6-stateless-04.txt   rfc3736.txt 
Network Working Group R. Droms Network Working Group R. Droms
Internet-Draft Cisco Systems Request for Comments: 3736 Cisco Systems
Expires: July 13, 2004 January 13, 2004 Category: Standards Track April 2004
Stateless DHCP Service for IPv6 Stateless Dynamic Host Configuration Protocol (DHCP) Service for IPv6
draft-ietf-dhc-dhcpv6-stateless-04.txt
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract Abstract
Stateless DHCP service for IPv6 (DHCPv6) is used by nodes to obtain Stateless Dynamic Host Configuration Protocol service for IPv6
configuration information such as the addresses of DNS recursive name (DHCPv6) is used by nodes to obtain configuration information, such
servers that does not require the maintenance of any dynamic state as the addresses of DNS recursive name servers, that does not require
for individual clients. A node that uses stateless DHCP must have the maintenance of any dynamic state for individual clients. A node
obtained its IPv6 addresses through some other mechanism, typically that uses stateless DHCP must have obtained its IPv6 addresses
stateless address autoconfiguration. This document explains which through some other mechanism, typically stateless address
parts of RFC3315 must be implemented in each of the different kinds autoconfiguration. This document explains which parts of RFC 3315
of DHCP agents so that that agent can support stateless DHCP. must be implemented in each of the different kinds of DHCP agents so
that agent can support stateless DHCP.
1. Introduction 1. Introduction
Nodes that have obtained IPv6 addresses through some other mechanism Nodes that have obtained IPv6 addresses through some other mechanism,
such as stateless address autoconfiguration [6] or manual such as stateless address autoconfiguration [6] or manual
configuration can use stateless DHCP to obtain other configuration configuration, can use stateless DHCP to obtain other configuration
information such as a list of DNS recursive name servers or SIP information such as a list of DNS recursive name servers or SIP
servers. A stateless DHCP server provides only configuration servers. A stateless DHCP 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 any Such a server is called "stateless" because it need not maintain any
dynamic state for individual clients. dynamic state for individual clients.
While the DHCP specification [1] defines more than 10 protocol While the DHCP 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 options
are required for stateless DHCP service. This document explains which are required for stateless DHCP service. This document explains
messages and options defined in RFC 3315 are required for stateless which messages and options defined in RFC 3315 are required for
DHCP service. The intended use of the document is to guide the stateless DHCP service. The intended use of the document is to guide
interoperable implementation of clients and servers that use the interoperable implementation of clients and servers that use
stateless DHCP service. stateless DHCP service.
The operation of relay agents is the same for stateless and stateful The operation of relay agents is the same for stateless and stateful
DHCP service. The operation of relay agents is described in the DHCP DHCP service. The operation of relay agents is described in the DHCP
specification. specification.
Section 4 of this document lists the sections of the DHCP document Section 4 of this document lists the sections of the DHCP document
that an implementor should read for an overview of the DHCP that an implementor should read for an overview of the DHCP
specification and the basic requirements of a DHCP service. Section 5 specification and the basic requirements of a DHCP service. Section
lists the specific messages and options that are specifically 5 lists the specific messages and options that are specifically
required for stateless DHCP service. Section 6 describes how required for stateless DHCP service. Section 6 describes how
stateless and stateful DHCP servers interact to provide service to stateless and stateful DHCP servers interact to provide service to
clients that require address assignment and clients that require only clients that require address assignment and 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 DHCP This document uses the terminology defined in RFC2460 [2], the DHCP
specification [1] and the DHCP DNS configuration options 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 configuration
information to clients that does not require the server to maintain information to clients that does not require the 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 configuration This document assumes that a node using stateless DHCP configuration
is not using DHCP for address assignment, and that a node has is not using DHCP for address assignment, and that a node has
determined at least a link-local address as described in section 5.3 determined at least a link-local address as described in section 5.3
of RFC2461 [4]. 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 carry
configuration information such as a list of DNS recursive name configuration information, such as a list of DNS recursive name
servers [3] and SIP servers [5]. servers [3] and SIP servers [5].
This document does not apply to the function of DHCP relay agents as This document does not apply to the function of DHCP relay agents as
described in RFC 3315. A network element can provide both DHCP server described in RFC 3315. A network element can provide both DHCP
and DHCP relay service. For example, a network element can provide server and DHCP relay service. For example, a network element can
stateless DHCP service to hosts requesting stateless DHCP service, provide stateless DHCP service to hosts requesting stateless DHCP
while relaying messages from hosts requesting address assignment service, while relaying messages from hosts requesting address
through DHCP to another DHCP server. assignment through DHCP to another DHCP 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 to
all implementations: all implementations:
1-4: give an introduction to DHCP and an overview of DHCP message 1-4: give an introduction to DHCP and an overview of DHCP message
flows 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: illustrate 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 information
by sending an Information-request message that includes an Option by sending an Information-request message that includes an Option
Request option specifying the options that it wishes to receive from Request option specifying the options that it wishes to receive from
the DHCP server. For example, if the client is attempting to obtain the DHCP server. For example, if the client is attempting to obtain
skipping to change at page 4, line 13 skipping to change at page 3, line 48
would respond with DNS configuration parameters. would respond with DNS configuration parameters.
As described in section 18.1.5 of RFC 3315, a node may include a As described in section 18.1.5 of RFC 3315, a node may include a
Client Identifier option in the Information-request message to Client Identifier option in the Information-request message to
identify itself to a server, because the server administrator may identify itself to a server, because the server administrator may
want to customize the server's response to each node, based on the want to customize the server's response to each node, based on the
node's identity. node's identity.
RFC 3315 does not define any mechanisms through which the time at RFC 3315 does not define any mechanisms through which the time at
which a host uses an Information-request message to obtain updated which a host uses an Information-request message to obtain updated
configuration parameters can be controlled. The dhc WG has configuration parameters can be controlled. The DHC WG has
undertaken the development of such a mechanism or mechanisms which undertaken the development of such a mechanism or mechanisms which
will be published as Standards-track RFC(s). will be published as Standards-track RFC(s).
RFC 3315 also does not provide any guidance about when a host might RFC 3315 also does not provide any guidance about when a host might
use an Information-request message to obtain updated configuration use an Information-request message to obtain updated configuration
parameters when the host has moved to a new link. The dhc WG is parameters when the host has moved to a new link. The DHC WG is
reviewing a related document, "Detection of Network Attachment (DNA) reviewing a related document, "Detection of Network Attachment (DNA)
in IPv4" [8], which describes how a host using IPv4 can determine 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 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. 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 DHCP DHCP service; the section numbers in this list refer to the DHCP
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 list
refer to the DHCP specification: refer to the DHCP specification:
Relay-forward: Sent by a DHCP relay agent to carry the client message Relay-forward: sent by a DHCP relay agent to carry the client 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 to Relay-reply: sent by a DHCP server to carry a response message 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 DHCP DHCP service; the section numbers in this list refer to the DHCP
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 Server Identifier: used to identify the server responding to a client
request (section 22.3) 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 the
DHCP specification: DHCP 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 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 be used when
the client (section 22.18) forwarding a message to 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 configuration
information to clients; note that other options for configuration information to clients; note that other options for configuration
information may be specified in future Internet Standards: information may be specified in future Internet Standards:
DNS Recursive Name Servers: specifies the DNS recursive name servers DNS Recursive Name Servers: specifies the DNS recursive name servers
[7] the client uses for name resolution; see "DNS Configuration [7] the client uses for name resolution;
options for DHCPv6" [3] see "DNS Configuration options for
DHCPv6" [3]
DNS search list: specifies the domain names to be searched DNS search list: specifies the domain names to be searched
during name resolution; see "DNS Configuration options for DHCPv6" during name resolution; see "DNS
[3] Configuration options for DHCPv6" [3]
SIP Servers: specifies the SIP servers the client uses SIP Servers: specifies the SIP servers the client uses
to obtain a list of domain names of IPv6 addresses that can be to obtain a list of domain names of IPv6
mapped to one or more SIP outbound proxy servers [5] 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 stateless
DHCP service; the section numbers in this list refer to the DHCP DHCP service; the section numbers in this list refer to the DHCP
specification: 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 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 information User Class: sent by a DHCP client to give additional information
to the server for selecting configuration parameters for the to the server for selecting configuration parameters
client (section 22.15) 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 information
about the client vendor and hardware to the server for selecting 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 in
options defined by vendors (section 22.17) 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 (section
22.2). Clients are not required to send this option; servers send 22.2). Clients are not required to send this
the option back if included in a message from a client option; 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 stateless
address autoconfiguration and DHCP for DNS configuration and clients address autoconfiguration and DHCP for DNS configuration and clients
that are using DHCP for stateful address configuration. Depending on that are using DHCP for stateful address configuration. Depending on
the deployment and configuration of relay agents, DHCP servers that the deployment and configuration of relay agents, DHCP servers that
are intended only for stateless configuration may receive messages are intended only for stateless configuration may receive messages
from clients that are performing stateful address configuration. 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 any
stateful address configuration messages exchanges. If there are stateful address configuration message exchanges. If there are other
other DHCP servers that are configured to provide stateful address DHCP servers that are configured to provide stateful address
assignment, one of those servers will provide the address assignment. assignment, one of those servers will provide the address assignment.
7. Security Considerations 7. Security Considerations
Stateless DHCP service is a proper subset of the DHCP service Stateless DHCP service is a proper subset of the DHCP service
described in the DHCP specification, RFC 3315. Therefore, stateless described in the DHCP specification, RFC 3315 [1]. Therefore,
DHCP service introduces no additional security considerations beyond stateless DHCP service introduces no additional security
those discussed in sections 21, 22.11 and 23 of the DHCP considerations beyond those discussed in sections 21, 22.11, and 23
specification. of the DHCP specification [1].
Configuration information provided to a node through stateless DHCP Configuration information provided to a node through stateless DHCP
service may be used to mount spoofing, man-in-the-middle, service may be used to mount spoofing, man-in-the-middle, denial-of-
denial-of-service and other attacks. These attacks are described in service, and other attacks. These attacks are described in more
more detail in the specifications for each of the options that carry detail in the specifications for each of the options that carry
configuration information. Authenticated DHCP, as described in configuration information. Authenticated DHCP, as described in
sections 21 and 22.11 of the DHCP specification, can be used to avoid sections 21 and 22.11 of the DHCP specification [1], can be used to
attacks mounted through the stateless DHCP service. avoid attacks mounted through the stateless DHCP 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, Pekka Savola and Juha Chown, Christian Huitema, Tatuya Jinmei, Pekka Savola, and Juha
Wiljakka for their review and comments. Wiljakka for their review and comments.
Normative References 9. References
[1] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M. 9.1. Normative References
Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 3315, July 2003. [1] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, C. and
M. Carney, "Dynamic Host Configuration Protocol for IPv6
(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 (IPv6)
Specification", RFC 2460, December 1998. Specification", RFC 2460, December 1998.
Informative References 9.2. Informative References
[3] Droms, R., "DNS Configuration options for Dynamic Host [3] Droms, R., Ed., "DNS Configuration options for Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)", RFC 3646, December Configuration Protocol for IPv6 (DHCPv6)", RFC 3646, December
2003. 2003.
[4] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for [4] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for
IP Version 6 (IPv6)", RFC 2461, December 1998. 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
Protocol (DHCPv6) Options for Session Initiation Protocol (SIP) (DHCPv6) Options for Session Initiation Protocol (SIP) Servers",
Servers", RFC 3319, July 2003. 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", STD
13, RFC 1034, November 1987. 13, RFC 1034, November 1987.
[8] Aboba, B., "Detection of Network Attachment (DNA) in IPv4", [8] Aboba, B., "Detection of Network Attachment (DNA) in IPv4", Work
draft-ietf-dhc-dna-ipv4-04 (work in progress), October 2003. in Progress.
Author's Address 10. 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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