draft-ietf-dhc-dhcpv6-stateless-03.txt   draft-ietf-dhc-dhcpv6-stateless-04.txt 
Network Working Group R. Droms Network Working Group R. Droms
Internet-Draft Cisco Systems Internet-Draft Cisco Systems
Expires: June 20, 2004 December 21, 2003 Expires: July 13, 2004 January 13, 2004
A Guide to Implementing Stateless DHCPv6 Service Stateless DHCP Service for IPv6
draft-ietf-dhc-dhcpv6-stateless-03.txt draft-ietf-dhc-dhcpv6-stateless-04.txt
Status of this Memo Status of this Memo
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Abstract Abstract
Stateless DHCPv6 service is used by nodes to obtain configuration Stateless DHCP service for IPv6 (DHCPv6) is used by nodes to obtain
information such as the addresses of DNS recursive name servers configuration information such as the addresses of DNS recursive name
that does not require the maintenance of any dynamic state for servers that does not require the maintenance of any dynamic state
individual clients. A node that uses stateless DHCP must have for individual clients. A node that uses stateless DHCP must have
obtained its IPv6 addresses through some other mechanism, obtained its IPv6 addresses through some other mechanism, typically
typically stateless address autoconfiguration. This document is a stateless address autoconfiguration. This document explains which
guide to the protocol messages and options that must be parts of RFC3315 must be implemented in each of the different kinds
implemented to provide stateless DHCPv6 service. of DHCP agents so that that agent can support stateless DHCP.
1. Introduction 1. Introduction
Nodes that have obtained IPv6 addresses through some other
mechanism such as stateless address autoconfiguration [6] or
manual 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 information to nodes 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 [1] defines more than 10 protocol Nodes that have obtained IPv6 addresses through some other mechanism
messages and 20 options, only a subset of those messages and such as stateless address autoconfiguration [6] or manual
options are required for stateless DHCPv6 service. This document configuration can use stateless DHCP to obtain other configuration
gives guidelines about which messages and options are required for information such as a list of DNS recursive name servers or SIP
stateless DHCPv6 service. The intended use of the document is to servers. A stateless DHCP server provides only configuration
guide the efficient and complete implementation of clients and information to nodes and does not perform any address assignment.
servers that use stateless DHCPv6 service. Such a server is called "stateless" because it need not maintain any
dynamic state for individual clients.
The operation of relay agents is the same for stateless and While the DHCP specification [1] defines more than 10 protocol
stateful DHCPv6 service. The operation of relay agents is messages and 20 options, only a subset of those messages and options
described in the DHCPv6 specification. are required for stateless DHCP service. This document explains which
messages and options defined in RFC 3315 are required for stateless
DHCP service. The intended use of the document is to guide the
interoperable implementation of clients and servers that use
stateless DHCP service.
Section 4 of this document lists the sections of the DHCPv6 The operation of relay agents is the same for stateless and stateful
document that an implementor should read for an overview of the DHCP service. The operation of relay agents is described in the DHCP
DHCPv6 specification and the basic requirements of a DHCPv6 specification.
service. Section 5 lists the specific messages and options that
are specifically required for stateless DHCPv6 service. Section 6 Section 4 of this document lists the sections of the DHCP document
describes how stateless and stateful DHCPv6 servers interact to that an implementor should read for an overview of the DHCP
provide service to clients that require address assignment and specification and the basic requirements of a DHCP service. Section 5
clients that require only stateless service. lists the specific messages and options that are specifically
required for stateless DHCP service. Section 6 describes how
stateless and stateful DHCP servers interact to provide service to
clients that require address assignment and 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 This document uses the terminology defined in RFC2460 [2], the DHCP
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 "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 [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 parameters for the node. The Reply message from the server can carry
carry configuration information such as a list of DNS recursive configuration information such as a list of DNS recursive name
name servers [3] and SIP servers [5]. servers [3] and SIP servers [5].
This document does not apply to the function of DHCPv6 relay This document does not apply to the function of DHCP relay agents as
agents as described in RFC 3315. A network element can provide described in RFC 3315. A network element can provide both DHCP server
both DHCPv6 server and DHCPv6 relay service. For example, a and DHCP relay service. For example, a network element can provide
network element can provide stateless DHCPv6 service to hosts stateless DHCP service to hosts requesting stateless DHCP service,
requesting stateless DHCP service, while relaying messages from while relaying messages from hosts requesting address assignment
hosts requesting address assignment through DHCPv6 to another through DHCP to another DHCP server.
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 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 DHCP 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) 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 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 a list of DNS recursive name a list of DNS recursive name servers, it identifies the DNS Recursive
servers, it identifies the DNS Recursive Name Server option in the Name Server option in the Information-request message. The server
Information-request message. The server determines the appropriate determines the appropriate configuration parameters for the client
configuration parameters for the client based on its configuration based on its configuration policies and responds with a Reply message
policies and responds with a Reply message containing the containing the requested parameters. In this example, the server
requested parameters. In this example, the server would respond would respond with DNS configuration parameters.
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 RFC 3315 also does not provide any guidance about when a host might
might use an Information-request message to obtain updated use an Information-request message to obtain updated configuration
configuration parameters when the host has moved to a new link. parameters when the host has moved to a new link. The dhc WG is
The dhc WG is reviewing a related document, "Detection of Network reviewing a related document, "Detection of Network Attachment (DNA)
Attachment (DNA) in IPv4" [8], which describes how a host using in IPv4" [8], which describes how a host using IPv4 can determine
IPv4 can determine when to use DHCPv4. Either the dhc WG or a WG when to use DHCPv4. Either the dhc WG or a WG formed from the dna
formed from the dna BOF will undertake development of a similar BOF will undertake development of a similar document for IPv6.
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 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 messages for stateless DHCP service; the section numbers in this list
list refer to the DHCPv6 specification: refer to the DHCP specification:
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 to
the relay agent (section 15.14)
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 DHCP
specification: specification:
Option Request: specifies the configuration information that Option Request: specifies the configuration information that the
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 Code: used to indicate completion status or other status
status information (section 22.13) information (section 22.13)
Server Identifier: used to identify the server responding to a Server Identifier: used to identify the server responding to a client
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 stateless DHCP service; the section numbers in this list refer to the
the DHCPv6 specification: DHCP 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; note that other options for information to clients; note that other options for configuration
configuration information may be specified in future Internet information may be specified in future Internet Standards:
Standards:
DNS Recursive Name Servers: specifies the DNS recursive name DNS Recursive Name Servers: specifies the DNS recursive name servers
servers [7] the client uses for name resolution; see "DNS [7] the client uses for name resolution; see "DNS Configuration
Configuration options for DHCPv6" [3] 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] [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]
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 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 DHCP
the DHCPv6 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 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: Used to pass information to clients Vendor-specific Information: Used to pass information to clients in
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 Client Identifier: Sent by a DHCP client to identify itself (section
(section 22.2). Clients are not required to send this option; 22.2). Clients are not required to send this option; servers send
servers send the option back if included in a message from a the option back if included in a message from a client
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 In some networks, there may be both clients that are using stateless
stateless address autoconfiguration and DHCP for DNS configuration address autoconfiguration and DHCP for DNS configuration and clients
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 DHCP service is a proper subset of the DHCP service
described in the DHCPv6 specification, RFC 3315. Therefore, described in the DHCP specification, RFC 3315. Therefore, stateless
stateless DHCPv6 service introduces no additional security DHCP service introduces no additional security considerations beyond
considerations beyond those discussed in sections 21, 22.11 and 23 those discussed in sections 21, 22.11 and 23 of the DHCP
of the DHCPv6 specification. specification.
Configuration information provided to a node through stateless Configuration information provided to a node through stateless DHCP
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 DHCP, as described in
described in sections 21 and 22.11 of the DHCPv6 specification, sections 21 and 22.11 of the DHCP specification, can be used to avoid
can be used to avoid attacks mounted through the stateless DHCPv6 attacks mounted through the stateless DHCP service.
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 Chown, Christian Huitema, Tatuya Jinmei, Pekka Savola and Juha
and Juha Wiljakka for their review and comments. 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 Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
(DHCPv6)", RFC 3315, July 2003. RFC 3315, July 2003.
[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.
Informative References Informative References
[3] Droms, R., "DNS Configuration options for Dynamic Host [3] Droms, R., "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 [4] 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.
[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 Protocol (DHCPv6) Options for Session Initiation Protocol (SIP)
(SIP) Servers", RFC 3319, July 2003. 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", [7] Mockapetris, P., "Domain names - concepts and facilities", STD
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",
draft-ietf-dhc-dna-ipv4-04 (work in progress), October 2003. 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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