Network Working Group R. Droms Internet-Draft Cisco Systems Expires:
October 5, 2003April 5, 2004 October 6, 2003 A Guide to Implementing Stateless DHCPv6 Service draft-ietf-dhc-dhcpv6-stateless-00.txtdraft-ietf-dhc-dhcpv6-stateless-01.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts.Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt.http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on OctoberApril 5, 2003.2004. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract Stateless DHCPv6 service is used by nodes to obtain configuration information such as the addresses of DNS recursive name servers that does not require the maintenance of any dynamic state for individual clients. A node that uses stateless DHCP must have obtained its IPv6 addresses through some other mechanism, typically stateless address autoconfiguration. This document is a guide to the protocol messages and options that must be implemented to provide stateless DHCPv6 service. 1. Introduction Nodes that have obtained IPv6 addresses through some other mechanism such as stateless address autoconfiguration  or manual configuration can use stateless DHCPv6 to obtain other configuration information such as a list of DNS recursive name servers or NTPSIP 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  defines more than 10 protocol messages and 20 options, only a subset of those messages and options are required for stateless DHCPv6 service. This document gives guidelines about which messages and options are required for stateless DHCPv6 service. The intended use of the document is to guide the efficient and complete implementation of clients and servers that use stateless DHCPv6 service. The operation of relay agents is the same for stateless and stateful DHCPv6 service. The operation of relay agents is described in the DHCPv6 specification. Section 4 of this document lists the sections of the DHCPv6 document that an implementor should read for an overview of the DHCPv6 specification and the basic requirements of a DHCPv6 service. Section 5 lists the specific messages and options that are specifically required for stateless DHCPv6 service. Section 6 describes how stateless and stateful DHCPv6 servers interact to provide service to clients that require address assignment and clients that require only stateless service. 2. Terminology Throughout this document, "DHCP" refers to DHCP for IPv6. This document uses the terminology defined in RFC2460 , the DHCP specification, the DHCP DNS configuration optionsspecification  and the DHCP NTPDNS configuration options specification .. "Stateless DHCP" refers to the use of DHCP to provide configuration information to clients that does not require the server to maintain dynamic state about the DHCP clients. 3. Overview This document assumes that a node using stateless DHCP configuration 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 of RFC2461  To obtain configuration parameters through stateless DHCP, a node uses the DHCP Information-request message. DHCP servers respond to the node's message with a Reply message that carries the DNS configuration parameters. The Reply message from the server can carry configuration information such as a list of DNS recursive name servers and NTPSIP servers. 4. Basic Requirements for Implementation of DHCP Several sections of the DHCP specification provide background information or define parts of the specification that are common to all implementations: 1-4: give an introduction to DHCPv6 and an overview of DHCP message flows 5: defines constants used throughout the protocol specification 6, 7: illustrates the format of DHCP messages 8: describes the representation of Domain Names 9: defines the "DHCP unique identifier" (DUID) optionally used to identify DHCP participants 13-16: describe DHCP message transmission, retransmission and validation 21: describes authentication for DHCP 5. Implementation of stateless DHCP The client indicates that it is requesting configuration information by sending an Information-request message that includes an Option Request option specifying the options that it wishes to receive from the DHCP server. For example, if the client is attempting to obtain DNS configuration information, it includes either or both of the DNS configuration options in the Information-request message. The server determines the appropriate configuration parameters for the client based on its configuration policies and responds with a Reply message containing the requested parameters. In this example, the server would respond with DNS configuration parameters. A node uses the DUIDClient 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. 5.1 Messages required for stateless DHCP Clients and servers implement the following messages for stateless DHCP service; the section numbers in this list refer to the DHCPv6 specification: Information-request: sent by a DHCP client to a server to request DNS configuration parameters (sections 18.1.5 and 18.2.5) Reply: sent by a DHCP server to a client containing the DNS configuration parameters (sections 18.2.6 and 18.2.8) In addition, servers and relay agents implement the following messages for stateless DHCP service: Relay-forward: Sent by a DHCP relay agent to carry the client message to a server (section 15.13) Relay-reply: Sent by a DHCP server to carry a response message to the relay agent (section 15.14) 5.2 Options required for stateless DHCP service Clients and servers implement the following options for stateless DHCP service; the section numbers in this list refer to the DHCPv6 specification: Option Request: specifies the configuration information that the client is requesting from the server (section 22.7) Status Code: used to indicate completion status or other status information (section 22.13) Server Identifier: used to identify the server responding to a client request (section 22.3) Servers and relay agents implement the following options for stateless DHCP service; the section numbers in this list refer to the DHCPv6 specification: Client message: Sent by a DHCP relay agent in a Relay-forward message to carry the client message to a server (section 20) Server message: Sent by a DHCP server in a Relay-reply message to carry a response message to the relay agent (section 20) Interface-ID: Sent by the DHCP relay agent and returned by the server to identify the interface to use to forward a message to the client (section 22.18) 5.3 Options used for configuration information Clients and servers use the following options to pass configuration information to clients:clients; note that other options for configuration information may be specified in future Internet Standards: DNS Recursive Name Servers: specifies the DNS recursive name servers  the client uses for name resolution; see "DNS Configuration options for DHCPv6"  DNS search list: specifies the domain names to be searched during name resolution; see "DNS Configuration options for DHCPv6" NTP SIP Servers: specifies the NTPSIP servers the client uses for synchronizing its clock; see "Time Configuration Options for DHCPv6"to obtain a list of domain names of IPv6 addresses that can be mapped to one or more SIP outbound proxy servers  5.4 Other options used in stateless DHCP Clients and servers may implement the following options for stateless DHCP service; the section numbers in this list refer to the DHCPv6 specification :specification, RFC 3315>: Preference: Sent by a DHCP server to indicate the preference level for the server (section 22.8) Elapsed time: Sent by a DHCP client to indicate the time since the client began the DHCP configuration process (section 22.9) User Class: Sent by a DHCP client to give additional information to the server for selecting configuration parameters for the client (section 22.15) Vendor Class: Sent by a DHCP client to give additional information about the client vendor and hardware to the server for selecting configuration parameters for the client (section 22.16) Vendor-specific Information: Sent by a DHCP serverUsed to pass information to clients in options defined by vendors (section 22.17) Client DUID:Identifier: Sent by a DHCP client to identify itself (section 22.2). Clients are not required to send this option; servers neversend thisthe option back if included in a message fro ma client Authentication: Used to provide authentication of DHCP messages (section 21) 6. Interaction with DHCP for Address Assignment In some networks, there may be both clients that are using stateless address autoconfiguration and DHCP for DNS configuration and clients that are using DHCP for stateful address configuration. Depending on the deployment and configuration of relay agents, DHCP servers that are intended only for stateless configuration may receive messages from clients that are performing stateful address configuration. A DHCP server that is only able to provide stateless configuration information through an Information-request/Reply message exchange discards any other DHCP messages it receives. Specifically, the server discards any messages other than Information-Request or Relay-forward it receives, and the server does not participate in any stateful address configuration messages exchanges. If there are other DHCP servers that are configured to provide stateful address assignment, one of those servers will provide the address assignment. 7. Security Considerations Stateless DHCPv6 service is a proper subset of the DHCPv6 service described in the DHCPv6 specification .specification, RFC 3315. Therefore, stateless DHCPv6 service introduces no additional security considerations beyond those discussed in sections 21, 22.11 and 23 of the DHCPv6 specification. Configuration information provided to a node through stateless DHCPv6 service may be used to mount spoofing, man-in-the-middle, denial-of-service and other attacks. These attacks are described in more detail in the specifications for each of the options that carry configuration information. Authenticated DHCPv6, as described in sections 21 and 22.11 of the DHCPv6 specification, can be used to avoid attacks mounted through the stateless DHCPv6 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  to authenticate and secure DHCPv6 messages exchanged between the node and the DHCPv6 server.8. Acknowledgments Jim Bound, Ted Lemon and Bernie Volz reviewed this document and contributed editorial suggestions. Thanks to Pekka Savola andPeter Barany, Christian Huitema and Pekka Savola for their review and comments. Normative References  Droms, R., Bound, J., Carney, M., Perkins, C.,Volz, B., Lemon, T., Volz, B.Perkins, C. and R. Droms (ed.),M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress), October 2002.RFC 3315, July 2003.  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998.  Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.Droms, R., "DNS Configuration optionsOptions for DHCPv6", draft-ietf- dhc-dhcpv6-opt-dnsconfig-01draft-ietf-dhc-dhcpv6-opt-dnsconfig-04 (work in progress), October 2002.August 2003.  Vijayabhaskar, A., "TimeSchulzrinne, H. and B. Volz, "Dynamic Host Configuration Protocol (DHCPv6) Options for DHCPv6", draft-ietf-dhc-dhcpv6-opt-timeconfig-00 (work in progress), February 2002.Session Initiation Protocol (SIP) Servers", RFC 3319, July 2003. Informative References  Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998.  Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987. Thomson, S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998.  Kent, S. Mockapetris, P., "Domain names - concepts and R. Atkinson, "Security Architecture for the Internet Protocol",facilities", STD 13, RFC 2401,1034, November 1998.1987. Author's Address Ralph Droms Cisco Systems 300 Apollo Drive Chelmsford,1414 Massachusetts Avenue Boxborough, MA 0182401719 USA Phone: +1 978 497 4733 EMail: firstname.lastname@example.org Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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