Internet Engineering Task Force J. Bound INTERNET DRAFT Compaq DHC Working Group M. Carney Obsoletes: draft-ietf-dhc-dhcpv6-20.txt Sun Microsystems, Inc C. Perkins Nokia Research Center R. Droms(ed.) Cisco Systems 21 Nov 2001 Dynamic Host Configuration Protocol for IPv6 (DHCPv6) draft-ietf-dhc-dhcpv6-21.txt Status of This Memo This document is a submission by the Dynamic Host Configuration Working Group of the Internet Engineering Task Force (IETF). Comments should be submitted to the dhcwg@ietf.org mailing list. Distribution of this memo is unlimited. 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 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 The list of Internet-Draft Shadow Directories can be accessed at: http://www.ietf.org/shadow.html. Abstract The Dynamic Host Configuration Protocol for IPv6 (DHCP) enables DHCP servers to pass configuration parameters such as IPv6 network addresses to IPv6 nodes. It offers the capability of automatic allocation of reusable network addresses and additional configuration flexibility. This protocol is a stateful counterpart to "IPv6 Stateless Address Autoconfiguration" [20], and can be used separately or concurrently with the latter to obtain configuration parameters. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page i] Internet Draft DHCP for IPv6 21 Nov 2001 Contents Status of This Memo i Abstract i 1. Introduction 1 2. Requirements 2 3. Background 2 4. Design Goals 3 5. Non-Goals 3 6. Terminology 4 6.1. IPv6 Terminology . . . . . . . . . . . . . . . . . . . . 4 6.2. DHCP Terminology . . . . . . . . . . . . . . . . . . . . 5 7. DHCP Constants 6 7.1. Multicast Addresses . . . . . . . . . . . . . . . . . . . 7 7.2. UDP ports . . . . . . . . . . . . . . . . . . . . . . . . 7 7.3. DHCP message types . . . . . . . . . . . . . . . . . . . 7 7.4. Status Codes . . . . . . . . . . . . . . . . . . . . . . 9 7.4.1. Generic Status Codes . . . . . . . . . . . . . . 9 7.4.2. Server-specific Status Codes . . . . . . . . . . 9 7.5. Configuration Variables . . . . . . . . . . . . . . . . . 10 8. Message Formats 10 8.1. DHCP Solicit Message Format . . . . . . . . . . . . . . . 11 8.2. DHCP Advertise Message Format . . . . . . . . . . . . . . 11 8.3. DHCP Request Message Format . . . . . . . . . . . . . . . 12 8.4. DHCP Confirm Message Format . . . . . . . . . . . . . . . 12 8.5. DHCP Renew Message Format . . . . . . . . . . . . . . . . 12 8.6. DHCP Rebind Message Format . . . . . . . . . . . . . . . 12 8.7. DHCP Reply Message Format . . . . . . . . . . . . . . . . 13 8.8. DHCP Release Message Format . . . . . . . . . . . . . . . 13 8.9. DHCP Decline Message Format . . . . . . . . . . . . . . . 13 8.10. DHCP Reconfigure-init Message Format . . . . . . . . . . 13 8.11. Inform Message Format . . . . . . . . . . . . . . . . . . 14 9. Relay messages 14 9.1. Relay-forward message . . . . . . . . . . . . . . . . . . 14 9.2. Relay-reply message . . . . . . . . . . . . . . . . . . . 15 10. DHCP unique identifier (DUID) 15 10.1. DUID contents . . . . . . . . . . . . . . . . . . . . . . 16 10.2. DUID based on link-layer address plus time . . . . . . . 16 10.3. Vendor-assigned unique ID. . . . . . . . . . . . . . . . 17 10.4. Link-layer address . . . . . . . . . . . . . . . . . . . 18 Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page ii] Internet Draft DHCP for IPv6 21 Nov 2001 11. Identity association 18 12. Selecting addresses for assignment to an IA 19 13. Reliability of Client Initiated Message Exchanges 19 14. Message validation 21 14.1. Use of Transaction-ID field . . . . . . . . . . . . . . . 21 14.2. Solicit message . . . . . . . . . . . . . . . . . . . . . 21 14.3. Advertise message . . . . . . . . . . . . . . . . . . . . 21 14.4. Request message . . . . . . . . . . . . . . . . . . . . . 22 14.5. Confirm message . . . . . . . . . . . . . . . . . . . . . 22 14.6. Renew message . . . . . . . . . . . . . . . . . . . . . . 22 14.7. Rebind message . . . . . . . . . . . . . . . . . . . . . 22 14.8. Decline messages . . . . . . . . . . . . . . . . . . . . 22 14.9. Release message . . . . . . . . . . . . . . . . . . . . . 23 14.10. Reply message . . . . . . . . . . . . . . . . . . . . . . 23 14.11. Reconfigure-init message . . . . . . . . . . . . . . . . 23 14.12. Inform message . . . . . . . . . . . . . . . . . . . . . 23 14.13. Relay-forward message . . . . . . . . . . . . . . . . . . 23 14.14. Relay-reply message . . . . . . . . . . . . . . . . . . . 23 15. DHCP Server Solicitation 24 15.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 24 15.1.1. Creation of Solicit messages . . . . . . . . . . 24 15.1.2. Transmission of Solicit Messages . . . . . . . . 24 15.1.3. Receipt of Advertise messages . . . . . . . . . . 25 15.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 26 15.2.1. Receipt of Solicit messages . . . . . . . . . . . 26 15.2.2. Creation and transmission of Advertise messages . 26 16. DHCP Client-Initiated Configuration Exchange 27 16.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 27 16.1.1. Creation and transmission of Request messages . . 28 16.1.2. Creation and transmission of Confirm messages . . 29 16.1.3. Creation and transmission of Renew messages . . . 30 16.1.4. Creation and transmission of Rebind messages . . 31 16.1.5. Creation and Transmission of Inform messages . . 33 16.1.6. Receipt of Reply message in response to a Request, Confirm, Renew, Rebind or Inform message . 33 16.1.7. Creation and transmission of Release messages . . 35 16.1.8. Receipt of Reply message in response to a Release message . . . . . . . . . . . . . . . . . 36 16.1.9. Creation and transmission of Decline messages . . 36 16.1.10. Receipt of Reply message in response to a Decline message . . . . . . . . . . . . . . . . . 37 16.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 38 16.2.1. Receipt of Request messages . . . . . . . . . . . 38 16.2.2. Receipt of Confirm messages . . . . . . . . . . . 39 16.2.3. Receipt of Renew messages . . . . . . . . . . . . 39 16.2.4. Receipt of Rebind messages . . . . . . . . . . . 40 16.2.5. Receipt of Inform messages . . . . . . . . . . . 41 16.2.6. Receipt of Release messages . . . . . . . . . . . 42 Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page iii] Internet Draft DHCP for IPv6 21 Nov 2001 16.2.7. Receipt of Decline messages . . . . . . . . . . . 42 16.2.8. Receipt of Decline messages . . . . . . . . . . . 43 16.2.9. Sending of Reply messages . . . . . . . . . . . . 43 17. DHCP Server-Initiated Configuration Exchange 43 17.1. Server Behavior . . . . . . . . . . . . . . . . . . . . . 43 17.1.1. Creation and transmission of Reconfigure-init messages . . . . . . . . . . . . . . . . . 43 17.1.2. Time out and retransmission of Reconfigure-init messages . . . . . . . . . . . . . . . . . 44 17.1.3. Receipt of Rebind messages . . . . . . . . . . . 44 17.2. Client Behavior . . . . . . . . . . . . . . . . . . . . . 45 17.2.1. Receipt of Reconfigure-init messages . . . . . . 45 17.2.2. Creation and sending of Rebind messages . . . . . 46 17.2.3. Time out and retransmission of Rebind messages . 46 17.2.4. Receipt of Reply messages . . . . . . . . . . . . 46 18. Relay Behavior 46 18.1. Relaying of client messages . . . . . . . . . . . . . . . 46 18.2. Relaying of server messages . . . . . . . . . . . . . . . 47 19. Authentication of DHCP messages 47 19.1. DHCP threat model . . . . . . . . . . . . . . . . . . . . 48 19.2. Security of messages sent between servers and relay agents 48 19.3. Summary of DHCP authentication . . . . . . . . . . . . . 48 19.4. Replay detection . . . . . . . . . . . . . . . . . . . . 49 19.5. Configuration token protocol . . . . . . . . . . . . . . 49 19.6. Delayed authentication protocol . . . . . . . . . . . . . 49 19.6.1. Management issues in the delayed authentication protocol . . . . . . . . . . . . . . . . . 50 19.6.2. Use of the Authentication option in the delayed authentication protocol . . . . . . . . . 50 19.6.3. Message validation . . . . . . . . . . . . . . . 51 19.6.4. Key utilization . . . . . . . . . . . . . . . . . 51 19.6.5. Client considerations for delayed authentication protocol . . . . . . . . . . . . . . . . . 52 19.6.6. Server considerations for delayed authentication protocol . . . . . . . . . . . . . . . . . 53 20. DHCP options 54 20.1. Format of DHCP options . . . . . . . . . . . . . . . . . 54 20.2. DHCP unique identifier option . . . . . . . . . . . . . . 54 20.3. Identity association option . . . . . . . . . . . . . . . 55 20.4. IA Address option . . . . . . . . . . . . . . . . . . . . 56 20.5. Option request option . . . . . . . . . . . . . . . . . . 57 20.6. Preference option . . . . . . . . . . . . . . . . . . . . 58 20.7. Elapsed Time . . . . . . . . . . . . . . . . . . . . . . 58 20.8. Client message option . . . . . . . . . . . . . . . . . . 58 20.9. Server message option . . . . . . . . . . . . . . . . . . 59 20.10. DSTM Global IPv4 Address Option . . . . . . . . . . . . . 59 20.11. Authentication option . . . . . . . . . . . . . . . . . . 60 20.12. Server unicast option . . . . . . . . . . . . . . . . . . 61 20.13. Domain Search Option . . . . . . . . . . . . . . . . . . 61 Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page iv] Internet Draft DHCP for IPv6 21 Nov 2001 20.14. Domain Name Server Option . . . . . . . . . . . . . . . . 62 20.15. Status Code Option . . . . . . . . . . . . . . . . . . . 63 20.16. Circuit-ID Option . . . . . . . . . . . . . . . . . . . . 63 20.17. User Class Option . . . . . . . . . . . . . . . . . . . . 64 20.18. Vendor Class Option . . . . . . . . . . . . . . . . . . . 65 21. Security Considerations 66 22. Year 2000 considerations 66 23. IANA Considerations 66 23.1. Multicast addresses . . . . . . . . . . . . . . . . . . . 66 23.2. DHCPv6 message types . . . . . . . . . . . . . . . . . . 66 23.3. DUID . . . . . . . . . . . . . . . . . . . . . . . . . . 67 23.4. DHCPv6 options . . . . . . . . . . . . . . . . . . . . . 67 23.5. Status codes . . . . . . . . . . . . . . . . . . . . . . 67 23.6. Authentication option . . . . . . . . . . . . . . . . . . 67 24. Acknowledgments 67 A. Full Copyright Statement 68 References 68 Chair's Address 70 Authors' Addresses 70 Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page v] 1. Introduction This document describes DHCP for IPv6 (DHCP), a UDP [18] client/server protocol designed to reduce the cost of management of IPv6 nodes in environments where network managers require more control over the allocation of IPv6 addresses and configuration of network stack parameters than that offered by "IPv6 Stateless Address Autoconfiguration" [20]. DHCP is a stateful counterpart to stateless autoconfiguration. Note that both stateful and stateless autoconfiguration can be used concurrently in the same environment, leveraging the strengths of both mechanisms in order to reduce the cost of ownership and management of network nodes. DHCP reduces the cost of ownership by centralizing the management of network resources such as IP addresses, routing information, OS installation information, directory service information, and other such information on a few DHCP servers, rather than distributing such information in local configuration files among each network node. DHCP is designed to be easily extended to carry new configuration parameters through the addition of new DHCP "options" defined to carry this information. Those readers familiar with DHCP for IPv4 [7] will findDHCP for IPv6 provides a superset of features, and benefits from the additional Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 1] Internet Draft DHCP for IPv6 21 Nov 2001 features of IPv6 and freedom from the constraints of backward compatibility with BOOTP [5]. 2. Requirements The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [3]. This document also makes use of internal conceptual variables to describe protocol behavior and external variables that an implementation must allow system administrators to change. The specific variable names, how their values change, and how their settings influence protocol behavior are provided to demonstrate protocol behavior. An implementation is not required to have them in the exact form described here, so long as its external behavior is consistent with that described in this document. 3. Background The IPv6 Specification provides the base architecture and design of IPv6. Related work in IPv6 that would best serve an implementor to study is the IPv6 Specification [6], the IPv6 Addressing Architecture [9], IPv6 Stateless Address Autoconfiguration [20], IPv6 Neighbor Discovery Processing [16], and Dynamic Updates to DNS [21]. These specifications enable DHCP to build upon the IPv6 work to provide both robust stateful autoconfiguration and autoregistration of DNS Host Names. The IPv6 Addressing Architecture specification [9] defines the address scope that can be used in an IPv6 implementation, and the various configuration architecture guidelines for network designers of the IPv6 address space. Two advantages of IPv6 are that support for multicast is required, and nodes can create link-local addresses during initialization. This means that a client can immediately use its link-local address and a well-known multicast address to begin communications to discover neighbors on the link. For instance, a client can send a Solicit message and locate a server or relay. IPv6 Stateless Address Autoconfiguration [20] specifies procedures by which a node may autoconfigure addresses based on router advertisements [16], and the use of a valid lifetime to support renumbering of addresses on the Internet. In addition the protocol interaction by which a node begins stateless or stateful autoconfiguration is specified. DHCP is one vehicle to perform stateful autoconfiguration. Compatibility with stateless address autoconfiguration is a design requirement of DHCP (see Section 4). IPv6 Neighbor Discovery [16] is the node discovery protocol in IPv6 which replaces and enhances functions of ARP [17]. To understand Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 2] Internet Draft DHCP for IPv6 21 Nov 2001 IPv6 and stateless address autoconfiguration it is strongly recommended that implementors understand IPv6 Neighbor Discovery. Dynamic Updates to DNS [21] is a specification that supports the dynamic update of DNS records for both IPv4 and IPv6. DHCP can use the dynamic updates to DNS to integrate addresses and name space to not only support autoconfiguration, but also autoregistration in IPv6. 4. Design Goals - DHCP is a mechanism rather than a policy. Network administrators set their administrative policies through the configuration parameters they place upon the DHCP servers in the DHCP domain they're managing. DHCP is simply used to deliver parameters according to that policy to each of the DHCP clients within the domain. - DHCP is compatible with IPv6 stateless address autoconfiguration [20], statically configured, non-participating nodes and with existing network protocol implementations. - DHCP does not require manual configuration of network parameters on DHCP clients, except in cases where such configuration is needed for security reasons. A node configuring itself using DHCP should require no user intervention. - DHCP does not require a server on each link. To allow for scale and economy, DHCP must work across DHCP relays. - DHCP clients can operate on a link without IPv6 routers present. - DHCP will provide the ability to renumber network(s) when required by network administrators [4]. - A DHCP client can make multiple, different requests for configuration parameters when necessary from one or more DHCP servers at any time. - DHCP will contain the appropriate time out and retransmission mechanisms to efficiently operate in environments with high latency and low bandwidth characteristics. 5. Non-Goals This specification explicitly does not cover the following: - Specification of a DHCP server to server protocol. - How a DHCP server stores its DHCP data. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 3] Internet Draft DHCP for IPv6 21 Nov 2001 - How to manage a DHCP domain or DHCP server. - How a DHCP relay is configured or what sort of information it may log. 6. Terminology This sections defines terminology specific to IPv6 and DHCP used in this document. 6.1. IPv6 Terminology IPv6 terminology relevant to this specification from the IPv6 Protocol [6], IPv6 Addressing Architecture [9], and IPv6 Stateless Address Autoconfiguration [20] is included below. address An IP layer identifier for an interface or a set of interfaces. unicast address An identifier for a single interface. A packet sent to a unicast address is delivered to the interface identified by that address. multicast address An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to a multicast address is delivered to all interfaces identified by that address. host Any node that is not a router. IP Internet Protocol Version 6 (IPv6). The terms IPv4 and IPv6 are used only in contexts where it is necessary to avoid ambiguity. interface A node's attachment to a link. link A communication facility or medium over which nodes can communicate at the link layer, i.e., the layer immediately below IP. Examples are Ethernet (simple or bridged); Token Ring; PPP links, X.25, Frame Relay, or ATM networks; and Internet (or higher) layer "tunnels", such as tunnels over IPv4 or IPv6 itself. link-layer identifier A link-layer identifier for an interface. Examples include IEEE 802 addresses for Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 4] Internet Draft DHCP for IPv6 21 Nov 2001 Ethernet or Token Ring network interfaces, and E.164 addresses for ISDN links. link-local address An IPv6 address having link-only scope, indicated by having the prefix (FE80::0000/64), that can be used to reach neighboring nodes attached to the same link. Every interface has a link-local address. message A unit of data carried in a packet, exchanged between DHCP agents and clients. neighbor A node attached to the same link. node A device that implements IP. packet An IP header plus payload. prefix The initial bits of an address, or a set of IP address that share the same initial bits. prefix length The number of bits in a prefix. router A node that forwards IP packets not explicitly addressed to itself. 6.2. DHCP Terminology Terminology specific to DHCP can be found below. agent address The address of a neighboring DHCP Agent on the same link as the DHCP client. binding A binding (or, client binding) is a group of server data records containing the information the server has about the addresses in an IA and any other configuration information assigned to the client. A binding is indexed by the tuple . DHCP Dynamic Host Configuration Protocol for IPv6. The terms DHCPv4 and DHCPv6 are used only in contexts where it is necessary to avoid ambiguity. configuration parameter An element of the configuration information set on the server and delivered to the client using DHCP. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 5] Internet Draft DHCP for IPv6 21 Nov 2001 Such parameters may be used to carry information to be used by a node to configure its network subsystem and enable communication on a link or internetwork, for example. DHCP client (or client) A node that initiates requests on a link to obtain configuration parameters from one or more DHCP servers. DHCP domain A set of links managed by DHCP and operated by a single administrative entity. DHCP server (or server) A server is a node that responds to requests from clients, and may or may not be on the same link as the client(s). DHCP relay (or relay) A node that acts as an intermediary to deliver DHCP messages between clients and servers, and is on the same link as a client. DHCP agent (or agent) Either a DHCP server on the same link as a client, or a DHCP relay. DUID A DHCP Unique IDentifier for a client. Identity association (IA) A collection of addresses assigned to a client. Each IA has an associated IAID. An IA may have 0 or more addresses associated with it. Identity association identifier (IAID) An identifier for an IA, chosen by the client. Each IA has an IAID, which is chosen to be unique among all IAIDs for IAs belonging to that client. transaction-ID An unsigned integer to match responses with replies initiated either by a client or server. 7. DHCP Constants This section describes various program and networking constants used by DHCP. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 6] Internet Draft DHCP for IPv6 21 Nov 2001 7.1. Multicast Addresses DHCP makes use of the following multicast addresses: All_DHCP_Agents address: FF02::1:2 This link-scoped multicast address is used by clients to communicate with the on-link agent(s) when they do not know the link-local address(es) for those agents. All agents (servers and relays) are members of this multicast group. All_DHCP_Servers address: FF05::1:3 This site-scoped multicast address is used by clients or relays to communicate with server(s), either because they want to send messages to all servers or because they do not know the server(s) unicast address(es). Note that in order for a client to use this address, it must have an address of sufficient scope to be reachable by the server(s). All servers within the site are members of this multicast group. 7.2. UDP ports DHCP uses the following destination UDP [18] port numbers. While source ports MAY be arbitrary, client implementations SHOULD permit their specification through a local configuration parameter to facilitate the use of DHCP through firewalls. 546 Client port. Used by servers as the destination port for messages sent to clients and relays. Used by relay agents as the destination port for messages sent to clients. 547 Agent port. Used as the destination port by clients for messages sent to agents. Used as the destination port by relays for messages sent to servers. 7.3. DHCP message types DHCP defines the following message types. More detail on these message types can be found in Section 8. Message types 0 and 13-255 are reserved for future use. The message code for each message type is shown with the message name. SOLICIT (1) The Solicit message is used by clients to locate servers. ADVERTISE (2) The Advertise message is used by servers responding to Solicits. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 7] Internet Draft DHCP for IPv6 21 Nov 2001 REQUEST (3) The Request message is used by clients to request configuration parameters from servers. CONFIRM (4) The Confirm message is used by clients to confirm that the addresses assigned to an IA and the lifetimes for those addresses, as well as the current configuration parameters assigned by the server to the client are still valid. RENEW (5) The Renew message is used by clients to update the addresses assigned to an IA and the lifetimes for those addresses, as well as the current configuration parameters assigned by the server to the client. A client sends a Renew message to the server that originally populated the IA at time T1. REBIND (6) The Rebind message is used by clients to extend the lifetimes of addresses assigned to an IA, as well as the current configuration parameters assigned by the server to the client. A client sends a Rebind message to all available DHCP servers at time T2 only after the client has been unable to contact the server that originally populated the IA with a Rebind message. REPLY (7) The Reply message is used by servers responding to Request, Confirm, Renew, Rebind, Release and Decline messages. In the case of responding to a Request, Confirm, Renew or Rebind message, the Reply contains configuration parameters destined for the client. RELEASE (8) The Release message is used by clients to return one or more IP addresses to servers. DECLINE (9) The Decline message is used by clients to indicate that the client has determined that one or more addresses in an IA are already in use on the link to which the client is connected. RECONFIG-INIT (10) The Reconfigure-init message is sent by server(s) to inform client(s) that the server(s) has new or updated configuration parameters, and that the client(s) are to initiate a Request/Reply transaction with the server(s) in order to receive the updated information. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 8] Internet Draft DHCP for IPv6 21 Nov 2001 INFORM (11) The Inform message is sent by clients to request configuration parameters without the assignment of any IP addresses to the client. RELAY-FORW (12) The Relay-forward message is used by relays to forward client messages to servers. The client message is encapsulated in an option in the Relay-forward message. RELAY-REPL (13) The Relay-reply message is used by servers to send messages to clients through a relay. The server encapsulates the client message as an option in the Relay-reply message, which the relay extracts and forwards to the client. 7.4. Status Codes This section describes status codes exchanged between DHCP implementations. These status codes may appear in the Status Code option or in the status field of an IA. 7.4.1. Generic Status Codes The status codes in this section are used between clients and servers to convey status conditions. The following table contains the status codes, the name for each code (as used in this document) and a brief description. Note that the numeric values do not start at 1, nor are they consecutive. The status codes are organized in logical groups. Name Code Description ---------- ---- ----------- Success 0 Success UnspecFail 16 Failure, reason unspecified AuthFailed 17 Authentication failed or nonexistent PoorlyFormed 18 Poorly formed message AddrUnavail 19 Addresses unavailable OptionUnavail 20 Requested options unavailable 7.4.2. Server-specific Status Codes The status codes in this section are used by servers to convey status conditions to clients. The following table contains the status codes, the name for each code (as used in this document) and a brief description. Note that the numeric values do not start at 1, nor are they consecutive. The status codes are organized in logical groups. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 9] Internet Draft DHCP for IPv6 21 Nov 2001 Name Code Description ---- ---- ----------- NoBinding 32 Client record (binding) unavailable ConfNoMatch 33 Client record Confirm not match IA RenwNoMatch 34 Client record Renew not match IA RebdNoMatch 35 Client record Rebind not match IA InvalidSource 36 Invalid Client IP address NoServer 37 Relay cannot find Server Address NoPrefixMatch 38 One or more prefixes of the addresses in the IA is not valid for the link from which the client message was received ICMPError 64 Server unreachable (ICMP error) 7.5. Configuration Variables This section presents a table of client and server configuration variables and the default or initial values for these variables. Parameter Default Description ------------------------------------- MIN_SOL_DELAY 1 sec Min delay of first Solicit MAX_SOL_DELAY 5 secs Max delay of first Solicit SOL_TIMEOUT 500 msecs Initial Solicit timeout SOL_MAX_RT 30 secs Max Solicit timeout value REQ_TIMEOUT 250 msecs Initial Request timeout REQ_MAX_RT 30 secs Max Request timeout value REQ_MAX_RC 10 Max Request retry attempts CNF_TIMEOUT 250 msecs Initial Confirm timeout CNF_MAX_RT 1 sec Max Confirm timeout CNF_MAX_RD 10 secs Max Confirm duration REN_TIMEOUT 10 sec Initial Renew timeout REN_MAX_RT 600 secs Max Renew timeout value REB_TIMEOUT 10 secs Initial Rebind timeout REB_MAX_RT 600 secs Max Rebind timeout value INF_TIMEOUT 500 ms Initial Inform timeout INF_MAX_RT 30 secs Max Inform timeout value REL_TIMEOUT 250 msecs Initial Release timeout REL_MAX_RT 1 sec Max Release timeout REL_MAX_RC 5 MAX Release/Decline attempts DEC_TIMEOUT 250 msecs Initial Release timeout DEC_MAX_RT 1 sec Max Release timeout DEC_MAX_RC 5 MAX Release/Decline attempts 8. Message Formats All DHCP messages sent between clients and servers share an identical fixed format header and a variable format area for options. Not all fields in the header are used in every message. All values in the message header and in options are in network byte order. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 10] Internet Draft DHCP for IPv6 21 Nov 2001 The following diagram illustrates the DHCP message header: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | msg-type | transaction-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | server-address | | (16 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . options . . (variable) . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The following sections describe the use of the fields in the DHCP message header in each of the DHCP messages. In these descriptions, fields that are not used in a message are marked as "unused". All unused fields in a message MUST be transmitted as zeroes and ignored by the receiver of the message. 8.1. DHCP Solicit Message Format msg-type SOLICIT transaction-ID An unsigned integer generated by the client used to identify this Solicit message. server-address (unused) MUST be 0 options See section 20. 8.2. DHCP Advertise Message Format msg-type ADVERTISE transaction-ID An unsigned integer used to identify this Advertise message. Copied from the Solicit message received from the client. server-address The IP address of the server that generated this message. The address must have sufficient scope to be reachable from the client. options See section 20. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 11] Internet Draft DHCP for IPv6 21 Nov 2001 8.3. DHCP Request Message Format msg-type REQUEST transaction-ID An unsigned integer generated by the client used to identify this Request message. server-address The IP address of the server to which this message is directed, copied from an Advertise message. options See section 20. 8.4. DHCP Confirm Message Format msg-type CONFIRM transaction-ID An unsigned integer generated by the client used to identify this Confirm message. server-address MUST be zero. options See section 20. 8.5. DHCP Renew Message Format msg-type RENEW transaction-ID An unsigned integer generated by the client used to identify this Renew message. server-address The IP address of the server to which this Renew message is directed, which MUST be the address of the server from which the IAs in this message were originally assigned. options See section 20. 8.6. DHCP Rebind Message Format msg-type REBIND transaction-ID An unsigned integer generated by the client used to identify this Rebind message. server-address MUST be zero. options See section 20. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 12] Internet Draft DHCP for IPv6 21 Nov 2001 8.7. DHCP Reply Message Format msg-type REPLY transaction-ID An unsigned integer used to identify this Reply message. Copied from the client Request, Confirm, Renew or Rebind message received from the client. server-address The IP address of the server. options See section 20. 8.8. DHCP Release Message Format msg-type RELEASE transaction-ID An unsigned integer generated by the client used to identify this Release message. server-address The IP address of the server that assigned the addresses. options See section 20. 8.9. DHCP Decline Message Format msg-type DECLINE transaction-ID An unsigned integer generated by the client used to identify this Decline message. server-address The IP address of the server that assigned the addresses. options See section 20. 8.10. DHCP Reconfigure-init Message Format msg-type RECONFIG-INIT transaction-ID An unsigned integer generated by the server used to identify this Reconfigure-init message. server-address The IP address of the DHCP server issuing the Reconfigure-init message. The address must have sufficient scope to be reachable from the client. options See section 20. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 13] Internet Draft DHCP for IPv6 21 Nov 2001 8.11. DHCP Inform Message Format msg-type INFORM transaction-ID An unsigned integer generated by the server used to identify this Inform message. server-address MUST be zero. options See section 20. 9. Relay messages Relay agents exchange messages with servers to forward messages between clients and servers that are not connected to the same link. There are two relay messages, which share the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | msg-type | | +-+-+-+-+-+-+-+-+ | | link-address | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | | | +-+-+-+-+-+-+-+-+ | | client-return-address | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | | | +-+-+-+-+-+-+-+-+ | . . . options (variable number and length) .... . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The following sections describe the use of the Relay message header. 9.1. Relay-forward message The following table defines the use of message fields in a Relay-forward message. msg-type RELAY-FORW Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 14] Internet Draft DHCP for IPv6 21 Nov 2001 link-address An address with a prefix that is assigned to the link from which the client should be assigned an address. client-return-address The source address from the IP datagram in which the message from the client was received by the relay agent options MUST include a "Client message option"; see section 20.8; MAY include other options added by the relay agent 9.2. Relay-reply message The following table defines the use of message fields in a Relay-forward message. msg-type RELAY-REPL link-address An address with a prefix that is assigned to the link from which the client should be assigned an address. client-return-address The source address from the IP datagram in which the message from the client was received by the relay agent options MUST include a "Server message option"; see section 20.9; MAY include other options 10. DHCP unique identifier (DUID) Each DHCP client has a DUID. DHCP servers use DUIDs to identify clients for the selection of configuration parameters and in the association of IAs with clients. See section 20.2 for the representation of a DUID in a DHCP message. Servers MUST treat DUIDs as opaque values and MUST only compare DUIDs for equality. Servers MUST NOT in any other way interpret DUIDs. Servers MUST NOT restrict DUIDs to the types defined in this document as additional DUID types may be defined in the future. The DUID is carried in an option because it may be variable length and because it is not required in all DHCP options (e.g., messages sent by servers need not include a DUID). The DUID must be unique across all DHCP clients, and it must also be consistent for the same client - that is, the DUID used by a client SHOULD NOT change over time; for example, as a result of network hardware reconfiguration. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 15] Internet Draft DHCP for IPv6 21 Nov 2001 The motivation for having more than one type of DUID is that the DUID must be globally unique, and must also be easy to generate. The sort of globally-unique identifier that is easy to generate for any given device can differ quite widely. Also, some devices may not contain any persistent storage. Retaining a generated DUID in such a device is not possible, so the DUID scheme must accommodate such devices. 10.1. DUID contents A DUID consists of a sixteen-bit type code represented in network order, followed by a variable number of octets that make up the actual identifier. A DUID can be no more than 256 octets long. The following types are currently defined: 1 Link-layer address plus time 2 Vendor-assigned unique ID 3 Link-layer address Formats for the variable field of the DUID for each of the above types are shown below. 10.2. DUID based on link-layer address plus time This type of DUID consists of four octets containing a time value, followed by a two octet network hardware type code, followed by link-layer address of any one network interface that is connected to the DHCP client device at the time that the DUID is generated. The time value is the time that the DUID is generated represented in seconds since midnight (UTC), January 1, 2000, modulo 2^32. The hardware type MUST be a valid hardware type assigned by the IANA as described in the section on ARP in RFC 826. Both the time and the hardware type are stored in network order. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Time (32 bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Hardware type (16 bits) | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . . . link-layer address (variable length) . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The choice of network interface can be completely arbitrary, as long as that interface provides a unique link-layer address, and the same DUID should be used in configuring all network interfaces connected Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 16] Internet Draft DHCP for IPv6 21 Nov 2001 to the device, regardless of which interface's link-layer address was used to generate the DUID. DHCP clients using this type of DUID MUST store the DUID in stable storage, and MUST continue to use this DUID even if the network interface used to generate the DUID is removed. DHCP clients that do not have any stable storage MUST NOT use this type of DUID. DHCP clients that use this DUID SHOULD attempt to configure the time prior to generating the DUID, if that is possible, and MUST use some sort of time source (e.g., a real-time clock) in generating the DUID, even if that time source is not configured by the user prior to generating the DUID. The use of a time source makes it unlikely that if the network interface is removed from the client and another client then uses the same network interface to generate a DUID, that two identical DUIDs will be generated. A DUID collision is very unlikely even if the clocks haven't been configured prior to generating the DUID. This method of DUID generation is recommended for all general purpose computing devices such as desktop computers and laptop computers, and also for devices such as printers, routers, and so on, that contain some form of writable non-volatile storage. 10.3. Vendor-assigned unique ID. The vendor-assigned unique ID consists of an eight-octet vendor-unique identifier, followed by the vendor's registered domain name. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VUID (64 bits) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . domain name (variable length) . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The structure of the VUID is left up to the vendor defining it, but each device containing such a VUID MUST be unique to each device that is using it, and MUST be assigned to the device at the time of manufacture and stored in some form of non-volatile storage. The VUID SHOULD be recorded in non-erasable storage. The domain name is simply any domain name that has been legally registered by the vendor in the domain name system, stored in canonical form. An example DUID of this type might look like this: Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 17] Internet Draft DHCP for IPv6 21 Nov 2001 +--+---+---+---+-+-+-+--+---+---+--+---+---+---+---+--+--+---+---+ |12|192|132|221|3|0|9|18|101|120|97|109|112|108|101|46|99|111|109| +--+---+---+---+-+-+-+--+---+---+--+---+---+---+---+--+--+---+---+ This is eight octets of VUID data, followed by "example.com" represented in ASCII. 10.4. Link-layer address This type of DUID consists of a two octet network hardware type code, followed by the link-layer address of any one network interface that is permanently connected to the DHCP client device. The hardware type MUST be a valid hardware type assigned by the IANA as described in the section on ARP in RFC 826. The hardware type is stored in network order. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Hardware type (16 bits) | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . . . link-layer address (variable length) . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The choice of network interface can be completely arbitrary, as long as that interface provides a unique link-layer address and is permanently attached to the device on which the DUID is being generated. The same DUID should be used in configuring all network interfaces connected to the device, regardless of which interface's link-layer address was used to generate the DUID. This type of DUID is recommended for devices that have a permanently-connected network interface with a link-layer address and do not have nonvolatile, writable stable storage. This type of DUID MUST NOT be used by DHCP clients that cannot tell whether or not a network interface is permanently attached to the device on which the DHCP client is running. 11. Identity association An "identity-association" (IA) is a construct through which a server and a client can identify, group and manage IPv6 addresses. Each IA consists of an IAID and associated configuration information. A client associates an IA with one of its interfaces and uses the IA to obtain configuration information for that interface from a server. The configuration information in an IA consists of one or more IPv6 addresses and other parameters. The parameters are specified as DHCP Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 18] Internet Draft DHCP for IPv6 21 Nov 2001 options within the IA, and are associated with the addresses in the IA and the interface to which the IA belongs. Other parameters that are not associated with a particular interface may be specified in the options section of a DHCP message, outside the scope of any IA. Each address in an IA has a preferred lifetime and a valid lifetime, as defined in RFC2462 [20]. The lifetimes are transmitted from the DHCP server to the client in the IA option. The lifetimes apply to the use of IPv6 addresses as described in section 5.5.4 of RFC2462. An address whose valid lifetime has expired MAY be discarded from the IA. See section 20.3 for the representation of an IA in a DHCP message. 12. Selecting addresses for assignment to an IA A server selects addresses to be assigned to an IA according to the address assignment policies determined by the server administrator and the specific information the server determines about the client from the following sources: - The link to which the client is attached: * If the server receives the message directly from the client and the source address in the IP datagram in which the message was received is a link-local address, then the client is on the same link to which the interface over which the message was received is attached * If the server receives the message directly from the client and the source address in the IP datagram in which the message was received is not a link-local address, then the client is on the link identified by the source address in the IP datagram * If the server receives the message from a forwarding relay agent, then the client is on the same link as the one to which the interface identified by the link-address field in the message from the relay is attached - The DUID supplied by the client - Other information in options supplied by the client - Other information in options supplied by the relay agent 13. Reliability of Client Initiated Message Exchanges DHCP clients are responsible for reliable delivery of messages in the client-initiated message exchanges described in sections 15 and 16. If a DHCP client fails to receive an expected response from a server, Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 19] Internet Draft DHCP for IPv6 21 Nov 2001 the client must retransmit its message. This section describes the retransmission strategy to be used by clients in client-initiated message exchanges. The client begins the message exchange by transmitting a message to the server. The message exchange terminates when either the client successfully receives the appropriate response or responses from a server or servers, or when the message exchange is considered to have failed according to the retransmission mechanism described below. The client retransmission behavior is controlled and describe by five variables: RT Retransmission timeout IRT Initial retransmission time MRC Maximum retransmission count MRT Maximum retransmission time MRD Maximum retransmission duration RAND Randomization factor With each message transmission or retransmission, the client sets RT according to the rules given below. If RT expires before the message exchange terminates, the client recomputes RT and retransmits the message. Each of the computations of a new RT include a randomization factor (RAND), which is a random number chosen with a uniform distribution between -0.1 and +0.1. The randomization factor is included to minimize synchronization of messages transmitted by DHCP clients. The algorithm for choosing a random number does not need to be cryptographically sound. The algorithm SHOULD produce a different sequence of numbers from each invocation of the DHCP client. RT for the first message transmission is based on IRT: RT = 2*IRT + RAND*IRT RT for each subsequent message transmission is based on the previous value of RT: RT = 2*RTprev + RAND*RTprev MRT specifies an upper bound on the value of RT. If MRT has a value of 0, there is no upper limit on the value of RT. Otherwise: if (RT > MRT) Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 20] Internet Draft DHCP for IPv6 21 Nov 2001 RT = MRT + RAND*MRT MRC specifies an upper bound on the number of times a client may retransmit a message. If MRC has a value of 0, the client MUST continue to retransmit the original message until a response is received. Otherwise, the message exchange fails if the client attempts to transmit the original message more than MRC times. MRD specifies an upper bound on the length of time a client may retransmit a message. If MRD has a value of 0, the client MUST continue to retransmit the original message until a response is received. Otherwise, the message exchange fails if the client attempts to transmit the original message more than MRD seconds. If both MRC and MRD are non-zero, the message exchange fails whenever either of the conditions specified in the previous paragraph are met. Implementations SHOULD verify that for retransmissions that MRC, MRT, and MRD are not all set to zero for any retransmission case. 14. Message validation Servers MUST discard any received messages that include authentication information and fail the authentication check by the server. Clients MUST discard any received messages that include authentication information and fail the authentication check by the client, except as noted in section 19.6.5.2. 14.1. Use of Transaction-ID field The "transaction-ID" field holds a value used by clients and servers to synchronize server responses to client messages. A client SHOULD choose a different transaction-ID for each new message it sends. A client MUST leave the transaction-ID unchanged in retransmissions of a message. 14.2. Solicit message Clients MUST discard any received Solicit messages. Relay agents MUST discard any Solicit messages received through port 546. 14.3. Advertise message Clients MUST discard any received Advertise messages in which the "Transaction-ID" field value does not match the value the client used in its Solicit message. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 21] Internet Draft DHCP for IPv6 21 Nov 2001 Servers and relay agents MUST discard any received Advertise messages. 14.4. Request message Clients MUST discard any received Request messages. Relay agents MUST discard any Request messages received through port 546. Servers MUST discard any received Request message in which the value in the ``server-address'' field does not match any of the addresses used by the server. 14.5. Confirm message Clients MUST discard any received Confirm messages. Relay agents MUST discard any Confirm messages received through port 546. 14.6. Renew message Clients MUST discard any received Renew messages. Relay agents MUST discard any Renew messages received through port 546. Servers MUST discard any received Renew message in which the value in the ``server-address'' field does not match any of the addresses used by the server. 14.7. Rebind message Clients MUST discard any received Rebind messages. Relay agents MUST discard any Rebind messages received through port 546. 14.8. Decline messages Clients MUST discard any received Decline messages. Relay agents MUST discard any Decline messages received through port 546. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 22] Internet Draft DHCP for IPv6 21 Nov 2001 Servers MUST discard any received Decline message in which the value in the ``server-address'' field does not match any of the addresses used by the server. 14.9. Release message Clients MUST discard any received Release messages. Relay agents MUST discard any Release messages received through port 546. Servers MUST discard any received Release message in which the value in the ``server-address'' field does not match any of the addresses used by the server. 14.10. Reply message Clients MUST discard any received Reply messages in which the ``transaction-ID'' field in the message does not match the value used in the original message. Servers and relay agents MUST discard any received Reply messages. 14.11. Reconfigure-init message Servers and relay agents MUST discard any received Reconfigure-init messages. Clients MUST discard any Reconfigure-init messages that do not contain an authentication option or that fail the authentication performed by the client. 14.12. Inform message Clients MUST discard any received Inform messages. Relay agents MUST discard any Inform messages received through port 546. 14.13. Relay-forward message Clients MUST discard any received Relay-forward messages. 14.14. Relay-reply message Clients and servers MUST discard any received Relay-reply messages. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 23] Internet Draft DHCP for IPv6 21 Nov 2001 15. DHCP Server Solicitation This section describes how a client locates servers that will assign addresses to IAs belonging to the client. The client is responsible for creating IAs and requesting that a server assign configuration information, including IPv6 addresses, to the IA. The client first creates an IA and assigns it an IAID. The client then transmits a Solicit message containing an IA option describing the IA. Servers that can assign configuration information to the IA respond to the client with an Advertise message. The client then initiates a configuration exchange as described in section 16. 15.1. Client Behavior A client uses the Solicit message to discover DHCP servers configured to serve addresses on the link to which the client is attached. 15.1.1. Creation of Solicit messages The client sets the "msg-type" field to SOLICIT. The client generates a transaction ID and inserts this value in the "transaction-ID" field. The client MUST include a DUID option to identify itself to the server. The client MUST include IA options for any IAs to which it wants the server to assign addresses. The client MAY include addresses in the IAs as a hint to the server about addresses for which the client may have a preference. The client MAY include an Option Request Option in the Solicit message. The client MUST NOT include any other options except those specifically allowed as defined by specific options. 15.1.2. Transmission of Solicit Messages The client sends the Solicit message to the All_DHCP_Agents multicast address. The client MUST use an IPv6 address assigned to the interface for which the client is interested in obtaining configuration information as the source address in the IP header of the datagram carrying the Solicit message. The Solicit message MUST be transmitted on the link that the interface for which configuration information is being obtained is attached to. The client SHOULD send the message through that interface. The client MAY send the message through another interface attached to the same link if and only if the client is certain the two interface are attached to the same link. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 24] Internet Draft DHCP for IPv6 21 Nov 2001 The first Solicit message from the client on the interface MUST be delayed by a random amount of time between MIN_SOL_DELAY and MAX_SOL_DELAY. This random delay desynchronizes clients which start at the same time (e.g., after a power outage). The client transmits the message according to section 13, using the following parameters: IRT SOL_TIMEOUT MRT SOL_MAX_RT MRC 0 MRD 0 The mechanism in section 13 is modified as follows for use in the transmission of Solicit messages. The message exchange is not terminated by the receipt of an Advertise before SOL_TIMEOUT has elapsed. Rather, the client collects Advertise messages until SOL_TIMEOUT has elapsed. The first RT MUST be selected to be strictly greater than SOL_TIMEOUT by choosing RAND to be strictly greater than 0. A client MUST collect Advertise messages for SOL_TIMEOUT seconds, unless it receives an Advertise message with a preference value of 255. The preference value is carried in the Preference option (section 20.6). Any Solicit that does not include a Preference option is considered to have a preference value of 0. If the client receives an Advertise message with a preference value of 255, then the client MAY act immediately on that Advertise message without waiting for any more additional Advertise messages. A DHCP client SHOULD choose MRC and MRD to be 0. If the DHCP client is configured with either MRC or MRD set to a value other than 0, it MUST stop trying to configure the interface if the message exchange fails. After the DHCP client stops trying to configure the interface, it MAY choose to restart the reconfiguration process after some external event, such as user input, system restart, or when the client is attached to a new link. 15.1.3. Receipt of Advertise messages The client MUST ignore any Advertise message that includes a Status Code option containing the value AddrUnavail, with the exception that the client MAY display the associated status message to the user. Upon receipt of one or more valid Advertise messages, the client selects one or more Advertise messages based upon the following criteria. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 25] Internet Draft DHCP for IPv6 21 Nov 2001 - Those Advertise messages with the highest server preference value are preferred over all other Advertise messages. - Within a group of Advertise messages with the same server preference value, a client MAY select those servers whose Advertise messages advertise information of interest to the client. For example, the client may choose a server that returned an advertisement with configuration options of interest to the client. - The client MAY choose a less-preferred server if that server has a better set of advertised parameters, such as the available addresses advertised in IAs. Once a client has selected Advertise message(s), the client will typically store information about each server, such as server preference value, addresses advertised, when the advertisement was received, and so on. Depending on the requirements of the user that invoked the DHCP client, the client MAY initiate a configuration exchange with the server(s) immediately, or MAY defer this exchange until later. If the client needs to select an alternate server in the case that a chosen server does not respond, the client chooses the next server according to the criteria given above. 15.2. Server Behavior A server sends an Advertise message in response to Solicit messages it receives to announce the availability of the server to the client. 15.2.1. Receipt of Solicit messages The server determines the information about the client and its location as described in section 12. If administrative policy permits the server to respond to the client, the server will generate and send an Advertise message to the client. 15.2.2. Creation and transmission of Advertise messages The server sets the "msg-type" field to ADVERTISE and copies the contents of the transaction-ID field from the Solicit message received from the client to the Advertise message. The server places one of its IP addresses (determined through administrator setting) in the "server-address" field of the Advertise message. The server MAY add a Preference option to carry the preference value for the Advertise message. The server implementation SHOULD allow the setting of a server preference value by the administrator. The server preference value Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 26] Internet Draft DHCP for IPv6 21 Nov 2001 MUST default to zero unless otherwise configured by the server administrator. The server MUST include IA options in the Advertise message containing any addresses that would be assigned to IAs contained in the Solicit message from the client. The server MAY include some or all of the IA options from the client in the Advertise message. If the server will not assign any addresses to IAs in a subsequent Request from the client, the server MAY either send an Advertise message to the client that includes only a status code option with the status code set to AddrUnavail and a status message for the user or discard the Advertise message. The server MAY include other options the server will return to the client in a subsequent Reply message. The information in these options will be used by the client in the selection of a server if the client receives more than one Advertise message. The server SHOULD include options specifying values for options requested by the client in an Option Request Option included in the Solicit message. If the Solicit message was received directly by the server, the server unicasts the Advertise message directly to the client using the address in the source address field from the IP datagram in which the Solicit message was received. The Advertise message MUST be unicast through the interface on which the Solicit message was received. If the Solicit message was received in a Relay-forward message, the server constructs a Relay-reply message with the Advertise message in the payload of a "server-message" option. The server unicasts the Relay-reply message directly to the relay agent using the address in the source address field from the IP datagram in which the Relay-forward message was received. 16. DHCP Client-Initiated Configuration Exchange A client initiates a message exchange with a server or servers to acquire or update configuration information of interest. The client may initiate the configuration exchange as part of the operating system configuration process or when requested to do so by the application layer. 16.1. Client Behavior A client will use Request, Confirm, Renew, Rebind and Inform messages to acquire and confirm the validity of configuration information. The client uses the server address information and information about IAs from previous Advertise messages for use in constructing Request messages. Note that a client may request configuration information from one or more servers at any time. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 27] Internet Draft DHCP for IPv6 21 Nov 2001 16.1.1. Creation and transmission of Request messages The client uses a Request message to populate IAs with addresses and obtain other configuration information. The client includes one or more IA options in the Request message, with addresses and information about the IAs that were obtained from the server in a previous Advertise message. The server then returns addresses and other information about the IAs to the client in IA options in a Reply message. The client generates a transaction ID and inserts this value in the "transaction-ID" field. The client places the address of the destination server in the "server-address" field. The client MUST include a DUID option to identify itself to the server. The client adds any other appropriate options, including one or more IA options (if the client is requesting that the server assign it some network addresses). The list of addresses in each included IA MUST include the addresses received by the client in a previous Advertise message. If the client has a source address of sufficient scope that can be used by the server as a return address and the client has received a Client Unicast option (section 20.12) from the server, the client SHOULD unicast the Request message to the server. Otherwise, the client MUST send the Request message to the All_DHCP_Agents multicast address. The client MUST use an address assigned to the interface for which the client is interested in obtaining configuration information as the source address in the IP header of the datagram carrying the Request message. DISCUSSION: Use of multicast and relay agents enables the inclusion of relay agent options in all messages sent by the client. The server should enable the use of unicast only when relay agent options will not be used. If the client multicasts the Request message, the message MUST be transmitted on the link that the interface for which configuration information is being obtained is attached to. The client SHOULD send the message through that interface. The client MAY send the message through another interface attached to the same link if and only if the client is certain the the two interface are attached to the same link. The client transmits the message according to section 13, using the following parameters: IRT REQ_TIMEOUT Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 28] Internet Draft DHCP for IPv6 21 Nov 2001 MRT REQ_MAX_RT MRC REQ_MAX_RC MRD 0 If the message exchange fails, the client MAY choose one of the following actions: - Select another server from a list of servers known to the client; e. g., servers that responded with an Advertise message - Initiate the server discovery process described in section 15 - Terminate the configuration process and report failure 16.1.2. Creation and transmission of Confirm messages Whenever a client may have moved to a new link, its IPv6 addresses and other configuration information may no longer be valid. Examples of times when a client may have moved to a new link include: o The client reboots o The client is physically disconnected from a wired connection o The client returns from sleep mode o The client using a wireless technology changes links In any situation when a client may have moved to a new link, the client MUST initiate a Confirm/Reply message exchange. The client includes any IAs, along with the addresses associated with those IAs, in its Confirm message. Any responding servers will indicate the acceptability of the addresses with the status in the Reply message it returns to the client. The client sets the "msg-type" field to CONFIRM. The client generates a transaction ID and inserts this value in the "transaction-ID" field. The client sets the "server-address" field to 0. The client MUST include a DUID option to identify itself to the server. The client adds any appropriate options, including one or more IA options. The client MUST include the addresses the client currently has associated with those IAs. The client sends the Confirm message to the All_DHCP_Agents multicast address. The client MUST use an IPv6 address assigned to the interface for which the client is interested in obtaining Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 29] Internet Draft DHCP for IPv6 21 Nov 2001 configuration information as the source address in the IP header of the datagram carrying the Confirm message. The Confirm message MUST be transmitted on the link that the interface for which configuration information is being obtained is attached to. The client SHOULD send the message through that interface. The client MAY send the message through another interface attached to the same link if and only if the client is certain the the two interface are attached to the same link. The client transmits the message according to section 13, using the following parameters: IRT CNF_TIMEOUT MRT CNF_MAX_RT MRC 0 MRD CNF_MAX_RD If the client receives no responses before the message transmission process as described in section 13 terminates, the client SHOULD continue to use any IP addresses, using the last known lifetimes for those addresses, and SHOULD continue to use any other previously obtained configuration parameters. 16.1.3. Creation and transmission of Renew messages To extend the valid and preferred lifetimes associated with addresses, the client sends a Renew message to the server containing an "IA option" for the IA and its associated addresses. The server determines new lifetimes for the addresses in the IA according to the administrative configuration of the server. The server may also add new addresses to the IA. The server may remove addresses from the IA by setting the preferred and valid lifetimes of those addresses to zero. The server controls the time at which the client contacts the server to extend the lifetimes on assigned addresses through the T1 and T2 parameters assigned to an IA. At time T1 for an IA, the client initiates a Renew/Reply message exchange to extend the lifetimes on any addresses in the IA. The client includes an IA option with all addresses currently assigned to the IA in its Renew message. The client sets the "msg-type" field to RENEW. The client generates a transaction ID and inserts this value in the "transaction-ID" field. The client places the address of the destination server in the "server-address" field. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 30] Internet Draft DHCP for IPv6 21 Nov 2001 The client MUST include a DUID option to identify itself to the server. The client adds any appropriate options, including one or more IA options (if the client is requesting that the server extend the lifetimes of the addresses assigned to those IAs; note that the client may check the status of other configuration parameters without asking for lifetime extensions). If the client does include any IA options, it MUST include the list of addresses the client currently has associated with that IA. If the client has a source address of sufficient scope that can be used by the server as a return address and the client has received a Client Unicast option (section 20.12) from the server, the client SHOULD unicast the Renew message to the server. Otherwise, the client sends the Renew message to the All_DHCP_Agents multicast address. The client MUST use an address assigned to the interface for which the client is interested in obtaining configuration information as the source address in the IP header of the datagram carrying the Renew message. If the Renew message is multicast, it MUST be transmitted on the link that the interface for which configuration information is being obtained is attached to. The client SHOULD send the message through that interface. The client MAY send the message through another interface attached to the same link if and only if the client is certain the the two interface are attached to the same link. The client transmits the message according to section 13, using the following parameters: IRT REN_TIMEOUT MRT REP_MAX_RT MRC 0 MRD 0 The mechanism in section 13 is modified as follows for use in the transmission of Renew messages. The message exchange is terminated when time T2 is reached (see section 16.1.4), at which time the client begins a Rebind message exchange. 16.1.4. Creation and transmission of Rebind messages At time T2 for an IA (which will only be reached if the server to which the Renew message was sent at time T1 has not responded), the client initiates a Rebind/Reply message exchange. The client includes an IA option with all addresses currently assigned to the IA in its Rebind message. The client sends this message to the All_DHCP_Agents multicast address. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 31] Internet Draft DHCP for IPv6 21 Nov 2001 The client sets the "msg-type" field to REBIND. The client generates a transaction ID and inserts this value in the "transaction-ID" field. The client sets the "server-address" field to 0. The client MUST include a DUID option to identify itself to the server. The client adds any appropriate options, including one or more IA options. If the client does include any IA options (if the client is requesting that the server extend the lifetimes of addresses assigned to those IAs; note that the client may check the status of other configuration parameters without asking for lifetime extensions), it MUST include the list of addresses the client currently has associated with that IA. The client sends the Rebind message to the All_DHCP_Agents multicast address. The client MUST use an IPv6 address assigned to the interface for which the client is interested in obtaining configuration information as the source address in the IP header of the datagram carrying the Rebind message. The Rebind message MUST be transmitted on the link that the interface for which configuration information is being obtained is attached to. The client SHOULD send the message through that interface. The client MAY send the message through another interface attached to the same link if and only if the client is certain the the two interface are attached to the same link. The client transmits the message according to section 13, using the following parameters: IRT REB_TIMEOUT MRT REB_MAX_RT MRC 0 MRD 0 The mechanism in section 13 is modified as follows for use in the transmission of Rebind messages. The message exchange is terminated when the lifetimes on the addresses assigned to the IA expire (see section 11), at which time the client has several alternative actions to choose from: - The client may choose to use a Solicit message to locate a new DHCP server and send a Request for the expired IA to the new server - The client may have other addresses in other IAs, so the client may choose to discard the expired IA and use the addresses in the other IAs Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 32] Internet Draft DHCP for IPv6 21 Nov 2001 16.1.5. Creation and Transmission of Inform messages The client uses an Inform message to obtain configuration information without having addresses assigned to it. The client sets the "msg-type" field to INFORM. The client generates a transaction ID and inserts this value in the "transaction-ID" field. The client sets the "server-address" field to 0. The client MUST include a DUID option to identify itself to the server. The client adds any appropriate options such as an ORO to indicate to the server what configuration information the client is interested in obtaining. The client MUST use an IPv6 address assigned to the interface for which the client is interested in obtaining configuration information as the source address in the IP header of the datagram carrying the Rebind message. If the client has an IPv6 address of sufficient scope, the client MAY choose to send the Inform message to the Allmulticast address. Otherwise, the client MUST send the Inform message to the All_DHCP_Agents multicast address. The Inform message MUST be transmitted on the link that the interface for which configuration information is being obtained is attached to. The client SHOULD send the message through that interface. The client MAY send the message through another interface attached to the same link if and only if the client is certain the the two interface are attached to the same link. The client transmits the message according to section 13, using the following parameters: IRT INF_TIMEOUT MRT INF_MAX_RT MRC 0 MRD 0 16.1.6. Receipt of Reply message in response to a Request, Confirm, Renew, Rebind or Inform message Upon the receipt of a valid Reply message in response to a Request, Confirm, Renew or Rebind message, the client extracts the configuration information contained in the Reply. The client MAY choose to report any status code or message from the status code option in the Reply message. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 33] Internet Draft DHCP for IPv6 21 Nov 2001 The client SHOULD perform duplicate address detection [20] on each of the addresses in any IAs it receives in the Reply message. If any of the addresses are found to be in use on the link, the client sends a Decline message to the server as described in section 16.1.9. The client records the T1 and T2 times for each IA in the Reply message. The client records any addresses included with IAs in the Reply message. The client updates the preferred and valid lifetimes for the addresses in the IA from the lifetime information in the IA option. The client leaves any addresses that the client has associated with the IA that are not included in the IA option unchanged. If the Reply was received in response to a Renew or Rebind message, the client must update the information in any IA option contained in the Reply message. The client adds any new addresses from the IA option to the IA, updates lifetimes for existing addresses in the IA from the IA option and discards any addresses with a lifetime of zero in the IA option. Management of the specific configuration information is detailed in the definition of each option, in section 20. When the client receives a NoPrefixMatch status in an IA from the server the client can assume it needs to send a Request to the server to obtain appropriate addresses for the IA. If the client receives any Reply messages that do not indicate a NoPrefixMatch status, the client can use the addresses in the IA and ignore any messages that do indicate a NoPrefixMatch status. When the client receives an AddrUnavail status in an IA from the server for a Request message the client will have to find a new server to create an IA. When the client receives a NoBinding status status in an IA from the server for a Confirm message the client can assume it needs to send a Request to reestablish an IA with the server. When the client receives a ConfNoMatch status in an IA from the server for a Confirm message the client can send a Renew message to the server to extend the lifetimes of the addresses. When the client receives a NoBinding status in an IA from the server for a Renew message the client can assume it needs to send a Request to reestablish an IA with the server. When the client receives a RenwNoMatch status in an IA from the server for a Renew message the client can assume it needs to send a Request to reestablish an IA with the server. When the client receives an AddrUnavail status in an IA from the server for a Renew message the client can assume it needs to send a Request to reestablish an IA with the server. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 34] Internet Draft DHCP for IPv6 21 Nov 2001 When the client receives a NoBinding status in an IA from the server for a Rebind message the client can assume it needs to send a Request to reestablish an IA with the server or try another server. When the client receives a RebdNoMatch status in an IA from the server for a Rebind message the client can assume it needs to send a Request to reestablish an IA with the server or try another server. When the client receives an AddrUnavail status in an IA from the server for a Rebind message the client can assume it needs to send a Request to reestablish an IA with the server or try another server. 16.1.7. Creation and transmission of Release messages The client sets the "msg-type" field to RELEASE. The client generates a transaction ID and places this value in the "transaction-ID" field. The client places the IP address of the server that allocated the address(es) in the "server-address" field. The client MUST include a DUID option to identify itself to the server. The client includes options containing the IAs it is releasing in the "options" field. The addresses to be released MUST be included in the IAs. The client continues to use any other addresses in the IA. The appropriate "status" field in the options MUST be set to indicate the reason for the release. The client MUST NOT use any of the addresses in the IAs in the message as the source address in the Release message or in any subsequently transmitted message. If the client has a source address of sufficient scope that can be used by the server as a return address and the client has received a Client Unicast option (section 20.12) from the server, the client SHOULD unicast the Release message to the server. Otherwise, the client MUST send the Release message to the All_DHCP_Agents multicast address. The client MUST use an address for the interface to which the IAs in the Release message are assigned as the source address for the Release message. DISCUSSION: Use of multicast and relay agents enables the inclusion of relay agent options in all messages sent by the client. The server MUST NOT enable the use of unicast for a client when relay agent options are required for that client. If the Release message is multicast, it MUST be transmitted on the link that the interface for which configuration information is being obtained is attached to. The client SHOULD send the message through that interface. The client MAY send the message through another Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 35] Internet Draft DHCP for IPv6 21 Nov 2001 interface attached to the same link if and only if the client is certain the the two interface are attached to the same link. A client MAY choose to wait for a Reply message from the server in response to the Release message. If the client does wait for a Reply, the client MAY choose to retransmit the Release message. The client transmits the message according to section 13, using the following parameters: IRT REL_TIMEOUT MRT 0 MRC REL_MAX_MRC MRD 0 The client MUST abandon the attempt to release addresses if the Release message exchange fails. The client MUST stop using all of the addresses in the IA(s) being released as soon as the client begins the Release message exchange process. If an IA is released but the Reply from a DHCP server is lost, the client will retransmit the Release message, and the server may respond with a Reply indicating a status of "Nobinding". Therefore, the client does not treat a Reply message with a status of "Nobinding" in a Release message exchange as if it indicates an error. Note that if the client fails to release the IA, the addresses assigned to the IA will be reclaimed by the server when the lifetime of the address expires. 16.1.8. Receipt of Reply message in response to a Release message Upon receipt of a valid Reply message, the client can consider the Release event successful. 16.1.9. Creation and transmission of Decline messages The client sets the "msg-type" field to DECLINE. The client generates a transaction ID and places this value in the "transaction-ID" field. The client places the IP address of the server that allocated the address(es) in the "server-address" field. The client MUST include a DUID option to identify itself to the server. The client includes options containing the IAs it is declining in the "options" field. The addresses to be declined MUST be included in the IAs. The client continues to use other addresses Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 36] Internet Draft DHCP for IPv6 21 Nov 2001 in the IAs. The appropriate "status" field in the options MUST be set to indicate the reason for declining the address. The client MUST NOT use any of the addresses in the IAs in the message as the source address in the Decline message or in any subsequently transmitted message. If the client has a source address of sufficient scope that can be used by the server as a return address and the client has received a Client Unicast option (section 20.12) from the server, the client SHOULD unicast the Decline message to the server. Otherwise, the client MUST send the Decline message to the All_DHCP_Agents multicast address. The client MUST use an IPv6 address for the interface to which the IAs in the Decline message are assigned as the source address for the Decline message. DISCUSSION: Use of multicast and relay agents enables the inclusion of relay agent options in all messages sent by the client. The server MUST NOT enable the use of unicast for a client when relay agent options are required for that client. If the Decline message is multicast, it MUST be transmitted on the link that the interface for which configuration information is being obtained is attached to. The client SHOULD send the message through that interface. The client MAY send the message through another interface attached to the same link if and only if the client is certain the the two interface are attached to the same link. The client transmits the message according to section 13, using the following parameters: IRT DEC_TIMEOUT MRT DEC_MAX_RT MRC DEC_MAX_RC MRD 0 The client MUST abandon the attempt to decline addresses if the Decline message exchange fails. 16.1.10. Receipt of Reply message in response to a Decline message Upon receipt of a valid Reply message, the client can consider the Decline event successful. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 37] Internet Draft DHCP for IPv6 21 Nov 2001 16.2. Server Behavior For this discussion, the Server is assumed to have been configured in an implementation specific manner with configuration of interest to clients. 16.2.1. Receipt of Request messages The server MAY choose to discard Request messages received via unicast from a client to which the server has not sent a unicast option. When the server receives a Request and IA option(s) are included the client is requesting the configuration of a new IA by the server. The server MUST take the IA from the client and associate a binding for that client in an implementation-specific manner within the configuration parameter database for DHCP clients managed by the server. Upon the receipt of a valid Request message from a client the server can respond to, (implementation-specific administrative policy satisfied) the server scans the options field. The server then constructs a Reply message and sends it to the client. The server SHOULD process each option for the client in an implementation-specific manner. The server MUST construct a Reply message containing the following values: msg-type REPLY transaction-ID The transaction-ID from the Request message. server address One of the IP addresses assigned to the interface through which the server received the message from the client. If the server finds that the prefix on one or more IP addresses in any IA in the message from the client is not a valid prefix for the link to which the client is connected, the server MUST return the IA to the client with the status field set to NoPrefixMatch. If the server cannot assign any addresses to any of the IAs in the message from the client, the server SHOULD include the IAs in the Reply message with the status field set to AddrUnavail and no addresses in the IA. For any IAs to which the server can assign addresses, server includes the IA with addresses and other configuration parameters a status of Success, and add the IA as a new client binding. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 38] Internet Draft DHCP for IPv6 21 Nov 2001 The server adds options to the Reply message for any other configuration information to be assigned to the client. 16.2.2. Receipt of Confirm messages When the server receives a Confirm message, the client is requesting confirmation that the configuration information it will use is valid. The server SHOULD locate the binding for that client and compare the information in the Confirm message from the client to the information associated with that client. Upon the receipt of a valid Confirm message from a client the server can respond to, (implementation-specific administrative policy satisfied) the server scans the options field. If the server cannot determine if the information in the Confirm message is valid or invalid, the server MUST NOT send a reply to the client. For example, if the server does not have a binding for the client, but the configuration information in the Confirm message appears valid, the server does not reply. If the server finds that the information for the client does not match what is in the binding for that client or the configuration information is not valid, the server sends a Reply message containing a Status Code option with the value ConfNoMatch. If the server finds that the information for the client does match the information in the binding for that client, and the configuration information is still valid, the server sends a Reply message containing a Status Code option with the value Success. The server SHOULD process each option for the client in an implementation-specific manner. The server MUST construct a Reply message containing the following values: msg-type REPLY transaction-ID The transaction-ID from the Confirm message. server address One of the IP addresses assigned to the interface through which the server received the message from the client. The Reply message from the server MUST contain a Status Code option and MUST NOT include any other options. 16.2.3. Receipt of Renew messages The server MAY choose to discard Renew messages received via unicast from a client to which the server has not sent a unicast option. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 39] Internet Draft DHCP for IPv6 21 Nov 2001 Upon the receipt of a valid Renew message from a client the server can respond to, (implementation-specific administrative policy satisfied) the server scans the options field. When the server receives a Renew and IA option from a client it SHOULD locate the clients binding and verify the information in the IA from the client matches the information stored for that client. If the server cannot find a client entry for this IA the server SHOULD return an IA containing no addresses with status set to NoBinding. If the server finds that the addresses in the IA for the client do not match the client binding the server should return an IA containing no addresses with status set to RenwNoMatch. If the server cannot Renew addresses for the client it SHOULD send back an IA containing no addresses to the client with the status field set to AddrUnavail. If the server finds the addresses in the IA for the client then the server SHOULD send back the IA to the client with new lifetimes and T1/T2 times if the default is not being used, and set status to Success. The server may choose to change the list of addresses and the lifetimes of addresses in IAs that are returned to the client. The server SHOULD process each option for the client in an implementation-specific manner. The server MUST construct a Reply message containing the following values: msg-type REPLY transaction-ID The transaction-ID from the Renew message. server address One of the IP addresses assigned to the interface through which the server received the message from the client. 16.2.4. Receipt of Rebind messages Upon the receipt of a valid Rebind message from a client the server can respond to, (implementation-specific administrative policy satisfied) the server scans the options field. When the server receives a Rebind and IA option from a client it SHOULD locate the clients binding and verify the information in the IA from the client matches the information stored for that client. If the server cannot find a client entry for this IA the server SHOULD return an IA containing no addresses with status set to NoBinding. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 40] Internet Draft DHCP for IPv6 21 Nov 2001 If the server finds that the addresses in the IA for the client do not match the client binding the server should return an IA containing no addresses with status set to RebdNoMatch. If the server cannot Rebind addresses for the client it SHOULD send back an IA containing no addresses to the client with the status field set to AddrUnavail. If the server finds the addresses in the IA for the client then the server SHOULD send back the IA to the client with new lifetimes and T1/T2 times if the default is not being used, and set status to Success. The server SHOULD process each option for the client in an implementation-specific manner. The server MUST construct a Reply message containing the following values: msg-type REPLY transaction-ID The transaction-ID from the Rebind message. server address One of the IP addresses assigned to the interface through which the server received the message from the client. There is a significant difference between Renew and Rebind messages: Because the Renew message is processed by a single server, the responding server can actually change the addresses in the IA. However, because multiple servers may respond to a Rebind, all they can safely do is update T1, T2 (for the IA) and lifetimes (for individual addresses). 16.2.5. Receipt of Inform messages When the server receives an Inform message, the client is requesting configuration information that does not include the assignment of any addresses. The server SHOULD determine all configuration parameters appropriate to the client, based on the server configuration policies known to the server. Upon the receipt of a valid Inform message from a client the server can respond to, (implementation-specific administrative policy satisfied) the server scans the options field. The server then constructs a Reply message and sends it to the client. The server SHOULD process each option for the client in an implementation-specific manner. The server MUST construct a Reply message containing the following values: msg-type REPLY transaction-ID The transaction-ID from the Inforrm message. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 41] Internet Draft DHCP for IPv6 21 Nov 2001 server address One of the IP addresses assigned to the interface through which the server received the message from the client. The server adds options to the Reply message for all of the configuration parameters to be returned to the client. 16.2.6. Receipt of Release messages The server MAY choose to discard Release messages received via unicast from a client to which the server has not sent a unicast option. Upon the receipt of a valid Release message, the server examines the IAs and the addresses in the IAs for validity. If the IAs in the message are in a binding for the client and the addresses in the IAs have been assigned by the server to those IAs, the server deletes the addresses from the IAs and makes the addresses available for assignment to other clients. If all of the IAs were valid and the addresses successfully released, the server generates a Reply message and includes a Status Code option with value Success. The server MUST NOT include any other options in the Reply message. A server is not required to (but may choose to as an implementation strategy) retain any record of an IA from which all of the addresses have been released. 16.2.7. Receipt of Decline messages The server MAY choose to discard Decline messages received via unicast from a client to which the server has not sent a unicast option. Upon the receipt of a valid Decline message, the server examines the IAs and the addresses in the IAs for validity. If the IAs in the message are in a binding for the client and the addresses in the IAs have been assigned by the server to those IA, the server deletes the addresses from the IAs. The server SHOULD mark the addresses declined by the client so that those addresses are not assigned to other clients, and MAY choose to make a notification that addresses were declined. If all of the IAs were valid and the addresses successfully declined, the server generates a Reply message and includes a Status Code option with value Success. The server MUST NOT include any other options in the Reply message. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 42] Internet Draft DHCP for IPv6 21 Nov 2001 16.2.8. Receipt of Decline messages Upon the receipt of a valid Inform message, the server determines the appropriate configuration parameters and returns those parameters to the client in a Reply message. The server MUST NOT include any IA options in the Reply message. 16.2.9. Sending of Reply messages If the Request, Confirm, Renew, Rebind, Release, Decline or Inform message from the client was originally received in a Relay-forward message from a relay, the server places the Reply message in the options field of a Relay-response message and copies the link-address and client-return-address fields from the Relay-forward message into the Relay-response message. The server then unicasts the Reply or Relay-reply to the source address from the IP datagram in which the original message was received. 17. DHCP Server-Initiated Configuration Exchange A server initiates a configuration exchange to cause DHCP clients to obtain new addresses and other configuration information. For example, an administrator may use a server-initiated configuration exchange when links in the DHCP domain are to be renumbered. Other examples include changes in the location of directory servers, addition of new services such as printing, and availability of new software (system or application). 17.1. Server Behavior A server sends a Reconfigure-init message to cause a client to initiate immediately a Rebind/Reply message exchange with the server. 17.1.1. Creation and transmission of Reconfigure-init messages The server sets the "msg-type" field to RECONFIG-INIT. The server generates a transaction-ID and inserts it in the "transaction-ID" field. The server places its address (of appropriate scope) in the "server-address" field. The server MAY include an ORO option to inform the client of what information has been changed or new information that has been added. In particular, the server specifies the IA option in the ORO if the server wants the client to obtain new address information. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 43] Internet Draft DHCP for IPv6 21 Nov 2001 The server MUST include an authentication option with the appropriate settings and add that option as the last option in the "options" field of the Reconfigure-init message. The server MUST NOT include any other options in the Reconfigure-init except as specifically allowed in the definition of individual options. A server sends each Reconfigure-init message to a single DHCP client, using an IPv6 unicast address of sufficient scope belonging to the DHCP client. The server may obtain the address of the client through the information that the server has about clients that have been in contact with the server, or the server may be configured with the address of the client through some external agent. To reconfigure more than one client, the server unicasts a separate message to each client. The server may initiate the reconfiguration of multiple clients concurrently; for example, a server may send a Reconfigure-init message to additional clients while previous reconfiguration message exchanges are still in progress. The Reconfigure-init message causes the client to initiate a Rebind/Reply message exchange with the server. The server interprets the receipt of a Rebind message from the client as satisfying the Reconfigure-init message request. 17.1.2. Time out and retransmission of Reconfigure-init messages If the server does not receive a Rebind message from the client in RECREP_MSG_TIMEOUT milliseconds, the server retransmits the Reconfigure-init message, doubles the RECREP_MSG_TIMEOUT value and waits again. The server continues this process until REC_MSG_ATTEMPTS unsuccessful attempts have been made, at which point the server SHOULD abort the reconfigure process for that client. Default and initial values for RECREP_MSG_TIMEOUT and REC_MSG_ATTEMPTS are documented in section 7.5. 17.1.3. Receipt of Rebind messages The server generates and sends Reply message(s) to the client as described in section 16.2.9, including in the "options" field new values for configuration parameters. It is possible that the client may send a Rebind message after the server has sent a Reconfigure-init but before the Reconfigure-init is received by the client. In this case, the Rebind message from the client may not include all of the IAs and requests for parameters to be reconfigured by the server. To accommodate this scenario, the server MAY choose to send a Reply with the IAs and other parameters Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 44] Internet Draft DHCP for IPv6 21 Nov 2001 to be reconfigured, even if those IAs and parameters were not in the Rebind message from the client. 17.2. Client Behavior A client MUST always monitor UDP port 546 for Reconfigure-init messages on interfaces upon which it has acquired DHCP parameters. Since the results of a reconfiguration event may affect application layer programs, the client SHOULD log these events, and MAY notify these programs of the change through an implementation-specific interface. 17.2.1. Receipt of Reconfigure-init messages Upon receipt of a valid Reconfigure-init message, the client initiates a Rebind/Reply transaction with the server. While the Rebind/Reply transaction is in progress, the client silently discards any Reconfigure-init messages it receives. DISCUSSION: The Reconfigure-init message acts as a trigger that signals the client to complete a successful Rebind/Reply message exchange. Once the client has received a Reconfigure-init, the client proceeds with the Rebind/Reply message exchange (retransmitting the Rebind if necessary); the client ignores any additional Reconfigure-init messages (regardless of the transaction ID in the Reconfigure-init message) until the Rebind/Reply exchange is complete. Subsequent Reconfigure-init messages (again independent of the transaction ID) cause the client to initiate a new Rebind/Reply exchange. How does this mechanism work in the face of duplicated or retransmitted Reconfigure-init messages? Duplicate messages will be ignored because the client will begin the Rebind/Reply exchange after the receipt of the first Reconfigure-init. Retransmitted messages will either trigger the Rebind/Reply exchange (if the first Reconfigure-init was not received by the client) or will be ignored. The server can discontinue retransmission of Reconfigure-init messages to the client once the server receives the Rebind from the client. It might be possible for a duplicate or retransmitted Reconfigure-init to be sufficiently delayed (and delivered out of order) to arrive at the client after the Rebind/Reply exchange (initiated by the original Reconfigure-init) has been completed. In this case, the client would initiate a redundant Rebind/Reply exchange. The likelihood of delayed and out of order delivery is small enough to be ignored. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 45] Internet Draft DHCP for IPv6 21 Nov 2001 The consequence of the redundant exchange is inefficiency rather than incorrect operation. 17.2.2. Creation and sending of Rebind messages When responding to a Reconfigure-init, the client creates and sends the Rebind message in exactly the same manner as outlined in section 16.1.1 with the following difference: IAs The client includes IA options containing the addresses the client currently has assigned to those IAs for the interface through which the Reconfigure-init message was received. 17.2.3. Time out and retransmission of Rebind messages The client uses the same variables and retransmission algorithm as it does with Rebind messages generated as part of a client-initiated configuration exchange. See section 16.1.1 for details. 17.2.4. Receipt of Reply messages Upon the receipt of a valid Reply message, the client extracts the contents of the "options" field, and sets (or resets) configuration parameters appropriately. The client records and updates the lifetimes for any addresses specified in IAs in the Reply message. If the configuration parameters changed were requested by the application layer, the client notifies the application layer of the changes using an implementation-specific interface. As discussed in section 17.1.3, the Reply from the server may include IAs and parameters that were not included in the Rebind message from the client. The client MUST configure itself with all of the IAs and parameters in the Reply from the server. 18. Relay Behavior For this discussion, the Relay MAY be configured to use a list of server destination addresses, which MAY include unicast addresses, the All_DHCP_Servers multicast address, or other multicast addresses selected by the network administrator. If the Relay has not been explicitly configured, it MUST use the All_DHCP_Servers multicast address as the default. 18.1. Relaying of client messages When a Relay receives a valid client message, it constructs a Relay-forward message. The relay places an address with a prefix assigned to the link on which the client should be assigned an Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 46] Internet Draft DHCP for IPv6 21 Nov 2001 address in the link-address field. This address will be used by the server to determine the link from which the client should be assigned an address and other configuration information. If the relay cannot use the address in the link-address field to identify the interface through which the response to the client will be forwarded, the relay MUST include a circuit-id option (see section 20.16)in the Relay-forward message. The server will include the circuit-id option in its Relay-reply message. The relay copies the source address from the IP datagram in which the message was received from the client into the client-return-address field in the Relay-forward message. The relay constructs a "client-message" option 20.8 that contains the entire message from the client in the data field of the option. The relay places the "relay-message" option along with any "relay-specific" options in the options field of the Relay-forward message. The Relay then sends the Relay-forward message to the list of server destination addresses that it has been configured with. 18.2. Relaying of server messages When the relay receives a Relay-reply message, it extracts the server message from the "server-message" option. If the Relay-reply message includes a circuit-id option, the relay forwards the message from the server to the client on the link identified by the circuit-id option. Otherwise, the relay forwards the message on the link identified by the link-address field. In either case, the relay forwards the message to the address in the client-return-address field in the Relay-reply message. 19. Authentication of DHCP messages Some network administrators may wish to provide authentication of the source and contents of DHCP messages. For example, clients may be subject to denial of service attacks through the use of bogus DHCP servers, or may simply be misconfigured due to unintentionally instantiated DHCP servers. Network administrators may wish to constrain the allocation of addresses to authorized hosts to avoid denial of service attacks in "hostile" environments where the network medium is not physically secured, such as wireless networks or college residence halls. Because of the risk of denial of service attacks against DHCP clients, the use of authentication is mandated in Reconfigure-init messages. A DHCP server MUST include an authentication option in Reconfigure-init messages sent to clients. The DHCP authentication mechanism is based on the design of authentication for DHCP for IPv4 [8]. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 47] Internet Draft DHCP for IPv6 21 Nov 2001 19.1. DHCP threat model The threat to DHCP is inherently an insider threat (assuming a properly configured network where DHCPv6 ports are blocked on the perimeter gateways of the enterprise). Regardless of the gateway configuration, however, the potential attacks by insiders and outsiders are the same. The attack specific to a DHCP client is the possibility of the establishment of a "rogue" server with the intent of providing incorrect configuration information to the client. The motivation for doing so may be to establish a "man in the middle" attack or it may be for a "denial of service" attack. There is another threat to DHCP clients from mistakenly or accidentally configured DHCP servers that answer DHCP client requests with unintentionally incorrect configuration parameters. The threat specific to a DHCP server is an invalid client masquerading as a valid client. The motivation for this may be for "theft of service", or to circumvent auditing for any number of nefarious purposes. The threat common to both the client and the server is the resource "denial of service" (DoS) attack. These attacks typically involve the exhaustion of valid addresses, or the exhaustion of CPU or network bandwidth, and are present anytime there is a shared resource. In current practice, redundancy mitigates DoS attacks the best. 19.2. Security of messages sent between servers and relay agents Relay agents and servers that choose to exchange messages securely use the IPsec mechanisms for IPv6 [10]. The way in which IPsec is employed by relay agents and servers is not specified in this document. 19.3. Summary of DHCP authentication Authentication of DHCP messages is accomplished through the use of the Authentication option. The authentication information carried in the Authentication option can be used to reliably identify the source of a DHCP message and to confirm that the contents of the DHCP message have not been tampered with. The Authentication option provides a framework for multiple authentication protocols. Two such protocols are defined here. Other protocols defined in the future will be specified in separate documents. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 48] Internet Draft DHCP for IPv6 21 Nov 2001 The protocol field in the Authentication option identifies the specific protocol used to generate the authentication information carried in the option. The algorithm field identifies a specific algorithm within the authentication protocol; for example, the algorithm field specifies the hash algorithm used to generate the message authentication code (MAC) in the authentication option. The replay detection method (RDM) field specifies the type of replay detection used in the replay detection field. 19.4. Replay detection The Replay Detection Method (RDM) field determines the type of replay detection used in the Replay Detection field. If the RDM field contains 0x00, the replay detection field MUST be set to the value of a monotonically increasing counter. Using a counter value such as the current time of day (e.g., an NTP-format timestamp [12]) can reduce the danger of replay attacks. This method MUST be supported by all protocols. 19.5. Configuration token protocol If the protocol field is 0, the authentication information field holds a simple configuration token. The configuration token is an opaque, unencoded value known to both the sender and receiver. The sender inserts the configuration token in the DHCP message and the receiver matches the token from the message to the shared token. If the configuration option is present and the token from the message does not match the shared token, the receiver MUST discard the message. Configuration token may be used to pass a plain-text configuration token and provides only weak entity authentication and no message authentication. This protocol is only useful for rudimentary protection against inadvertently instantiated DHCP servers. DISCUSSION: The intent here is to pass a constant, non-computed token such as a plain-text password. Other types of entity authentication using computed tokens such as Kerberos tickets or one-time passwords will be defined as separate protocols. 19.6. Delayed authentication protocol If the protocol field is 1, the message is using the "delayed authentication" mechanism. In delayed authentication, the client requests authentication in its Solicit message and the server replies with an Advertise message that includes authentication information. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 49] Internet Draft DHCP for IPv6 21 Nov 2001 This authentication information contains a nonce value generated by the source as a message authentication code (MAC) to provide message authentication and entity authentication. The use of a particular technique based on the HMAC protocol [11] using the MD5 hash [19] is defined here. 19.6.1. Management issues in the delayed authentication protocol The "delayed authentication" protocol does not attempt to address situations where a client may roam from one administrative domain to another, i.e. interdomain roaming. This protocol is focused on solving the intradomain problem where the out-of-band exchange of a shared secret is feasible. 19.6.2. Use of the Authentication option in the delayed authentication protocol In a Solicit message, the Authentication option carries the Protocol, Algorithm, RDM and Replay detection fields, but no Authentication information. In an Advertise, Request, Renew, Rebind or Confirm message, the Authentication option carries the Protocol, Algorithm, RDM and Replay detection fields and Authentication information. The format of the Authentication information is: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Secret ID (32 bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | HMAC-MD5 (128 bits) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The following definitions will be used in the description of the authentication information for delayed authentication, algorithm 1: Replay Detection - as defined by the RDM field K - a secret value shared between the source and destination of the message; each secret has a unique identifier (secret ID) secret ID - the unique identifier for the secret value used to generate the MAC for this message HMAC-MD5 - the MAC generating function. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 50] Internet Draft DHCP for IPv6 21 Nov 2001 The sender computes the MAC using the HMAC generation algorithm [11] and the MD5 hash function [19]. The entire DHCP message (except the MAC field of the authentication option itself), including the DHCP message header and the options field, is used as input to the HMAC-MD5 computation function. The 'secret ID' field MUST be set to the identifier of the secret used to generate the MAC. DISCUSSION: Algorithm 1 specifies the use of HMAC-MD5. Use of a different technique, such as HMAC-SHA, will be specified as a separate protocol. Delayed authentication requires a shared secret key for each client on each DHCP server with which that client may wish to use the DHCP protocol. Each secret key has a unique identifier that can be used by a receiver to determine which secret was used to generate the MAC in the DHCP message. Therefore, delayed authentication may not scale well in an architecture in which a DHCP client connects to multiple administrative domains. 19.6.3. Message validation To validate an incoming message, the receiver first checks that the value in the replay detection field is acceptable according to the replay detection method specified by the RDM field. Next, the receiver computes the MAC as described in [11]. The receiver MUST set the 'MAC' field of the authentication option to all 0s for computation of the MAC. If the MAC computed by the receiver does not match the MAC contained in the authentication option, the receiver MUST discard the DHCP message. 19.6.4. Key utilization Each DHCP client has a key, K. The client uses its key to encode any messages it sends to the server and to authenticate and verify any messages it receives from the server. The client's key SHOULD be initially distributed to the client through some out-of-band mechanism, and SHOULD be stored locally on the client for use in all authenticated DHCP messages. Once the client has been given its key, it SHOULD use that key for all transactions even if the client's configuration changes; e.g., if the client is assigned a new network address. Each DHCP server MUST know, or be able to obtain in a secure manner, the keys for all authorized clients. If all clients use the same key, clients can perform both entity and message authentication for all messages received from servers. However, the sharing of keys is strongly discouraged as it allows for unauthorized clients to masquerade as authorized clients by obtaining a copy of the shared Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 51] Internet Draft DHCP for IPv6 21 Nov 2001 key. To authenticate the identity of individual clients, each client MUST be configured with a unique key. 19.6.5. Client considerations for delayed authentication protocol 19.6.5.1. Sending Solicit messages When the client sends a Solicit message and wishes to use authentication, it includes an Authentication option with the desired protocol, algorithm, RDM and replay detection field as described in section 19.6. The client does not include any authentication information in the Authentication option. 19.6.5.2. Receiving Advertise messages The client validates any Advertise messages containing an Authentication option specifying the delayed authentication protocol using the validation test described in section 19.6.3. Client behavior if no Advertise messages include authentication information or pass the validation test is controlled by local policy on the client. According to client policy, the client MAY choose to respond to a Advertise message that has not been authenticated. The decision to set local policy to accept unauthenticated messages should be made with care. Accepting an unauthenticated Advertise message can make the client vulnerable to spoofing and other attacks. If local users are not explicitly informed that the client has accepted an unauthenticated Advertise message, the users may incorrectly assume that the client has received an authenticated address and is not subject to DHCP attacks through unauthenticated messages. A client MUST be configurable to discard unauthenticated messages, and SHOULD be configured by default to discard unauthenticated messages. A client MAY choose to differentiate between Advertise messages with no authentication information and Advertise messages that do not pass the validation test; for example, a client might accept the former and discard the latter. If a client does accept an unauthenticated message, the client SHOULD inform any local users and SHOULD log the event. 19.6.5.3. Sending Request, Confirm, Renew, Rebind or Release messages If the client authenticated the Advertise message through which the client selected the server, the client MUST generate authentication information for subsequent Request, Confirm, Renew, Rebind or Release messages sent to the server as described in section 19.6. When the client sends a subsequent message, it MUST use the same secret used by the server to generate the authentication information. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 52] Internet Draft DHCP for IPv6 21 Nov 2001 19.6.5.4. Receiving Reply messages If the client authenticated the Advertise it accepted, the client MUST validate the associated Reply message from the server. The client MUST discard the Reply if the message fails to pass validation and MAY log the validation failure. If the Reply fails to pass validation, the client MUST restart the DHCP configuration process by sending a Solicit message. The client MAY choose to remember which server replied with a Reply message that failed to pass validation and discard subsequent messages from that server. If the client accepted an Advertise message that did not include authentication information or did not pass the validation test, the client MAY accept an unauthenticated Reply message from the server. 19.6.6. Server considerations for delayed authentication protocol 19.6.6.1. Receiving Solicit messages and Sending Advertise messages The server selects a secret for the client and includes authentication information in the Advertise message returned to the client as specified in section 19.6. The server MUST record the identifier of the secret selected for the client and use that same secret for validating subsequent messages with the client. 19.6.6.2. Receiving Request, Confirm, Renew, Rebind or Release messages and Sending Reply messages The server uses the secret identified in the message and validates the message as specified in section 19.6.3. If the message fails to pass validation or the server does not know the secret identified by the 'secret ID' field, the server MUST discard the message and MAY choose to log the validation failure. If the message passes the validation procedure, the server responds to the specific message as described in section 16.2. The server MUST include authentication information generated using the secret identified in the received message as specified in section 19.6. 19.6.6.3. Sending Reconfigure-Init messages The server MUST include authentication information in a Reconfigure-Init message, generated as specified in section 19.6 using the secret the server initially selected for the client to which the Reconfigure-Init message is to be sent. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 53] Internet Draft DHCP for IPv6 21 Nov 2001 20. DHCP options Options are used to carry additional information and parameters in DHCP messages. Every option shares a common base format, as described in section 20.1. This document describes the DHCP options defined as part of the base DHCP specification. Other options may be defined in the future in a separate document. 20.1. Format of DHCP options 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | option-code | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | option-data | | (option-len octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code An unsigned integer identifying the specific option type carried in this option. option-len An unsigned integer giving the length of the data in this option in octets. option-data The data for the option; the format of this data depends on the definition of the option. 20.2. DHCP unique identifier option The DHCP unique identifier option is used to carry a DUID. The format for the DUID is keyed to mark the type of identifier and is of variable length. The format of the DUID option is: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION DUID | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DUID type | DUID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | . DUID (cont.) . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 54] Internet Draft DHCP for IPv6 21 Nov 2001 20.3. Identity association option The identity association option is used to carry an identity association, the parameters associated with the IA and the addresses assigned to the IA. The format of the IA option is: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION IA | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IAID (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | T1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | T2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IA Status | | +-+-+-+-+-+-+-+-+ | . Options . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_IA (TBD) option-len Variable; equal to 13 + number of bytes required for ``options'' IAID The unique identifier for this IA; chosen by the client T1 The time at which the client contacts the server from which the addresses in the IA were obtained to extend the lifetimes of the addresses assigned to the IA. T2 The time at which the client contacts any available server to extend the lifetimes of the addresses assigned to the IA. IA status Status of the IA in this option. options Options associated with this IA Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 55] Internet Draft DHCP for IPv6 21 Nov 2001 The Options field carries those options that are specific to this IA. This includes all of the Address Options to carry the addresses associated with this IA. Note that an IA has no explicit "lifetime" or "lease length" of its own. When the lifetimes of all of the addresses in an IA have expired, the IA can be considered as having expired. T1 and T2 are included to give servers explicit control over when a client recontacts the server about a specific IA. 20.4. IA Address option 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_IAADDR | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |T| addr status | prefix length | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | IPv6 address | | (16 octets) | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | preferred lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | pref. lifetime (cont.) | valid lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | valid lifetime (cont.) | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . . . Options . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_IADDR (TBD) option-len The number of bytes in the data area of this option T When set to 1, indicates that this address is a "temporary address" [15]; when set to 0, the address is not a temporary address. The 'T' bit identifies the associated address as a temporary address. If the server is configured to assign temporary addresses to the client, the server marks those temporary addresses with the 'T' bit. The number of temporary addresses assigned to the client and the lifetimes of those addresses is determined by the administrative configuration of the server. The 'T' bit only identifies an address Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 56] Internet Draft DHCP for IPv6 21 Nov 2001 as a temporary address; identification of an address as "temporary" has no implication on the lifetime of the extensibility of the lifetime of the address. addr status Status of this address in this IA. prefix length Prefix length for this address. IPv6 address An IPv6 address preferred lifetime The preferred lifetime for the IPv6 address in the option. valid lifetime The valid lifetime for the IPv6 address in the option options Options associated with this address The IA Address option is used to specify IPv6 addresses associated with an IA. It may only appear in an IA option. The Options field carries those options that are specific to this address. 20.5. Option request option 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_ORO | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | requested-option-code-1 | requested-option-code-2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_ORO (TBD) option-len Variable; equal to twice the number of option codes carried in this option. option-data A list of the option codes for the options requested in this option. A client MAY include an Option Request option in a Solicit, Request, Renew, Rebind or Confirm message to inform the server about options the client wants the server to send to the client. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 57] Internet Draft DHCP for IPv6 21 Nov 2001 20.6. Preference option 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_PREFERENCE | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | pref value | +-+-+-+-+-+-+-+-+ option-code OPTION_PREFERENCE (TBD) option-len MUST be 1 option-data The preference value for the server in this message. A server MAY include a Preference option in an Advertise message to control the selection of a server by the client. See section 15.1.3 for the use of the Preference option by the client and the interpretation of Preference option data value. 20.7. Elapsed Time 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_ELAPSED_TIME | option_len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | elapsed time | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_ELAPSED_TIME (TBD) option-len MUST be 2 option-data The amount of time since the client began its current DHCP transaction. This time is expressed in hundredths of a second (10^-2 seconds). A client MAY include an Elapsed Time option in messages to indicate how long the client has been trying to complete a DHCP transaction. Servers MAY use the data value in this option as input to policy controlling how a server responds to a client message. 20.8. Client message option Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 58] Internet Draft DHCP for IPv6 21 Nov 2001 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_CLIENT_MSG | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DHCP client message | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_CLIENT_MSG (TBD) option-len Variable; equal to the length of the forwarded DHCP client message. option-data The message received from the client; forwarded verbatim to the server. A relay agent forwards a message from a client to a server as the contents of a Client Message option in a Relay-forward message. 20.9. Server message option 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_SERVER_MSG | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DHCP server message | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_SERVER_MSG (TBD) option-len Variable; equal to the length of the forwarded DHCP server message. option-data The message received from the server; forwarded verbatim to the client. A server sends a DHCP message to be forwarded to a client by a relay agent as the contents of a Server Message option in a Relay-reply message. 20.10. DSTM Global IPv4 Address Option The DSTM Global IPv4 Address Option informs a client or server that the Identity Association Option (IA) following this option will contain an IPv4-Mapped IPv6 Address [9] in the case of a Client receiving the option, or is a Request for an IPv4-Mapped IPv6 Address Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 59] Internet Draft DHCP for IPv6 21 Nov 2001 from a client in the case of a DHCPv6 Server receiving the option. The option can also provide a set of IPv6 addresses to be used as the Tunnel Endpoint (TEP) to encapsulate an IPv6 packet within IPv6. This option can be used with the Request, Reply, and Reconfigure-Init Messages for cases where a server wants to assign to clients IPv4-Mapped IPv6 Addresses, thru the Option Request Option (ORO). 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_DSTM | option-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tunnel End Point (TEP) | | (If Present) | | (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option code OPTION_DSTM (TBD) option length Variable: 0 or multiple of 16 tunnel end point IPv6 Address or addresses if Present A DSTM IPv4 Global Address Option MUST only apply to the IA following this option. 20.11. Authentication option The Authentication option carries authentication information to authenticate the identity and contents of DHCP messages. The use of the Authentication option is described in section 19. The format of the Authentication option is: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_AUTH | option-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Protocol | Algorithm | RDM | Replay detect.| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Replay Detection (64 bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Replay cont. | Auth. Info | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Authentication Information | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 60] Internet Draft DHCP for IPv6 21 Nov 2001 option-code OPTION_AUTH (TBD) option-length Variable protocol The authentication protocol used in this authentication option algorithm The algorithm used in the authentication protocol RDM The replay detection method used in this authentication option Replay detection The replay detection information for the RDM Authentication information The authentication information, as specified by the protocol and algorithm used in this authentication option 20.12. Server unicast option This option is used by a server to send to a client to inform the client it MAY send a Request, Renew, Release, and Decline by unicasting directly to the server instead of the All_DHCPv6_Agents Multicast address as an optimization, when the client as an address of sufficient scope to reach the server. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_UNICAST | option-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_UNICAST (TBD) option-length 0 This option only applies to the server address that sends this to the client. 20.13. Domain Search Option This option provides a list of domain names a client can use to resolve DNS names. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 61] Internet Draft DHCP for IPv6 21 Nov 2001 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_DOMAIN_SEARCH_LIST | option-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Domain Search List | | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_DOMAIN_SEARCH_LIST (TBD) option-length variable Domain Search List The DNS domain search list the client should use to resolve names. So that the search list may be encoded compactly and uniformly, search strings in the search list are concatenated and encoded using the technique described in section 3.1 of [13]. For use in this specification, the compression pointer (see section 4.1.4 of [13]) refers to the offset within the SearchString portion of the option. 20.14. Domain Name Server Option This option provides a list of Domain Name System [13] that a client name resolver can use to access DNS services. There must be at least 1 server listed in this option. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_DNS_SERVERS | option_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | DNS server (IP address) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | DNS server (IP address) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_DNS_SERVERS (11) Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 62] Internet Draft DHCP for IPv6 21 Nov 2001 option-length variable DNS server IPv6 address of a DNS name server for the client to use. The DNS servers are listed in the order of preference for use by the client resolver. 20.15. Status Code Option This option returns indications of status not related to a specific option. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_STATUS_CODE | option-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | status-code | status-message | | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_STATUS_CODE (TBD) option-length variable status-code The numeric code for the status encoded in this option. The status codes are defined in section 7.4. status-message A UTF-8 encoded text string, which MUST NOT be null-terminated. 20.16. Circuit-ID Option This option provides a mechanism through which a relay agent can identify the network attachment point through which a message was received from a DHCP client. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_CIRCUIT_ID | option_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Circuit-ID | . . . . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 63] Internet Draft DHCP for IPv6 21 Nov 2001 option-code OPTION_CIRCUIT_ID (TBD) option-length variable Circuit-ID An opaque value of arbitrary length; this value must uniquely identify one of the network attachments used by the relay agent 20.17. User Class Option This option is used by a client to identify the type or category of user or applications it represents. The information contained in this option is an opaque field that represents the user class of which the client is a member. Based on this class, a DHCP server selects the appropriate address pool to assign an address to the client and the appropriate configuration parameters. 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_USER_CLASS | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | user class data | | . . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code TBD option-len Variable; If n user classes are carried by the option, the length of the option option-len = sum of each of the user class lengths + 2*n. option-data The user classes carried by the client. The user class option may contain one or more instances of user class data. Each instance of the user class data is formatted as follows: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+ | user class1 len | user1 class data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+ The user class length is two octets long and specifies the length of the opaque user class data in network byte order. Servers may interpret the meanings of multiple class specifications in an implementation dependent or configuration dependent manner, and so the use of multiple classes by a DHCP client should be based Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 64] Internet Draft DHCP for IPv6 21 Nov 2001 on the specific server implementation and configuration which will be used to process that User class option. Servers not equipped to interpret the user class information sent by a client MUST ignore it (although it may be reported). 20.18. Vendor Class Option This option is used by clients and servers to exchange vendor- specific information. The definition of this information is vendor specific. The vendor is indicated in the vendor class identifier option. Servers not equipped to interpret the vendor-specific information sent by a client MUST ignore it (although it may be reported). Clients which do not receive desired vendor-specific information SHOULD make an attempt to operate without it, although they may do so(and announce they are doing so) in a degraded mode. 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_VENDOR_CLASS | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | option-data | | . . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code TBD option-len Variable option-data The information is an opaque object of option-len octets, presumably interpreted by vendor-specific code on the clients and servers If a vendor potentially encodes more than one item of information in this option, then the vendor SHOULD encode the option using "Encapsulated vendor-specific options". The Encapsulated vendor-specific options field SHOULD be encoded as a sequence of code/length/value fields of identical syntax to the DHCP options field. When encapsulated vendor-specific extensions are used, each of the encapsulated options is formatted as follows. 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | opt_code | opt_len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | option-data | | . . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 65] Internet Draft DHCP for IPv6 21 Nov 2001 opt_code The code for the encapsulated option opt_len The length of the encapsulated option option-data The data area for the encapsulated option 21. Security Considerations Section 19 describes a threat model and an option that provides an authentication framework to defend against that threat model. 22. Year 2000 considerations Since all times are relative to the current time of the transaction, there is no problem within the DHCPv6 protocol related to any hardcoded dates or two-digit representation of the current year. 23. IANA Considerations This document defines several new name spaces associated with DHCPv6 and DHCPv6 options. IANA is requested to manage the allocation of values from these name spaces, which are described in the remainder of this section. These name spaces are all to be managed separately from the name spaces defined for DHCPv4 [7, 2]. New values in each of these name spaces should be approved by the process of IETF consensus [14]. 23.1. Multicast addresses Section 7.1 defines the following multicast addresses, which have been assigned by IANA for use by DHCPv6: All_DHCP_Agents address: FF02::1:2 All_DHCP_Servers address: FF05::1:3 IANA is requested to manage definition of additional multicast addresses in the future. 23.2. DHCPv6 message types IANA is requested to record the message types defined in section 7.3. IANA is requested to manage definition of additional message types in the future. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 66] Internet Draft DHCP for IPv6 21 Nov 2001 23.3. DUID IANA is requested to record the DUID types defined in section 10.1. IANA is requested to manage definition of additional DUID types in the future. 23.4. DHCPv6 options IANA is requested to assign option-codes to the options defined in section 20.1. IANA is requested to manage the definition of additional DHCPv6 option-codes in the future. 23.5. Status codes IANA is requested to record the status codes defined in section 7.4. IANA is requested to manage the definition of additional status codes in the future. 23.6. Authentication option Section 19 defines three new name spaces associated with the Authentication Option (section 20.11), which are to be created and maintained by IANA: Protocol, Algorithm and RDM. Initial values assigned from the Protocol name space are 0 (for the configuration token Protocol in section 19.5) and 1 (for the delayed authentication Protocol in section 19.6). Additional protocols may be defined in the future. The Algorithm name space is specific to individual Protocols. That is, each Protocol has its own Algorithm name space. The guidelines for assigning Algorithm name space values for a particular protocol should be specified along with the definition of a new Protocol. For the configuration token Protocol, the Algorithm field MUST be 0, as described in section 19.5. For the delayed authentication Protocol, the Algorithm value 1 is assigned to the HMAC-MD5 generating function as defined in section 19.6. Additional algorithms for the delayed authentication protocol may be defined in the future. The initial value of 0 from the RDM name space is assigned to the use of a monotonically increasing value as defined in section 19.4. Additional replay detection methods may be defined in the future. 24. Acknowledgments Thanks to the DHC Working Group for their time and input into the specification. Ralph Droms and Thomas Narten have had a major Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 67] Internet Draft DHCP for IPv6 21 Nov 2001 role in shaping the continued improvement of the protocol by their careful reviews. Many thanks to Matt Crawford, Erik Nordmark, Gerald Maguire, and Mike Carney for their studied review as part of the Last Call process. Thanks also for the consistent input, ideas, and review by (in alphabetical order) Brian Carpenter, Francis DuPont, Ted Lemon, Jack McCann, Yakov Rekhter, Matt Thomas, Sue Thomson, Bernie Volz and Phil Wells. Thanks to Steve Deering and Bob Hinden, who have consistently taken the time to discuss the more complex parts of the IPv6 specifications. Bill Arbaugh reviewed the authentication mechanism described in section 19. The Domain Search option described in section 20.13 is based on the DHCPv4 domain search option, [1], and was reviewed by Bernard Aboba. A. Full Copyright Statement Copyright (C) The Internet Society (2001). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. References [1] B. Aboba. DHCP Domain Search Option. Internet Draft, Internet Engineering Task Force, December 2000. Work in progress. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 68] Internet Draft DHCP for IPv6 21 Nov 2001 [2] S. Alexander and R. Droms. DHCP Options and BOOTP Vendor Extensions, March 1997. RFC 2132. [3] S. Bradner. Key words for use in RFCs to Indicate Requirement Levels, March 1997. RFC 2119. [4] S. Bradner and A. Mankin. The Recommendation for the IP Next Generation Protocol, January 1995. RFC 1752. [5] W.J. Croft and J. Gilmore. Bootstrap Protocol, September 1985. RFC 951. [6] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6) Specification, December 1998. RFC 2460. [7] R. Droms. Dynamic Host Configuration Protocol, March 1997. RFC 2131. [8] R. Droms and W. Arbaugh. Authentication for DHCP Messages. Internet Draft, Internet Engineering Task Force, January 2001. Work in progress. [9] R. Hinden and S. Deering. IP Version 6 Addressing Architecture, July 1998. RFC 2373. [10] S. Kent and R. Atkinson. Security Architecture for the Internet Protocol, November 1998. RFC 2401. [11] H. Krawczyk, M. Bellare, and R. Canetti. HMAC: Keyed-Hashing for Message Authentication, February 1997. RFC 2104. [12] David L. Mills. Network Time Protocol (Version 3) Specification, Implementation, March 1992. RFC 1305. [13] P.V. Mockapetris. Domain names - implementation and specification, November 1987. RFC 1035. [14] T. Narten and H. Alvestrand. Guidelines for Writing an IANA Considerations Section in RFCs, October 1998. RFC 2434. [15] T. Narten and R. Draves. Privacy Extensions for Stateless Address Autoconfiguration in IPv6, January 2001. RFC 3041. [16] T. Narten, E. Nordmark, and W. Simpson. Neighbor Discovery for IP Version 6 (IPv6), December 1998. RFC 2461. [17] D.C. Plummer. Ethernet Address Resolution Protocol: Or converting network protocol addresses to 48.bit Ethernet address for transmission on Ethernet hardware, November 1982. RFC 826. [18] J. Postel. User Datagram Protocol, August 1980. RFC 768. Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 69] Internet Draft DHCP for IPv6 21 Nov 2001 [19] R. Rivest. The MD5 Message-Digest Algorithm, April 1992. RFC 1321. [20] S. Thomson and T. Narten. IPv6 Stateless Address Autoconfiguration, December 1998. RFC 2462. [21] P. Vixie, Ed., S. Thomson, Y. Rekhter, and J. Bound. Dynamic Updates in the Domain Name System (DNS UPDATE), April 1997. RFC 2136. Chair's Address The working group can be contacted via the current chair: Ralph Droms Cisco Systems 300 Apollo Drive Chelmsford, MA 01824 Phone: (978) 244-4733 E-mail: rdroms@cisco.com Authors' Addresses Questions about this memo can be directed to: Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 70] Internet Draft DHCP for IPv6 21 Nov 2001 Jim Bound Compaq Computer Corporation ZK3-3/W20 110 Spit Brook Road Nashua, NH 03062-2698 USA Phone: +1 603 884 0062 Email: Jim.Bound@compaq.com Mike Carney Sun Microsystems, Inc Mail Stop: UMPK17-202 901 San Antonio Road Palo Alto, CA 94303-4900 USA Phone: +1-650-786-4171 Email: mwc@eng.sun.com Charles E. Perkins Communications Systems Lab Nokia Research Center 313 Fairchild Drive Mountain View, California 94043 USA Phone: +1-650 625-2986 Email: charliep@iprg.nokia.com Fax: +1 650 625-2502 Ralph Droms Cisco Systems 300 Apollo Drive Chelmsford, MA 01824 USA Phone: +1 978 244 4733 Email: rdroms@cisco.com Bound, Carney, Perkins, Droms (ed.) Expires 30 Apr 2002 [Page 71]