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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (June 9, 2002) is 7991 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: 'DUID-LLT' on line 887 -- Looks like a reference, but probably isn't: 'DUID-EN' on line 950 -- Looks like a reference, but probably isn't: 'DUID-LL' on line 992 ** Obsolete normative reference: RFC 2460 (ref. '4') (Obsoleted by RFC 8200) -- Possible downref: Non-RFC (?) normative reference: ref. '7' ** Obsolete normative reference: RFC 2373 (ref. '8') (Obsoleted by RFC 3513) -- Possible downref: Non-RFC (?) normative reference: ref. '9' ** Obsolete normative reference: RFC 2401 (ref. '10') (Obsoleted by RFC 4301) ** Downref: Normative reference to an Informational RFC: RFC 2104 (ref. '11') ** Obsolete normative reference: RFC 1305 (ref. '12') (Obsoleted by RFC 5905) ** Obsolete normative reference: RFC 2434 (ref. '14') (Obsoleted by RFC 5226) ** Obsolete normative reference: RFC 3041 (ref. '15') (Obsoleted by RFC 4941) ** Obsolete normative reference: RFC 2461 (ref. '16') (Obsoleted by RFC 4861) ** Downref: Normative reference to an Informational RFC: RFC 1321 (ref. '19') ** Obsolete normative reference: RFC 2462 (ref. '20') (Obsoleted by RFC 4862) -- Possible downref: Non-RFC (?) normative reference: ref. '21' Summary: 14 errors (**), 0 flaws (~~), 6 warnings (==), 10 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Internet Engineering Task Force R. Droms (ed.), Cisco 2 INTERNET DRAFT J. Bound, Hewlett Packard 3 DHC Working Group Bernie Volz, Ericsson 4 Obsoletes: draft-ietf-dhc-dhcpv6-25.txt Ted Lemon, Nominum 5 C. Perkins, Nokia Research Center 6 M. Carney, Sun Microsystems 7 June 9, 2002 9 Dynamic Host Configuration Protocol for IPv6 (DHCPv6) 10 draft-ietf-dhc-dhcpv6-26.txt 12 Status of This Memo 14 This document is a submission by the Dynamic Host Configuration 15 Working Group of the Internet Engineering Task Force (IETF). Comments 16 should be submitted to the dhcwg@ietf.org mailing list. 18 Distribution of this memo is unlimited. 20 This document is an Internet-Draft and is in full conformance with 21 all provisions of Section 10 of RFC2026. Internet-Drafts are working 22 documents of the Internet Engineering Task Force (IETF), its areas, 23 and its working groups. Note that other groups may also distribute 24 working documents as Internet-Drafts. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at 28 any time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 The list of current Internet-Drafts can be accessed at: 32 http://www.ietf.org/ietf/1id-abstracts.txt 33 The list of Internet-Draft Shadow Directories can be accessed at: 34 http://www.ietf.org/shadow.html. 36 Abstract 38 The Dynamic Host Configuration Protocol for IPv6 (DHCP) enables 39 DHCP servers to pass configuration parameters such as IPv6 network 40 addresses to IPv6 nodes. It offers the capability of automatic 41 allocation of reusable network addresses and additional configuration 42 flexibility. This protocol is a stateful counterpart to "IPv6 43 Stateless Address Autoconfiguration" (RFC2462), and can be used 44 separately or concurrently with the latter to obtain configuration 45 parameters. 47 Contents 49 Status of This Memo i 51 Abstract i 53 1. Introduction and Overview 2 54 1.1. Protocols and addressing . . . . . . . . . . . . . . . . 2 55 1.2. Client-server exchanges involving two messages . . . . . 3 56 1.3. Client-server exchanges involving four messages . . . . . 3 58 2. Requirements 4 60 3. Background 4 62 4. Terminology 5 63 4.1. IPv6 Terminology . . . . . . . . . . . . . . . . . . . . 5 64 4.2. DHCP Terminology . . . . . . . . . . . . . . . . . . . . 6 66 5. DHCP Constants 8 67 5.1. Multicast Addresses . . . . . . . . . . . . . . . . . . . 8 68 5.2. UDP ports . . . . . . . . . . . . . . . . . . . . . . . . 8 69 5.3. DHCP message types . . . . . . . . . . . . . . . . . . . 8 70 5.4. Status Codes . . . . . . . . . . . . . . . . . . . . . . 10 71 5.5. Transmission and Retransmission Parameters . . . . . . . 11 73 6. Message Formats 11 75 7. Relay agent messages 12 76 7.1. Relay-forward message . . . . . . . . . . . . . . . . . . 13 77 7.2. Relay-reply message . . . . . . . . . . . . . . . . . . . 13 79 8. Representation and use of domain names 13 81 9. DHCP unique identifier (DUID) 14 82 9.1. DUID contents . . . . . . . . . . . . . . . . . . . . . . 14 83 9.2. DUID based on link-layer address plus time [DUID-LLT] . . 14 84 9.3. DUID assigned by vendor based on Enterprise number 85 [DUID-EN] . . . . . . . . . . . . . . . . . . . . . . 16 86 9.4. DUID based on link-layer address [DUID-LL] . . . . . . . 17 88 10. Identity association 17 90 11. Selecting addresses for assignment to an IA 18 92 12. Management of temporary addresses 19 94 13. Transmission of messages by a client 19 96 14. Reliability of Client Initiated Message Exchanges 20 98 15. Message validation 21 99 15.1. Use of Transaction IDs . . . . . . . . . . . . . . . . . 21 100 15.2. Solicit message . . . . . . . . . . . . . . . . . . . . . 22 101 15.3. Advertise message . . . . . . . . . . . . . . . . . . . . 22 102 15.4. Request message . . . . . . . . . . . . . . . . . . . . . 22 103 15.5. Confirm message . . . . . . . . . . . . . . . . . . . . . 22 104 15.6. Renew message . . . . . . . . . . . . . . . . . . . . . . 23 105 15.7. Rebind message . . . . . . . . . . . . . . . . . . . . . 23 106 15.8. Decline messages . . . . . . . . . . . . . . . . . . . . 23 107 15.9. Release message . . . . . . . . . . . . . . . . . . . . . 23 108 15.10. Reply message . . . . . . . . . . . . . . . . . . . . . . 24 109 15.11. Reconfigure message . . . . . . . . . . . . . . . . . . . 24 110 15.12. Information-request message . . . . . . . . . . . . . . . 25 111 15.13. Relay-forward message . . . . . . . . . . . . . . . . . . 25 112 15.14. Relay-reply message . . . . . . . . . . . . . . . . . . . 25 114 16. Client Source Address and Interface Selection 25 116 17. DHCP Server Solicitation 25 117 17.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 26 118 17.1.1. Creation of Solicit messages . . . . . . . . . . 26 119 17.1.2. Transmission of Solicit Messages . . . . . . . . 27 120 17.1.3. Receipt of Advertise messages . . . . . . . . . . 28 121 17.1.4. Receipt of Reply message . . . . . . . . . . . . 29 122 17.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 29 123 17.2.1. Receipt of Solicit messages . . . . . . . . . . . 29 124 17.2.2. Creation and transmission of Advertise messages . 29 125 17.2.3. Creation and Transmission of Reply messages . . . 30 127 18. DHCP Client-Initiated Configuration Exchange 31 128 18.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 31 129 18.1.1. Creation and transmission of Request messages . . 32 130 18.1.2. Creation and transmission of Confirm messages . . 33 131 18.1.3. Creation and transmission of Renew messages . . . 34 132 18.1.4. Creation and transmission of Rebind messages . . 35 133 18.1.5. Creation and Transmission of Information-request 134 messages . . . . . . . . . . . . . . . . . 36 135 18.1.6. Creation and transmission of Release messages . . 37 136 18.1.7. Creation and transmission of Decline messages . . 38 137 18.1.8. Receipt of Reply messages . . . . . . . . . . . . 38 138 18.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 40 139 18.2.1. Receipt of Request messages . . . . . . . . . . . 40 140 18.2.2. Receipt of Confirm messages . . . . . . . . . . . 41 141 18.2.3. Receipt of Renew messages . . . . . . . . . . . . 41 142 18.2.4. Receipt of Rebind messages . . . . . . . . . . . 42 143 18.2.5. Receipt of Information-request messages . . . . . 43 144 18.2.6. Receipt of Release messages . . . . . . . . . . . 44 145 18.2.7. Receipt of Decline messages . . . . . . . . . . . 44 146 18.2.8. Transmission of Reply messages . . . . . . . . . 45 148 19. DHCP Server-Initiated Configuration Exchange 45 149 19.1. Server Behavior . . . . . . . . . . . . . . . . . . . . . 45 150 19.1.1. Creation and transmission of Reconfigure messages 45 151 19.1.2. Time out and retransmission of Reconfigure 152 messages . . . . . . . . . . . . . . . . . 46 153 19.2. Receipt of Renew messages . . . . . . . . . . . . . . . . 47 154 19.3. Receipt of Information-request messages . . . . . . . . . 47 155 19.4. Client Behavior . . . . . . . . . . . . . . . . . . . . . 47 156 19.4.1. Receipt of Reconfigure messages . . . . . . . . . 47 157 19.4.2. Creation and transmission of Renew messages . . . 48 158 19.4.3. Creation and transmission of Information-request 159 messages . . . . . . . . . . . . . . . . . 48 160 19.4.4. Time out and retransmission of Renew or 161 Information-request messages . . . . . . . 49 162 19.4.5. Receipt of Reply messages . . . . . . . . . . . . 49 164 20. Relay Agent Behavior 49 165 20.1. Forwarding a client message or a Relay-forward message . 49 166 20.1.1. Forwarding a message from a client . . . . . . . 49 167 20.1.2. Forwarding a message from a relay agent . . . . . 50 168 20.2. Forwarding a Relay-reply message . . . . . . . . . . . . 50 169 20.3. Construction of Relay-reply messages . . . . . . . . . . 51 171 21. Authentication of DHCP messages 51 172 21.1. DHCP threat model . . . . . . . . . . . . . . . . . . . . 51 173 21.2. Security of messages sent between servers and relay agents 52 174 21.3. Summary of DHCP authentication . . . . . . . . . . . . . 52 175 21.4. Replay detection . . . . . . . . . . . . . . . . . . . . 53 176 21.5. Delayed authentication protocol . . . . . . . . . . . . . 53 177 21.5.1. Use of the Authentication option in the delayed 178 authentication protocol . . . . . . . . . 53 179 21.5.2. Message validation . . . . . . . . . . . . . . . 55 180 21.5.3. Key utilization . . . . . . . . . . . . . . . . . 55 181 21.5.4. Client considerations for delayed authentication 182 protocol . . . . . . . . . . . . . . . . . 55 183 21.5.5. Server considerations for delayed authentication 184 protocol . . . . . . . . . . . . . . . . . 57 186 22. DHCP options 57 187 22.1. Format of DHCP options . . . . . . . . . . . . . . . . . 58 188 22.2. Client Identifier option . . . . . . . . . . . . . . . . 58 189 22.3. Server Identifier option . . . . . . . . . . . . . . . . 59 190 22.4. Identity Association option . . . . . . . . . . . . . . . 60 191 22.5. Identity Association for Temporary Addresses option . . . 61 192 22.6. IA Address option . . . . . . . . . . . . . . . . . . . . 63 193 22.7. Option Request option . . . . . . . . . . . . . . . . . . 64 194 22.8. Preference option . . . . . . . . . . . . . . . . . . . . 65 195 22.9. Elapsed Time option . . . . . . . . . . . . . . . . . . . 65 196 22.10. Relay Message option . . . . . . . . . . . . . . . . . . 66 197 22.11. Authentication option . . . . . . . . . . . . . . . . . . 66 198 22.12. Server unicast option . . . . . . . . . . . . . . . . . . 67 199 22.13. Status Code Option . . . . . . . . . . . . . . . . . . . 68 200 22.14. Rapid Commit option . . . . . . . . . . . . . . . . . . . 69 201 22.15. User Class option . . . . . . . . . . . . . . . . . . . . 70 202 22.16. Vendor Class Option . . . . . . . . . . . . . . . . . . . 71 203 22.17. Vendor-specific Information option . . . . . . . . . . . 72 204 22.18. Interface-Id Option . . . . . . . . . . . . . . . . . . . 73 205 22.19. Reconfigure Message option . . . . . . . . . . . . . . . 74 206 22.20. Reconfigure Nonce option . . . . . . . . . . . . . . . . 74 208 23. Security Considerations 75 210 24. IANA Considerations 76 211 24.1. Multicast addresses . . . . . . . . . . . . . . . . . . . 77 212 24.2. DHCP message types . . . . . . . . . . . . . . . . . . . 77 213 24.3. DHCP options . . . . . . . . . . . . . . . . . . . . . . 78 214 24.4. Status codes . . . . . . . . . . . . . . . . . . . . . . 79 215 24.5. DUID . . . . . . . . . . . . . . . . . . . . . . . . . . 79 217 25. Acknowledgments 79 219 26. Changes in draft-ietf-dhc-dhcpv6-25.txt 80 221 27. Changes in draft-ietf-dhc-dhcpv6-26.txt 82 223 References 83 225 Chair's Address 84 227 Authors' Addresses 85 229 A. Appearance of Options in Message Types 86 231 B. Appearance of Options in the Options Field of DHCP Options 86 233 C. Full Copyright Statement 87 235 1. Introduction and Overview 237 This document describes DHCP for IPv6 (DHCP), a client/server 238 protocol that provides managed configuration of devices. 240 DHCP can provide a device with addresses assigned by a DHCP server 241 and other configuration information, which are carried in options. 242 DHCP can be extended through the definition of new options to carry 243 configuration information not specified in this document. 245 DHCP is the "stateful address autoconfiguration protocol" and the 246 "stateful autoconfiguration protocol" referred to in "IPv6 Stateless 247 Address Autoconfiguration" [20]. 249 The operational models and relevant configuration information 250 for DHCPv4 and DHCPv6 are sufficiently different that integration 251 between the two services is not included in this document. If there 252 is sufficient interest and demand, integration can be specified 253 in a document that extends DHCPv6 to carry IPv4 addresses and 254 configuration information. 256 The remainder of this introduction summarizes DHCP, explaining 257 the message exchange mechanisms and example message flows. The 258 message flows in sections 1.2 and 1.3 are intended as illustrations 259 of DHCP operation rather than an exhaustive list of all possible 260 client-server interactions. Sections 17, 18 and 19 explain client 261 and server operation in detail. 263 1.1. Protocols and addressing 265 Clients and servers exchange DHCP messages using UDP [18]. The 266 client uses a link-local address or addresses determined through 267 other mechanisms for transmitting and receiving DHCP messages. 269 DHCP servers receive messages from clients using a reserved, 270 link-scoped multicast address. A DHCP client transmits most messages 271 to this reserved multicast address, so that the client need not be 272 configured with the address or addresses of DHCP servers. 274 To allow a DHCP client to send a message to a DHCP server that is not 275 attached to the same link, a DHCP relay agent on the client's link 276 will forward messages between the client and server. The operation 277 of the relay agent is transparent to the client and the discussion 278 of message exchanges in the remainder of this section will omit the 279 description of message forwarding by relay agents. 281 Once the client has determined the address of a server, it may 282 under some circumstances send messages directly to the server using 283 unicast. 285 1.2. Client-server exchanges involving two messages 287 When a DHCP client does not need to have a DHCP server assign 288 it IP addresses, the client can obtain configuration information 289 such as a list of available DNS servers [7] or NTP servers [21] 290 through a single message and reply exchanged with a DHCP server. 291 To obtain configuration information the client first sends an 292 Information-Request message to the All_DHCP_Relay_Agents_and_Servers 293 multicast address. The server responds with a Reply message 294 containing the configuration information for the client. 296 This message exchange assumes that the client requires only 297 configuration information and does not require the assignment of any 298 IPv6 addresses. 300 When a server has IPv6 addresses and other configuration information 301 committed to a client, the client and server may be able to complete 302 the exchange using only two messages, instead of four messages as 303 described in the next section. In this case, the client sends a 304 Solicit message to the All_DHCP_Relay_Agents_and_Servers requesting 305 the assignment of addresses and other configuration information. 306 This message includes an indication that the client is willing to 307 accept an immediate Reply message from the server. The server that 308 is willing to commit the assignment of addresses to the client 309 immediately responds with a Reply message. The configuration 310 information and the addresses in the Reply message are then 311 immediately available for use by the client. 313 Each address assigned to the client has associated preferred and 314 valid lifetimes specified by the server. To request an extension 315 of the lifetimes assigned to an address, the client sends a Renew 316 message to the server. The server sends a Reply message to the 317 client with the new lifetimes, allowing the client to continue to use 318 the address without interruption. 320 1.3. Client-server exchanges involving four messages 322 To request the assignment of one or more IPv6 addresses, a 323 client first locates a DHCP server and then requests the 324 assignment of addresses and other configuration information 325 from the server. The client sends a Solicit message to the 326 All_DHCP_Relay_Agents_and_Servers address to find available DHCP 327 servers. Any server that can meet the client's requirements 328 responds with an Advertise message. The client then chooses one 329 of the servers and sends a Request message to the server asking 330 for confirmed assignment of addresses and other configuration 331 information. The server responds with a Reply message that contains 332 the confirmed addresses and configuration. 334 As described in the previous section, the client sends a Renew 335 messages to the server to extend the lifetimes associated with its 336 addresses, allowing the client to continue to use those addresses 337 without interruption. 339 2. Requirements 341 The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, 342 SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this 343 document, are to be interpreted as described in [2]. 345 This document also makes use of internal conceptual variables 346 to describe protocol behavior and external variables that an 347 implementation must allow system administrators to change. The 348 specific variable names, how their values change, and how their 349 settings influence protocol behavior are provided to demonstrate 350 protocol behavior. An implementation is not required to have them in 351 the exact form described here, so long as its external behavior is 352 consistent with that described in this document. 354 3. Background 356 The IPv6 Specification provides the base architecture and design of 357 IPv6. Related work in IPv6 that would best serve an implementor 358 to study includes the IPv6 Specification [4], the IPv6 Addressing 359 Architecture [8], IPv6 Stateless Address Autoconfiguration [20], IPv6 360 Neighbor Discovery Processing [16], and Dynamic Updates to DNS [22]. 361 These specifications enable DHCP to build upon the IPv6 work to 362 provide both robust stateful autoconfiguration and autoregistration 363 of DNS Host Names. 365 The IPv6 Addressing Architecture specification [8] defines the 366 address scope that can be used in an IPv6 implementation, and the 367 various configuration architecture guidelines for network designers 368 of the IPv6 address space. Two advantages of IPv6 are that support 369 for multicast is required, and nodes can create link-local addresses 370 during initialization. This means that a client can immediately use 371 its link-local address and a well-known multicast address to begin 372 communications to discover neighbors on the link. For instance, a 373 client can send a Solicit message and locate a server or relay agent. 375 IPv6 Stateless Address Autoconfiguration [20] specifies procedures 376 by which a node may autoconfigure addresses based on router 377 advertisements [16], and the use of a valid lifetime to support 378 renumbering of addresses on the Internet. In addition the 379 protocol interaction by which a node begins stateless or stateful 380 autoconfiguration is specified. DHCP is one vehicle to perform 381 stateful autoconfiguration. Compatibility with stateless address 382 autoconfiguration is a design requirement of DHCP. 384 IPv6 Neighbor Discovery [16] is the node discovery protocol in IPv6 385 which replaces and enhances functions of ARP [17]. To understand 386 IPv6 and stateless address autoconfiguration it is strongly 387 recommended that implementors understand IPv6 Neighbor Discovery. 389 Dynamic Updates to DNS [22] is a specification that supports the 390 dynamic update of DNS records for both IPv4 and IPv6. DHCP can use 391 the dynamic updates to DNS to integrate addresses and name space to 392 not only support autoconfiguration, but also autoregistration in 393 IPv6. 395 4. Terminology 397 This sections defines terminology specific to IPv6 and DHCP used in 398 this document. 400 4.1. IPv6 Terminology 402 IPv6 terminology relevant to this specification from the IPv6 403 Protocol [4], IPv6 Addressing Architecture [8], and IPv6 Stateless 404 Address Autoconfiguration [20] is included below. 406 address An IP layer identifier for an interface 407 or a set of interfaces. 409 host Any node that is not a router. 411 IP Internet Protocol Version 6 (IPv6). The 412 terms IPv4 and IPv6 are used only in 413 contexts where it is necessary to avoid 414 ambiguity. 416 interface A node's attachment to a link. 418 link A communication facility or medium over 419 which nodes can communicate at the link 420 layer, i.e., the layer immediately 421 below IP. Examples are Ethernet (simple 422 or bridged); Token Ring; PPP links, 423 X.25, Frame Relay, or ATM networks; and 424 Internet (or higher) layer "tunnels", 425 such as tunnels over IPv4 or IPv6 426 itself. 428 link-layer identifier A link-layer identifier for an 429 interface. Examples include IEEE 802 430 addresses for Ethernet or Token Ring 431 network interfaces, and E.164 addresses 432 for ISDN links. 434 link-local address An IPv6 address having link-only 435 scope, indicated by having the prefix 436 (FE80::0000/10), that can be used to 437 reach neighboring nodes attached to 438 the same link. Every interface has a 439 link-local address. 441 multicast address An identifier for a set of interfaces 442 (typically belonging to different 443 nodes). A packet sent to a multicast 444 address is delivered to all interfaces 445 identified by that address. 447 neighbor A node attached to the same link. 449 node A device that implements IP. 451 packet An IP header plus payload. 453 prefix The initial bits of an address, or a 454 set of IP addresses that share the same 455 initial bits. 457 prefix length The number of bits in a prefix. 459 router A node that forwards IP packets not 460 explicitly addressed to itself. 462 unicast address An identifier for a single interface. 463 A packet sent to a unicast address is 464 delivered to the interface identified by 465 that address. 467 4.2. DHCP Terminology 469 Terminology specific to DHCP can be found below. 471 appropriate to the link an address is "appropriate to the link" 472 when the address is consistent with the 473 DHCP server's knowledge of the network 474 topology, prefix assignment and address 475 assignment policies 477 binding A binding (or, client binding) is a 478 group of server data records containing 479 the information the server has about 480 the addresses in an IA or configuration 481 information explicitly assigned to the 482 client. Configuration information that 483 has been returned to a client through a 484 policy - for example, the information 485 returned to all clients on the same 486 link - does not require a binding. A 487 binding containing information about 488 an IA is indexed by the tuple (where IA-type is the 490 type of address in the IA; for example, 491 temporary). A binding containing 492 configuration information for a client 493 is indexed by . 495 configuration parameter An element of the configuration 496 information set on the server and 497 delivered to the client using DHCP. 498 Such parameters may be used to carry 499 information to be used by a node to 500 configure its network subsystem and 501 enable communication on a link or 502 internetwork, for example. 504 DHCP Dynamic Host Configuration Protocol 505 for IPv6. The terms DHCPv4 and DHCPv6 506 are used only in contexts where it is 507 necessary to avoid ambiguity. 509 DHCP client (or client) A node that initiates requests on a link 510 to obtain configuration parameters from 511 one or more DHCP servers. 513 DHCP domain A set of links managed by DHCP and 514 operated by a single administrative 515 entity. 517 DHCP relay agent (or relay agent) A node that acts as an 518 intermediary to deliver DHCP messages 519 between clients and servers, and is on 520 the same link as the client. 522 DHCP server (or server) A node that responds to requests from 523 clients, and may or may not be on the 524 same link as the client(s). 526 DUID A DHCP Unique IDentifier for a DHCP 527 participant; each DHCP client and server 528 has exactly one DUID. See section 9 for 529 details of the ways in which a DUID may 530 be constructed. 532 Identity association (IA) A collection of addresses assigned to 533 a client. Each IA has an associated 534 IAID. A client may have more than one 535 IA assigned to it; for example, one for 536 each of its interfaces. 538 Identity association identifier (IAID) An identifier for an IA, 539 chosen by the client. Each IA has an 540 IAID, which is chosen to be unique among 541 all IAIDs for IAs belonging to that 542 client. 544 message A unit of data carried as the payload 545 of a UDP datagram, exchanged among DHCP 546 servers, relay agents and clients. 548 reconfiguration nonce An opaque value used to provide security 549 for Reconfigure messages. 551 transaction ID An opaque value used to match responses 552 with replies initiated either by a 553 client or server. 555 5. DHCP Constants 557 This section describes various program and networking constants used 558 by DHCP. 560 5.1. Multicast Addresses 562 DHCP makes use of the following multicast addresses: 564 All_DHCP_Relay_Agents_and_Servers (FF02::1:2) A link-scoped 565 multicast address used by a client to communicate with 566 neighboring (i.e., on-link) relay agents and servers. 567 All servers and relay agents are members of this 568 multicast group. 570 All_DHCP_Servers (FF05::1:3) A site-scoped multicast address used 571 by a relay agent to communicate with servers, either 572 because the relay agent wants to send messages to 573 all servers or because it does not know the unicast 574 addresses of the servers. Note that in order for 575 a relay agent to use this address, it must have an 576 address of sufficient scope to be reachable by the 577 servers. All servers within the site are members of 578 this multicast group. 580 5.2. UDP ports 582 Clients listen for DHCP messages on UDP port 546. Servers and relay 583 agents listen for DHCP messages on UDP port 547. 585 5.3. DHCP message types 587 DHCP defines the following message types. More detail on these 588 message types can be found in Section 6. Message types not listed 589 here are reserved for future use. The message code for each message 590 type is shown with the message name. 592 SOLICIT (1) A client sends a Solicit message to locate 593 servers. 595 ADVERTISE (2) A server sends an Advertise message to indicate 596 that it is available for DHCP service, in 597 response to a Solicit message received from a 598 client. 600 REQUEST (3) A client sends a Request message to request 601 configuration parameters, including IP 602 addresses, from a specific server. 604 CONFIRM (4) A client sends a Confirm message to any 605 available server to determine whether the 606 addresses it was assigned are still appropriate 607 to the link to which the client is connected. 609 RENEW (5) A client sends a Renew message to the server 610 that originally provided the client's addresses 611 and configuration parameters to extend the 612 leases on the addresses assigned to the client 613 and to update other configuration parameters. 615 REBIND (6) A client sends a Rebind message to any 616 available server to extend the leases on the 617 addresses assigned to the client and to update 618 other configuration parameters; this message is 619 sent after a client receives no response to a 620 Renew message. 622 REPLY (7) A server sends a Reply message containing 623 assigned addresses and configuration parameters 624 in response to a Solicit, Request, Renew, 625 Rebind message received from a client. A 626 server sends a Reply message containing 627 configuration parameters in response to an 628 Information-request message. A server sends a 629 Reply message confirming or denying the that 630 the client's addresses are appropriate to 631 the link to which the client is connected in 632 response to a Confirm message. A server sends 633 a Reply message to acknowledge receipt of a 634 Release or Decline message. 636 A server sends a Reply message containing 637 assigned addresses and configuration parameters 638 in response to a Solicit, Request, Renew, 639 Rebind message received from a client. A 640 server sends a Reply message containing 641 configuration parameters in response to an 642 Information-request message. A server sends a 643 Reply message in response to a Confirm message 644 confirming or denying that the addresses 645 assigned to the client are appropriate to the 646 link to which the client is connected. A 647 server sends a Reply message to acknowledge 648 receipt of a Release or Decline message. 650 RELEASE (8) A client sends a Release message to the server 651 that assigned addresses to the client to 652 indicate that the client will no longer use one 653 or more of the assigned addresses. 655 DECLINE (9) A client sends a Decline message to a server to 656 indicate that the client has determined that 657 one or more addresses assigned by the server 658 are already in use on the link to which the 659 client is connected. 661 RECONFIGURE (10) A server sends a Reconfigure message to a 662 client to inform the client that the server has 663 new or updated configuration parameters, and 664 that the client is to initiate a Renew/Reply 665 or Information-request/Reply transaction with 666 the server in order to receive the updated 667 information. 669 INFORMATION-REQUEST (11) A client sends an Information-request 670 message to a server to request configuration 671 parameters without the assignment of any IP 672 addresses to the client. 674 RELAY-FORW (12) A relay agent sends a Relay-forward message 675 to forward client messages to servers, either 676 directly or through another relay agent. The 677 client message is encapsulated in an option in 678 the Relay-forward message. 680 RELAY-REPL (13) A server sends a Relay-reply message to a relay 681 agent, either directly or through another relay 682 agent, to send messages to clients through 683 the relay agent. The server encapsulates the 684 client message as an option in the Relay-reply 685 message, which the relay agent extracts and 686 forwards to the client. 688 5.4. Status Codes 690 DHCPv6 uses status codes to communicate the success or failure of 691 operations requested in messages from clients and servers, and to 692 provide additional information about the specific cause of the 693 failure of a message. The specific status codes are defined in 694 section 24.4. 696 5.5. Transmission and Retransmission Parameters 698 This section presents a table of values used to describe the message 699 transmission behavior of clients and servers. 701 Parameter Default Description 702 ------------------------------------- 703 MAX_SOL_DELAY 1 sec Max delay of first Solicit 704 SOL_TIMEOUT 1 sec Initial Solicit timeout 705 SOL_MAX_RT 120 secs Max Solicit timeout value 706 REQ_TIMEOUT 1 sec Initial Request timeout 707 REQ_MAX_RT 30 secs Max Request timeout value 708 REQ_MAX_RC 10 Max Request retry attempts 709 CNF_TIMEOUT 1 sec Initial Confirm timeout 710 CNF_MAX_RT 4 secs Max Confirm timeout 711 CNF_MAX_RD 10 secs Max Confirm duration 712 REN_TIMEOUT 10 sec Initial Renew timeout 713 REN_MAX_RT 600 secs Max Renew timeout value 714 REB_TIMEOUT 10 secs Initial Rebind timeout 715 REB_MAX_RT 600 secs Max Rebind timeout value 716 INF_TIMEOUT 1 sec Initial Information-request timeout 717 INF_MAX_RT 120 secs Max Information-request timeout value 718 REL_TIMEOUT 1 sec Initial Release timeout 719 REL_MAX_RT 0 Max Release timeout 720 REL_MAX_RC 5 MAX Release attempts 721 DEC_TIMEOUT 1 sec Initial Decline timeout 722 DEC_MAX_RT 0 Max Decline timeout 723 DEC_MAX_RC 5 Max Decline attempts 724 REC_TIMEOUT 2 sec Initial Reconfigure timeout 725 REC_MAX_RC 8 Max Reconfigure attempts 726 HOP_COUNT_LIMIT 4 Max hop count in a Relay-forward message 728 6. Message Formats 730 All DHCP messages sent between clients and servers share an identical 731 fixed format header and a variable format area for options. 733 All values in the message header and in options are in network byte 734 order. 736 Options are stored serially in the options field, with no padding 737 between the options. Options are byte-aligned but are not aligned in 738 any other way such as on 2 or 4 byte boundaries. 740 The following diagram illustrates the format of DHCP messages sent 741 between clients and servers: 743 0 1 2 3 744 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 1 745 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 746 | msg-type | transaction-id | 747 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 748 | | 749 . options . 750 . (variable) . 751 | | 752 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 754 msg-type Identifies the DHCP message type; the 755 available message types are listed in 756 section 5.3. 758 transaction-id The transaction ID for this message exchange. 760 options Options carried in this message; options are 761 described in section 22. 763 7. Relay agent messages 765 Relay agents exchange messages with servers to forward messages 766 between clients and servers that are not connected to the same link. 768 There are two relay agent messages, which share the following format: 770 0 1 2 3 771 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 1 772 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 773 | msg-type | hop-count | | 774 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 775 | | 776 | link-address | 777 | | 778 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 779 | | | 780 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 781 | | 782 | peer-address | 783 | | 784 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 785 | | | 786 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 787 . . 788 . options (variable number and length) .... . 789 | | 790 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 792 The following sections describe the use of the Relay Agent message 793 header. 795 7.1. Relay-forward message 797 The following table defines the use of message fields in a 798 Relay-forward message. 800 msg-type RELAY-FORW 802 hop-count Number of relay agents that have forwarded this 803 message 805 link-address A global or site-local address that will be used by 806 the server to identify the link on which the client 807 is located. 809 peer-address The address of the client or relay agent from which 810 the message to be forwarded was received 812 options MUST include a "Relay Message option" (see 813 section 22.10); MAY include other options added by 814 the relay agent 816 7.2. Relay-reply message 818 The following table defines the use of message fields in a 819 Relay-reply message. 821 msg-type RELAY-REPL 823 hop-count Number of relay agents that have forwarded this 824 message 826 link-address Copied from the Relay-forward message 828 peer-address The client or relay agent address to which the 829 message contained in the Relay Message option in 830 this Relay-reply message is to be forwarded 832 options MUST include a "Relay Message option"; see 833 section 22.10; MAY include other options 835 8. Representation and use of domain names 837 So that domain names may be encoded uniformly, a domain name or a 838 list of domain names is encoded using the technique described in 839 section 3.1 of RFC1035 [13]. A domain name or list of domain names 840 in DHCP MUST NOT be stored in compressed form as described in section 841 4.1.4 of RFC1035. 843 9. DHCP unique identifier (DUID) 845 Each DHCP client and server has a DUID. DHCP servers use DUIDs to 846 identify clients for the selection of configuration parameters and 847 in the association of IAs with clients. DHCP clients use DUIDs to 848 identify a server in messages where a server needs to be identified. 849 See sections 22.2 and 22.3 for the representation of a DUID in a DHCP 850 message. 852 Clients and servers MUST treat DUIDs as opaque values and MUST only 853 compare DUIDs for equality. Clients and servers MUST NOT in any 854 other way interpret DUIDs. Clients and servers MUST NOT restrict 855 DUIDs to the types defined in this document as additional DUID types 856 may be defined in the future. 858 The DUID is carried in an option because it may be variable length 859 and because it is not required in all DHCP messages. The DUID is 860 designed to be unique across all DHCP clients and servers, and stable 861 for any specific client or server - that is, the DUID used by a 862 client or server SHOULD NOT change over time if at all possible; for 863 example, a device's DUID should not change as a result of a change in 864 the device's network hardware. 866 The motivation for having more than one type of DUID is that the DUID 867 must be globally unique, and must also be easy to generate. The sort 868 of globally-unique identifier that is easy to generate for any given 869 device can differ quite widely. Also, some devices may not contain 870 any persistent storage. Retaining a generated DUID in such a device 871 is not possible, so the DUID scheme must accommodate such devices. 873 9.1. DUID contents 875 A DUID consists of a two octet type code represented in network byte 876 order, followed by a variable number of octets that make up the 877 actual identifier. A DUID can be no more than 256 octets long (not 878 including the type code). The following types are currently defined: 880 1 Link-layer address plus time 881 2 Vendor-assigned unique ID based on Enterprise Number 882 3 Link-layer address 884 Formats for the variable field of the DUID for each of the above 885 types are shown below. 887 9.2. DUID based on link-layer address plus time [DUID-LLT] 889 This type of DUID consists of a two octet type field containing the 890 value 1, a two octet hardware type code, four octets containing 891 a time value, followed by link-layer address of any one network 892 interface that is connected to the DHCP device at the time that the 893 DUID is generated. The time value is the time that the DUID is 894 generated represented in seconds since midnight (UTC), January 1, 895 2000, modulo 2^32. The hardware type MUST be a valid hardware type 896 assigned by the IANA as described in the section on ARP in RFC 826. 897 Both the time and the hardware type are stored in network byte order. 898 The link-layer address is stored in canonical form, as described in 899 RFC2464 [3]. 901 The following diagram illustrates the format of a DUID-LLT: 903 0 1 2 3 904 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 1 905 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 906 | 1 | Hardware type (16 bits) | 907 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 908 | Time (32 bits) | 909 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 910 . . 911 . link-layer address (variable length) . 912 . . 913 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 915 The choice of network interface can be completely arbitrary, as long 916 as that interface provides a globally unique link-layer address for 917 the link type, and the same DUID-LLT should be used in configuring 918 all network interfaces connected to the device, regardless of which 919 interface's link-layer address was used to generate the DUID-LLT. 921 Clients and servers using this type of DUID MUST store the DUID-LLT 922 in stable storage, and MUST continue to use this DUID-LLT even if the 923 network interface used to generate the DUID-LLT is removed. Clients 924 and servers that do not have any stable storage MUST NOT use this 925 type of DUID. 927 Clients and servers that use this DUID SHOULD attempt to configure 928 the time prior to generating the DUID, if that is possible, and MUST 929 use some sort of time source (for example, a real-time clock) in 930 generating the DUID, even if that time source could not be configured 931 prior to generating the DUID. The use of a time source makes it 932 unlikely that two identical DUID-LLTs will be generated if the 933 network interface is removed from the client and another client then 934 uses the same network interface to generate a DUID-LLT. A collision 935 between two DUID-LLTs is very unlikely even if the clocks haven't 936 been configured prior to generating the DUID. 938 This method of DUID generation is recommended for all general purpose 939 computing devices such as desktop computers and laptop computers, and 940 also for devices such as printers, routers, and so on, that contain 941 some form of writable non-volatile storage. 943 Despite our best efforts, it is possible that this algorithm for 944 generating a DUID could result in a client identifier collision. 946 A DHCP client that generates a DUID-LLT using this mechanism MUST 947 provide an administrative interface that replaces the existing DUID 948 with a newly-generated DUID-LLT. 950 9.3. DUID assigned by vendor based on Enterprise number [DUID-EN] 952 This form of DUID is assigned by the vendor to the device. It 953 consists of the vendor's registered Private Enterprise Number as 954 maintained by IANA [9] followed by a unique identifier assigned by 955 the vendor. 957 The following diagram summarizes the structure of a DUID-EN: 959 0 1 2 3 960 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 1 961 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 962 | 2 | enterprise-number | 963 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 964 | enterprise-number (contd) | | 965 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 966 . identifier . 967 . (variable length) . 968 . . 969 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 971 The source of the identifier is left up to the vendor defining it, 972 but each identifier part of each DUID-EN MUST be unique to the device 973 that is using it, and MUST be assigned to the device at the time of 974 manufacture and stored in some form of non-volatile storage. The 975 generated DUID SHOULD be recorded in non-erasable storage. The 976 enterprise-number is the vendor's registered Private Enterprise 977 Number as maintained by IANA [9]. The enterprise-number is stored as 978 an unsigned 32 bit number. 980 An example DUID of this type might look like this: 982 +---+---+---+---+---+---+---+---+ 983 | 0 | 2 | 0 | 0 | 0 | 9| 12|192| 984 +---+---+---+---+---+---+---+---+ 985 |132|221| 3 | 0 | 9 | 18| 986 +---+---+---+---+---+---+ 988 This example includes the two-octet type of 2, the Enterprise 989 Number (9), followed by eight octets of identifier data 990 (0x0CC084D303000912). 992 9.4. DUID based on link-layer address [DUID-LL] 994 This type of DUID consists of two octets containing the DUID type 3, 995 a two octet network hardware type code, followed by the link-layer 996 address of any one network interface that is permanently connected to 997 the client or server device. For example, a host that has a network 998 interface implemented in a chip that is unlikely to be removed and 999 used elsewhere could use a DUID-LL. The hardware type MUST be a valid 1000 hardware type assigned by the IANA as described in the section on 1001 ARP in RFC 826. The hardware type is stored in network byte order. 1002 The link-layer address is stored in canonical form, as described in 1003 RFC2464 [3]. 1005 The following diagram illustrates the format of a DUID-LL: 1007 0 1 2 3 1008 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 1009 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1010 | 3 | Hardware type (16 bits) | 1011 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1012 . . 1013 . link-layer address (variable length) . 1014 . . 1015 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1017 The choice of network interface can be completely arbitrary, as 1018 long as that interface provides a unique link-layer address and is 1019 permanently attached to the device on which the DUID-LL is being 1020 generated. The same DUID should be used in configuring all network 1021 interfaces connected to the device, regardless of which interface's 1022 link-layer address was used to generate the DUID. 1024 DUID-LL is recommended for devices that have a permanently-connected 1025 network interface with a link-layer address and do not have 1026 nonvolatile, writable stable storage. DUID-LL MUST NOT be used by 1027 DHCP clients or servers that cannot tell whether or not a network 1028 interface is permanently attached to the device on which the DHCP 1029 client is running. 1031 10. Identity association 1033 An "identity-association" (IA) is a construct through which a server 1034 and a client can identify, group and manage a set of related IPv6 1035 addresses. Each IA consists of an IAID and associated configuration 1036 information. 1038 A client must associate at least one distinct IA with each of 1039 its network interfaces and uses that IA to obtain configuration 1040 information from a server for that interface. Each IA must be 1041 associated with exactly one interface. 1043 The IAID uniquely identifies the IA and must be chosen to be unique 1044 among the IAIDs on the client. The IAID is chosen by the client. 1045 For any given use of an IA by the client, the IAID for that IA MUST 1046 be consistent across restarts of the DHCP client. The client may 1047 maintain consistency either by storing the IAID in non-volatile 1048 storage or by using an algorithm that will consistently produce the 1049 same IAID as long as the configuration of the client has not changed. 1050 There may be no way for a client to maintain consistency of the IAIDs 1051 if it does not have non-volatile storage and the client's hardware 1052 configuration changes. 1054 The configuration information in an IA consists of one or more IPv6 1055 addresses along with the times T1 and T2 for the IA. See section 22.4 1056 for the representation of an IA in a DHCP message. 1058 Each address in an IA has a preferred lifetime and a valid lifetime, 1059 as defined in RFC2462 [20]. The lifetimes are transmitted from the 1060 DHCP server to the client in the IA option. The lifetimes apply to 1061 the use of IPv6 addresses as described in section 5.5.4 of RFC2462. 1063 11. Selecting addresses for assignment to an IA 1065 A server selects addresses to be assigned to an IA according to the 1066 address assignment policies determined by the server administrator 1067 and the specific information the server determines about the client 1068 from some combination of the following sources: 1070 - The link to which the client is attached. The server determines 1071 the link as follows: 1073 * If the server receives the message directly from the client 1074 and the source address in the IP datagram in which the 1075 message was received is a link-local address, then the client 1076 is on the same link to which the interface over which the 1077 message was received is attached 1079 * If the server receives the message from a forwarding relay 1080 agent, then the client is on the same link as the one to 1081 which the interface identified by the link-address field in 1082 the message from the relay agent is attached 1084 * If the server receives the message directly from the client 1085 and the source address in the IP datagram in which the 1086 message was received is not a link-local address, then the 1087 client is on the link identified by the source address in the 1088 IP datagram (note that this situation can occur only if the 1089 server has enabled the use of unicast message delivery by the 1090 client and the client has sent a message for which unicast 1091 delivery is allowed) 1093 - The DUID supplied by the client 1094 - Other information in options supplied by the client 1096 - Other information in options supplied by the relay agent 1098 Any unicast address assigned by a server that is based on an 1099 EUI-64 identifier MUST include an interface identifier with the "u" 1100 (universal/local) and "g" (individual/group) bits of the interface 1101 identifier set appropriately, as indicated in section 2.5.1 of RFC 1102 2373 [8]. 1104 A server MUST NOT assign an address that is otherwise reserved for 1105 some other purpose. For example, a server MUST NOT assign reserved 1106 anycast addresses, as defined in RFC2526, from any subnet. 1108 12. Management of temporary addresses 1110 A client may be assigned temporary addresses (temporary addresses are 1111 defined in RFC 3041 [15]). DHCPv6 handling of address assignment 1112 is no different for temporary addresses. DHCPv6 says nothing about 1113 details of temporary addresses like lifetimes, how clients use 1114 temporary addresses, rules for generating successive temporary 1115 addresses, etc. 1117 Clients ask for temporary addresses and servers assign them. 1118 Temporary addresses are carried in the Identity Association for 1119 Temporary Addresses (IA_TA) option (see section 22.5). Each IA_TA 1120 option contains at most one temporary address for each of the 1121 prefixes on the link to which the client is attached. 1123 Unless otherwise stated, an IA_TA option is used in the same way 1124 as an IA option. In the protocol specification, unless otherwise 1125 stated, a reference to an IA should be read as either an IA or an 1126 IA_TA. 1128 The IAID number space for the IA_TA option IAID number space is 1129 separate from the IA option IAID number space. 1131 The server MAY update the DNS for a temporary address as described in 1132 section 4 of RFC3041. 1134 13. Transmission of messages by a client 1136 Unless otherwise specified in this document or in a document that 1137 describes how IPv6 is carried over a specific type of link (for link 1138 types that do not support multicast), a client sends DHCP messages to 1139 the All_DHCP_Relay_Agents_and_Servers. 1141 A client uses multicast to reach all servers or an individual server. 1142 An individual server is indicated by specifying that server's DUID in 1143 a Server Identifier option (see section 22.3) in the client's message 1144 (all servers will receive this message but only the indicated server 1145 will respond). All servers are indicated by not supplying this 1146 option. 1148 A client may send some messages directly to a server using unicast, 1149 as described in section 22.12. 1151 14. Reliability of Client Initiated Message Exchanges 1153 DHCP clients are responsible for reliable delivery of messages in the 1154 client-initiated message exchanges described in sections 17 and 18. 1155 If a DHCP client fails to receive an expected response from a server, 1156 the client must retransmit its message. This section describes the 1157 retransmission strategy to be used by clients in client-initiated 1158 message exchanges. 1160 Note that the procedure described in this section is slightly 1161 modified when used with the Solicit message. The modified procedure 1162 is described in section 17.1.2. 1164 The client begins the message exchange by transmitting a message to 1165 the server. The message exchange terminates when either the client 1166 successfully receives the appropriate response or responses from a 1167 server or servers, or when the message exchange is considered to have 1168 failed according to the retransmission mechanism described below. 1170 The client retransmission behavior is controlled and described by the 1171 following variables: 1173 RT Retransmission timeout 1175 IRT Initial retransmission time 1177 MRC Maximum retransmission count 1179 MRT Maximum retransmission time 1181 MRD Maximum retransmission duration 1183 RAND Randomization factor 1185 With each message transmission or retransmission, the client sets RT 1186 according to the rules given below. If RT expires before the message 1187 exchange terminates, the client recomputes RT and retransmits the 1188 message. 1190 Each of the computations of a new RT include a randomization factor 1191 (RAND), which is a random number chosen with a uniform distribution 1192 between -0.1 and +0.1. The randomization factor is included to 1193 minimize synchronization of messages transmitted by DHCP clients. 1194 The algorithm for choosing a random number does not need to be 1195 cryptographically sound. The algorithm SHOULD produce a different 1196 sequence of random numbers from each invocation of the DHCP client. 1198 RT for the first message transmission is based on IRT: 1200 RT = IRT + RAND*IRT 1202 RT for each subsequent message transmission is based on the previous 1203 value of RT: 1205 RT = 2*RTprev + RAND*RTprev 1207 MRT specifies an upper bound on the value of RT. If MRT has a value 1208 of 0, there is no upper limit on the value of RT. Otherwise: 1210 if (RT > MRT) 1211 RT = MRT + RAND*MRT 1213 MRC specifies an upper bound on the number of times a client may 1214 retransmit a message. Unless MRC is zero, the message exchange fails 1215 once the client has transmitted the message MRC times. 1217 MRD specifies an upper bound on the length of time a client may 1218 retransmit a message. Unless MRD is zero, the message exchange fails 1219 once MRD seconds have elapsed since the client first transmitted the 1220 message. 1222 If both MRC and MRD are non-zero, the message exchange fails whenever 1223 either of the conditions specified in the previous two paragraphs are 1224 met. 1226 If both MRC and MRD are zero, the client continues to transmit the 1227 message until it receives a response. 1229 15. Message validation 1231 Clients and servers SHOULD discard any messages that contain options 1232 that are not allowed to appear in the received message. For example, 1233 an Information-request message must not include an IA option. 1234 Clients and server MAY choose to extract information from such a 1235 message if the information is of use to the recipient. 1237 Message validation based on DHCP authentication is discussed in 1238 section 21.5.2. 1240 15.1. Use of Transaction IDs 1242 The "transaction-id" field holds a value used by clients and servers 1243 to synchronize server responses to client messages. A client 1244 SHOULD generate a random number that cannot easily be guessed or 1245 predicted to use as the transaction ID for each new message it sends. 1247 Note that if a client generates easily predictable transaction 1248 identifiers, it may become more vulnerable to certain kinds of 1249 attacks from off-path intruders. A client MUST leave the transaction 1250 ID unchanged in retransmissions of a message. 1252 15.2. Solicit message 1254 Clients MUST discard any received Solicit messages. 1256 Servers MUST discard any Solicit messages that do not include a 1257 Client Identifier option or that do include a Server Identifier 1258 option. 1260 15.3. Advertise message 1262 Clients MUST discard any received Advertise messages that meet any of 1263 the following conditions: 1265 - the message does not include a Server Identifier option 1267 - the message does not include a Client Identifier option 1269 - the contents of the Client Identifier option does not match the 1270 client's DUID 1272 - the "transaction-id" field value does not match the value the 1273 client used in its Solicit message 1275 Servers and relay agents MUST discard any received Advertise 1276 messages. 1278 15.4. Request message 1280 Clients MUST discard any received Request messages. 1282 Servers MUST discard any received Request message that meet any of 1283 the following conditions: 1285 - the message does not include a Server Identifier option 1287 - the contents of the Server Identifier option do not match the 1288 server's DUID 1290 - the message does not include a Client Identifier option 1292 15.5. Confirm message 1294 Clients MUST discard any received Confirm messages. 1296 Servers MUST discard any received Confirm messages that do not 1297 include a Client Identifier option or that do include a Server 1298 Identifier option. 1300 15.6. Renew message 1302 Clients MUST discard any received Renew messages. 1304 Servers MUST discard any received Renew message that fails to meet 1305 any of the following conditions: 1307 - the message MUST include a Server Identifier option 1309 - the contents of the Server Identifier option MUST match the 1310 server's identifier 1312 - the message MUST include a Client Identifier option 1314 15.7. Rebind message 1316 Clients MUST discard any received Rebind messages. 1318 Servers MUST discard any received Rebind messages that do not include 1319 a Client Identifier option or that do include a Server Identifier 1320 option. 1322 15.8. Decline messages 1324 Clients MUST discard any received Decline messages. 1326 Servers MUST discard any received Decline message that fails to meet 1327 any of the following conditions: 1329 - the message MUST include a Server Identifier option 1331 - the contents of the Server Identifier option MUST match the 1332 server's identifier 1334 - the message MUST include a Client Identifier option 1336 15.9. Release message 1338 Clients MUST discard any received Release messages. 1340 Servers MUST discard any received Release message that fails to meet 1341 any of the following conditions: 1343 - the message MUST include a Server Identifier option 1344 - the contents of the Server Identifier option MUST match the 1345 server's identifier 1347 - the message MUST include a Client Identifier option 1349 15.10. Reply message 1351 Clients MUST discard any received Reply message that fails to meet 1352 any of the following conditions: 1354 - the message MUST include a Server Identifier option 1356 - the "transaction-id" field in the message MUST match the value 1357 used in the original message 1359 - the message MUST include a Client Identifier option and the 1360 original message from the client contained a Client Identifier 1361 option 1363 - if the client included a Client Identifier option in the original 1364 message, the message MUST include a Client Identifier option 1365 and the contents of the Client Identifier option MUST match the 1366 DUID of the client or, if the client did not include a Client 1367 Identifier option in the original message, the Reply message MUST 1368 NOT include a Client Identifier option 1370 Servers and relay agents MUST discard any received Reply messages. 1372 15.11. Reconfigure message 1374 Servers and relay agents MUST discard any received Reconfigure 1375 messages. 1377 Clients MUST discard any Reconfigure messages that fails any of the 1378 following conditions: 1380 - the message MUST include a Server Identifier option 1382 - the message MUST include a Client Identifier option that contains 1383 the client's DUID 1385 - the message MUST include one of the available security 1386 mechanisms: 1388 * the server sends a Reconfigure Nonce option whose value 1389 matches the current server nonce value known to the client 1391 * the server uses DHCP authentication: 1393 + the message MUST contain an authentication option 1394 + the message MUST pass the authentication validation 1395 performed by the client 1397 15.12. Information-request message 1399 Clients MUST discard any received Information-request messages. 1401 Servers MUST discard any received Information-request message that 1402 includes a Server Identifier option and the DUID in the option does 1403 not match the server's DUID. 1405 15.13. Relay-forward message 1407 Clients MUST discard any received Relay-forward messages. 1409 15.14. Relay-reply message 1411 Clients and servers MUST discard any received Relay-reply messages. 1413 16. Client Source Address and Interface Selection 1415 When a client sends a DHCP message to the 1416 All_DHCP_Relay_Agents_and_Servers address, it SHOULD send the 1417 message through the interface for which configuration information is 1418 being requested. However, the client MAY send the message through 1419 another interface attached to the same link if and only if the 1420 client is certain the two interface are attached to the same link. 1421 In addition, the client SHOULD use an IP address assigned to the 1422 interface for which it is requesting configuration information as 1423 the source address in the header of the IP datagram. If the client 1424 uses a different address as the source address, the address MUST 1425 be assigned to an interface that will be attached to the same link 1426 as the interface for which the client is requesting configuration 1427 information when the response is received from the server. 1429 When a client sends a DHCP message directly to a server using unicast 1430 (after receiving the Server Unicast option from that server), the 1431 source address in the header of the IP datagram MUST be an address 1432 assigned to the interface for which the client is interested in 1433 obtaining configuration and which is suitable for use by the server 1434 in responding to the client. 1436 17. DHCP Server Solicitation 1438 This section describes how a client locates servers that will assign 1439 addresses to IAs belonging to the client. 1441 The client is responsible for creating IAs and requesting that a 1442 server assign configuration information, including IPv6 addresses, 1443 to the IA. The client first creates an IA and assigns it an IAID. 1444 The client then transmits a Solicit message containing an IA option 1445 describing the IA. Servers that can assign configuration information 1446 to the IA respond to the client with an Advertise message. The 1447 client then initiates a configuration exchange as described in 1448 section 18. 1450 Whenever a client initiates server solicitation with a Solicit 1451 message, it discards any reconfigure nonce values it may have 1452 previously recorded. 1454 17.1. Client Behavior 1456 A client uses the Solicit message to discover DHCP servers configured 1457 to assign addresses or return other configuration parameters on the 1458 link to which the client is attached. 1460 17.1.1. Creation of Solicit messages 1462 The client sets the "msg-type" field to SOLICIT. The client generates 1463 a transaction ID and inserts this value in the "transaction-id" 1464 field. 1466 The client MUST include a Client Identifier option to identify itself 1467 to the server. The client includes IA options for any IAs to which 1468 it wants the server to assign addresses. The client MAY include 1469 addresses in the IAs as a hint to the server about addresses for 1470 which the client has a preference. The client MUST NOT include any 1471 other options in the Solicit message except as specifically allowed 1472 in the definition of individual options. 1474 The client uses IA options to request the assignment of non-temporary 1475 addresses and uses IA_TA options to request the assignment of 1476 temporary addresses. Either IA or IA_TA options, or a combination of 1477 both can be included in DHCP messages. 1479 The client MUST include an Option Request option (see section 22.7) 1480 to indicate the options the client is interested in receiving. The 1481 client MAY include options with data values as hints to the server 1482 about parameter values the client would like to have returned. 1484 If the client will accept a Reply message with committed address 1485 assignments and other resources in response to the Solicit message, 1486 the client includes a Rapid Commit option (see section 22.14) in the 1487 Solicit message. 1489 17.1.2. Transmission of Solicit Messages 1491 The first Solicit message from the client on the interface MUST be 1492 delayed by a random amount of time between 0 and MAX_SOL_DELAY. In 1493 the case of a Solicit message transmitted when DHCP is initiated 1494 by IPv6 Neighbor Discovery, the delay gives the amount of time to 1495 wait after IPv6 Neighbor Discovery causes the client to invoke the 1496 stateful address autoconfiguration protocol (see section 5.5.3 of 1497 RFC2462). This random delay desynchronizes clients which start at 1498 the same time (for example, after a power outage). 1500 The client transmits the message according to section 14, using the 1501 following parameters: 1503 IRT SOL_TIMEOUT 1505 MRT SOL_MAX_RT 1507 MRC 0 1509 MRD 0 1511 If the client has included a Rapid Commit option in its Solicit 1512 message, the client terminates the waiting process as soon as a 1513 Reply message with a Rapid Commit option is received. If the client 1514 receives an Advertise message that includes a Preference option 1515 with a preference value of 255, the client immediately begins a 1516 client-initiated message exchange (as described in section 18) by 1517 sending a Request message to the server from which the Advertise 1518 message was received. If the client receives an Advertise message 1519 that does not include a Preference option with a preference value of 1520 255, the client continues to wait until the first RT elapses. If the 1521 first RT elapses and the client has received an Advertise message, 1522 the client SHOULD continue with a client-initiated message exchange 1523 by sending a Request message. 1525 If the client is waiting for an Advertise message, the mechanism in 1526 section 14 is modified as follows for use in the transmission of 1527 Solicit messages. The message exchange is not terminated by the 1528 receipt of an Advertise before the first RT has elapsed. Rather, the 1529 client collects Advertise messages until the first RT has elapsed. 1530 Also, the first RT MUST be selected to be strictly greater than IRT 1531 by choosing RAND to be strictly greater than 0. 1533 A client MUST collect Advertise messages for the first RT seconds, 1534 unless it receives an Advertise message with a preference value 1535 of 255. The preference value is carried in the Preference option 1536 (section 22.8). Any Advertise that does not include a Preference 1537 option is considered to have a preference value of 0. If the client 1538 receives an Advertise message with a preference value of 255, then 1539 the client SHOULD act immediately on that Advertise message without 1540 waiting for any additional Advertise messages. 1542 If the client does not receive any Advertise messages before 1543 the first RT has elapsed, it begins the retransmission mechanism 1544 described in section 14. The client terminates the retransmission 1545 process as soon as it receives any Advertise message, and the client 1546 acts on the received Advertise message without waiting for any 1547 additional Advertise messages. 1549 A DHCP client SHOULD choose MRC and MRD to be 0. If the DHCP client 1550 is configured with either MRC or MRD set to a value other than 1551 0, it MUST stop trying to configure the interface if the message 1552 exchange fails. After the DHCP client stops trying to configure 1553 the interface, it SHOULD restart the reconfiguration process after 1554 some external event, such as user input, system restart, or when the 1555 client is attached to a new link. 1557 17.1.3. Receipt of Advertise messages 1559 The client MUST ignore any Advertise message that includes a Status 1560 Code option containing the value NoAddrsAvail, with the exception 1561 that the client MAY display the associated status message to the 1562 user. 1564 Upon receipt of one or more valid Advertise messages, the client 1565 selects one or more Advertise messages based upon the following 1566 criteria. 1568 - Those Advertise messages with the highest server preference value 1569 are preferred over all other Advertise messages. 1571 - Within a group of Advertise messages with the same server 1572 preference value, a client MAY select those servers whose 1573 Advertise messages advertise information of interest to the 1574 client. For example, the client may choose a server that 1575 returned an advertisement with configuration options of interest 1576 to the client. 1578 - The client MAY choose a less-preferred server if that server has 1579 a better set of advertised parameters, such as the available 1580 addresses advertised in IAs. 1582 Once a client has selected Advertise message(s), the client will 1583 typically store information about each server, such as server 1584 preference value, addresses advertised, when the advertisement was 1585 received, and so on. 1587 If the client needs to select an alternate server in the case that a 1588 chosen server does not respond, the client chooses the next server 1589 according to the criteria given above. 1591 17.1.4. Receipt of Reply message 1593 If the client includes a Rapid Commit option in the Solicit message, 1594 it will expect a Reply message that includes a Rapid Commit option 1595 in response. The client discards any Reply messages it receives 1596 that do not include a Rapid Commit option. If the client receives 1597 a valid Reply message that includes a Rapid Commit option, it 1598 processes the message as described in section 18.1.8. If it does 1599 not receive such a Reply message and does receive a valid Advertise 1600 message, the client processes the Advertise message as described in 1601 section 17.1.3. 1603 17.2. Server Behavior 1605 A server sends an Advertise message in response to valid Solicit 1606 messages it receives to announce the availability of the server to 1607 the client. 1609 17.2.1. Receipt of Solicit messages 1611 The server determines the information about the client and its 1612 location as described in section 11 and checks its administrative 1613 policy about responding to the client. If the server is not 1614 permitted to respond to the client, the server discards the Solicit 1615 message. 1617 If the client has included a Rapid Commit option in the Solicit 1618 message and the server has been configured to respond with committed 1619 address assignments and other resources, the server responds to 1620 the Solicit with a Reply message as described in section 17.2.3. 1621 Otherwise, the server ignores the Rapid Commit option and processes 1622 the remainder of the message as if no Rapid Commit option were 1623 present. 1625 17.2.2. Creation and transmission of Advertise messages 1627 The server sets the "msg-type" field to ADVERTISE and copies the 1628 contents of the transaction-id field from the Solicit message 1629 received from the client to the Advertise message. The server 1630 includes its server identifier in a Server Identifier option and 1631 copies the Client Identifier from the Solicit message into the 1632 Advertise message. 1634 The server MAY add a Preference option to carry the preference value 1635 for the Advertise message. The server implementation SHOULD allow 1636 the setting of a server preference value by the administrator. 1637 The server preference value MUST default to zero unless otherwise 1638 configured by the server administrator. 1640 The server includes options the server will return to the client in 1641 a subsequent Reply message. The information in these options may 1642 be used by the client in the selection of a server if the client 1643 receives more than one Advertise message. If the client has included 1644 an Option Request option in the Solicit message, the server includes 1645 options in the Advertise message containing configuration parameters 1646 for all of the options identified in the Option Request option 1647 that the server has been configured to return to the client. The 1648 server MAY return additional options to the client if it has been 1649 configured to do so. The server SHOULD limit the options returned to 1650 the client so that the DHCP message header and options do not cause 1651 fragmentation. 1653 If the Solicit message from the client included one or more IA 1654 options, the server MUST include IA or IAID options in the Advertise 1655 message containing any addresses that would be assigned to IAs 1656 contained in the Solicit message from the client. 1658 If the server will not assign any addresses to any IAs in a 1659 subsequent Request from the client, the server MUST send an Advertise 1660 message to the client that includes only a Status Code option with 1661 code NoAddrsAvail, a status message for the user, a Server Identifier 1662 option with the server's DUID and a Client Identifier option with the 1663 client's DUID. 1665 If the Solicit message was received directly by the server, the 1666 server unicasts the Advertise message directly to the client using 1667 the address in the source address field from the IP datagram in which 1668 the Solicit message was received. The Advertise message MUST be 1669 unicast on the link from which the Solicit message was received. 1671 If the Solicit message was received in a Relay-forward message, 1672 the server constructs a Relay-reply message with the Advertise 1673 message in the payload of a "server-message" option. If the 1674 Relay-forward messages included an Interface-id option, the server 1675 copies that option to the Relay-reply message. The server unicasts 1676 the Relay-reply message directly to the relay agent using the 1677 address in the source address field from the IP datagram in which the 1678 Relay-forward message was received. 1680 17.2.3. Creation and Transmission of Reply messages 1682 The server MUST commit the assignment of any addresses or other 1683 configuration information message before sending a Reply message to a 1684 client in response to a Solicit message. 1686 DISCUSSION: 1688 When using the Solicit-Reply message exchange, the server 1689 commits the assignment of any addresses before sending the 1690 Reply message. The client can assume it has been assigned 1691 the addresses in the Reply message and does not need to send 1692 a Request message for those addresses. 1694 Typically, servers that are configured to use the 1695 Solicit-Reply message exchange will be deployed so that only 1696 one server will respond to a Solicit message. If more than 1697 one server responds, the client will only use the addresses 1698 from one of the servers and the addresses from the other 1699 servers will be committed to the client but not used by the 1700 client. 1702 The problem of unused addresses can be minimized, for 1703 example, by designing the DHCP service so that only one 1704 server responds to the Solicit or by using relatively short 1705 lifetimes for assigned addresses. 1707 The server includes a Rapid Commit option in the Reply message to 1708 indicate that the Reply is in response to a Solicit message. 1710 The server produces the Reply message as though it had received 1711 a Request message, as described in section 18.2.1. The server 1712 transmits the Reply message as described in section 18.2.8. 1714 18. DHCP Client-Initiated Configuration Exchange 1716 A client initiates a message exchange with a server or servers 1717 to acquire or update configuration information of interest. The 1718 client may initiate the configuration exchange as part of the 1719 operating system configuration process, when requested to do 1720 so by the application layer, when required by Stateless Address 1721 Autoconfiguration or as required to extend the lifetime of an address 1722 (Renew and Rebind messages). 1724 18.1. Client Behavior 1726 A client uses Request, Confirm, Renew, Rebind and Information-request 1727 messages to acquire and confirm the validity of configuration 1728 information. 1730 If the client has a source address of sufficient scope that can be 1731 used by the server as a return address and the client has received 1732 a Server Unicast option (section 22.12) from the server, the client 1733 SHOULD unicast any Request, Renew, Release and Decline messages to 1734 the server. 1736 DISCUSSION: 1738 Use of unicast may avoid delays due to forwarding of 1739 messages by relay agents as well as avoid overhead and 1740 duplicate responses by servers due to delivery of client 1741 messages to multiple servers. Requiring the client to 1742 relay all DHCP messages through a relay agent enables the 1743 inclusion of relay agent options in all messages sent by the 1744 client. The server should enable the use of unicast only 1745 when relay agent options will not be used. 1747 18.1.1. Creation and transmission of Request messages 1749 The client uses a Request message to populate IAs with addresses and 1750 obtain other configuration information. The client includes one or 1751 more IA options in the Request message. The server then returns 1752 addresses and other information about the IAs to the client in IA 1753 options in a Reply message. 1755 The client generates a transaction ID and inserts this value in the 1756 "transaction-id" field. 1758 The client places the identifier of the destination server in a 1759 Server Identifier option. 1761 The client MUST include a Client Identifier option to identify itself 1762 to the server. The client adds any other appropriate options, 1763 including one or more IA options (if the client is requesting that 1764 the server assign it some network addresses). 1766 The client MUST include an Option Request option (see section 22.7) 1767 to indicate the options the client is interested in receiving. The 1768 client MAY include options with data values as hints to the server 1769 about parameter values the client would like to have returned. 1771 The client transmits the message according to section 14, using the 1772 following parameters: 1774 IRT REQ_TIMEOUT 1776 MRT REQ_MAX_RT 1778 MRC REQ_MAX_RC 1780 MRD 0 1782 If the message exchange fails, the client takes an action based on 1783 the client's local policy. Examples of actions the client might take 1784 include: 1786 - Select another server from a list of servers known to the client; 1787 for example, servers that responded with an Advertise message 1789 - Initiate the server discovery process described in section 17 1791 - Terminate the configuration process and report failure 1793 18.1.2. Creation and transmission of Confirm messages 1795 Whenever a client may have moved to a new link, the prefixes from the 1796 addresses assigned to the interfaces on that link may no longer be 1797 appropriate to the link. Examples of times when a client may have 1798 moved to a new link include: 1800 Whenever a client may have moved to a new link, the prefixes from the 1801 addresses assigned to the interfaces on that link may no longer be 1802 appropriate to the link to which the client is attached. Examples of 1803 times when a client may have moved to a new link include: 1805 o The client reboots 1807 o The client is physically disconnected from a wired connection 1809 o The client returns from sleep mode 1811 o The client using a wireless technology changes access points 1813 In any situation when a client may have moved to a new link, the 1814 client MUST initiate a Confirm/Reply message exchange. The client 1815 includes any IAs, along with the addresses associated with those IAs, 1816 in its Confirm message. Any responding servers will indicate whether 1817 those addresses are appropriate to the link to which the client is 1818 attached with the status in the Reply message it returns to the 1819 client. 1821 In any situation when a client may have moved to a new link, the 1822 client MUST initiate a Confirm/Reply message exchange. The client 1823 includes any IAs, along with the addresses associated with those IAs, 1824 in its Confirm message. Any responding servers will indicate whether 1825 those addresses are appropriate to the link to which the client is 1826 attached with the status in the Reply message it returns to the 1827 client. 1829 The client sets the "msg-type" field to CONFIRM. The client generates 1830 a transaction ID and inserts this value in the "transaction-id" 1831 field. 1833 The client MUST include a Client Identifier option to identify itself 1834 to the server. The client includes IA options for all of the IAs 1835 currently in use by the client. The IA options include all of the 1836 addresses the client currently has associated with those IAs. The 1837 client SHOULD set the T1 and T2 fields in the IA options and the 1838 preferred-lifetime and valid-lifetime fields in the IA Address 1839 options to 0, and the server will ignore these fields. 1841 The client transmits the message according to section 14, using the 1842 following parameters: 1844 IRT CNF_TIMEOUT 1845 MRT CNF_MAX_RT 1847 MRC 0 1849 MRD CNF_MAX_RD 1851 If the client receives no responses before the message transmission 1852 process as described in section 14 terminates, the client SHOULD 1853 continue to use any IP addresses, using the last known lifetimes for 1854 those addresses, and SHOULD continue to use any other previously 1855 obtained configuration parameters. 1857 18.1.3. Creation and transmission of Renew messages 1859 To extend the valid and preferred lifetimes for the addresses 1860 associated with an IA, the client sends a Renew message to the server 1861 from which the client obtained the addresses in the IA containing 1862 an IA option for the IA. The client includes IA Address options in 1863 the IA option for the addresses associated with the IA. The server 1864 determines new lifetimes for the addresses in the IA according to the 1865 administrative configuration of the server. The server may also add 1866 new addresses to the IA. The server may remove addresses from the IA 1867 by setting the preferred and valid lifetimes of those addresses to 1868 zero. 1870 The server controls the time at which the client contacts the server 1871 to extend the lifetimes on assigned addresses through the T1 and T2 1872 parameters assigned to an IA. 1874 If T1 or T2 is set to 0 by the server, the client does not send a 1875 Renew or Rebind message, respectively, for the IA. 1877 At time T1 for an IA, the client initiates a Renew/Reply message 1878 exchange to extend the lifetimes on any addresses in the IA. The 1879 client includes an IA option with all addresses currently assigned to 1880 the IA in its Renew message. 1882 The client sets the "msg-type" field to RENEW. The client generates a 1883 transaction ID and inserts this value in the "transaction-id" field. 1885 The client places the identifier of the destination server in a 1886 Server Identifier option. 1888 The client MUST include a Client Identifier option to identify 1889 itself to the server. The client adds any appropriate options, 1890 including one or more IA options. The client MUST include the list 1891 of addresses the client currently has associated with the IAs in the 1892 Renew message. 1894 The client MUST include an Option Request option (see section 22.7) 1895 to indicate the options the client is interested in receiving. The 1896 client MAY include options with data values as hints to the server 1897 about parameter values the client would like to have returned. 1899 The client transmits the message according to section 14, using the 1900 following parameters: 1902 IRT REN_TIMEOUT 1904 MRT REN_MAX_RT 1906 MRC 0 1908 MRD Remaining time until T2 1910 The message exchange is terminated when time T2 is reached (see 1911 section 18.1.4), at which time the client begins a Rebind message 1912 exchange. 1914 18.1.4. Creation and transmission of Rebind messages 1916 At time T2 for an IA (which will only be reached if the server to 1917 which the Renew message was sent at time T1 has not responded), 1918 the client initiates a Rebind/Reply message exchange with any 1919 available server. The client sends the Rebind message to the 1920 All_DHCP_Relay_Agents_and_Servers multicast address. The client 1921 includes an IA option with all addresses currently assigned to the IA 1922 in its Rebind message. 1924 The client sets the "msg-type" field to REBIND. The client generates 1925 a transaction ID and inserts this value in the "transaction-id" 1926 field. 1928 The client MUST include a Client Identifier option to identify 1929 itself to the server. The client adds any appropriate options, 1930 including one or more IA options. The client MUST include the list 1931 of addresses the client currently has associated with the IAs in the 1932 Rebind message. 1934 The client MUST include an Option Request option (see section 22.7) 1935 to indicate the options the client is interested in receiving. The 1936 client MAY include options with data values as hints to the server 1937 about parameter values the client would like to have returned. 1939 The client transmits the message according to section 14, using the 1940 following parameters: 1942 IRT REB_TIMEOUT 1944 MRT REB_MAX_RT 1946 MRC 0 1947 MRD Remaining time until valid lifetimes of all addresses have 1948 expired 1950 The mechanism in section 14 is modified as follows for use in the 1951 transmission of Rebind messages. The message exchange is terminated 1952 when the valid lifetimes of all of the addresses assigned to the 1953 IA expire (see section 10), at which time the client has several 1954 alternative actions to choose from: 1956 - The client may choose to use a Solicit message to locate a new 1957 DHCP server and send a Request for the expired IA to the new 1958 server 1960 - The client may have other addresses in other IAs, so the client 1961 may choose to discard the expired IA and use the addresses in the 1962 other IAs 1964 18.1.5. Creation and Transmission of Information-request messages 1966 The client uses an Information-request message to obtain 1967 configuration information without having addresses assigned to it. 1969 The client sets the "msg-type" field to INFORMATION-REQUEST. The 1970 client generates a transaction ID and inserts this value in the 1971 "transaction-id" field. 1973 The client SHOULD include a Client Identifier option to identify 1974 itself to the server. If the client does not include a Client 1975 Identifier option, the server will not be able to return any 1976 client-specific options to the client, or the server may choose not 1977 to respond to the message at all. 1979 The client MUST include an Option Request option (see section 22.7) 1980 to indicate the options the client is interested in receiving. The 1981 client MAY include options with data values as hints to the server 1982 about parameter values the client would like to have returned. 1984 The client transmits the message according to section 14, using the 1985 following parameters: 1987 IRT INF_TIMEOUT 1989 MRT INF_MAX_RT 1991 MRC 0 1993 MRD 0 1995 18.1.6. Creation and transmission of Release messages 1997 To release one or more addresses, a client sends a Release message to 1998 the server. 2000 The client sets the "msg-type" field to RELEASE. The client generates 2001 a transaction ID and places this value in the "transaction-id" field. 2003 The client places the identifier of the server that allocated the 2004 address(es) in a Server Identifier option. 2006 The client MUST include a Client Identifier option to identify itself 2007 to the server. The client includes options containing the IAs for 2008 the addresses it is releasing in the "options" field. The addresses 2009 to be released MUST be included in the IAs. Any addresses for the 2010 IAs the client wishes to continue to use MUST NOT be in added to the 2011 IAs. 2013 The client MUST NOT use any of the addresses it is releasing as 2014 the source address in the Release message or in any subsequently 2015 transmitted message. 2017 Because Release messages may be lost, the client should retransmit 2018 the Release if no Reply is received. However, there are scenarios 2019 where the client may not wish to wait for the normal retransmission 2020 timeout before giving up (e.g., on power down). Implementations 2021 SHOULD retransmit one or more times, but MAY choose to terminate the 2022 retransmission procedure early. 2024 The client transmits the message according to section 14, using the 2025 following parameters: 2027 IRT REL_TIMEOUT 2029 MRT 0 2031 MRC REL_MAX_MRC 2033 MRD 0 2035 The client MUST stop using all of the addresses being released as 2036 soon as the client begins the Release message exchange process. If 2037 addresses are released but the Reply from a DHCP server is lost, 2038 the client will retransmit the Release message, and the server may 2039 respond with a Reply indicating a status of NoBinding. Therefore, 2040 the client does not treat a Reply message with a status of NoBinding 2041 in a Release message exchange as if it indicates an error. 2043 Note that if the client fails to release the addresses, the addresses 2044 assigned to the IA will be reclaimed by the server when the valid 2045 lifetime of the address expires. 2047 18.1.7. Creation and transmission of Decline messages 2049 If a client detects that one or more addresses assigned to it by a 2050 server are already in use by another node, the client sends a Decline 2051 message to the server to inform it that the address is suspect. 2053 The client sets the "msg-type" field to DECLINE. The client generates 2054 a transaction ID and places this value in the "transaction-id" field. 2056 The client places the identifier of the server that allocated the 2057 address(es) in a Server Identifier option. 2059 The client MUST include a Client Identifier option to identify itself 2060 to the server. The client includes options containing the IAs for 2061 the addresses it is declining in the "options" field. The addresses 2062 to be declined MUST be included in the IAs. Any addresses for the 2063 IAs the client wishes to continue to use should not be in added to 2064 the IAs. 2066 The client MUST NOT use any of the addresses it is declining as 2067 the source address in the Decline message or in any subsequently 2068 transmitted message. 2070 The client transmits the message according to section 14, using the 2071 following parameters: 2073 IRT DEC_TIMEOUT 2075 MRT DEC_MAX_RT 2077 MRC DEC_MAX_RC 2079 MRD 0 2081 If addresses are released but the Reply from a DHCP server is lost, 2082 the client will retransmit the Decline message, and the server may 2083 respond with a Reply indicating a status of NoBinding. Therefore, 2084 the client does not treat a Reply message with a status of NoBinding 2085 in a Decline message exchange as if it indicates an error. 2087 18.1.8. Receipt of Reply messages 2089 Upon the receipt of a valid Reply message in response to a Request, 2090 Confirm, Renew, Rebind or Information-request message, the client 2091 extracts the configuration information contained in the Reply. The 2092 client MAY choose to report any status code or message from the 2093 status code option in the Reply message. 2095 The client SHOULD perform duplicate address detection [20] on each 2096 of the addresses in any IAs it receives in the Reply message before 2097 using that address for traffic. If any of the addresses are found 2098 to be in use on the link, the client sends a Decline message to the 2099 server as described in section 18.1.7. 2101 The client records the T1 and T2 times for each IA in the Reply 2102 message. The client records any addresses included with IAs in the 2103 Reply message. The client updates the preferred and valid lifetimes 2104 for the addresses in the IA from the lifetime information in the 2105 IA option, and discards any addresses with valid lifetime set to 0 2106 in the IA option. The client leaves any addresses that the client 2107 has associated with the IA that are not included in the IA option 2108 unchanged. 2110 If the Reply was received in response to a Request, Renew or Rebind 2111 message, the client must update the information it has recorded about 2112 IAs from the IA options contained in the Reply message: 2114 - Add any new addresses in the IA option to the IA as recorded by 2115 the client 2117 - Update lifetimes for any addresses in the IA option that the 2118 client already has recorded in the IA 2120 - Discard any addresses from the IA as recorded by the client that 2121 have a lifetime of 0 in the IA Address option 2123 Management of the specific configuration information is detailed in 2124 the definition of each option, in section 22. 2126 When the client receives a Reply message with a Status Code option 2127 with value UseMulticast, the client records the receipt of the 2128 message and sends subsequent messages to the server through the 2129 interface on which the message was received using multicast. The 2130 client resends the original message using multicast. 2132 When the client receives a NotOnLink status from the server in 2133 response to a Confirm message, the client performs DHCP server 2134 solicitation as described in section 17 and client-initiated 2135 configuration as described in section 18. If the client receives any 2136 Reply messages that do not indicate a NotOnLink status, the client 2137 can use the addresses in the IA and ignore any messages that do 2138 indicate a NotOnLink status. 2140 When the client receives a status code with value NoBinding in an IA 2141 from the server in response to a Renew message or a Rebind message, 2142 the client sends a Request to reestablish an IA with the server. 2144 When the client receives a valid Reply message in response to a 2145 Release message, the client considers the Release event completed, 2146 regardless of the Status Code option(s) returned by the server. 2148 When the client receives a valid Reply message in response to a 2149 Decline message, the client considers the Decline event completed, 2150 regardless of the Status Code option(s) returned by the server. 2152 18.2. Server Behavior 2154 For this discussion, the Server is assumed to have been configured in 2155 an implementation specific manner with configuration of interest to 2156 clients. 2158 In most instances, the server will send a Reply in response to a 2159 client message. This Reply message MUST always contain the Server 2160 Identifier option containing the server's DUID and the Client 2161 Identifier option from the client message if one was present. 2163 18.2.1. Receipt of Request messages 2165 When the server receives a Request message via unicast from a 2166 client to which the server has not sent a unicast option, the server 2167 discards the Request message and responds with a Reply message 2168 containing a Status Code option with value UseMulticast, a Server 2169 Identifier option containing the server's DUID, the Client Identifier 2170 option from the client message and no other options. 2172 When the server receives a valid Request message, the server creates 2173 the bindings for that client according to the server's policy and 2174 configuration information and records the IAs and other information 2175 requested by the client. 2177 The server constructs a Reply message by setting the "msg-type" field 2178 to REPLY, copying the transaction ID from the Request message into 2179 the transaction-id field. 2181 The server MUST include a Server Identifier option containing the 2182 server's DUID and the Client Identifier option from the Request 2183 message in the Reply message. 2185 If the server finds that the prefix on one or more IP addresses in 2186 any IA in the message from the client is not appropriate to the link 2187 to which the client is connected, the server MUST return the IA to 2188 the client with a Status Code option with value NotOnLink. 2190 If the server cannot assign any addresses to any of the IAs in the 2191 message from the client, the server MUST include the IAs in the Reply 2192 message with Status Code option set to NoAddrsAvail and no addresses 2193 in the IA. 2195 For any IAs to which the server can assign addresses, the server 2196 includes the IA with addresses and other configuration parameters and 2197 records the IA as a new client binding. 2199 If the server will use a reconfigure nonce value for security of 2200 Reconfigure messages, the server generates a new nonce value for the 2201 client, records the value and includes it in a Reconfigure Nonce 2202 option (see section 22.20) in the Reply message. 2204 The server includes other options containing configuration 2205 information to be returned to the client. The server SHOULD limit 2206 the options returned to the client so that the DHCP message header 2207 and options do not cause fragmentation. If the client has included 2208 an Option Request option in the Solicit message, the server includes 2209 options in the Advertise message containing configuration parameters 2210 for all of the options identified in the Option Request option that 2211 the server has been configured to return to the client. The server 2212 MAY return additional options to the client if it has been configured 2213 to do so. 2215 18.2.2. Receipt of Confirm messages 2217 When the server receives a Confirm message, the server determines 2218 if the addresses in the Confirm message are appropriate to the 2219 link to which the client is attached. The server ignores the T1 2220 and T2 fields in the IA options and the preferred-lifetime and 2221 valid-lifetime fields in the IA Address options. 2223 If all of the addresses in the Confirm message pass this test, the 2224 server returns a status of Success. If any of the addresses do not 2225 pass this test, the server returns a status of NotOnLink. 2227 If the server does not find any addresses that are not appropriate to 2228 the link to which the client is connected, but cannot determine if 2229 some of the addresses are appropriate to the link or not appropriate 2230 to the link, the server MUST NOT send a reply to the client. For 2231 example, if the server does not have information about prefixes on 2232 the link to which the client is connected, the server does not reply. 2234 The server constructs a Reply message by setting the "msg-type" field 2235 to REPLY, copying the transaction ID from the Confirm message into 2236 the transaction-id field. 2238 The server MUST include a Server Identifier option containing the 2239 server's DUID and the Client Identifier option from the Confirm 2240 message in the Reply message. The server includes a Status Code 2241 option indicating the status of the Confirm message. 2243 18.2.3. Receipt of Renew messages 2245 When the server receives a Renew message via unicast from a client to 2246 which the server has not sent a unicast option, the server discards 2247 the Renew message and responds with a Reply message containing a 2248 Status Code option with value UseMulticast, a Server Identifier 2249 option containing the server's DUID, the Client Identifier option 2250 from the client message and no other options. 2252 When the server receives a Renew message that contains an IA option 2253 from a client, it locates the client's binding and verifies that the 2254 information in the IA from the client matches the information stored 2255 for that client. 2257 If the server cannot find a client entry for the IA the server 2258 returns the IA containing no addresses with a Status Code option set 2259 to NoBinding in the Reply message. 2261 If the server finds that any of the addresses are not appropriate 2262 to the link to which the client is attached, the server returns the 2263 address to the client with lifetimes of 0. 2265 If the server finds the addresses in the IA for the client then the 2266 server sends back the IA to the client with new lifetimes and T1/T2 2267 times, and includes a Status Code option with value Success. The 2268 server may choose to change the list of addresses and the lifetimes 2269 of addresses in IAs that are returned to the client. 2271 The server constructs a Reply message by setting the "msg-type" field 2272 to REPLY, copying the transaction ID from the Renew message into the 2273 transaction-id field. 2275 The server MUST include a Server Identifier option containing the 2276 server's DUID and the Client Identifier option from the Renew message 2277 in the Reply message. 2279 18.2.4. Receipt of Rebind messages 2281 When the server receives a Rebind message that contains an IA option 2282 from a client, it locates the client's binding and verifies that the 2283 information in the IA from the client matches the information stored 2284 for that client. 2286 If the server cannot find a client entry for the IA the server 2287 returns the IA containing no addresses with a Status Code option set 2288 to NoBinding in the Reply message. 2290 If the server finds that the any of the addresses are no longer 2291 appropriate to the link to which the client is attache, the server 2292 returns the address to the client with lifetimes of 0. 2294 If the server finds the addresses in the IA for the client then the 2295 server SHOULD send back the IA to the client with new lifetimes and 2296 T1/T2 times. 2298 The server constructs a Reply message by setting the "msg-type" field 2299 to REPLY, copying the transaction ID from the Rebind message into the 2300 transaction-id field. 2302 The server MUST include a Server Identifier option containing the 2303 server's DUID and the Client Identifier option from the Rebind 2304 message in the Reply message. 2306 The server includes other options containing configuration 2307 information to be returned to the client. The server SHOULD limit 2308 the options returned to the client so that the DHCP message header 2309 and options do not cause fragmentation. If the client has included 2310 an Option Request option in the Solicit message, the server includes 2311 options in the Advertise message containing configuration parameters 2312 for all of the options identified in the Option Request option that 2313 the server has been configured to return to the client . The server 2314 MAY return additional options to the client if it has been configured 2315 to do so. 2317 18.2.5. Receipt of Information-request messages 2319 When the server receives an Information-request message, the 2320 client is requesting configuration information that does not 2321 include the assignment of any addresses. The server determines all 2322 configuration parameters appropriate to the client, based on the 2323 server configuration policies known to the server. 2325 If the Information-request message specifies an IA option or an IA_TA 2326 option, the server responds by sending a Reply message containing 2327 a Server Identifier option, a Client Identifier option if one was 2328 included in the Information-request message and a Status Code option 2329 with status UnSpecFail. 2331 The server constructs a Reply message by setting the "msg-type" field 2332 to REPLY, copying the transaction ID from the Information-request 2333 message into the transaction-id field. 2335 The server MUST include a Server Identifier option containing the 2336 server's DUID in the Reply message. If the client included a Client 2337 Identification option in the Information-request message, the server 2338 copies that option to the Reply message. 2340 The server includes options containing configuration information 2341 to be returned to the client. The server SHOULD limit the options 2342 returned to the client so that the DHCP message header and options 2343 do not cause fragmentation. If the client has included an Option 2344 Request option in the Solicit message, the server includes options in 2345 the Advertise message containing configuration parameters for all of 2346 the options identified in the Option Request option that the server 2347 has been configured to return to the client . The server MAY return 2348 additional options to the client if it has been configured to do so. 2350 If the Information-request message received from the client did 2351 not include a Client Identifier option, the server SHOULD respond 2352 with a Reply message containing any configuration parameters 2353 that are not determined by the client's identity. If the server 2354 chooses not to respond, the client may continue to retransmit the 2355 Information-request message indefinitely. 2357 18.2.6. Receipt of Release messages 2359 When the server receives a Release message via unicast from a 2360 client to which the server has not sent a unicast option, the server 2361 discards the Release message and responds with a Reply message 2362 containing a Status Code option with value UseMulticast, a Server 2363 Identifier option containing the server's DUID, the Client Identifier 2364 option from the client message and no other options. 2366 Upon the receipt of a valid Release message, the server examines 2367 the IAs and the addresses in the IAs for validity. If the IAs in 2368 the message are in a binding for the client and the addresses in 2369 the IAs have been assigned by the server to those IAs, the server 2370 deletes the addresses from the IAs and makes the addresses available 2371 for assignment to other clients. The server ignores addresses not 2372 assigned to the IA, and it may make a notification if it finds such 2373 an address. 2375 After all the addresses have been processed, the server generates a 2376 Reply message and includes a Status Code option with value Success, 2377 a Server Identifier option with the server's DUID and a Client 2378 Identifier option with the client's DUID. For each IA in the Release 2379 message for which the server has no binding information, the server 2380 adds an IA option using the IAID from the Release message and 2381 includes a Status Code option with the value NoBinding in the IA 2382 option. No other options are included in the IA option. 2384 A server may choose to retain a record of assigned addresses and IAs 2385 after the lifetimes on the addresses have expired to allow the server 2386 to reassign the previously assigned addresses to a client. 2388 18.2.7. Receipt of Decline messages 2390 When the server receives a Decline message via unicast from a 2391 client to which the server has not sent a unicast option, the server 2392 discards the Decline message and responds with a Reply message 2393 containing a Status Code option with value UseMulticast, a Server 2394 Identifier option containing the server's DUID, the Client Identifier 2395 option from the client message and no other options. 2397 Upon the receipt of a valid Decline message, the server examines the 2398 IAs and the addresses in the IAs for validity. If the IAs in the 2399 message are in a binding for the client and the addresses in the IAs 2400 have been assigned by the server to those IA, the server deletes 2401 the addresses from the IAs. The server SHOULD mark the addresses 2402 declined by the client so that those addresses are not assigned to 2403 other clients, and MAY choose to make a notification that addresses 2404 were declined. The server ignores addresses not assigned to the IA 2405 (though it may choose to log an error if it finds such an address). 2407 After all the address have been processed, the server generates a 2408 Reply message and includes a Status Code option with value Success, 2409 a Server Identifier option with the server's DUID and a Client 2410 Identifier option with the client's DUID. For each IA in the Decline 2411 message for which the server has no binding information, the server 2412 adds an IA option using the IAID from the Release message and 2413 includes a Status Code option with the value NoBinding in the IA 2414 option. No other options are included in the IA option. 2416 18.2.8. Transmission of Reply messages 2418 If the original message was received directly by the server, the 2419 server unicasts the Reply message directly to the client using the 2420 address in the source address field from the IP datagram in which the 2421 original message was received. The Reply message MUST be unicast 2422 through the interface on which the original message was received. 2424 If the original message was received in a Relay-forward message, the 2425 server constructs a Relay-reply message with the Reply message in the 2426 payload of a "server-message" option. If the Relay-forward messages 2427 included an Interface-id option, the server copies that option to the 2428 Relay-reply message. The server unicasts the Relay-reply message 2429 directly to the relay agent using the address in the source address 2430 field from the IP datagram in which the Relay-forward message was 2431 received. 2433 19. DHCP Server-Initiated Configuration Exchange 2435 A server initiates a configuration exchange to cause DHCP clients 2436 to obtain new addresses and other configuration information. For 2437 example, an administrator may use a server-initiated configuration 2438 exchange when links in the DHCP domain are to be renumbered. Other 2439 examples include changes in the location of directory servers, 2440 addition of new services such as printing, and availability of new 2441 software. 2443 19.1. Server Behavior 2445 A server sends a Reconfigure message to cause a client to initiate 2446 immediately a Renew/Reply or Information-request/Reply message 2447 exchange with the server. 2449 19.1.1. Creation and transmission of Reconfigure messages 2451 The server sets the "msg-type" field to RECONFIGURE. The server 2452 sets the transaction-id field to 0. The server includes a Server 2453 Identifier option containing its DUID and a Client Identifier option 2454 containing the client's DUID in the Reconfigure message. 2456 The server MAY include an Option Request option to inform the client 2457 of what information has been changed or new information that has been 2458 added. In particular, the server specifies the IA option in the 2459 Option Request option if the server wants the client to obtain new 2460 address information. 2462 Because of the risk of denial of service attacks against DHCP 2463 clients, the use of a security mechanism is mandated in Reconfigure 2464 messages. The server MUST use one of the following two security 2465 mechanisms: 2467 - The server includes a Reconfigure Nonce option containing the 2468 reconfigure nonce value currently assigned to the client 2470 - The server includes an authentication option in the Reconfigure 2471 message 2473 The server MUST include a Reconfigure Message option (defined in 2474 section 22.19) to select whether the client responds with a Renew 2475 message or an Information-Request message. 2477 The server MUST NOT include any other options in the Reconfigure 2478 except as specifically allowed in the definition of individual 2479 options. 2481 A server sends each Reconfigure message to a single DHCP client, 2482 using an IPv6 unicast address of sufficient scope belonging to the 2483 DHCP client. The server may obtain the address of the client through 2484 the information that the server has about clients that have been in 2485 contact with the server, or the server may be configured with the 2486 address of the client through some external agent. 2488 To reconfigure more than one client, the server unicasts a separate 2489 message to each client. The server may initiate the reconfiguration 2490 of multiple clients concurrently; for example, a server may 2491 send a Reconfigure message to additional clients while previous 2492 reconfiguration message exchanges are still in progress. 2494 The Reconfigure message causes the client to initiate a Renew/Reply 2495 or Information-request/Reply message exchange with the server. The 2496 server interprets the receipt of a Renew or Information-request 2497 message (whichever was specified in the original Reconfigure message) 2498 from the client as satisfying the Reconfigure message request. 2500 19.1.2. Time out and retransmission of Reconfigure messages 2502 If the server does not receive a Renew or Information-request 2503 message from the client in REC_TIMEOUT milliseconds, the server 2504 retransmits the Reconfigure message, doubles the REC_TIMEOUT value 2505 and waits again. The server continues this process until REC_MAX_RC 2506 unsuccessful attempts have been made, at which point the server 2507 SHOULD abort the reconfigure process for that client. 2509 Default and initial values for REC_TIMEOUT and REC_MAX_RC are 2510 documented in section 5.5. 2512 19.2. Receipt of Renew messages 2514 The server generates and sends a Reply message to the client as 2515 described in sections 18.2.3 and 18.2.8, including options for 2516 configuration parameters. 2518 The server MAY include options containing the IAs and new values for 2519 other configuration parameters in the Reply message, even if those 2520 IAs and parameters were not requested in the Renew message from the 2521 client. 2523 19.3. Receipt of Information-request messages 2525 The server generates and sends a Reply message to the client as 2526 described in sections 18.2.5 and 18.2.8, including options for 2527 configuration parameters. 2529 The server MAY include options containing new values for other 2530 configuration parameters in the Reply message, even if those 2531 parameters were not requested in the Information-request message from 2532 the client. 2534 19.4. Client Behavior 2536 A client MUST accept Reconfigure messages sent to UDP port 546 on 2537 interfaces for which it has acquired configuration information 2538 through DHCP. These messages may be sent at any time. Since the 2539 results of a reconfiguration event may affect application layer 2540 programs, the client SHOULD log these events, and MAY notify these 2541 programs of the change through an implementation-specific interface. 2543 19.4.1. Receipt of Reconfigure messages 2545 Upon receipt of a valid Reconfigure message, the client initiates a 2546 transaction with the server by sending a Renew or Information-request 2547 message. The client ignores the transaction-id field in the received 2548 Reconfigure message. While the transaction is in progress, the 2549 client silently discards any Reconfigure messages it receives. 2551 The client responds with either a Renew message or an 2552 Information-request message as indicated by the Reconfigure 2553 Message option (as defined in section 22.19). 2555 DISCUSSION: 2557 The Reconfigure message acts as a trigger that signals the 2558 client to complete a successful message exchange. Once 2559 the client has received a Reconfigure, the client proceeds 2560 with the message exchange (retransmitting the Renew or 2561 Information-request message if necessary); the client 2562 ignores any additional Reconfigure messages until the 2563 exchange is complete. Subsequent Reconfigure messages cause 2564 the client to initiate a new exchange. 2566 How does this mechanism work in the face of duplicated or 2567 retransmitted Reconfigure messages? Duplicate messages 2568 will be ignored because the client will begin the exchange 2569 after the receipt of the first Reconfigure. Retransmitted 2570 messages will either trigger the exchange (if the first 2571 Reconfigure was not received by the client) or will be 2572 ignored. The server can discontinue retransmission of 2573 Reconfigure messages to the client once the server receives 2574 the Renew or Information-request message from the client. 2576 It might be possible for a duplicate or retransmitted 2577 Reconfigure to be sufficiently delayed (and delivered out of 2578 order) to arrive at the client after the exchange (initiated 2579 by the original Reconfigure) has been completed. In this 2580 case, the client would initiate a redundant exchange. The 2581 likelihood of delayed and out of order delivery is small 2582 enough to be ignored. The consequence of the redundant 2583 exchange is inefficiency rather than incorrect operation. 2585 19.4.2. Creation and transmission of Renew messages 2587 When responding to a Reconfigure, the client creates and sends 2588 the Renew message in exactly the same manner as outlined in 2589 section 18.1.3, with the exception: if the Reconfigure message 2590 contains an Option Request option that includes the IA option code, 2591 the client MUST include IA options containing the addresses the 2592 client currently has assigned to ALL IAs for the interface through 2593 which the Reconfigure message was received. 2595 19.4.3. Creation and transmission of Information-request messages 2597 When responding to a Reconfigure, the client creates and sends the 2598 Information-request message in exactly the same manner as outlined in 2599 section 18.1.5, with the exception that the client includes a Server 2600 Identifier option with the identifier from the Reconfigure message to 2601 which the client is responding. 2603 19.4.4. Time out and retransmission of Renew or Information-request 2604 messages 2606 The client uses the same variables and retransmission algorithm as 2607 it does with Renew or Information-request messages generated as part 2608 of a client-initiated configuration exchange. See sections 18.1.3 2609 and 18.1.5 for details. If the client does not receive a response 2610 from the server by the end of the retransmission process, the client 2611 ignores and discards the Reconfigure message. 2613 19.4.5. Receipt of Reply messages 2615 Upon the receipt of a valid Reply message, the client processes the 2616 options and sets (or resets) configuration parameters appropriately. 2617 The client records and updates the lifetimes for any addresses 2618 specified in IAs in the Reply message. 2620 20. Relay Agent Behavior 2622 The relay agent MAY be configured to use a list of destination 2623 addresses, which MAY include unicast addresses, the All_DHCP_Servers 2624 multicast address, or other addresses selected by the network 2625 administrator. If the relay agent has not been explicitly 2626 configured, it MUST use the All_DHCP_Servers multicast address as the 2627 default. 2629 20.1. Forwarding a client message or a Relay-forward message 2631 A relay agent forwards both messages from clients and Relay-forward 2632 messages from other relay agents. When a relay agent receives a 2633 valid message to be forwarded, it constructs a new Relay-forward 2634 message. The relay agent copies the source address from the 2635 header of the IP datagram in which the message was received to the 2636 peer-address field of the Relay-forward message. The relay agent 2637 copies the received DHCP message (excluding any IP or UDP headers) 2638 into a Relay Message option in the new message. The relay agent adds 2639 to the Relay-forward message any other options it is configured to 2640 include. 2642 20.1.1. Forwarding a message from a client 2644 If the relay agent received the message to be forwarded from a 2645 client, the relay agent places a global or site-scoped address with a 2646 prefix assigned to the link on which the client should be assigned an 2647 address in the link-address field. This address will be used by the 2648 server to determine the link from which the client should be assigned 2649 an address and other configuration information. The hop-count in the 2650 Relay-forward message is set to 0. 2652 If the relay agent cannot use the address in the link-address field 2653 to identify the interface through which the response to the client 2654 will be forwarded, the relay agent MUST include an Interface-id 2655 option (see section 22.18) in the Relay-forward message. The server 2656 will include the Interface-id option in its Relay-reply message. 2657 The relay agent fills in the link-address field as described in the 2658 previous paragraph regardless of whether the relay agent includes an 2659 Interface-id option in the Relay-forward message. 2661 20.1.2. Forwarding a message from a relay agent 2663 If the message received by the relay agent is a Relay-forward 2664 message and the hop-count in the message is greater than or equal to 2665 HOP_COUNT_LIMIT, the relay agent discards the received message. 2667 The relay agent sets the link-address field to 0 and sets the 2668 hop-count field to the value of the hop-count field in the received 2669 message incremented by 1. 2671 The relay agent copies the source address from the IP datagram in 2672 which the message was received from the client into the peer-address 2673 field in the Relay-forward message. 2675 20.2. Forwarding a Relay-reply message 2677 The relay agent processes any options included in the Relay-reply 2678 message in addition to the Relay Message option and then discards 2679 those options. 2681 The relay agent extracts the message from the Relay Message option 2682 and forwards it to the address contained in the peer-address field of 2683 the Relay-reply message. 2685 If the Relay-reply message includes an Interface-id option, the 2686 relay agent forwards the message from the server to the client on 2687 the link identified by the Interface-id option. Otherwise, if the 2688 link-address field is not set to zero, the relay agent forwards the 2689 message on the link identified by the link-address field. 2691 If the Relay-reply message does not include an Interface-id option 2692 and the link-address field is zero, the address in the peer-address 2693 field must be a global address or a site-local address (and the 2694 device on which the relay agent is running belongs to only one 2695 site). If the address in the peer-address field does not meet this 2696 condition, the relay agent discards the Relay-reply message and 2697 SHOULD communicate an error condition. 2699 20.3. Construction of Relay-reply messages 2701 A server uses a Relay-reply message to return a response to a client 2702 if the original message from the client was forwarded to the server 2703 in a Relay-forward message. The response to the client MUST be 2704 forwarded through the same relay agents as the original client 2705 message. The server causes this to happen by creating a Relay-reply 2706 message that includes a Relay Message option containing the message 2707 for the next relay agent in the return path to the client. The 2708 contained Relay-reply message contains another Relay Message option 2709 to be sent to the next relay agent, and so on. The server must 2710 record the contents of the peer-address fields in the received 2711 message so it can construct the appropriate Relay-reply message 2712 carrying the response from the server. 2714 For example, if client C sent a message that was forwarded by relay 2715 agent A to relay agent B and then to the server, the server would the 2716 following Relay-Reply message to relay agent B: 2718 msg-type: RELAY-REPLY 2719 hop-count: 0 2720 link-address: 0 2721 peer-address: A 2722 Relay Message option, containing: 2723 msg-type: RELAY-REPLY 2724 hop-count: 0 2725 link-address: address from link to which C is attached 2726 peer-address: C 2727 Relay Message option: 2729 21. Authentication of DHCP messages 2731 Some network administrators may wish to provide authentication of 2732 the source and contents of DHCP messages. For example, clients may 2733 be subject to denial of service attacks through the use of bogus 2734 DHCP servers, or may simply be misconfigured due to unintentionally 2735 instantiated DHCP servers. Network administrators may wish to 2736 constrain the allocation of addresses to authorized hosts to avoid 2737 denial of service attacks in "hostile" environments where the network 2738 medium is not physically secured, such as wireless networks or 2739 college residence halls. 2741 The DHCP authentication mechanism is based on the design of 2742 authentication for DHCPv4 [6]. 2744 21.1. DHCP threat model 2746 The threat to DHCP is inherently an insider threat (assuming a 2747 properly configured network where DHCPv6 ports are blocked on the 2748 perimeter gateways of the enterprise). Regardless of the gateway 2749 configuration, however, the potential attacks by insiders and 2750 outsiders are the same. 2752 The attack specific to a DHCP client is the possibility of the 2753 establishment of a "rogue" server with the intent of providing 2754 incorrect configuration information to the client. The motivation 2755 for doing so may be to establish a "man in the middle" attack or it 2756 may be for a "denial of service" attack. 2758 There is another threat to DHCP clients from mistakenly or 2759 accidentally configured DHCP servers that answer DHCP client requests 2760 with unintentionally incorrect configuration parameters. 2762 The threat specific to a DHCP server is an invalid client 2763 masquerading as a valid client. The motivation for this may be for 2764 "theft of service", or to circumvent auditing for any number of 2765 nefarious purposes. 2767 The threat common to both the client and the server is the resource 2768 "denial of service" (DoS) attack. These attacks typically involve 2769 the exhaustion of available addresses, or the exhaustion of CPU 2770 or network bandwidth, and are present anytime there is a shared 2771 resource. 2773 This threat model does not consider the privacy of the contents 2774 of DHCP messages to be important. DHCP is not used to exchange 2775 authentication or configuration information that must be kept secret 2776 from other networks nodes. 2778 21.2. Security of messages sent between servers and relay agents 2780 Relay agents and servers that choose to exchange messages securely 2781 use the IPsec mechanisms for IPv6 [10]. Relay agents and servers 2782 MUST support manual configuration and installation of static keys. 2783 If a client message is forwarded through multiple relay agents, each 2784 of the relay agents must have established independent, pairwise trust 2785 relationships. That is, if messages from client C will be forwarded 2786 by relay agent A to relay agent B and then to the server, relay 2787 agents A and B must be configured to use IPSec for the messages they 2788 exchange, and relay agent B and the server must be configured to use 2789 IPSec for the messages they exchange. 2791 21.3. Summary of DHCP authentication 2793 Authentication of DHCP messages is accomplished through the use of 2794 the Authentication option (see section 22.11). The authentication 2795 information carried in the Authentication option can be used to 2796 reliably identify the source of a DHCP message and to confirm that 2797 the contents of the DHCP message have not been tampered with. 2799 The Authentication option provides a framework for multiple 2800 authentication protocols. One such protocol is defined here. 2801 Other protocols defined in the future will be specified in separate 2802 documents. 2804 The protocol field in the Authentication option identifies the 2805 specific protocol used to generate the authentication information 2806 carried in the option. The algorithm field identifies a specific 2807 algorithm within the authentication protocol; for example, the 2808 algorithm field specifies the hash algorithm used to generate the 2809 message authentication code (MAC) in the authentication option. The 2810 replay detection method (RDM) field specifies the type of replay 2811 detection used in the replay detection field. 2813 21.4. Replay detection 2815 The Replay Detection Method (RDM) field determines the type of replay 2816 detection used in the Replay Detection field. 2818 If the RDM field contains 0x00, the replay detection field MUST 2819 be set to the value of a monotonically increasing counter. Using 2820 a counter value such as the current time of day (for example, an 2821 NTP-format timestamp [12]) can reduce the danger of replay attacks. 2822 This method MUST be supported by all protocols. 2824 21.5. Delayed authentication protocol 2826 If the protocol field is 1, the message is using the "delayed 2827 authentication" mechanism. In delayed authentication, the client 2828 requests authentication in its Solicit message and the server replies 2829 with an Advertise message that includes authentication information. 2830 This authentication information contains a nonce value generated by 2831 the source as a message authentication code (MAC) to provide message 2832 authentication and entity authentication. 2834 The use of a particular technique based on the HMAC protocol [11] 2835 using the MD5 hash [19] is defined here. 2837 21.5.1. Use of the Authentication option in the delayed authentication 2838 protocol 2840 In a Solicit message, the Authentication option carries the Protocol, 2841 Algorithm and fields, but no Replay detection or Authentication 2842 information. 2844 In an Advertise, Request, Renew, Rebind, Confirm, Decline, Release 2845 or Information-request message, the Authentication option carries 2846 the Protocol, Algorithm, RDM and Replay detection fields and 2847 Authentication information. 2849 A DHCP message MUST NOT contain more than one Authentication option 2850 when using the delayed authentication protocol. 2852 The format of the Authentication information is: 2854 0 1 2 3 2855 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 2856 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2857 | Key ID | 2858 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2859 | | 2860 | HMAC-MD5 | 2861 | (128 bits) | 2862 | | 2863 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2865 The following definitions will be used in the description of the 2866 authentication information for delayed authentication, algorithm 1: 2868 Replay Detection - as defined by the RDM field 2869 K - a key (secret value) shared 2870 between the source and 2871 destination of the message; 2872 each key has a unique 2873 identifier (key ID) 2874 key ID - the unique identifier for the key value 2875 used to generate the MAC for this message 2876 HMAC-MD5 - the MAC generating function. 2878 The sender computes the MAC using the HMAC generation algorithm [11] 2879 and the MD5 hash function [19]. The entire DHCP message (setting 2880 the MAC field of the authentication option to zero), including the 2881 DHCP message header and the options field, is used as input to the 2882 HMAC-MD5 computation function. The 'key ID' field MUST be set to the 2883 identifier of the key used to generate the MAC. 2885 DISCUSSION: 2887 Algorithm 1 specifies the use of HMAC-MD5. Use of a 2888 different technique, such as HMAC-SHA, will be specified as 2889 a separate protocol. 2891 Delayed authentication requires a shared secret key for each 2892 client on each DHCP server with which that client may wish 2893 to use the DHCP protocol. Each key has a unique identifier 2894 that can be used by a receiver to determine which key was 2895 used to generate the MAC in the DHCP message. Therefore, 2896 delayed authentication may not scale well in an architecture 2897 in which a DHCP client connects to multiple administrative 2898 domains. 2900 21.5.2. Message validation 2902 Any DHCP message that includes more than one authentication option 2903 MUST be discarded. 2905 To validate an incoming message, the receiver first checks that 2906 the value in the replay detection field is acceptable according to 2907 the replay detection method specified by the RDM field. Next, the 2908 receiver computes the MAC as described in [11]. The entire DHCP 2909 message (setting the MAC field of the authentication option to 0), 2910 is used as input to the HMAC-MD5 computation function. If the MAC 2911 computed by the receiver does not match the MAC contained in the 2912 authentication option, the receiver MUST discard the DHCP message. 2914 21.5.3. Key utilization 2916 Each DHCP client has a key, K. The server uses the client's DUID to 2917 identify the client's key. The client uses its key to encode any 2918 messages it sends to the server and to authenticate and verify any 2919 messages it receives from the server. The client's key is initially 2920 distributed to the client through some out-of-band mechanism, and 2921 is stored locally on the client for use in all authenticated DHCP 2922 messages. Once the client has been given its key, it uses that key 2923 for all transactions even if the client's configuration changes; for 2924 example, if the client is assigned a new network address. 2926 Each DHCP server stores or is able to obtain in a secure manner the 2927 keys for all authorized clients. To authenticate the identity of 2928 individual clients, each client must be configured with a unique key 2929 and a key ID for that key. 2931 21.5.4. Client considerations for delayed authentication protocol 2933 21.5.4.1. Sending Solicit messages 2935 When the client sends a Solicit message and wishes to use 2936 authentication, it includes an Authentication option with the desired 2937 protocol, algorithm and RDM as described in section 21.5. The client 2938 does not include any replay detection or authentication information 2939 in the Authentication option. 2941 21.5.4.2. Receiving Advertise messages 2943 The client validates any Advertise messages containing an 2944 Authentication option specifying the delayed authentication protocol 2945 using the validation test described in section 21.5.2. 2947 Client behavior if no Advertise messages include authentication 2948 information or pass the validation test is controlled by local policy 2949 on the client. According to client policy, the client MAY choose to 2950 respond to a Advertise message that has not been authenticated. 2952 The decision to set local policy to accept unauthenticated messages 2953 should be made with care. Accepting an unauthenticated Advertise 2954 message can make the client vulnerable to spoofing and other 2955 attacks. If local users are not explicitly informed that the client 2956 has accepted an unauthenticated Advertise message, the users may 2957 incorrectly assume that the client has received an authenticated 2958 address and is not subject to DHCP attacks through unauthenticated 2959 messages. 2961 A client MUST be configurable to discard unauthenticated messages, 2962 and SHOULD be configured by default to discard unauthenticated 2963 messages if the client has been configured with an authentication 2964 key or other authentication information. A client MAY choose to 2965 differentiate between Advertise messages with no authentication 2966 information and Advertise messages that do not pass the validation 2967 test; for example, a client might accept the former and discard the 2968 latter. If a client does accept an unauthenticated message, the 2969 client SHOULD inform any local users and SHOULD log the event. 2971 21.5.4.3. Sending Request, Confirm, Renew, Rebind, Decline or Release 2972 messages 2974 If the client authenticated the Advertise message through which the 2975 client selected the server, the client MUST generate authentication 2976 information for subsequent Request, Confirm, Renew, Rebind or Release 2977 messages sent to the server as described in section 21.5. When the 2978 client sends a subsequent message, it MUST use the same key used by 2979 the server to generate the authentication information. 2981 21.5.4.4. Sending Information-request messages 2983 If the server has selected a key for the client in a previous message 2984 exchange (see section 21.5.5.1), the client MUST use the same key 2985 to generate the authentication information. If the client has not 2986 previously been given a key with the server, the client MUST use 2987 a key that has been selected for the client through some external 2988 mechanism. 2990 21.5.4.5. Receiving Reply messages 2992 If the client authenticated the Advertise it accepted, the client 2993 MUST validate the associated Reply message from the server. The 2994 client MUST discard the Reply if the message fails to pass validation 2995 and MAY log the validation failure. If the Reply fails to pass 2996 validation, the client MUST restart the DHCP configuration process by 2997 sending a Solicit message. 2999 If the client accepted an Advertise message that did not include 3000 authentication information or did not pass the validation test, the 3001 client MAY accept an unauthenticated Reply message from the server. 3003 21.5.4.6. Receiving Reconfigure messages 3005 The client MUST discard the Reconfigure if the message fails to pass 3006 validation and MAY log the validation failure. 3008 21.5.5. Server considerations for delayed authentication protocol 3010 21.5.5.1. Receiving Solicit messages and Sending Advertise messages 3012 The server selects a key for the client and includes authentication 3013 information in the Advertise message returned to the client as 3014 specified in section 21.5. The server MUST record the identifier of 3015 the key selected for the client and use that same key for validating 3016 subsequent messages with the client. 3018 21.5.5.2. Receiving Request, Confirm, Renew, Rebind or Release messages 3019 and Sending Reply messages 3021 The server uses the key identified in the message and validates the 3022 message as specified in section 21.5.2. If the message fails to pass 3023 validation or the server does not know the key identified by the 'key 3024 ID' field, the server MUST discard the message and MAY choose to log 3025 the validation failure. 3027 If the message passes the validation procedure, the server responds 3028 to the specific message as described in section 18.2. The server 3029 MUST include authentication information generated using the key 3030 identified in the received message as specified in section 21.5. 3032 21.5.5.3. Sending Reconfigure messages 3034 The server MUST include an Authentication option in a Reconfigure 3035 message, generated as specified in section 21.5 using the key the 3036 server initially selected for the client to which the Reconfigure 3037 message is to be sent. 3039 If the server has not previously selected a key for the client, the 3040 server MUST use a key that has been selected for the client through 3041 some external mechanism. 3043 22. DHCP options 3045 Options are used to carry additional information and parameters 3046 in DHCP messages. Every option shares a common base format, as 3047 described in section 22.1. All values in options are represented in 3048 network byte order. 3050 This document describes the DHCP options defined as part of the base 3051 DHCP specification. Other options may be defined in the future in 3052 separate documents. 3054 Unless otherwise noted, each option may appear only in the options 3055 area of a DHCP message and may appear only once. If an option does 3056 appear multiple times, each instance is considered separate and the 3057 data areas of the options MUST NOT be concatenated or otherwise 3058 combined. 3060 22.1. Format of DHCP options 3062 The format of DHCP options is: 3064 0 1 2 3 3065 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 3066 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3067 | option-code | option-len | 3068 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3069 | option-data | 3070 | (option-len octets) | 3071 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3073 option-code An unsigned integer identifying the specific option 3074 type carried in this option. 3076 option-len An unsigned integer giving the length of the 3077 option-data field in this option in octets. 3079 option-data The data for the option; the format of this data 3080 depends on the definition of the option. 3082 DHCPv6 options are scoped by using encapsulation. Some options apply 3083 generally to the client, some are specific to an IA, and some are 3084 specific to the addresses within an IA. These latter two cases are 3085 discussed in sections 22.4 and 22.6. 3087 22.2. Client Identifier option 3089 The Client Identifier option is used to carry a DUID identifying a 3090 client between a client and a server. 3092 The format of the Client Identifier option is: 3094 0 1 2 3 3095 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 3096 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3097 | OPTION_CLIENTID | option-len | 3098 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3099 . . 3100 . DUID . 3101 . (variable length) . 3102 . . 3103 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3105 option-code OPTION_CLIENTID (1) 3107 option-len Length of DUID in octets 3109 DUID The DUID for the client 3111 22.3. Server Identifier option 3113 The Server Identifier option is used to carry a DUID identifying a 3114 server between a client and a server. 3116 The format of the Server Identifier option is: 3118 0 1 2 3 3119 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 3120 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3121 | OPTION_SERVERID | option-len | 3122 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3123 . . 3124 . DUID . 3125 . (variable length) . 3126 . . 3127 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3129 option-code OPTION_SERVERID (2) 3131 option-len Length of DUID in octets 3133 DUID The DUID for the server 3135 A server MUST process any message it receives that contains a Server 3136 Identifier option with a DUID that matches the server's DUID. 3138 22.4. Identity Association option 3140 The Identity Association option (IA option) is used to carry an 3141 identity association, the parameters associated with the IA and the 3142 addresses associated with the IA. 3144 Addresses appearing in an IA option are not temporary addresses (see 3145 section 22.5). The format of the IA option is: 3147 0 1 2 3 3148 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 3149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3150 | OPTION_IA | option-len | 3151 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3152 | IAID (4 octets) | 3153 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3154 | T1 | 3155 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3156 | T2 | 3157 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3158 | | 3159 . IA-options . 3160 . . 3161 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3163 option-code OPTION_IA (3) 3165 option-len 12 + length of IA-options field 3167 IAID The unique identifier for this IA; the IAID 3168 must be unique among the identifiers for all 3169 of this client's IAs. The number space for 3170 IA IAIDs is separate from the number space 3171 for IA_TA IAIDs. 3173 T1 The time at which the client contacts the 3174 server from which the addresses in the IA 3175 were obtained to extend the lifetimes of 3176 the addresses assigned to the IA; T1 is a 3177 time duration relative to the current time 3178 expressed in units of seconds 3180 T2 The time at which the client contacts any 3181 available server to extend the lifetimes of 3182 the addresses assigned to the IA; T2 is a 3183 time duration relative to the current time 3184 expressed in units of seconds 3186 IA-options Options associated with this IA. 3188 The IA-options field encapsulates those options that are specific 3189 to this IA. For example, all of the IA Address Options carrying the 3190 addresses associated with this IA are in the IA-options field. 3192 An IA option may only appear in the options area of a DHCP message. 3193 A DHCP message may contain multiple IA options. 3195 The status of any operations involving this IA is indicated in a 3196 Status Code option in the IA-options field. 3198 Note that an IA has no explicit "lifetime" or "lease length" of its 3199 own. When the valid lifetimes of all of the addresses in an IA 3200 have expired, the IA can be considered as having expired. T1 and 3201 T2 are included to give servers explicit control over when a client 3202 recontacts the server about a specific IA. 3204 In a message sent by a client to a server, values in the T1 and 3205 T2 fields indicate the client's preference for those parameters. 3206 The client may send 0 if it has no preference for T1 and T2. In a 3207 message sent by a server to a client, the client MUST use the values 3208 in the T1 and T2 fields for the T1 and T2 parameters. The values in 3209 the T1 and T2 fields are the number of seconds until T1 and T2. 3211 The server selects the T1 and T2 times to allow the client to extend 3212 the lifetimes of any addresses in the IA before the lifetimes expire, 3213 even if the server is unavailable for some short period of time. 3214 Recommended values for T1 and T2 are .5 and .8 times the shortest 3215 preferred lifetime of the addresses in the IA, respectively. If the 3216 server does not intend for a client to extend the lifetimes of the 3217 addresses in an IA, the server sets T1 and T2 to 0. 3219 T1 is the time at which the client begins the lifetime extension 3220 process by sending a Renew message to the server that originally 3221 assigned the addresses to the IA. T2 is the time at which the client 3222 starts sending a Rebind message to any server. 3224 T1 and T2 are specified as unsigned integers that specify the time 3225 in seconds relative to the time at which the messages containing the 3226 option is received. 3228 22.5. Identity Association for Temporary Addresses option 3230 The Identity Association for Temporary Addresses (IA_TA) option is 3231 used to carry an IA, the parameters associated with the IA and the 3232 addresses associated with the IA. All of the addresses in this option 3233 are used by the client as temporary addresses, as defined in RFC 3234 3041. 3236 The format of the IA_TA option is: 3238 0 1 2 3 3239 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 3240 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3241 | OPTION_IA_TA | option-len | 3242 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3243 | IAID (4 octets) | 3244 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3245 | | 3246 . IA-options . 3247 . . 3248 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3250 option-code OPTION_IA_TA (4) 3252 option-len 4 + length of IA-options field 3254 IAID The unique identifier for this IA; the IAID 3255 must be unique among the identifiers for all 3256 of this client's IAs. The number space for 3257 IA_TA IAIDs is separate from the number space 3258 for IA IAIDs. 3260 IA-options Options associated with this IA. 3262 The IA-Options field encapsulates those options that are specific 3263 to this IA. For example, all of the IA Address Options carrying the 3264 addresses associated with this IA are in the IA-options field. 3266 Each IA_TA carries one "set" of temporary addresses; that is, at most 3267 one address from each prefix assigned to the link to which the client 3268 is attached. 3270 An IA_TA option may only appear in the options area of a DHCP 3271 message. A DHCP message may contain multiple IA_TA options. 3273 The status of any operations involving this IA is indicated in a 3274 Status Code option in the IA-options field. 3276 Note that an IA has no explicit "lifetime" or "lease length" of its 3277 own. When the valid lifetimes of all of the addresses in an IA have 3278 expired, the IA can be considered as having expired. 3280 An IA_TA option does not include values for T1 and T2. A client 3281 MAY request that the lifetimes on temporary addresses be extended 3282 by including the addresses in a IA_TA option sent in a Renew or 3283 Rebind message to a server. For example, a client would request 3284 an extension on the lifetime of a temporary address to allow an 3285 application to continue to use an established TCP connection. 3287 The client obtains new temporary addresses by sending an IA_TA option 3288 with a new IAID to a server. Requesting new temporary addresses from 3289 the server is the equivalent of generating new temporary addresses 3290 as described in RFC 3041. The server will generate new temporary 3291 addresses and return them to the client. The client should request 3292 new temporary addresses before the lifetimes on the previously 3293 assigned addresses expire. 3295 A server MUST return the same set of temporary address for the same 3296 IA_TA (as identified by the IAID) as long as those addresses are 3297 still valid. After the lifetimes of the addresses in an IA_TA have 3298 expired, the IAID may be reused to identify a new IA_TA with new 3299 temporary addresses. 3301 This option MAY appear in a Confirm message if the lifetimes on the 3302 temporary addresses in the associated IA have not expired. 3304 22.6. IA Address option 3306 The IA Address option is used to specify IPv6 addresses associated 3307 with an IA. The IA Address option must be encapsulated in the 3308 Options field of an Identity Association option. The Options field 3309 encapsulates those options that are specific to this address. 3311 The format of the IA Address option is: 3313 0 1 2 3 3314 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 3315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3316 | OPTION_IAADDR | option-len | 3317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3318 | | 3319 | IPv6 address | 3320 | | 3321 | | 3322 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3323 | preferred-lifetime | 3324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3325 | valid-lifetime | 3326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3327 . . 3328 . IAaddr-options . 3329 . . 3330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3332 option-code OPTION_IAADDR (5) 3334 option-len 24 + length of IAaddr-options field 3335 IPv6 address An IPv6 address 3337 preferred-lifetime The preferred lifetime for the IPv6 address in 3338 the option, expressed in units of seconds 3340 valid-lifetime The valid lifetime for the IPv6 address in the 3341 option, expressed in units of seconds 3343 IAaddr-options Options associated with this address 3345 In a message sent by a client to a server, values in the preferred 3346 and valid lifetime fields indicate the client's preference for those 3347 parameters. The client may send 0 if it has no preference for the 3348 preferred and valid lifetimes. In a message sent by a server to a 3349 client, the client MUST use the values in the preferred and valid 3350 lifetime fields for the preferred and valid lifetimes. The values in 3351 the preferred and valid lifetimes are the number of seconds remaining 3352 in each lifetime. 3354 An IA Address option may appear only in an IA option or an IA_TA 3355 option. More than one IA Address Options can appear in an IA option 3356 or an IA_TA option. 3358 The status of any operations involving this IA Address is indicated 3359 in a Status Code option in the IAaddr-options field. 3361 22.7. Option Request option 3363 The Option Request option is used to identify a list of options in 3364 a message between a client and a server. The format of the Option 3365 Request option is: 3367 0 1 2 3 3368 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 3369 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3370 | OPTION_ORO | option-len | 3371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3372 | requested-option-code-1 | requested-option-code-2 | 3373 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3374 | ... | 3375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3377 option-code OPTION_ORO (6) 3379 option-len 2 * number of requested options 3381 requested-option-code-n The option code for an option requested by 3382 the client. 3384 A client MAY include an Option Request option in a Solicit, Request, 3385 Renew, Rebind, Confirm or Information-request message to inform 3386 the server about options the client wants the server to send to 3387 the client. A server MAY include an Option Request option in a 3388 Reconfigure option to indicate which options the client should 3389 request from the server. 3391 22.8. Preference option 3393 The Preference option is sent by a server to a client to affect the 3394 selection of a server by the client. The format of the Preference 3395 option is: 3397 0 1 2 3 3398 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 3399 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3400 | OPTION_PREFERENCE | option-len | 3401 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3402 | pref-value | 3403 +-+-+-+-+-+-+-+-+ 3405 option-code OPTION_PREFERENCE (7) 3407 option-len 1 3409 pref-value The preference value for the server in this message. 3411 A server MAY include a Preference option in an Advertise message to 3412 control the selection of a server by the client. See section 17.1.3 3413 for the use of the Preference option by the client and the 3414 interpretation of Preference option data value. 3416 22.9. Elapsed Time option 3418 0 1 2 3 3419 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 3420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3421 | OPTION_ELAPSED_TIME | option-len | 3422 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3423 | elapsed-time | 3424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3426 option-code OPTION_ELAPSED_TIME (8) 3428 option-len 2. 3430 elapsed-time The amount of time since the client began its 3431 current DHCP transaction. This time is expressed in 3432 hundredths of a second (10^-2 seconds). 3434 A client MUST include an Elapsed Time option in messages to indicate 3435 how long the client has been trying to complete a DHCP message 3436 exchange. The elapsed time is measured from the time at which the 3437 client sent the first message in the message exchange, and the 3438 elapsed-time field is set to 0 in the first message in the message 3439 exchange. Servers and Relay Agents use the data value in this option 3440 as input to policy controlling how a server responds to a client 3441 message. For example, the elapsed time option allows a secondary 3442 DHCP server to respond to a request when a primary server hasn't 3443 answered in a reasonable time. 3445 22.10. Relay Message option 3447 The Relay Message option carries a DHCP message in a Relay-forward or 3448 Relay-reply message. 3450 The format of the Relay Message option is: 3452 0 1 2 3 3453 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 3454 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3455 | OPTION_RELAY_MSG | option-len | 3456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3457 | | 3458 . DHCP-relay-message . 3459 . . 3460 . . 3461 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3463 option-code OPTION_RELAY_MSG (9) 3465 option-len Length of DHCP-relay-message 3467 DHCP-relay-message In a Relay-forward message, the received 3468 message, forwarded verbatim to the next relay agent 3469 or server; in a Relay-reply message, the message to 3470 be copied and forwarded to the relay agent or client 3471 whose address is in the peer-address field of the 3472 Relay-reply message 3474 22.11. Authentication option 3476 The Authentication option carries authentication information to 3477 authenticate the identity and contents of DHCP messages. The use of 3478 the Authentication option is described in section 21. 3480 The format of the Authentication option is: 3482 0 1 2 3 3483 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 3484 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3485 | OPTION_AUTH | option-len | 3486 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3487 | Protocol | Algorithm | RDM | | 3488 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 3489 | | 3490 | Replay Detection (64 bits) +-+-+-+-+-+-+-+-+ 3491 | | Auth. Info | 3492 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 3493 . . 3494 . Authentication Information . 3495 . (variable length) . 3496 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3498 option-code OPTION_AUTH (11) 3500 option-len 15 + length of Authentication 3501 Information field 3503 protocol The authentication protocol used in 3504 this authentication option 3506 algorithm The algorithm used in the 3507 authentication protocol 3509 RDM The replay detection method used in 3510 this authentication option 3512 Replay detection The replay detection information for 3513 the RDM 3515 Authentication information The authentication information, 3516 as specified by the protocol and 3517 algorithm used in this authentication 3518 option 3520 22.12. Server unicast option 3522 The server sends this option to a client to indicate to the client 3523 that it is allowed to unicast messages to the server. 3525 The format of the Server Unicast option is: 3527 0 1 2 3 3528 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 3529 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3530 | OPTION_UNICAST | option-len | 3531 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3532 | | 3533 | server-address | 3534 | | 3535 | | 3536 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3538 option-code OPTION_UNICAST (12) 3540 option-len 16 3542 server-address The IP address to which the client should send 3543 messages delivered using unicast 3545 The server specifies the IPv6 address to which the client is to send 3546 unicast messages in the server-address field. When a client receives 3547 this option, where permissible and appropriate, the client sends 3548 messages directly to the server using the IPv6 address specified in 3549 the server-address field of the option. 3551 Details about when the client may send messages to the server using 3552 unicast are in section 18. 3554 22.13. Status Code Option 3556 This option returns a status indication related to the DHCP message 3557 or option in which it appears. The format of the Status Code option 3558 is: 3560 0 1 2 3 3561 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 3562 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3563 | OPTION_STATUS_CODE | option-len | 3564 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3565 | status-code | | 3566 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 3567 . . 3568 . status-message . 3569 . . 3570 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3572 option-code OPTION_STATUS_CODE (13) 3573 option-len 2 + length of status-message 3575 status-code The numeric code for the status encoded in 3576 this option. The status codes are defined in 3577 section 24.4. 3579 status-message A UTF-8 encoded text string suitable for 3580 display to an end user, which MUST NOT be 3581 null-terminated. 3583 A Status Code option may appear in the options field of a DHCP 3584 message and/or in the options field of another option. If the Status 3585 Code option does not appear in a message in which the option could 3586 appear, the status of the message is assumed to be Success. 3588 22.14. Rapid Commit option 3590 The Rapid Commit option is used to signal the use of the two message 3591 exchange for address assignment. The format of the Rapid Commit 3592 option is: 3594 0 1 2 3 3595 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 3596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3597 | OPTION_RAPID_COMMIT | 0 | 3598 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3600 option-code OPTION_RAPID_COMMIT (14) 3602 option-len 0 3604 A client MAY include this option in a Solicit message if the client 3605 is prepared to perform the Solicit-Reply message exchange described 3606 in section 17.1.1. 3608 A server MUST include this option in a Reply message sent in response 3609 to a Solicit message when completing the Solicit-Reply message 3610 exchange. 3612 DISCUSSION: 3614 Each server that responds with a Reply to a Solicit that 3615 includes a Rapid Commit option will commit the assigned 3616 addresses in the Reply message to the client, and will not 3617 receive any confirmation that the client has received the 3618 Reply message. Therefore, if more than one server responds 3619 to a Solicit that includes a Rapid Commit option, some 3620 servers will commit addresses that are not actually used by 3621 the client. 3623 The problem of unused addresses can be minimized, for 3624 example, by designing the DHCP service so that only one 3625 server responds to the Solicit or by using relatively short 3626 lifetimes for assigned addresses. 3628 22.15. User Class option 3630 The User Class option is used by a client to identify the type or 3631 category of user or applications it represents. 3633 The format of the User Class option is: 3635 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 3636 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3637 | OPTION_USER_CLASS | option-len | 3638 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3639 . . 3640 . user-class-data . 3641 . . 3642 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3644 option-code OPTION_USER_CLASS (15) 3646 option-len Length of user class data field 3648 user-class-data The user classes carried by the client. 3650 The information contained in the data area of this option is 3651 contained in one or more opaque fields that represent the user 3652 class or classes of which the client is a member. A server selects 3653 configuration information for the client based on the classes 3654 identified in this option. For example, the User Class option can be 3655 used to configure all clients of people in the accounting department 3656 with a different printer than clients of people in the marketing 3657 department. The user class information carried in this option MUST 3658 be configurable on the client. 3660 The data area of the user class option MUST contain one or more 3661 instances of user class data. Each instance of the user class data 3662 is formatted as follows: 3664 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+ 3665 | user-class-len | opaque-data | 3666 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+ 3668 The user-class-len is two octets long and specifies the length of the 3669 opaque user class data in network byte order. 3671 A server interprets the classes identified in this option according 3672 to its configuration to select the appropriate configuration 3673 information for the client. A server may use only those user 3674 classes that it is configured to interpret in selecting configuration 3675 information for a client and ignore any other user classes. In 3676 response to a message containing a User Class option, a server 3677 includes a User Class option containing those classes that were 3678 successfully interpreted by the server, so that the client can be 3679 informed of the classes interpreted by the server. 3681 22.16. Vendor Class Option 3683 This option is used by a client to identify the vendor that 3684 manufactured the hardware on which the client is running. The 3685 information contained in the data area of this option is contained 3686 in one or more opaque fields that identify details of the hardware 3687 configuration. The format of the Vendor Class option is: 3689 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 3690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3691 | OPTION_VENDOR_CLASS | option-len | 3692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3693 | enterprise-number | 3694 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3695 . . 3696 . vendor-class-data . 3697 . . . . . 3698 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3700 option-code OPTION_VENDOR_CLASS (16) 3702 option-len 4 + length of vendor class data field 3704 enterprise-number The vendor's registered Enterprise Number as 3705 registered with IANA. 3707 vendor-class-data The hardware configuration of the host on 3708 which the client is running. 3710 The vendor-class-data is composed of a series of separate items, 3711 each of which describes some characteristic of the client's hardware 3712 configuration. Examples of vendor-class-data instances might include 3713 the version of the operating system the client is running or the 3714 amount of memory installed on the client. 3716 Each instance of the vendor-class-data is formatted as follows: 3718 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+ 3719 | vendor-class-len | opaque-data | 3720 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+ 3722 The vendor-class-len is two octets long and specifies the length of 3723 the opaque vendor class data in network byte order. 3725 22.17. Vendor-specific Information option 3727 This option is used by clients and servers to exchange 3728 vendor-specific information. The format of this option 3729 is: 3731 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 3732 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3733 | OPTION_VENDOR_OPTS | option-len | 3734 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3735 | enterprise-number | 3736 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3737 . . 3738 . option-data . 3739 . . 3740 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3742 option-code OPTION_VENDOR_OPTS (17) 3744 option-len 4 + length of option-data field 3746 enterprise-number The vendor's registered Enterprise Number as 3747 registered with IANA. 3749 option-data An opaque object of option-len octets, 3750 interpreted by vendor-specific code on the 3751 clients and servers 3753 The definition of the information carried in this option is vendor 3754 specific. The vendor is indicated in the enterprise-number field. 3755 Use of vendor-specific information allows enhanced operation, 3756 utilizing additional features in a vendor's DHCP implementation. 3757 A DHCP client that does not receive requested vendor-specific 3758 information will still configure the host device's IPv6 stack to be 3759 functional. 3761 The encapsulated vendor-specific options field MUST be encoded as a 3762 sequence of code/length/value fields of identical format to the DHCP 3763 options field. The option codes are defined by the vendor identified 3764 in the enterprise-number field and are not managed by IANA. 3766 Each of the encapsulated options is formatted as follows. 3768 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 3769 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3770 | opt-code | option-len | 3771 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3772 . . 3773 . option-data . 3774 . . 3775 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3777 opt-code The code for the encapsulated option 3779 option-len An unsigned integer giving the length of the 3780 option-data field in this encapsulated option 3781 in octets. 3783 option-data The data area for the encapsulated option 3785 Multiple instances of the Vendor-specific Information option may 3786 appear in a DHCP message. Each instance of the option is interpreted 3787 according to the option codes defined by the vendor identified by the 3788 Enterprise Number in that option. A DHCP message MUST NOT contain 3789 more than one Vendor-specific Information option with the same 3790 Enterprise Number. 3792 22.18. Interface-Id Option 3794 The relay agent MAY send the Interface-id option to identify the 3795 interface on which the client message was received. If a relay agent 3796 receives a Relay-reply message with an Interface-id option, the 3797 relay agent forwards the message to the client through the interface 3798 identified by the option. 3800 The format of the Interface ID option is: 3802 0 1 2 3 3803 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 3804 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3805 | OPTION_INTERFACE_ID | option-len | 3806 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3807 . . 3808 . interface-id . 3809 . . 3810 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3812 option-code OPTION_INTERFACE_ID (18) 3814 option-len Length of interface-id field 3815 interface-id An opaque value of arbitrary length generated 3816 by the relay agent to identify one of the 3817 relay agent's interfaces 3819 The server MUST copy the Interface-Id option from the Relay-Forward 3820 message into the Relay-Reply message the server sends to the relay 3821 agent in response to the Relay-Forward message. This option MUST NOT 3822 appear in any message except a Relay-Forward or Relay-Reply message. 3824 Servers MAY use the Interface-ID for parameter assignment policies. 3825 The Interface-ID SHOULD be considered an opaque value, with policies 3826 based on exact match only; that is, the Interface-ID SHOULD NOT be 3827 internally parsed by the server. The Interface-ID value for an 3828 interface SHOULD be stable and remain unchanged, for example, after 3829 the relay agent is restarted; if the Interface-ID changes, a server 3830 will not be able to use it reliably in parameter assignment policies. 3832 22.19. Reconfigure Message option 3834 A server includes a Reconfigure Message option in a Reconfigure 3835 message to indicate to the client whether the client responds with a 3836 Renew message or an Information-request message. The format of this 3837 option is: 3839 0 1 2 3 3840 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 3841 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3842 | OPTION_RECONF_MSG | option-len | 3843 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3844 | msg-type | 3845 +-+-+-+-+-+-+-+-+ 3847 option-code OPTION_RECONF_MSG (19) 3849 option-len 1 3851 msg-type 5 for Renew message, 11 for 3852 Information-request message 3854 The Reconfigure Message option can only appear in a Reconfigure 3855 message. 3857 22.20. Reconfigure Nonce option 3859 If a server uses a reconfigure nonce to provide security for 3860 Reconfigure messages, the server maintains a nonce value for each 3861 client. It initially informs the client of the nonce value and then 3862 includes the nonce value in any Reconfigure message sent to the 3863 client. 3865 The following figure gives the format of the Reconfigure Nonce 3866 option: 3868 0 1 2 3 3869 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 3870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3871 | OPTION_RECONF_NONCE | option-len | 3872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3873 | reconfigure-nonce | 3874 | | 3875 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3877 option-code OPTION_RECONF_NONCE (20) 3879 option-len 8 3881 reconfigure-nonce reconfigure nonce value sent to the client; 3882 the nonce MUST be a cryptographically strong 3883 random number that cannot easily be guessed 3884 or predicted. 3886 The Reconfigure Nonce option MUST NOT appear in any DHCP message 3887 other than Reply or Reconfigure. 3889 23. Security Considerations 3891 Section 21 describes the DHCP threat model. The primary threat 3892 to a DHCP client is the incorrect configuration of the client 3893 through a DHCP exchange with a malicious DHCP server. The incorrect 3894 configuration may present a denial of service attack by causing 3895 communication with a service to fail, or a masquerade attack by 3896 causing the client to communicate with a malicious server instead of 3897 a valid server for some service such as DNS or NTP. 3899 A DHCP server may be subject to a theft of service attack by a 3900 malicious client representing itself as a valid client, or a denial 3901 of service attack in which a malicious client exhausts the supply of 3902 available addresses or consumes all of the computation resources or 3903 network bandwidth available to the DHCP server. 3905 A DHCP client may also be subject to attack through the receipt 3906 of a Reconfigure message from a malicious server that causes the 3907 client to obtain incorrect configuration information from that 3908 server. Note that although a client sends its response (Renew or 3909 Information-request message) through a relay agent and, therefore, 3910 that response will only be received by servers to which DHCP messages 3911 are forwarded, a malicious server could send a Reconfigure message to 3912 a client, followed (after an appropriate delay) by a Reply message 3913 that would be accepted by the client. Thus, a malicious server that 3914 is not on the network path between the client and the server may 3915 still be able to mount a Reconfigure attack on a client. The use of 3916 transaction IDs that are cryptographically sound and cannot easily be 3917 predicted will also reduce the probability that such an attack will 3918 be successful. 3920 DHCP authentication provides for authentication of the identity of 3921 DHCP clients and servers, and for the integrity of messages delivered 3922 between DHCP clients and servers. DHCP authentication does not 3923 provide any privacy for the contents of DHCP messages. 3925 The "delayed authentication" protocol described in section 21.5 3926 uses a secret key that is shared between a client and a server and 3927 does not attempt to address situations where a client may roam from 3928 one administrative domain to another, i.e. interdomain roaming. 3929 The use of shared keys may not scale well and does not provide for 3930 repudiation of compromised keys. This protocol is focused on solving 3931 the intradomain problem where the out-of-band exchange of a shared 3932 key is feasible. 3934 The Reconfigure Nonce option (see section 22.20) provides a way 3935 for a client to confirm the identity of the server from which it 3936 has received a Reconfigure message. The Reconfigure Nonce option 3937 protects the client from attack by a malicious server that is not on 3938 the network path from the server to the client; a malicious server 3939 between the server and the client can read the nonce value sent 3940 from the server to the client and spoof the server's identity in a 3941 Reconfigure message. 3943 Communication between a server and a relay agent can be secured 3944 through the use of IPSec. The use of manual configuration and 3945 installation of static keys are acceptable in this instance because 3946 the relay agent and server will belong to the same administrative 3947 domain and the relay agent will require other specific configuration 3948 (for example, configuration of the DHCP server address) as well as 3949 the IPSec configuration. 3951 24. IANA Considerations 3953 This document defines several new name spaces associated with DHCPv6 3954 and DHCPv6 options: 3956 - Message types 3958 - Status codes 3960 - DUID 3962 - Option codes 3964 IANA is requested to manage a registry of values for each of these 3965 name spaces, which are described in the remainder of this section. 3967 These name spaces are all to be managed separately from the name 3968 spaces defined for DHCPv4 [5, 1]. 3970 New multicast addresses, message types, status codes and DUID types 3971 are assigned via Standards Action [14]. 3973 New DHCP option codes are tentatively assigned after the 3974 specification for the associated option, published as an Internet 3975 Draft, has received expert review by a designated expert [14]. 3976 The final assignment of DHCP option codes is through Standards 3977 Action [14]. 3979 This document also references three name spaces in section 21 that 3980 are associated with the Authentication Option (section 22.11). These 3981 name spaces are defined by the authentication mechanism for DHCPv4 in 3982 RFC3118 [6]. 3984 The authentication name spaces currently registered by IANA will 3985 apply to both DHCPv6 and DHCPv4. In the future, specifications that 3986 define new Protocol, Algorithm and RDM mechanisms will explicitly 3987 define whether the new mechanisms are used with DHCPv4, DHCPv6 or 3988 both. 3990 24.1. Multicast addresses 3992 Section 5.1 defines the following multicast addresses, which have 3993 been assigned by IANA for use by DHCPv6: 3995 All_DHCP_Relay_Agents_and_Servers address: FF02::1:2 3997 All_DHCP_Servers address: FF05::1:3 3999 24.2. DHCP message types 4001 IANA is requested to record the following message types (defined 4002 in section 5.3). IANA is requested to maintain a registry of DHCP 4003 message types. 4005 SOLICIT 1 4007 ADVERTISE 2 4009 REQUEST 3 4011 CONFIRM 4 4013 RENEW 5 4015 REBIND 6 4017 REPLY 7 4018 RELEASE 8 4020 DECLINE 9 4022 RECONFIGURE 10 4024 INFORMATION-REQUEST 11 4026 RELAY-FORW 12 4028 RELAY-REPL 13 4030 24.3. DHCP options 4032 IANA is requested to record the following option-codes (as defined in 4033 section 22). IANA is requested to maintain a registry of DHCP option 4034 codes. 4036 OPTION_CLIENTID 1 4038 OPTION_SERVERID 2 4040 OPTION_IA 3 4042 OPTION_IA_TMP 4 4044 OPTION_IAADDR 5 4046 OPTION_ORO 6 4048 OPTION_PREFERENCE 7 4050 OPTION_ELAPSED_TIME 8 4052 OPTION_CLIENT_MSG 9 4054 OPTION_SERVER_MSG 10 4056 OPTION_AUTH 11 4058 OPTION_UNICAST 12 4060 OPTION_STATUS_CODE 13 4062 OPTION_RAPID_COMMIT 14 4064 OPTION_USER_CLASS 15 4066 OPTION_VENDOR_CLASS 16 4068 OPTION_VENDOR_OPTS 17 4069 OPTION_INTERFACE_ID 18 4071 OPTION_RECONF_MSG 19 4073 OPTION_RECONF_NONCE 20 4075 24.4. Status codes 4077 IANA is requested to record the status codes defined in the following 4078 table. IANA is requested to manage the definition of additional 4079 status codes in the future. 4081 Name Code Description 4082 ---------- ---- ----------- 4083 Success 0 Success 4084 UnspecFail 1 Failure, reason unspecified; this 4085 status code is sent by either a client 4086 or a server to indicate a failure 4087 not explicitly specified in this 4088 document 4089 AuthFailed 2 Authentication failed or nonexistent 4090 AddrUnavail 3 Address unavailable 4091 NoAddrsAvail 4 Server has no addresses available to assign to 4092 the IA(s) 4093 NoBinding 5 Client record (binding) unavailable 4094 ConfNoMatch 6 Client record Confirm doesn't match IA 4095 NotOnLink 7 The prefix for the address is not appropriate to 4096 the link to which the client is attached 4097 UseMulticast 8 Sent by a server to a client to force the 4098 client to send messages to the server 4099 using the All_DHCP_Relay_Agents_and_Servers 4100 address 4102 24.5. DUID 4104 IANA is requested to record the following DUID types (as defined in 4105 section 9.1). IANA is requested to manage definition of additional 4106 DUID types in the future. 4108 DUID-LLT 1 4110 DUID-EN 2 4112 DUID-LL 3 4114 25. Acknowledgments 4116 Thanks to the DHC Working Group and the members of the IETF for 4117 their time and input into the specification. In particular, thanks 4118 also for the consistent input, ideas, and review by (in alphabetical 4119 order) Bill Arbaugh, Thirumalesh Bhat, Steve Bellovin, A. K. 4120 Vijayabhaskar, Brian Carpenter, Matt Crawford, Francis Dupont, Tony 4121 Lindstrom, Josh Littlefield, Gerald Maguire, Jack McCann, Thomas 4122 Narten, Erik Nordmark, Yakov Rekhter, Mark Stapp, Matt Thomas, Sue 4123 Thomson, Tatuya Jinmei and Phil Wells. 4125 Thanks to Steve Deering and Bob Hinden, who have consistently 4126 taken the time to discuss the more complex parts of the IPv6 4127 specifications. 4129 And, thanks to Steve Deering for pointing out at IETF 51 in London 4130 that the DHCPv6 specification has the highest revision number of any 4131 Internet Draft. 4133 26. Changes in draft-ietf-dhc-dhcpv6-25.txt 4135 - Eliminated definition of VUID-DN. 4137 - Changed the second sentence in section 17.1.2 to: 4139 In the case of a Solicit message transmitted when DHCP is 4140 initiated by IPv6 Neighbor Discovery, the delay gives the amount 4141 of time to wait after IPv6 Neighbor Discovery causes the client 4142 to invoke the stateful address autoconfiguration protocol (see 4143 section 5.5.3 of RFC2462). 4145 - Changed Rapid Commit to allow client to use Advertise messages 4146 received while waiting for Reply, rather than restarting with 4147 Solicit; if client receives Advertise with preference 255, client 4148 immediately sends Request to that server. 4150 - Removed the use of All_DHCP_Servers multicast address as 4151 destination address in section 18.1.5. 4153 - Added text improving summary description of Confirm, Renew, 4154 Rebind. 4156 - Removed restriction on extension of lifetimes for temporary 4157 addresses; added text pointing to RFC 3041 for guidance on 4158 extending lifetimes for temporary addresses and when to request 4159 additional temporary addresses. 4161 - Clarified text in section 20 to emphasize that the relay agent 4162 puts an address in the link-address field regardless of whether 4163 it includes an Interface-ID option; added text explaining why the 4164 interface-identifier for an interface should remain stable. 4166 - Changed use of T1/T2 and lifetimes in Confirm message from 4167 client: client uses those fields for preferred values or sets 4168 to 0; server checks only addresses for correctness and returns 4169 values chosen by server for T1/T2 and lifetimes. Clarified 4170 that server checks addresses and returns current configuration 4171 information for the client. 4173 - Description of User Class option extended with an example 4174 and clarified to indicate that use of User Class options is 4175 determined by configuration/policies on server. 4177 - Clarified description of the use of Vendor-specific information 4178 to indicate that client need not receive all requested 4179 vendor-specific information before proceeding with normal 4180 operation. 4182 - Clarified use of Status Code option in Release message. 4184 - Edited section 14 to make clear that a client transmits until it 4185 receives a response only if both MRC and MRD are zero. 4187 - Removed suggestions about ordering options (for example, for 4188 improved performance). 4190 - Edited section 16 to clarify interface selection. 4192 - Removed use of anycast; use of anycast over individual link 4193 technologies will be specified in separate documents. 4195 - Removed replay detection information field from Solicit message 4196 to avoid potential DOS attack. 4198 - Clarified capabilities and constraints on relay agent forwarding. 4200 - Edited definition of vendor class data to clarify that instances 4201 of vendor-class-data are individual characteristics of the 4202 client. 4204 - Added text in section 21.5.3 to specify that client key is 4205 identified by client DUID. 4207 - Removed "Year 2000 Considerations" section; hope we don't need a 4208 "Year 3000 Consideration" section. 4210 - Authentication mechanism now shares Protocol, Algorithm and RDM 4211 name spaces with DHCPv4. 4213 - Added text to specify return of NoBinding if server cannot 4214 find binding for IA in Decline; added text allowing client to 4215 disregard NoBinding in Reply to Decline. 4217 - Clarified that Solicit, Confirm and Rebind are invalid if Server 4218 Identifier option is included. 4220 - Edited text about Option Request option to clarify that the 4221 option is a hint from the client to the server about options the 4222 client has a preference to receive; includes recommendation that 4223 client send Option Request option if it has options it requires. 4225 - Added nonce value for security of Reconfigure messages. 4227 27. Changes in draft-ietf-dhc-dhcpv6-26.txt 4229 - Clarified section 18.1.1 to allow Request message to be sent at 4230 any time. 4232 - Fixed Reconfigure Message option so that msg-type field is one 4233 octet and uses the DHCP message code to indicate which message 4234 the client sends back to the server. 4236 - Added text anticipating description of how to emulate multicast 4237 in specific "IPv6 over X" documents. 4239 - Reconfigure message now requires Client Identifier option with 4240 receiving client's DUID. 4242 - Added text to allow a relay agent to forward a message from a 4243 client to another relay agent as well as to a server. Added text 4244 in authentication section specifying use of IPSec between relay 4245 agents and servers for message security. 4247 - Fixed definition of "binding" to allow a binding with no IAs to 4248 be indexed by just . 4250 - Clarified text in section 17.2.2 to explain that AddrUnavail is 4251 returned only if the Solicit message from the client included one 4252 or more IA options. 4254 - Edited text about Option Request option to clarify that the 4255 client is required to include the option and to identify all 4256 options the client has a preference to receive; also clarified 4257 that a server may include additional options if the server is 4258 configured to do so. 4260 - Added text explaining why DHCPv6 and DHCPv4 are not integrated in 4261 this document. 4263 - Changed use of Confirm so that server simply checks whether 4264 addresses are appropriate to link to which client is attached. 4266 - Expanded Security Considerations section to give more detail on 4267 threat model and limitations to authentication. 4269 - Client now restarts with server solicitation when server returns 4270 NotOnLink to Confirm message. 4272 - Modified several retransmission parameters (in section 5.5) for 4273 consistency and anticipated operation. 4275 - Defined "appropriate to the link" and changed "valid on the link" 4276 to "appropriate to the link" throughout for clarity 4278 - Added text requiring transaction IDs to be not predictable and 4279 described potential attack in security considerations 4281 References 4283 [1] S. Alexander and R. Droms. DHCP Options and BOOTP Vendor 4284 Extensions, March 1997. RFC 2132. 4286 [2] S. Bradner. Key words for use in RFCs to Indicate Requirement 4287 Levels, March 1997. RFC 2119. 4289 [3] M. Crawford. Transmission of IPv6 Packets over Ethernet 4290 Networks, December 1998. RFC 2464. 4292 [4] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6) 4293 Specification, December 1998. RFC 2460. 4295 [5] R. Droms. Dynamic Host Configuration Protocol, March 1997. RFC 4296 2131. 4298 [6] R. Droms, Editor, W. Arbaugh, and Editor. Authentication for 4299 DHCP Messages, June 2001. RFC 3118. 4301 [7] R. (ed.) Droms. DNS Configuration options for DHCPv6. Internet 4302 Draft, Internet Engineering Task Force, April 2002. Work in 4303 progress. 4305 [8] R. Hinden and S. Deering. IP Version 6 Addressing Architecture, 4306 July 1998. RFC 2373. 4308 [9] IANA. Private Enterprise Numbers. 4309 http://www.iana.org/assignments/enterprise-numbers. 4311 [10] S. Kent and R. Atkinson. Security Architecture for the Internet 4312 Protocol, November 1998. RFC 2401. 4314 [11] H. Krawczyk, M. Bellare, and R. Canetti. HMAC: Keyed-Hashing 4315 for Message Authentication, February 1997. RFC 2104. 4317 [12] David L. Mills. Network Time Protocol (Version 3) 4318 Specification, Implementation, March 1992. RFC 1305. 4320 [13] P.V. Mockapetris. Domain names - implementation and 4321 specification, November 1987. RFC 1035. 4323 [14] T. Narten and H. Alvestrand. Guidelines for Writing an IANA 4324 Considerations Section in RFCs, October 1998. RFC 2434. 4326 [15] T. Narten and R. Draves. Privacy Extensions for Stateless 4327 Address Autoconfiguration in IPv6, January 2001. RFC 3041. 4329 [16] T. Narten, E. Nordmark, and W. Simpson. Neighbor Discovery for 4330 IP Version 6 (IPv6), December 1998. RFC 2461. 4332 [17] D.C. Plummer. Ethernet Address Resolution Protocol: Or 4333 converting network protocol addresses to 48.bit Ethernet address 4334 for transmission on Ethernet hardware, November 1982. RFC 826. 4336 [18] J. Postel. User Datagram Protocol, August 1980. RFC 768. 4338 [19] R. Rivest. The MD5 Message-Digest Algorithm, April 1992. RFC 4339 1321. 4341 [20] S. Thomson and T. Narten. IPv6 Stateless Address 4342 Autoconfiguration, December 1998. RFC 2462. 4344 [21] A. K. Vijayabhaskar. Time Configuration Options for DHCPv6. 4345 Internet Draft, Internet Engineering Task Force, May 2002. Work 4346 in progress. 4348 [22] P. Vixie, Ed., S. Thomson, Y. Rekhter, and J. Bound. Dynamic 4349 Updates in the Domain Name System (DNS UPDATE), April 1997. RFC 4350 2136. 4352 Chair's Address 4354 The working group can be contacted via the current chair: 4356 Ralph Droms 4357 Cisco Systems 4358 300 Apollo Drive 4359 Chelmsford, MA 01824 4361 Phone: (978) 244-4733 4362 E-mail: rdroms@cisco.com 4364 Authors' Addresses 4366 Questions about this document can be directed to: 4368 Jim Bound 4369 Hewlett Packard Corporation 4370 ZK3-3/W20 4371 110 Spit Brook Road 4372 Nashua, NH 03062-2698 4373 USA 4374 Voice: +1 603 884 0062 4375 E-mail: Jim.Bound@hp.com 4377 Bernie Volz 4378 Ericsson 4379 959 Concord St 4380 Framingham, MA 01701 4381 USA 4382 Voice: +1-508-875-3162 4383 E-mail: bernie.volz@ericsson.com 4385 Ted Lemon 4386 Nominum, Inc. 4387 950 Charter Street 4388 Redwood City, CA 94043 4389 USA 4390 E-mail: Ted.Lemon@nominum.com 4392 Charles E. Perkins 4393 Communications Systems Lab 4394 Nokia Research Center 4395 313 Fairchild Drive 4396 Mountain View, California 94043 4397 USA 4398 Voice: +1-650 625-2986 4399 E-mail: charliep@iprg.nokia.com 4401 Mike Carney 4402 Sun Microsystems, Inc 4403 Mail Stop: UMPK17-202 4404 901 San Antonio Road 4405 Palo Alto, CA 94303-4900 4406 USA 4407 Voice: +1-650-786-4171 4408 E-mail: mwc@eng.sun.com 4410 A. Appearance of Options in Message Types 4412 The following table indicates with a "*" the options are allowed in 4413 each DHCP message type: 4415 Client Server IA/ Option Pref Time Client Server 4416 ID ID IA_TA Request Msg. Msg. 4417 Solicit * * * * 4418 Advert. * * * * * 4419 Request * * * * * 4420 Confirm * * * * 4421 Renew * * * * * 4422 Rebind * * * * 4423 Decline * * * * * 4424 Release * * * * * 4425 Reply * * * * * 4426 Reconf. * * * 4427 Inform. * (see note) * * 4428 R-forw. * 4429 R-repl. * 4431 NOTE: 4433 Only included in Information-Request messages that are sent 4434 in response to a Reconfigure (see section 19.4.3). 4436 Auth Server Status Rap. User Vendor Vendor Inter. Recon. 4437 Unica. Code Comm. Class Class Spec. ID Msg. 4438 Solicit * * * * * 4439 Advert. * * * * * 4440 Request * * * * 4441 Confirm * * * * 4442 Renew * * * * 4443 Rebind * * * * 4444 Decline * * * * * 4445 Release * * * * * 4446 Reply * * * * * * 4447 Reconf. * * 4448 Inform. * * * * 4449 R-forw. * * * * * 4450 R-repl. * * * * * 4452 B. Appearance of Options in the Options Field of DHCP Options 4454 The following table indicates with a "*" where options can appear in 4455 the options field of other options: 4457 Option IA/ IAADDR Relay Relay 4458 Field IA_TA Forw. Reply 4459 Client ID * 4460 Server ID * 4461 IA/IA_TA * 4462 IAADDR * 4463 ORO * 4464 Pref * 4465 Time * 4466 Authentic. * 4467 Server Uni. * 4468 Status Code * * * * * 4469 Rapid Comm. * 4470 User Class * 4471 Vendor Class * 4472 Vendor Info. * 4473 Interf. ID * * 4474 Reconf. msg. * 4476 C. Full Copyright Statement 4478 Copyright (C) The Internet Society (2002). All Rights Reserved. 4480 This document and translations of it may be copied and furnished to 4481 others, and derivative works that comment on or otherwise explain it 4482 or assist in its implementation may be prepared, copied, published 4483 and distributed, in whole or in part, without restriction of any 4484 kind, provided that the above copyright notice and this paragraph 4485 are included on all such copies and derivative works. However, 4486 this document itself may not be modified in any way, such as by 4487 removing the copyright notice or references to the Internet Society 4488 or other Internet organizations, except as needed for the purpose 4489 of developing Internet standards in which case the procedures 4490 for copyrights defined in the Internet Standards process must be 4491 followed, or as required to translate it into languages other than 4492 English. 4494 The limited permissions granted above are perpetual and will not be 4495 revoked by the Internet Society or its successors or assigns. 4497 This document and the information contained herein is provided on an 4498 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 4499 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 4500 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 4501 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 4502 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.