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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: '17' on line 610 ** Obsolete normative reference: RFC 3315 (Obsoleted by RFC 8415) ** Obsolete normative reference: RFC 3633 (Obsoleted by RFC 8415) ** Obsolete normative reference: RFC 7083 (Obsoleted by RFC 8415) == Outdated reference: A later version (-02) exists of draft-ietf-mif-mpvd-dhcp-support-01 Summary: 3 errors (**), 0 flaws (~~), 2 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group O. Troan 3 Internet-Draft B. Volz 4 Updates: 3315,3633 (if approved) Cisco Systems, Inc. 5 Intended status: Standards Track M. Siodelski 6 Expires: September 21, 2015 ISC 7 March 20, 2015 9 Issues and Recommendations with Multiple Stateful DHCPv6 Options 10 draft-ietf-dhc-dhcpv6-stateful-issues-12.txt 12 Abstract 14 The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) 15 specification defined two stateful options, IA_NA and IA_TA, but did 16 not anticipate the development of additional stateful options. 17 DHCPv6 Prefix Delegation added the IA_PD option, which is stateful. 18 Applications that use IA_NA and IA_PD together have revealed issues 19 that need to be addressed. This document updates RFC 3315 and RFC 20 3633 to address these issues. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on September 21, 2015. 39 Copyright Notice 41 Copyright (c) 2015 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 This document may contain material from IETF Documents or IETF 55 Contributions published or made publicly available before November 56 10, 2008. The person(s) controlling the copyright in some of this 57 material may not have granted the IETF Trust the right to allow 58 modifications of such material outside the IETF Standards Process. 59 Without obtaining an adequate license from the person(s) controlling 60 the copyright in such materials, this document may not be modified 61 outside the IETF Standards Process, and derivative works of it may 62 not be created outside the IETF Standards Process, except to format 63 it for publication as an RFC or to translate it into languages other 64 than English. 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 69 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 70 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 71 4. Handling of Multiple IA Option Types . . . . . . . . . . . . 4 72 4.1. Placement of Status Codes in an Advertise Message . . . . 5 73 4.2. Advertise Message Processing by a Client . . . . . . . . 7 74 4.3. T1/T2 Timers . . . . . . . . . . . . . . . . . . . . . . 8 75 4.4. Renew and Rebind Messages . . . . . . . . . . . . . . . . 9 76 4.4.1. Renew Message . . . . . . . . . . . . . . . . . . . . 9 77 4.4.2. Rebind Message . . . . . . . . . . . . . . . . . . . 10 78 4.4.3. Updates to section 18.1.3 of RFC 3315 . . . . . . . . 10 79 4.4.4. Updates to Section 18.1.4 of RFC 3315 . . . . . . . . 12 80 4.4.5. Updates to Section 18.1.8 of RFC 3315 . . . . . . . . 13 81 4.4.6. Updates to Section 18.2.3 of RFC 3315 . . . . . . . . 15 82 4.4.7. Updates to Section 18.2.4 of RFC 3315 . . . . . . . . 17 83 4.4.8. Updates to RFC 3633 . . . . . . . . . . . . . . . . . 18 84 4.5. Confirm Message . . . . . . . . . . . . . . . . . . . . . 19 85 4.6. Decline Should Not Necessarily Trigger a Release . . . . 20 86 4.7. Multiple Provisioning Domains . . . . . . . . . . . . . . 21 87 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 88 6. Security Considerations . . . . . . . . . . . . . . . . . . . 21 89 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21 90 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 91 8.1. Normative References . . . . . . . . . . . . . . . . . . 21 92 8.2. Informative References . . . . . . . . . . . . . . . . . 22 93 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 95 1. Introduction 97 DHCPv6 [RFC3315] was written without the expectation that additional 98 stateful DHCPv6 options would be developed. DHCPv6 Prefix Delegation 99 [RFC3633] since added a new stateful option for Prefix Delegation to 100 DHCPv6. Implementation experience of the Customer Edge Router (CER) 101 model described in [RFC7084] has shown issues with the DHCPv6 102 protocol in supporting multiple stateful option types, in particular 103 IA_NA (non-temporary addresses) and IA_PD (delegated prefixes). 105 This document describes a number of problems encountered with 106 coexistence of the IA_NA and IA_PD option types and specifies changes 107 to the DHCPv6 protocol to address these problems. 109 The intention of this work is to clarify and, where needed, modify 110 the DHCPv6 protocol specification to support IA_NA and IA_PD option 111 types within a single DHCPv6 session. 113 Note that while IA_TA (temporary addresses) options may be included 114 with other IA option type requests, these generally are not renewed 115 (there are no T1/T2 times) and have a separate life cycle from IA_NA 116 and IA_PD option types. Therefore, the IA_TA option type is mostly 117 out of scope for this document. 119 The changes described in this document are intended to be 120 incorporated in a new revision of the DHCPv6 protocol specification 121 ([I-D.dhcwg-dhc-rfc3315bis]). 123 2. Conventions 125 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 126 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 127 document are to be interpreted as described in [RFC2119]. 129 3. Terminology 131 In addition to the terminology defined in [RFC3315], [RFC3633], and 132 [RFC7227], the following terminology is used in this document: 134 Identity association (IA): Throughout this document, "IA" is 135 used to refer to the Identity 136 Association containing addresses or 137 prefixes assigned to a client and 138 carried in the IA_NA or IA_PD options 139 respectively. 141 IA option types: This is used to generally mean an 142 IA_NA and/or IA_PD option. 144 Stateful options: Options that require dynamic binding 145 state per client on the server. 147 Top-level options: Top-level options are DHCPv6 options 148 that are not encapsulated within 149 other options, excluding the Relay- 150 Message option. Options encapsulated 151 by Relay-message options, but not by 152 any other option, are still top-level 153 options, whether they appear in a 154 relay agent message or a server 155 message. See [RFC7227]. 157 4. Handling of Multiple IA Option Types 159 The DHCPv6 specification [RFC3315] was written with the assumption 160 that the only stateful options were for assigning addresses. DHCPv6 161 Prefix Delegation [RFC3633] describes how to extend the DHCPv6 162 protocol to handle prefix delegation, but does not clearly specify 163 how the DHCP address assignment and prefix delegation co-exist. 165 If a client requests multiple IA option types, but the server is 166 configured to only offer a subset of them, the client could react in 167 several ways: 169 1. Reset the state machine and continue to send Solicit messages, 171 2. Create separate DHCP sessions for each IA option type and 172 continue to Solicit for the unfulfilled IA options, or 174 3. The client could continue with the single session, and include 175 the unfulfilled IA options in subsequent messages to the server. 177 Resetting the state machine and continuing to send Solicit messages 178 may result in the client never completing DHCP and is generally not 179 considered a good solution. It can also result in a packet storm if 180 the client does not appropriately rate limit its sending of Solicit 181 messages or there are many clients on the network. Client 182 implementors that follow this approach, SHOULD implement the updates 183 to RFC-3315 specified in [RFC7083]. 185 Creating a separate DHCP session (separate instances of the client 186 state machine) per IA option type, while conceptually simple, causes 187 a number of issues: additional host resources required to create and 188 maintain multiple instances of the state machine in clients, 189 additional DHCP protocol traffic, unnecessary duplication of other 190 configuration options and the potential for conflict, divergence in 191 that each IA option type specification specifies its 'own' version of 192 the DHCP protocol. 194 The single session and state machine allows the client to use the 195 best configuration it is able to obtain from a single DHCP server 196 during the configuration exchange. Note, however, that the server 197 may not be configured to deliver the entire configuration requested 198 by the client. In that case the client could continue to operate 199 only using the configuration received, even if other servers can 200 provide the missing configuration. In practice, especially in the 201 case of handling IA_NA and IA_PD, this situation should be rare or a 202 temporary operational error. So, it is more likely for the client to 203 get all configuration if it continues, in each subsequent 204 configuration exchange, to request all the configuration information 205 it is programmed to try to obtain, including any stateful 206 configuration options for which no results were returned in previous 207 exchanges. 209 One major issue of this last approach is that it is difficult to 210 allow it with the current DHCPv6 specifications; in some cases they 211 are not clear enough, and in other cases existing restrictions can 212 make it impossible. This document introduces some clarifications and 213 small modifications to the current specifications to address these 214 concerns. 216 While all approaches have their own pros and cons, approach 3 SHOULD 217 be used and is the focus of this document because it is deemed to 218 work best for common cases of the mixed use of IA_NA and IA_PD. But 219 this document does not exclude other approaches. Also, in some 220 corner cases it may not be feasible to maintain a single DHCPv6 221 session for both IA_NA and IA_PD. These corner cases are beyond the 222 scope of this document and may depend on the network in which the 223 client (CER) is designed to operate and on the functions the client 224 is required to perform. 226 The sections which follow update RFC 3315 and RFC 3633 to accommodate 227 the recommendation, though many of the changes are also applicable 228 even if other approaches are used. 230 4.1. Placement of Status Codes in an Advertise Message 232 In Reply messages IA specific status codes (i.e., NoAddrsAvail, 233 NotOnLink, NoBinding, NoPrefixAvail) are encapsulated in the IA 234 option. In Advertise messages though, the NoAddrsAvail code is 235 returned at in the top level. This makes sense if the client is only 236 interested in the assignment of the addresses and the failure case is 237 fatal. However, if the client sends both IA_NA and IA_PD options in 238 a Solicit message, it is possible that the server offers no addresses 239 but it offers some prefixes, and the client may choose to send a 240 Request message to obtain the offered prefixes. In this case, it is 241 better if the Status Code option for IA specific status codes is 242 encapsulated in the IA option to indicate that the failure occurred 243 for the specific IA. This also makes the NoAddrsAvail and 244 NoPrefixAvail Status Code option placement for Advertise messages 245 identical to Reply messages. 247 In addition, how a server formats the Advertise message when 248 addresses are not available has been a point of some confusion and 249 implementations seem to vary (some strictly follow RFC 3315 while 250 others assumed it was encapsulated in the IA option as for Reply 251 messages). 253 We have chosen the following solution: 255 Clients MUST handle each of the following Advertise messages formats 256 when there are no addresses available (even when no other IA option 257 types were in the Solicit): 259 1. Advertise containing the IA_NAs and/or IA_TAs with encapsulated 260 Status Code option of NoAddrsAvail and no top-level Status Code 261 option. 263 2. Advertise containing just a top-level Status Code option of 264 NoAddrsAvail and no IA_NAs/IA_TAs. 266 3. Advertise containing a top-level Status Code option of 267 NoAddrsAvail and IA_NAs and/or IA_TAs with a Status Code option 268 of NoAddrsAvail. 270 Note: Clients MUST handle the last two formats listed above to 271 facilitate backward compatibility with the servers which have not 272 been updated to this specification. 274 See Section 4.2 for updated text for Section 17.1.3 of RFC 3315 and 275 Section 11.1 of RFC 3633. 277 Servers MUST return the Status Code option of NoAddrsAvail 278 encapsulated in IA_NA/IA_TA options and MUST NOT return a top-level 279 Status Code option of NoAddrsAvail when no addresses will be assigned 280 (1 in the above list). This means that the Advertise response 281 matches the Reply response with respect to the handling of the 282 NoAddrsAvail status. 284 Replace the following paragraph in RFC 3315, section 17.2.2: 286 If the server will not assign any addresses to any IAs in a 287 subsequent Request from the client, the server MUST send an 288 Advertise message to the client that includes only a Status 289 Code option with code NoAddrsAvail and a status message for 290 the user, a Server Identifier option with the server's DUID, 291 and a Client Identifier option with the client's DUID. 293 With: 295 If the server will not assign any addresses to an IA in a 296 subsequent Request from the client, the server MUST include 297 the IA in the Advertise message with no addresses in the IA 298 and a Status Code option encapsulated in the IA containing 299 status code NoAddrsAvail. 301 4.2. Advertise Message Processing by a Client 303 [RFC3315] specifies that a client must ignore an Advertise message if 304 a server will not assign any addresses to a client, and [RFC3633] 305 specifies that a client must ignore an Advertise message if a server 306 returns the NoPrefixAvail status to a requesting router. Thus, a 307 client requesting both IA_NA and IA_PD, with a server that only 308 offers either addresses or delegated prefixes, is not supported by 309 the current protocol specifications. 311 Solution: a client SHOULD accept Advertise messages, even when not 312 all IA option types are being offered. And, in this case, the client 313 SHOULD include the not offered IA option types in its Request. A 314 client SHOULD only ignore an Advertise message when none of the 315 requested IA options include offered addresses or delegated prefixes. 316 Note that ignored messages MUST still be processed for SOL_MAX_RT and 317 INF_MAX_RT options as specified in [RFC7083]. 319 Replace Section 17.1.3 of RFC 3315: (existing errata) 321 The client MUST ignore any Advertise message that includes a Status 322 Code option containing the value NoAddrsAvail, with the exception 323 that the client MAY display the associated status message(s) to the 324 user. 326 With (this includes the changes made by [RFC7083]): 328 The client MUST ignore any Advertise message that contains no 329 addresses (IAADDR options encapsulated in IA_NA or IA_TA options) 330 and no delegated prefixes (IAPREFIX options encapsulated in IA_PD 331 options, see RFC 3633) with the exception that the client: 332 - MUST process an included SOL_MAX_RT option (RFC 7083) and 333 - MUST process an included INF_MAX_RT option (RFC 7083). 334 A client can display any associated status message(s) to the user 335 or activity log. 337 The client ignoring this Advertise message MUST NOT restart the 338 Solicit retransmission timer. 340 And, replace: 342 - The client MAY choose a less-preferred server if that server 343 has a better set of advertised parameters, such as the 344 available addresses advertised in IAs. 346 With: 348 - The client MAY choose a less-preferred server if that server has 349 a better set of advertised parameters, such as the available set 350 of IAs, as well as the set of other configuration options 351 advertised. 353 And, replace the last paragraph of Section 11.1 of RFC 3633 with: 355 The requesting router MUST ignore any Advertise message that 356 contains no addresses (IAADDR options encapsulated in IA_NA or 357 IA_TA options) and no delegated prefixes (IAPREFIX options 358 encapsulated in IA_PD options, see RFC 3633) with the exception 359 that the requesting router: 360 - MUST process an included SOL_MAX_RT option (RFC 7083) and 361 - MUST process an included INF_MAX_RT option (RFC 7083). 362 A client can display any associated status message(s) to the user 363 or activity log. 365 The requesting router ignoring this Advertise message MUST NOT 366 restart the Solicit retransmission timer. 368 4.3. T1/T2 Timers 370 The T1 and T2 times determine when the client will contact the server 371 to extend lifetimes of information received in an IA. How should a 372 client handle the case where multiple IA options have different T1 373 and T2 times? 374 In a multiple IA option type model, the T1/T2 times are protocol 375 timers, that should be independent of the IA options themselves. If 376 we were to redo the DHCP protocol from scratch the T1/T2 times should 377 be carried in a separate DHCP option. 379 Solution: The server MUST set the T1/T2 times in all IA options in a 380 Reply or Advertise message to the same value. To deal with the case 381 where servers have not yet been updated to do that, the client MUST 382 select a T1 and T2 time from all IA options which will guarantee that 383 the client will send Renew/Rebind messages not later than at the T1/ 384 T2 times associated with any of the client's bindings. 386 As an example, if the client receives a Reply with T1_NA of 3600 / 387 T2_NA of 5760 and T1_PD of 0 / T2_PD of 1800, the client SHOULD use 388 the T1_PD of 0 / T2_PD of 1800. The reason for this is that a T1 of 389 0 means that the Renew time is at the client's discretion, but this 390 value cannot be greater than the T2 value (1800). 392 The following paragraph should be added to Sections 18.2.1, 18.2.3, 393 and 18.2.4 of RFC 3315: 395 The T1/T2 times set in each applicable IA option for a Reply MUST 396 be the same values across all IAs. The server MUST determine the 397 T1/T2 times across all of the applicable client's bindings in the 398 Reply. This facilitates the client being able to renew all of the 399 bindings at the same time. 401 Note: This additional paragraph has also been included in the revised 402 text later for Sections 18.2.3 and 18.2.4 of RFC 3315. 404 Changes for client T1/T2 handling are included in Section 4.4.3 and 405 Section 4.4.4. 407 4.4. Renew and Rebind Messages 409 This section presents issues with handling multiple IA option types 410 in the context of creation and processing the Renew and Rebind 411 messages. It also introduces relevant updates to the [RFC3315] and 412 [RFC3633]. 414 4.4.1. Renew Message 416 In multiple IA option type model, the client may include multiple IA 417 options in the Request message, and the server may create bindings 418 only for a subset of the IA options included by the client. For the 419 IA options in the Request message for which the server does not 420 create the bindings, the server sends the IA options in the Reply 421 message with the NoAddrsAvail or NoPrefixAvail status codes. 423 The client may accept the bindings created by the server, but may 424 desire the other bindings to be created once they become available, 425 e.g. when the server configuration is changed. The client which 426 accepted the bindings created by the server will periodically send a 427 Renew message to extend their lifetimes. However, the Renew message, 428 as described in the [RFC3315], does not support the ability for the 429 client to extend the lifetimes of the bindings for some IAs, while 430 requesting bindings for other IAs. 432 Solution: The client, which sends a Renew message to extend the 433 lifetimes of the bindings assigned to the client, SHOULD include IA 434 options for these bindings as well as IA options for all other 435 bindings that the client desires but has been unable to obtain. The 436 client and server processing need to be modified. Note that this 437 change makes the server's IA processing of Renew similar to the 438 Request processing. 440 4.4.2. Rebind Message 442 According to the Section 4.4.1, the client includes IA options in a 443 Renew message for the bindings it desires but has been unable to 444 obtain by sending a Request message, apart from the IA options for 445 the existing bindings. 447 At time T2, the client stops sending Renew messages to the server and 448 initiates the Rebind/Reply message exchange with any available 449 server. In this case, it should be possible to continue trying to 450 obtain new bindings using the Rebind message if the client failed to 451 get the response from the server to the Renew message. 453 Solution: The client SHOULD continue to include the IA options 454 received from the server and it MAY include additional IA options to 455 request creation of the additional bindings. 457 4.4.3. Updates to section 18.1.3 of RFC 3315 459 Replace Section 18.1.3 of RFC 3315 with the following text: 461 To extend the valid and preferred lifetimes for the addresses 462 assigned to an IA, the client sends a Renew message to the server 463 from which the addresses were obtained, which includes an IA option 464 for the IA whose address lifetimes are to be extended. The client 465 includes IA Address options within the IA option for the addresses 466 assigned to the IA. The server determines new lifetimes for these 467 addresses according to the administrative configuration of the 468 server. The server may also add new addresses to the IA. The 469 server can remove addresses from the IA by returning IA Address 470 options for such addresses with preferred and valid lifetimes set 471 to zero. 473 The server controls the time at which the client contacts the 474 server to extend the lifetimes on assigned addresses through the T1 475 and T2 parameters assigned to an IA. However, as the client 476 Renews/Rebinds all IAs from the server at the same time, the client 477 MUST select a T1 and T2 time from all IA options which will 478 guarantee that the client will send Renew/Rebind messages not later 479 than at the T1/T2 times associated with any of the client's 480 bindings. 482 At time T1, the client initiates a Renew/Reply message exchange to 483 extend the lifetimes on any addresses in the IA. 485 If T1 or T2 had been set to 0 by the server (for an IA_NA) or there 486 are no T1 or T2 times (for an IA_TA) in a previous Reply, the 487 client may send a Renew or Rebind message, respectively, at the 488 client's discretion. 490 The client sets the "msg-type" field to RENEW. The client 491 generates a transaction ID and inserts this value in the 492 "transaction-id" field. 494 The client places the identifier of the destination server in a 495 Server Identifier option. 497 The client MUST include a Client Identifier option to identify 498 itself to the server. The client adds any appropriate options, 499 including one or more IA options. 501 For IAs to which addresses have been assigned, the client includes 502 a corresponding IA option containing an IA Address option for each 503 address assigned to the IA. The client MUST NOT include addresses 504 in any IA option that the client did not obtain from the server or 505 that are no longer valid (that have a zero valid lifetime). 507 The client MAY include an IA option for each binding it desires but 508 has been unable to obtain. This IA option MUST NOT contain any 509 addresses. However, it MAY contain the IA Address option with IPv6 510 address field set to 0 to indicate the client's preference for the 511 preferred and valid lifetimes for any newly assigned addresses. 513 The client MUST include an Option Request option (see section 22.7) 514 to indicate the options the client is interested in receiving. The 515 client MAY include options with data values as hints to the server 516 about parameter values the client would like to have returned. 518 The client transmits the message according to section 14, using the 519 following parameters: 521 IRT REN_TIMEOUT 523 MRT REN_MAX_RT 525 MRC 0 527 MRD Remaining time until T2 529 The message exchange is terminated when time T2 is reached (see 530 section 18.1.4), at which time the client begins a Rebind message 531 exchange. 533 4.4.4. Updates to Section 18.1.4 of RFC 3315 535 Replace Section 18.1.4 of RFC 3315 with the following text: 537 At time T2 (which will only be reached if the server to which the 538 Renew message was sent at time T1 has not responded), the client 539 initiates a Rebind/Reply message exchange with any available 540 server. 542 The client constructs the Rebind message as described in 18.1.3 543 with the following differences: 545 - The client sets the "msg-type" field to REBIND. 547 - The client does not include the Server Identifier option in the 548 Rebind message. 550 The client transmits the message according to section 14, using the 551 following parameters: 553 IRT REB_TIMEOUT 555 MRT REB_MAX_RT 557 MRC 0 559 MRD Remaining time until valid lifetimes of all addresses in 560 all IAs have expired 562 If all addresses for an IA have expired the client may choose to 563 include this IA without any addresses (or with only a hint for 564 lifetimes) in subsequent Rebind messages to indicate that the 565 client is interested in assignment of the addresses to this IA. 567 The message exchange is terminated when the valid lifetimes of all 568 addresses across all IAs have expired, at which time the client 569 uses Solicit message to locate a new DHCP server and sends a 570 Request for the expired IAs to the new server. 572 4.4.5. Updates to Section 18.1.8 of RFC 3315 574 Replace Section 18.1.8 of RFC 3315 with the following text: 576 Upon the receipt of a valid Reply message in response to a Solicit 577 (with a Rapid Commit option), Request, Confirm, Renew, Rebind or 578 Information-request message, the client extracts the configuration 579 information contained in the Reply. The client MAY choose to 580 report any status code or message from the status code option in 581 the Reply message. 583 If the client receives a Reply message with a Status Code 584 containing UnspecFail, the server is indicating that it was unable 585 to process the message due to an unspecified failure condition. If 586 the client retransmits the original message to the same server to 587 retry the desired operation, the client MUST limit the rate at 588 which it retransmits the message and limit the duration of the time 589 during which it retransmits the message. 591 When the client receives a Reply message with a Status Code option 592 with the value UseMulticast, the client records the receipt of the 593 message and sends subsequent messages to the server through the 594 interface on which the message was received using multicast. The 595 client resends the original message using multicast. 597 When the client receives a NotOnLink status from the server in 598 response to a Confirm message, the client performs DHCP server 599 solicitation, as described in section 17, and client-initiated 600 configuration as described in section 18. If the client receives 601 any Reply messages that do not indicate a NotOnLink status, the 602 client can use the addresses in the IA and ignore any messages that 603 indicate a NotOnLink status. 605 When the client receives a NotOnLink status from the server in 606 response to a Request, the client can either re-issue the Request 607 without specifying any addresses or restart the DHCP server 608 discovery process (see section 17). 610 The client SHOULD perform duplicate address detection [17] on each 611 of the received addresses in any IAs, on which it has not performed 612 duplicate address detection during processing of any of the 613 previous Reply messages from the server. The client performs the 614 duplicate address detection before using the received addresses for 615 the traffic. If any of the addresses are found to be in use on the 616 link, the client sends a Decline message to the server for those 617 addresses as described in section 18.1.7. 619 If the Reply was received in response to a Solicit (with a Rapid 620 Commit option), Request, Renew or Rebind message, the client 621 updates the information it has recorded about IAs from the IA 622 options contained in the Reply message: 624 - Record T1 and T2 times. 626 - Add any new addresses in the IA option to the IA as recorded by 627 the client. 629 - Update lifetimes for any addresses in the IA option that the 630 client already has recorded in the IA. 632 - Discard any addresses from the IA, as recorded by the client, 633 that have a valid lifetime of 0 in the IA Address option. 635 - Leave unchanged any information about addresses the client has 636 recorded in the IA but that were not included in the IA from the 637 server. 639 Management of the specific configuration information is detailed in 640 the definition of each option in section 22. 642 The client examines the status code in each IA individually. If 643 the client receives a NoAddrsAvail status code, the client has 644 received no usable addresses in the IA. 646 If the client can operate with the addresses obtained from the 647 server the client uses addresses and other information from any IAs 648 that do not contain a Status Code option with the NoAddrsAvail 649 status code. The client MAY include the IAs for which it received 650 the NoAddrsAvail status code, with no addresses, in subsequent 651 Renew and Rebind messages sent to the server, to retry obtaining 652 the addresses for these IAs. 654 If the client cannot operate without the addresses for the IAs for 655 which it received the NoAddrsAvail status code, the client may try 656 another server (perhaps by restarting the DHCP server discovery 657 process). 659 If the client finds no usable addresses in any of the IAs, it may 660 either try another server (perhaps restarting the DHCP server 661 discovery process) or use the Information-request message to obtain 662 other configuration information only. 664 When the client receives a Reply message in response to a Renew or 665 Rebind message, the client: 667 - sends a Request message if any of the IAs in the Reply message 668 contains the NoBinding status code. The client places IA 669 options in this message for only those IAs for which the server 670 returned the NoBinding status code in the Reply message. The 671 client continues to use other bindings for which the server did 672 not return an error 674 - sends a Renew/Rebind if any of the IAs is not in the Reply 675 message, but in this case the client MUST limit the rate at 676 which it sends these messages, to avoid the Renew/Rebind storm 678 - otherwise accepts the information in the IA. 680 When the client receives a valid Reply message in response to a 681 Release message, the client considers the Release event completed, 682 regardless of the Status Code option(s) returned by the server. 684 When the client receives a valid Reply message in response to a 685 Decline message, the client considers the Decline event completed, 686 regardless of the Status Code option(s) returned by the server. 688 4.4.6. Updates to Section 18.2.3 of RFC 3315 690 Replace Section 18.2.3 of RFC 3315 with the following text: 692 When the server receives a Renew message via unicast from a client 693 to which the server has not sent a unicast option, the server 694 discards the Renew message and responds with a Reply message 695 containing a Status Code option with the value UseMulticast, a 696 Server Identifier option containing the server's DUID, the Client 697 Identifier option from the client message, and no other options. 699 For each IA in the Renew message from a client, the server locates 700 the client's binding and verifies that the information in the IA 701 from the client matches the information stored for that client. 703 If the server finds the client entry for the IA the server sends 704 back the IA to the client with new lifetimes and, if applicable, 705 T1/T2 times. If the server is unable to extend the lifetimes of an 706 address in the IA, the server MAY choose not to include the IA 707 Address option for this address. 709 The server may choose to change the list of addresses and the 710 lifetimes of addresses in IAs that are returned to the client. 712 If the server finds that any of the addresses in the IA are not 713 appropriate for the link to which the client is attached, the 714 server returns the address to the client with lifetimes of 0. 716 For each IA for which the server cannot find a client entry, the 717 server has the following choices depending on the server's policy 718 and configuration information: 720 - If the server is configured to create new bindings as a result 721 of processing Renew messages, the server SHOULD create a binding 722 and return the IA with allocated addresses with lifetimes and, 723 if applicable, T1/T2 times and other information requested by 724 the client. The server MAY use values in the IA Address option 725 (if included) as a hint. 727 - If the server is configured to create new bindings as a result 728 of processing Renew messages, but the server will not assign any 729 addresses to an IA, the server returns the IA option containing 730 a Status Code option with the NoAddrsAvail status code and a 731 status message for a user. 733 - If the server does not support creation of new bindings for the 734 client sending a Renew message, or if this behavior is disabled 735 according to the server's policy or configuration information, 736 the server returns the IA option containing a Status code option 737 with the NoBinding status code and a status message for a user. 739 The server constructs a Reply message by setting the "msg-type" 740 field to REPLY, and copying the transaction ID from the Renew 741 message into the transaction-id field. 743 The server MUST include a Server Identifier option containing the 744 server's DUID and the Client Identifier option from the Renew 745 message in the Reply message. 747 The server includes other options containing configuration 748 information to be returned to the client as described in section 749 18.2. 751 The T1/T2 times set in each applicable IA option for a Reply MUST 752 be the same values across all IAs. The server MUST determine the 753 T1/T2 times across all of the applicable client's bindings in the 754 Reply. This facilitates the client being able to renew all of the 755 bindings at the same time. 757 4.4.7. Updates to Section 18.2.4 of RFC 3315 759 Replace Section 18.2.4 of RFC 3315 with the following text: 761 When the server receives a Rebind message that contains an IA 762 option from a client, it locates the client's binding and verifies 763 that the information in the IA from the client matches the 764 information stored for that client. 766 If the server finds the client entry for the IA and the server 767 determines that the addresses in the IA are appropriate for the 768 link to which the client's interface is attached according to the 769 server's explicit configuration information, the server SHOULD 770 send back the IA to the client with new lifetimes and, if 771 applicable, T1/T2 times. If the server is unable to extend the 772 lifetimes of an address in the IA, the server MAY choose not to 773 include the IA Address option for this address. 775 If the server finds the client entry for the IA and any of the 776 addresses are no longer appropriate for the link to which the 777 client's interface is attached according to the server's explicit 778 configuration information, the server returns the address to the 779 client with lifetimes of 0. 781 If the server cannot find a client entry for the IA, the IA 782 contains addresses and the server determines that the addresses in 783 the IA are not appropriate for the link to which the client's 784 interface is attached according to the server's explicit 785 configuration information, the server MAY send a Reply message to 786 the client containing the client's IA, with the lifetimes for the 787 addresses in the IA set to 0. This Reply constitutes an explicit 788 notification to the client that the addresses in the IA are no 789 longer valid. In this situation, if the server does not send a 790 Reply message it silently discards the Rebind message. 792 Otherwise, for each IA for which the server cannot find a client 793 entry, the server has the following choices depending on the 794 server's policy and configuration information: 796 - If the server is configured to create new bindings as a result 797 of processing Rebind messages (also see the note about the 798 Rapid Commit option below), the server SHOULD create a binding 799 and return the IA with allocated addresses with lifetimes and, 800 if applicable, T1/T2 times and other information requested by 801 the client. The server MAY use values in the IA Address option 802 (if included) as a hint. 804 - If the server is configured to create new bindings as a result 805 of processing Rebind messages, but the server will not assign 806 any addresses to an IA, the server returns the IA option 807 containing a Status Code option with the NoAddrsAvail status 808 code and a status message for a user. 810 - If the server does not support creation of new bindings for the 811 client sending a Rebind message, or if this behavior is 812 disabled according to the server's policy or configuration 813 information, the server returns the IA option containing a 814 Status Code option with the NoBinding status code and a status 815 message for a user. 817 When the server creates new bindings for the IA it is possible 818 that other servers also create bindings as a result of receiving 819 the same Rebind message. This is the same issue as in the 820 Discussion under the Rapid Commit option, see section 22.14. 821 Therefore, the server SHOULD only create new bindings during 822 processing of a Rebind message if the server is configured to 823 respond with a Reply message to a Solicit message containing the 824 Rapid Commit option. 826 The server constructs a Reply message by setting the "msg-type" 827 field to REPLY, and copying the transaction ID from the Rebind 828 message into the transaction-id field. 830 The server MUST include a Server Identifier option containing the 831 server's DUID and the Client Identifier option from the Rebind 832 message in the Reply message. 834 The server includes other options containing configuration 835 information to be returned to the client as described in section 836 18.2. 838 The T1/T2 times set in each applicable IA option for a Reply MUST 839 be the same values across all IAs. The server MUST determine the 840 T1/T2 times across all of the applicable client's bindings in the 841 Reply. This facilitates the client being able to renew all of the 842 bindings at the same time. 844 4.4.8. Updates to RFC 3633 846 Replace the following text in Section 12.1 of RFC 3633: 848 Each prefix has valid and preferred lifetimes whose durations are 849 specified in the IA_PD Prefix option for that prefix. The 850 requesting router uses Renew and Rebind messages to request the 851 extension of the lifetimes of a delegated prefix. 853 With: 855 Each prefix has valid and preferred lifetimes whose durations are 856 specified in the IA_PD Prefix option for that prefix. The 857 requesting router uses Renew and Rebind messages to request the 858 extension of the lifetimes of a delegated prefix. 860 The requesting router MAY include IA_PD options without any 861 prefixes, i.e. without IA Prefix option or with IPv6 prefix field 862 of IA Prefix option set to 0, in a Renew or Rebind message to 863 obtain bindings it desires but has been unable to obtain. The 864 requesting router MAY set the prefix-length field of the IA Prefix 865 option as a hint to the server. As in [RFC3315], the requesting 866 router MAY also provide lifetime hints in the IA Prefix option. 868 Replace the following text in Section 12.2 of RFC 3633: 870 The delegating router behaves as follows when it cannot find a 871 binding for the requesting router's IA_PD: 873 With: 875 For the Renew or Rebind, if the IA_PD contains no IA Prefix option 876 or it contains an IA Prefix option with the IPv6 prefix field set 877 to 0, the delegating router SHOULD assign prefixes to the IA_PD 878 according to the delegating router's explicit configuration 879 information. In this case, if the IA_PD contains an IA Prefix 880 option with the IPv6 prefix field set to 0, the delegating router 881 MAY use the value in the prefix-length field of the IA Prefix 882 option as a hint for the length of the prefixes to be assigned. 883 The delegating router MAY also respect lifetime hints provided by 884 the requesting router in the IA Prefix option. 886 The delegating router behaves as follows when it cannot find a 887 binding for the requesting router's IA_PD containing prefixes: 889 4.5. Confirm Message 891 The Confirm message, as described in [RFC3315], is specific to 892 address assignment. It allows a server without a binding to reply to 893 the message, under the assumption that the server only needs 894 knowledge about the prefix(es) on the link, to inform the client that 895 the address is likely valid or not. This message is sent when e.g. 896 the client has moved and needs to validate its addresses. Not all 897 bindings can be validated by servers and the Confirm message provides 898 for this by specifying that a server that is unable to determine the 899 on-link status MUST NOT send a Reply. 901 Note: Confirm has a specific meaning and does not overload Renew/ 902 Rebind. It also is lower processing cost as the server does NOT need 903 to extend lease times or otherwise send back other configuration 904 options. 906 The Confirm message is used by the client to verify that it has not 907 moved to a different link. For IAs with addresses, the mechanism 908 used to verify if a client has moved or not, is by matching the 909 link's on-link prefix(es) (typically a /64) against the prefix-length 910 first bits of the addresses provided by the client in the IA_NA or 911 IA_TA IA-types. As a consequence Confirm can only be used when the 912 client has an IA with address(es) (IA_NA or IA_TA). 914 A client MUST have a binding including an IA with addresses to use 915 the Confirm message. A client with IAs with addresses as well as 916 other IA-types MAY, depending on the IA-type, use the Confirm message 917 to detect if the client has moved to a different link. A client that 918 does not have a binding with an IA with addresses MUST use the Rebind 919 message instead. 921 IA_PD requires verification that the delegating router (server) has 922 the binding for the IAs. In that case a requesting router (client) 923 MUST use the Rebind message in place of the Confirm message and it 924 MUST include all of its bindings, even address IAs. 926 Note that Section 18.1.2 of RFC 3315 states that a client MUST 927 initiate a Confirm when it may have moved to a new link. This is 928 relaxed to a SHOULD as a client may have determined whether it has or 929 has not moved using other techniques, such as described in [RFC6059]. 930 And, as stated above, a client with delegated prefixes, MUST send a 931 Rebind instead of a Confirm. 933 4.6. Decline Should Not Necessarily Trigger a Release 935 Some client implementations have been found to send a Release message 936 for other bindings they may have received after they determine a 937 conflict and have correctly sent a Decline message for the 938 conflicting address(es). 940 A client SHOULD NOT send a Release message for other bindings it may 941 have received just because it sent a Decline message. The client 942 SHOULD retain the non-conflicting bindings. The client SHOULD treat 943 the failure to acquire a binding as a result of the conflict, to be 944 equivalent to not having received the binding, insofar as it behaves 945 when sending Renew and Rebind messages. 947 4.7. Multiple Provisioning Domains 949 This document has assumed that all DHCP servers on a network are in a 950 single provisioning domain and thus should be "equal" in the service 951 that they offer. This was also assumed by [RFC3315] and [RFC3633]. 953 One could envision a network where the DHCP servers are in multiple 954 provisioning domains, and it may be desirable to have the DHCP client 955 obtain different IA types from different provisioning domains. How a 956 client detects the multiple provisioning domains and how it would 957 interact with the multiple servers in these different domains is 958 outside the scope of this document (see [I-D.ietf-mif-mpvd-arch] and 959 [I-D.ietf-mif-mpvd-dhcp-support]). 961 5. IANA Considerations 963 This specification does not require any IANA actions. 965 6. Security Considerations 967 There are no new security considerations pertaining to this document. 969 7. Acknowledgements 971 Thanks to many people that contributed to identify the stateful 972 issues addressed by this document and for reviewing drafts of the 973 document, including Ralph Droms, John Brzozowski, Ted Lemon, Hemant 974 Singh, Wes Beebee, Gaurau Halwasia, Bud Millword, Tim Winters, Rob 975 Shakir, Jinmei Tatuya, Andrew Yourtchenko, Fred Templin, Tomek 976 Mrugalski, Suresh Krishnan, and Ian Farrer. 978 8. References 980 8.1. Normative References 982 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 983 Requirement Levels", BCP 14, RFC 2119, March 1997. 985 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 986 and M. Carney, "Dynamic Host Configuration Protocol for 987 IPv6 (DHCPv6)", RFC 3315, July 2003. 989 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 990 Host Configuration Protocol (DHCP) version 6", RFC 3633, 991 December 2003. 993 [RFC7083] Droms, R., "Modification to Default Values of SOL_MAX_RT 994 and INF_MAX_RT", RFC 7083, November 2013. 996 8.2. Informative References 998 [I-D.dhcwg-dhc-rfc3315bis] 999 Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 1000 Richardson, M., Jiang, S., and T. Lemon, "Dynamic Host 1001 Configuration Protocol for IPv6 (DHCPv6) bis", draft- 1002 dhcwg-dhc-rfc3315bis-04 (work in progress), February 2015. 1004 [I-D.ietf-mif-mpvd-arch] 1005 Anipko, D., "Multiple Provisioning Domain Architecture", 1006 draft-ietf-mif-mpvd-arch-11 (work in progress), March 1007 2015. 1009 [I-D.ietf-mif-mpvd-dhcp-support] 1010 Krishnan, S., Korhonen, J., and S. Bhandari, "Support for 1011 multiple provisioning domains in DHCPv6", draft-ietf-mif- 1012 mpvd-dhcp-support-01 (work in progress), March 2015. 1014 [RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for 1015 Detecting Network Attachment in IPv6", RFC 6059, November 1016 2010. 1018 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 1019 Requirements for IPv6 Customer Edge Routers", RFC 7084, 1020 November 2013. 1022 [RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and 1023 S. Krishnan, "Guidelines for Creating New DHCPv6 Options", 1024 BCP 187, RFC 7227, May 2014. 1026 Authors' Addresses 1028 Ole Troan 1029 Cisco Systems, Inc. 1030 Philip Pedersens vei 20 1031 N-1324 Lysaker 1032 Norway 1034 Email: ot@cisco.com 1036 Bernie Volz 1037 Cisco Systems, Inc. 1038 1414 Massachusetts Ave 1039 Boxborough, MA 01719 1040 USA 1042 Email: volz@cisco.com 1043 Marcin Siodelski 1044 ISC 1045 950 Charter Street 1046 Redwood City, CA 94063 1047 USA 1049 Email: msiodelski@gmail.com