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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) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Dynamic Host Configuration L. Colitti 3 Internet-Draft J. Linkova 4 Updates: 2563 (if approved) Google 5 Intended status: Standards Track M. Richardson 6 Expires: January 14, 2021 Sandelman 7 T. Mrugalski 8 ISC 9 July 13, 2020 11 IPv6-Only-Preferred Option for DHCPv4 12 draft-ietf-dhc-v6only-05 14 Abstract 16 This document specifies a DHCPv4 option to indicate that a host 17 supports an IPv6-only mode and willing to forgo obtaining an IPv4 18 address if the network provides IPv6 connectivity. It also updates 19 RFC2563 to specify the DHCPv4 server behavior when the server 20 receives a DHCPDISCOVER not containing the Auto-Configure option. 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 https://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 January 14, 2021. 39 Copyright Notice 41 Copyright (c) 2020 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 (https://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 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 58 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 59 2. Reasons to Signal IPv6-Only Support in DHCPv4 Packets . . . . 5 60 3. IPv6-Only Preferred Option . . . . . . . . . . . . . . . . . 5 61 3.1. Option format . . . . . . . . . . . . . . . . . . . . . . 5 62 3.2. DHCPv4 Client Behavior . . . . . . . . . . . . . . . . . 6 63 3.3. DHCPv4 Server Behavior . . . . . . . . . . . . . . . . . 7 64 3.3.1. Interaction with RFC2563 . . . . . . . . . . . . . . 8 65 3.4. Constants and Configuration Variables . . . . . . . . . . 9 66 4. IPv6-Only Transition Technologies Considerations . . . . . . 9 67 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 68 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 69 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 70 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 71 8.1. Normative References . . . . . . . . . . . . . . . . . . 11 72 8.2. Informative References . . . . . . . . . . . . . . . . . 12 73 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 75 1. Introduction 77 One of the biggest challenges of deploying IPv6-only LANs is that 78 such networks might contain rather heterogeneous collection of hosts. 79 While some hosts are capable of operating in IPv6-only mode (either 80 because the OS and all applications are IPv6-only capable or because 81 the host has some form of 464XLAT [RFC6877] deployed), others might 82 still have IPv4 dependencies and need IPv4 addresses to operate 83 properly. To incrementally rollout IPv6-only, network operators 84 might need to provide IPv4 on demand whereby a host receives an IPv4 85 address if it needs it, while IPv6-only capable hosts (such as modern 86 mobile devices) are not allocated IPv4 addresses. Traditionally that 87 goal is achieved by placing IPv6-only capable devices into a 88 dedicated IPv6-only network segment or WiFi SSID, while dual-stack 89 devices reside in another network with IPv4 and DHCPv4 enabled. 90 However such approach has a number of drawbacks, including but not 91 limited to: 93 o Doubling the number of network segments leads to operational 94 complexity and performance impact, for instance due to high memory 95 utilization caused by an increased number of ACL entries. 97 o Placing a host into the correct network segment is problematic. 98 For example, in the case of 802.11 Wi-Fi the user might select the 99 wrong SSID. In the case of wired 802.1x authentication the 100 authentication server might not have all the information required 101 to make the correct decision and choose between an IPv6-only and a 102 dual-stack VLAN. 104 It would be beneficial for IPv6 deployment if operators could 105 implement IPv6-mostly (or IPv4-on-demand) segments where IPv6-only 106 hosts co-exist with legacy dual-stack devices. The trivial solution 107 of disabling IPv4 stack on IPv6-only capable hosts is not feasible as 108 those clients must be able to operate on IPv4-only networks as well. 109 While IPv6-only capable devices might use a heuristic approach to 110 learning if the network provides IPv6-only functionality and stop 111 using IPv4 if it does, such approach might be practically 112 undesirable. One important reason is that when a host connects to a 113 network, it does not know if the network is IPv4-only, dual-stack or 114 IPv6-only. To ensure that the connectivity over whatever protocol is 115 present becomes available as soon as possible the host usually starts 116 configuring both IPv4 and IPv6 immediately. If hosts were to delay 117 requesting IPv4 until IPv6 reachability is confirmed, that would 118 penalize IPv4-only and dual-stack networks, which does not seem 119 practical. Requesting IPv4 and then releasing it later, after IPv6 120 reachability is confirmed, might cause user-visible errors as it 121 would be disruptive for applications which have started using the 122 assigned IPv4 address already. Instead it would be useful to have a 123 mechanism which would allow a host to indicate that its request for 124 an IPv4 address is optional and a network to signal that IPv6-only 125 functionality (such as NAT64, [RFC6146]) is available. The proposed 126 solution is to introduce a new DHCPv4 option which a client uses to 127 indicate that it does not need an IPv4 address if the network 128 provides IPv6-only connectivity (as NAT64 and DNS64). If the 129 particular network segment provides IPv4-on-demand such clients would 130 not be supplied with IPv4 addresses, while on IPv4-only or dual-stack 131 segments without NAT64 services IPv4 addresses will be provided. 133 [RFC2563] introduces the Auto-Configure DHCPv4 option and describes 134 DHCPv4 servers behavior if no address is chosen for a host. This 135 document updates [RFC2563] to modify the server behavior if the 136 DHCPOFFER contains the IPv6-only Preferred option. 138 1.1. Requirements Language 140 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 141 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 142 "OPTIONAL" in this document are to be interpreted as described in BCP 143 14 [RFC2119] [RFC8174] when, and only when, they appear in all 144 capitals, as shown here. 146 1.2. Terminology 148 IPv6-only capable host: a host which does not require an IPv4 address 149 and can operate on IPv6-only networks. Strictly speaking IPv6-only 150 capability is specific to a given interface of the host: if some 151 application on a host require IPv4 and 464XLAT CLAT [RFC6877] is only 152 enabled on one interface, the host is IPv6-only capable if connected 153 to a NAT64 network via that interface. This document currently 154 implies that IPv6-only capable hosts reach IPv4-only destinations via 155 NAT64 service provided by the network. Section 4 discusses 156 hypothetical scenarios of other transition technologies being used. 158 IPv4-requiring host: a host which is not IPv6-only capable and can 159 not operate in IPv6-only network providing NAT64 service. 161 IPv4-on-demand: a deployment scenario when end hosts are expected to 162 operate in IPv6-only mode by default and IPv4 addresses can be 163 assigned to some hosts if those hosts explicitly opt-in to receiving 164 IPv4 addresses. 166 IPv6-mostly network: a network which provides NAT64 (possibly with 167 DNS64) service as well as IPv4 connectivity and allows coexistence of 168 IPv6-only, dual-stack and IPv4-only hosts on the same segment. Such 169 deployment scenario allows operators to incrementally turn off IPv4 170 on end hosts, while still providing IPv4 to devices which require 171 IPv4 to operate. But, IPv6-only capable devices need not be assigned 172 IPv4 addresses. 174 IPv6-only mode: a mode of operation when a host acts as an IPv6-only 175 capable host and does not have IPv4 addresses assigned (except that 176 IPv4 link-local addresses [RFC3927] may have been configured). 178 IPv6-Only network: a network which does not provide routing 179 functionality for IPv4 packets. Such networks may or may not allow 180 intra-LAN IPv4 connectivity. IPv6-Only network usually provides 181 access to IPv4-only resources via NAT64 [RFC6146]. 183 NAT64: Network Address and Protocol Translation from IPv6 Clients to 184 IPv4 Servers [RFC6146]. 186 RA: Router Advertisement, a message used by IPv6 routers to advertise 187 their presence together with various link and Internet parameters 188 [RFC4861]. 190 DNS64: a mechanism for synthesizing AAAA records from A records 191 [RFC6147]. 193 2. Reasons to Signal IPv6-Only Support in DHCPv4 Packets 195 For networks which contain a mix of both IPv6-only capable hosts and 196 IPv4-requiring hosts, and which utilize DHCPv4 for configuring the 197 IPv4 network stack on hosts, it seems natural to leverage the same 198 protocol to signal that IPv4 is discretional on a given segment. An 199 ability to remotely disable IPv4 on a host can be seen as a new 200 denial-of-service attack vector. The proposed approach limits the 201 attack surface to DHCPv4-related attacks without introducing new 202 vulnerable elements. 204 Another benefit of using DHCPv4 for signaling is that IPv4 will be 205 disabled only if both the client and the server indicate IPv6-only 206 capability. It allows IPv6-only capable hosts to turn off IPv4 only 207 upon receiving an explicit signal from the network and operate in 208 dual-stack or IPv4-only mode otherwise. In addition, the proposed 209 mechanism does not introduce any additional delays to the process of 210 configuring IP stack on hosts. If the network does not support IPv6- 211 only/IPv4-on-demand mode, an IPv6-only capable host would configure 212 an IPv4 address as quickly as on any other host. 214 Being a client/server protocol, DHCPv4 allows IPv4 to be selectively 215 disabled on a per-host basis on a given network segment. Coexistence 216 of IPv6-only, dual-stack and even IPv4-only hosts on the same LAN 217 would not only allow network administrators to preserve scarce IPv4 218 addresses but would also drastically simplify incremental deployment 219 of IPv6-only networks, positively impacting IPv6 adoption. 221 3. IPv6-Only Preferred Option 223 3.1. Option format 225 0 1 2 3 226 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 1 227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 228 | Code | Length | Value | 229 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 230 | Value (contd) | 231 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 233 Figure 1: IPv6-Only Preferred Option Format 235 Fields: 237 Code: 8-bit identifier of the IPv6-Only Preferred option code as 238 assigned by IANA: TBD 239 Length: 8-bit unsigned integer. The length of the option excluding 240 the Code and Length Fields. The server MUST set the length 241 field to 4. The client MUST ignore the IPv6-Only Preferred 242 option if the length field value is not 4. 243 Value: 32-bit unsigned integer. 244 The number of seconds the client should disable DHCPv4 for 245 (V6ONLY_WAIT configuration variable). 246 If the server pool is explicitly configured with a 247 V6ONLY_WAIT timer the server MUST set the field to that 248 configured value. Otherwise the server MUST set it to zero. 249 The client MUST process that field as described in 250 Section 3.2. 252 3.2. DHCPv4 Client Behavior 254 A DHCPv4 client SHOULD allow a device administrator to configure 255 IPv6-only preferred mode either for a specific interface (to indicate 256 that the device is IPv6-only capable if connected to a NAT64 network 257 via that interface) or for all interfaces. If only a specific 258 interface is configured as IPv6-only capable the DHCPv4 client MUST 259 NOT consider the host to be an IPv6-only capable for the purpose of 260 sending/receiving DHCPv4 packets over any other interfaces. 262 The DHCPv4 client on an IPv4-requiring host MUST NOT include the 263 IPv6-only Preferred option in the Parameter Request List of any 264 DHCPv4 packets and MUST ignore that option in packets received from 265 DHCPv4 servers. 267 DHCPv4 clients running on IPv6-only capable hosts SHOULD include the 268 IPv6-only Preferred option code in the Parameter Request List in 269 DHCPDISCOVER and DHCPREQUEST messages for interfaces so enabled and 270 follow the processing as described below on a per interface enabled 271 basis. 273 If the client did not include the IPv6-only Preferred option code in 274 the Parameter Request List option in the DHCPDISCOVER or DHCPREQUEST 275 message it MUST ignore the IPv6-only Preferred option in any messages 276 received from the server. 278 If the client includes the IPv6-only Preferred option in the 279 Parameter Request List and the DHCPOFFER message from the server 280 contains a valid IPv6-only Preferred option, the client SHOULD NOT 281 request the IPv4 address provided in the DHCPOFFER. If the IPv6-only 282 Preferred option returned by the server contains a value greater or 283 equal to MIN_V6ONLY_WAIT, the client SHOULD set the V6ONLY_WAIT timer 284 to that value. Otherwise, the client SHOULD set the V6ONLY_WAIT 285 timer to MIN_V6ONLY_WAIT. The client SHOULD stop the DHCPv4 286 configuration process for at least V6ONLY_WAIT seconds or until a 287 network attachment event happens. The host MAY disable the IPv4 288 stack completely for V6ONLY_WAIT seconds or until the network 289 disconnection event happens. 291 The IPv6-only Preferred option SHOULD be included in the Parameter 292 Request List option in DHCPREQUEST messages (after receiving a 293 DHCPOFFER without this option, for a INIT-REBOOT, or when renewing or 294 rebinding a leased address). If the DHCPv4 server responds with a 295 DHCPACK that includes the IPv6-only Preferred option, the client MAY 296 send a DHCPRELEASE message and MAY either stop the DHCPv4 297 configuration process or disable IPv4 stack completely for 298 V6ONLY_WAIT seconds or until the network disconnection event happens. 299 Alternatively the client MAY continue to use the assigned IPv4 300 address until further DHCPv4 reconfiguration events. 302 If the client includes the IPv6-only Preferred option in the 303 Parameter Request List and the server responds with DHCPOFFER message 304 without a valid IPv6-only Preferred option, the client MUST proceed 305 as normal with a DHCPREQUEST. 307 If the client waits for multiple DHCPOFFER responses and selects one 308 of them, it MUST follow the processing for the IPv6-only Preferred 309 option based on the selected response. A client MAY use the presence 310 of the IPv6-only Preferred option as a selection criteria. 312 When an IPv6-only capable client receives the IPv6-Only Preferred 313 option from the server, the client MAY configure IPv4 link-local 314 address [RFC3927]. In that case IPv6-Only capable devices might 315 still be able to communicate over IPv4 to other devices on the link. 316 The Auto-Configure Option [RFC2563] can be used to control IPv4 link- 317 local addresses autoconfiguration. Section 3.3.1 discusses the 318 interaction between the IPv6-only Preferred and the Auto-Configure 319 options. 321 3.3. DHCPv4 Server Behavior 323 The DHCPv4 server SHOULD be able to configure certain pools to 324 include the IPv6-only preferred option in DHCPv4 responses if the 325 client included the option code in the Parameter Request List option. 326 The DHCPv4 server MAY have a configuration option to specify 327 V6ONLY_WAIT timer for all or individual IPv6-mostly pools. 329 The server MUST NOT include the IPv6-only Preferred option in the 330 DHCPOFFER or DHCPACK message if the YIADDR field in the message does 331 not belong to a pool configured as IPv6-mostly. The server MUST NOT 332 include the IPv6-only Preferred option in the DHCPOFFER or DHCPACK 333 message if the option was not present in the Parameter Request List 334 sent by the client. 336 If the IPv6-only Preferred option is present in the Parameter Request 337 List received from the client and the corresponding DHCPv4 pool is 338 explicitly configured as belonging to an IPv6-mostly network segment, 339 the server MUST include the IPv6-only Preferred option when 340 responding with the DHCPOFFER or DHCPACK message. If the server 341 responds with the IPv6-only Preferred option and the V6ONLY_WAIT 342 timer is configured for the pool, the server MUST copy the configured 343 value to the IPv6-only Preferred option value field. Otherwise it 344 MUST set the field to zero. The server SHOULD NOT assign an address 345 for the pool. Instead it SHOULD return 0.0.0.0 as the offered 346 address. Alternatively, the server MAY include an available IPv4 347 address from the pool into the DHCPOFFER as per recommendations in 348 [RFC2131]. In this case, the offered address MUST be a valid address 349 that is not committed to any other client. Because the client is not 350 expected ever to request this address, the server SHOULD NOT reserve 351 the address and SHOULD NOT verify its uniqueness. If the client then 352 issues a DHCPREQUEST for the address, the server MUST process it per 353 [RFC2131], including replying with a DHCPACK for the address if in 354 the meantime it has not been committed to another client. 356 If a client includes both a Rapid-Commit option [RFC4039] and 357 IPv6-Only Preferred option in the DHCPDISCOVER message the server 358 SHOULD NOT honor the Rapid-Commit option if the response would 359 contain the IPv6-only Preferred option to the client. It SHOULD 360 instead respond with a DHCPOFFER as indicated above. 362 3.3.1. Interaction with RFC2563 364 [RFC2563] defines an Auto-Configure DHCPv4 option to disable IPv4 365 link-local address configuration for IPv4 clients. Clients can 366 support both, neither or just one of IPv6-Only Preferred and Auto- 367 Configure options. If a client sends both IPv6-Only Preferred and 368 Auto-Configure options the network administrator can prevent the host 369 from configuring an IPv4 link-local address on IPv6-mostly network. 370 To achieve this the server needs to send DHCPOFFER which contains a 371 'yiaddr' of 0x00000000, and the Auto-Configure flag saying 372 "DoNotAutoConfigure". 374 However special care should be taken in a situation when a server 375 supports both options and receives just IPv6-Only Preferred option 376 from a client. Section 2.3 of [RFC2563] states that if no address is 377 chosen for the host (which would be the case for IPv6-only capable 378 clients on IPv6-mostly network) then: "If the DHCPDISCOVER does not 379 contain the Auto-Configure option, it is not answered." Such 380 behavior would be undesirable for clients supporting the IPv6-Only 381 Preferred option w/o supporting the Auto-Configure option as they 382 would not receive any response from the server and would keep asking, 383 instead of disabling DHCPv4 for V6ONLY_WAIT seconds. Therefore the 384 following update is proposed to Section 2.3 of [RFC2563]" 386 OLD TEXT: 388 --- 390 However, if no address is chosen for the host, a few additional steps 391 MUST be taken. 393 If the DHCPDISCOVER does not contain the Auto-Configure option, it is 394 not answered. 396 --- 398 NEW TEXT: 400 --- 402 However, if no address is chosen for the host, a few additional steps 403 MUST be taken. 405 If the DHCPDISCOVER does not contain the Auto-Configure option and 406 the IPv6-Only Preferred option is not present, it is not answered. 407 If the DHCPDISCOVER does not contain the Auto-Configure option but 408 contains the IPv6-Only Preferred option, the processing rules for the 409 IPv6-Only Preferred option apply. 411 --- 413 3.4. Constants and Configuration Variables 415 V6ONLY_WAIT The minimum time the client SHOULD stop the DHCPv4 416 configuration process for. The value MUST NOT be less 417 than MIN_V6ONLY_WAIT seconds. Default: 1800 seconds 418 MIN_V6ONLY_WAIT The lower boundary for V6ONLY_WAIT. Value: 300 419 seconds 421 4. IPv6-Only Transition Technologies Considerations 423 Until IPv6 adoption in the Internet reaches 100%, communication 424 between an IPv6-only host and IPv4-only destination requires some 425 form of transition mechanism deployed in the network. At the time of 426 writing, the only such mechanism that is widely supported by end 427 hosts is NAT64 [RFC6146] (either with or without 464XLAT). Therefore 428 the IPv6-only Preferred option is only sent by hosts capable of 429 operating on NAT64 networks. In a typical deployment scenario, a 430 network administrator would not configure the DHCPv4 server to return 431 the IPv6-only Preferred option unless the network provides NAT64 432 service. 434 Hypothetically it is possible for multiple transition technologies to 435 coexist. In such scenario some form of negotiation would be required 436 between a client and a server to ensure that the transition 437 technology supported by the client is the one the network provides. 438 However it seems unlikely that any new transition technology would 439 arise and be widely adopted in any foreseeable future. Therefore 440 adding support for non-existing technologies seems to be suboptimal 441 and the proposed mechanism implies that NAT64 is used to facilitate 442 connectivity between IPv6 and IPv4. In the unlikely event that a new 443 transition mechanism becomes widely deployed, the applicability of 444 the IPv6-Only-Preferred option to that mechanism will depend on the 445 nature of the new mechanism. If the new mechanism is designed in 446 such a way that it's fully transparent for hosts that support NAT64 447 and the IPv6-Only-Preferred option, then the option can continue to 448 be used with the new mechanism. If the new mechanism is not 449 compatible with NAT64, and implementation on the host side is 450 required to support it, then a new DHCPv4 option needs to be defined. 452 It should be also noted that declaring a host or (strictly speaking, 453 a host interface) IPv6-only capable is a policy decision. For 454 example, 456 o An operating system vendor may make such decision and configure 457 their DHCPv4 clients to send the IPv6-Only Preferred option by 458 default if the OS has 464XLAT CLAT [RFC6877] enabled. 460 o An enterprise network administrator may provision the corporate 461 hosts as IPv6-only capable if all applications users are supposed 462 to run have been tested in IPv6-only environment (or if 464XLAT 463 CLAT is enabled on the devices). 465 o IoT devices may be shipped in IPv6-only capable mode if they are 466 designed to connect to IPv6-enabled cloud destination only. 468 5. IANA Considerations 470 The IANA is requested to assign a new DHCPv4 Option code for the 471 IPv6-Only Preferred option from the BOOTP Vendor Extensions and 472 DHCPv4 Options registry, located at https://www.iana.org/assignments/ 473 bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml#options . If 474 possible, please assign option code 108. 476 +----------------------------+-------+ 477 | Option Name | Code | 478 +----------------------------+-------+ 479 | IPv6-only Preferred option | (TBD) | 480 +----------------------------+-------+ 482 Table 1 484 6. Security Considerations 486 The proposed mechanism is not introducing any new security 487 implications. While clients using the IPv6-only Preferred option are 488 vulnerable to attacks related to a rogue DHCPv4 server, enabling 489 IPv6-only Preferred option does not provide an attacker with any 490 additional mechanisms. 492 It should be noted that disabling IPv4 on a host upon receiving the 493 IPv6-only Preferred option from the DHCPv4 server protects the host 494 from IPv4-related attacks and therefore could be considered a 495 security feature. 497 7. Acknowledgements 499 Thanks to the following people (in alphabetical order) for their 500 review and feedback: Mohamed Boucadair, Russ Housley, Sheng Jiang, 501 Ted Lemon, Roy Marples, Bjorn Mork, Peng Shuping, Pascal Thubert, 502 Bernie Volz, Eric Vyncke. Authors would like to thank Bob Hinden and 503 Brian Carpenter for the initial idea of signaling IPv6-only 504 capability to hosts. Special thanks to Erik Kline, Mark Townsley and 505 Maciej Zenczykowski for the discussion which led to the idea of 506 signalling IPv6-only capability over DHCPv4. 508 8. References 510 8.1. Normative References 512 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 513 Requirement Levels", BCP 14, RFC 2119, 514 DOI 10.17487/RFC2119, March 1997, 515 . 517 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 518 RFC 2131, DOI 10.17487/RFC2131, March 1997, 519 . 521 [RFC2563] Troll, R., "DHCP Option to Disable Stateless Auto- 522 Configuration in IPv4 Clients", RFC 2563, 523 DOI 10.17487/RFC2563, May 1999, 524 . 526 [RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic 527 Configuration of IPv4 Link-Local Addresses", RFC 3927, 528 DOI 10.17487/RFC3927, May 2005, 529 . 531 [RFC4039] Park, S., Kim, P., and B. Volz, "Rapid Commit Option for 532 the Dynamic Host Configuration Protocol version 4 533 (DHCPv4)", RFC 4039, DOI 10.17487/RFC4039, March 2005, 534 . 536 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 537 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 538 DOI 10.17487/RFC4861, September 2007, 539 . 541 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 542 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 543 May 2017, . 545 8.2. Informative References 547 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 548 NAT64: Network Address and Protocol Translation from IPv6 549 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 550 April 2011, . 552 [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van 553 Beijnum, "DNS64: DNS Extensions for Network Address 554 Translation from IPv6 Clients to IPv4 Servers", RFC 6147, 555 DOI 10.17487/RFC6147, April 2011, 556 . 558 [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: 559 Combination of Stateful and Stateless Translation", 560 RFC 6877, DOI 10.17487/RFC6877, April 2013, 561 . 563 Authors' Addresses 564 Lorenzo Colitti 565 Google 566 Shibuya 3-21-3 567 Shibuya, Tokyo 150-0002 568 JP 570 Email: lorenzo@google.com 572 Jen Linkova 573 Google 574 1 Darling Island Rd 575 Pyrmont, NSW 2009 576 AU 578 Email: furry@google.com 580 Michael C. Richardson 581 Sandelman Software Works 583 Email: mcr+ietf@sandelman.ca 584 URI: http://www.sandelman.ca/ 586 Tomek Mrugalski 587 Internet Systems Consortium, Inc. 588 950 Charter Street 589 Redwood City, CA 94063 590 USA 592 Email: tomasz.mrugalski@gmail.com