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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: If the IPv6-only Preferred option is present in the Parameter Request List received from the client and the corresponding DHCP pool is explicitly configured as belonging to an IPv6-mostly network segment, the server MUST include the IPv6-only Preferred option when responding with the DHCPOFFER or DHCPACK message. If the server responds with the IPv6-only Preferred option and the V6ONLY_WAIT timer is configured for the pool, the server MUST copy the configured value to the IPv6-only Preferred option value field. Otherwise it MUST set the field to zero. The server SHOULD not assign an address for the pool. Instead it SHOULD return 0.0.0.0 as the offered address. Alternatively, the server MAY include an available IPv4 address from the pool into the DHCPOFFER as per recommendations in [RFC2131] but SHOULD NOT reserve the address and SHOULD NOT verify its uniqueness. (Using the creation date from RFC2563, updated by this document, for RFC5378 checks: 1998-08-14) -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (March 9, 2020) is 1501 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) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 3 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: September 10, 2020 Sandelman 7 T. Mrugalski 8 ISC 9 March 9, 2020 11 IPv6-Only-Preferred Option for DHCP 12 draft-ietf-dhc-v6only-00 14 Abstract 16 This document specifies a DHCP 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. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at https://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on September 10, 2020. 37 Copyright Notice 39 Copyright (c) 2020 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (https://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 56 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Reasons to Signal IPv6-Only Support in DHCPv4 Packets . . . . 4 58 3. IPv6-Only Preferred Option . . . . . . . . . . . . . . . . . 5 59 3.1. Option format . . . . . . . . . . . . . . . . . . . . . . 5 60 3.2. DHCPv4 Client Behaviour . . . . . . . . . . . . . . . . . 5 61 3.3. DHCPv4 Server Behaviour . . . . . . . . . . . . . . . . . 7 62 3.3.1. Interoperability with RFC2563 . . . . . . . . . . . . 8 63 3.4. Constants and Configuration Variables . . . . . . . . . . 9 64 4. IPv6-Only Transition Technologies Considerations . . . . . . 9 65 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 66 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 67 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 68 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 69 8.1. Normative References . . . . . . . . . . . . . . . . . . 11 70 8.2. Informative References . . . . . . . . . . . . . . . . . 11 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 73 1. Introduction 75 One of the biggest challenges of deploying IPv6-only LANs is that 76 such networks might contain rather heterogeneous collection of hosts. 77 While some hosts are capable of operating in IPv6-only mode (either 78 because the OS and all applications are IPv6-only capable or because 79 the host has some form of 464XLAT [RFC6877] deployed), others might 80 still have IPv4 dependencies and need IPv4 addresses to operate 81 properly. To incrementally rollout IPv6-only, network operators 82 might need to provide IPv4 on demand whereby a host receives an IPv4 83 address if it needs it, while IPv6-only capable hosts (such as modern 84 mobile devices) are not allocated IPv4 addresses. Traditionally that 85 goal is achieved by placing IPv6-only capable devices into a 86 dedicated IPv6-only network segment or WiFi SSID, while dual-stack 87 devices reside in another network with IPv4 and DHCP enabled. 88 However such approach has a number of drawbacks, including but not 89 limited to: 91 o Doubling the number of network segments leads to operational 92 complexity and performance impact, for instance due to high memory 93 utilization caused by an increased number of ACL entries. 95 o Placing a host into the correct network segment is problematic. 96 For example, in the case of 802.11 Wi-Fi the user might select the 97 wrong SSID. In the case of wired 802.1x authentication the 98 authentication server might not have all the information required 99 to make the correct decision and choose between an IPv6-only and a 100 dual-stack VLAN. 102 It would be beneficial for IPv6 deployment if operators could 103 implement IPv6-mostly (or IPv4-on-demand) segments where IPv6-only 104 hosts co-exist with legacy dual-stack devices. The trivial solution 105 of disabling IPv4 stack on IPv6-only capable hosts is not feasible as 106 those clients must be able to operate on IPv4-only networks as well. 107 While IPv6-only capable devices might use a heuristic approach to 108 learning if the network provides IPv6-only functionality and stop 109 using IPv4 if it does, it might be practically undesirable. One 110 important reason is that when a host connects to a network, it does 111 not know if the network is IPv4-only, dual-stack or IPv6-only. To 112 ensure that the connectivity over whatever protocol is present 113 becomes available as soon as possible the host usually starts 114 configuring both IPv4 and IPv6 immediately. If hosts were to delay 115 requesting IPv4 until IPv6 reachability is confirmed, that would 116 penalize IPv4-only and dual-stack networks, which does not seem 117 practical. Requesting IPv4 and then releasing it later, after IPv6 118 reachability is confirmed, might cause user-visible errors as it 119 would be disruptive for applications which have started using the 120 assigned IPv4 address already. Instead it would be useful to have a 121 mechanism which would allow a host to indicate that its request for 122 an IPv4 address is optional and a network to signal that IPv6-only 123 functionality (such as NAT64) is available. The proposed solution is 124 to introduce a new DHCP option which a client uses to indicate that 125 it does not need an IPv4 address if the network provides IPv6-only 126 connectivity (as NAT64 and DNS64). If the particular network segment 127 provides IPv4-on-demand such clients would not be supplied with IPv4 128 addresses, while on IPv4-only or dual-stack segments without NAT64 129 services IPv4 addresses will be provided. 131 1.1. Requirements Language 133 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 134 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 135 "OPTIONAL" in this document are to be interpreted as described in BCP 136 14 [RFC2119] [RFC8174] when, and only when, they appear in all 137 capitals, as shown here. 139 1.2. Terminology 141 IPv6-only capable host: a host which does not require an IPv4 address 142 and can operate on IPv6-only networks. Strictly speaking IPv6-only 143 capability is specific to a given interface of the host: if some 144 application on a host require IPv4 and 464XLAT CLAT [RFC6877] is only 145 enabled on one interface, the host is IPv6-only capable if connected 146 to a NAT64 network via that interface. 148 IPv4-on-demand: a deployment scenario when end hosts are expected to 149 operate in IPv6-only mode by default and IPv4 addresses can be 150 assigned to some hosts if those hosts explicitly opt-in to receiving 151 IPv4 addresses. 153 IPv6-mostly network: a network which provides NAT64 (possibly with 154 DNS64) service as well as IPv4 connectivity and allows coexistence of 155 IPv6-only, dual-stack and IPv4-only hosts on the same segment. Such 156 deployment scenario allows operators to incrementally turn off IPv4 157 on end hosts, while still providing IPv4 to devices which require 158 IPv4 to operate. But, IPv6-only capable devices need not be assigned 159 IPv4 addresses. 161 IPv6-Only network: a network which does not provide routing 162 functionality for IPv4 packets. Such networks may or may not allow 163 intra-LAN IPv4 connectivity. IPv6-Only network usually provides 164 access to IPv4-only resources via NAT64 [RFC6147]. 166 NAT64: Network Address and Protocol Translation from IPv6 Clients to 167 IPv4 Servers [RFC6146]. 169 RA: Router Advertisement, a message used by IPv6 routers to advertise 170 their presence together with various link and Internet parameters 171 [RFC4861]. 173 DNS64: a mechanism for synthesizing AAAA records from A records 174 [RFC6147]. 176 2. Reasons to Signal IPv6-Only Support in DHCPv4 Packets 178 For networks which contain both IPv6-capable and IPv4-requiring 179 devices and utilize DHCP for configuring the IPv4 network stack on 180 hosts, it seems only natural to leverage the same protocol to signal 181 that IPv4 is discretional on a given segment. Such an approach 182 limits the attack surface to DHCP-related attacks without introducing 183 new vulnerable elements. 185 Another benefit of using DHCPv4 for signaling is that IPv4 will be 186 disabled only if both the client and the server indicate IPv6-only 187 capability. It allows IPv6-only capable hosts to turn off IPv4 only 188 upon receiving an explicit signal from the network and operate in 189 dual-stack or IPv4-only mode otherwise. In addition, the proposed 190 mechanism does not introduce any additional delays to the process of 191 configuring IP stack on hosts. If the network does not support IPv6- 192 only/IPv4-on-demand mode, an IPv6-only capable host would configure 193 an IPv4 address as quickly as on any other host. 195 Coexistence of IPv6-only, dual-stack and even IPv4-only hosts on the 196 same LAN would not only allow network administrators to preserve 197 scarce IPv4 addresses but would also drastically simplify incremental 198 deployment of IPv6-only networks, positively impacting IPv6 adoption. 200 3. IPv6-Only Preferred Option 202 3.1. Option format 204 0 1 2 3 205 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 1 206 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 207 | Code | Length | Value | 208 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 209 | Value (contd) | 210 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 212 Figure 1: IPv6-Only Preferred Option Format 214 Fields: 216 Code 8-bit identifier of the IPv6-Only Preferred option code as 217 assigned by IANA: TBD 218 Length 8-bit unsigned integer. The length of the option excluding 219 the Code and Length Fields. The server MUST set the length 220 field to 4. The receiver MUST ignore the IPv6-Only Preferred 221 option if the length field value is not 4. 222 Value 32-bit unsigned 223 integer. The number of 224 seconds the client should disable DHCPv4 for (V6ONLY_WAIT 225 configuration variable). 226 If the server pool is explicitly configured with a V6ONLY_WAIT 227 timer the server MUST set the field to that configured value. 228 Otherwise the server MUST set it to zero. 229 The client MUST ignore V6ONLY_WAIT timer received from the 230 server if the value is less than MIN_V6ONLY_WAIT. 232 3.2. DHCPv4 Client Behaviour 234 A DHCP client SHOULD allow a device administrator to configure 235 IPv6-only preferred mode either for a specific interface (to indicate 236 that the device is IPv6-only capable if connected to a NAT64 network 237 via that interface) or for all interfaces. If only a specific 238 interface is configured as IPv6-only capable the DHCP client MUST NOT 239 be considered as an IPv6-capable for the purpose of sending/receiving 240 DHCP packets over any other interfaces. 242 If a host is not capable of operating in an IPv6-only NAT64 243 environment its DHCP client MUST NOT include the IPv6-only Preferred 244 option in the Parameter Request List of any DHCP packets and MUST 245 ignore that option in packets received from DHCP servers. 247 DHCP clients running on IPv6-only capable hosts SHOULD include the 248 IPv6-only Preferred option code in the Parameter Request List in 249 DHCPDISCOVER and DHCPREQUEST messages for interfaces so enabled and 250 follow the processing as described below on a per interface enabled 251 basis. 253 If the client did not include the IPv6-only Preferred option code in 254 the Parameter Request List option in the DHCPDISCOVER or DHCPREQUEST 255 message it MUST ignore the IPv6-only Preferred option in any messages 256 received from the server. 258 If the client includes the IPv6-only Preferred option in the 259 Parameter Request List and the DHCPOFFER message from the server 260 contains a valid IPv6-only Preferred option, the client MUST NOT 261 configure the IPv4 address provided in the DHCPOFFER. If the 262 IPv6-only Preferred option returned by the server contains non-zero 263 value greater or equal to MIN_V6ONLY_WAIT, the client SHOULD set the 264 V6ONLY_WAIT timer to that value. Otherwise, the client MUST use its 265 own configuration for V6ONLY_WAIT timer. The client SHOULD stop the 266 DHCP configuration process for at least V6ONLY_WAIT seconds or until 267 a network attachment event happens. The host MAY disable the IPv4 268 stack completely for V6ONLY_WAIT seconds or until the network 269 disconnection event happens. 271 The client SHOULD include the IPv6-only Preferred option in the 272 Parameter Request List option in DHCPREQUEST messages (after 273 receiving a DHCPOFFER without this option, for a INIT-REBOOT, or when 274 renewing or rebinding a leased address). If the DHCP server responds 275 with a DHCPACK that includes the IPv6-only Preferred option, the 276 client MAY send a DHCPRELEASE message and MAY either stop the DHCP 277 configuration process or disable IPv4 stack completely for 278 V6ONLY_WAIT seconds or until the network disconnection event happens. 279 Alternatively the client MAY continue to use the assigned IPv4 280 address until further DHCP reconfiguration events. 282 If the client includes the IPv6-only Preferred option in the 283 Parameter Request List and the server responds with DHCPOFFER message 284 without a valid IPv6-only Preferred option, the client MUST proceed 285 as normal with a DHCPREQUEST. 287 If the client waits for multiple DHCPOFFER responses and selects one 288 of them, it MUST follow the processing for the IPv6-only Preferred 289 option based on the selected response. A client MAY use the presence 290 of the IPv6-only Preferred option as a selection criteria. 292 When an IPv6-only capable client receives the IPv6-Only Preferred 293 option from the server, the client MAY configure IPv4 link-local 294 address [RFC3927]. In that case IPv6-Only capable devices might 295 still be able to communicate over IPv4 to other devices on the link. 296 The Auto-Configure Option [RFC2563] can be used to control IPv4 link- 297 local addresses autoconfiguration. Section 3.3.1 discusses 298 interoperability between the IPv6-only Preferred and the Auto- 299 Configure options. 301 3.3. DHCPv4 Server Behaviour 303 The DHCP server SHOULD be able to configure certain pools to include 304 the IPv6-only preferred option in DHCP responses if the client 305 included the option code in the Parameter Request List option. The 306 DHCP server MAY have a configuration option to specify V6ONLY_WAIT 307 timer for all or individual IPv6-mostly pools. 309 The server MUST NOT include the IPv6-only Preferred option in the 310 DHCPOFFER or DHCPACK message if the YIADDR field in the message does 311 not belong to a pool configured as IPv6-mostly. The server MUST NOT 312 include the IPv6-only Preferred option in the DHCPOFFER or DHCPACK 313 message if the option was not present in the Parameter Request List 314 sent by the client. 316 If the IPv6-only Preferred option is present in the Parameter Request 317 List received from the client and the corresponding DHCP pool is 318 explicitly configured as belonging to an IPv6-mostly network segment, 319 the server MUST include the IPv6-only Preferred option when 320 responding with the DHCPOFFER or DHCPACK message. If the server 321 responds with the IPv6-only Preferred option and the V6ONLY_WAIT 322 timer is configured for the pool, the server MUST copy the configured 323 value to the IPv6-only Preferred option value field. Otherwise it 324 MUST set the field to zero. The server SHOULD not assign an address 325 for the pool. Instead it SHOULD return 0.0.0.0 as the offered 326 address. Alternatively, the server MAY include an available IPv4 327 address from the pool into the DHCPOFFER as per recommendations in 328 [RFC2131] but SHOULD NOT reserve the address and SHOULD NOT verify 329 its uniqueness. 331 If a client includes both a Rapid-Commit option [RFC4039] and 332 IPv6-Only Preferred option in the DHCPDISCOVER message the server 333 SHOULD NOT honor the Rapid-Commit option if the response would 334 contain the IPv6-only Preferred option to the client. It SHOULD 335 instead respond with a DHCPOFFER as indicated above. 337 3.3.1. Interoperability with RFC2563 339 [RFC2563] defines an Auto-Configure DHCP option to disable IPv4 link- 340 local address configuration for IPv4 clients. Clients can support 341 both, neither or just one of IPv6-Only Preferred and Auto-Configure 342 options. If a client sends both IPv6-Only Preferred and Auto- 343 Configure options the network administrator can prevent the host from 344 configuring an IPv4 link-local address on IPv6-mostly network. To 345 achieve this the server needs to send DHCPOFFER which contains a 346 'yiaddr' of 0x00000000, and the Auto-Configure flag saying 347 "DoNotAutoConfigure". 349 However special care should be taken in a situation when a server 350 supports both options and receives just IPv6-Only Preferred option 351 from a client. Section 2.3 of [RFC2563] states that if no address is 352 chosen for the host (which would be the case for IPv6-only capable 353 clients on IPv6-mostly network) then: "If the DHCPDISCOVER does not 354 contain the Auto-Configure option, it is not answered." Such 355 behaviour would be undesirable for clients supporting the IPv6-Only 356 Preferred option w/o supporting the Auto-Configure option as they 357 would not receive any response from the server and would keep asking, 358 instead of disabling DHCP for V6ONLY_WAIT second. Therefore the 359 following update is proposed to Section 2.3 of [RFC2563]" 361 OLD TEXT: 363 --- 365 However, if no address is chosen for the host, a few additional steps 366 MUST be taken. 368 If the DHCPDISCOVER does not contain the Auto-Configure option, it is 369 not answered. 371 --- 373 NEW TEXT: 375 --- 377 However, if no address is chosen for the host, a few additional steps 378 MUST be taken. 380 If the DHCPDISCOVER does not contain the Auto-Configure option and 381 the IPv6-Only Preferred option is not present, it is not answered. 382 If the DHCPDISCOVER does not contain the Auto-Configure option but 383 contains the IPv6-Only Preferred option, the processing rules for the 384 IPv6-Only Preferred option apply. 386 --- 388 3.4. Constants and Configuration Variables 390 V6ONLY_WAIT The minimum time the client SHOULD stop the DHCP 391 configuration process for. MUST be no less than 392 MIN_V6ONLY_WAIT seconds. Default: 1800 seconds 393 MIN_V6ONLY_WAIT The lower boundary for V6ONLY_WAIT. Value: 300 394 seconds 396 4. IPv6-Only Transition Technologies Considerations 398 Until IPv6 adoption in the Internet reaches 100%, communication 399 between an IPv6-only host and IPv4-only destination requires some 400 form of transition mechanism deployed in the network. At the time of 401 writing, the only such mechanism is NAT64 [RFC6146]. Therefore the 402 IPv6-only Preferred option is only sent by hosts capable of operating 403 on NAT64 networks. In a typical deployment scenario, a network 404 administrator would not configure the DHCP server to return the 405 IPv6-only Preferred option unless the network provides NAT64 service. 407 Hypothetically it is possible for multiple transition technologies to 408 coexist. In such scenario some form of negotiation would be required 409 between a client and a server to ensure that the transition 410 technology supported by the client is the one the network provides. 411 However it seems unlikely that any new transition technology would 412 arise and be widely adopted in any foreseeable future. Therefore 413 adding support for non-existing technologies seems to be suboptimal 414 and the proposed mechanism implies that NAT64 is used to facilitate 415 connectivity between IPv6 and IPv4. 417 It should be also noted that declaring a host or (strictly speaking, 418 a host interface) IPv6-only capable is a policy decision. For 419 example, 421 o An operating system vendor may make such decision and configure 422 their DHCP clients to send the IPv6-Only Preferred option by 423 default if the OS has 464XLAT CLAT [RFC6877] enabled. 425 o An enterprise network administrator may provision the corporate 426 hosts as IPv6-only capable if all applications users are supposed 427 to run have been tested in IPv6-only environment (or if 464XLAT 428 CLAT is enabled on the devices). 430 o IoT devices may be shipped in IPv6-only capable mode if they are 431 designed to connect to IPv6-enabled cloud destination only. 433 5. IANA Considerations 435 The IANA is requested to assign a new DHCP Option code for the 436 IPv6-Only Preferred option from the BOOTP Vendor Extensions and DHCP 437 Options registry, located at https://www.iana.org/assignments/bootp- 438 dhcp-parameters/bootp-dhcp-parameters.xhtml#options . If possible, 439 please assign option code 108. 441 +----------------------------+-------+ 442 | Option Name | Code | 443 +----------------------------+-------+ 444 | IPv6-only Preferred option | (TBD) | 445 +----------------------------+-------+ 447 Table 1 449 6. Security Considerations 451 The proposed mechanism is not introducing any new security 452 implications. While clients using the IPv6-only Preferred option are 453 vulnerable to attacks related to a rogue DHCP server, enabling 454 IPv6-only Preferred option does not provide an attacker with any 455 additional mechanisms. 457 It should be noted that disabling IPv4 on a host upon receiving the 458 IPv6-only Preferred option from the DHCP server protects the host 459 from IPv4-related attacks and therefore could be considered a 460 security feature. 462 7. Acknowledgements 464 Thanks to the following people (in alphabetical order) for their 465 review and feedback: Mohamed Boucadair, Ted Lemon, Roy Marples, Bjorn 466 Mork, Bernie Volz (AI: add more names here). Authors would like to 467 thank Bob Hinden and Brian Carpenter for the initial idea of 468 signaling IPv6-only capability to hosts. 470 8. References 471 8.1. Normative References 473 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 474 Requirement Levels", BCP 14, RFC 2119, 475 DOI 10.17487/RFC2119, March 1997, 476 . 478 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 479 RFC 2131, DOI 10.17487/RFC2131, March 1997, 480 . 482 [RFC2563] Troll, R., "DHCP Option to Disable Stateless Auto- 483 Configuration in IPv4 Clients", RFC 2563, 484 DOI 10.17487/RFC2563, May 1999, 485 . 487 [RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic 488 Configuration of IPv4 Link-Local Addresses", RFC 3927, 489 DOI 10.17487/RFC3927, May 2005, 490 . 492 [RFC4039] Park, S., Kim, P., and B. Volz, "Rapid Commit Option for 493 the Dynamic Host Configuration Protocol version 4 494 (DHCPv4)", RFC 4039, DOI 10.17487/RFC4039, March 2005, 495 . 497 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 498 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 499 DOI 10.17487/RFC4861, September 2007, 500 . 502 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 503 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 504 May 2017, . 506 8.2. Informative References 508 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 509 NAT64: Network Address and Protocol Translation from IPv6 510 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 511 April 2011, . 513 [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van 514 Beijnum, "DNS64: DNS Extensions for Network Address 515 Translation from IPv6 Clients to IPv4 Servers", RFC 6147, 516 DOI 10.17487/RFC6147, April 2011, 517 . 519 [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: 520 Combination of Stateful and Stateless Translation", 521 RFC 6877, DOI 10.17487/RFC6877, April 2013, 522 . 524 Authors' Addresses 526 Lorenzo Colitti 527 Google 528 Shibuya 3-21-3 529 Shibuya, Tokyo 150-0002 530 JP 532 Email: lorenzo@google.com 534 Jen Linkova 535 Google 536 1 Darling Island Rd 537 Pyrmont, NSW 2009 538 AU 540 Email: furry@google.com 542 Michael C. Richardson 543 Sandelman Software Works 545 Email: mcr+ietf@sandelman.ca 546 URI: http://www.sandelman.ca/ 548 Tomek Mrugalski 549 Internet Systems Consortium, Inc. 550 950 Charter Street 551 Redwood City, CA 94063 552 USA 554 Email: tomasz.mrugalski@gmail.com