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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 DHCPv4 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]. In this case, the offered address MUST be a valid address that is not committed to any other client. Because the client is not expected ever to request this address, the server SHOULD NOT reserve the address and SHOULD NOT verify its uniqueness. If the client then issues a DHCPREQUEST for the address, the server MUST process it per [RFC2131], including replying with a DHCPACK for the address if in the meantime it has not been committed to another client. (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 (June 15, 2020) is 1411 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: 1 error (**), 0 flaws (~~), 2 warnings (==), 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: December 17, 2020 Sandelman 7 T. Mrugalski 8 ISC 9 June 15, 2020 11 IPv6-Only-Preferred Option for DHCPv4 12 draft-ietf-dhc-v6only-02 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 December 17, 2020. 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 . . . . 4 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. 155 IPv4-requiring host: a host which is not IPv6-only capable and can 156 not operate in IPv6-only network providing NAT64 service. 158 IPv4-on-demand: a deployment scenario when end hosts are expected to 159 operate in IPv6-only mode by default and IPv4 addresses can be 160 assigned to some hosts if those hosts explicitly opt-in to receiving 161 IPv4 addresses. 163 IPv6-mostly network: a network which provides NAT64 (possibly with 164 DNS64) service as well as IPv4 connectivity and allows coexistence of 165 IPv6-only, dual-stack and IPv4-only hosts on the same segment. Such 166 deployment scenario allows operators to incrementally turn off IPv4 167 on end hosts, while still providing IPv4 to devices which require 168 IPv4 to operate. But, IPv6-only capable devices need not be assigned 169 IPv4 addresses. 171 IPv6-Only network: a network which does not provide routing 172 functionality for IPv4 packets. Such networks may or may not allow 173 intra-LAN IPv4 connectivity. IPv6-Only network usually provides 174 access to IPv4-only resources via NAT64 [RFC6146]. 176 NAT64: Network Address and Protocol Translation from IPv6 Clients to 177 IPv4 Servers [RFC6146]. 179 RA: Router Advertisement, a message used by IPv6 routers to advertise 180 their presence together with various link and Internet parameters 181 [RFC4861]. 183 DNS64: a mechanism for synthesizing AAAA records from A records 184 [RFC6147]. 186 2. Reasons to Signal IPv6-Only Support in DHCPv4 Packets 188 For networks which contain both IPv6-only capable and IPv4-requiring 189 hosts and utilize DHCPv4 for configuring the IPv4 network stack on 190 hosts, it seems only natural to leverage the same protocol to signal 191 that IPv4 is discretional on a given segment. An ability to remotely 192 disable IPv4 on a host can be seen as a new denial-of-service attack 193 vector. The proposed approach limits the attack surface to 194 DHCPv4-related attacks without introducing new vulnerable elements. 196 Another benefit of using DHCPv4 for signaling is that IPv4 will be 197 disabled only if both the client and the server indicate IPv6-only 198 capability. It allows IPv6-only capable hosts to turn off IPv4 only 199 upon receiving an explicit signal from the network and operate in 200 dual-stack or IPv4-only mode otherwise. In addition, the proposed 201 mechanism does not introduce any additional delays to the process of 202 configuring IP stack on hosts. If the network does not support IPv6- 203 only/IPv4-on-demand mode, an IPv6-only capable host would configure 204 an IPv4 address as quickly as on any other host. 206 Being a client/server protocol, DHCPv4 allows IPv4 to be selectively 207 disabled on a per-host basis on a given network segment. Coexistence 208 of IPv6-only, dual-stack and even IPv4-only hosts on the same LAN 209 would not only allow network administrators to preserve scarce IPv4 210 addresses but would also drastically simplify incremental deployment 211 of IPv6-only networks, positively impacting IPv6 adoption. 213 3. IPv6-Only Preferred Option 215 3.1. Option format 217 0 1 2 3 218 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 1 219 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 220 | Code | Length | Value | 221 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 222 | Value (contd) | 223 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 225 Figure 1: IPv6-Only Preferred Option Format 227 Fields: 229 Code: 8-bit identifier of the IPv6-Only Preferred option code as 230 assigned by IANA: TBD 231 Length: 8-bit unsigned integer. The length of the option excluding 232 the Code and Length Fields. The server MUST set the length 233 field to 4. The client MUST ignore the IPv6-Only Preferred 234 option if the length field value is not 4. 235 Value: 32-bit unsigned integer. 236 The number of seconds the client should disable DHCPv4 for 237 (V6ONLY_WAIT configuration variable). 238 If the server pool is explicitly configured with a 239 V6ONLY_WAIT timer the server MUST set the field to that 240 configured value. Otherwise the server MUST set it to zero. 241 The client MUST process that field as described in 242 Section 3.2. 244 3.2. DHCPv4 Client Behavior 246 A DHCPv4 client SHOULD allow a device administrator to configure 247 IPv6-only preferred mode either for a specific interface (to indicate 248 that the device is IPv6-only capable if connected to a NAT64 network 249 via that interface) or for all interfaces. If only a specific 250 interface is configured as IPv6-only capable the DHCPv4 client MUST 251 NOT consider the host to be an IPv6-only capable for the purpose of 252 sending/receiving DHCPv4 packets over any other interfaces. 254 The DHCPv4 client on an IPv4-requiring host MUST NOT include the 255 IPv6-only Preferred option in the Parameter Request List of any 256 DHCPv4 packets and MUST ignore that option in packets received from 257 DHCPv4 servers. 259 DHCPv4 clients running on IPv6-only capable hosts SHOULD include the 260 IPv6-only Preferred option code in the Parameter Request List in 261 DHCPDISCOVER and DHCPREQUEST messages for interfaces so enabled and 262 follow the processing as described below on a per interface enabled 263 basis. 265 If the client did not include the IPv6-only Preferred option code in 266 the Parameter Request List option in the DHCPDISCOVER or DHCPREQUEST 267 message it MUST ignore the IPv6-only Preferred option in any messages 268 received from the server. 270 If the client includes the IPv6-only Preferred option in the 271 Parameter Request List and the DHCPOFFER message from the server 272 contains a valid IPv6-only Preferred option, the client SHOULD NOT 273 request the IPv4 address provided in the DHCPOFFER. If the IPv6-only 274 Preferred option returned by the server contains a value greater or 275 equal to MIN_V6ONLY_WAIT, the client SHOULD set the V6ONLY_WAIT timer 276 to that value. Otherwise, the client SHOULD set the V6ONLY_WAIT 277 timer to MIN_V6ONLY_WAIT. The client SHOULD stop the DHCPv4 278 configuration process for at least V6ONLY_WAIT seconds or until a 279 network attachment event happens. The host MAY disable the IPv4 280 stack completely for V6ONLY_WAIT seconds or until the network 281 disconnection event happens. 283 The IPv6-only Preferred option SHOULD be included in the Parameter 284 Request List option in DHCPREQUEST messages (after receiving a 285 DHCPOFFER without this option, for a INIT-REBOOT, or when renewing or 286 rebinding a leased address). If the DHCPv4 server responds with a 287 DHCPACK that includes the IPv6-only Preferred option, the client MAY 288 send a DHCPRELEASE message and MAY either stop the DHCPv4 289 configuration process or disable IPv4 stack completely for 290 V6ONLY_WAIT seconds or until the network disconnection event happens. 291 Alternatively the client MAY continue to use the assigned IPv4 292 address until further DHCPv4 reconfiguration events. 294 If the client includes the IPv6-only Preferred option in the 295 Parameter Request List and the server responds with DHCPOFFER message 296 without a valid IPv6-only Preferred option, the client MUST proceed 297 as normal with a DHCPREQUEST. 299 If the client waits for multiple DHCPOFFER responses and selects one 300 of them, it MUST follow the processing for the IPv6-only Preferred 301 option based on the selected response. A client MAY use the presence 302 of the IPv6-only Preferred option as a selection criteria. 304 When an IPv6-only capable client receives the IPv6-Only Preferred 305 option from the server, the client MAY configure IPv4 link-local 306 address [RFC3927]. In that case IPv6-Only capable devices might 307 still be able to communicate over IPv4 to other devices on the link. 308 The Auto-Configure Option [RFC2563] can be used to control IPv4 link- 309 local addresses autoconfiguration. Section 3.3.1 discusses the 310 interaction between the IPv6-only Preferred and the Auto-Configure 311 options. 313 3.3. DHCPv4 Server Behavior 315 The DHCPv4 server SHOULD be able to configure certain pools to 316 include the IPv6-only preferred option in DHCPv4 responses if the 317 client included the option code in the Parameter Request List option. 318 The DHCPv4 server MAY have a configuration option to specify 319 V6ONLY_WAIT timer for all or individual IPv6-mostly pools. 321 The server MUST NOT include the IPv6-only Preferred option in the 322 DHCPOFFER or DHCPACK message if the YIADDR field in the message does 323 not belong to a pool configured as IPv6-mostly. The server MUST NOT 324 include the IPv6-only Preferred option in the DHCPOFFER or DHCPACK 325 message if the option was not present in the Parameter Request List 326 sent by the client. 328 If the IPv6-only Preferred option is present in the Parameter Request 329 List received from the client and the corresponding DHCPv4 pool is 330 explicitly configured as belonging to an IPv6-mostly network segment, 331 the server MUST include the IPv6-only Preferred option when 332 responding with the DHCPOFFER or DHCPACK message. If the server 333 responds with the IPv6-only Preferred option and the V6ONLY_WAIT 334 timer is configured for the pool, the server MUST copy the configured 335 value to the IPv6-only Preferred option value field. Otherwise it 336 MUST set the field to zero. The server SHOULD not assign an address 337 for the pool. Instead it SHOULD return 0.0.0.0 as the offered 338 address. Alternatively, the server MAY include an available IPv4 339 address from the pool into the DHCPOFFER as per recommendations in 340 [RFC2131]. In this case, the offered address MUST be a valid address 341 that is not committed to any other client. Because the client is not 342 expected ever to request this address, the server SHOULD NOT reserve 343 the address and SHOULD NOT verify its uniqueness. If the client then 344 issues a DHCPREQUEST for the address, the server MUST process it per 345 [RFC2131], including replying with a DHCPACK for the address if in 346 the meantime it has not been committed to another client. 348 If a client includes both a Rapid-Commit option [RFC4039] and 349 IPv6-Only Preferred option in the DHCPDISCOVER message the server 350 SHOULD NOT honor the Rapid-Commit option if the response would 351 contain the IPv6-only Preferred option to the client. It SHOULD 352 instead respond with a DHCPOFFER as indicated above. 354 3.3.1. Interaction with RFC2563 356 [RFC2563] defines an Auto-Configure DHCPv4 option to disable IPv4 357 link-local address configuration for IPv4 clients. Clients can 358 support both, neither or just one of IPv6-Only Preferred and Auto- 359 Configure options. If a client sends both IPv6-Only Preferred and 360 Auto-Configure options the network administrator can prevent the host 361 from configuring an IPv4 link-local address on IPv6-mostly network. 362 To achieve this the server needs to send DHCPOFFER which contains a 363 'yiaddr' of 0x00000000, and the Auto-Configure flag saying 364 "DoNotAutoConfigure". 366 However special care should be taken in a situation when a server 367 supports both options and receives just IPv6-Only Preferred option 368 from a client. Section 2.3 of [RFC2563] states that if no address is 369 chosen for the host (which would be the case for IPv6-only capable 370 clients on IPv6-mostly network) then: "If the DHCPDISCOVER does not 371 contain the Auto-Configure option, it is not answered." Such 372 behavior would be undesirable for clients supporting the IPv6-Only 373 Preferred option w/o supporting the Auto-Configure option as they 374 would not receive any response from the server and would keep asking, 375 instead of disabling DHCPv4 for V6ONLY_WAIT second. Therefore the 376 following update is proposed to Section 2.3 of [RFC2563]" 378 OLD TEXT: 380 --- 382 However, if no address is chosen for the host, a few additional steps 383 MUST be taken. 385 If the DHCPDISCOVER does not contain the Auto-Configure option, it is 386 not answered. 388 --- 390 NEW TEXT: 392 --- 394 However, if no address is chosen for the host, a few additional steps 395 MUST be taken. 397 If the DHCPDISCOVER does not contain the Auto-Configure option and 398 the IPv6-Only Preferred option is not present, it is not answered. 399 If the DHCPDISCOVER does not contain the Auto-Configure option but 400 contains the IPv6-Only Preferred option, the processing rules for the 401 IPv6-Only Preferred option apply. 403 --- 405 3.4. Constants and Configuration Variables 407 V6ONLY_WAIT The minimum time the client SHOULD stop the DHCPv4 408 configuration process for. MUST be no less than 409 MIN_V6ONLY_WAIT seconds. Default: 1800 seconds 410 MIN_V6ONLY_WAIT The lower boundary for V6ONLY_WAIT. Value: 300 411 seconds 413 4. IPv6-Only Transition Technologies Considerations 415 Until IPv6 adoption in the Internet reaches 100%, communication 416 between an IPv6-only host and IPv4-only destination requires some 417 form of transition mechanism deployed in the network. At the time of 418 writing, the only such mechanism that is widely supported by end 419 hosts is NAT64 [RFC6146] (either with or without 464XLAT). Therefore 420 the IPv6-only Preferred option is only sent by hosts capable of 421 operating on NAT64 networks. In a typical deployment scenario, a 422 network administrator would not configure the DHCPv4 server to return 423 the IPv6-only Preferred option unless the network provides NAT64 424 service. 426 Hypothetically it is possible for multiple transition technologies to 427 coexist. In such scenario some form of negotiation would be required 428 between a client and a server to ensure that the transition 429 technology supported by the client is the one the network provides. 430 However it seems unlikely that any new transition technology would 431 arise and be widely adopted in any foreseeable future. Therefore 432 adding support for non-existing technologies seems to be suboptimal 433 and the proposed mechanism implies that NAT64 is used to facilitate 434 connectivity between IPv6 and IPv4. 436 It should be also noted that declaring a host or (strictly speaking, 437 a host interface) IPv6-only capable is a policy decision. For 438 example, 440 o An operating system vendor may make such decision and configure 441 their DHCPv4 clients to send the IPv6-Only Preferred option by 442 default if the OS has 464XLAT CLAT [RFC6877] enabled. 444 o An enterprise network administrator may provision the corporate 445 hosts as IPv6-only capable if all applications users are supposed 446 to run have been tested in IPv6-only environment (or if 464XLAT 447 CLAT is enabled on the devices). 449 o IoT devices may be shipped in IPv6-only capable mode if they are 450 designed to connect to IPv6-enabled cloud destination only. 452 5. IANA Considerations 454 The IANA is requested to assign a new DHCPv4 Option code for the 455 IPv6-Only Preferred option from the BOOTP Vendor Extensions and 456 DHCPv4 Options registry, located at https://www.iana.org/assignments/ 457 bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml#options . If 458 possible, please assign option code 108. 460 +----------------------------+-------+ 461 | Option Name | Code | 462 +----------------------------+-------+ 463 | IPv6-only Preferred option | (TBD) | 464 +----------------------------+-------+ 466 Table 1 468 6. Security Considerations 470 The proposed mechanism is not introducing any new security 471 implications. While clients using the IPv6-only Preferred option are 472 vulnerable to attacks related to a rogue DHCPv4 server, enabling 473 IPv6-only Preferred option does not provide an attacker with any 474 additional mechanisms. 476 It should be noted that disabling IPv4 on a host upon receiving the 477 IPv6-only Preferred option from the DHCPv4 server protects the host 478 from IPv4-related attacks and therefore could be considered a 479 security feature. 481 7. Acknowledgements 483 Thanks to the following people (in alphabetical order) for their 484 review and feedback: Mohamed Boucadair, Ted Lemon, Roy Marples, Bjorn 485 Mork, Peng Shuping, Bernie Volz, Eric Vyncke. Authors would like to 486 thank Bob Hinden and Brian Carpenter for the initial idea of 487 signaling IPv6-only capability to hosts. Special thanks to Erik 488 Kline, Mark Townsley and Maciej Zenczykowski for the discussion which 489 led to the idea of signalling IPv6-only capability over DHCPv4. 491 8. References 493 8.1. Normative References 495 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 496 Requirement Levels", BCP 14, RFC 2119, 497 DOI 10.17487/RFC2119, March 1997, 498 . 500 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 501 RFC 2131, DOI 10.17487/RFC2131, March 1997, 502 . 504 [RFC2563] Troll, R., "DHCP Option to Disable Stateless Auto- 505 Configuration in IPv4 Clients", RFC 2563, 506 DOI 10.17487/RFC2563, May 1999, 507 . 509 [RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic 510 Configuration of IPv4 Link-Local Addresses", RFC 3927, 511 DOI 10.17487/RFC3927, May 2005, 512 . 514 [RFC4039] Park, S., Kim, P., and B. Volz, "Rapid Commit Option for 515 the Dynamic Host Configuration Protocol version 4 516 (DHCPv4)", RFC 4039, DOI 10.17487/RFC4039, March 2005, 517 . 519 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 520 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 521 DOI 10.17487/RFC4861, September 2007, 522 . 524 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 525 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 526 May 2017, . 528 8.2. Informative References 530 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 531 NAT64: Network Address and Protocol Translation from IPv6 532 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 533 April 2011, . 535 [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van 536 Beijnum, "DNS64: DNS Extensions for Network Address 537 Translation from IPv6 Clients to IPv4 Servers", RFC 6147, 538 DOI 10.17487/RFC6147, April 2011, 539 . 541 [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: 542 Combination of Stateful and Stateless Translation", 543 RFC 6877, DOI 10.17487/RFC6877, April 2013, 544 . 546 Authors' Addresses 548 Lorenzo Colitti 549 Google 550 Shibuya 3-21-3 551 Shibuya, Tokyo 150-0002 552 JP 554 Email: lorenzo@google.com 555 Jen Linkova 556 Google 557 1 Darling Island Rd 558 Pyrmont, NSW 2009 559 AU 561 Email: furry@google.com 563 Michael C. Richardson 564 Sandelman Software Works 566 Email: mcr+ietf@sandelman.ca 567 URI: http://www.sandelman.ca/ 569 Tomek Mrugalski 570 Internet Systems Consortium, Inc. 571 950 Charter Street 572 Redwood City, CA 94063 573 USA 575 Email: tomasz.mrugalski@gmail.com