idnits 2.17.1 draft-ietf-dhc-v6only-01.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The abstract seems to contain references ([RFC2563]), which it shouldn't. Please replace those with straight textual mentions of the documents in question. 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]. 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 (May 31, 2020) is 1426 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 2, 2020 Sandelman 7 T. Mrugalski 8 ISC 9 May 31, 2020 11 IPv6-Only-Preferred Option for DHCP 12 draft-ietf-dhc-v6only-01 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. It also updates 19 [RFC2563] to specify the DHCP 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 2, 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 . . . . . . . . . . . . . . . . . . . 10 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 DHCP 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, it might be practically undesirable. One 112 important reason is that when a host connects to a network, it does 113 not know if the network is IPv4-only, dual-stack or IPv6-only. To 114 ensure that the connectivity over whatever protocol is present 115 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) is available. The proposed solution is 126 to introduce a new DHCP option which a client uses to indicate that 127 it does not need an IPv4 address if the network provides IPv6-only 128 connectivity (as NAT64 and DNS64). If the particular network segment 129 provides IPv4-on-demand such clients would not be supplied with IPv4 130 addresses, while on IPv4-only or dual-stack segments without NAT64 131 services IPv4 addresses will be provided. 133 [RFC2563] introduces the Auto-Configure DHCP option and describes 134 DHCP 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 DHCP 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. Such an approach 192 limits the attack surface to DHCP-related attacks without introducing 193 new vulnerable elements. 195 Another benefit of using DHCPv4 for signaling is that IPv4 will be 196 disabled only if both the client and the server indicate IPv6-only 197 capability. It allows IPv6-only capable hosts to turn off IPv4 only 198 upon receiving an explicit signal from the network and operate in 199 dual-stack or IPv4-only mode otherwise. In addition, the proposed 200 mechanism does not introduce any additional delays to the process of 201 configuring IP stack on hosts. If the network does not support IPv6- 202 only/IPv4-on-demand mode, an IPv6-only capable host would configure 203 an IPv4 address as quickly as on any other host. 205 Coexistence of IPv6-only, dual-stack and even IPv4-only hosts on the 206 same LAN would not only allow network administrators to preserve 207 scarce IPv4 addresses but would also drastically simplify incremental 208 deployment of IPv6-only networks, positively impacting IPv6 adoption. 210 3. IPv6-Only Preferred Option 212 3.1. Option format 214 0 1 2 3 215 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 1 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 | Code | Length | Value | 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 219 | Value (contd) | 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 222 Figure 1: IPv6-Only Preferred Option Format 224 Fields: 226 Code: 8-bit identifier of the IPv6-Only Preferred option code as 227 assigned by IANA: TBD 228 Length: 8-bit unsigned integer. The length of the option excluding 229 the Code and Length Fields. The server MUST set the length 230 field to 4. The receiver MUST ignore the IPv6-Only Preferred 231 option if the length field value is not 4. 232 Value: 32-bit unsigned integer. 233 The number of seconds the client should disable DHCPv4 for 234 (V6ONLY_WAIT configuration variable). 235 If the server pool is explicitly configured with a 236 V6ONLY_WAIT timer the server MUST set the field to that 237 configured value. Otherwise the server MUST set it to zero. 238 The client MUST process that field as described in 239 Section 3.2. 241 3.2. DHCPv4 Client Behavior 243 A DHCP client SHOULD allow a device administrator to configure 244 IPv6-only preferred mode either for a specific interface (to indicate 245 that the device is IPv6-only capable if connected to a NAT64 network 246 via that interface) or for all interfaces. If only a specific 247 interface is configured as IPv6-only capable the DHCP client MUST NOT 248 consider the host to be an IPv6-only capable for the purpose of 249 sending/receiving DHCP packets over any other interfaces. 251 The DHCP client on an IPv4-requiring host MUST NOT include the 252 IPv6-only Preferred option in the Parameter Request List of any DHCP 253 packets and MUST ignore that option in packets received from DHCP 254 servers. 256 DHCP clients running on IPv6-only capable hosts SHOULD include the 257 IPv6-only Preferred option code in the Parameter Request List in 258 DHCPDISCOVER and DHCPREQUEST messages for interfaces so enabled and 259 follow the processing as described below on a per interface enabled 260 basis. 262 If the client did not include the IPv6-only Preferred option code in 263 the Parameter Request List option in the DHCPDISCOVER or DHCPREQUEST 264 message it MUST ignore the IPv6-only Preferred option in any messages 265 received from the server. 267 If the client includes the IPv6-only Preferred option in the 268 Parameter Request List and the DHCPOFFER message from the server 269 contains a valid IPv6-only Preferred option, the client SHOULD NOT 270 request the IPv4 address provided in the DHCPOFFER. If the IPv6-only 271 Preferred option returned by the server contains a value greater or 272 equal to MIN_V6ONLY_WAIT, the client SHOULD set the V6ONLY_WAIT timer 273 to that value. Otherwise, the client SHOULD set the V6ONLY_WAIT 274 timer to MIN_V6ONLY_WAIT. The client SHOULD stop the DHCP 275 configuration process for at least V6ONLY_WAIT seconds or until a 276 network attachment event happens. The host MAY disable the IPv4 277 stack completely for V6ONLY_WAIT seconds or until the network 278 disconnection event happens. 280 The IPv6-only Preferred option SHOULD be included in the Parameter 281 Request List option in DHCPREQUEST messages (after receiving a 282 DHCPOFFER without this option, for a INIT-REBOOT, or when renewing or 283 rebinding a leased address). If the DHCP server responds with a 284 DHCPACK that includes the IPv6-only Preferred option, the client MAY 285 send a DHCPRELEASE message and MAY either stop the DHCP configuration 286 process or disable IPv4 stack completely for V6ONLY_WAIT seconds or 287 until the network disconnection event happens. Alternatively the 288 client MAY continue to use the assigned IPv4 address until further 289 DHCP reconfiguration events. 291 If the client includes the IPv6-only Preferred option in the 292 Parameter Request List and the server responds with DHCPOFFER message 293 without a valid IPv6-only Preferred option, the client MUST proceed 294 as normal with a DHCPREQUEST. 296 If the client waits for multiple DHCPOFFER responses and selects one 297 of them, it MUST follow the processing for the IPv6-only Preferred 298 option based on the selected response. A client MAY use the presence 299 of the IPv6-only Preferred option as a selection criteria. 301 When an IPv6-only capable client receives the IPv6-Only Preferred 302 option from the server, the client MAY configure IPv4 link-local 303 address [RFC3927]. In that case IPv6-Only capable devices might 304 still be able to communicate over IPv4 to other devices on the link. 305 The Auto-Configure Option [RFC2563] can be used to control IPv4 link- 306 local addresses autoconfiguration. Section 3.3.1 discusses the 307 interaction between the IPv6-only Preferred and the Auto-Configure 308 options. 310 3.3. DHCPv4 Server Behavior 312 The DHCP server SHOULD be able to configure certain pools to include 313 the IPv6-only preferred option in DHCP responses if the client 314 included the option code in the Parameter Request List option. The 315 DHCP server MAY have a configuration option to specify V6ONLY_WAIT 316 timer for all or individual IPv6-mostly pools. 318 The server MUST NOT include the IPv6-only Preferred option in the 319 DHCPOFFER or DHCPACK message if the YIADDR field in the message does 320 not belong to a pool configured as IPv6-mostly. The server MUST NOT 321 include the IPv6-only Preferred option in the DHCPOFFER or DHCPACK 322 message if the option was not present in the Parameter Request List 323 sent by the client. 325 If the IPv6-only Preferred option is present in the Parameter Request 326 List received from the client and the corresponding DHCP pool is 327 explicitly configured as belonging to an IPv6-mostly network segment, 328 the server MUST include the IPv6-only Preferred option when 329 responding with the DHCPOFFER or DHCPACK message. If the server 330 responds with the IPv6-only Preferred option and the V6ONLY_WAIT 331 timer is configured for the pool, the server MUST copy the configured 332 value to the IPv6-only Preferred option value field. Otherwise it 333 MUST set the field to zero. The server SHOULD not assign an address 334 for the pool. Instead it SHOULD return 0.0.0.0 as the offered 335 address. Alternatively, the server MAY include an available IPv4 336 address from the pool into the DHCPOFFER as per recommendations in 337 [RFC2131]. In this case, the offered address MUST be a valid address 338 that is not committed to any other client. Because the client is not 339 expected ever to request this address, the server SHOULD NOT reserve 340 the address and SHOULD NOT verify its uniqueness. If the client then 341 issues a DHCPREQUEST for the address, the server MUST process it per 342 [RFC2131], including replying with a DHCPACK for the address if in 343 the meantime it has not been committed to another client. 345 If a client includes both a Rapid-Commit option [RFC4039] and 346 IPv6-Only Preferred option in the DHCPDISCOVER message the server 347 SHOULD NOT honor the Rapid-Commit option if the response would 348 contain the IPv6-only Preferred option to the client. It SHOULD 349 instead respond with a DHCPOFFER as indicated above. 351 3.3.1. Interaction with RFC2563 353 [RFC2563] defines an Auto-Configure DHCP option to disable IPv4 link- 354 local address configuration for IPv4 clients. Clients can support 355 both, neither or just one of IPv6-Only Preferred and Auto-Configure 356 options. If a client sends both IPv6-Only Preferred and Auto- 357 Configure options the network administrator can prevent the host from 358 configuring an IPv4 link-local address on IPv6-mostly network. To 359 achieve this the server needs to send DHCPOFFER which contains a 360 'yiaddr' of 0x00000000, and the Auto-Configure flag saying 361 "DoNotAutoConfigure". 363 However special care should be taken in a situation when a server 364 supports both options and receives just IPv6-Only Preferred option 365 from a client. Section 2.3 of [RFC2563] states that if no address is 366 chosen for the host (which would be the case for IPv6-only capable 367 clients on IPv6-mostly network) then: "If the DHCPDISCOVER does not 368 contain the Auto-Configure option, it is not answered." Such 369 behavior would be undesirable for clients supporting the IPv6-Only 370 Preferred option w/o supporting the Auto-Configure option as they 371 would not receive any response from the server and would keep asking, 372 instead of disabling DHCP for V6ONLY_WAIT second. Therefore the 373 following update is proposed to Section 2.3 of [RFC2563]" 375 OLD TEXT: 377 --- 379 However, if no address is chosen for the host, a few additional steps 380 MUST be taken. 382 If the DHCPDISCOVER does not contain the Auto-Configure option, it is 383 not answered. 385 --- 387 NEW TEXT: 389 --- 391 However, if no address is chosen for the host, a few additional steps 392 MUST be taken. 394 If the DHCPDISCOVER does not contain the Auto-Configure option and 395 the IPv6-Only Preferred option is not present, it is not answered. 396 If the DHCPDISCOVER does not contain the Auto-Configure option but 397 contains the IPv6-Only Preferred option, the processing rules for the 398 IPv6-Only Preferred option apply. 400 --- 402 3.4. Constants and Configuration Variables 404 V6ONLY_WAIT The minimum time the client SHOULD stop the DHCP 405 configuration process for. MUST be no less than 406 MIN_V6ONLY_WAIT seconds. Default: 1800 seconds 407 MIN_V6ONLY_WAIT The lower boundary for V6ONLY_WAIT. Value: 300 408 seconds 410 4. IPv6-Only Transition Technologies Considerations 412 Until IPv6 adoption in the Internet reaches 100%, communication 413 between an IPv6-only host and IPv4-only destination requires some 414 form of transition mechanism deployed in the network. At the time of 415 writing, the only such mechanism that is widely supported by end 416 hosts is NAT64 [RFC6146] (either with or without 464XLAT). Therefore 417 the IPv6-only Preferred option is only sent by hosts capable of 418 operating on NAT64 networks. In a typical deployment scenario, a 419 network administrator would not configure the DHCP server to return 420 the IPv6-only Preferred option unless the network provides NAT64 421 service. 423 Hypothetically it is possible for multiple transition technologies to 424 coexist. In such scenario some form of negotiation would be required 425 between a client and a server to ensure that the transition 426 technology supported by the client is the one the network provides. 427 However it seems unlikely that any new transition technology would 428 arise and be widely adopted in any foreseeable future. Therefore 429 adding support for non-existing technologies seems to be suboptimal 430 and the proposed mechanism implies that NAT64 is used to facilitate 431 connectivity between IPv6 and IPv4. 433 It should be also noted that declaring a host or (strictly speaking, 434 a host interface) IPv6-only capable is a policy decision. For 435 example, 437 o An operating system vendor may make such decision and configure 438 their DHCP clients to send the IPv6-Only Preferred option by 439 default if the OS has 464XLAT CLAT [RFC6877] enabled. 441 o An enterprise network administrator may provision the corporate 442 hosts as IPv6-only capable if all applications users are supposed 443 to run have been tested in IPv6-only environment (or if 464XLAT 444 CLAT is enabled on the devices). 446 o IoT devices may be shipped in IPv6-only capable mode if they are 447 designed to connect to IPv6-enabled cloud destination only. 449 5. IANA Considerations 451 The IANA is requested to assign a new DHCP Option code for the 452 IPv6-Only Preferred option from the BOOTP Vendor Extensions and DHCP 453 Options registry, located at https://www.iana.org/assignments/bootp- 454 dhcp-parameters/bootp-dhcp-parameters.xhtml#options . If possible, 455 please assign option code 108. 457 +----------------------------+-------+ 458 | Option Name | Code | 459 +----------------------------+-------+ 460 | IPv6-only Preferred option | (TBD) | 461 +----------------------------+-------+ 463 Table 1 465 6. Security Considerations 467 The proposed mechanism is not introducing any new security 468 implications. While clients using the IPv6-only Preferred option are 469 vulnerable to attacks related to a rogue DHCP server, enabling 470 IPv6-only Preferred option does not provide an attacker with any 471 additional mechanisms. 473 It should be noted that disabling IPv4 on a host upon receiving the 474 IPv6-only Preferred option from the DHCP server protects the host 475 from IPv4-related attacks and therefore could be considered a 476 security feature. 478 7. Acknowledgements 480 Thanks to the following people (in alphabetical order) for their 481 review and feedback: Mohamed Boucadair, Ted Lemon, Roy Marples, Bjorn 482 Mork, Peng Shuping, Bernie Volz. Authors would like to thank Bob 483 Hinden and Brian Carpenter for the initial idea of signaling 484 IPv6-only capability to hosts. Special thanks to Erik Kline, Mark 485 Townsley and Maciej Zenczykowski for the discussion which led to the 486 idea of signalling IPv6-only capability over DHCPv4. 488 8. References 490 8.1. Normative References 492 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 493 Requirement Levels", BCP 14, RFC 2119, 494 DOI 10.17487/RFC2119, March 1997, 495 . 497 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 498 RFC 2131, DOI 10.17487/RFC2131, March 1997, 499 . 501 [RFC2563] Troll, R., "DHCP Option to Disable Stateless Auto- 502 Configuration in IPv4 Clients", RFC 2563, 503 DOI 10.17487/RFC2563, May 1999, 504 . 506 [RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic 507 Configuration of IPv4 Link-Local Addresses", RFC 3927, 508 DOI 10.17487/RFC3927, May 2005, 509 . 511 [RFC4039] Park, S., Kim, P., and B. Volz, "Rapid Commit Option for 512 the Dynamic Host Configuration Protocol version 4 513 (DHCPv4)", RFC 4039, DOI 10.17487/RFC4039, March 2005, 514 . 516 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 517 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 518 DOI 10.17487/RFC4861, September 2007, 519 . 521 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 522 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 523 May 2017, . 525 8.2. Informative References 527 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 528 NAT64: Network Address and Protocol Translation from IPv6 529 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 530 April 2011, . 532 [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van 533 Beijnum, "DNS64: DNS Extensions for Network Address 534 Translation from IPv6 Clients to IPv4 Servers", RFC 6147, 535 DOI 10.17487/RFC6147, April 2011, 536 . 538 [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: 539 Combination of Stateful and Stateless Translation", 540 RFC 6877, DOI 10.17487/RFC6877, April 2013, 541 . 543 Authors' Addresses 545 Lorenzo Colitti 546 Google 547 Shibuya 3-21-3 548 Shibuya, Tokyo 150-0002 549 JP 551 Email: lorenzo@google.com 553 Jen Linkova 554 Google 555 1 Darling Island Rd 556 Pyrmont, NSW 2009 557 AU 559 Email: furry@google.com 561 Michael C. Richardson 562 Sandelman Software Works 564 Email: mcr+ietf@sandelman.ca 565 URI: http://www.sandelman.ca/ 566 Tomek Mrugalski 567 Internet Systems Consortium, Inc. 568 950 Charter Street 569 Redwood City, CA 94063 570 USA 572 Email: tomasz.mrugalski@gmail.com