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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 198 has weird spacing: '...96 bits prefi...' -- The document date (December 19, 2019) is 877 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) -- Looks like a reference, but probably isn't: '1' on line 462 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPv6 Maintenance L. Colitti 3 Internet-Draft J. Linkova 4 Intended status: Standards Track Google 5 Expires: June 21, 2020 December 19, 2019 7 Discovering PREF64 in Router Advertisements 8 draft-ietf-6man-ra-pref64-09 10 Abstract 12 This document specifies a Neighbor Discovery option to be used in 13 Router Advertisements to communicate NAT64 prefixes to hosts. 15 Status of This Memo 17 This Internet-Draft is submitted in full conformance with the 18 provisions of BCP 78 and BCP 79. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF). Note that other groups may also distribute 22 working documents as Internet-Drafts. The list of current Internet- 23 Drafts is at https://datatracker.ietf.org/drafts/current/. 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than as "work in progress." 30 This Internet-Draft will expire on June 21, 2020. 32 Copyright Notice 34 Copyright (c) 2019 IETF Trust and the persons identified as the 35 document authors. All rights reserved. 37 This document is subject to BCP 78 and the IETF Trust's Legal 38 Provisions Relating to IETF Documents 39 (https://trustee.ietf.org/license-info) in effect on the date of 40 publication of this document. Please review these documents 41 carefully, as they describe your rights and restrictions with respect 42 to this document. Code Components extracted from this document must 43 include Simplified BSD License text as described in Section 4.e of 44 the Trust Legal Provisions and are provided without warranty as 45 described in the Simplified BSD License. 47 Table of Contents 49 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 50 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 51 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 52 2. Use cases for communicating the NAT64 prefix to hosts . . . . 3 53 3. Why include the NAT64 prefix in Router Advertisements . . . . 3 54 4. Option format . . . . . . . . . . . . . . . . . . . . . . . . 4 55 4.1. Scaled Lifetime Processing . . . . . . . . . . . . . . . 5 56 5. Usage Guidelines . . . . . . . . . . . . . . . . . . . . . . 6 57 5.1. Handling Multiple NAT64 Prefixes . . . . . . . . . . . . 6 58 5.2. PREF64 Consistency . . . . . . . . . . . . . . . . . . . 7 59 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 60 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 61 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 62 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 63 9.1. Normative References . . . . . . . . . . . . . . . . . . 9 64 9.2. Informative References . . . . . . . . . . . . . . . . . 9 65 9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 11 66 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 68 1. Introduction 70 NAT64 [RFC6146] with DNS64 [RFC6147] is a widely-deployed mechanism 71 to provide IPv4 access on IPv6-only networks. In various scenarios, 72 the host must be aware of the NAT64 prefix in use by the network. 73 This document specifies a Neighbor Discovery [RFC4861] option to be 74 used in Router Advertisements to communicate NAT64 prefixes to hosts. 76 1.1. Requirements Language 78 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 79 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 80 "OPTIONAL" in this document are to be interpreted as described in BCP 81 14 [RFC2119] [RFC8174] when, and only when, they appear in all 82 capitals, as shown here. 84 1.2. Terminology 86 PREF64 (or NAT64 prefix): an IPv6 prefix used for IPv6 address 87 synthesis [RFC6146]; 89 NAT64: Network Address and Protocol Translation from IPv6 Clients to 90 IPv4 Servers [RFC6146]; 92 RA: Router Advertisement, a message used by IPv6 routers to advertise 93 their presence together with various link and Internet parameters 94 [RFC4861]; 95 DNS64: a mechanism for synthesizing AAAA records from A records 96 [RFC6147]; 98 2. Use cases for communicating the NAT64 prefix to hosts 100 On networks employing NAT64, it is useful for hosts to know the NAT64 101 prefix for several reasons, including the following: 103 o Enabling DNS64 functions on end hosts. In particular: 105 * Local DNSSEC validation (DNS64 in stub-resolver mode). As 106 discussed in [RFC6147] section 2, the stub resolver in the host 107 "will try to obtain (real) AAAA RRs, and in case they are not 108 available, the DNS64 function will synthesize AAAA RRs for 109 internal usage." Therefore to perform the DNS64 function the 110 stub resolver needs to know the NAT64 prefix. This is required 111 in order to use DNSSEC on a NAT64 network. 113 * Trusted DNS server. AAAA synthesis is required for the host to 114 be able to use a DNS server not provided by the network (e.g., 115 a DNS-over-TLS [RFC7858] or DNS-over-HTTPS [RFC8484] server 116 with which the host has an existing trust relationship). 118 * Networks with no DNS64 server. Hosts that support AAAA 119 synthesis and that are aware of the NAT64 prefix in use do not 120 need the network to perform the DNS64 function at all. 122 o Enabling NAT64 address translation functions on end hosts. For 123 example: 125 * IPv4 address literals on an IPv6-only host. As described in 126 [RFC8305] section 7.1, IPv6-only hosts connecting to IPv4 127 address literals can translate the IPv4 literal to an IPv6 128 literal. 130 * 464XLAT [RFC6877]. 464XLAT requires the host be aware of the 131 NAT64 prefix. 133 3. Why include the NAT64 prefix in Router Advertisements 135 Fate sharing: NAT64 requires routing to be configured. IPv6 routing 136 configuration requires receiving an IPv6 Router Advertisement 137 [RFC4861]. Therefore using Router Advertisements to provide hosts 138 with NAT64 prefix ensures that NAT64 reachability information shares 139 fate with the rest of network configuration on the host. 141 Atomic configuration: including the NAT64 prefix in the Router 142 Advertisement minimizes the number of packets required to configure a 143 host. Only one packet (a Router Advertisement) is required to 144 complete the network configuration. This speeds up the process of 145 connecting to a network that supports NAT64/DNS64, and simplifies 146 host implementation by removing the possibility that the host can 147 have an incomplete layer 3 configuration (e.g., IPv6 addresses and 148 prefixes, but no NAT64 prefix). 150 Updatability: it is possible to change the NAT64 prefix at any time, 151 because when it changes, it is possible to notify hosts by sending a 152 new Router Advertisement. 154 Deployability: all IPv6 hosts and networks are required to support 155 Neighbor Discovery [RFC4861] so just a minor extension to the 156 existing implementation is required. Other options such as [RFC7225] 157 require implementing other protocols (e.g. PCP [RFC7225]) which 158 could be considered an obstacle for deployment. 160 4. Option format 162 0 1 2 3 163 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 1 164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 165 | Type | Length | Scaled Lifetime | PLC | 166 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 167 | | 168 + + 169 | Highest 96 bits of the Prefix | 170 + + 171 | | 172 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 174 Figure 1: NAT64 Prefix Option Format 176 Fields: 178 Type 8-bit identifier of the PREF64 option type as assigned by 179 IANA: TBD 180 Length 8-bit unsigned integer. The length of the option 181 (including the Type and Length fields) is in units of 8 182 octets. The sender MUST set the length to 2. The receiver 183 MUST ignore the PREF64 option if the length field value is 184 not 2. 186 Scaled 13-bit unsigned integer. The maximum time in units of 8 187 Lifetime seconds over which this NAT64 prefix MAY be used. See 188 Section 4.1 for the Scaled Lifetime field processing rules. 190 PLC 3-bit unsigned integer. This field encodes the NAT64 Prefix 191 (Prefix Length defined in [RFC6052]. The PLC field values 0, 1, 2, 192 Length 3, 4 and 5 indicate the NAT64 prefix length of 96, 64, 56, 193 Code) 48, 40 and 32 bits respectively. The receiver MUST ignore 194 the PREF64 option if the prefix length code field is not set 195 to one of those values. 197 Highest 96-bit unsigned integer. Contains bits 0 - 95 of the NAT64 198 96 bits prefix. 199 of the 200 prefix 202 4.1. Scaled Lifetime Processing 204 It would be highly undesirable for the NAT64 prefix to have a 205 lifetime shorter than the Router Lifetime, which is defined in the 206 Section 4.2 of [RFC4861] as 16-bit unsigned integer. If the NAT64 207 prefix lifetime is not at least equal to the default router lifetime 208 it might lead to scenarios when the NAT64 prefix lifetime expires 209 before the arrival of the next unsolicited RA. Therefore the Scaled 210 Lifetime encodes the NAT64 prefix lifetime in units of 8 seconds. 211 The receiver MUST multiply the Scaled Lifetime value by 8 (for 212 example, by logical left shift) to calculate the maximum time in 213 seconds the prefix MAY be used. The maximum lifetime of the NAT64 214 prefix is thus 65528 seconds. To ensure that the NAT64 prefix does 215 not expire before the default router, when using this option it is 216 NOT RECOMMENDED to configure default router lifetimes greater than 217 65528 seconds. Lifetime of 0 indicates that the prefix SHOULD NOT be 218 used anymore. 220 The value of the Scaled Lifetime field SHOULD by default be set to 221 the lesser of 3 x MaxRtrAdvInterval ([RFC4861]) divided by 8, or 222 8191. 224 Router vendors SHOULD allow administrators to specify non-zero 225 lifetime values which are not divisible by 8. In such cases the 226 router SHOULD round the provided value up to the nearest integer that 227 is divisible by 8 and smaller than 65536, then divide the result by 8 228 (or perform a logical right-shift by 3), and set the Scaled Lifetime 229 field to the resulting value. If such a non-zero lifetime value to 230 be divided by 8 (to be subjected to a logical right-shift by 3) is 231 less than 8 then the Scaled Lifetime field SHOULD be set to 1. This 232 last step ensures that lifetimes under 8 seconds are encoded as a 233 non-zero Scaled Lifetime. 235 5. Usage Guidelines 237 This option specifies exactly one NAT64 prefix for all IPv4 238 destinations. If the network operator desires to route different 239 parts of the IPv4 address space to different NAT64 devices, this can 240 be accomplished by routing more specific sub-prefixes of the NAT64 241 prefix to those devices. For example, suppose an operator is using 242 the [RFC1918] address space 10.0.0.0/8 internally. That operator 243 might want to route 10.0.0.0/8 through NAT64 device A, and the rest 244 of the IPv4 space through NAT64 device B. If the operator's NAT64 245 prefix is 2001:db8:a:b::/96, then the operator can route 246 2001:db8:a:b::a00:0/104 to NAT64 A and 2001:db8:a:b::/96 to NAT64 B. 248 This option may appear more than once in a Router Advertisement (e.g. 249 in case of graceful renumbering the network from one NAT64 prefix to 250 another). Host behaviour with regards to synthesizing IPv6 addresses 251 from IPv4 addresses SHOULD follow the recommendations given in 252 Section 3 of [RFC7050], limited to the NAT64 prefixes that have non- 253 zero lifetime. 255 In a network (or a provisioning domain) that provides both IPv4 and 256 NAT64, it may be desirable for certain IPv4 addresses not to be 257 translated. An example might be private address ranges that are 258 local to the network/provisioning domain and should not be reached 259 through the NAT64. This type of configuration cannot be conveyed to 260 hosts using this option, or through other NAT64 prefix provisioning 261 mechanisms such as [RFC7050] or [RFC7225]. This problem does not 262 apply in IPv6-only networks, because in such networks, the host does 263 not have an IPv4 address and cannot reach any IPv4 destinations 264 without the NAT64. 266 5.1. Handling Multiple NAT64 Prefixes 268 In some cases a host may receive multiple NAT64 prefixes from 269 different sources. Possible scenarios include (but are not limited 270 to): 272 o the host is using multiple mechanisms to discover PREF64 prefixes 273 (e.g. by using PCP [RFC7225]) and/or by resolving IPv4-only fully 274 qualified domain name [RFC7050] in addition to receiving the 275 PREF64 RA option); 277 o the PREF64 option presents in a single RA more than once; 279 o the host receives multiple RAs with different PREF64 prefixes on a 280 given interface. 282 When multiple PREF64 were discovered via RA PREF64 Option (the Option 283 presents more than once in a single RA or multiple RAs were 284 received), host behaviour with regards to synthesizing IPv6 addresses 285 from IPv4 addresses SHOULD follow the recommendations given in 286 Section 3 of [RFC7050], limited to the NAT64 prefixes that have non- 287 zero lifetime. 289 When different PREF64 are discovered by using multiple mechanisms, 290 hosts SHOULD select one source of information only. The RECOMMENDED 291 order is: 293 o PCP-discovered prefixes [RFC7225], if supported; 295 o PREF64 discovered via RA Option; 297 o PREF64 resolving IPv4-only fully qualified domain name [RFC7050] 299 Note that if the network provides PREF64 both via this RA option and 300 [RFC7225], hosts that receive the PREF64 via RA option may choose to 301 use it immediately before waiting for PCP to complete, and therefore 302 some traffic may not reflect any more detailed configuration provided 303 by PCP. 305 The host SHOULD treat the PREF64 as being specific to the network 306 interface it was received on. Provisioning Domain (PvD, [RFC7556]) 307 aware hosts MUST treat the PREF64 as being scoped to the implicit or 308 explicit PvD. 310 5.2. PREF64 Consistency 312 Section 6.2.7 of [RFC4861] recommends that routers inspect RAs sent 313 by other routers to ensure that all routers onlink advertise 314 consistent information. Routers SHOULD inspect valid PREF64 options 315 received on a given link and verify the consistency. Detected 316 inconsistencies indicate that one or more routers might be 317 misconfigured. Routers SHOULD log such cases to system or network 318 management. Routers SHOULD check and compare the following 319 information: 321 o set of PREF64 with non-zero lifetime; 322 o set of PREF64 with zero lifetime. 324 Provisioning Domain (PvD, [RFC7556]) aware routers MUST only compare 325 information scoped to the same implicit or explicit PvD. 327 6. IANA Considerations 329 The IANA is requested to assign a new IPv6 Neighbor Discovery Option 330 type for the PREF64 option defined in this document. 332 +---------------+-------+ 333 | Option Name | Type | 334 +---------------+-------+ 335 | PREF64 option | (TBD) | 336 +---------------+-------+ 338 Table 1 340 The IANA registry for these options is: 342 https://www.iana.org/assignments/icmpv6-parameters [1] 344 7. Security Considerations 346 Because Router Advertisements are required in all IPv6 configuration 347 scenarios, on IPv6-only networks, Router Advertisements must already 348 be secured, e.g., by deploying RA guard [RFC6105]. Providing all 349 configuration in Router Advertisements reduces the attack surface to 350 be targeted by malicious attackers to provide hosts with invalid 351 configuration as compared to distributing the configuration through 352 multiple different mechanisms that need to be secured independently. 354 If a host is provided with an incorrect NAT64 prefix the IPv6-only 355 host might not be able to communicate with IPv4-only destinations. 356 Connectivity to destinations reachable over IPv6 would not be 357 impacted just by providing a host with an incorrect prefix (however 358 if attackers are capable of sending rogue RAs they can perform 359 denial-of-service or man-in-the-middle attacks, as described in 360 [RFC6104]). 362 The security measures that must already be in place to ensure that 363 Router Advertisements are only received from legitimate sources 364 eliminate the problem of NAT64 prefix validation described in section 365 3.1 of [RFC7050]. 367 8. Acknowledgements 369 Thanks to the following people (in alphabetical order) for their 370 review and feedback: Mikael Abrahamsson, Mark Andrews, Brian E 371 Carpenter, David Farmer, Nick Heatley, Robert Hinden, Martin Hunek, 372 Tatuya Jinmei, Benjamin Kaduk, Erik Kline, Suresh Krishnan, Warren 373 Kumari, David Lamparter, Barry Leiba, Jordi Palet Martinez, Tommy 374 Pauly, Alexandre Petrescu, Michael Richardson, David Schinazi, Ole 375 Troan, Eric Vynke, Bernie Volz. 377 9. References 379 9.1. Normative References 381 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 382 Requirement Levels", BCP 14, RFC 2119, 383 DOI 10.17487/RFC2119, March 1997, 384 . 386 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 387 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 388 DOI 10.17487/RFC4861, September 2007, 389 . 391 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 392 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 393 DOI 10.17487/RFC6052, October 2010, 394 . 396 [RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of 397 the IPv6 Prefix Used for IPv6 Address Synthesis", 398 RFC 7050, DOI 10.17487/RFC7050, November 2013, 399 . 401 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 402 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 403 May 2017, . 405 9.2. Informative References 407 [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., 408 and E. Lear, "Address Allocation for Private Internets", 409 BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996, 410 . 412 [RFC6104] Chown, T. and S. Venaas, "Rogue IPv6 Router Advertisement 413 Problem Statement", RFC 6104, DOI 10.17487/RFC6104, 414 February 2011, . 416 [RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. 417 Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, 418 DOI 10.17487/RFC6105, February 2011, 419 . 421 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 422 NAT64: Network Address and Protocol Translation from IPv6 423 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 424 April 2011, . 426 [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van 427 Beijnum, "DNS64: DNS Extensions for Network Address 428 Translation from IPv6 Clients to IPv4 Servers", RFC 6147, 429 DOI 10.17487/RFC6147, April 2011, 430 . 432 [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: 433 Combination of Stateful and Stateless Translation", 434 RFC 6877, DOI 10.17487/RFC6877, April 2013, 435 . 437 [RFC7225] Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the 438 Port Control Protocol (PCP)", RFC 7225, 439 DOI 10.17487/RFC7225, May 2014, 440 . 442 [RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain 443 Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015, 444 . 446 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 447 and P. Hoffman, "Specification for DNS over Transport 448 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 449 2016, . 451 [RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: 452 Better Connectivity Using Concurrency", RFC 8305, 453 DOI 10.17487/RFC8305, December 2017, 454 . 456 [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS 457 (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, 458 . 460 9.3. URIs 462 [1] https://www.iana.org/assignments/icmpv6-parameters 464 Authors' Addresses 466 Lorenzo Colitti 467 Google 468 Shibuya 3-21-3 469 Shibuya, Tokyo 150-0002 470 JP 472 Email: lorenzo@google.com 474 Jen Linkova 475 Google 476 1 Darling Island Rd 477 Pyrmont, NSW 2009 478 AU 480 Email: furry@google.com