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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: December 30, 2019 June 28, 2019 7 Discovering PREF64 in Router Advertisements 8 draft-ietf-6man-ra-pref64-01 10 Abstract 12 This document specifies a Router Advertisement option to communicate 13 NAT64 prefixes to clients. 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 December 30, 2019. 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. Semantics . . . . . . . . . . . . . . . . . . . . . . . . . . 4 55 5. Option format . . . . . . . . . . . . . . . . . . . . . . . . 4 56 6. Handling Multiple NAT64 Prefixes . . . . . . . . . . . . . . 6 57 7. Multihoming . . . . . . . . . . . . . . . . . . . . . . . . . 7 58 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 59 9. Security Considerations . . . . . . . . . . . . . . . . . . . 8 60 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 61 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 62 11.1. Normative References . . . . . . . . . . . . . . . . . . 8 63 11.2. Informative References . . . . . . . . . . . . . . . . . 9 64 11.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 10 65 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 67 1. Introduction 69 NAT64 [RFC6146] with DNS64 [RFC6147] is a widely-deployed mechanism 70 to provide IPv4 access on IPv6-only networks. In various scenarios, 71 the host must be aware of the NAT64 prefix in use by the network. 72 This document specifies a Router Advertisement [RFC4861] option to 73 communicate the NAT64 prefix to hosts. 75 1.1. Requirements Language 77 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 78 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 79 document are to be interpreted as described in RFC 2119 [RFC2119]. 81 1.2. Terminology 83 Pref64 (or NAT64 prefix): an IPv6 prefix used for IPv6 address 84 synthesis [RFC6146]; 86 NAT64: Network Address and Protocol Translation from IPv6 Clients to 87 IPv4 Servers ([RFC6146]); 89 RA: Router Advertisement, a message used by IPv6 routers to advertise 90 their presence together with various link and Internet parameters 91 ([RFC4861]); 93 DNS64: a mechanism for synthesizing AAAA records from A records 94 ([RFC6147]); 96 2. Use cases for communicating the NAT64 prefix to hosts 98 On networks employing NAT64, it is useful for hosts to know the NAT64 99 prefix for several reasons, including the following: 101 o Local DNSSEC validation. As discussed in [RFC6147] section 2, the 102 stub resolver in the host "will try to obtain (real) AAAA RRs, and 103 in case they are not available, the DNS64 function will synthesize 104 AAAA RRs for internal usage." This is required in order to use 105 DNSSEC on a NAT64 network. 107 o IPv4 address literals on an IPv6-only host. As described in 108 [RFC8305] section 7.1, IPv6-only hosts connecting to IPv4 address 109 literals can resolve the IPv4 literal to an IPv6 address. 111 o 464XLAT [RFC6877]. 464XLAT is widely deployed and requires that 112 the host be aware of the NAT64 prefix. 114 o Trusted DNS server. AAAA synthesis is required for the host to be 115 able to use a DNS server not provided by the network (e.g., a DNS- 116 over-TLS server with which the host has an existing trust 117 relationship). 119 o Networks with no DNS64 server. Hosts that support AAAA synthesis 120 and that are aware of the NAT64 prefix in use do not need the 121 network to perform the DNS64 function at all. 123 3. Why include the NAT64 prefix in Router Advertisements 125 Fate sharing: NAT64 requires a routing to be configured. IPv6 126 routing configuration requires receiving an IPv6 Router Advertisement 127 [RFC4861]. Compared to currently-deployed NAT64 prefix discovery 128 methods such as [RFC7050], including the NAT64 prefix in the Router 129 Advertisement minimizes the number of packets required to configure a 130 host. This speeds up the process of connecting to a network that 131 supports NAT64/DNS64, and simplifies host implementation by removing 132 the possibility that the host can have an incomplete layer 3 133 configuration (e.g., IPv6 addresses and prefixes, but no NAT64 134 prefix). 136 Updatability: it is possible to change the NAT64 prefix at any time, 137 because when it changes, it is possible to notify hosts by sending a 138 new Router Advertisement. 140 Deployability: all IPv6 hosts and networks are required to support 141 [RFC4861]. Other options such as [RFC7225] require implementing 142 other protocols. 144 4. Semantics 146 To support prefix lengths defined in ([RFC6052]) this option contains 147 the prefix length field. However as /96 prefix is considered to be 148 the most common usecase, the prefix length field is optional and only 149 presents for non-/96 prefixes. It allows to keep the option length 150 to a minimum (16 bytes) for the most common case and increase it to 151 20 bytes for non-/96 prefixes only (see Section 5 below for more 152 details). 154 This option specifies exactly one NAT64 prefix for all IPv4 155 destinations. If the network operator desires to route different 156 parts of the IPv4 address space to different NAT64 devices, this can 157 be accomplished by routing more specifics of the NAT64 prefix to 158 those devices. For example, if the operator would like to route 159 10.0.0.0/8 through NAT64 device A and the rest of the IPv4 space 160 through NAT64 device B, and the operator's NAT64 prefix is 161 2001:db8:a:b::/96, then the operator can route 162 2001:db8:a:b::a00:0/104 to NAT64 A and 2001:db8:a:b::/64 to NAT64 B. 164 This option may appear more than once in a Router Advertisement (e.g. 165 in case of graceful renumbering the network from one NAT64 prefix to 166 another). Host behaviour with regards to synthesizing IPv6 addresses 167 from IPv4 addresses SHOULD follow the recommendations given in 168 Section 3 of [RFC7050], limited to the NAT64 prefixes that have non- 169 zero lifetime. 171 In a network (or a provisioning domain) that provides both IPv4 and 172 NAT64, it may be desirable for certain IPv4 addresses not to be 173 translated. An example might be private address ranges that are 174 local to the network/provisioning domain and should not be reached 175 through the NAT64. This type of configuration cannot be conveyed to 176 hosts using this option, or through other NAT64 prefix provisioning 177 mechanisms such as [RFC7050] or [RFC7225]. This problem does not 178 apply in IPv6-only networks, because in such networks, the host does 179 not have an IPv4 address and cannot reach any IPv4 destinations 180 without the NAT64. The multihoming and multiple provisioning domains 181 scenarios are discussed in Section 7. 183 5. Option format 184 0 1 2 3 185 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 1 186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 187 | Type | Length | Lifetime | 188 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 189 | | 190 + + 191 | Highest 96 bits of the Prefix | 192 + + 193 | | 194 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 195 | Lowest bits (96-127) of the prefix (optional, if Length > 2) | 196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 197 | Prefix Length | Reserved | 198 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 200 Figure 1: NAT64 Prefix Option Format 202 Fields: 204 Type 8-bit identifier of the Pref64 option type as assigned by 205 IANA: TBD 206 Length 8-bit unsigned integer. The length of the option (including 207 the Type and Length fields) is in units of 8 octets. If the 208 prefix length is 96 bits the sender MUST set the Length to 2 209 and include the 96 bits of the prefix in the option. If the 210 prefix length is not 96 bits then the sender MUST set the 211 length to 3 and include all 128 bits of the prefix in the 212 Prefix field and set the Prefix Length field to the prefix 213 length. The receiver MUST ignore the Pref64 option if the 214 length field value is 1. If the Length field value exceeds 215 3, the receiver MUST utilize the first 21 octets and ignore 216 the rest of the option. 218 Lifetime 16-bit unsigned integer. The maximum time in seconds over 219 which this NAT64 prefix MAY be used. The value of Lifetime 220 SHOULD by default be set to lesser of 3 x MaxRtrAdvInterval 221 or 65535 seconds. A value of zero means that the prefix 222 MUST no longer be used. 224 Highest 96-bit unsigned integer. Contains bits 0 - 95 of the NAT64 225 96 bits prefix. 226 of the 227 prefix 229 Lowest 32-bit unsigned integer. Contains bits 96 - 127 of the NAT64 230 bits of prefix. 231 the 232 prefix 234 Prefix 8-bit unsigned integer. The sender MUST set it only to one 235 Length of the following values: 32, 40, 48, 56, 64 ([RFC6052]. The 236 receiver MUST ignore the Pref64 option if the prefix length 237 value is not set to one of those numbers. 239 Reserved A 3-byte unused field. It MUST be initialized to zero by 240 the sender and MUST be ignored by the receiver. 242 6. Handling Multiple NAT64 Prefixes 244 In some cases a host may receive multiple NAT64 prefixes from 245 different sources. Possible scenarios include (but are not limited 246 to): 248 o the host is using multiple mechanisms to discover Pref64 prefixes 249 (e.g. by using PCP ([RFC7225]) and/or by resolving IPv4-only fully 250 qualified domain name ([RFC7050]) in addition to receiving the 251 Pref64 RA option); 253 o The pref64 option presents in a single RA more than once; 255 o the host receives multiple RAs with different Pref64 prefixes on 256 one or multiple interfaces. 258 When multiple Pref64 were discovered via RA Pref64 Option (the Option 259 presents more than once in a singe RA or multiple RAs were received), 260 host behaviour with regards to synthesizing IPv6 addresses from IPv4 261 addresses SHOULD follow the recommendations given in Section 3 of 262 [RFC7050], limited to the NAT64 prefixes that have non-zero 263 lifetime.. 265 When different Pref64 are discovered by using multiple mechanisms, 266 hosts SHOULD select one source of infromation only. The RECOMMENDED 267 order is: 269 o PCP-discovered prefixes ([RFC7225]), if supported; 271 o Pref64 discovered via RA Option; 273 o Pref64 resolving IPv4-only fully qualified domain name ([RFC7050]) 275 Note that if the network provides Pref64 both via this RA option and 276 [RFC7225], hosts that receive the Pref64 via RA option may choose to 277 use it imediately before waiting for PCP to complete, and therefore 278 some traffic may not reflect any more detailed configuration provided 279 by PCP. 281 7. Multihoming 283 Like most IPv6 configuration information, the Pref64 option is 284 specific to the network on which it is received. For example, a 285 Pref64 option received on a particular wireless network may not be 286 usable unless the traffic is also sourced on that network. 287 Similarly, a host connected to a cellular network that povides NAT64 288 generally cannot use that NAT64 for destinations reached through a 289 VPN tunnel that terminates outside that network. 291 Thus, correct use of this option on a multihomed host generally 292 requires the host to support the concept of multiple Provisioning 293 Domains (PvD, a set of configuration information associated with a 294 network, [RFC7556]) and to be able to use these PvDs. 296 This issue is not specific to the Pref64 RA option and, for example, 297 is quite typical for DNS resolving on multihomed hosts (e.g. a host 298 might resolve a destination name by using the corporate DNS server 299 via the VPN tunnel but then send the traffic via its Internet-facing 300 interface). 302 8. IANA Considerations 304 The IANA is requested to assign a new IPv6 Neighbor Discovery Option 305 type for the PREF64 option defined in this document. 307 +---------------+-------+ 308 | Option Name | Type | 309 +---------------+-------+ 310 | PREF64 option | (TBD) | 311 +---------------+-------+ 313 Table 1 315 The IANA registry for these options is: 317 https://www.iana.org/assignments/icmpv6-parameters [1] 319 9. Security Considerations 321 Because Router Advertisements are required in all IPv6 configuration 322 scenarios, on IPv6-only networks, Router Advertisements must already 323 be secured, e.g., by deploying RA guard [RFC6105]. Providing all 324 configuration in Router Advertisements increases security by ensuring 325 that no other protocols can be abused by malicious attackers to 326 provide hosts with invalid configuration. 328 The security measures that must already be in place to ensure that 329 Router Advertisements are only received from legitimate sources 330 eliminate the problem of NAT64 prefix validation described in section 331 3.1 of [RFC7050]. 333 10. Acknowledgements 335 Thanks to the following people (in alphabetical order) for their 336 review and feedback: Mikael Abrahamsson, Mark Andrews, Brian E 337 Carpenter, Nick Heatley, Martin Hunek, Tatuya Jinmei, Erik Kline, 338 Michael Richardson, David Schinazi. 340 11. References 342 11.1. Normative References 344 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 345 Requirement Levels", BCP 14, RFC 2119, 346 DOI 10.17487/RFC2119, March 1997, 347 . 349 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 350 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 351 DOI 10.17487/RFC6052, October 2010, 352 . 354 11.2. Informative References 356 [I-D.ietf-intarea-provisioning-domains] 357 Pfister, P., Vyncke, E., Pauly, T., Schinazi, D., and W. 358 Shao, "Discovering Provisioning Domain Names and Data", 359 draft-ietf-intarea-provisioning-domains-05 (work in 360 progress), June 2019. 362 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 363 Rose, "DNS Security Introduction and Requirements", 364 RFC 4033, DOI 10.17487/RFC4033, March 2005, 365 . 367 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 368 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 369 DOI 10.17487/RFC4861, September 2007, 370 . 372 [RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. 373 Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, 374 DOI 10.17487/RFC6105, February 2011, 375 . 377 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 378 NAT64: Network Address and Protocol Translation from IPv6 379 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 380 April 2011, . 382 [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van 383 Beijnum, "DNS64: DNS Extensions for Network Address 384 Translation from IPv6 Clients to IPv4 Servers", RFC 6147, 385 DOI 10.17487/RFC6147, April 2011, 386 . 388 [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: 389 Combination of Stateful and Stateless Translation", 390 RFC 6877, DOI 10.17487/RFC6877, April 2013, 391 . 393 [RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of 394 the IPv6 Prefix Used for IPv6 Address Synthesis", 395 RFC 7050, DOI 10.17487/RFC7050, November 2013, 396 . 398 [RFC7225] Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the 399 Port Control Protocol (PCP)", RFC 7225, 400 DOI 10.17487/RFC7225, May 2014, 401 . 403 [RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain 404 Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015, 405 . 407 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 408 and P. Hoffman, "Specification for DNS over Transport 409 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 410 2016, . 412 [RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: 413 Better Connectivity Using Concurrency", RFC 8305, 414 DOI 10.17487/RFC8305, December 2017, 415 . 417 11.3. URIs 419 [1] https://www.iana.org/assignments/icmpv6-parameters 421 Authors' Addresses 423 Lorenzo Colitti 424 Google 425 Roppongi 6-10-1 426 Minato, Tokyo 106-6126 427 JP 429 Email: lorenzo@google.com 431 Jen Linkova 432 Google 433 1 Darling Island Rd 434 Pyrmont, NSW 2009 435 AU 437 Email: furry@google.com