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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 E. Kline 4 Intended status: Standards Track J. Linkova 5 Expires: September 25, 2019 Google 6 March 24, 2019 8 Discovering PREF64 in Router Advertisements 9 draft-ietf-6man-ra-pref64-00 11 Abstract 13 This document specifies a Router Advertisement option to communicate 14 NAT64 prefixes to clients. 16 Status of This Memo 18 This Internet-Draft is submitted in full conformance with the 19 provisions of BCP 78 and BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF). Note that other groups may also distribute 23 working documents as Internet-Drafts. The list of current Internet- 24 Drafts is at https://datatracker.ietf.org/drafts/current/. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 This Internet-Draft will expire on September 25, 2019. 33 Copyright Notice 35 Copyright (c) 2019 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (https://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents 42 carefully, as they describe your rights and restrictions with respect 43 to this document. Code Components extracted from this document must 44 include Simplified BSD License text as described in Section 4.e of 45 the Trust Legal Provisions and are provided without warranty as 46 described in the Simplified BSD License. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 51 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 52 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 53 2. Use cases for communicating the NAT64 prefix to hosts . . . . 3 54 3. Why include the NAT64 prefix in Router Advertisements . . . . 3 55 4. Semantics . . . . . . . . . . . . . . . . . . . . . . . . . . 4 56 5. Option format . . . . . . . . . . . . . . . . . . . . . . . . 4 57 6. Handling Multiple NAT64 Prefixes . . . . . . . . . . . . . . 5 58 7. Multihoming . . . . . . . . . . . . . . . . . . . . . . . . . 6 59 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 60 9. Security Considerations . . . . . . . . . . . . . . . . . . . 7 61 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 62 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 63 11.1. Normative References . . . . . . . . . . . . . . . . . . 7 64 11.2. Informative References . . . . . . . . . . . . . . . . . 8 65 11.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 9 66 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 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 Router Advertisement [RFC4861] option to 74 communicate the NAT64 prefix to hosts. 76 1.1. Requirements Language 78 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 79 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 80 document are to be interpreted as described in RFC 2119 [RFC2119]. 82 1.2. Terminology 84 Pref64: an IPv6 prefix used for IPv6 address synthesis [RFC6146]; 86 PvD: Provisioning Domain, a set of network configuration information; 87 for more information, see [RFC7556]. 89 PvD-aware host A host that supports the association of network 90 configuration information into PvDs and the use of these PvDs. Also 91 named PvD-aware node in [RFC7556]. 93 RA: Router Advertisement, a message used by IPv6 routers to advertise 94 their presence together with various link and Internet parameters 95 ([RFC4861]); 97 2. Use cases for communicating the NAT64 prefix to hosts 99 On networks employing NAT64, it is useful for hosts to know the NAT64 100 prefix for several reasons, including the following: 102 o Local DNSSEC validation. As discussed in [RFC6147] section 2, the 103 stub resolver in the host "will try to obtain (real) AAAA RRs, and 104 in case they are not available, the DNS64 function will synthesize 105 AAAA RRs for internal usage." This is required in order to use 106 DNSSEC on a NAT64 network. 108 o IPv4 address literals on an IPv6-only host. As described in 109 [RFC8305] section 7.1, IPv6-only hosts connecting to IPv4 address 110 literals can resolve the IPv4 literal to an IPv6 address. 112 o 464XLAT [RFC6877]. 464XLAT is widely deployed and requires that 113 the host be aware of the NAT64 prefix. 115 o Trusted DNS server. AAAA synthesis is required for the host to be 116 able to use a DNS server not provided by the network (e.g., a DNS- 117 over-TLS server with which the host has an existing trust 118 relationship). 120 o Networks with no DNS64 server. Hosts that support AAAA synthesis 121 and that are aware of the NAT64 prefix in use do not need the 122 network to perform the DNS64 function at all. 124 3. Why include the NAT64 prefix in Router Advertisements 126 Fate sharing: NAT64 requires a routing to be configured. IPv6 127 routing configuration requires receiving an IPv6 Router Advertisement 128 [RFC4861]. Compared to currently-deployed NAT64 prefix discovery 129 methods such as [RFC7050], including the NAT64 prefix in the Router 130 Advertisement minimizes the number of packets required to configure a 131 host. This speeds up the process of connecting to a network that 132 supports NAT64/DNS64, and simplifies host implementation by removing 133 the possibility that the host can have an incomplete layer 3 134 configuration (e.g., IPv6 addresses and prefixes, but no NAT64 135 prefix). 137 Updatability: it is possible to change the NAT64 prefix at any time, 138 because when it changes, it is possible to notify hosts by sending a 139 new Router Advertisement. 141 Deployability: all IPv6 hosts and networks are required to support 142 [RFC4861]. Other options such as [RFC7225] require implementing 143 other protocols. 145 4. Semantics 147 This option only supports a NAT64 prefix length of 96 bits, as this 148 is by the most common configuration used by hosts and supporting 149 variable prefix length would significantly increase the option size. 150 Networks using one of the other prefix lengths supported in 151 ([RFC6052]) can use other mechanisms such as [RFC7050] or [RFC7225]. 152 If different prefix lengths become common, another RA option can be 153 created to configure them. 155 This option specifies exactly one NAT64 prefix for all IPv4 156 destinations. If the network operator desires to route different 157 parts of the IPv4 address space to different NAT64 devices, this can 158 be accomplished by routing more specifics of the NAT64 prefix to 159 those devices. For example, if the operator would like to route 160 10.0.0.0/8 through NAT64 device A and the rest of the IPv4 space 161 through NAT64 device B, and the operator's NAT64 prefix is 162 2001:db8:a:b::/96, then the operator can route 163 2001:db8:a:b::a00:0/104 to NAT64 A and 2001:db8:a:b::/64 to NAT64 B. 165 This option may appear more than once in a Router Advertisement (e.g. 166 in case of graceful renumbering the network from one NAT64 prefix to 167 another). Host behaviour with regards to synthesizing IPv6 addresses 168 from IPv4 addresses SHOULD follow the recommendations given in 169 Section 3 of [RFC7050], limited to the NAT64 prefixes that have non- 170 zero lifetime. 172 In a network that provides both IPv4 and NAT64, it may be desirable 173 for certain IPv4 addresses not to be translated. An example might be 174 private address ranges that are local to the network and should not 175 be reached through the NAT64. This type of configuration cannot be 176 conveyed to hosts using this option, or through other NAT64 prefix 177 provisioning mechanisms such as [RFC7050] or [RFC7225]. This problem 178 does not apply in IPv6-only networks, because in such networks, the 179 host does not have an IPv4 address and cannot reach any IPv4 180 destinations without the NAT64. 182 5. Option format 183 0 1 2 3 184 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 1 185 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 186 | Type | Length | Lifetime | 187 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 188 | | 189 + Prefix + 190 | | 191 + + 192 | | 193 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 195 Figure 1: NAT64 Prefix Option Format 197 Fields: 199 Type 8-bit identifier of the RDNSS option type as assigned by 200 IANA: TBD 201 Length 8-bit unsigned integer. The length of the option (including 202 the Type and Length fields) is in units of 8 octets. The 203 sender MUST set the Length to 2. A host MUST ignore the 204 NAT64 prefix option if the length field value is 1. If the 205 Length field value exceeds 2, the host MUST utilize the 206 first 16 octets and ignore the rest of the option. 207 Lifetime 16-bit unsigned integer. The maximum time in seconds over 208 which this NAT64 prefix MAY be used. The value of Lifetime 209 SHOULD by default be set to lesser of 3 x MaxRtrAdvInterval 210 or 65535 seconds. A value of zero means that the prefix 211 MUST no longer be used. 212 Prefix The 96-bit NAT64 prefix. 214 6. Handling Multiple NAT64 Prefixes 216 In some cases a host may receive multiple NAT64 prefixes from 217 different sources. Possible scenarios include (but are not limited 218 to): 220 o the host is using multiple mechanisms to discover Pref64 prefixes 221 (e.g. by using PCP ([RFC7225]) and/or by resolving IPv4-only fully 222 qualified domain name ([RFC7050]) in addition to receiving the 223 Pref64 RA option); 225 o The pref64 option presents in a single RA more than once; 227 o the host receives multiple RAs with different Pref64 prefixes on 228 one or multiple interfaces. 230 When multiple Pref64 were discovered via RA Pref64 Option (the Option 231 presents more than once in a singe RA or multiple RAs were received), 232 host behaviour with regards to synthesizing IPv6 addresses from IPv4 233 addresses SHOULD follow the recommendations given in Section 3 of 234 [RFC7050], limited to the NAT64 prefixes that have non-zero 235 lifetime.. 237 When different Pref64 are discovered by using multiple mechanisms, 238 hosts SHOULD select one source of infromation only. The RECOMMENDED 239 order is: 241 o PCP-discovered prefixes ([RFC7225]), if supported; 243 o Pref64 discovered via RA Option; 245 o Pref64 resolving IPv4-only fully qualified domain name ([RFC7050]) 247 Note that if the network provides Pref64 both via this RA option and 248 [RFC7225], hosts that receive the Pref64 via RA option may choose to 249 use it imediately before waiting for PCP to complete, and therefore 250 some traffic may not reflect any more detailed configuration provided 251 by PCP. 253 7. Multihoming 255 Like most IPv6 configuration information, the Pref64 option is 256 specific to the network on which it is received. For example, a 257 Pref64 option received on a particular wireless network may not be 258 usable unless the traffic is also sourced on that network. 259 Similarly, a host connected to a cellular network that povides NAT64 260 generally cannot use that NAT64 for destinations reached through a 261 VPN tunnel that terminates outside that network. 263 Thus, correct use of this option on a multihomed host generally 264 requires the host to be PVD-aware. 266 This issue is not specific to the Pref64 RA option and, for example, 267 is quite typical for DNS resolving on multihomed hosts (e.g. a host 268 might resolve a destination name by using the corporate DNS server 269 via the VPN tunnel but then send the traffic via its Internet-facing 270 interface). 272 8. IANA Considerations 274 The IANA is requested to assign a new IPv6 Neighbor Discovery Option 275 type for the PREF64 option defined in this document. 277 +---------------+-------+ 278 | Option Name | Type | 279 +---------------+-------+ 280 | PREF64 option | (TBD) | 281 +---------------+-------+ 283 Table 1 285 The IANA registry for these options is: 287 https://www.iana.org/assignments/icmpv6-parameters [1] 289 9. Security Considerations 291 Because Router Advertisements are required in all IPv6 configuration 292 scenarios, on IPv6-only networks, Router Advertisements must already 293 be secured, e.g., by deploying RA guard [RFC6105]. Providing all 294 configuration in Router Advertisements increases security by ensuring 295 that no other protocols can be abused by malicious attackers to 296 provide hosts with invalid configuration. 298 The security measures that must already be in place to ensure that 299 Router Advertisements are only received from legitimate sources 300 eliminate the problem of NAT64 prefix validation described in section 301 3.1 of [RFC7050]. 303 10. Acknowledgements 305 Thanks to the following people (in alphabetical order) for their 306 review and feedback: Mikael Abrahamsson, Brian E Carpenter, Nick 307 Heatley, Tatuya Jinmei, David Schinazi. 309 11. References 311 11.1. Normative References 313 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 314 Requirement Levels", BCP 14, RFC 2119, 315 DOI 10.17487/RFC2119, March 1997, 316 . 318 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 319 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 320 DOI 10.17487/RFC6052, October 2010, 321 . 323 11.2. Informative References 325 [I-D.ietf-intarea-provisioning-domains] 326 Pfister, P., Vyncke, E., Pauly, T., Schinazi, D., and W. 327 Shao, "Discovering Provisioning Domain Names and Data", 328 draft-ietf-intarea-provisioning-domains-04 (work in 329 progress), March 2019. 331 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 332 Rose, "DNS Security Introduction and Requirements", 333 RFC 4033, DOI 10.17487/RFC4033, March 2005, 334 . 336 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 337 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 338 DOI 10.17487/RFC4861, September 2007, 339 . 341 [RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. 342 Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, 343 DOI 10.17487/RFC6105, February 2011, 344 . 346 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 347 NAT64: Network Address and Protocol Translation from IPv6 348 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 349 April 2011, . 351 [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van 352 Beijnum, "DNS64: DNS Extensions for Network Address 353 Translation from IPv6 Clients to IPv4 Servers", RFC 6147, 354 DOI 10.17487/RFC6147, April 2011, 355 . 357 [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: 358 Combination of Stateful and Stateless Translation", 359 RFC 6877, DOI 10.17487/RFC6877, April 2013, 360 . 362 [RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of 363 the IPv6 Prefix Used for IPv6 Address Synthesis", 364 RFC 7050, DOI 10.17487/RFC7050, November 2013, 365 . 367 [RFC7225] Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the 368 Port Control Protocol (PCP)", RFC 7225, 369 DOI 10.17487/RFC7225, May 2014, 370 . 372 [RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain 373 Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015, 374 . 376 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 377 and P. Hoffman, "Specification for DNS over Transport 378 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 379 2016, . 381 [RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: 382 Better Connectivity Using Concurrency", RFC 8305, 383 DOI 10.17487/RFC8305, December 2017, 384 . 386 11.3. URIs 388 [1] https://www.iana.org/assignments/icmpv6-parameters 390 Authors' Addresses 392 Lorenzo Colitti 393 Google 394 Roppongi 6-10-1 395 Minato, Tokyo 106-6126 396 JP 398 Email: lorenzo@google.com 400 Erik Kline 401 Google 402 Roppongi 6-10-1 403 Minato, Tokyo 106-6126 404 JP 406 Email: ek@google.com 408 Jen Linkova 409 Google 410 1 Darling Island Rd 411 Pyrmont, NSW 2009 412 AU 414 Email: furry@google.com