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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: April 2, 2020 September 30, 2019 7 Discovering PREF64 in Router Advertisements 8 draft-ietf-6man-ra-pref64-05 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 April 2, 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. Usage Guidelines . . . . . . . . . . . . . . . . . . . . . . 4 55 5. Option format . . . . . . . . . . . . . . . . . . . . . . . . 5 56 6. Handling Multiple NAT64 Prefixes . . . . . . . . . . . . . . 6 57 7. PREF64 Consistency . . . . . . . . . . . . . . . . . . . . . 7 58 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 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 Enabling DNS64 functions on end hosts. In particular: 103 * Local DNSSEC validation (DNS64 in stub-resolver mode). As 104 discussed in [RFC6147] section 2, the stub resolver in the host 105 "will try to obtain (real) AAAA RRs, and in case they are not 106 available, the DNS64 function will synthesize AAAA RRs for 107 internal usage." This is required in order to use DNSSEC on a 108 NAT64 network. 110 * Trusted DNS server. AAAA synthesis is required for the host to 111 be able to use a DNS server not provided by the network (e.g., 112 a DNS-over-TLS server [RFC7858] with which the host has an 113 existing trust relationship). 115 * Networks with no DNS64 server. Hosts that support AAAA 116 synthesis and that are aware of the NAT64 prefix in use do not 117 need the network to perform the DNS64 function at all. 119 o Enabling NAT64 address translation functions on end hosts. For 120 example: 122 * IPv4 address literals on an IPv6-only host. As described in 123 [RFC8305] section 7.1, IPv6-only hosts connecting to IPv4 124 address literals can translate the IPv4 literal to an IPv6 125 literal. 127 * 464XLAT [RFC6877]. 464XLAT requires the host be aware of the 128 NAT64 prefix. 130 3. Why include the NAT64 prefix in Router Advertisements 132 Fate sharing: NAT64 requires routing to be configured. IPv6 routing 133 configuration requires receiving an IPv6 Router Advertisement 134 [RFC4861]. Therefore using Router Advertisements to provide hosts 135 with NAT64 prefix ensures that NAT64 reachability information shares 136 fate with the rest of network configuration on the host. 138 Atomic configuration: including the NAT64 prefix in the Router 139 Advertisement minimizes the number of packets required to configure a 140 host. Only one packet (a Router Advertisement) is required to 141 complete the network configuration. This speeds up the process of 142 connecting to a network that supports NAT64/DNS64, and simplifies 143 host implementation by removing the possibility that the host can 144 have an incomplete layer 3 configuration (e.g., IPv6 addresses and 145 prefixes, but no NAT64 prefix). 147 Updatability: it is possible to change the NAT64 prefix at any time, 148 because when it changes, it is possible to notify hosts by sending a 149 new Router Advertisement. 151 Deployability: all IPv6 hosts and networks are required to support 152 Neighbor Discovery [RFC4861] so just a minor extension to the 153 existing implementation is required. Other options such as [RFC7225] 154 require implementing other protocols (e.g. PCP [RFC7225]) which 155 could be considered an obstacle for deplyoment. 157 4. Usage Guidelines 159 To support prefix lengths defined in [RFC6052] this option contains 160 the prefix length field. However as /96 prefix is considered to be 161 the most common use case, the prefix length field is optional and 162 only presents for non-/96 prefixes. It allows to keep the option 163 length to a minimum (16 octets) for the most common case and increase 164 it to 24 octets for non-/96 prefixes only (see Section 5 below for 165 more details). 167 This option specifies exactly one NAT64 prefix for all IPv4 168 destinations. If the network operator desires to route different 169 parts of the IPv4 address space to different NAT64 devices, this can 170 be accomplished by routing more specifics of the NAT64 prefix to 171 those devices. For example, if the operator would like to route 172 10.0.0.0/8 through NAT64 device A and the rest of the IPv4 space 173 through NAT64 device B, and the operator's NAT64 prefix is 174 2001:db8:a:b::/96, then the operator can route 175 2001:db8:a:b::a00:0/104 to NAT64 A and 2001:db8:a:b::/64 to NAT64 B. 177 This option may appear more than once in a Router Advertisement (e.g. 178 in case of graceful renumbering the network from one NAT64 prefix to 179 another). Host behaviour with regards to synthesizing IPv6 addresses 180 from IPv4 addresses SHOULD follow the recommendations given in 181 Section 3 of [RFC7050], limited to the NAT64 prefixes that have non- 182 zero lifetime. 184 In a network (or a provisioning domain) that provides both IPv4 and 185 NAT64, it may be desirable for certain IPv4 addresses not to be 186 translated. An example might be private address ranges that are 187 local to the network/provisioning domain and should not be reached 188 through the NAT64. This type of configuration cannot be conveyed to 189 hosts using this option, or through other NAT64 prefix provisioning 190 mechanisms such as [RFC7050] or [RFC7225]. This problem does not 191 apply in IPv6-only networks, because in such networks, the host does 192 not have an IPv4 address and cannot reach any IPv4 destinations 193 without the NAT64.. 195 5. Option format 197 0 1 2 3 198 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 1 199 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 200 | Type | Length | Lifetime | PL | 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 202 | | 203 + + 204 | Highest 96 bits of the Prefix | 205 + + 206 | | 207 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 209 Figure 1: NAT64 Prefix Option Format 211 Fields: 213 Type 8-bit identifier of the PREF64 option type as assigned by 214 IANA: TBD 215 Length 8-bit unsigned integer. The length of the option (including 216 the Type and Length fields) is in units of 8 octets. The 217 sender MUST set the length to 2. The receiver MUST ignore 218 the PREF64 option if the length field value is not 2. 220 Lifetime 13-bit unsigned integer. The maximum time in units of 8 221 secons over which this NAT64 prefix MAY be used. The value 222 of Lifetime SHOULD by default be set to the lesser of 3 x 223 MaxRtrAdvInterval divided by 8 or 8192. The reciever MUST 224 multiply the Lifetime value by 8 to calculate the maximum 225 time in seconds the prefix MAY be used. Lifetime of 0 226 indicates that the prefix SHOULD NOT be used anymore. Router 227 vendors SHOULD allow adminstrators to specify non-zero 228 lifetime values which are not divisible by 8. In such cases 229 the router SHOULD round the provided value up to the lesser 230 of nearest integer divisible by 8 or 65536, divide the 231 result by 8 and set the Lifetime field to the resulting 232 value. 234 PL 3-bit unsigned integer.This field encodes the NAT64 Prefix 235 (Prefix Length. The PL field values 0,1,2,3,4 and 5 indicate the 236 Length) NAT64 prefix length of 96,64,56,48,40 and 32 bits 237 respectively. The reciever MUST ignore the PREF64 option if 238 the prefix length field is not set to one of those values. 240 Highest 96-bit unsigned integer. Contains bits 0 - 95 of the NAT64 241 96 bits prefix. 242 of the 243 prefix 245 6. Handling Multiple NAT64 Prefixes 247 In some cases a host may receive multiple NAT64 prefixes from 248 different sources. Possible scenarios include (but are not limited 249 to): 251 o the host is using multiple mechanisms to discover PREF64 prefixes 252 (e.g. by using PCP [RFC7225]) and/or by resolving IPv4-only fully 253 qualified domain name [RFC7050] in addition to receiving the 254 PREF64 RA option); 256 o The pref64 option presents in a single RA more than once; 258 o the host receives multiple RAs with different PREF64 prefixes on 259 one or multiple interfaces. 261 When multiple PREF64 were discovered via RA PREF64 Option (the Option 262 presents more than once in a single RA or multiple RAs were 263 received), host behaviour with regards to synthesizing IPv6 addresses 264 from IPv4 addresses SHOULD follow the recommendations given in 265 Section 3 of [RFC7050], limited to the NAT64 prefixes that have non- 266 zero lifetime.. 268 When different PREF64 are discovered by using multiple mechanisms, 269 hosts SHOULD select one source of information only. The RECOMMENDED 270 order is: 272 o PCP-discovered prefixes [RFC7225], if supported; 274 o PREF64 discovered via RA Option; 276 o PREF64 resolving IPv4-only fully qualified domain name [RFC7050] 278 Note that if the network provides PREF64 both via this RA option and 279 [RFC7225], hosts that receive the PREF64 via RA option may choose to 280 use it immediately before waiting for PCP to complete, and therefore 281 some traffic may not reflect any more detailed configuration provided 282 by PCP. 284 7. PREF64 Consistency 286 Section 6.2.7 of [RFC4861] recommends that routers inspect RAs sent 287 by other routers to ensure that all routers onlink advertise the 288 consistent information. Routers SHOULD inspect valid PREF64 options 289 received on a given link and verify the consistency. Detected 290 inconsistencies indicate that one or more routers might be 291 misconfigured. Routers SHOULD log such cases to system or network 292 management. Routers SHOULD check and compare the following 293 information: 295 o set of PREF64 with non-zero lifetime; 297 o set of PREF64 with zero lifetime. 299 PvD-aware routers MUST only compare information scoped to the same 300 implicit or explicit PvD. 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, David Farmer, Nick Heatley, Robert Hinden, Martin Hunek, 338 Tatuya Jinmei, Erik Kline, David Lamparter, Jordi Palet Martinez, 339 Tommy Pauly, Michael Richardson, David Schinazi, Ole Troan. 341 11. References 343 11.1. Normative References 345 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 346 Requirement Levels", BCP 14, RFC 2119, 347 DOI 10.17487/RFC2119, March 1997, 348 . 350 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 351 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 352 DOI 10.17487/RFC4861, September 2007, 353 . 355 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 356 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 357 DOI 10.17487/RFC6052, October 2010, 358 . 360 [RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of 361 the IPv6 Prefix Used for IPv6 Address Synthesis", 362 RFC 7050, DOI 10.17487/RFC7050, November 2013, 363 . 365 11.2. Informative References 367 [I-D.ietf-intarea-provisioning-domains] 368 Pfister, P., Vyncke, E., Pauly, T., Schinazi, D., and W. 369 Shao, "Discovering Provisioning Domain Names and Data", 370 draft-ietf-intarea-provisioning-domains-07 (work in 371 progress), September 2019. 373 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 374 Rose, "DNS Security Introduction and Requirements", 375 RFC 4033, DOI 10.17487/RFC4033, March 2005, 376 . 378 [RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. 379 Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, 380 DOI 10.17487/RFC6105, February 2011, 381 . 383 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 384 NAT64: Network Address and Protocol Translation from IPv6 385 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 386 April 2011, . 388 [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van 389 Beijnum, "DNS64: DNS Extensions for Network Address 390 Translation from IPv6 Clients to IPv4 Servers", RFC 6147, 391 DOI 10.17487/RFC6147, April 2011, 392 . 394 [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: 395 Combination of Stateful and Stateless Translation", 396 RFC 6877, DOI 10.17487/RFC6877, April 2013, 397 . 399 [RFC7225] Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the 400 Port Control Protocol (PCP)", RFC 7225, 401 DOI 10.17487/RFC7225, May 2014, 402 . 404 [RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain 405 Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015, 406 . 408 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 409 and P. Hoffman, "Specification for DNS over Transport 410 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 411 2016, . 413 [RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: 414 Better Connectivity Using Concurrency", RFC 8305, 415 DOI 10.17487/RFC8305, December 2017, 416 . 418 11.3. URIs 420 [1] https://www.iana.org/assignments/icmpv6-parameters 422 Authors' Addresses 424 Lorenzo Colitti 425 Google 426 Roppongi 6-10-1 427 Minato, Tokyo 106-6126 428 JP 430 Email: lorenzo@google.com 432 Jen Linkova 433 Google 434 1 Darling Island Rd 435 Pyrmont, NSW 2009 436 AU 438 Email: furry@google.com