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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 234 has weird spacing: '...96 bits prefi...' -- The document date (October 3, 2019) is 1666 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 398 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: April 5, 2020 October 3, 2019 7 Discovering PREF64 in Router Advertisements 8 draft-ietf-6man-ra-pref64-06 10 Abstract 12 This document specifies a Router Advertisement option to communicate 13 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 April 5, 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 . . . . . . . . . . . . . . . . . . . . . . . . 4 56 6. Handling Multiple NAT64 Prefixes . . . . . . . . . . . . . . 6 57 7. PREF64 Consistency . . . . . . . . . . . . . . . . . . . . . 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 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 deployment. 157 4. Usage Guidelines 159 This option specifies exactly one NAT64 prefix for all IPv4 160 destinations. If the network operator desires to route different 161 parts of the IPv4 address space to different NAT64 devices, this can 162 be accomplished by routing more specifics of the NAT64 prefix to 163 those devices. For example, if the operator would like to route 164 10.0.0.0/8 through NAT64 device A and the rest of the IPv4 space 165 through NAT64 device B, and the operator's NAT64 prefix is 166 2001:db8:a:b::/96, then the operator can route 167 2001:db8:a:b::a00:0/104 to NAT64 A and 2001:db8:a:b::/64 to NAT64 B. 169 This option may appear more than once in a Router Advertisement (e.g. 170 in case of graceful renumbering the network from one NAT64 prefix to 171 another). Host behaviour with regards to synthesizing IPv6 addresses 172 from IPv4 addresses SHOULD follow the recommendations given in 173 Section 3 of [RFC7050], limited to the NAT64 prefixes that have non- 174 zero lifetime. 176 In a network (or a provisioning domain) that provides both IPv4 and 177 NAT64, it may be desirable for certain IPv4 addresses not to be 178 translated. An example might be private address ranges that are 179 local to the network/provisioning domain and should not be reached 180 through the NAT64. This type of configuration cannot be conveyed to 181 hosts using this option, or through other NAT64 prefix provisioning 182 mechanisms such as [RFC7050] or [RFC7225]. This problem does not 183 apply in IPv6-only networks, because in such networks, the host does 184 not have an IPv4 address and cannot reach any IPv4 destinations 185 without the NAT64.. 187 5. Option format 188 0 1 2 3 189 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 1 190 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 191 | Type | Length | Lifetime | PLC | 192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 193 | | 194 + + 195 | Highest 96 bits of the Prefix | 196 + + 197 | | 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. The 208 sender MUST set the length to 2. The receiver MUST ignore 209 the PREF64 option if the length field value is not 2. 211 Lifetime 13-bit unsigned integer. The maximum time in units of 8 212 seconds over which this NAT64 prefix MAY be used. The value 213 of Lifetime SHOULD by default be set to the lesser of 3 x 214 MaxRtrAdvInterval divided by 8, or 8191. The receiver MUST 215 multiply the Lifetime value by 8 (for example, by logical 216 left shift) to calculate the maximum time in seconds the 217 prefix MAY be used. Lifetime of 0 indicates that the prefix 218 SHOULD NOT be used anymore. Router vendors SHOULD allow 219 administrators to specify non-zero lifetime values which are 220 not divisible by 8. In such cases the router SHOULD round 221 the provided value up to the lesser of nearest integer 222 divisible by 8, or 65528 and divide the result by 8 (or just 223 perform a logical right-shift by 3) and set the Lifetime 224 field to the resulting value. 226 PLC 3-bit unsigned integer. This field encodes the NAT64 Prefix 227 (Prefix Length defined in [RFC6052]. The PLC field values 0, 1, 2, 228 Length 3, 4 and 5 indicate the NAT64 prefix length of 96, 64, 56, 229 Code) 48, 40 and 32 bits respectively. The receiver MUST ignore 230 the PREF64 option if the prefix length code field is not set 231 to one of those values. 233 Highest 96-bit unsigned integer. Contains bits 0 - 95 of the NAT64 234 96 bits prefix. 235 of the 236 prefix 238 6. Handling Multiple NAT64 Prefixes 240 In some cases a host may receive multiple NAT64 prefixes from 241 different sources. Possible scenarios include (but are not limited 242 to): 244 o the host is using multiple mechanisms to discover PREF64 prefixes 245 (e.g. by using PCP [RFC7225]) and/or by resolving IPv4-only fully 246 qualified domain name [RFC7050] in addition to receiving the 247 PREF64 RA option); 249 o the PREF64 option presents in a single RA more than once; 250 o the host receives multiple RAs with different PREF64 prefixes on 251 one or multiple interfaces. 253 When multiple PREF64 were discovered via RA PREF64 Option (the Option 254 presents more than once in a single RA or multiple RAs were 255 received), host behaviour with regards to synthesizing IPv6 addresses 256 from IPv4 addresses SHOULD follow the recommendations given in 257 Section 3 of [RFC7050], limited to the NAT64 prefixes that have non- 258 zero lifetime.. 260 When different PREF64 are discovered by using multiple mechanisms, 261 hosts SHOULD select one source of information only. The RECOMMENDED 262 order is: 264 o PCP-discovered prefixes [RFC7225], if supported; 266 o PREF64 discovered via RA Option; 268 o PREF64 resolving IPv4-only fully qualified domain name [RFC7050] 270 Note that if the network provides PREF64 both via this RA option and 271 [RFC7225], hosts that receive the PREF64 via RA option may choose to 272 use it immediately before waiting for PCP to complete, and therefore 273 some traffic may not reflect any more detailed configuration provided 274 by PCP. 276 7. PREF64 Consistency 278 Section 6.2.7 of [RFC4861] recommends that routers inspect RAs sent 279 by other routers to ensure that all routers onlink advertise the 280 consistent information. Routers SHOULD inspect valid PREF64 options 281 received on a given link and verify the consistency. Detected 282 inconsistencies indicate that one or more routers might be 283 misconfigured. Routers SHOULD log such cases to system or network 284 management. Routers SHOULD check and compare the following 285 information: 287 o set of PREF64 with non-zero lifetime; 289 o set of PREF64 with zero lifetime. 291 PvD-aware routers MUST only compare information scoped to the same 292 implicit or explicit PvD. 294 8. IANA Considerations 296 The IANA is requested to assign a new IPv6 Neighbor Discovery Option 297 type for the PREF64 option defined in this document. 299 +---------------+-------+ 300 | Option Name | Type | 301 +---------------+-------+ 302 | PREF64 option | (TBD) | 303 +---------------+-------+ 305 Table 1 307 The IANA registry for these options is: 309 https://www.iana.org/assignments/icmpv6-parameters [1] 311 9. Security Considerations 313 Because Router Advertisements are required in all IPv6 configuration 314 scenarios, on IPv6-only networks, Router Advertisements must already 315 be secured, e.g., by deploying RA guard [RFC6105]. Providing all 316 configuration in Router Advertisements increases security by ensuring 317 that no other protocols can be abused by malicious attackers to 318 provide hosts with invalid configuration. 320 The security measures that must already be in place to ensure that 321 Router Advertisements are only received from legitimate sources 322 eliminate the problem of NAT64 prefix validation described in section 323 3.1 of [RFC7050]. 325 10. Acknowledgements 327 Thanks to the following people (in alphabetical order) for their 328 review and feedback: Mikael Abrahamsson, Mark Andrews, Brian E 329 Carpenter, David Farmer, Nick Heatley, Robert Hinden, Martin Hunek, 330 Tatuya Jinmei, Erik Kline, David Lamparter, Jordi Palet Martinez, 331 Tommy Pauly, Alexandre Petrescu, Michael Richardson, David Schinazi, 332 Ole Troan, Bernie Volz. 334 11. References 336 11.1. Normative References 338 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 339 Requirement Levels", BCP 14, RFC 2119, 340 DOI 10.17487/RFC2119, March 1997, 341 . 343 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 344 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 345 DOI 10.17487/RFC4861, September 2007, 346 . 348 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 349 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 350 DOI 10.17487/RFC6052, October 2010, 351 . 353 [RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of 354 the IPv6 Prefix Used for IPv6 Address Synthesis", 355 RFC 7050, DOI 10.17487/RFC7050, November 2013, 356 . 358 11.2. Informative References 360 [RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. 361 Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, 362 DOI 10.17487/RFC6105, February 2011, 363 . 365 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 366 NAT64: Network Address and Protocol Translation from IPv6 367 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 368 April 2011, . 370 [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van 371 Beijnum, "DNS64: DNS Extensions for Network Address 372 Translation from IPv6 Clients to IPv4 Servers", RFC 6147, 373 DOI 10.17487/RFC6147, April 2011, 374 . 376 [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: 377 Combination of Stateful and Stateless Translation", 378 RFC 6877, DOI 10.17487/RFC6877, April 2013, 379 . 381 [RFC7225] Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the 382 Port Control Protocol (PCP)", RFC 7225, 383 DOI 10.17487/RFC7225, May 2014, 384 . 386 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 387 and P. Hoffman, "Specification for DNS over Transport 388 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 389 2016, . 391 [RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: 392 Better Connectivity Using Concurrency", RFC 8305, 393 DOI 10.17487/RFC8305, December 2017, 394 . 396 11.3. URIs 398 [1] https://www.iana.org/assignments/icmpv6-parameters 400 Authors' Addresses 402 Lorenzo Colitti 403 Google 404 Shibuya 3-21-3 405 Shibuya, Tokyo 150-0002 406 JP 408 Email: lorenzo@google.com 410 Jen Linkova 411 Google 412 1 Darling Island Rd 413 Pyrmont, NSW 2009 414 AU 416 Email: furry@google.com