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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 241 has weird spacing: '...96 bits prefi...' -- The document date (November 27, 2019) is 1606 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 419 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: May 30, 2020 November 27, 2019 7 Discovering PREF64 in Router Advertisements 8 draft-ietf-6man-ra-pref64-08 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 May 30, 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 . . . . . . . . . . . . . . . . . . . . . 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 Neighbor Discovery [RFC4861] option to be 73 used in Router Advertisements to communicate NAT64 prefixes to hosts. 75 1.1. Requirements Language 77 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 78 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 79 "OPTIONAL" in this document are to be interpreted as described in BCP 80 14 [RFC2119] [RFC8174] when, and only when, they appear in all 81 capitals, as shown here. 83 1.2. Terminology 85 PREF64 (or NAT64 prefix): an IPv6 prefix used for IPv6 address 86 synthesis [RFC6146]; 88 NAT64: Network Address and Protocol Translation from IPv6 Clients to 89 IPv4 Servers [RFC6146]; 91 RA: Router Advertisement, a message used by IPv6 routers to advertise 92 their presence together with various link and Internet parameters 93 [RFC4861]; 94 DNS64: a mechanism for synthesizing AAAA records from A records 95 [RFC6147]; 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 Enabling DNS64 functions on end hosts. In particular: 104 * Local DNSSEC validation (DNS64 in stub-resolver mode). As 105 discussed in [RFC6147] section 2, the stub resolver in the host 106 "will try to obtain (real) AAAA RRs, and in case they are not 107 available, the DNS64 function will synthesize AAAA RRs for 108 internal usage." This is required in order to use DNSSEC on a 109 NAT64 network. 111 * Trusted DNS server. AAAA synthesis is required for the host to 112 be able to use a DNS server not provided by the network (e.g., 113 a DNS-over-TLS [RFC7858] or DNS-over-HTTPS [RFC8484] server 114 with which the host has an existing trust relationship). 116 * Networks with no DNS64 server. Hosts that support AAAA 117 synthesis and that are aware of the NAT64 prefix in use do not 118 need the network to perform the DNS64 function at all. 120 o Enabling NAT64 address translation functions on end hosts. For 121 example: 123 * IPv4 address literals on an IPv6-only host. As described in 124 [RFC8305] section 7.1, IPv6-only hosts connecting to IPv4 125 address literals can translate the IPv4 literal to an IPv6 126 literal. 128 * 464XLAT [RFC6877]. 464XLAT requires the host be aware of the 129 NAT64 prefix. 131 3. Why include the NAT64 prefix in Router Advertisements 133 Fate sharing: NAT64 requires routing to be configured. IPv6 routing 134 configuration requires receiving an IPv6 Router Advertisement 135 [RFC4861]. Therefore using Router Advertisements to provide hosts 136 with NAT64 prefix ensures that NAT64 reachability information shares 137 fate with the rest of network configuration on the host. 139 Atomic configuration: including the NAT64 prefix in the Router 140 Advertisement minimizes the number of packets required to configure a 141 host. Only one packet (a Router Advertisement) is required to 142 complete the network configuration. This speeds up the process of 143 connecting to a network that supports NAT64/DNS64, and simplifies 144 host implementation by removing the possibility that the host can 145 have an incomplete layer 3 configuration (e.g., IPv6 addresses and 146 prefixes, but no NAT64 prefix). 148 Updatability: it is possible to change the NAT64 prefix at any time, 149 because when it changes, it is possible to notify hosts by sending a 150 new Router Advertisement. 152 Deployability: all IPv6 hosts and networks are required to support 153 Neighbor Discovery [RFC4861] so just a minor extension to the 154 existing implementation is required. Other options such as [RFC7225] 155 require implementing other protocols (e.g. PCP [RFC7225]) which 156 could be considered an obstacle for deployment. 158 4. Usage Guidelines 160 This option specifies exactly one NAT64 prefix for all IPv4 161 destinations. If the network operator desires to route different 162 parts of the IPv4 address space to different NAT64 devices, this can 163 be accomplished by routing more specifics of the NAT64 prefix to 164 those devices. For example, if the operator is using the RFC1918 165 address space, e.g. 10.0.0.0/8 internally and would like to route 166 10.0.0.0/8 through NAT64 device A and the rest of the IPv4 space 167 through NAT64 device B, and the operator's NAT64 prefix is 168 2001:db8:a:b::/96, then the operator can route 169 2001:db8:a:b::a00:0/104 to NAT64 A and 2001:db8:a:b::/96 to NAT64 B. 171 This option may appear more than once in a Router Advertisement (e.g. 172 in case of graceful renumbering the network from one NAT64 prefix to 173 another). Host behaviour with regards to synthesizing IPv6 addresses 174 from IPv4 addresses SHOULD follow the recommendations given in 175 Section 3 of [RFC7050], limited to the NAT64 prefixes that have non- 176 zero lifetime. 178 In a network (or a provisioning domain) that provides both IPv4 and 179 NAT64, it may be desirable for certain IPv4 addresses not to be 180 translated. An example might be private address ranges that are 181 local to the network/provisioning domain and should not be reached 182 through the NAT64. This type of configuration cannot be conveyed to 183 hosts using this option, or through other NAT64 prefix provisioning 184 mechanisms such as [RFC7050] or [RFC7225]. This problem does not 185 apply in IPv6-only networks, because in such networks, the host does 186 not have an IPv4 address and cannot reach any IPv4 destinations 187 without the NAT64. 189 5. Option format 191 0 1 2 3 192 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 1 193 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 194 | Type | Length | Scaled Lifetime | PLC | 195 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 196 | | 197 + + 198 | Highest 96 bits of the Prefix | 199 + + 200 | | 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 203 Figure 1: NAT64 Prefix Option Format 205 Fields: 207 Type 8-bit identifier of the PREF64 option type as assigned by 208 IANA: TBD 209 Length 8-bit unsigned integer. The length of the option 210 (including the Type and Length fields) is in units of 8 211 octets. The sender MUST set the length to 2. The receiver 212 MUST ignore the PREF64 option if the length field value is 213 not 2. 215 Scaled 13-bit unsigned integer. The maximum time in units of 8 216 Lifetime seconds over which this NAT64 prefix MAY be used. The value 217 of the Scaled Lifetime field SHOULD by default be set to the 218 lesser of 3 x MaxRtrAdvInterval divided by 8, or 8191. The 219 receiver MUST multiply the Scaled Lifetime value by 8 (for 220 example, by logical left shift) to calculate the maximum 221 time in seconds the prefix MAY be used. Lifetime of 0 222 indicates that the prefix SHOULD NOT be used anymore. Router 223 vendors SHOULD allow administrators to specify non-zero 224 lifetime values which are not divisible by 8. In such cases 225 the router SHOULD round the provided value up to the lesser 226 of nearest integer divisible by 8, or 65528 and divide the 227 result by 8 (or just perform a logical right-shift by 3) and 228 set the Scaled Lifetime field to the resulting value. If 229 such a non-zero lifetime value to be divided by 8 (to be 230 subjected to a logical right-shift by 3) is less than 8 then 231 the Scaled Lifetime field SHOULD by default be set to 1. 233 PLC 3-bit unsigned integer. This field encodes the NAT64 Prefix 234 (Prefix Length defined in [RFC6052]. The PLC field values 0, 1, 2, 235 Length 3, 4 and 5 indicate the NAT64 prefix length of 96, 64, 56, 236 Code) 48, 40 and 32 bits respectively. The receiver MUST ignore 237 the PREF64 option if the prefix length code field is not set 238 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 Provisioning Domain (PvD, [RFC7556])-aware routers MUST only compare 300 information scoped to the same 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 reduces the attack surface to 325 be targeted by malicious attackers to provide hosts with invalid 326 configuration as compared to distributing the configuration through 327 multiple different mechanisms that need to be secured independently. 329 The security measures that must already be in place to ensure that 330 Router Advertisements are only received from legitimate sources 331 eliminate the problem of NAT64 prefix validation described in section 332 3.1 of [RFC7050]. 334 10. Acknowledgements 336 Thanks to the following people (in alphabetical order) for their 337 review and feedback: Mikael Abrahamsson, Mark Andrews, Brian E 338 Carpenter, David Farmer, Nick Heatley, Robert Hinden, Martin Hunek, 339 Tatuya Jinmei, Erik Kline, Suresh Krishnan, David Lamparter, Jordi 340 Palet Martinez, Tommy Pauly, Alexandre Petrescu, Michael Richardson, 341 David Schinazi, Ole Troan, Bernie Volz. 343 11. References 345 11.1. Normative References 347 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 348 Requirement Levels", BCP 14, RFC 2119, 349 DOI 10.17487/RFC2119, March 1997, 350 . 352 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 353 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 354 DOI 10.17487/RFC4861, September 2007, 355 . 357 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 358 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 359 DOI 10.17487/RFC6052, October 2010, 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 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 368 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 369 May 2017, . 371 11.2. Informative References 373 [RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. 374 Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, 375 DOI 10.17487/RFC6105, February 2011, 376 . 378 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 379 NAT64: Network Address and Protocol Translation from IPv6 380 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 381 April 2011, . 383 [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van 384 Beijnum, "DNS64: DNS Extensions for Network Address 385 Translation from IPv6 Clients to IPv4 Servers", RFC 6147, 386 DOI 10.17487/RFC6147, April 2011, 387 . 389 [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: 390 Combination of Stateful and Stateless Translation", 391 RFC 6877, DOI 10.17487/RFC6877, April 2013, 392 . 394 [RFC7225] Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the 395 Port Control Protocol (PCP)", RFC 7225, 396 DOI 10.17487/RFC7225, May 2014, 397 . 399 [RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain 400 Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015, 401 . 403 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 404 and P. Hoffman, "Specification for DNS over Transport 405 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 406 2016, . 408 [RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: 409 Better Connectivity Using Concurrency", RFC 8305, 410 DOI 10.17487/RFC8305, December 2017, 411 . 413 [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS 414 (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, 415 . 417 11.3. URIs 419 [1] https://www.iana.org/assignments/icmpv6-parameters 421 Authors' Addresses 423 Lorenzo Colitti 424 Google 425 Shibuya 3-21-3 426 Shibuya, Tokyo 150-0002 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