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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPv6 Operations L. Colitti 3 Internet-Draft V. Cerf 4 Intended status: Best Current Practice Google 5 Expires: September 10, 2016 S. Cheshire 6 D. Schinazi 7 Apple Inc. 8 March 9, 2016 10 Host address availability recommendations 11 draft-ietf-v6ops-host-addr-availability-06 13 Abstract 15 This document recommends that networks provide general-purpose end 16 hosts with multiple global IPv6 addresses when they attach, and 17 describes the benefits of and the options for doing so. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on September 10, 2016. 36 Copyright Notice 38 Copyright (c) 2016 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 55 2. Common IPv6 deployment model . . . . . . . . . . . . . . . . 3 56 3. Benefits of providing multiple addresses . . . . . . . . . . 3 57 4. Problems with restricting the number of addresses per host . 4 58 5. Overcoming limits using Network Address Translation . . . . . 5 59 6. Options for providing more than one address . . . . . . . . . 6 60 7. Number of addresses required . . . . . . . . . . . . . . . . 7 61 8. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 8 62 9. Operational considerations . . . . . . . . . . . . . . . . . 8 63 9.1. Host tracking . . . . . . . . . . . . . . . . . . . . . . 8 64 9.2. Address space management . . . . . . . . . . . . . . . . 9 65 9.3. Addressing link layer scalability issues via IP routing . 10 66 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 67 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 68 12. Security Considerations . . . . . . . . . . . . . . . . . . . 11 69 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 70 13.1. Normative References . . . . . . . . . . . . . . . . . . 11 71 13.2. Informative References . . . . . . . . . . . . . . . . . 11 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 74 1. Introduction 76 In most aspects, the IPv6 protocol is very similar to IPv4. This 77 similarity can create a tendency to think of IPv6 as 128-bit IPv4, 78 and thus lead network designers and operators to apply identical 79 configurations and operational practices to both. This is generally 80 a good thing because it eases the transition to IPv6 and the 81 operation of dual-stack networks. However, in some design and 82 operational areas it can lead to carrying over IPv4 practices that 83 are limiting or not appropriate in IPv6 due to differences between 84 the protocols. 86 One such area is IP addressing, particularly IP addressing of hosts. 87 This is substantially different because unlike IPv4 addresses, IPv6 88 addresses are not a scarce resource. In IPv6, a single link provides 89 over four billion times more address space than the whole IPv4 90 Internet [RFC7421]. Thus, unlike IPv4, IPv6 networks are not forced 91 by address availability considerations to provide only one address 92 per host. On the other hand, providing multiple addresses has many 93 benefits including application functionality and simplicity, privacy, 94 flexibility to accommodate future applications, and the ability to 95 provide Internet access without the use of NAT. Providing only one 96 IPv6 address per host negates these benefits. 98 This document describes the benefits of providing multiple addresses 99 per host and the problems with not doing so. It recommends that 100 networks provide general-purpose end hosts with multiple global 101 addresses when they attach, and lists current options for doing so. 102 It does not specify any changes to protocols or host behavior. 104 1.1. Requirements Language 106 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 107 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 108 "OPTIONAL" in this document are to be interpreted as described in 109 "Key words for use in RFCs to Indicate Requirement Levels" [RFC2119]. 111 2. Common IPv6 deployment model 113 IPv6 is designed to support multiple addresses, including multiple 114 global addresses, per interface ([RFC4291] section 2.1, [RFC6434] 115 section 5.9.4). Today, many general-purpose IPv6 hosts are 116 configured with three or more addresses per interface: a link-local 117 address, a stable address (e.g., using EUI-64 or Opaque Interface 118 Identifiers [RFC7217]), one or more privacy addresses [RFC4941], and 119 possibly one or more temporary or non-temporary addresses obtained 120 using DHCPv6 [RFC3315]. 122 In most general-purpose IPv6 networks, including all 3GPP networks 123 ([RFC6459] section 5.2) and Ethernet and Wi-Fi networks using SLAAC 124 [RFC4862], IPv6 hosts have the ability to configure additional IPv6 125 addresses from the link prefix(es) without explicit requests to the 126 network. 128 3. Benefits of providing multiple addresses 130 Today, there are many host functions that require more than one IP 131 address to be available to the host, including: 133 o Privacy addressing to prevent tracking by off-network hosts 134 [RFC4941]. 136 o Multiple processors inside the same device. For example, in many 137 mobile devices both the application processor and baseband 138 processor need to communicate with the network, particularly for 139 recent technologies like ePDG. 141 o Extending the network (e.g., "tethering"). 143 o Running virtual machines on hosts. 145 o Translation-based transition technologies such as 464XLAT 146 [RFC6877] that provide IPv4 over IPv6. Some of these technologies 147 require the availability of a dedicated IPv6 address in order to 148 determine whether inbound packets are translated or native 149 ([RFC6877] section 6.3). 151 o ILA ("Identifier-locator addressing") [I-D.herbert-nvo3-ila]. 153 o Future applications (e.g., per-application IPv6 addresses [TARP]). 155 Examples of how the availability of multiple addresses per host has 156 already allowed substantial deployment of new applications without 157 explicit requests to the network are: 159 o 464XLAT. 464XLAT is usually deployed within a particular network, 160 and in this model the operator can ensure that the network is 161 appropriately configured to provide the CLAT with the additional 162 IPv6 address it needs to implement 464XLAT. However, there are 163 deployments where the PLAT (i.e., NAT64) is provided as a service 164 by a different network, without the knowledge or cooperation of 165 the residential ISP (e.g., the IPv6v4 Exchange Service 166 ). This type of 167 deployment is only possible because those residential ISPs provide 168 multiple IP addresses to their users, and thus those users can 169 freely obtain the extra IPv6 address required to run 464XLAT. 171 o /64 sharing [RFC7278]. When the topology supports it, this is a 172 way to provide IPv6 tethering without needing to wait for network 173 operators to deploy DHCPv6 PD, which is only available in 3GPP 174 release 10 ([RFC6459] section 5.3). 176 4. Problems with restricting the number of addresses per host 178 Providing a restricted number of addresses per host implies that 179 functions that require multiple addresses will either be unavailable 180 (e.g., if the network provides only one IPv6 address per host, or if 181 the host has reached the limit of the number of addresses available), 182 or that the functions will only be available after an explicit 183 request to the network is granted. The necessity of explicit 184 requests has the following drawbacks: 186 o Increased latency, because a provisioning operation, and possibly 187 human intervention with an update to the service level agreement, 188 must complete before the functionality is available. 190 o Uncertainty, because it is not known in advance if a particular 191 operation function will be available. 193 o Complexity, because implementations need to deal with failures and 194 somehow present them to the user. Failures may manifest as 195 timeouts, which may be slow and frustrating to users. 197 o Increased load on the network's provisioning servers. 199 Some operators may desire to configure their networks to limit the 200 number of IPv6 addresses per host. Reasons might include hardware 201 limitations (e.g., TCAM or neighbor cache table size constraints), 202 business models (e.g., a desire to charge the network's users on a 203 per-device basis), or operational consistency with IPv4 (e.g., an IP 204 address management system that only supports one address per host). 205 However, hardware limitations are expected to ease over time, and an 206 attempt to generate additional revenue by charging per device may 207 prove counterproductive if customers respond (as they did with IPv4) 208 by using NAT, which results in no additional revenue, but leads to 209 more operational problems and higher support costs. 211 5. Overcoming limits using Network Address Translation 213 These limits can mostly be overcome by end hosts by using NAT, and 214 indeed in IPv4 most of these functions are provided by using NAT on 215 the host. Thus, the limits could be overcome in IPv6 as well by 216 implementing NAT66 on the host. 218 Unfortunately NAT has well-known drawbacks. For example, it causes 219 application complexity due to the need to implement NAT traversal. 220 It hinders development of new applications. On mobile devices, it 221 reduces battery life due to the necessity of frequent keepalives, 222 particularly for UDP. Applications using UDP that need to work on 223 most of the Internet are forced to send keepalives at least every 30 224 seconds . For example, the QUIC protocol uses a 15-second keepalive 226 [I-D.tsvwg-quic-protocol]. Other drawbacks of NAT are well known and 227 documented [RFC2993]. While IPv4 NAT is inevitable due to the 228 limited amount of IPv4 space available, that argument does not apply 229 to IPv6. Guidance from the IAB is that deployment of IPv6 NAT is not 230 desirable [RFC5902]. 232 The desire to overcome the problems listed in Section 4 without 233 disabling any features has resulted in developers implementing IPv6 234 NAT. There are fully-stateful address+port NAT66 implementations in 235 client operating systems today: for example, Linux has supported 236 NAT66 since late 2012 . A popular software 238 hypervisor also recently implemented NAT66 to work around these 239 issues . Wide 240 deployment of networks that provide a restricted number of addresses 241 will cause proliferation of NAT66 implementations. 243 This is not a desirable outcome. It is not desirable for users 244 because they may experience application brittleness. It is likely 245 not desirable for network operators either, as they may suffer higher 246 support costs, and even when the decision to provide only one IPv6 247 address per device is dictated by the network's business model, there 248 may be little in the way of incremental revenue, because devices can 249 share their IPv6 address with other devices. Finally, it is not 250 desirable for operating system manufacturers and application 251 developers, who will have to build more complexity, lengthening 252 development time and/or reducing the time spent on other features. 254 Indeed, it could be argued that the main reason for deploying IPv6, 255 instead of continuing to scale the Internet using only IPv4 and 256 large-scale NAT44, is because doing so can provide all the hosts on 257 the planet with end-to-end connectivity that is constrained not by 258 accidental technical limitations, but only by intentional security 259 policies. 261 6. Options for providing more than one address 263 Multiple IPv6 addresses can be provided in the following ways: 265 o Using Stateless Address Autoconfiguration [RFC4862]. SLAAC allows 266 hosts to create global IPv6 addresses on demand by simply forming 267 new addresses from the global prefix(es) assigned to the link. 268 Typically, SLAAC is used on shared links, but it is also possible 269 to use SLAAC while providing a dedicated /64 prefix to each host. 270 This is the case, for example, if the host is connected via a 271 point-to-point link such as in 3GPP networks, on a network where 272 each host has its own dedicated VLAN, or on a wireless network 273 where every MAC address is placed in its own broadcast domain. 275 o Using stateful DHCPv6 address assignment [RFC3315]. Most DHCPv6 276 clients only ask for one non-temporary address, but the protocol 277 allows requesting multiple temporary and even multiple non- 278 temporary addresses, and the server could choose to provide 279 multiple addresses. It is also technically possible for a client 280 to request additional addresses using a different DUID, though the 281 DHCPv6 specification implies that this is not expected behavior 282 ([RFC3315] section 9). The DHCPv6 server will decide whether to 283 grant or reject the request based on information about the client, 284 including its DUID, MAC address, and so on. The maximum number of 285 IPv6 addresses that can be provided in a single DHCPv6 packet, 286 given a typical MTU of 1500 bytes or smaller, is approximately 30. 288 o DHCPv6 prefix delegation [RFC3633]. DHCPv6 PD allows the client 289 to request and be delegated a prefix, from which it can 290 autonomously form other addresses. If the prefix is shorter than 291 /64, it can be divided into multiple subnets which can be further 292 delegated to downstream clients. If the prefix is a /64, it can 293 be extended via L2 bridging, ND proxying [RFC4389] or /64 sharing 294 [RFC7278], but it cannot be further subdivided, as a prefix longer 295 than /64 is outside the current IPv6 specifications [RFC7421]. 296 While [RFC3633] assumes that the DHCPv6 client is a router, DHCPv6 297 PD itself does not require that the client forward IPv6 packets 298 not addressed to itself, and thus does not require that the client 299 be an IPv6 router as defined in [RFC2460]. 301 +--------------------------+-------+-------------+--------+---------+ 302 | | SLAAC | DHCPv6 | DHCPv6 | DHCPv4 | 303 | | | IA_NA / | PD | | 304 | | | IA_TA | | | 305 +--------------------------+-------+-------------+--------+---------+ 306 | Can extend network | No+ | No | Yes | Yes | 307 | | | | | (NAT44) | 308 | Can number "unlimited" | Yes* | Yes* | No | No | 309 | endpoints | | | | | 310 | Uses stateful, request- | No | Yes | Yes | Yes | 311 | based assignment | | | | | 312 | Is immune to layer 3 on- | No | Yes | Yes | Yes | 313 | link resource exhaustion | | | | | 314 | attacks | | | | | 315 +--------------------------+-------+-------------+--------+---------+ 317 [*] Subject to network limitations, e.g., ND cache entry size limits. 318 [+] Except on certain networks, e.g., [RFC7278]. 320 Table 1: Comparison of multiple address assignment options 322 7. Number of addresses required 324 If we itemize the use cases from section Section 3, we can estimate 325 the number of addresses currently used in normal operations. In 326 typical implementations, privacy addresses use up to 8 addresses - 327 one per day ([RFC4941] section 3.5). Current mobile devices may 328 typically support 8 clients, with each one requiring one or more 329 addresses. A client might choose to run several virtual machines. 330 Current implementations of 464XLAT require use of a separate address. 331 Some devices require another address for their baseband chip. Even a 332 host performing just a few of these functions simultaneously might 333 need on the order of 20 addresses at the same time. Future 334 applications designed to use an address per application or even per 335 resource will require many more. These will not function on networks 336 that enforce a hard limit on the number of addresses provided to 337 hosts. 339 8. Recommendations 341 In order to avoid the problems described above, and preserve the 342 Internet's ability to support new applications that use more than one 343 IPv6 address, it is RECOMMENDED that IPv6 network deployments provide 344 multiple IPv6 addresses from each prefix to general-purpose hosts. 345 To support future use cases, it is RECOMMENDED to not impose a hard 346 limit on the size of the address pool assigned to a host. 347 Particularly, it is NOT RECOMMENDED to limit a host to only one IPv6 348 address per prefix. 350 Due to the drawbacks imposed by requiring explicit requests for 351 address space (see section Section 4), it is RECOMMENDED that the 352 network give the host the ability to use new addresses without 353 requiring explicit requests. This can be achieved either by allowing 354 the host to form new addresses autonomously (e.g., via SLAAC), or by 355 providing the host with a dedicated /64 prefix. The prefix MAY be 356 provided using DHCPv6 PD, SLAAC with per-device VLANs, or any other 357 means. 359 Using stateful address assignment (DHCPv6 IA_NA or IA_TA) to provide 360 multiple addresses when the host connects (e.g. the approximately 30 361 addresses that can fit into a single packet) would accommodate 362 current clients, but sets a limit on the number of addresses 363 available to hosts when they attach and would limit the development 364 of future applications. 366 9. Operational considerations 368 9.1. Host tracking 370 Some network operators - often operators of networks that provide 371 services to third parties such as university campus networks - are 372 required to track which IP addresses are assigned to which hosts on 373 their network. Maintaining persistent logs that map user IP 374 addresses and timestamps to hardware identifiers such as MAC 375 addresses may be used to avoid liability for copyright infringement 376 or other illegal activity. 378 It is worth noting that this requirement can be met without using 379 DHCPv6 address assignment. For example, it is possible to maintain 380 these mappings by monitoring IPv6 neighbor table: routers typically 381 allow periodic dumps of the neighbor cache via SNMP or other means, 382 and many can be configured to log every change to the neighbor cache. 383 Using SLAAC with a dedicated /64 prefix simplifies tracking, as it 384 does not require logging each address formed by the host, but only 385 the prefix assigned to the host when it attaches to the network. 386 Similarly, providing address space using DHCPv6 PD has the same 387 tracking properties as DHCPv6 address assignment, but allows the 388 network to provide unrestricted address space. 390 Many large enterprise networks are fully dual-stack and implement 391 address monitoring without using or supporting DHCPv6. The authors 392 are directly aware of several networks that operate in this way, 393 including the Universities of Loughborough, Minnesota, Reading, 394 Southampton, Wisconsin and Imperial College London, in addition to 395 the enterprise networks of the authors' employers. 397 It should also be noted that using DHCPv6 address assignment does not 398 ensure that the network can reliably track the IPv6 addresses used by 399 hosts. On any shared network without L2 edge port security, hosts 400 are able to choose their own addresses regardless of what address 401 provisioning methodology is in use. The only way to restrict the 402 addresses used by hosts is to use layer 2 security mechanisms that 403 enforce that particular IPv6 addresses are used by particular link- 404 layer addresses (for example, SAVI [RFC7039]). If those mechanisms 405 are available, it is possible to use them to provide tracking; this 406 form of tracking is more secure and reliable than server logs because 407 it operates independently of how addresses are allocated. Finally, 408 tracking address information via DHCPv6 server logs is likely to 409 become decreasingly viable due to ongoing efforts to improve the 410 privacy of DHCPv6 [I-D.ietf-dhc-anonymity-profile]. 412 9.2. Address space management 414 In IPv4, all but the world's largest networks can be addressed using 415 private space [RFC1918], with each host receiving one IPv4 address. 416 Many networks can be numbered in 192.168.0.0/16 which has roughly 64k 417 addresses. In IPv6, that is equivalent to a /48, with each of 64k 418 hosts receiving a /64 prefix. Under current RIR policies, a /48 is 419 easy to obtain for an enterprise network. Networks that need a 420 bigger block of private space use 10.0.0.0/8, which has roughly 16 421 million addresses. In IPv6, that is equivalent to a /40, with each 422 host receiving /64 prefix. Enterprises of such size can easily 423 obtain a /40 under current RIR policies. 425 In the above cases, aggregation and routing can be equivalent to 426 IPv4: if a network aggregates per-host IPv4 addresses into prefixes 427 of length /32 - n, it can aggregate per-host /64 prefixes into the 428 same number of prefixes of length /64 - n. 430 Currently, residential users typically receive one IPv4 address and a 431 /48, /56 or /60 IPv6 prefix. While such networks do not provide 432 enough space to assign a /64 per host, such networks almost 433 universally use SLAAC, and thus do not pose any particular limit to 434 the number of addresses hosts can use. 436 Unlike IPv4 where addresses came at a premium, in all these networks, 437 there is enough IPv6 address space to supply clients with multiple 438 IPv6 addresses. 440 9.3. Addressing link layer scalability issues via IP routing 442 The number of IPv6 addresses on a link has direct impact for 443 networking infrastructure nodes (routers, switches) and other nodes 444 on the link. Setting aside exhaustion attacks via Layer 2 address 445 spoofing, every (Layer 2, IP) address pair impacts networking 446 hardware requirements in terms of memory, MLD snooping, solicited 447 node multicast groups, etc. Many of these costs are incurred by 448 neighboring hosts. 450 Hosts on such networks that create unreasonable numbers of addresses 451 risk impairing network connectivity for themselves and other hosts on 452 the network, and in extreme cases (e.g., hundreds or thousands of 453 addresses) may even find their network access restricted by denial- 454 of-service protection mechanisms. 456 We expect these scaling limitations to change over time as hardware 457 and applications evolve. However, switching to a dedicated /64 458 prefix per host can resolve these scaling limitations. If the prefix 459 is provided via DHCPv6 PD, or if the prefix can be used by only one 460 link-layer address (e.g., if the link layer uniquely identifies or 461 authenticates hosts based on MAC addresses), then there will be only 462 one routing entry and one ND cache entry per host on the network. 463 Furthermore, if the host is aware that the prefix is dedicated (e.g., 464 if it was provided via DHCPv6 PD and not SLAAC), it is possible for 465 the host to assign IPv6 addresses from this prefix to an internal 466 interface such as a loopback interface. This obviates the need to 467 perform Neighbor Discovery and Duplicate Address Detection on the 468 network interface for these addresses, reducing network traffic. 470 Thus, assigning a dedicated /64 prefix per host is operationally 471 prudent. Clearly, however, it requires more IPv6 address space than 472 using shared links, so the benefits provided must be weighed with the 473 operational overhead of address space management. 475 10. Acknowledgements 477 The authors thank Tore Anderson, Brian Carpenter, David Farmer, 478 Wesley George, Geoff Huston, Erik Kline, Victor Kuarsingh, Shucheng 479 (Will) Liu, Dieter Siegmund, Mark Smith, Sander Steffann, Fred 480 Templin and James Woodyatt for their input and contributions. 482 11. IANA Considerations 484 This memo includes no request to IANA. 486 12. Security Considerations 488 As mentioned in section 9.3, on shared networks using SLAAC it is 489 possible for hosts to attempt to exhaust network resources and 490 possibly deny service to other hosts by creating unreasonable numbers 491 (e.g., hundreds or thousands) of addresses. Networks that provide 492 access to untrusted hosts can mitigate this threat by providing a 493 dedicated /64 prefix per host. It is also possible to mitigate the 494 threat by limiting the number of ND cache entries that can be created 495 for a particular host, but care must be taken to ensure that the 496 network does not restrict the IP addresses available to non-malicious 497 hosts. 499 Security issues related to host tracking are discussed in section 500 9.1. 502 13. References 504 13.1. Normative References 506 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 507 Requirement Levels", BCP 14, RFC 2119, 508 DOI 10.17487/RFC2119, March 1997, 509 . 511 13.2. Informative References 513 [I-D.herbert-nvo3-ila] 514 Herbert, T., "Identifier-locator addressing for network 515 virtualization", draft-herbert-nvo3-ila-01 (work in 516 progress), October 2015. 518 [I-D.ietf-dhc-anonymity-profile] 519 Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity 520 profile for DHCP clients", draft-ietf-dhc-anonymity- 521 profile-08 (work in progress), February 2016. 523 [I-D.tsvwg-quic-protocol] 524 Hamilton, R., Iyengar, J., Swett, I., and A. Wilk, "QUIC: 525 A UDP-Based Secure and Reliable Transport for HTTP/2", 526 draft-tsvwg-quic-protocol-02 (work in progress), January 527 2016. 529 [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., 530 and E. Lear, "Address Allocation for Private Internets", 531 BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996, 532 . 534 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 535 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 536 December 1998, . 538 [RFC2993] Hain, T., "Architectural Implications of NAT", RFC 2993, 539 DOI 10.17487/RFC2993, November 2000, 540 . 542 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 543 C., and M. Carney, "Dynamic Host Configuration Protocol 544 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 545 2003, . 547 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 548 Host Configuration Protocol (DHCP) version 6", RFC 3633, 549 DOI 10.17487/RFC3633, December 2003, 550 . 552 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 553 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 554 2006, . 556 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 557 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 558 2006, . 560 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 561 Address Autoconfiguration", RFC 4862, 562 DOI 10.17487/RFC4862, September 2007, 563 . 565 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 566 Extensions for Stateless Address Autoconfiguration in 567 IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, 568 . 570 [RFC5902] Thaler, D., Zhang, L., and G. Lebovitz, "IAB Thoughts on 571 IPv6 Network Address Translation", RFC 5902, 572 DOI 10.17487/RFC5902, July 2010, 573 . 575 [RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node 576 Requirements", RFC 6434, DOI 10.17487/RFC6434, December 577 2011, . 579 [RFC6459] Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen, 580 T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation 581 Partnership Project (3GPP) Evolved Packet System (EPS)", 582 RFC 6459, DOI 10.17487/RFC6459, January 2012, 583 . 585 [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: 586 Combination of Stateful and Stateless Translation", 587 RFC 6877, DOI 10.17487/RFC6877, April 2013, 588 . 590 [RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed., 591 "Source Address Validation Improvement (SAVI) Framework", 592 RFC 7039, DOI 10.17487/RFC7039, October 2013, 593 . 595 [RFC7217] Gont, F., "A Method for Generating Semantically Opaque 596 Interface Identifiers with IPv6 Stateless Address 597 Autoconfiguration (SLAAC)", RFC 7217, 598 DOI 10.17487/RFC7217, April 2014, 599 . 601 [RFC7278] Byrne, C., Drown, D., and A. Vizdal, "Extending an IPv6 602 /64 Prefix from a Third Generation Partnership Project 603 (3GPP) Mobile Interface to a LAN Link", RFC 7278, 604 DOI 10.17487/RFC7278, June 2014, 605 . 607 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 608 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 609 Boundary in IPv6 Addressing", RFC 7421, 610 DOI 10.17487/RFC7421, January 2015, 611 . 613 [TARP] Gleitz, PM. and SM. Bellovin, "Transient Addressing for 614 Related Processes: Improved Firewalling by Using IPv6 and 615 Multiple Addresses per Host", August 2001. 617 Authors' Addresses 619 Lorenzo Colitti 620 Google 621 Roppongi 6-10-1 622 Minato, Tokyo 106-6126 623 JP 625 Email: lorenzo@google.com 627 Vint Cerf 628 Google 629 1875 Explorer St 630 10th Floor 631 Reston, VA 20190 632 US 634 Email: vint@google.com 636 Stuart Cheshire 637 Apple Inc. 638 1 Infinite Loop 639 Cupertino, CA 95014 640 US 642 Email: cheshire@apple.com 644 David Schinazi 645 Apple Inc. 646 1 Infinite Loop 647 Cupertino, CA 95014 648 US 650 Email: dschinazi@apple.com