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Checking references for intended status: Best Current Practice ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-07) exists of draft-ietf-6man-slaac-renum-02 Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPv6 Operations Working Group (v6ops) F. Gont 3 Internet-Draft SI6 Networks 4 Updates: 7084 (if approved) J. Zorz 5 Intended status: Best Current Practice 6connect 6 Expires: November 28, 2021 R. Patterson 7 Sky UK 8 B. Volz 9 Cisco 10 May 27, 2021 12 Improving the Reaction of Customer Edge Routers to IPv6 Renumbering 13 Events 14 draft-ietf-v6ops-cpe-slaac-renum-08 16 Abstract 18 This document specifies improvements to Customer Edge Routers that 19 help mitigate the problems that may arise when network configuration 20 information becomes invalid, without any explicit signaling of that 21 condition to the local nodes. This document updates RFC7084. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at https://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on November 28, 2021. 40 Copyright Notice 42 Copyright (c) 2021 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (https://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 58 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2 59 3. Improved Customer Edge Router Behavior . . . . . . . . . . . 3 60 3.1. Automatic DHCPv6 RELEASEs . . . . . . . . . . . . . . . . 4 61 3.2. Stability of IAIDs . . . . . . . . . . . . . . . . . . . 4 62 3.3. Interface Between WAN-side and LAN-side . . . . . . . . . 4 63 3.4. LAN-side Option Lifetimes . . . . . . . . . . . . . . . . 5 64 3.5. Signaling Stale Configuration Information . . . . . . . . 7 65 4. Recommended Option Lifetimes Configuration Values . . . . . . 9 66 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 67 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 68 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 69 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 70 8.1. Normative References . . . . . . . . . . . . . . . . . . 10 71 8.2. Informative References . . . . . . . . . . . . . . . . . 11 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 74 1. Introduction 76 In scenarios where network configuration information becomes invalid 77 without any explicit signaling of that condition (such as when a 78 Customer Edge Router crashes and reboots without knowledge of the 79 previously-employed configuration information), hosts on the local 80 network will continue using stale information for an unacceptably 81 long period of time, thus resulting in connectivity problems. This 82 problem is documented in detail in [RFC8978]. 84 This document specifies improvements to Customer Edge (CE) Routers 85 that help mitigate the aforementioned problem for residential and 86 small office scenarios. It specifies recommendations for the default 87 behavior of CE Routers, and does not preclude the availability of 88 configuration knobs that might allow an operator or user to manually- 89 configure the CE Router to deviate from these recommendations. This 90 document updates RFC7084. 92 2. Requirements Language 94 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 95 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 96 "OPTIONAL" in this document are to be interpreted as described in BCP 97 14 [RFC2119] [RFC8174] when, and only when, they appear in all 98 capitals, as shown here. 100 3. Improved Customer Edge Router Behavior 102 This section specifies and clarifies requirements for Customer Edge 103 Routers that can help mitigate the problem discussed in Section 1, 104 particularly when they employ prefixes learned via DHCPv6-Prefix 105 Delegation (DHCPv6-PD) [RFC8415] on the WAN-side with Stateless 106 Address Autoconfiguration (SLAAC) [RFC4862] or DHCPv6 [RFC8415] on 107 the LAN-side. The recommendations in this document help improve 108 robustness at the Customer Edge Router (on which the user or ISP may 109 have no control), and do not preclude implementation of host-side 110 improvements such as those specified in [I-D.ietf-6man-slaac-renum]. 112 This document specifies additional prefix-delegation requirements to 113 those specified in [RFC7084]: 115 o WPD-9: CE routers SHOULD NOT automatically send DHCPv6-PD RELEASE 116 messages upon reboot events. See Section 3.1 for further details. 118 o WPD-10: CE Routers MUST by default use a WAN-side IAID value that 119 is stable between CE Router restarts, DHCPv6 client restarts, or 120 interface state changes (e.g., Transient PPP interfaces), unless 121 the CE Router employs the IAID techniques discussed in Section 4.5 122 of [RFC7844]. See Section 3.2 for further details. 124 This document also replaces LAN-side requirement L-13 from [RFC7084] 125 with: 127 o L-13: CE routers MUST signal stale configuration information as 128 specified in Section 3.5. 130 Finally, this document specifies the following additional LAN-side 131 requirements to those from [RFC7084]: 133 o L-15: CE routers MUST NOT advertise prefixes via SLAAC or assign 134 addresses or delegate prefixes via DHCPv6 on the LAN-side, 135 employing lifetimes that exceed the remaining lifetimes of the 136 corresponding prefixes learned from the WAN-side via DHCPv6-PD. 137 For more details, see Section 3.3. 139 o L-16: CE routers SHOULD advertise capped SLAAC option lifetimes 140 and capped DHCPv6 IA Address Option and IA Prefix Option 141 lifetimes, as specified in Section 3.4. 143 3.1. Automatic DHCPv6 RELEASEs 145 Some CE Routers are known to automatically send DHCPv6-PD RELEASE 146 messages upon reboot events. However, this may inadvertently trigger 147 a flash-renumbering scenario, along with the associated problems 148 discussed in [RFC8978], that this document attempts to mitigate. 150 As a result, requirement WPD-9 from Section 3 specifies that CE 151 routers SHOULD NOT automatically send DHCPv6-PD RELEASE messages upon 152 reboot events. 154 3.2. Stability of IAIDs 156 [RFC8415] requires that the IAID for an IA MUST be consistent across 157 restarts of the DHCP client. However, some popular CE Routers are 158 known to select new random IAIDs e.g. everytime the underlying PPP 159 session is established. This could be the result of extrapolating 160 the behavior described in [RFC7844], or simply a consequence of not 161 storing IAIDs on stable storage along with failing to employ an 162 algorithm that consistently generates the same IAID upon reboots. 163 Thus, requirement WPD-10 from Section 3 prevents CE Routers from 164 inadvertently triggering flash-renumbering events on the local 165 network. 167 3.3. Interface Between WAN-side and LAN-side 169 The "Preferred Lifetime" and "Valid Lifetime" of Prefix Information 170 Options (PIOs) [RFC4861] corresponding to prefixes learned via 171 DHCPv6-PD MUST NOT span past the remaining preferred and valid 172 lifetimes of the corresponding DHCPv6-PD prefixes. This means that 173 the "Preferred Lifetime" and the "Valid Lifetime" advertised in PIOs 174 by the CE router MUST be dynamically adjusted such that they never 175 span past the remaining preferred and valid lifetimes of the 176 corresponding prefixes delegated via DHCPv6-PD on the WAN-side. 178 Similarly, the "preferred-lifetime" and "valid-lifetime" of DHCPv6 IA 179 Address Options and DHCPv6 IA Prefix Options employed with DHCPv6 on 180 the LAN-side MUST NOT span past the remaining preferred and valid 181 lifetimes of the corresponding prefixes leased via DHCPv6-PD on the 182 WAN-side. This means that the "preferred-lifetime" and "valid- 183 lifetime" of DHCPv6 IA Address Options and DHCPv6 IA Prefix Options 184 employed with DHCPv6 on the LAN-side MUST be dynamically adjusted 185 such that they never span past the remaining preferred and valid 186 lifetimes of the corresponding prefixes delegated to the CE router on 187 the WAN-side via DHCPv6-PD. 189 RATIONALE: 191 * The lifetime values employed for the "Preferred Lifetime" 192 (AdvPreferredLifetime) and "Valid Lifetime" (AdvValidLifetime) 193 of SLAAC Prefix Information Options must never be larger than 194 the remaining lifetimes for the corresponding prefix (as 195 learned via DHCPv6-PD on the WAN-side). This is in line with 196 the requirement from Section 6.3 of [RFC8415], which states 197 that "if the delegated prefix or a prefix derived from it is 198 advertised for stateless address autoconfiguration [RFC4862], 199 the advertised preferred and valid lifetimes MUST NOT exceed 200 the corresponding remaining lifetimes of the delegated prefix." 202 * The lifetime values of prefixes advertised on the LAN-side via 203 SLAAC must be dynamically updated (rather than static values), 204 otherwise the advertised lifetimes would eventually span past 205 the DHCPv6-PD lifetimes. 207 * The same considerations apply for the valid-lifetime and 208 preferred-lifetime of IA Address Options and IA Prefix Options 209 employed with DHCPv6 on the LAN-side. 211 3.4. LAN-side Option Lifetimes 213 CE Routers SHOULD override the default lifetime values of Neighbor 214 Discovery options that depend in any way on changes in the prefix 215 employed for address configuration on the LAN-side, and employ 216 shorter lifetime values to improve the robustness to renumbering 217 events, while complying with the requirements from Section 3.3 of 218 this document and the recommendations in [RFC7772]. 220 CE Routers SHOULD set the Router Lifetime to ND_PREFERRED_LIMIT. 222 CE Routers SHOULD also set the PIO Preferred Lifetime to the lesser 223 of the remaining preferred lifetime (see Section 3.3) and 224 ND_PREFERRED_LIMIT, and the PIO Valid Lifetime to the lesser of the 225 remaining valid lifetime and ND_VALID_LIMIT. Additionally, the Route 226 Lifetime of Route Information Options (RIOs) [RFC4191], the Lifetime 227 of Recursive DNS Search Options (RDNSSO) [RFC8106], and the Lifetime 228 of DNS Search List Options (DNSSLO) [RFC8106] SHOULD be set to the 229 lesser of the longest valid-lifetime in a DHCPv6 IA Prefix Option 230 (received via DHCPv6 on the WAN-side) and ND_VALID_LIMIT, if any of 231 these options are included in Router Advertisement messages. 233 NOTES: In scenarios where the valid-lifetime and the preferred- 234 lifetime of the prefix leased via DHCPv6 on the WAN-side are 235 always larger than ND_VALID_LIMIT and ND_PREFERRED_LIMIT, 236 respectively, the lifetime values advertised on the LAN-side will 237 not experience actual changes. 239 The above text refers to the Neighbor Discovery Options that are 240 typically employed by CE Routers. A CE Router may need to apply 241 the same policy for setting the lifetime of other Neighbor 242 Discovery options it employs, if and where applicable. 244 CE Routers providing stateful address configuration via DHCPv6 SHOULD 245 set the DHCPv6 IA Address Option preferred-lifetime to the lesser of 246 the remaining preferred lifetime (see Section 3.3) and 247 ND_PREFERRED_LIMIT, and the valid-lifetime of the same option to the 248 lesser of the remaining valid lifetime and ND_VALID_LIMIT. 250 CE Routers providing DHCPv6-PD on the LAN-side SHOULD set the DHCPv6 251 IA Prefix Option preferred-lifetime to the lesser of the remaining 252 preferred lifetime (see Section 3.3) and ND_PREFERRED_LIMIT, and the 253 valid-lifetime of the same option to the lesser of the remaining 254 valid lifetime and ND_VALID_LIMIT. 256 RATIONALE: 258 * The Valid Lifetime and Preferred Lifetime of PIOs have a direct 259 impact on three different aspects: 261 + The amount of time hosts may end up employing stale network 262 configuration information (see [RFC8978]). 264 + The amount of time CE Routers need to persist trying to 265 deprecate stale network configuration information (e.g. to 266 handle cases where hosts miss Router Advertisements and thus 267 still consider the stale information as valid). 269 + The amount of information that CE Routers need to maintain 270 when e.g. multiple crash-and-reboot events occur in the 271 timespan represented by the option lifetimes employed on the 272 LAN-side. 274 * CE Routers need not employ the (possibly long) WAN-side 275 DHCPv6-PD lifetimes for the Valid Lifetime and Preferred 276 Lifetime of PIOs sent in Router Advertisements messages to 277 advertise sub-prefixes of the leased prefix. Instead, CE 278 Routers SHOULD use shorter values for the Valid Lifetime and 279 Preferred Lifetime of PIOs, since subsequent Router 280 Advertisement messages will nevertheless refresh the associated 281 lifetimes, leading to the same effective lifetimes as specified 282 by the WAN-side DHCPv6-PD lifetimes. 284 * Similarly, CE Routers need not employ the (possibly long) WAN- 285 side DHCPv6-PD lifetimes for the valid-lifetime and preferred- 286 lifetime of IA Address Options and IA Prefix Option employed by 287 DHCPv6 on the LAN-side, since the renewal of bindings by DHCPv6 288 clients will lead to the same effective lifetimes as specified 289 by the WAN-side DHCPv6-PD lifetimes. 291 3.5. Signaling Stale Configuration Information 293 When a CE Router provides LAN-side address-configuration information 294 via SLAAC: 296 o A CE Router sending RAs that advertise dynamically-learned 297 prefixes (e.g. via DHCPv6-PD) SHOULD record, on stable storage, 298 the list of prefixes being advertised via PIOs on each network 299 segment, and the state of the "A" and "L" flags of the 300 corresponding PIOs. 302 o Upon changes to the advertised prefixes, and after bootstrapping, 303 the CE Router advertising prefix information via SLAAC proceeds as 304 follows: 306 * Any prefixes that were previously advertised by the CE Router 307 via PIOs in RA messages, but that have now become stale, MUST 308 be advertised with a PIO that has the "Valid Lifetime" and the 309 "Preferred Lifetime" set to 0, and the "A" and "L" bits 310 unchanged. 312 * The aforementioned advertisement MUST be performed for at least 313 the "Valid Lifetime" previously employed for such prefix. The 314 CE Router MUST advertise this information with unsolicited 315 Router Advertisements as described in Section 6.2.4 of 316 [RFC4861], and MAY advertise this information via unicast 317 Router Advertisements when possible and applicable. 319 + Note: If requirement L-16 (Section 3.4) is followed, the 320 Valid Lifetime need not be saved and the stale prefix can 321 simply be advertised for a period of ND_VALID_LIMIT. 323 o CE Routers receiving DHCPv6 Prefix Delegations with a 0 valid- 324 lifetime MUST advertise the corresponding sub-prefixes (as they 325 would be generated for the same leased prefix with a non-zero 326 lifetime) with a PIO with both the Preferred Lifetime and the 327 Valid Lifetime set to 0, for at least the WAN-side DHCPv6-PD 328 valid-lifetime, or for a period of ND_VALID_LIMIT if the 329 recommended lifetimes from Section 3.4 are employed. 331 When a CE Router provides LAN-side DHCPv6 (address assignment or 332 prefix delegation), then: 334 o The CE Router SHOULD record, on stable storage, the DHCPv6 address 335 and delegated-prefix bindings corresponding to the LAN-side. 337 o If the CE Router finds that the prefix to be employed for address 338 assignment and/or prefix delegation has changed (e.g., upon a 339 crash-and-reboot event) or the CE Router receives DHCPv6 Prefix 340 Delegations with 0 lifetimes, the CE Router MUST: 342 * In Replies to DHCPv6 Request, Renew, and Rebind messages, send 343 IA Address Options or IA Prefix Options (as appropriate) for 344 any address assignments or prefix delegations for the 345 deprecated prefixes. The aforementioned options MUST be sent 346 with both the valid-lifetime and the preferred-lifetime set to 347 0, for at least the valid-lifetime originally employed for 348 them, or for a period of ND_VALID_LIMIT if the recommended 349 lifetimes from Section 3.4 are employed. 351 * Initiate sending Reconfigure messages (if possible - i.e., 352 client requests Reconfigure support and the CE Router offers 353 it) to those clients with address assignments or prefix 354 delegations for the deprecated prefixes. 356 RATIONALE: 358 * IPv6 network renumbering is expected to take place in a planned 359 manner, with old/stale prefixes being phased-out via reduced 360 prefix lifetimes while new prefixes (with normal lifetimes) are 361 introduced. However, a number of scenarios may lead to the so- 362 called "flash-renumbering" events, where the prefix being 363 employed on a network suddenly becomes invalid and replaced by 364 a new prefix [RFC8978]. One such scenario is when a DHCPv6 365 server employs dynamic prefixes and the Customer Edge Router 366 crashes and reboots. The requirements in this section are 367 meant to allow Customer Edge Routers to deprecate stale 368 information in such scenarios. 370 * The recommendations in this section expand from requirement 371 L-13 in Section 4.3 of [RFC7084], and Section 6.3 of [RFC8415]. 373 * Host configuring addresses via SLAAC on the local network may 374 employ addresses configured for the previously advertised 375 prefixes for at most the "Valid Lifetime" of the corresponding 376 PIO of the last received Router Advertisement message. Since 377 Router Advertisement messages may be lost or fail to be 378 received for various reasons, Customer Edge Routers need to try 379 to deprecate stale prefixes for a period of time equal to the 380 "Valid Lifetime" of the PIO employed when originally 381 advertising the prefix. 383 * The requirement in this section is conveyed as a "SHOULD" (as 384 opposed to a "MUST"), since the requirement to store 385 information on stable storage may represent a challenge for 386 some implementations. 388 * Advertising DHCPv6-leased prefixes with zero lifetimes on the 389 LAN-side would handle the case where a CE Router has no stable 390 storage but receives the prefixes via DHCPv6 with 0 lifetimes. 392 * The above text does not include DHCPv6 Advertise messages sent 393 in response to DHCPv6 Solicit messages, since Section 18.3.9 of 394 [RFC8415] requires that a DHCPv6 server that is not going to 395 assign an address or delegated prefix received as a hint in the 396 Solicit message MUST NOT include that address or delegated 397 prefix in the Advertise message. Additionally, any subsequent 398 Request messages will trigger the response specified in this 399 section, and therefore cause the address or prefix to be 400 deprecated. 402 4. Recommended Option Lifetimes Configuration Values 404 o ND_PREFERRED_LIMIT: 2700 seconds (45 minutes) 406 o ND_VALID_LIMIT: 5400 seconds (90 minutes) 408 RATIONALE: 409 These values represent a trade-off among a number of factors, 410 including responsiveness and possible impact on the battery life 411 of connected devices [RFC7772]. 413 ND_PREFERRED_LIMIT is set according to the recommendations in 414 [RFC7772] for Router Lifetime, following the rationale from 415 Section 3.2 of [RFC8978]. 417 ND_VALID_LIMIT is set to 2 * ND_PREFERRED_LIMIT to provide some 418 additional leeway before configuration information is finally 419 discarded by the host. 421 5. IANA Considerations 423 This document has no actions for IANA. 425 6. Security Considerations 427 This document discusses a problem that may arise in scenarios where 428 dynamic IPv6 prefixes are employed, and proposes improvements to 429 Customer Edge Routers [RFC7084] to mitigate the problem for 430 residential or small office scenarios. It does not introduce new 431 security issues, and thus the same security considerations as for 432 [RFC4861], [RFC4862], [RFC7084], and [RFC8415] apply. 434 7. Acknowledgments 436 The authors would like to thank Owen DeLong, Philip Homburg, Erik 437 Kline, and Ted Lemon, for their valuable help in improving this 438 document via successive detailed reviews. 440 The authors would like to thank Mikael Abrahamsson, Luis Balbinot, 441 Tim Chown, Brian Carpenter, Lorenzo Colitti, Alejandro D'Egidio, Gert 442 Doering, Fernando Frediani, Guillermo Gont, Steinar Haug, Nick 443 Hilliard, Lee Howard, Christian Huitema, Sheng Jiang, Benjamin Kaduk, 444 Suresh Krishnan, Warren Kumari, Albert Manfredi, Olorunloba Olopade, 445 Jordi Palet Martinez, Richard Patterson, Pete Resnick, Michael 446 Richardson, Mark Smith, Job Snijders, Sander Steffann, Tarko Tikan, 447 Ole Troan, Loganaden Velvindron, Eric Vyncke, Robert Wilton, Timothy 448 Winters, Christopher Wood, and Chongfeng Xie, for providing valuable 449 comments on earlier versions of this document. 451 Fernando would also like to thank Brian Carpenter who, over the 452 years, has answered many questions and provided valuable comments 453 that have benefited his protocol-related work. 455 8. References 457 8.1. Normative References 459 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 460 Requirement Levels", BCP 14, RFC 2119, 461 DOI 10.17487/RFC2119, March 1997, 462 . 464 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 465 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 466 November 2005, . 468 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 469 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 470 DOI 10.17487/RFC4861, September 2007, 471 . 473 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 474 Address Autoconfiguration", RFC 4862, 475 DOI 10.17487/RFC4862, September 2007, 476 . 478 [RFC7772] Yourtchenko, A. and L. Colitti, "Reducing Energy 479 Consumption of Router Advertisements", BCP 202, RFC 7772, 480 DOI 10.17487/RFC7772, February 2016, 481 . 483 [RFC7844] Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity 484 Profiles for DHCP Clients", RFC 7844, 485 DOI 10.17487/RFC7844, May 2016, 486 . 488 [RFC8106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 489 "IPv6 Router Advertisement Options for DNS Configuration", 490 RFC 8106, DOI 10.17487/RFC8106, March 2017, 491 . 493 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 494 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 495 May 2017, . 497 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 498 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 499 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 500 RFC 8415, DOI 10.17487/RFC8415, November 2018, 501 . 503 8.2. Informative References 505 [I-D.ietf-6man-slaac-renum] 506 Gont, F., Zorz, J., and R. Patterson, "Improving the 507 Robustness of Stateless Address Autoconfiguration (SLAAC) 508 to Flash Renumbering Events", draft-ietf-6man-slaac- 509 renum-02 (work in progress), January 2021. 511 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 512 Requirements for IPv6 Customer Edge Routers", RFC 7084, 513 DOI 10.17487/RFC7084, November 2013, 514 . 516 [RFC8978] Gont, F., Zorz, J., and R. Patterson, "Reaction of IPv6 517 Stateless Address Autoconfiguration (SLAAC) to Flash- 518 Renumbering Events", RFC 8978, DOI 10.17487/RFC8978, March 519 2021, . 521 Authors' Addresses 522 Fernando Gont 523 SI6 Networks 524 Segurola y Habana 4310, 7mo Piso 525 Villa Devoto, Ciudad Autonoma de Buenos Aires 526 Argentina 528 Email: fgont@si6networks.com 529 URI: https://www.si6networks.com 531 Jan Zorz 532 6connect 534 Email: jan@6connect.com 536 Richard Patterson 537 Sky UK 539 Email: richard.patterson@sky.uk 541 Bernie Volz 542 Cisco Systems, Inc. 543 300 Beaver Brook Rd 544 Boxborough, MA 01719 545 USA 547 Email: volz@cisco.com