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Carpenter 5 Intended status: Standards Track Univ. of Auckland 6 Expires: April 10, 2017 October 7, 2016 8 First-hop router selection by hosts in a multi-prefix network 9 draft-ietf-6man-multi-homed-host-10 11 Abstract 13 This document describes expected IPv6 host behavior in a scenario 14 that has more than one prefix, each allocated by an upstream network 15 that is assumed to implement BCP 38 ingress filtering, when the host 16 has multiple routers to choose from. It also applies to other 17 scenarios such as the usage of stateful firewalls that effectively 18 act as address-based filters. Host behavior in choosing a first-hop 19 router may interact with source address selection in a given 20 implementation. However, the selection of the source address for a 21 packet is done before the first-hop router for that packet is chosen. 22 Given that the network or host is, or appears to be, multihomed with 23 multiple provider-allocated addresses, that the host has elected to 24 use a source address in a given prefix, and that some but not all 25 neighboring routers are advertising that prefix in their Router 26 Advertisement Prefix Information Options, this document specifies to 27 which router a host should present its transmission. It updates RFC 28 4861. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on April 10, 2017. 47 Copyright Notice 49 Copyright (c) 2016 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction and Applicability . . . . . . . . . . . . . . . 2 65 1.1. Host Model . . . . . . . . . . . . . . . . . . . . . . . 3 66 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 5 67 2. Sending context expected by the host . . . . . . . . . . . . 5 68 2.1. Expectations the host has of the network . . . . . . . . 5 69 2.2. Expectations of multihomed networks . . . . . . . . . . . 7 70 3. Reasonable expectations of the host . . . . . . . . . . . . . 7 71 3.1. Interpreting Router Advertisements . . . . . . . . . . . 7 72 3.2. Default Router Selection . . . . . . . . . . . . . . . . 8 73 3.3. Source Address Selection . . . . . . . . . . . . . . . . 9 74 3.4. Redirects . . . . . . . . . . . . . . . . . . . . . . . . 9 75 3.5. History . . . . . . . . . . . . . . . . . . . . . . . . . 9 76 4. Residual issues . . . . . . . . . . . . . . . . . . . . . . . 10 77 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 78 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 79 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 80 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 81 8.1. Normative References . . . . . . . . . . . . . . . . . . 11 82 8.2. Informative References . . . . . . . . . . . . . . . . . 11 83 Appendix A. Change Log (RFC Editor: please delete) . . . . . . . 12 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 86 1. Introduction and Applicability 88 This document describes the expected behavior of an IPv6 [RFC2460] 89 host in a network that has more than one prefix, each allocated by an 90 upstream network that is assumed to implement BCP 38 [RFC2827] 91 ingress filtering, and in which the host is presented with a choice 92 of routers. It expects that the network will implement some form of 93 egress routing, so that packets sent to a host outside the local 94 network from a given ISP's prefix will go to that ISP. If the packet 95 is sent to the wrong egress, it is liable to be discarded by the BCP 96 38 filter. However, the mechanics of egress routing once the packet 97 leaves the host are out of scope. The question here is how the host 98 interacts with that network. 100 Various aspects of this issue, and possible solution approaches, are 101 discussed in the document IPv6 Multihoming without Network Address 102 Translation [RFC7157]. 104 BCP 38 filtering by ISPs is not the only scenario where such behavior 105 is valuable. Implementations that combine existing recommendations, 106 such as [RFC6092] [RFC7084] can also result in such filtering. 107 Another case is when the connections to the upstream networks include 108 stateful firewalls, such that return packets in a stream will be 109 discarded if they do not return via the firewall that created state 110 for the outgoing packets. A similar cause of such discards is 111 unicast reverse path forwarding (uRPF) [RFC3704]. 113 In this document, the term "filter" is used for simplicity to cover 114 all such cases. In any case, one cannot assume the host to be aware 115 whether an ingress filter, a stateful firewall, or any other type of 116 filter is in place. Therefore, the only known consistent solution is 117 to implement the features defined in this document. 119 Note that, apart from ensuring that a message with a given source 120 address is given to a first-hop router that appears to know about the 121 prefix in question, this specification is consistent with [RFC4861]. 122 Nevertheless, implementers of Sections 6.2.3, 6.3.4, 6.3.6 and 8.1 of 123 RFC 4861 should extend their implementations accordingly. This 124 specification is fully consistent with [RFC6724] and depends on 125 support for its Rule 5.5 (see Section 3.3). Hosts that do not 126 support these features may fail to communicate in the presence of 127 filters as described above. 129 1.1. Host Model 131 It could be argued that the proposal of this document, which is to 132 send messages using a source address in a given prefix to the router 133 that advertised the prefix in its Router Advertisement (RA), is a 134 form of [RFC1122]'s Strong End System (ES, e.g. Host) Model, 135 discussed in section 3.3.4.2 of that document. In short, [RFC1122] 136 identifies two basic models, in which the "strong host" model models 137 the host as a set of hosts in one chassis, each of which uses a 138 single address on a single interface, and always both sends and 139 receives on that interface, and the "weak host" model treats the host 140 as one system with zero or more addresses on every interface, and 141 capable of using any interface for any communication. As noted 142 there, neither model is completely satisfactory. For example, a host 143 with a link-local-only interface and a default route pointing to that 144 interface will necessarily send packets using that interface but with 145 a source address derived from some other interface, and will 146 therefore be a de facto weak host. If the router upstream from such 147 a host implements BCP 38 Ingress Filtering [RFC2827], such as by 148 implementing uRPF on each interface, the router might prevent 149 communication by weak hosts. 151 +-----------------+ 152 | | 153 | MIF Router +---/--- other interfaces 154 | | 155 +---+---------+---+ 156 | | Two interfaces with subnets 157 | | from a common prefix 158 --+-+-- --+-+-- 159 | | 160 +--+---------+--+ 161 | MIF Host | 162 +---------------+ 164 Figure 1: Hypothetical MIF interconnection 166 The proposal also differs slightly from [RFC1122]'s language for the 167 Strong Host Model. The proposal is that the packet will go to a 168 router that advertised a given prefix, but does not specify what 169 interface that might happen on. Hence, if the router is a multi- 170 interface (MIF) router and is using a common prefix spanning two or 171 more LANs shared by the host (as in Figure 1), the host might use 172 either of those LANs, according to this proposal. The Strong Host 173 Model is not stated in those terms, but in terms of the interface 174 used. A Strong host would treat such a MIF router as two separate 175 routers when obeying the rules from RFC 1122 as they apply in the 176 Strong case: 178 (A) A host MUST silently discard an incoming datagram whose 179 destination address does not correspond to the physical interface 180 through which it is received. 182 (B) A host MUST restrict itself to sending (non-source- routed) IP 183 datagrams only through the physical interface that corresponds to 184 the IP source address of the datagrams. 186 However, comparing the presumptive route lookup mechanisms in each 187 model, this proposal is indeed most similar to the Strong Host Model, 188 as is any source/destination routing paradigm. 190 Strong: route(src IP addr, dest IP addr, TOS) -> gateway 191 Weak: route(dest IP addr, TOS) -> gateway, interface 193 In the hypothetical MIF model suggested in Figure 1, the address 194 fails to identify a single interface, but it does identify a single 195 gateway. 197 1.2. Requirements Language 199 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 200 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 201 document are to be interpreted as described in [RFC2119]. 203 2. Sending context expected by the host 205 2.1. Expectations the host has of the network 207 A host receives prefixes in a Router Advertisement [RFC4861], which 208 goes on to identify whether they are usable by SLAAC [RFC4862] with 209 any type of interface identifier [RFC4941] [RFC7217]. When no 210 prefixes are usable for SLAAC, the Router Advertisement would 211 normally signal the availability of DHCPv6 [RFC3315] and the host 212 would use it to configure its addresses. In the latter case (or if 213 both SLAAC and DHCPv6 are used on the same link for some reason) it 214 will generally be the case that the configured addresses match one of 215 the prefixes advertised in a Router Advertisement that are supposed 216 to be on-link for that link. 218 The simplest multihomed network implementation in which a host makes 219 choices among routers might be a LAN with one or more hosts on it and 220 two or more routers, one for each upstream network, or a host that is 221 served by disjoint networks on separate interfaces. In such a 222 network, especially the latter, there is not necessarily a routing 223 protocol, and the two routers may not even know that the other is a 224 router as opposed to a host, or may be configured to ignore its 225 presence. One might expect that the routers may or may not receive 226 each other's RAs and form an address in the other router's prefix 227 (which is not per [RFC4862], but is implemented by some stub router 228 implementations). However, all hosts in such a network might be 229 expected to create an address in each prefix so advertised. 231 +---------+ +---------+ +---------+ +---------+ 232 | ISP | | ISP | | ISP | | ISP | 233 +----+----+ +----+----+ +----+----+ +----+----+ 234 | | | | 235 | | | | 236 +----+----+ +----+----+ +----+----+ +----+----+ 237 | Router | | Router | | Router | | Router | 238 +----+----+ +----+----+ +----+----+ +----+----+ 239 | | | | 240 +------+------+ | +--------+ | 241 | +--+ Host +--+ 242 +----+----+ +--------+ 243 | Host | 244 +---------+ 245 Common LAN Case Disjoint LAN Case 246 (Multihomed Network) (Multihomed Host) 248 Figure 2: Two simple networks 250 If there is no routing protocol among those routers, there is no 251 mechanism by which packets can be deterministically forwarded between 252 the routers (as described in BCP 84 [RFC3704]) in order to avoid 253 filters. Even if there was routing, it would result in an indirect 254 route, rather than a direct route originating with the host; this is 255 not "wrong", but can be inefficient. Therefore the host would do 256 well to select the appropriate router itself. 258 Since the host derives fundamental default routing information from 259 the Router Advertisement, this implies that, in any network with 260 hosts using multiple prefixes, each prefix SHOULD be advertised via a 261 Prefix Information Option (PIO) [RFC4861] by one of the attached 262 routers, even if addresses are being assigned using DHCPv6. A router 263 that advertises a prefix indicates that it is able to appropriately 264 route packets with source addresses within that prefix, regardless of 265 the setting of the L and A flags in the PIO. 267 In some circumstances both L and A might be zero. If SLAAC is not 268 wanted (A=0) and there is no reason to announce an on-link prefix 269 (L=0), a PIO SHOULD be sent to inform hosts that they should use the 270 router in question as the first hop for packets with source addresses 271 in the PIO prefix. An example case is the MIF router in Figure 1, 272 which could send PIOs with A=L=0 for the common prefix. Although 273 this does not violate the existing standard [RFC4861], such a PIO has 274 not previously been common, and it is possible that existing host 275 implementations simply ignore such a PIO or that existing router 276 implementations are not capable of sending such a PIO. Newer 277 implementations that support this mechanism should be updated 278 accordingly: 280 o A host SHOULD NOT ignore a PIO simply because both L and A flags 281 are cleared (extending Section 6.3.4 of [RFC4861]). 283 o A router SHOULD be able to send such a PIO (extending 284 Section 6.2.3 of [RFC4861]). 286 2.2. Expectations of multihomed networks 288 Networking equipment needs to support source/destination routing for 289 at least some of the routes in the Forwarding Information Base (FIB), 290 such as default egress routes differentiated by source prefix. 291 Installation of source/destination routes in the FIB might be 292 accomplished using static routes, SDN technologies, or dynamic 293 routing protocols. 295 3. Reasonable expectations of the host 297 3.1. Interpreting Router Advertisements 299 As described in [RFC4191] and [RFC4861], a Router Advertisement may 300 contain zero or more Prefix information Options (PIOs), or zero or 301 more Route Information Options (RIOs). In their original intent, 302 these indicate general information to a host: "the router whose 303 address is found in the source address field of this packet is one of 304 your default routers", "you might create an address in this prefix", 305 or "this router would be a good place to send traffic directed to a 306 given destination prefix". In a multi-prefix network with multiple 307 exits, the host's characterization of each default router SHOULD 308 include the prefixes it has announced (extending Section 6.3.4 of 309 [RFC4861]). In other words, the PIO is reinterpreted to also imply 310 that the advertising router would be a reasonable first hop for any 311 packet using a source address in any advertised prefix, regardless of 312 Default Router Preference. 314 +---------+ | 315 ( ISP A ) - + Bob-A +--+ +-----+ 316 +-------+ / +---------+ +--+ | 317 | | / | | | 318 | Alice +--/--( The Internet ) | Bob | 319 | | \ | | | 320 +-------+ \ +---------+ +--+ | 321 ( ISP B ) - + Bob-B +--+ +-----+ 322 +---------+ | 324 Figure 3: PIOs, RIOs, and Default Routes 326 The implications bear consideration. Imagine, Figure 3, that hosts 327 Alice and Bob are in communication. Bob's network consists at least 328 of Bob (the computer), 2 routers (Bob-A and Bob-B), and the links 329 between them; it may be much larger, for example a campus or 330 corporate network. Bob's network is therefore multihomed, and Bob's 331 first hop routers are Bob-A (to upstream ISP A advertising prefix PA) 332 and Bob-B (to upstream network B and advertising prefix PB). We 333 assume that Bob is not applying Rule 5.5 of [RFC6724]. If Bob is 334 responding to a message from Alice, his choice of source address is 335 forced to be the address Alice used as a destination (which we may 336 presume to have been in prefix PA). Hence, Bob created or was 337 assigned an address in PA, and can only reasonably send traffic using 338 it to Bob-A as a first hop router. If there are several routers in 339 Bob's network advertising the prefix PA (referred to as Bob-Ax 340 routers), then Bob should choose its first-hop router only from among 341 those routers. From among the multiple Bob-Ax routers, Bob should 342 choose the first-hop router based on the criteria specified in 343 Section 3 of [RFC4191]. If none of the Bob-Ax routers has advertised 344 an RA with a non-zero Router Lifetime or an RIO with a non-zero Route 345 Lifetime that includes Alice, but router Bob-B has, it is irrelevant. 346 Bob is using the address allocated in PA and courts a BCP 38 discard 347 if he doesn't send the packet to Bob-A. 349 In the special case that Bob is initiating the conversation, an RIO 350 might, however, influence source address choice. Bob could 351 presumably use any address allocated to him, in this case his address 352 in PA or PB. If Bob-B has advertised an RIO for Alice's prefix and 353 Bob-A has not, Bob MAY take that fact into account in address 354 selection - choosing an address that would allow him to make use of 355 the RIO. 357 3.2. Default Router Selection 359 Default Router Selection (Section 6.3.6 of [RFC4861]) is extended as 360 follows: A host SHOULD select default routers for each prefix it is 361 assigned an address in. Routers that have advertised the prefix in 362 its Router Advertisement message SHOULD be preferred over routers 363 that do not advertise the prefix, regardless of Default Router 364 Preference. Note that this document does not change the way in which 365 default router preferences are communicated [RFC4191]. 367 If no router has advertised the prefix in an RA, normal routing 368 metrics will apply. An example is a host connected to the Internet 369 via one router, and at the same time connected by a VPN to a private 370 domain which is also connected to the global Internet. 372 As a result of this, when a host sends a packet using a source 373 address in one of those prefixes and has no history directing it 374 otherwise, it SHOULD send it to the indicated default router. In the 375 "simplest" network described in Section 2.1, that would get it to the 376 only router that is directly capable of getting it to the right ISP. 377 This will also apply in more complex networks, even when more than 378 one physical or virtual interface is involved. 380 In more complex cases, wherein routers advertise RAs for multiple 381 prefixes whether or not they have direct or isolated upstream 382 connectivity, the host is dependent on the routing system already. 383 If the host gives the packet to a router advertising its source 384 prefix, it should be able to depend on the router to do the right 385 thing. 387 3.3. Source Address Selection 389 There is an interaction with Default Address Selection [RFC6724]. A 390 host following the recommendation in the previous section will store 391 information about which next-hops advertised which prefixes. Rule 392 5.5 of RFC 6724 states that the source address used to send to a 393 given destination address should if possible be chosen from a prefix 394 known to be advertised by the next-hop router for that destination. 395 This selection rule SHOULD therefore be implemented in a host 396 following the recommendation in the previous section. 398 3.4. Redirects 400 There is potential for adverse interaction with any off-link Redirect 401 (Redirect for a destination that is not on-link) message sent by a 402 router in accordance with Section 8 of [RFC4861]. Hosts SHOULD apply 403 off-link redirects only for the specific pair of source and 404 destination addresses concerned, so the host's Destination Cache 405 might need to contain appropriate source-specific entries. This 406 extends the validity check specified in Section 8.1 of [RFC4861]. 408 3.5. History 410 Some modern hosts maintain history, in terms of what has previously 411 worked or not worked for a given address or prefix and in some cases 412 the effective window and MSS values for TCP or other protocols. This 413 might include a next hop address for use when a packet is sent to the 414 indicated address. 416 When such a host makes a successful exchange with a remote 417 destination using a particular address pair, and the host has 418 previously received a PIO that matches the source address, then the 419 host SHOULD include the prefix in such history, whatever the setting 420 of the L and A flags in the PIO. On subsequent attempts to 421 communicate with that destination, if it has an address in that 422 prefix at that time, a host MAY use an address in the remembered 423 prefix for the session. 425 4. Residual issues 427 Consider a network where routers on a link run a routing protocol and 428 are configured with the same information. Thus, on each link all 429 routers advertise all prefixes on the link. The assumption that 430 packets will be forwarded to the appropriate egress by the local 431 routing system might cause at least one extra hop in the local 432 network (from the host to the wrong router, and from there to another 433 router on the same link). 435 In a slightly more complex situation such as the disjoint LAN case of 436 Figure 2, for example a home plus corporate home-office 437 configuration, the two upstream routers might be on different LANs 438 and therefore different subnets (e.g., the host is itself multi- 439 homed). In that case, there is no way for the "wrong" router to 440 detect the existence of the "right" router, or to route to it. 442 In such a case it is particularly important that hosts take the 443 responsibility to memorize and select the best first-hop as described 444 in Section 3. 446 5. IANA Considerations 448 This memo asks the IANA for no new parameters. 450 6. Security Considerations 452 This document is intended to avoid connectivity issues in the 453 presence of BCP 38 ingress filters or stateful firewalls combined 454 with multihoming. It does not in itself create any new security or 455 privacy exposures. However, since the solution is designed to ensure 456 that routing occurs correctly in situations where it previously 457 failed, this might result in unexpected exposure of networks that 458 were previously unreachable. 460 There might be a small privacy improvement: with the current 461 practice, a multihomed host that sends packets with the wrong address 462 to an upstream router or network discloses the prefix of one upstream 463 to the other upstream network. This practice reduces the probability 464 of that occurrence. 466 7. Acknowledgements 468 Comments were received from Jinmei Tatuya and Ole Troan, who have 469 suggested important text, plus Mikael Abrahamsson, Steven Barth, 470 Carlos Bernardos Cano, Chris Bowers, Zhen Cao, Juliusz Chroboczek, 471 Toerless Eckert, David Farmer, Bob Hinden, Ben Laurie, Dusan Mudric, 472 Tadahisa Okimoto, Pierre Pfister, Behcet Sarikaya, Mark Smith and 473 James Woodyatt. 475 8. References 477 8.1. Normative References 479 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 480 Requirement Levels", BCP 14, RFC 2119, 481 DOI 10.17487/RFC2119, March 1997, 482 . 484 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 485 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 486 December 1998, . 488 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 489 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 490 November 2005, . 492 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 493 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 494 DOI 10.17487/RFC4861, September 2007, 495 . 497 [RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown, 498 "Default Address Selection for Internet Protocol Version 6 499 (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012, 500 . 502 8.2. Informative References 504 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 505 Communication Layers", STD 3, RFC 1122, 506 DOI 10.17487/RFC1122, October 1989, 507 . 509 [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: 510 Defeating Denial of Service Attacks which employ IP Source 511 Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827, 512 May 2000, . 514 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 515 C., and M. Carney, "Dynamic Host Configuration Protocol 516 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 517 2003, . 519 [RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed 520 Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March 521 2004, . 523 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 524 Address Autoconfiguration", RFC 4862, 525 DOI 10.17487/RFC4862, September 2007, 526 . 528 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 529 Extensions for Stateless Address Autoconfiguration in 530 IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, 531 . 533 [RFC6092] Woodyatt, J., Ed., "Recommended Simple Security 534 Capabilities in Customer Premises Equipment (CPE) for 535 Providing Residential IPv6 Internet Service", RFC 6092, 536 DOI 10.17487/RFC6092, January 2011, 537 . 539 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 540 Requirements for IPv6 Customer Edge Routers", RFC 7084, 541 DOI 10.17487/RFC7084, November 2013, 542 . 544 [RFC7157] Troan, O., Ed., Miles, D., Matsushima, S., Okimoto, T., 545 and D. Wing, "IPv6 Multihoming without Network Address 546 Translation", RFC 7157, DOI 10.17487/RFC7157, March 2014, 547 . 549 [RFC7217] Gont, F., "A Method for Generating Semantically Opaque 550 Interface Identifiers with IPv6 Stateless Address 551 Autoconfiguration (SLAAC)", RFC 7217, 552 DOI 10.17487/RFC7217, April 2014, 553 . 555 Appendix A. Change Log (RFC Editor: please delete) 557 Initial Version: 2015-08-05 559 Version 01: Update text on PIOs, added text on Redirects, and 560 clarified the concept of a "simple" network, 2015-08-13. 562 Version 02: Clarifications after WG discussions, 2015-08-19. 564 Version 03: More clarifications after more WG discussions, 565 especially adding stateful firewalls, uRPF, and more precise 566 discussion of RFC 4861, 2015-09-03. 568 Version 04: Responds to various comments including 570 * Questions regarding RFC 1122's strong and weak host models. 571 This model is, strictly speaking, neither, but is most similar 572 to the strong host model. 574 * Some wording errors. 576 * Requests for discussion of the handling of the RIO, PIO, and 577 Default Router List in an RA. 579 WG Versions 00-02: More clarifications after more WG discussions, 580 2015-11-03. 582 WG Version 03: A final clarification re uRPF, 2015-12-15. 584 WG Versions 04-07: Various clarifications and review comments, 585 2016-06-23. 587 WG Version 08-10: Fixes for IETF Last Call and IESG comments, 588 2016-10-07. 590 Authors' Addresses 592 Fred Baker 593 Santa Barbara, California 93117 594 USA 596 Email: FredBaker.IETF@gmail.com 598 Brian Carpenter 599 Department of Computer Science 600 University of Auckland 601 PB 92019 602 Auckland 1142 603 New Zealand 605 Email: brian.e.carpenter@gmail.com