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Thubert, Ed. 3 Internet-Draft Cisco Systems 4 Updates: 4861, 8505 (if approved) C. Perkins 5 Intended status: Standards Track Futurewei 6 Expires: July 20, 2019 E. Levy-Abegnoli 7 Cisco Systems 8 January 16, 2019 10 IPv6 Backbone Router 11 draft-ietf-6lo-backbone-router-10 13 Abstract 15 This document updates RFC 4861 and RFC 8505 in order to enable proxy 16 services for IPv6 Neighbor Discovery by Routing Registrars called 17 Backbone Routers. Backbone Routers are placed along the wireless 18 edge of a Backbone, and federate multiple wireless links to form a 19 single MultiLink Subnet. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at https://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on July 20, 2019. 38 Copyright Notice 40 Copyright (c) 2019 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (https://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 57 2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 2.2. New Terms . . . . . . . . . . . . . . . . . . . . . . . . 5 59 2.3. Acronym Definitions . . . . . . . . . . . . . . . . . . . 6 60 2.4. References . . . . . . . . . . . . . . . . . . . . . . . 7 61 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7 62 3.1. Updating RFC 6775 and RFC 8505 . . . . . . . . . . . . . 9 63 3.2. Access Link . . . . . . . . . . . . . . . . . . . . . . . 10 64 3.3. Route-Over Mesh . . . . . . . . . . . . . . . . . . . . . 11 65 3.4. The Binding Table . . . . . . . . . . . . . . . . . . . . 12 66 3.5. Primary and Secondary 6BBRs . . . . . . . . . . . . . . . 13 67 3.6. Using Optimistic DAD . . . . . . . . . . . . . . . . . . 13 68 4. MultiLink Subnet Considerations . . . . . . . . . . . . . . . 14 69 5. Optional 6LBR serving the MultiLink Subnet . . . . . . . . . 14 70 6. Using IPv6 ND Over the Backbone Link . . . . . . . . . . . . 15 71 7. Routing Proxy Operations . . . . . . . . . . . . . . . . . . 15 72 8. Bridging Proxy Operations . . . . . . . . . . . . . . . . . . 16 73 9. Creating and Maintaining a Binding . . . . . . . . . . . . . 17 74 9.1. Operation on a Binding in Tentative State . . . . . . . . 19 75 9.2. Operation on a Binding in Reachable State . . . . . . . . 20 76 9.3. Operation on a Binding in Stale State . . . . . . . . . . 21 77 10. Registering Node Considerations . . . . . . . . . . . . . . . 21 78 11. Security Considerations . . . . . . . . . . . . . . . . . . . 22 79 12. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 22 80 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 81 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 82 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 23 83 15.1. Normative References . . . . . . . . . . . . . . . . . . 23 84 15.2. Informative References . . . . . . . . . . . . . . . . . 24 85 Appendix A. Possible Future Extensions . . . . . . . . . . . . . 27 86 Appendix B. Applicability and Requirements Served . . . . . . . 27 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29 89 1. Introduction 91 IEEE STD. 802.1 [IEEEstd8021] Ethernet Bridging provides an efficient 92 and reliable broadcast service for wired networks; applications and 93 protocols have been built that heavily depend on that feature for 94 their core operation. Unfortunately, Low-Power Lossy Networks (LLNs) 95 and local wireless networks generally do not provide the broadcast 96 capabilities of Ethernet Bridging in an economical fashion. 98 As a result, protocols designed for bridged networks that rely on 99 multicast and broadcast often exhibit disappointing behaviours when 100 employed unmodified on a local wireless medium (see 101 [I-D.ietf-mboned-ieee802-mcast-problems]). 103 Wi-Fi [IEEEstd80211] Access Points (APs) deployed in an Extended 104 Service Set (ESS) act as Ethernet Bridges [IEEEstd8021], with the 105 property that the bridging state is established at the time of 106 association. This ensures connectivity to the node (STA) and 107 protects the wireless medium against broadcast-intensive Transparent 108 Bridging reactive Lookups. In other words, the association process 109 is used to register the MAC Address of the STA to the AP. The AP 110 subsequently proxies the bridging operation and does not need to 111 forward the broadcast Lookups over the radio. 113 Like Transparent Bridging, IPv6 [RFC8200] Neighbor Discovery 114 [RFC4861] [RFC4862] Protocol (IPv6 ND) is a reactive protocol, based 115 on multicast transmissions to locate an on-link correspondent and 116 ensure the uniqueness of an IPv6 address. The mechanism for 117 Duplicate Address Detection (DAD) [RFC4862] was designed for the 118 efficient broadcast operation of Ethernet Bridging. Since broadcast 119 can be unreliable over wireless media, DAD often fails to discover 120 duplications [I-D.yourtchenko-6man-dad-issues]. In practice, IPv6 121 addresses very rarely conflict because of the entropy of the 64-bit 122 Interface IDs, not because address duplications are detected and 123 resolved. 125 The IPv6 ND Neighbor Solicitation (NS) [RFC4861] message is used for 126 DAD and address Lookup when a node moves, or wakes up and reconnects 127 to the wireless network. The NS message is targeted to a Solicited- 128 Node Multicast Address (SNMA) [RFC4291] and should in theory only 129 reach a very small group of nodes. But in reality, IPv6 multicast 130 messages are typically broadcast on the wireless medium, and so they 131 are processed by most of the wireless nodes over the subnet (e.g., 132 the ESS fabric) regardless of how few of the nodes are subscribed to 133 the SNMA. As a result, IPv6 ND address Lookups and DADs over a large 134 wireless and/or a LowPower Lossy Network (LLN) can consume enough 135 bandwidth to cause a substantial degradation to the unicast traffic 136 service. 138 Because IPv6 ND messages sent to the SNMA group are broadcasted at 139 the radio MAC Layer, wireless nodes that do not belong to the SNMA 140 group still have to keep their radio turned on to listen to multicast 141 NS messages, which is a total waste of energy for them. In order to 142 reduce their power consumption, certain battery-operated devices such 143 as IoT sensors and smartphones ignore some of the broadcasts, making 144 IPv6 ND operations even less reliable. 146 These problems can be alleviated by reducing the IPv6 ND broadcasts 147 over wireless access links. This has been done by splitting the 148 broadcast domains and routes between subnets, or even by assigning a 149 /64 prefix to each wireless node (see [RFC8273]). 151 Another way is to proxy at the boundary of the wired and wireless 152 domains the Layer-3 protocols that rely on MAC Layer broadcast 153 operations. For instance, IEEE 802.11 [IEEEstd80211] situates proxy- 154 ARP (IPv4) and proxy-ND (IPv6) functions at the Access Points (APs). 155 The 6BBR provides a proxy-ND function and can be extended for proxy- 156 ARP in a continuation specification. 158 IPv6 proxy-ND services can be obtained by snooping the IPV6 ND 159 protocol (see [I-D.bi-savi-wlan]). Proprietary techniques for IPv6 160 ND and DHCP snooping have been used; although snooping does eliminate 161 undesirable broadcast transmissions, it has been found to be 162 unreliable. An IPv6 address may not be discovered immediately due to 163 a packet loss, or if a "silent" node is not currently using one of 164 its addresses. A change of state (e.g. due to movement) may be 165 missed or misordered, leading to unreliable connectivity and 166 incomplete knowledge of the state of the network. 168 This specification defines the 6BBR as a Routing Registrar [RFC8505] 169 that provide proxy services for IPv6 Neighbor Discovery. Backbone 170 Routers federate multiple LLNs over a Backbone Link to form a 171 MultiLink Subnet (MLSN). Backbone Routers placed along the LLN edge 172 of the Backbone handle IPv6 Neighbor Discovery, and forward packets 173 on behalf of registered nodes. 175 An LLN node (6LN) registers all its IPv6 Addresses using an NS(EARO) 176 as specified in [RFC8505] to the 6BBR. The 6BBR is also a Border 177 Router that performs IPv6 Neighbor Discovery (IPv6 ND) operations on 178 its Backbone interface on behalf of the 6LNs that have registered 179 addresses on its LLN interfaces without the need of a broadcast over 180 the wireless medium. Additional benefits are discussed in 181 Appendix B. 183 2. Terminology 185 2.1. BCP 14 187 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 188 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 189 "OPTIONAL" in this document are to be interpreted as described in BCP 190 14 [RFC2119] [RFC8174] when, and only when, they appear in all 191 capitals, as shown here. 193 2.2. New Terms 195 This document introduces the following terminology: 197 Federated 199 A subnet that comprises a Backbone and one or more (wireless) 200 access links, is said to be federated into one MultiLink 201 Subnet. The proxy-ND operation of 6BBRs over the Backbone and 202 the access links provides the appearance of a subnet for IPv6 203 ND. 205 Sleeping Proxy 207 A 6BBR acts as a Sleeping Proxy if it answers ND Neighbor 208 Solicitations over the Backbone on behalf of a Registered Node. 210 Routing Proxy 212 A Routing Proxy provides IPv6 ND proxy functions and enables 213 the MLSN operation over federated links that may not be 214 compatible for bridging. The Routing Proxy advertises its own 215 MAC Address as the TLLA in the proxied NAs over the Backbone, 216 and routes at the Network Layer between the federated links. 218 Bridging Proxy 220 A Bridging Proxy provides IPv6 ND proxy functions while 221 preserving forwarding continuity at the MAC Layer. The 222 Bridging Proxy advertises the MAC Address of the Registering 223 Node as the TLLA in the proxied NAs over the Backbone. In that 224 case, the MAC Address and the mobility of 6LN is still visible 225 across the bridged Backbone, and the 6BR may be configured to 226 proxy for Link Local Addresses. 228 Binding Table 230 The Binding Table is an abstract database that is maintained by 231 the 6BBR to store the state associated with its registrations. 233 Binding 235 A Binding is an abstract state associated to one registration, 236 in other words one entry in the Binding Table. 238 2.3. Acronym Definitions 240 This document uses the following acronyms: 242 6BBR: 6LoWPAN Backbone Router 244 6LBR: 6LoWPAN Border Router 246 6LN: 6LoWPAN Node 248 6LR: 6LoWPAN Router 250 6CIO: Capability Indication Option 252 EARO: (Extended) Address Registration Option -- (E)ARO 254 EDAR: (Extended) Duplicate Address Request -- (E)DAR 256 EDAC: (Extended) Duplicate Address Confirmation -- (E)DAC 258 DAD: Duplicate Address Detection 260 DODAG: Destination-Oriented Directed Acyclic Graph 262 IPv6 ND: IPv6 Neighbor Discovery 264 LLN: Low-Power and Lossy Network 266 NA: Neighbor Advertisement 268 NCE: Neighbor Cache Entry 270 NS: Neighbor Solicitation 272 ROVR: Registration Ownership Verifier 274 RPL: IPv6 Routing Protocol for LLNs 276 RA: Router Advertisement 278 RS: Router Solicitation 280 TID: Transaction ID (a sequence counter in the EARO) 282 2.4. References 284 In this document, readers will encounter terms and concepts that are 285 discussed in the following documents: 287 o "Neighbor Discovery for IP version 6" [RFC4861], "IPv6 Stateless 288 Address Autoconfiguration" [RFC4862] and "Optimistic Duplicate 289 Address Detection" [RFC4429], 291 o "Neighbor Discovery Proxies (proxy-ND)" [RFC4389] and "MultiLink 292 Subnet Issues" [RFC4903], 294 o "Problem Statement and Requirements for IPv6 over Low-Power 295 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606], and 297 o Neighbor Discovery Optimization for Low-Power and Lossy Networks 298 [RFC6775] and "Registration Extensions for 6LoWPAN Neighbor 299 Discovery" [RFC8505]. 301 3. Overview 303 Figure 1 illustrates backbone link federating a collection of LLNs as 304 a single IPv6 Subnet, with a number of 6BBRs providing proxy-ND 305 services to their attached LLNs. 307 | 308 +-----+ 309 | | Gateway (default) Router 310 | | 311 +-----+ 312 | 313 | Backbone side 314 +-------------------------+----------------------+ 315 | | | 316 +------+ +------+ +------+ 317 | 6BBR | | 6BBR | | 6BBR | 318 | | | | | | 319 +------+ +------+ +------+ 320 o Wireless side o o o o o 321 o o o o o o o o o o o o o o 322 o o o o o o o o o o o o o o o 323 o o o o o o o o o o 324 o o o o o o o 326 LLN LLN LLN 328 Figure 1: Backbone Link and Backbone Routers 330 The LLN may be a hub-and-spoke access link such as (Low-Power) IEEE 331 STD. 802.11 (Wi-Fi) [IEEEstd80211] and IEEE STD. 802.15.1 (Bluetooth) 332 [IEEEstd802151], or a Mesh-Under or a Route-Over network [RFC8505]. 333 The proxy state can be distributed across multiple 6BBRs attached to 334 the same Backbone. 336 The main features of a 6BBR are as follows: 338 o Multilink-subnet functions (provided by the 6BBR on the backbone) 339 performed on behalf of registered 6LNs, and 341 o Routing registrar services that reduce multicast within the LLN: 343 * Binding Table management 345 * failover, e.g., due to mobility 347 Each Backbone Router (6BBR) maintains a data structure for its 348 Registered Nodes called a Binding Table. The combined Binding Tables 349 of all the 6BBRs on a backbone form a distributed database of 6LNs 350 that reside in the LLNs or on the IPv6 Backbone. 352 Unless otherwise configured, a 6BBR does the following: 354 o Create a new entry in a Binding Table for a new Registered Address 355 and ensure that the Address is not duplicated over the Backbone 357 o Defend a Registered Address over the Backbone using NA messages on 358 behalf of the sleeping 6LN 360 o Advertise a Registered Address over the Backbone using NA 361 messages, asynchronously or as a response to a Neighbor 362 Solicitation messages. 364 o Deliver packets arriving from the LLN, using Neighbor Solicitation 365 messages to look up the destination over the Backbone. 367 o Forward or bridge packets between the LLN and the Backbone. 369 o Verify liveness for a registration, when needed. 371 The first of these functions enables the 6BBR to fulfill its role as 372 a Routing Registrar for each of its attached LLNs. The remaining 373 functions fulfill the role of the 6BBRs as the border routers 374 connecting the Multi-link IPv6 subnet to the Internet. 376 The proxy-ND operation can co-exist with IPv6 ND over the Backbone. 378 The 6BBR may co-exist with a proprietary snooping or a traditional 379 bridging functionality in an Access Point, in order to support legacy 380 nodes that do not support this specification. In the case, the co- 381 existing function may turn multicastsinto a series of unicast to the 382 legacy nodes. 384 The registration to a proxy service uses an NS/NA(EARO) exchange. 385 The 6BBR operation resembles that of a Mobile IPv6 (MIPv6) [RFC6275] 386 Home Agent (HA). The combination of a 6BBR and a MIPv6 HA enables 387 full mobility support for 6LNs, inside and outside the links that 388 form the subnet. 390 The 6BBRs use the Extended Address Registration Option (EARO) defined 391 in [RFC8505] as follows: 393 o The EARO is used in the IPv6 ND exchanges over the Backbone 394 between the 6BBRs to help distinguish duplication from movement. 395 Extended Duplicate Address Messages (EDAR and EDAC) MAY also be 396 used with a 6LBR, if one is present, and the 6BBR. Address 397 duplication is detected using the ROVR field. Conflicting 398 registrations to different 6BBRs for the same 6LR address are 399 resolved using the TID field. 401 o The Link Layer Address (LLA) that the 6BBR advertises for the 402 Registered Address on behalf of the Registered Node over the 403 Backbone can belong to the Registering Node; in that case, the 404 6BBR (acting as a Bridging Proxy (see Section 8)) bridges the 405 unicast packets. Alternatively, the LLA can be that of the 6BBR 406 on the Backbone interface, in which case the 6BBR (acting as a 407 Routing Proxy(see Section 7)) receives the unicast packets at 408 Layer-2 and routes them. 410 3.1. Updating RFC 6775 and RFC 8505 412 This specification adds the EARO as a possible option in RS, NS(DAD) 413 and NA messages over the backbone. [RFC8505] requires that the 414 registration NS(EARO) contains an SLLAO. This specification details 415 the use of those messages over the backbone. 417 Note: [RFC6775] requires that the registration NS(EARO) contains an 418 SLLAO and [RFC4862] that the NS(DAD) is sent from the unspecified 419 address for which there cannot be a SLLAO. Consequently, an NS(DAD) 420 cannot be confused with a registration. 422 This specification adds the capability to insert IPv6 ND options in 423 the EDAR and EDAC messages. In particular, a 6BBR acting as a 6LR 424 for the Registered Address can insert an SLLAO in the EDAR to the 425 6LBR in order to avoid a Lookup back. 427 3.2. Access Link 429 Figure 2 illustrates a flow where 6LN forms an IPv6 Address and 430 registers it to a 6BBR acting as a 6LR [RFC8505]. The 6BBRs applies 431 ODAD (see Section 3.6) to the registered address to enable 432 connectivity while the message flow is still in progress. In that 433 example, a 6LBR is deployed on the backbone link to serve the whole 434 subnet, and EDAR / EDAC messages are used in combination with DAD to 435 enable coexistence with IPv6 ND over the backbone. 437 6LN(STA) 6BBR(AP) 6LBR default GW 438 | | | | 439 | LLN Access Link | IPv6 Backbone (e.g., Ethernet) | 440 | | | | 441 | RS(multicast) | | | 442 |---------------->| | | 443 | RA(PIO, Unicast)| | | 444 |<----------------| | | 445 | NS(EARO) | | | 446 |---------------->| | | 447 | | Extended DAR | | 448 | |--------------->| | 449 | | Extended DAC | | 450 | |<---------------| | 451 | | | 452 | | NS-DAD(EARO, multicast) | 453 | |--------> | 454 | |-------------------------------->| 455 | | | 456 | | RS(no SLLAO, for ODAD) | 457 | |-------------------------------->| 458 | | (if no fresher Binding) NS(Lookup) | 459 | | <-------------| 460 | |<--------------------------------| 461 | | NA(SLLAO, not(O), EARO) | 462 | |-------------------------------->| 463 | | RA(unicast) | 464 | |<--------------------------------| 465 | | | 466 | IPv6 Packets in optimistic mode | 467 |<------------------------------------------------->| 468 | | | 469 | | 470 | NA(EARO) | 471 |<----------------| 472 | | 474 Figure 2: Initial Registration Flow to a 6BBR acting as Routing Proxy 476 3.3. Route-Over Mesh 478 Figure 3 illustrates IPv6 signaling that enables a 6LN to form a 479 Global or a Unique-Local Address and register it to the 6LBR that 480 serves its LLN using [RFC8505]. The 6LBR (acting as Registering 481 Node) proxies the registration to the 6BBR, using [RFC8505] to 482 register the addresses the 6LN (Registered Node) on its behalf to the 483 6BBR, and obtain proxy-ND services from the 6BBR. 485 6LoWPAN Node 6LR 6LBR 6BBR 486 (mesh leaf) (mesh router) (mesh root) 487 | | | | 488 | 6LoWPAN ND |6LoWPAN ND | 6LoWPAN ND | IPv6 ND 489 | LLN link |Route-Over mesh|Ethernet/serial| Backbone 490 | | |/Internal call | 491 | IPv6 ND RS | | | 492 |-------------->| | | 493 |-----------> | | | 494 |------------------> | | 495 | IPv6 ND RA | | | 496 |<--------------| | | 497 | | | | 498 | NS(EARO) | | | 499 |-------------->| | | 500 | 6LoWPAN ND | Extended DAR | | 501 | |-------------->| | 502 | | | NS(EARO) | 503 | | |-------------->| 504 | | | (proxied) | NS-DAD 505 | | | |------> 506 | | | | (EARO) 507 | | | | 508 | | | NA(EARO) | 509 | | |<--------------| 510 | | Extended DAC | | 511 | |<--------------| | 512 | NA(EARO) | | | 513 |<--------------| | | 514 | | | | 516 Figure 3: Initial Registration Flow over Route-Over Mesh 518 As a non-normative example of a Route-Over Mesh, the 6TiSCH 519 architecture [I-D.ietf-6tisch-architecture] suggests using RPL 520 [RFC6550] and collocating the RPL root with a 6LBR that serves the 521 LLN, and is either collocated with or connected to the 6BBR over an 522 IPv6 Link. 524 3.4. The Binding Table 526 Addresses in a LLN that are reachable from the Backbone by way of the 527 6BBR function must be registered to that 6BBR, using an NS(EARO) with 528 the R flag set [RFC8505]. A 6BBR maintains a state for its active 529 registrations in an abstract Binding Table. 531 An entry in the Binding Table Entry is called a "Binding". A Binding 532 may be in Tentative, Reachable or Stale state. 534 The 6BBR uses a combination of [RFC8505] and IPv6 ND over the 535 Backbone to advertise the registration and avoid a duplication. 536 Conflicting registrations are solved by the 6BBRs transparently to 537 the Registering Nodes. 539 Only one 6LN may register a given Address, but the Address may be 540 registered to Multiple 6BBRs for higher availability. 542 Over the LLN, Binding Table management is as follows: 544 o De-registrations (newer TID, same ROVR, null Lifetime) are 545 accepted with a status of 4 ("Removed"); the entry is deleted; 547 o Newer registrations (newer TID, same ROVR, non-null Lifetime) are 548 accepted with a status of 0 (Success); the Binding is updated with 549 the new TID, the Registration Lifetime and the Registering Node; 550 in Tentative state the EDAC response is held and may be 551 overwritten; in other states the Registration Lifetime timer is 552 restarted and the entry is placed in Reachable state. 554 o Identical registrations (same TID, same ROVR) from a same 555 Registering Node are accepted with a status of 0 (Success). In 556 Tentative state, the response is held and may be overwritten, but 557 the response MUST be eventually produced, carrying the result of 558 the DAD process; 560 o Older registrations (older TID, same ROVR) from the same 561 Registering Node are discarded; 563 o Identical and older registrations (not-newer TID, same ROVR) from 564 a different Registering Node are rejected with a status of 3 565 (Moved); this may be rate limited to avoid undue interference; 567 o Any registration for the same address but with a different ROVR is 568 rejected with a status of 1 (Duplicate). 570 3.5. Primary and Secondary 6BBRs 572 A same address may be successfully registered to more than one 6BBR, 573 in which case the Registering Node uses the same EARO in all the 574 parallel registrations. To allow for this, ND(DAD) and NA messages 575 with an EARO that indicate an identical Binding in another 6BBR (same 576 Registered address, same TID, same ROVR) as silently ignored. 578 A 6BBR MAY be primary or secondary. The primary is the 6BBR that has 579 the highest EUI-64 Address of all the 6BBRs that share a registration 580 for the same Registered Address, with the same ROVR and same 581 Transaction ID, the EUI-64 Address being considered as an unsigned 582 64bit integer. A given 6BBR can be primary for a given Address and 583 secondary for another Address, regardless of whether or not the 584 Addresses belong to the same 6LN. 586 In the following sections, is is expected that an NA is sent over the 587 backbone only if the node is primary or does not support the concept 588 of primary. More than one 6BBR claiming or defending an address 589 generates unwanted traffic but no reachability issue since all 6BBRs 590 provide reachability from the Backbone to the 6LN. 592 3.6. Using Optimistic DAD 594 Optimistic Duplicate Address Detection [RFC4429] (ODAD) specifies how 595 an IPv6 Address can be used before completion of Duplicate Address 596 Detection (DAD). ODAD guarantees that this behavior will not cause 597 harm if the new Address is a duplicate. 599 Support for ODAD avoids delays in installing the Neighbor Cache Entry 600 (NCE) in the 6BBRs and the default router, enabling immediate 601 connectivity to the registered node. As shown in Figure 2, if the 602 6BBR is aware of the Link-Layer Address (LLA) of a router, then the 603 6BBR sends a Router Solicitation (RS), using the Registered Address 604 as the IP Source Address, to the known router(s). The RS MUST be 605 sent without a Source LLA Option (SLLAO), to avoid invalidating a 606 preexisting NCE in the router. 608 Following ODAD, the router may then send a unicast RA to the 609 Registered Address, and it may resolve that Address using an 610 NS(Lookup) message. In response, the 6BBR sends an NA with an EARO 611 and the Override (O) flag [RFC4861] that is not set. The router can 612 then determine the freshest EARO in case of a conflicting NA(EARO) 613 messages, using the method described in section 5.2.1 of [RFC8505]. 614 If the NA(EARO) is the freshest answer, the default router creates a 615 Binding with the SLLAO of the 6BBR (in Routing Proxy mode) or that of 616 the Registering Node (in Bridging Proxy mode) so that traffic from/to 617 the Registered Address can flow immediately. 619 4. MultiLink Subnet Considerations 621 The Backbone and the federated LLN Links are considered as different 622 links in the MultiLink Subnet, even if multiple LLNs are attached to 623 the same 6BBR. ND messages are link-scoped and are not forwarded by 624 the 6BBR between the backbone and the LLNs though some packets may be 625 reinjected in Bridging Proxy mode (see Section 8). 627 Nodes located inside the subnet do not perform the IPv6 Path MTU 628 Discovery [RFC8201]. For that reason, the MTU must have a same value 629 on the Backbone and all attached LLNs. To achieve this, the 6BBR 630 MUST use the same MTU value in RAs over the Backbone and in the RAs 631 that it transmits towards the LLN links. 633 5. Optional 6LBR serving the MultiLink Subnet 635 A 6LBR can be deployed to serve the whole MLSN. It may be attached 636 to the backbone, in which case it can be discovered by its capability 637 advertisement (see section 4.3. of [RFC8505]) in RA messages. 639 When a 6LBR is present, the 6BBR uses an EDAR/EDAC message exchange 640 with the 6LBR to check for duplication or movement. This is done 641 prior to the NS(DAD) process, which may be avoided of the 6LBR 642 already maintains a conflicting state for the Registered Address. 644 This specification enables an address to be registered to more than 645 one 6BBR. It results that a 6LBR MUST be capable to maintain a state 646 for each of the 6BBR having registered with a same TID and same ROVR. 648 If this registration is duplicate or not the freshest, then the 6LBR 649 replies with an EDAC message with a status code of 1 ("Duplicate 650 Address") or 3 ("Moved"), respectively. If this registration is the 651 freshest, then the 6LBR replies with a status code of 0. In that 652 case, if this registration is fresher than an existing registration 653 for another 6BBR, then the 6LBR also sends an asynchronous EDAC with 654 a status of 4 ("Removed") to that other 6BBR. 656 The EDAC message SHOULD carry the SLLAO used in NS messages by the 657 6BBR for that Binding, and the EDAR message SHOULD carry the TLLAO 658 associated with the currently accepted registration. This enables a 659 6BBR to locate the new position of a mobile 6LN in the case of a 660 Routing Proxy operation, and opens the capability for the 6LBR to 661 serve as a mapping server in the future. 663 Note that if Link Local addresses are registered, then the scope of 664 uniqueness on which the address duplication is checked is the total 665 collection of links that the 6LBR serves as opposed to the sole link 666 on which the Link Local address is assigned. 668 6. Using IPv6 ND Over the Backbone Link 670 On the Backbone side, the 6BBR MUST join the SNMA group corresponding 671 to a Registered Address as soon as it creates a Binding for that 672 Address, and maintain that SNMA membership as long as it maintains 673 the registration. 675 The 6BBR uses either the SNMA or plain unicast to defend the 676 Registered Addresses in its Binding Table over the Backbone (as 677 specified in [RFC4862]). 679 The 6BBR advertises and defends the Registered Addresses over the 680 Backbone Link using RS, NS(DAD) and NA messages with the Registered 681 Address as the Source or Target address, respectively. 683 The 6BBR MUST place an EARO in the IPv6 ND messages that it generates 684 on behalf of the Registered Node. Note that an NS(DAD) does not 685 contain an SLLAO and cannot be confused with a proxy registration 686 such as performed by a 6LBR. 688 An NA message generated in response to an NS(DAD) MUST have the 689 Override flag set and a status of 1 (Duplicate) or 3 (Moved) in the 690 EARO. An NA message generated in response to an NS(Lookup) or an 691 NS(NUD) MUST NOT have the Override flag set. 693 This specification enables proxy operation for the IPv6 ND resolution 694 of LLN devices and a prefix that is used across a MultiLink Subnet 695 MAY be advertised as on-link over the Backbone. This is done for 696 backward compatibility with existing IPv6 hosts by setting the L flag 697 in the Prefix Information Option (PIO) of RA messages [RFC4861]. 699 For movement involving a slow reattachment, the Neighbor 700 Unreachability Detection (NUD) defined in [RFC4861] may time out too 701 quickly. Nodes on the backbone SHOULD support [RFC7048] whenever 702 possible. 704 7. Routing Proxy Operations 706 A Routing Proxy provides IPv6 ND proxy functions for Global and 707 Unique Local addresses between the LLN and the backbone, but not for 708 Link-Local addresses. It operates as an IPv6 border router and 709 provides a full Link-Layer isolation. 711 In this mode, it is not required that the MAC addresses of the 6LNs 712 are visible at Layer-2 over the Backbone. It is thus useful when the 713 messaging over the Backbone that is associated to wireless mobility 714 becomes expensive, e.g., when the Layer-2 topology is virtualized 715 over a wide area IP underlay. 717 This mode is definitely required when the LLN uses a MAC address 718 format that is different from that on the Backbone (e.g., EUI-64 vs. 719 EUI-48). Since a 6LN may not be able to resolve an arbitrary 720 destination in the MLSN directly, the MLSN prefix MUST NOT be 721 advertised as on-link in RA messages sent towards the LLN. 723 In order to maintain IP connectivity, the 6BBR installs a connected 724 Host route to the Registered Address on the LLN interface, via the 725 Registering Node as identified by the Source Address and the SLLA 726 option in the NS(EARO) messages. 728 When operating as a Routing Proxy, the 6BBR MUST use its Layer-2 729 Address on its Backbone Interface in the SLLAO of the RS messages and 730 the TLLAO of the NA messages that it generates to advertise the 731 Registered Addresses. 733 For each Registered Address, multiple peers on the Backbone may have 734 resolved the Address with the 6BBR MAC Address, maintaining that 735 mapping in their Neighbor Cache. The 6BBR SHOULD maintain a list of 736 the peers on the Backbone which have associated its MAC Address with 737 the Registered Address. If that Registered Address moves to a new 738 6BBR, the previous 6BBR SHOULD unicast a gratuitous NA with the 739 Override flag set to each such peer, to supply the LLA of the new 740 6BBR in the TLLA option for the Address. A 6BBR that does not 741 maintain this list MAY multicast a gratuitous NA with the Override 742 flag; this NA will possibly hit all the nodes on the Backbone, 743 whether or not they maintain an NCE for the Registered Address. 745 If a correspondent fails to receive the gratuitous NA, it will keep 746 sending traffic to a 6BBR to which the node was previously 747 registered. Since the previous 6BBR removed its Host route to the 748 Registered Address, it will look up the address over the backbone, 749 resolve the address with the LLA of the new 6BBR, and forward the 750 packet to the correct 6BBR. The previous 6BBR SHOULD also issue a 751 redirect message [RFC4861] to update the cache of the correspondent. 753 8. Bridging Proxy Operations 755 A Bridging Proxy provides IPv6 ND proxy functions between the LLN and 756 the backbone while preserving the forwarding continuity at the MAC 757 Layer. It acts as a Layer-2 Bridge for all types unicast packets 758 including link-scoped, and appears as an IPv6 Host on the Backbone. 760 The Bridging Proxy registers any Binding including for a Link-Local 761 address to the 6LBR (if present) and defends it over the backbone in 762 IPv6 ND procedures. 764 To achieve this, the Bridging Proxy intercepts the IPv6 ND messages 765 and may reinject them on the other side, respond directly or drop 766 them. For instance, an ND(Lookup) from the backbone that matches a 767 Binding can be responded directly, or turned into a unicast on the 768 LLN side to let the 6LN respond. 770 As a Bridging Proxy, the 6BBR MUST use the Registering Node's Layer-2 771 Address in the SLLAO of the NS/RS messages and the TLLAO of the NA 772 messages that it generates to advertise the Registered Addresses. 773 The Registering Node's Layer-2 address is found in the SLLA of the 774 registration NS(EARO), and maintained in the Binding Table. 776 The MultiLink Subnet prefix SHOULD NOT be advertised as on-link in RA 777 messages sent towards the LLN. If a destination address is seen as 778 on-link, then a 6LN may use NS(Lookup) messages to resolve that 779 address. In that case, the 6BBR MUST either answer directly to the 780 NS(Lookup) message or reinject the message on the backbone, either as 781 a Layer-2 unicast or a multicast. 783 If the Registering Node owns the Registered Address, then its 784 mobility does not impact existing NCEs over the Backbone. Otherwise, 785 when the 6LN selects another Registering Node, the new Registering 786 Node SHOULD send a multicast NA with the Override flag set to fix the 787 existing NCEs across the Backbone. This method can fail if the 788 multicast message is not received; one or more correspondent nodes on 789 the Backbone might maintain an stale NCE, and packets to the 790 Registered Address may be lost. When this condition happens, it is 791 eventually be discovered and resolved using Neighbor Unreachability 792 Detection (NUD) as defined in [RFC4861]. 794 9. Creating and Maintaining a Binding 796 Upon receiving a registration for a new Address (i.e., an NS(EARO) 797 with the R flag set), the 6BBR creates a Binding and operates as a 798 6LR according to [RFC8505], interacting with the 6LBR if one is 799 present. 801 An implementation of a Routing Proxy that creates a Binding MUST also 802 create an associated Host route pointing on the registering node in 803 the LLN interface from which the registration was received. 805 The 6LR operation is modified as follows: 807 o EDAR and EDAC messages SHOULD carry a SLLAO and a TLLAO, 808 respectively. 810 o A Bridging Proxy MAY register Link Local addresses to the 6BBR and 811 proxy ND for those addresses over the backbone. 813 o An EDAC message with a status of 9 (6LBR Registry Saturated) is 814 assimilated as a status of 0 if a following DAD process protects 815 the address against duplication. 817 This specification enables nodes on a Backbone Link to co-exist along 818 with nodes implementing IPv6 ND [RFC4861] as well as other non- 819 normative specifications such as [I-D.bi-savi-wlan]. It is possible 820 that not all IPv6 addresses on the Backbone are registered and known 821 to the 6LBR, and an EDAR/EDAC echange with the 6LBR might succeed 822 even for a duplicate address. Consequently, and unless 823 administratively overridden, the 6BBR still needs to perform IPv6 ND 824 DAD over the backbone after an EDAC with a status code of 0 or 9. 826 For the DAD operation, the Binding is placed in Tentative state for a 827 duration of TENTATIVE_DURATION, and an NS(DAD) message is sent as a 828 multicast message over the Backbone to the SNMA associated with the 829 registered Address [RFC4862]. The EARO from the registration MUST be 830 placed unchanged in the NS(DAD) message. 832 If a registration is received for an existing Binding with a non-null 833 Registration Lifetime and the registration is fresher (same ROVR, 834 fresher TID), then the Binding is updated, with the new Registration 835 Lifetime, TID, and possibly Registering Node. In Tentative state 836 (see Section 9.1), the current DAD operation continues as it was. In 837 other states (see Section 9.2 and Section 9.3 ), the Binding is 838 placed in Reachable state for the Registration Lifetime, and the 6BBR 839 returns an NA(EARO) to the Registering Node with a status of 0 840 (Success). 842 Upon a registration that is identical (same ROVR, TID, and 843 Registering Node), the 6BBR returns an NA(EARO) back to the 844 Registering Node with a status of 0 (Success). A registration that 845 is not as fresh (same ROVR, older TID) is ignored. 847 If a registration is received for an existing Binding and a 848 registration Lifetime of zero, then the Binding is removed, and the 849 6BBR returns an NA(EARO) back to the Registering Node with a status 850 of 0 (Success). An implementation of a Routing Proxy that removes a 851 binding MUST remove the associated Host route pointing on the 852 registering node. It MAY preserve a temporary state in order to 853 forward packets in flight. The state may be a NCE formed based on a 854 received NA message, or a Binding in Stale state and pointing at the 855 new 6BBR on the backbone. 857 The implementation should also use REDIRECT messages as specified in 858 [RFC4861] to update the correspondents for the Registered Address, 859 pointing the new 6BBR. 861 9.1. Operation on a Binding in Tentative State 863 The Tentative state covers a DAD period over the backbone during 864 which an address being registered is checked for duplication using 865 procedures defined in [RFC4862]. 867 For a Binding in Tentative state: 869 o The Binding MUST be removed if an NA message is received over the 870 Backbone for the Registered Address with no EARO, or containing an 871 EARO with a status of 1 (Duplicate) that indicates an existing 872 registration owned by a different Registering Node. In that case, 873 an NA MUST be sent back to the Registering Node with a status of 1 874 (Duplicate) in the EARO. This behavior might be overriden by 875 policy, in particular if the registration is trusted, e.g., based 876 on the validation of the ROVR field (see [I-D.ietf-6lo-ap-nd]). 878 o An NS(DAD) with no EARO or with an EARO that indicates a duplicate 879 registration (i.e. different ROVR) MUST be answered with an NA 880 message containing an EARO with a status of 1 (Duplicate) and the 881 Override flag not set. This behavior might be overriden by 882 policy, in particular if the registration is not trusted. 884 o The Binding MUST be removed if an NA message is received over the 885 Backbone for the Registered Address containing an EARO with a 886 status of 3 (Moved), or an NS(DAD) with an EARO that indicates a 887 fresher registration ([RFC8505]) for the same Registered Node 888 (i.e. same ROVR). A status of 3 is returned in the NA(EARO) back 889 to the Registering Node. 891 o NS(DAD) and NA messages containing an EARO that indicates a 892 registration for the same Registered Node that is not as fresh as 893 this SHOULD be answered with an NA message containing an EARO with 894 a status of 3 (Moved) in order to clean up the situation 895 immediately. 897 o Other NS(DAD) and NA messages from the Backbone are ignored. 899 o NS(Lookup) and NS(NUD) messages SHOULD be optimistically answered 900 with an NA message containing an EARO with a status of 0 and the 901 Override flag not set (see Section 3.6). If optimistic DAD is 902 disabled, then they SHOULD be queued to be answered when the 903 Binding goes to Reachable state. 905 When the TENTATIVE_DURATION timer elapses, the Binding is placed in 906 Reachable state for the Registration Lifetime, and the 6BBR returns 907 an NA(EARO) to the Registering Node with a status of 0 (Success). 909 The 6BBR also attempts to take over any existing Binding from other 910 6BBRs and to update existing NCEs in backbone nodes. This is done by 911 sending an NA message with an EARO and the Override flag set over the 912 backbone (see Section 7 and Section 8). 914 9.2. Operation on a Binding in Reachable State 916 The Reachable state covers an active registration after a successful 917 DAD process. 919 An NS(DAD) with no EARO or with an EARO that indicates a duplicate If 920 the Registration Lifetime is of a long duration, an implementation 921 might be configured to reassess the availability of the Registering 922 Node at a lower period, using a NUD procedure as specified in 923 [RFC7048]. If the NUD procedure fails, the Binding SHOULD be placed 924 in Stale state immediately. 926 For a Binding in Reachable state: 928 o The Binding MUST be removed if an NA or an NS(DAD) message is 929 received over the Backbone for the Registered Address containing 930 an EARO that indicates a fresher registration ([RFC8505]) for the 931 same Registered Node (i.e. same ROVR). A status of 4 (Removed) is 932 returned in an asynchronous NA(EARO) to the Registering Node. 933 Based on configuration, an implementation may delay this operation 934 by a small timer in order to a allow for a parallel registration 935 to arrive to this node, in which case the NA might be ignored. 937 o An NS(DAD) with no EARO or with an EARO that indicates a duplicate 938 registration (i.e. different ROVR) MUST be answered with an NA 939 message containing an EARO with a status of 1 (Duplicate) and the 940 Override flag not set. 942 o NS(DAD) and NA messages containing an EARO that indicates a 943 registration for the same Registered Node that is not as fresh as 944 this MUST be answered with an NA message containing an EARO with a 945 status of 3 (Moved). 947 o Other NS(DAD) and NA messages from the Backbone are ignored. 949 o NS(Lookup) and NS(NUD) messages SHOULD be answered with an NA 950 message containing an EARO with a status of 0 and the Override 951 flag not set. The 6BBR MAY check whether the Registering Node is 952 still available using a NUD procedure over the LLN prior to 953 answering; this behaviour depends on the use case and is subject 954 to configuration. 956 When the Registration Lifetime timer elapses, the Binding is placed 957 in Stale state for a duration of STALE_DURATION. 959 9.3. Operation on a Binding in Stale State 961 The Stale state enables tracking of the Backbone peers that have a 962 NCE pointing to this 6BBR in case the Registered Address shows up 963 later. 965 If the Registered Address is claimed by another 6LN on the Backbone, 966 with an NS(DAD) or an NA, the 6BBR does not defend the Address. 968 For a Binding in Stale state: 970 o The Binding MUST be removed if an NA or an NS(DAD) message is 971 received over the Backbone for the Registered Address containing 972 no EARO or an EARO that indicates either a fresher registration 973 for the same Registered Node or a duplicate registration. A 974 status of 4 (Removed) MAY be returned in an asynchronous NA(EARO) 975 to the Registering Node. 977 o NS(DAD) and NA messages containing an EARO that indicates a 978 registration for the same Registered Node that is not as fresh as 979 this MUST be answered with an NA message containing an EARO with a 980 status of 3 (Moved). 982 o If the 6BBR receives an NS(Lookup) or an NS(NUD) message for the 983 Registered Address, the 6BBR MUST attempts a NUD procedure as 984 specified in [RFC7048] to the Registering Node, targeting the 985 Registered Address, prior to answering. If the NUD procedure 986 succeeds, the operation in Reachable state applies. If the NUD 987 fails, the 6BBR refrains from answering. 989 o Other NS(DAD) and NA messages from the Backbone are ignored. 991 When the STALE_DURATION timer elapses, the Binding MUST be removed. 993 10. Registering Node Considerations 995 A Registering Node MUST implement [RFC8505] in order to interact with 996 a 6BBR (which acts as a routing registrar). Following [RFC8505], the 997 Registering Node signals that it requires IPv6 proxy-ND services from 998 a 6BBR by registering the corresponding IPv6 Address using an 999 NS(EARO) message with the R flag set. 1001 The Registering Node may be the 6LN owning the IPv6 Address, or a 1002 6LBR that performs the registration on its behalf in a Route-Over 1003 mesh. 1005 The Registering Node SHOULD register all of its IPv6 Addresses to its 1006 6LR, which is the 6BBR when they are connected at Layer-2. Failure 1007 to register an address may result in the address being unreachable by 1008 other parties if the 6BBR cancels the NS(Lookup) over the LLN or to 1009 selected LLN nodes that are known to register their addresses. 1011 The Registering Node MUST refrain from using multicast NS(Lookup) 1012 when the destination is not known as on-link, e.g., if the prefix is 1013 advertised in a PIO with the L flag that is not set. In that case, 1014 the Registering Node sends its packets directly to its 6LR. 1016 The Registering Node SHOULD also follow [RFC7772] in order to limit 1017 the use of multicast RAs. It SHOULD also implement Simple Procedures 1018 for Detecting Network Attachment in IPv6 [RFC6059] (DNA procedures) 1019 to detect movements, and support Packet-Loss Resiliency for Router 1020 Solicitations [RFC7559] in order to improve reliability for the 1021 unicast RS messages. 1023 11. Security Considerations 1025 This specification applies to LLNs in which the link layer is 1026 protected, either by means of physical or IP security for the 1027 Backbone Link or MAC-layer security. In particular, the LLN MAC is 1028 required to provide secure unicast to/from the Backbone Router and 1029 secure Broadcast from the Backbone Router in a way that prevents 1030 tampering with or replaying the RA messages. 1032 A possible attack over the backbone can be done by sending an NS with 1033 an EARO and expecting the NA(EARO) back to contain the TID and ROVR 1034 fields of the existing state. With that information, the attacker 1035 can easily increase the TID and take over the Binding. 1036 [I-D.ietf-6lo-ap-nd] guarantees the ownership of a registered address 1037 based on a proof-of-ownership encoded in the ROVR field and protects 1038 against address theft and impersonation. 1040 12. Protocol Constants 1042 This Specification uses the following constants: 1044 TENTATIVE_DURATION: 800 milliseconds 1046 STALE_DURATION: see below 1048 In LLNs with long-lived Addresses such as LPWANs, STALE_DURATION 1049 SHOULD be configured with a relatively long value, by default 24 1050 hours. In LLNs where addresses are renewed rapidly, e.g. for privacy 1051 reasons, STALE_DURATION SHOULD be configured with a relatively long 1052 value, by default 5 minutes. 1054 13. IANA Considerations 1056 This document has no request to IANA. 1058 14. Acknowledgments 1060 Many thanks to Dorothy Stanley, Thomas Watteyne and Jerome Henry for 1061 their various contributions. 1063 15. References 1065 15.1. Normative References 1067 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1068 Requirement Levels", BCP 14, RFC 2119, 1069 DOI 10.17487/RFC2119, March 1997, 1070 . 1072 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1073 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1074 2006, . 1076 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 1077 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 1078 . 1080 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1081 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1082 DOI 10.17487/RFC4861, September 2007, 1083 . 1085 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1086 Address Autoconfiguration", RFC 4862, 1087 DOI 10.17487/RFC4862, September 2007, 1088 . 1090 [RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for 1091 Detecting Network Attachment in IPv6", RFC 6059, 1092 DOI 10.17487/RFC6059, November 2010, 1093 . 1095 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1096 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1097 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1098 Low-Power and Lossy Networks", RFC 6550, 1099 DOI 10.17487/RFC6550, March 2012, 1100 . 1102 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1103 Bormann, "Neighbor Discovery Optimization for IPv6 over 1104 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1105 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1106 . 1108 [RFC7048] Nordmark, E. and I. Gashinsky, "Neighbor Unreachability 1109 Detection Is Too Impatient", RFC 7048, 1110 DOI 10.17487/RFC7048, January 2014, 1111 . 1113 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1114 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1115 May 2017, . 1117 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1118 (IPv6) Specification", STD 86, RFC 8200, 1119 DOI 10.17487/RFC8200, July 2017, 1120 . 1122 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 1123 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 1124 DOI 10.17487/RFC8201, July 2017, 1125 . 1127 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1128 Perkins, "Registration Extensions for IPv6 over Low-Power 1129 Wireless Personal Area Network (6LoWPAN) Neighbor 1130 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1131 . 1133 15.2. Informative References 1135 [I-D.bi-savi-wlan] 1136 Bi, J., Wu, J., Wang, Y., and T. Lin, "A SAVI Solution for 1137 WLAN", draft-bi-savi-wlan-16 (work in progress), November 1138 2018. 1140 [I-D.ietf-6lo-ap-nd] 1141 Thubert, P., Sethi, M., Struik, R., and B. Sarikaya, 1142 "Address Protected Neighbor Discovery for Low-power and 1143 Lossy Networks", draft-ietf-6lo-ap-nd-09 (work in 1144 progress), December 2018. 1146 [I-D.ietf-6man-rs-refresh] 1147 Nordmark, E., Yourtchenko, A., and S. Krishnan, "IPv6 1148 Neighbor Discovery Optional RS/RA Refresh", draft-ietf- 1149 6man-rs-refresh-02 (work in progress), October 2016. 1151 [I-D.ietf-6tisch-architecture] 1152 Thubert, P., "An Architecture for IPv6 over the TSCH mode 1153 of IEEE 802.15.4", draft-ietf-6tisch-architecture-19 (work 1154 in progress), December 2018. 1156 [I-D.ietf-mboned-ieee802-mcast-problems] 1157 Perkins, C., McBride, M., Stanley, D., Kumari, W., and J. 1158 Zuniga, "Multicast Considerations over IEEE 802 Wireless 1159 Media", draft-ietf-mboned-ieee802-mcast-problems-04 (work 1160 in progress), November 2018. 1162 [I-D.nordmark-6man-dad-approaches] 1163 Nordmark, E., "Possible approaches to make DAD more robust 1164 and/or efficient", draft-nordmark-6man-dad-approaches-02 1165 (work in progress), October 2015. 1167 [I-D.yourtchenko-6man-dad-issues] 1168 Yourtchenko, A. and E. Nordmark, "A survey of issues 1169 related to IPv6 Duplicate Address Detection", draft- 1170 yourtchenko-6man-dad-issues-01 (work in progress), March 1171 2015. 1173 [IEEEstd8021] 1174 IEEE standard for Information Technology, "IEEE Standard 1175 for Information technology -- Telecommunications and 1176 information exchange between systems Local and 1177 metropolitan area networks Part 1: Bridging and 1178 Architecture". 1180 [IEEEstd80211] 1181 IEEE standard for Information Technology, "IEEE Standard 1182 for Information technology -- Telecommunications and 1183 information exchange between systems Local and 1184 metropolitan area networks-- Specific requirements Part 1185 11: Wireless LAN Medium Access Control (MAC) and Physical 1186 Layer (PHY) Specifications". 1188 [IEEEstd802151] 1189 IEEE standard for Information Technology, "IEEE Standard 1190 for Information Technology - Telecommunications and 1191 Information Exchange Between Systems - Local and 1192 Metropolitan Area Networks - Specific Requirements. - Part 1193 15.1: Wireless Medium Access Control (MAC) and Physical 1194 Layer (PHY) Specifications for Wireless Personal Area 1195 Networks (WPANs)". 1197 [IEEEstd802154] 1198 IEEE standard for Information Technology, "IEEE Standard 1199 for Local and metropolitan area networks -- Part 15.4: 1200 Low-Rate Wireless Personal Area Networks (LR-WPANs)". 1202 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 1203 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 1204 2006, . 1206 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 1207 DOI 10.17487/RFC4903, June 2007, 1208 . 1210 [RFC5415] Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley, 1211 Ed., "Control And Provisioning of Wireless Access Points 1212 (CAPWAP) Protocol Specification", RFC 5415, 1213 DOI 10.17487/RFC5415, March 2009, 1214 . 1216 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 1217 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 1218 2011, . 1220 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1221 Statement and Requirements for IPv6 over Low-Power 1222 Wireless Personal Area Network (6LoWPAN) Routing", 1223 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1224 . 1226 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 1227 Locator/ID Separation Protocol (LISP)", RFC 6830, 1228 DOI 10.17487/RFC6830, January 2013, 1229 . 1231 [RFC7559] Krishnan, S., Anipko, D., and D. Thaler, "Packet-Loss 1232 Resiliency for Router Solicitations", RFC 7559, 1233 DOI 10.17487/RFC7559, May 2015, 1234 . 1236 [RFC7772] Yourtchenko, A. and L. Colitti, "Reducing Energy 1237 Consumption of Router Advertisements", BCP 202, RFC 7772, 1238 DOI 10.17487/RFC7772, February 2016, 1239 . 1241 [RFC8273] Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix 1242 per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017, 1243 . 1245 Appendix A. Possible Future Extensions 1247 With the current specification, the 6LBR is not leveraged to avoid 1248 multicast NS(Lookup) on the Backbone. This could be done by adding a 1249 lookup procedure in the EDAR/EDAC exchange. 1251 By default the specification does not have a trust model, e.g., 1252 whereby nodes that associate their address with a proof-of-ownership 1253 [I-D.ietf-6lo-ap-nd] should be more trusted than nodes that do not. 1254 Such a trust model and related signaling could be added in the future 1255 to override the default operation and favor trusted nodes. 1257 Future documents may extend this specification by allowing the 6BBR 1258 to redistribute Host routes in routing protocols that would operate 1259 over the Backbone, or in MIPv6, or FMIP, or the Locator/ID Separation 1260 Protocol (LISP) [RFC6830] to support mobility on behalf of the 6LNs, 1261 etc... LISP may also be used to provide an equivalent to the EDAR/ 1262 EDAC exchange using a Map Server / Map Resolver as a replacement to 1263 the 6LBR. 1265 Appendix B. Applicability and Requirements Served 1267 This document specifies proxy-ND functions that can be used to 1268 federate an IPv6 Backbone Link and multiple IPv6 LLNs into a single 1269 MultiLink Subnet. The proxy-ND functions enable IPv6 ND services for 1270 Duplicate Address Detection (DAD) and Address Lookup that do not 1271 require broadcasts over the LLNs. 1273 The term LLN is used to cover multiple types of WLANs and WPANs, 1274 including (Low-Power) Wi-Fi, BLUETOOTH(R) Low Energy, IEEE STD 1275 802.11ah and IEEE STD.802.15.4 wireless meshes, meeting the 1276 requirements listed in Appendix B.3 of [RFC8505] "Requirements 1277 Related to Various Low-Power Link Types". 1279 Each LLN in the subnet is attached at an IPv6 Backbone Router (6BBR). 1280 The Backbone Routers interconnect the LLNs and advertise the 1281 Addresses of the 6LNs over the Backbone Link using proxy-ND 1282 operations. 1284 This specification updates IPv6 ND over the Backbone to distinguish 1285 Address movement from duplication and eliminate stale state in the 1286 Backbone routers and Backbone nodes once a 6LN has roamed. In this 1287 way, mobile nodes may roam rapidly from one 6BBR to the next and 1288 requirements in Appendix B.1 of [RFC8505] "Requirements Related to 1289 Mobility" are met. 1291 A 6LN can register its IPv6 Addresses and thereby obtain proxy-ND 1292 services over the Backbone, meeting the requirements expressed in 1293 Appendix B.4 of [RFC8505], "Requirements Related to Proxy 1294 Operations". 1296 The IPv6 ND operation is minimized as the number of 6LNs grows in the 1297 LLN. This meets the requirements in Appendix B.6 of [RFC8505] 1298 "Requirements Related to Scalability", as long has the 6BBRs are 1299 dimensioned for the number of registrations that each needs to 1300 support. 1302 In the case of a Wi-Fi access link, a 6BBR may be collocated with the 1303 Access Point (AP), or with a Fabric Edge (FE) or a CAPWAP [RFC5415] 1304 Wireless LAN Controller (WLC). In those cases, the wireless client 1305 (STA) is the 6LN that makes use of [RFC8505] to register its IPv6 1306 Address(es) to the 6BBR acting as Routing Registrar. The 6LBR can be 1307 centralized and either connected to the Backbone Link or reachable 1308 over IP. The 6BBR proxy-ND operations eliminate the need for 1309 wireless nodes to respond synchronously when a Lookup is performed 1310 for their IPv6 Addresses. This provides the function of a Sleep 1311 Proxy for ND [I-D.nordmark-6man-dad-approaches]. 1313 For the TimeSlotted Channel Hopping (TSCH) mode of [IEEEstd802154], 1314 the 6TiSCH architecture [I-D.ietf-6tisch-architecture] describes how 1315 a 6LoWPAN ND host could connect to the Internet via a RPL mesh 1316 Network, but doing so requires extensions to the 6LOWPAN ND protocol 1317 to support mobility and reachability in a secure and manageable 1318 environment. The extensions detailed in this document also work for 1319 the 6TiSCH architecture, serving the requirements listed in 1320 Appendix B.2 of [RFC8505] "Requirements Related to Routing 1321 Protocols". 1323 The registration mechanism may be seen as a more reliable alternate 1324 to snooping [I-D.bi-savi-wlan]. It can be noted that registration 1325 and snooping are not mutually exclusive. Snooping may be used in 1326 conjunction with the registration for nodes that do not register 1327 their IPv6 Addresses. The 6BBR assumes that if a node registers at 1328 least one IPv6 Address to it, then the node registers all of its 1329 Addresses to the 6BBR. With this assumption, the 6BBR can possibly 1330 cancel all undesirable multicast NS messages that would otherwise 1331 have been delivered to that node. 1333 Scalability of the MultiLink Subnet [RFC4903] requires avoidance of 1334 multicast/broadcast operations as much as possible even on the 1335 Backbone [I-D.ietf-mboned-ieee802-mcast-problems]. Although hosts 1336 can connect to the Backbone using IPv6 ND operations, multicast RAs 1337 can be saved by using [I-D.ietf-6man-rs-refresh], which also requires 1338 the support of [RFC7559]. 1340 Authors' Addresses 1342 Pascal Thubert (editor) 1343 Cisco Systems, Inc 1344 Building D 1345 45 Allee des Ormes - BP1200 1346 MOUGINS - Sophia Antipolis 06254 1347 FRANCE 1349 Phone: +33 497 23 26 34 1350 Email: pthubert@cisco.com 1352 Charles E. Perkins 1353 Futurewei 1354 2330 Central Expressway 1355 Santa Clara 95050 1356 United States of America 1358 Email: charliep@computer.org 1360 Eric Levy-Abegnoli 1361 Cisco Systems, Inc 1362 Building D 1363 45 Allee des Ormes - BP1200 1364 MOUGINS - Sophia Antipolis 06254 1365 FRANCE 1367 Phone: +33 497 23 26 20 1368 Email: elevyabe@cisco.com