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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 6lo P. Thubert, Ed. 3 Internet-Draft Cisco Systems 4 Updates: 6775, 8505 (if approved) C. Perkins 5 Intended status: Standards Track Futurewei 6 Expires: March 29, 2020 E. Levy-Abegnoli 7 Cisco Systems 8 September 26, 2019 10 IPv6 Backbone Router 11 draft-ietf-6lo-backbone-router-13 13 Abstract 15 This document updates RFC 6775 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 March 29, 2020. 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. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . 14 68 4. MultiLink Subnet Considerations . . . . . . . . . . . . . . . 14 69 5. Optional 6LBR serving the MultiLink Subnet . . . . . . . . . 15 70 6. Using IPv6 ND Over the Backbone Link . . . . . . . . . . . . 15 71 7. Routing Proxy Operations . . . . . . . . . . . . . . . . . . 16 72 8. Bridging Proxy Operations . . . . . . . . . . . . . . . . . . 17 73 9. Creating and Maintaining a Binding . . . . . . . . . . . . . 18 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 . . . . . . . . . . . . . . . 22 78 11. Security Considerations . . . . . . . . . . . . . . . . . . . 23 79 12. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 23 80 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 81 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 82 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 83 15.1. Normative References . . . . . . . . . . . . . . . . . . 24 84 15.2. Informative References . . . . . . . . . . . . . . . . . 25 85 Appendix A. Possible Future Extensions . . . . . . . . . . . . . 28 86 Appendix B. Applicability and Requirements Served . . . . . . . 28 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30 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 Knowledge of which address to proxy for can be obtained by snooping 159 the IPV6 ND protocol (see [I-D.bi-savi-wlan]), but it has been found 160 to be unreliable. An IPv6 address may not be discovered immediately 161 due to a packet loss, or if a "silent" node is not currently using 162 one of its addresses. A change of state (e.g. due to movement) may 163 be missed or misordered, leading to unreliable connectivity and 164 incomplete knowledge of the state of the network. 166 This specification defines the 6BBR as a Routing Registrar [RFC8505] 167 that provide proxy services for IPv6 Neighbor Discovery. Backbone 168 Routers federate multiple LLNs over a Backbone Link to form a 169 MultiLink Subnet (MLSN). Backbone Routers placed along the LLN edge 170 of the Backbone handle IPv6 Neighbor Discovery, and forward packets 171 on behalf of registered nodes. 173 An LLN node (6LN) registers all its IPv6 Addresses using an NS(EARO) 174 as specified in [RFC8505] to the 6BBR. The 6BBR is also a Border 175 Router that performs IPv6 Neighbor Discovery (IPv6 ND) operations on 176 its Backbone interface on behalf of the 6LNs that have registered 177 addresses on its LLN interfaces without the need of a broadcast over 178 the wireless medium. Additional benefits are discussed in 179 Appendix B. 181 2. Terminology 183 2.1. BCP 14 185 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 186 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 187 "OPTIONAL" in this document are to be interpreted as described in BCP 188 14 [RFC2119] [RFC8174] when, and only when, they appear in all 189 capitals, as shown here. 191 2.2. New Terms 193 This document introduces the following terminology: 195 Federated 197 A subnet that comprises a Backbone and one or more (wireless) 198 access links, is said to be federated into one MultiLink 199 Subnet. The proxy-ND operation of 6BBRs over the Backbone and 200 the access links provides the appearance of a subnet for IPv6 201 ND. 203 Sleeping Proxy 205 A 6BBR acts as a Sleeping Proxy if it answers ND Neighbor 206 Solicitations over the Backbone on behalf of a Registered Node. 208 Routing Proxy 210 A Routing Proxy provides IPv6 ND proxy functions and enables 211 the MLSN operation over federated links that may not be 212 compatible for bridging. The Routing Proxy advertises its own 213 MAC Address as the TLLA in the proxied NAs over the Backbone, 214 and routes at the Network Layer between the federated links. 216 Bridging Proxy 218 A Bridging Proxy provides IPv6 ND proxy functions while 219 preserving forwarding continuity at the MAC Layer. The 220 Bridging Proxy advertises the MAC Address of the Registering 221 Node as the TLLA in the proxied NAs over the Backbone. In that 222 case, the MAC Address and the mobility of 6LN is still visible 223 across the bridged Backbone, and the 6BR may be configured to 224 proxy for Link Local Addresses. 226 Binding Table 228 The Binding Table is an abstract database that is maintained by 229 the 6BBR to store the state associated with its registrations. 231 Binding 233 A Binding is an abstract state associated to one registration, 234 in other words one entry in the Binding Table. 236 2.3. Abbreviations 238 This document uses the following abbreviations: 240 6BBR: 6LoWPAN Backbone Router 242 6LBR: 6LoWPAN Border Router 244 6LN: 6LoWPAN Node 246 6LR: 6LoWPAN Router 248 6CIO: Capability Indication Option 250 ARO: Address Registration Option 252 DAC: Duplicate Address Confirmation 254 DAD: Duplicate Address Detection 256 DAR: Duplicate Address Request 258 EDAC: Extended Duplicate Address Confirmation 260 EDAR: Extended Duplicate Address Request 262 DODAG: Destination-Oriented Directed Acyclic Graph 264 LLN: Low-Power and Lossy Network 266 NA: Neighbor Advertisement 268 NCE: Neighbor Cache Entry 270 ND: Neighbor Discovery 272 NDP: Neighbor Discovery Protocol 274 NS: Neighbor Solicitation 276 ROVR: Registration Ownership Verifier 278 RPL: IPv6 Routing Protocol for LLNs 280 RA: Router Advertisement 282 RS: Router Solicitation 283 TID: Transaction ID 285 2.4. References 287 In this document, readers will encounter terms and concepts that are 288 discussed in the following documents: 290 o "Neighbor Discovery for IP version 6" [RFC4861], "IPv6 Stateless 291 Address Autoconfiguration" [RFC4862] and "Optimistic Duplicate 292 Address Detection" [RFC4429], 294 o "Neighbor Discovery Proxies (proxy-ND)" [RFC4389] and "MultiLink 295 Subnet Issues" [RFC4903], 297 o "Problem Statement and Requirements for IPv6 over Low-Power 298 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606], and 300 o Neighbor Discovery Optimization for Low-Power and Lossy Networks 301 [RFC6775] and "Registration Extensions for 6LoWPAN Neighbor 302 Discovery" [RFC8505]. 304 3. Overview 306 Figure 1 illustrates backbone link federating a collection of LLNs as 307 a single IPv6 Subnet, with a number of 6BBRs providing proxy-ND 308 services to their attached LLNs. 310 | 311 +-----+ +-----+ +-----+ 312 (default) | | (Optional) | | | | IPv6 313 Router | | 6LBR | | | | Node 314 +-----+ +-----+ +-----+ 315 | Backbone side | | 316 ----+-------+-----------------+---+-------------+----+----- 317 | | | 318 +------+ +------+ +------+ 319 | 6BBR | | 6BBR | | 6BBR | 320 | | | | | | 321 +------+ +------+ +------+ 322 o Wireless side o o o o o 323 o o o o o o o o o o o o o o 324 o o o o o o o o o o o o o o o 325 o o o o o o o o o o 326 o o o o o o o 328 LLN LLN LLN 330 Figure 1: Backbone Link and Backbone Routers 332 The LLN may be a hub-and-spoke access link such as (Low-Power) IEEE 333 STD. 802.11 (Wi-Fi) [IEEEstd80211] and IEEE STD. 802.15.1 (Bluetooth) 334 [IEEEstd802151], or a Mesh-Under or a Route-Over network [RFC8505]. 335 The proxy state can be distributed across multiple 6BBRs attached to 336 the same Backbone. 338 The main features of a 6BBR are as follows: 340 o Multilink-subnet functions (provided by the 6BBR on the backbone) 341 performed on behalf of registered 6LNs, and 343 o Routing registrar services that reduce multicast within the LLN: 345 * Binding Table management 347 * failover, e.g., due to mobility 349 Each Backbone Router (6BBR) maintains a data structure for its 350 Registered Nodes called a Binding Table. The combined Binding Tables 351 of all the 6BBRs on a backbone form a distributed database of 6LNs 352 that reside in the LLNs or on the IPv6 Backbone. 354 Unless otherwise configured, a 6BBR does the following: 356 o Create a new entry in a Binding Table for a new Registered Address 357 and ensure that the Address is not duplicated over the Backbone 359 o Advertise a Registered Address over the Backbone using NA 360 messages, asynchronously or as a response to a Neighbor 361 Solicitation messages. This includes participating to the 362 solicited-node multicast address associated to the Registered 363 Address as specified in section 7.2.1. of [RFC4861] over the 364 Backbone. 366 o Either respond using NA messages as a proxy or bridge as a unicast 367 frame the IPv6 ND messages (multicast DAD and Address Lookup, and 368 unicast NUD) received for the Registered Address over the 369 Backbone. This may include responding on behalf of a sleeping 370 node, or checking the liveliness of the Registering Node before 371 answering on its behalf. 373 o Deliver packets arriving from the LLN, using Neighbor Solicitation 374 messages to look up the destination over the Backbone. 376 o Forward or bridge packets between the LLN and the Backbone. 378 o Verify liveness for a registration, when needed. 380 The first of these functions enables the 6BBR to fulfill its role as 381 a Routing Registrar for each of its attached LLNs. The remaining 382 functions fulfill the role of the 6BBRs as the border routers 383 connecting the Multi-link IPv6 subnet to the Internet. 385 The proxy-ND operation can co-exist with IPv6 ND over the Backbone. 387 The 6BBR may co-exist with a proprietary snooping or a traditional 388 bridging functionality in an Access Point, in order to support legacy 389 nodes that do not support this specification. In the case, the co- 390 existing function may turn multicasts into a series of unicast to the 391 legacy nodes. 393 The registration to a proxy service uses an NS/NA(EARO) exchange. 394 The 6BBR operation resembles that of a Mobile IPv6 (MIPv6) [RFC6275] 395 Home Agent (HA). The combination of a 6BBR and a MIPv6 HA enables 396 full mobility support for 6LNs, inside and outside the links that 397 form the subnet. 399 The 6BBRs use the Extended Address Registration Option (EARO) defined 400 in [RFC8505] as follows: 402 o The EARO is used in the IPv6 ND exchanges over the Backbone 403 between the 6BBRs to help distinguish duplication from movement. 404 Extended Duplicate Address Messages (EDAR and EDAC) MAY also be 405 used with a 6LBR, if one is present, and the 6BBR. Address 406 duplication is detected using the ROVR field. Conflicting 407 registrations to different 6BBRs for the same Registered Address 408 are resolved using the TID field. 410 o The Link Layer Address (LLA) that the 6BBR advertises for the 411 Registered Address on behalf of the Registered Node over the 412 Backbone can belong to the Registering Node; in that case, the 413 6BBR (acting as a Bridging Proxy (see Section 8)) bridges the 414 unicast packets. Alternatively, the LLA can be that of the 6BBR 415 on the Backbone interface, in which case the 6BBR (acting as a 416 Routing Proxy(see Section 7)) receives the unicast packets at 417 Layer-3 and routes over. 419 3.1. Updating RFC 6775 and RFC 8505 421 This specification adds the EARO as a possible option in RS, NS(DAD) 422 and NA messages over the backbone. [RFC8505] requires that the 423 registration NS(EARO) contains an SLLAO. This specification details 424 the use of those messages over the backbone. 426 Note: [RFC6775] requires that the registration NS(EARO) contains an 427 SLLAO and [RFC4862] that the NS(DAD) is sent from the unspecified 428 address for which there cannot be a SLLAO. Consequently, an NS(DAD) 429 cannot be confused with a registration. 431 This specification adds the capability to insert IPv6 ND options in 432 the EDAR and EDAC messages. In particular, a 6BBR acting as a 6LR 433 for the Registered Address can insert an SLLAO in the EDAR to the 434 6LBR in order to avoid a Lookup back. This enables the 6LBR to store 435 the MAC address associated to the Registered Address on a Link and to 436 serve as a mapping server as described in 437 [I-D.thubert-6lo-unicast-lookup]. 439 3.2. Access Link 441 Figure 2 illustrates a flow where 6LN forms an IPv6 Address and 442 registers it to a 6BBR acting as a 6LR [RFC8505]. The 6BBRs applies 443 ODAD (see Section 3.6) to the registered address to enable 444 connectivity while the message flow is still in progress. In that 445 example, a 6LBR is deployed on the backbone link to serve the whole 446 subnet, and EDAR / EDAC messages are used in combination with DAD to 447 enable coexistence with IPv6 ND over the backbone. 449 6LN(STA) 6BBR(AP) 6LBR default GW 450 | | | | 451 | LLN Access Link | IPv6 Backbone (e.g., Ethernet) | 452 | | | | 453 | RS(multicast) | | | 454 |---------------->| | | 455 | RA(PIO, Unicast)| | | 456 |<----------------| | | 457 | NS(EARO) | | | 458 |---------------->| | | 459 | | Extended DAR | | 460 | |--------------->| | 461 | | Extended DAC | | 462 | |<---------------| | 463 | | | 464 | | NS-DAD(EARO, multicast) | 465 | |--------> | 466 | |----------------------------------->| 467 | | | 468 | | RS(no SLLAO, for ODAD) | 469 | |----------------------------------->| 470 | | if (no fresher Binding) NS(Lookup) | 471 | | <----------------| 472 | |<-----------------------------------| 473 | | NA(SLLAO, not(O), EARO) | 474 | |----------------------------------->| 475 | | RA(unicast) | 476 | |<-----------------------------------| 477 | | | 478 | IPv6 Packets in optimistic mode | 479 |<---------------------------------------------------->| 480 | | | 481 | | 482 | NA(EARO) | 483 |<----------------| 484 | | 486 Figure 2: Initial Registration Flow to a 6BBR acting as Routing Proxy 488 3.3. Route-Over Mesh 490 Figure 3 illustrates IPv6 signaling that enables a 6LN to form a 491 Global or a Unique-Local Address and register it to the 6LBR that 492 serves its LLN using [RFC8505]. The 6LBR (acting as Registering 493 Node) proxies the registration to the 6BBR, using [RFC8505] to 494 register the addresses the 6LN (Registered Node) on its behalf to the 495 6BBR, and obtain proxy-ND services from the 6BBR. 497 6LoWPAN Node 6LR 6LBR 6BBR 498 (mesh leaf) (mesh router) (mesh root) 499 | | | | 500 | 6LoWPAN ND |6LoWPAN ND | 6LoWPAN ND | IPv6 ND 501 | LLN link |Route-Over mesh|Ethernet/serial| Backbone 502 | | |/Internal call | 503 | IPv6 ND RS | | | 504 |-------------->| | | 505 |-----------> | | | 506 |------------------> | | 507 | IPv6 ND RA | | | 508 |<--------------| | | 509 | | | | 510 | NS(EARO) | | | 511 |-------------->| | | 512 | 6LoWPAN ND | Extended DAR | | 513 | |-------------->| | 514 | | | NS(EARO) | 515 | | |-------------->| 516 | | | (proxied) | NS-DAD 517 | | | |------> 518 | | | | (EARO) 519 | | | | 520 | | | NA(EARO) | 521 | | |<--------------| 522 | | Extended DAC | | 523 | |<--------------| | 524 | NA(EARO) | | | 525 |<--------------| | | 526 | | | | 528 Figure 3: Initial Registration Flow over Route-Over Mesh 530 As a non-normative example of a Route-Over Mesh, the 6TiSCH 531 architecture [I-D.ietf-6tisch-architecture] suggests using RPL 532 [RFC6550] and collocating the RPL root with a 6LBR that serves the 533 LLN, and is either collocated with or connected to the 6BBR over an 534 IPv6 Link. 536 3.4. The Binding Table 538 Addresses in a LLN that are reachable from the Backbone by way of the 539 6BBR function must be registered to that 6BBR, using an NS(EARO) with 540 the R flag set [RFC8505]. A 6BBR maintains a state for its active 541 registrations in an abstract Binding Table. 543 An entry in the Binding Table is called a "Binding". A Binding may 544 be in Tentative, Reachable or Stale state. 546 The 6BBR uses a combination of [RFC8505] and IPv6 ND over the 547 Backbone to advertise the registration and avoid a duplication. 548 Conflicting registrations are solved by the 6BBRs transparently to 549 the Registering Nodes. 551 Only one 6LN may register a given Address, but the Address may be 552 registered to Multiple 6BBRs for higher availability. 554 Over the LLN, Binding Table management is as follows: 556 o De-registrations (newer TID, same ROVR, null Lifetime) are 557 accepted with a status of 4 ("Removed"); the entry is deleted; 559 o Newer registrations (newer TID, same ROVR, non-null Lifetime) are 560 accepted with a status of 0 (Success); the Binding is updated with 561 the new TID, the Registration Lifetime and the Registering Node; 562 in Tentative state the EDAC response is held and may be 563 overwritten; in other states the Registration Lifetime timer is 564 restarted and the entry is placed in Reachable state. 566 o Identical registrations (same TID, same ROVR) from a same 567 Registering Node are accepted with a status of 0 (Success). In 568 Tentative state, the response is held and may be overwritten, but 569 the response MUST be eventually produced, carrying the result of 570 the DAD process; 572 o Older registrations (older TID, same ROVR) from the same 573 Registering Node are discarded; 575 o Identical and older registrations (not-newer TID, same ROVR) from 576 a different Registering Node are rejected with a status of 3 577 (Moved); this may be rate limited to avoid undue interference; 579 o Any registration for the same address but with a different ROVR is 580 rejected with a status of 1 (Duplicate). 582 3.5. Primary and Secondary 6BBRs 584 A same address may be successfully registered to more than one 6BBR, 585 in which case the Registering Node uses the same EARO in all the 586 parallel registrations. To allow for this, ND(DAD) and NA messages 587 with an EARO that indicate an identical Binding in another 6BBR (same 588 Registered address, same TID, same ROVR) as silently ignored. 590 A 6BBR MAY optionally be primary or secondary. The primary is the 591 6BBR that has the highest EUI-64 Address of all the 6BBRs that share 592 a registration for the same Registered Address, with the same ROVR 593 and same Transaction ID, the EUI-64 Address being considered as an 594 unsigned 64bit integer. A given 6BBR can be primary for a given 595 Address and secondary for another Address, regardless of whether or 596 not the Addresses belong to the same 6LN. 598 In the following sections, is is expected that an NA is sent over the 599 backbone only if the node is primary or does not support the concept 600 of primary. More than one 6BBR claiming or defending an address 601 generates unwanted traffic but no reachability issue since all 6BBRs 602 provide reachability from the Backbone to the 6LN. 604 3.6. Using Optimistic DAD 606 Optimistic Duplicate Address Detection [RFC4429] (ODAD) specifies how 607 an IPv6 Address can be used before completion of Duplicate Address 608 Detection (DAD). ODAD guarantees that this behavior will not cause 609 harm if the new Address is a duplicate. 611 Support for ODAD avoids delays in installing the Neighbor Cache Entry 612 (NCE) in the 6BBRs and the default router, enabling immediate 613 connectivity to the registered node. As shown in Figure 2, if the 614 6BBR is aware of the Link-Layer Address (LLA) of a router, then the 615 6BBR sends a Router Solicitation (RS), using the Registered Address 616 as the IP Source Address, to the known router(s). The RS MUST be 617 sent without a Source LLA Option (SLLAO), to avoid invalidating a 618 preexisting NCE in the router. 620 Following ODAD, the router may then send a unicast RA to the 621 Registered Address, and it may resolve that Address using an 622 NS(Lookup) message. In response, the 6BBR sends an NA with an EARO 623 and the Override (O) flag [RFC4861] that is not set. The router can 624 then determine the freshest EARO in case of a conflicting NA(EARO) 625 messages, using the method described in section 5.2.1 of [RFC8505]. 626 If the NA(EARO) is the freshest answer, the default router creates a 627 Binding with the SLLAO of the 6BBR (in Routing Proxy mode) or that of 628 the Registering Node (in Bridging Proxy mode) so that traffic from/to 629 the Registered Address can flow immediately. 631 4. MultiLink Subnet Considerations 633 The Backbone and the federated LLN Links are considered as different 634 links in the MultiLink Subnet, even if multiple LLNs are attached to 635 the same 6BBR. ND messages are link-scoped and are not forwarded by 636 the 6BBR between the backbone and the LLNs though some packets may be 637 reinjected in Bridging Proxy mode (see Section 8). 639 Nodes located inside the subnet do not perform the IPv6 Path MTU 640 Discovery [RFC8201]. For that reason, the MTU must have a same value 641 on the Backbone and all attached LLNs. To achieve this, the 6BBR 642 MUST use the same MTU value in RAs over the Backbone and in the RAs 643 that it transmits towards the LLN links. 645 5. Optional 6LBR serving the MultiLink Subnet 647 A 6LBR can be deployed to serve the whole MLSN. It may be attached 648 to the backbone, in which case it can be discovered by its capability 649 advertisement (see section 4.3. of [RFC8505]) in RA messages. 651 When a 6LBR is present, the 6BBR uses an EDAR/EDAC message exchange 652 with the 6LBR to check for duplication or movement. This is done 653 prior to the NS(DAD) process, which may be avoided of the 6LBR 654 already maintains a conflicting state for the Registered Address. 656 This specification enables an address to be registered to more than 657 one 6BBR. It results that a 6LBR MUST be capable to maintain a state 658 for each of the 6BBR having registered with a same TID and same ROVR. 660 If this registration is duplicate or not the freshest, then the 6LBR 661 replies with an EDAC message with a status code of 1 ("Duplicate 662 Address") or 3 ("Moved"), respectively. If this registration is the 663 freshest, then the 6LBR replies with a status code of 0. In that 664 case, if this registration is fresher than an existing registration 665 for another 6BBR, then the 6LBR also sends an asynchronous EDAC with 666 a status of 4 ("Removed") to that other 6BBR. 668 The EDAR message SHOULD carry the SLLAO used in NS messages by the 669 6BBR for that Binding, and the EDAC message SHOULD carry the TLLAO 670 associated with the currently accepted registration. This enables a 671 6BBR to locate the new position of a mobile 6LN in the case of a 672 Routing Proxy operation, and opens the capability for the 6LBR to 673 serve as a mapping server in the future. 675 Note that if Link Local addresses are registered, then the scope of 676 uniqueness on which the address duplication is checked is the total 677 collection of links that the 6LBR serves as opposed to the sole link 678 on which the Link Local address is assigned. 680 6. Using IPv6 ND Over the Backbone Link 682 On the Backbone side, the 6BBR MUST join the SNMA group corresponding 683 to a Registered Address as soon as it creates a Binding for that 684 Address, and maintain that SNMA membership as long as it maintains 685 the registration. 687 The 6BBR uses either the SNMA or plain unicast to defend the 688 Registered Addresses in its Binding Table over the Backbone (as 689 specified in [RFC4862]). 691 The 6BBR advertises and defends the Registered Addresses over the 692 Backbone Link using RS, NS(DAD) and NA messages with the Registered 693 Address as the Source or Target address, respectively. 695 The 6BBR MUST place an EARO in the IPv6 ND messages that it generates 696 on behalf of the Registered Node. Note that an NS(DAD) does not 697 contain an SLLAO and cannot be confused with a proxy registration 698 such as performed by a 6LBR. 700 An NA message generated in response to an NS(DAD) MUST have the 701 Override flag set and a status of 1 (Duplicate) or 3 (Moved) in the 702 EARO. An NA message generated in response to an NS(Lookup) or an 703 NS(NUD) MUST NOT have the Override flag set. 705 This specification enables proxy operation for the IPv6 ND resolution 706 of LLN devices and a prefix that is used across a MultiLink Subnet 707 MAY be advertised as on-link over the Backbone. This is done for 708 backward compatibility with existing IPv6 hosts by setting the L flag 709 in the Prefix Information Option (PIO) of RA messages [RFC4861]. 711 For movement involving a slow reattachment, the Neighbor 712 Unreachability Detection (NUD) defined in [RFC4861] may time out too 713 quickly. Nodes on the backbone SHOULD support [RFC7048] whenever 714 possible. 716 7. Routing Proxy Operations 718 A Routing Proxy provides IPv6 ND proxy functions for Global including 719 Unique Local addresses between the LLN and the backbone, but not for 720 Link-Local addresses. It operates as an IPv6 border router and 721 provides a full Link-Layer isolation. 723 In this mode, it is not required that the MAC addresses of the 6LNs 724 are visible at Layer-2 over the Backbone. It is thus useful when the 725 messaging over the Backbone that is associated to wireless mobility 726 becomes expensive, e.g., when the Layer-2 topology is virtualized 727 over a wide area IP underlay. 729 This mode is definitely required when the LLN uses a MAC address 730 format that is different from that on the Backbone (e.g., EUI-64 vs. 731 EUI-48). Since a 6LN may not be able to resolve an arbitrary 732 destination in the MLSN directly, the MLSN prefix MUST NOT be 733 advertised as on-link in RA messages sent towards the LLN. 735 In order to maintain IP connectivity, the 6BBR installs a connected 736 Host route to the Registered Address on the LLN interface, via the 737 Registering Node as identified by the Source Address and the SLLA 738 option in the NS(EARO) messages. 740 When operating as a Routing Proxy, the 6BBR MUST use its Layer-2 741 Address on its Backbone Interface in the SLLAO of the RS messages and 742 the TLLAO of the NA messages that it generates to advertise the 743 Registered Addresses. 745 For each Registered Address, multiple peers on the Backbone may have 746 resolved the Address with the 6BBR MAC Address, maintaining that 747 mapping in their Neighbor Cache. The 6BBR SHOULD maintain a list of 748 the peers on the Backbone which have associated its MAC Address with 749 the Registered Address. If that Registered Address moves to a new 750 6BBR, the previous 6BBR SHOULD unicast a gratuitous NA with the 751 Override flag set to each such peer, to supply the LLA of the new 752 6BBR in the TLLA option for the Address. A 6BBR that does not 753 maintain this list MAY multicast a gratuitous NA with the Override 754 flag; this NA will possibly hit all the nodes on the Backbone, 755 whether or not they maintain an NCE for the Registered Address. 757 If a correspondent fails to receive the gratuitous NA, it will keep 758 sending traffic to a 6BBR to which the node was previously 759 registered. Since the previous 6BBR removed its Host route to the 760 Registered Address, it will look up the address over the backbone, 761 resolve the address with the LLA of the new 6BBR, and forward the 762 packet to the correct 6BBR. The previous 6BBR SHOULD also issue a 763 redirect message [RFC4861] to update the cache of the correspondent. 765 8. Bridging Proxy Operations 767 A Bridging Proxy provides IPv6 ND proxy functions between the LLN and 768 the backbone while preserving the forwarding continuity at the MAC 769 Layer. It acts as a Layer-2 Bridge for all types unicast packets 770 including link-scoped, and appears as an IPv6 Host on the Backbone. 772 The Bridging Proxy registers any Binding including for a Link-Local 773 address to the 6LBR (if present) and defends it over the backbone in 774 IPv6 ND procedures. 776 To achieve this, the Bridging Proxy intercepts the IPv6 ND messages 777 and may reinject them on the other side, respond directly or drop 778 them. For instance, an ND(Lookup) from the backbone that matches a 779 Binding can be responded directly, or turned into a unicast on the 780 LLN side to let the 6LN respond. 782 As a Bridging Proxy, the 6BBR MUST use the Registering Node's Layer-2 783 Address in the SLLAO of the NS/RS messages and the TLLAO of the NA 784 messages that it generates to advertise the Registered Addresses. 785 The Registering Node's Layer-2 address is found in the SLLA of the 786 registration NS(EARO), and maintained in the Binding Table. 788 The MultiLink Subnet prefix SHOULD NOT be advertised as on-link in RA 789 messages sent towards the LLN. If a destination address is seen as 790 on-link, then a 6LN may use NS(Lookup) messages to resolve that 791 address. In that case, the 6BBR MUST either answer directly to the 792 NS(Lookup) message or reinject the message on the backbone, either as 793 a Layer-2 unicast or a multicast. 795 If the Registering Node owns the Registered Address, then its 796 mobility does not impact existing NCEs over the Backbone. Otherwise, 797 when the 6LN selects another Registering Node, the new Registering 798 Node SHOULD send a multicast NA with the Override flag set to fix the 799 existing NCEs across the Backbone. This method can fail if the 800 multicast message is not received; one or more correspondent nodes on 801 the Backbone might maintain an stale NCE, and packets to the 802 Registered Address may be lost. When this condition happens, it is 803 eventually be discovered and resolved using Neighbor Unreachability 804 Detection (NUD) as defined in [RFC4861]. 806 9. Creating and Maintaining a Binding 808 Upon receiving a registration for a new Address (i.e., an NS(EARO) 809 with the R flag set), the 6BBR creates a Binding and operates as a 810 6LR according to [RFC8505], interacting with the 6LBR if one is 811 present. 813 An implementation of a Routing Proxy that creates a Binding MUST also 814 create an associated Host route pointing on the registering node in 815 the LLN interface from which the registration was received. 817 The 6LR operation is modified as follows: 819 o EDAR and EDAC messages SHOULD carry a SLLAO and a TLLAO, 820 respectively. 822 o A Bridging Proxy MAY register Link Local addresses to the 6BBR and 823 proxy ND for those addresses over the backbone. 825 o An EDAC message with a status of 9 (6LBR Registry Saturated) is 826 assimilated as a status of 0 if a following DAD process protects 827 the address against duplication. 829 This specification enables nodes on a Backbone Link to co-exist along 830 with nodes implementing IPv6 ND [RFC4861] as well as other non- 831 normative specifications such as [I-D.bi-savi-wlan]. It is possible 832 that not all IPv6 addresses on the Backbone are registered and known 833 to the 6LBR, and an EDAR/EDAC echange with the 6LBR might succeed 834 even for a duplicate address. Consequently, and unless 835 administratively overridden, the 6BBR still needs to perform IPv6 ND 836 DAD over the backbone after an EDAC with a status code of 0 or 9. 838 For the DAD operation, the Binding is placed in Tentative state for a 839 duration of TENTATIVE_DURATION, and an NS(DAD) message is sent as a 840 multicast message over the Backbone to the SNMA associated with the 841 registered Address [RFC4862]. The EARO from the registration MUST be 842 placed unchanged in the NS(DAD) message. 844 If a registration is received for an existing Binding with a non-null 845 Registration Lifetime and the registration is fresher (same ROVR, 846 fresher TID), then the Binding is updated, with the new Registration 847 Lifetime, TID, and possibly Registering Node. In Tentative state 848 (see Section 9.1), the current DAD operation continues as it was. In 849 other states (see Section 9.2 and Section 9.3 ), the Binding is 850 placed in Reachable state for the Registration Lifetime, and the 6BBR 851 returns an NA(EARO) to the Registering Node with a status of 0 852 (Success). 854 Upon a registration that is identical (same ROVR, TID, and 855 Registering Node), the 6BBR returns an NA(EARO) back to the 856 Registering Node with a status of 0 (Success). A registration that 857 is not as fresh (same ROVR, older TID) is ignored. 859 If a registration is received for an existing Binding and a 860 registration Lifetime of zero, then the Binding is removed, and the 861 6BBR returns an NA(EARO) back to the Registering Node with a status 862 of 0 (Success). An implementation of a Routing Proxy that removes a 863 binding MUST remove the associated Host route pointing on the 864 registering node. It MAY preserve a temporary state in order to 865 forward packets in flight. The state may be a NCE formed based on a 866 received NA message, or a Binding in Stale state and pointing at the 867 new 6BBR on the backbone. 869 The implementation should also use REDIRECT messages as specified in 870 [RFC4861] to update the correspondents for the Registered Address, 871 pointing the new 6BBR. 873 9.1. Operation on a Binding in Tentative State 875 The Tentative state covers a DAD period over the backbone during 876 which an address being registered is checked for duplication using 877 procedures defined in [RFC4862]. 879 For a Binding in Tentative state: 881 o The Binding MUST be removed if an NA message is received over the 882 Backbone for the Registered Address with no EARO, or containing an 883 EARO with a status of 1 (Duplicate) that indicates an existing 884 registration owned by a different Registering Node. In that case, 885 an NA MUST be sent back to the Registering Node with a status of 1 886 (Duplicate) in the EARO. This behavior might be overriden by 887 policy, in particular if the registration is trusted, e.g., based 888 on the validation of the ROVR field (see [I-D.ietf-6lo-ap-nd]). 890 o An NS(DAD) with no EARO or with an EARO that indicates a duplicate 891 registration (i.e. different ROVR) MUST be answered with an NA 892 message containing an EARO with a status of 1 (Duplicate) and the 893 Override flag not set. This behavior might be overriden by 894 policy, in particular if the registration is not trusted. 896 o The Binding MUST be removed if an NA message is received over the 897 Backbone for the Registered Address containing an EARO with a 898 status of 3 (Moved), or an NS(DAD) with an EARO that indicates a 899 fresher registration ([RFC8505]) for the same Registered Node 900 (i.e. same ROVR). A status of 3 is returned in the NA(EARO) back 901 to the Registering Node. 903 o NS(DAD) and NA messages containing an EARO that indicates a 904 registration for the same Registered Node that is not as fresh as 905 this SHOULD be answered with an NA message containing an EARO with 906 a status of 3 (Moved) in order to clean up the situation 907 immediately. 909 o Other NS(DAD) and NA messages from the Backbone are ignored. 911 o NS(Lookup) and NS(NUD) messages SHOULD be optimistically answered 912 with an NA message containing an EARO with a status of 0 and the 913 Override flag not set (see Section 3.6). If optimistic DAD is 914 disabled, then they SHOULD be queued to be answered when the 915 Binding goes to Reachable state. 917 When the TENTATIVE_DURATION timer elapses, the Binding is placed in 918 Reachable state for the Registration Lifetime, and the 6BBR returns 919 an NA(EARO) to the Registering Node with a status of 0 (Success). 921 The 6BBR also attempts to take over any existing Binding from other 922 6BBRs and to update existing NCEs in backbone nodes. This is done by 923 sending an NA message with an EARO and the Override flag set over the 924 backbone (see Section 7 and Section 8). 926 9.2. Operation on a Binding in Reachable State 928 The Reachable state covers an active registration after a successful 929 DAD process. 931 An NS(DAD) with no EARO or with an EARO that indicates a duplicate If 932 the Registration Lifetime is of a long duration, an implementation 933 might be configured to reassess the availability of the Registering 934 Node at a lower period, using a NUD procedure as specified in 935 [RFC7048]. If the NUD procedure fails, the Binding SHOULD be placed 936 in Stale state immediately. 938 For a Binding in Reachable state: 940 o The Binding MUST be removed if an NA or an NS(DAD) message is 941 received over the Backbone for the Registered Address containing 942 an EARO that indicates a fresher registration ([RFC8505]) for the 943 same Registered Node (i.e. same ROVR). A status of 4 (Removed) is 944 returned in an asynchronous NA(EARO) to the Registering Node. 945 Based on configuration, an implementation may delay this operation 946 by a small timer in order to a allow for a parallel registration 947 to arrive to this node, in which case the NA might be ignored. 949 o An NS(DAD) with no EARO or with an EARO that indicates a duplicate 950 registration (i.e. different ROVR) MUST be answered with an NA 951 message containing an EARO with a status of 1 (Duplicate) and the 952 Override flag not set. 954 o NS(DAD) and NA messages containing an EARO that indicates a 955 registration for the same Registered Node that is not as fresh as 956 this MUST be answered with an NA message containing an EARO with a 957 status of 3 (Moved). 959 o Other NS(DAD) and NA messages from the Backbone are ignored. 961 o NS(Lookup) and NS(NUD) messages SHOULD be answered with an NA 962 message containing an EARO with a status of 0 and the Override 963 flag not set. The 6BBR MAY check whether the Registering Node is 964 still available using a NUD procedure over the LLN prior to 965 answering; this behaviour depends on the use case and is subject 966 to configuration. 968 When the Registration Lifetime timer elapses, the Binding is placed 969 in Stale state for a duration of STALE_DURATION. 971 9.3. Operation on a Binding in Stale State 973 The Stale state enables tracking of the Backbone peers that have a 974 NCE pointing to this 6BBR in case the Registered Address shows up 975 later. 977 If the Registered Address is claimed by another 6LN on the Backbone, 978 with an NS(DAD) or an NA, the 6BBR does not defend the Address. 980 For a Binding in Stale state: 982 o The Binding MUST be removed if an NA or an NS(DAD) message is 983 received over the Backbone for the Registered Address containing 984 no EARO or an EARO that indicates either a fresher registration 985 for the same Registered Node or a duplicate registration. A 986 status of 4 (Removed) MAY be returned in an asynchronous NA(EARO) 987 to the Registering Node. 989 o NS(DAD) and NA messages containing an EARO that indicates a 990 registration for the same Registered Node that is not as fresh as 991 this MUST be answered with an NA message containing an EARO with a 992 status of 3 (Moved). 994 o If the 6BBR receives an NS(Lookup) or an NS(NUD) message for the 995 Registered Address, the 6BBR MUST attempts a NUD procedure as 996 specified in [RFC7048] to the Registering Node, targeting the 997 Registered Address, prior to answering. If the NUD procedure 998 succeeds, the operation in Reachable state applies. If the NUD 999 fails, the 6BBR refrains from answering. 1001 o Other NS(DAD) and NA messages from the Backbone are ignored. 1003 When the STALE_DURATION timer elapses, the Binding MUST be removed. 1005 10. Registering Node Considerations 1007 A Registering Node MUST implement [RFC8505] in order to interact with 1008 a 6BBR (which acts as a routing registrar). Following [RFC8505], the 1009 Registering Node signals that it requires IPv6 proxy-ND services from 1010 a 6BBR by registering the corresponding IPv6 Address using an 1011 NS(EARO) message with the R flag set. 1013 The Registering Node may be the 6LN owning the IPv6 Address, or a 1014 6LBR that performs the registration on its behalf in a Route-Over 1015 mesh. 1017 The Registering Node SHOULD register all of its IPv6 Addresses to its 1018 6LR, which is the 6BBR when they are connected at Layer-2. Failure 1019 to register an address may result in the address being unreachable by 1020 other parties if the 6BBR cancels the NS(Lookup) over the LLN or to 1021 selected LLN nodes that are known to register their addresses. 1023 The Registering Node MUST refrain from using multicast NS(Lookup) 1024 when the destination is not known as on-link, e.g., if the prefix is 1025 advertised in a PIO with the L flag that is not set. In that case, 1026 the Registering Node sends its packets directly to its 6LR. 1028 The Registering Node SHOULD also follow [RFC7772] in order to limit 1029 the use of multicast RAs. It SHOULD also implement Simple Procedures 1030 for Detecting Network Attachment in IPv6 [RFC6059] (DNA procedures) 1031 to detect movements, and support Packet-Loss Resiliency for Router 1032 Solicitations [RFC7559] in order to improve reliability for the 1033 unicast RS messages. 1035 11. Security Considerations 1037 This specification applies to LLNs in which the link layer is 1038 protected, either by means of physical or IP security for the 1039 Backbone Link or MAC-layer security. In particular, the LLN MAC is 1040 required to provide secure unicast to/from the Backbone Router and 1041 secure Broadcast from the Backbone Router in a way that prevents 1042 tampering with or replaying the RA messages. 1044 A possible attack over the backbone can be done by sending an NS with 1045 an EARO and expecting the NA(EARO) back to contain the TID and ROVR 1046 fields of the existing state. With that information, the attacker 1047 can easily increase the TID and take over the Binding. 1048 [I-D.ietf-6lo-ap-nd] guarantees the ownership of a registered address 1049 based on a proof-of-ownership encoded in the ROVR field and protects 1050 against address theft and impersonation. 1052 12. Protocol Constants 1054 This Specification uses the following constants: 1056 TENTATIVE_DURATION: 800 milliseconds 1058 STALE_DURATION: see below 1060 In LLNs with long-lived Addresses such as LPWANs, STALE_DURATION 1061 SHOULD be configured with a relatively long value, by default 24 1062 hours. In LLNs where addresses are renewed rapidly, e.g. for privacy 1063 reasons, STALE_DURATION SHOULD be configured with a relatively long 1064 value, by default 5 minutes. 1066 13. IANA Considerations 1068 This document has no request to IANA. 1070 14. Acknowledgments 1072 Many thanks to Dorothy Stanley, Thomas Watteyne and Jerome Henry for 1073 their various contributions. 1075 15. References 1077 15.1. Normative References 1079 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1080 Requirement Levels", BCP 14, RFC 2119, 1081 DOI 10.17487/RFC2119, March 1997, 1082 . 1084 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1085 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1086 2006, . 1088 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 1089 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 1090 . 1092 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1093 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1094 DOI 10.17487/RFC4861, September 2007, 1095 . 1097 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1098 Address Autoconfiguration", RFC 4862, 1099 DOI 10.17487/RFC4862, September 2007, 1100 . 1102 [RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for 1103 Detecting Network Attachment in IPv6", RFC 6059, 1104 DOI 10.17487/RFC6059, November 2010, 1105 . 1107 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1108 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1109 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1110 Low-Power and Lossy Networks", RFC 6550, 1111 DOI 10.17487/RFC6550, March 2012, 1112 . 1114 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1115 Bormann, "Neighbor Discovery Optimization for IPv6 over 1116 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1117 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1118 . 1120 [RFC7048] Nordmark, E. and I. Gashinsky, "Neighbor Unreachability 1121 Detection Is Too Impatient", RFC 7048, 1122 DOI 10.17487/RFC7048, January 2014, 1123 . 1125 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1126 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1127 May 2017, . 1129 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1130 (IPv6) Specification", STD 86, RFC 8200, 1131 DOI 10.17487/RFC8200, July 2017, 1132 . 1134 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 1135 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 1136 DOI 10.17487/RFC8201, July 2017, 1137 . 1139 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1140 Perkins, "Registration Extensions for IPv6 over Low-Power 1141 Wireless Personal Area Network (6LoWPAN) Neighbor 1142 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1143 . 1145 15.2. Informative References 1147 [I-D.bi-savi-wlan] 1148 Bi, J., Wu, J., Wang, Y., and T. Lin, "A SAVI Solution for 1149 WLAN", draft-bi-savi-wlan-17 (work in progress), May 2019. 1151 [I-D.ietf-6lo-ap-nd] 1152 Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 1153 "Address Protected Neighbor Discovery for Low-power and 1154 Lossy Networks", draft-ietf-6lo-ap-nd-12 (work in 1155 progress), April 2019. 1157 [I-D.ietf-6man-rs-refresh] 1158 Nordmark, E., Yourtchenko, A., and S. Krishnan, "IPv6 1159 Neighbor Discovery Optional RS/RA Refresh", draft-ietf- 1160 6man-rs-refresh-02 (work in progress), October 2016. 1162 [I-D.ietf-6tisch-architecture] 1163 Thubert, P., "An Architecture for IPv6 over the TSCH mode 1164 of IEEE 802.15.4", draft-ietf-6tisch-architecture-26 (work 1165 in progress), August 2019. 1167 [I-D.ietf-mboned-ieee802-mcast-problems] 1168 Perkins, C., McBride, M., Stanley, D., Kumari, W., and J. 1169 Zuniga, "Multicast Considerations over IEEE 802 Wireless 1170 Media", draft-ietf-mboned-ieee802-mcast-problems-08 (work 1171 in progress), August 2019. 1173 [I-D.nordmark-6man-dad-approaches] 1174 Nordmark, E., "Possible approaches to make DAD more robust 1175 and/or efficient", draft-nordmark-6man-dad-approaches-02 1176 (work in progress), October 2015. 1178 [I-D.thubert-6lo-unicast-lookup] 1179 Thubert, P. and E. Levy-Abegnoli, "IPv6 Neighbor Discovery 1180 Unicast Lookup", draft-thubert-6lo-unicast-lookup-00 (work 1181 in progress), January 2019. 1183 [I-D.yourtchenko-6man-dad-issues] 1184 Yourtchenko, A. and E. Nordmark, "A survey of issues 1185 related to IPv6 Duplicate Address Detection", draft- 1186 yourtchenko-6man-dad-issues-01 (work in progress), March 1187 2015. 1189 [IEEEstd8021] 1190 IEEE standard for Information Technology, "IEEE Standard 1191 for Information technology -- Telecommunications and 1192 information exchange between systems Local and 1193 metropolitan area networks Part 1: Bridging and 1194 Architecture". 1196 [IEEEstd80211] 1197 IEEE standard for Information Technology, "IEEE Standard 1198 for Information technology -- Telecommunications and 1199 information exchange between systems Local and 1200 metropolitan area networks-- Specific requirements Part 1201 11: Wireless LAN Medium Access Control (MAC) and Physical 1202 Layer (PHY) Specifications". 1204 [IEEEstd802151] 1205 IEEE standard for Information Technology, "IEEE Standard 1206 for Information Technology - Telecommunications and 1207 Information Exchange Between Systems - Local and 1208 Metropolitan Area Networks - Specific Requirements. - Part 1209 15.1: Wireless Medium Access Control (MAC) and Physical 1210 Layer (PHY) Specifications for Wireless Personal Area 1211 Networks (WPANs)". 1213 [IEEEstd802154] 1214 IEEE standard for Information Technology, "IEEE Standard 1215 for Local and metropolitan area networks -- Part 15.4: 1216 Low-Rate Wireless Personal Area Networks (LR-WPANs)". 1218 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 1219 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 1220 2006, . 1222 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 1223 DOI 10.17487/RFC4903, June 2007, 1224 . 1226 [RFC5415] Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley, 1227 Ed., "Control And Provisioning of Wireless Access Points 1228 (CAPWAP) Protocol Specification", RFC 5415, 1229 DOI 10.17487/RFC5415, March 2009, 1230 . 1232 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 1233 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 1234 2011, . 1236 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1237 Statement and Requirements for IPv6 over Low-Power 1238 Wireless Personal Area Network (6LoWPAN) Routing", 1239 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1240 . 1242 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 1243 Locator/ID Separation Protocol (LISP)", RFC 6830, 1244 DOI 10.17487/RFC6830, January 2013, 1245 . 1247 [RFC7559] Krishnan, S., Anipko, D., and D. Thaler, "Packet-Loss 1248 Resiliency for Router Solicitations", RFC 7559, 1249 DOI 10.17487/RFC7559, May 2015, 1250 . 1252 [RFC7772] Yourtchenko, A. and L. Colitti, "Reducing Energy 1253 Consumption of Router Advertisements", BCP 202, RFC 7772, 1254 DOI 10.17487/RFC7772, February 2016, 1255 . 1257 [RFC8273] Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix 1258 per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017, 1259 . 1261 Appendix A. Possible Future Extensions 1263 With the current specification, the 6LBR is not leveraged to avoid 1264 multicast NS(Lookup) on the Backbone. This could be done by adding a 1265 lookup procedure in the EDAR/EDAC exchange. 1267 By default the specification does not have a trust model, e.g., 1268 whereby nodes that associate their address with a proof-of-ownership 1269 [I-D.ietf-6lo-ap-nd] should be more trusted than nodes that do not. 1270 Such a trust model and related signaling could be added in the future 1271 to override the default operation and favor trusted nodes. 1273 Future documents may extend this specification by allowing the 6BBR 1274 to redistribute Host routes in routing protocols that would operate 1275 over the Backbone, or in MIPv6, or FMIP, or the Locator/ID Separation 1276 Protocol (LISP) [RFC6830] to support mobility on behalf of the 6LNs, 1277 etc... LISP may also be used to provide an equivalent to the EDAR/ 1278 EDAC exchange using a Map Server / Map Resolver as a replacement to 1279 the 6LBR. 1281 Appendix B. Applicability and Requirements Served 1283 This document specifies proxy-ND functions that can be used to 1284 federate an IPv6 Backbone Link and multiple IPv6 LLNs into a single 1285 MultiLink Subnet. The proxy-ND functions enable IPv6 ND services for 1286 Duplicate Address Detection (DAD) and Address Lookup that do not 1287 require broadcasts over the LLNs. 1289 The term LLN is used to cover multiple types of WLANs and WPANs, 1290 including (Low-Power) Wi-Fi, BLUETOOTH(R) Low Energy, IEEE STD 1291 802.11ah and IEEE STD.802.15.4 wireless meshes, meeting the 1292 requirements listed in Appendix B.3 of [RFC8505] "Requirements 1293 Related to Various Low-Power Link Types". 1295 Each LLN in the subnet is attached at an IPv6 Backbone Router (6BBR). 1296 The Backbone Routers interconnect the LLNs and advertise the 1297 Addresses of the 6LNs over the Backbone Link using proxy-ND 1298 operations. 1300 This specification updates IPv6 ND over the Backbone to distinguish 1301 Address movement from duplication and eliminate stale state in the 1302 Backbone routers and Backbone nodes once a 6LN has roamed. In this 1303 way, mobile nodes may roam rapidly from one 6BBR to the next and 1304 requirements in Appendix B.1 of [RFC8505] "Requirements Related to 1305 Mobility" are met. 1307 A 6LN can register its IPv6 Addresses and thereby obtain proxy-ND 1308 services over the Backbone, meeting the requirements expressed in 1309 Appendix B.4 of [RFC8505], "Requirements Related to Proxy 1310 Operations". 1312 The IPv6 ND operation is minimized as the number of 6LNs grows in the 1313 LLN. This meets the requirements in Appendix B.6 of [RFC8505] 1314 "Requirements Related to Scalability", as long has the 6BBRs are 1315 dimensioned for the number of registrations that each needs to 1316 support. 1318 In the case of a Wi-Fi access link, a 6BBR may be collocated with the 1319 Access Point (AP), or with a Fabric Edge (FE) or a CAPWAP [RFC5415] 1320 Wireless LAN Controller (WLC). In those cases, the wireless client 1321 (STA) is the 6LN that makes use of [RFC8505] to register its IPv6 1322 Address(es) to the 6BBR acting as Routing Registrar. The 6LBR can be 1323 centralized and either connected to the Backbone Link or reachable 1324 over IP. The 6BBR proxy-ND operations eliminate the need for 1325 wireless nodes to respond synchronously when a Lookup is performed 1326 for their IPv6 Addresses. This provides the function of a Sleep 1327 Proxy for ND [I-D.nordmark-6man-dad-approaches]. 1329 For the TimeSlotted Channel Hopping (TSCH) mode of [IEEEstd802154], 1330 the 6TiSCH architecture [I-D.ietf-6tisch-architecture] describes how 1331 a 6LoWPAN ND host could connect to the Internet via a RPL mesh 1332 Network, but doing so requires extensions to the 6LOWPAN ND protocol 1333 to support mobility and reachability in a secure and manageable 1334 environment. The extensions detailed in this document also work for 1335 the 6TiSCH architecture, serving the requirements listed in 1336 Appendix B.2 of [RFC8505] "Requirements Related to Routing 1337 Protocols". 1339 The registration mechanism may be seen as a more reliable alternate 1340 to snooping [I-D.bi-savi-wlan]. It can be noted that registration 1341 and snooping are not mutually exclusive. Snooping may be used in 1342 conjunction with the registration for nodes that do not register 1343 their IPv6 Addresses. The 6BBR assumes that if a node registers at 1344 least one IPv6 Address to it, then the node registers all of its 1345 Addresses to the 6BBR. With this assumption, the 6BBR can possibly 1346 cancel all undesirable multicast NS messages that would otherwise 1347 have been delivered to that node. 1349 Scalability of the MultiLink Subnet [RFC4903] requires avoidance of 1350 multicast/broadcast operations as much as possible even on the 1351 Backbone [I-D.ietf-mboned-ieee802-mcast-problems]. Although hosts 1352 can connect to the Backbone using IPv6 ND operations, multicast RAs 1353 can be saved by using [I-D.ietf-6man-rs-refresh], which also requires 1354 the support of [RFC7559]. 1356 Authors' Addresses 1358 Pascal Thubert (editor) 1359 Cisco Systems, Inc 1360 Building D 1361 45 Allee des Ormes - BP1200 1362 MOUGINS - Sophia Antipolis 06254 1363 FRANCE 1365 Phone: +33 497 23 26 34 1366 Email: pthubert@cisco.com 1368 Charles E. Perkins 1369 Futurewei 1370 2330 Central Expressway 1371 Santa Clara 95050 1372 United States of America 1374 Email: charliep@computer.org 1376 Eric Levy-Abegnoli 1377 Cisco Systems, Inc 1378 Building D 1379 45 Allee des Ormes - BP1200 1380 MOUGINS - Sophia Antipolis 06254 1381 FRANCE 1383 Phone: +33 497 23 26 20 1384 Email: elevyabe@cisco.com