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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: August 10, 2020 E. Levy-Abegnoli 7 Cisco Systems 8 February 7, 2020 10 IPv6 Backbone Router 11 draft-ietf-6lo-backbone-router-15 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 Multi-Link 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 August 10, 2020. 38 Copyright Notice 40 Copyright (c) 2020 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 . . . . . . . . . . . . . . . . . . . . . . . . . 5 57 2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 5 58 2.2. New Terms . . . . . . . . . . . . . . . . . . . . . . . . 5 59 2.3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 6 60 2.4. References . . . . . . . . . . . . . . . . . . . . . . . 7 61 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 8 62 3.1. Updating RFC 6775 and RFC 8505 . . . . . . . . . . . . . 11 63 3.2. Access Link . . . . . . . . . . . . . . . . . . . . . . . 11 64 3.3. Route-Over Mesh . . . . . . . . . . . . . . . . . . . . . 13 65 3.4. The Binding Table . . . . . . . . . . . . . . . . . . . . 15 66 3.5. Primary and Secondary 6BBRs . . . . . . . . . . . . . . . 16 67 3.6. Using Optimistic DAD . . . . . . . . . . . . . . . . . . 17 68 4. Multi-Link Subnet Considerations . . . . . . . . . . . . . . 17 69 5. Optional 6LBR serving the Multi-Link Subnet . . . . . . . . . 18 70 6. Using IPv6 ND Over the Backbone Link . . . . . . . . . . . . 19 71 7. Routing Proxy Operations . . . . . . . . . . . . . . . . . . 19 72 8. Bridging Proxy Operations . . . . . . . . . . . . . . . . . . 20 73 9. Creating and Maintaining a Binding . . . . . . . . . . . . . 21 74 9.1. Operations on a Binding in Tentative State . . . . . . . 23 75 9.2. Operations on a Binding in Reachable State . . . . . . . 24 76 9.3. Operations on a Binding in Stale State . . . . . . . . . 25 77 10. Registering Node Considerations . . . . . . . . . . . . . . . 25 78 11. Security Considerations . . . . . . . . . . . . . . . . . . . 26 79 12. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 27 80 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 81 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27 82 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 27 83 15.1. Normative References . . . . . . . . . . . . . . . . . . 27 84 15.2. Informative References . . . . . . . . . . . . . . . . . 29 85 Appendix A. Possible Future Extensions . . . . . . . . . . . . . 31 86 Appendix B. Applicability and Requirements Served . . . . . . . 32 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33 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 end node (the Wi-Fi 107 STA) and protects the wireless medium against broadcast-intensive 108 Transparent Bridging reactive Lookups. 110 In other words, the association process is used to register the MAC 111 Address of the STA to the AP. The AP subsequently proxies the 112 bridging operation and does not need to forward the broadcast Lookups 113 over the radio. 115 In the same way as Transparent Bridging, IPv6 [RFC8200] Neighbor 116 Discovery [RFC4861] [RFC4862] Protocol (IPv6 ND) is a reactive 117 protocol, based on multicast transmissions to locate an on-link 118 correspondent and ensure the uniqueness of an IPv6 address. The 119 mechanism for Duplicate Address Detection (DAD) [RFC4862] was 120 designed for the efficient broadcast operation of Ethernet Bridging. 121 Since broadcast can be unreliable over wireless media, DAD often 122 fails to discover duplications [I-D.yourtchenko-6man-dad-issues]. In 123 practice, the fact that IPv6 addresses very rarely conflict is mostly 124 attributable to the entropy of the 64-bit Interface IDs as opposed to 125 the succesful operation of the IPv6 ND duplicate address detection 126 and resolution mechanisms. 128 The IPv6 ND Neighbor Solicitation (NS) [RFC4861] message is used for 129 DAD and address Lookup when a node moves, or wakes up and reconnects 130 to the wireless network. The NS message is targeted to a Solicited- 131 Node Multicast Address (SNMA) [RFC4291] and should in theory only 132 reach a very small group of nodes. But in reality, IPv6 multicast 133 messages are typically broadcast on the wireless medium, and so they 134 are processed by most of the wireless nodes over the subnet (e.g., 135 the ESS fabric) regardless of how few of the nodes are subscribed to 136 the SNMA. As a result, IPv6 ND address Lookups and DADs over a large 137 wireless and/or a LowPower Lossy Network (LLN) can consume enough 138 bandwidth to cause a substantial degradation to the unicast traffic 139 service. 141 Because IPv6 ND messages sent to the SNMA group are broadcast at the 142 radio MAC Layer, wireless nodes that do not belong to the SNMA group 143 still have to keep their radio turned on to listen to multicast NS 144 messages, which is a total waste of energy for them. In order to 145 reduce their power consumption, certain battery-operated devices such 146 as IoT sensors and smartphones ignore some of the broadcasts, making 147 IPv6 ND operations even less reliable. 149 These problems can be alleviated by reducing the IPv6 ND broadcasts 150 over wireless access links. This has been done by splitting the 151 broadcast domains and routes between subnets, or even by assigning a 152 /64 prefix to each wireless node (see [RFC8273]). 154 Another way is to proxy at the boundary of the wired and wireless 155 domains the Layer 3 protocols that rely on MAC Layer broadcast 156 operations. For instance, IEEE 802.11 [IEEEstd80211] situates proxy- 157 ARP (IPv4) and proxy-ND (IPv6) functions at the Access Points (APs). 158 The 6BBR provides a proxy-ND function and can be extended for proxy- 159 ARP in a continuation specification. 161 Knowledge of which address to proxy for can be obtained by snooping 162 the IPV6 ND protocol (see [I-D.bi-savi-wlan]), but it has been found 163 to be unreliable. An IPv6 address may not be discovered immediately 164 due to a packet loss, or if a "silent" node is not currently using 165 one of its addresses. A change of state (e.g., due to movement) may 166 be missed or misordered, leading to unreliable connectivity and 167 incomplete knowledge of the state of the network. 169 This specification defines the 6BBR as a Routing Registrar [RFC8505] 170 that provides proxy services for IPv6 Neighbor Discovery. As 171 represented in Figure 1, Backbone Routers federate multiple LLNs over 172 a Backbone Link to form a Multi-Link Subnet (MLSN). The MLSN breaks 173 the Layer 2 continuity and splits the broadcast domain, in a fashion 174 that each Link, including the backbone, is its own broadcast domain. 175 This means that devices that rely on a link-scope multicast on the 176 backbone will only reach other nodes on the backbone but not LLN 177 nodes. The same goes a packet that is sent with a hop limit of 1 or 178 using a Link-Local destination address. This packet may reach other 179 nodes on the backbone but not LLN Nodes. In order to enable the 180 continuity of IPv6 ND operations beyond the backbone, and enable 181 communication using Global or Unique Local Addresses between any pair 182 of nodes in the MLSN, Backbone Routers placed along the LLN edge of 183 the Backbone handle IPv6 ND on behalf of Registered Nodes and forward 184 IPv6 packets back and forth. 186 A 6LoWPAN node (6LN) registers all its IPv6 Addresses using an 187 NS(EARO) as specified in [RFC8505] to the 6BBR. The 6BBR is also a 188 Border Router that performs IPv6 Neighbor Discovery (IPv6 ND) 189 operations on its Backbone interface on behalf of the 6LNs that have 190 registered addresses on its LLN interfaces without the need of a 191 broadcast over the wireless medium. A 6LN that resides on the 192 backbone does not register to the SNMA groups associated to its 193 Registered Addresses and defers to the 6BBR to answer or preferably 194 forward to it as unicast the corresponding multicast packets. 196 Additional benefits are discussed in Appendix B. 198 2. Terminology 200 2.1. BCP 14 202 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 203 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 204 "OPTIONAL" in this document are to be interpreted as described in BCP 205 14 [RFC2119] [RFC8174] when, and only when, they appear in all 206 capitals, as shown here. 208 2.2. New Terms 210 This document introduces the following terminology: 212 Federated 214 A subnet that comprises a Backbone and one or more (wireless) 215 access links, is said to be federated into one Multi-Link 216 Subnet. The proxy-ND operation of 6BBRs over the Backbone and 217 the access links provides the appearance of a subnet for IPv6 218 ND. 220 Sleeping Proxy 222 A 6BBR acts as a Sleeping Proxy if it answers ND Neighbor 223 Solicitations over the Backbone on behalf of the Registering 224 Node which might be in a sleep state in a low power network. 225 The Sleeping Proxy that is also a Bridging Proxy will 226 preferably forward the relevant messages to the Registering 227 Node as unicast frames in accord to the duty cycle of the 228 Registering Node and let it respond. 230 Routing Proxy 232 A Routing Proxy provides IPv6 ND proxy functions and enables 233 the MLSN operation over federated links that may not be 234 compatible for bridging. The Routing Proxy advertises its own 235 MAC Address as the Target Link Layer Address (TLLA) in the 236 proxied NAs over the Backbone, and routes at the Network Layer 237 between the federated links. 239 Bridging Proxy 240 A Bridging Proxy provides IPv6 ND proxy functions while 241 preserving forwarding continuity at the MAC Layer. The 242 Bridging Proxy advertises the MAC Address of the Registering 243 Node as the TLLA in the proxied NAs over the Backbone. In that 244 case, the MAC Address and the mobility of 6LN is still visible 245 across the bridged Backbone, and the 6BBR may be configured to 246 proxy for Link Local Addresses. 248 Binding Table 250 The Binding Table is an abstract database that is maintained by 251 the 6BBR to store the state associated with its registrations. 253 Binding 255 A Binding is an abstract state associated to one registration, 256 in other words one entry in the Binding Table. 258 2.3. Abbreviations 260 This document uses the following abbreviations: 262 6BBR: 6LoWPAN Backbone Router 264 6LBR: 6LoWPAN Border Router 266 6LN: 6LoWPAN Node 268 6LR: 6LoWPAN Router 270 6CIO: Capability Indication Option 272 ARO: Address Registration Option 274 DAC: Duplicate Address Confirmation 276 DAD: Duplicate Address Detection 278 DAR: Duplicate Address Request 280 EARO: Extended Address Registration Option 282 EDAC: Extended Duplicate Address Confirmation 284 EDAR: Extended Duplicate Address Request 286 DODAG: Destination-Oriented Directed Acyclic Graph 287 ID: Identifier 289 LLN: Low-Power and Lossy Network 291 NA: Neighbor Advertisement 293 NCE: Neighbor Cache Entry 295 ND: Neighbor Discovery 297 NDP: Neighbor Discovery Protocol 299 NS: Neighbor Solicitation 301 NS(DAD): NDP NS message used for the purpose of duplication 302 avoidance (multicast) 304 NS(Lookup): NDP NS message used for the purpose of address 305 resolution (multicast) 307 NS(NUD): NDP NS message used for the purpose of unreachability 308 detection (unicast) 310 NUD: Neighbor Unreachability Detection 312 ROVR: Registration Ownership Verifier 314 RPL: IPv6 Routing Protocol for LLNs 316 RA: Router Advertisement 318 RS: Router Solicitation 320 SNMA: Solicited-Node Multicast Address 322 LLA: Link Layer Address (aka MAC address) 324 SLLA: Source Link Layer Address 326 TLLA: Target Link Layer Address 328 TID: Transaction ID 330 2.4. References 332 In this document, readers will encounter terms and concepts that are 333 discussed in the following documents: 335 o "Neighbor Discovery for IP version 6" [RFC4861], "IPv6 Stateless 336 Address Autoconfiguration" [RFC4862] and "Optimistic Duplicate 337 Address Detection" [RFC4429], 339 o "Neighbor Discovery Proxies (proxy-ND)" [RFC4389] and "Multi-Link 340 Subnet Issues" [RFC4903], 342 o "Problem Statement and Requirements for IPv6 over Low-Power 343 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606], and 345 o Neighbor Discovery Optimization for Low-Power and Lossy Networks 346 [RFC6775] and "Registration Extensions for 6LoWPAN Neighbor 347 Discovery" [RFC8505]. 349 3. Overview 351 This section and its subsections present a non-normative high level 352 view of the operation of the 6BBR. The following sections cover the 353 normative part. Figure 1 illustrates a backbone link that federates 354 a collection of LLNs as a single IPv6 Subnet, with a number of 6BBRs 355 providing proxy-ND services to their attached LLNs. 357 The LLN may be a hub-and-spoke access link such as (Low-Power) IEEE 358 STD. 802.11 (Wi-Fi) [IEEEstd80211] and IEEE STD. 802.15.1 (Bluetooth) 359 [IEEEstd802151], or a Mesh-Under or a Route-Over network [RFC8505]. 360 The proxy state can be distributed across multiple 6BBRs attached to 361 the same Backbone. 363 | 364 +-----+ +-----+ +-----+ IPv6 365 (default) | | (Optional) | | | | Node 366 Router | | 6LBR | | | | or 367 +-----+ +-----+ +-----+ 6LN 368 | Backbone side | | 369 ----+-------+-----------------+---+-------------+----+----- 370 | | | 371 +------+ +------+ +------+ 372 | 6BBR | | 6BBR | | 6BBR | 373 | | | | | | 374 +------+ +------+ +------+ 375 o Wireless side o o o o o o 376 o o o o o o o o o o o o o o o o o o o o 377 o o o o o o o o o o o o o o o o o o o 378 o o o o o o o o o LLN o o o o o o o o o 379 o o o o o o o o o o o o o o 380 o o o 382 Figure 1: Backbone Link and Backbone Routers 384 The main features of a 6BBR are as follows: 386 o Multi-Link-subnet functions (provided by the 6BBR on the backbone) 387 performed on behalf of registered 6LNs, and 389 o Routing registrar services that reduce multicast within the LLN: 391 * Binding Table management 393 * failover, e.g., due to mobility 395 Each Backbone Router (6BBR) maintains a data structure for its 396 Registered Addresses called a Binding Table. The combined Binding 397 Tables of all the 6BBRs on a backbone form a distributed database of 398 6LNs that reside in the LLNs or on the IPv6 Backbone. 400 Unless otherwise configured, a 6BBR does the following: 402 o Create a new entry in a Binding Table for a new Registered Address 403 and ensure that the Address is not duplicated over the Backbone 405 o Advertise a Registered Address over the Backbone using an 406 unsolicited NA message, asynchronously or as a response to a NS 407 message. This includes joining the multicast group associated to 408 the SNMA derived from the Registered Address as specified in 409 section 7.2.1. of [RFC4861] over the Backbone. 411 o The 6BBR may respond immediately as a Proxy in lieu of the 412 Registering Node, e.g., if the Registering Node has a sleeping 413 cycle that the 6BBR does not want to interrupt, and if the 6BR has 414 a recent state that is deemed fresh enough to permit the proxied 415 response. It is preferred, though, that the 6BBR checks whether 416 the Registering Node is still responsive on the Registered 417 Address. to that effect: 419 * as a Bridging Proxy, the 6BBR forwards the multicast DAD and 420 Address Lookup messages as a unicast MAC-Layer frames to the 421 MAC address of the Registering Node that matches the Target in 422 the ND message, and forwards as is the unicast Neighbor 423 Unreachability Detection (NUD) messages, so as to let the 424 Registering Node answer with the ND Message and options that it 425 sees fit; 427 * as a Routing Proxy, the 6BBR checks the liveliness of the 428 Registering Node, e.g., using a NUD verification, before 429 answering on its behalf. 431 o Deliver packets arriving from the LLN, using Neighbor Solicitation 432 messages to look up the destination over the Backbone. 434 o Forward or bridge packets between the LLN and the Backbone. 436 o Verify liveness for a registration, when needed. 438 The first of these functions enables the 6BBR to fulfill its role as 439 a Routing Registrar for each of its attached LLNs. The remaining 440 functions fulfill the role of the 6BBRs as the border routers 441 connecting the Multi-link IPv6 subnet to the Internet. 443 The operation of IPv6 ND and of proxy-ND are not mutually exclusive 444 on the Backbone, meaning that nodes attached to the Backbone and 445 using IPv6 ND can transparently interact with 6LNs that rely on a 446 6BBR to proxy ND for them, whether the 6LNs are reachable over an LLN 447 or directly attached to the Backbone. 449 The [RFC8505] registration mechanism used to learn addresses to be 450 proxied for may co-exist in a 6BBR with a proprietary snooping or the 451 traditional bridging functionality of an Access Point, in order to 452 support legacy LLN nodes that do not support this specification. 454 The registration to a proxy service uses an NS/NA(EARO) exchange. 455 The 6BBR operation resembles that of a Mobile IPv6 (MIPv6) [RFC6275] 456 Home Agent (HA). The combination of a 6BBR and a MIPv6 HA enables 457 full mobility support for 6LNs, inside and outside the links that 458 form the subnet. 460 The 6BBRs use the Extended Address Registration Option (EARO) defined 461 in [RFC8505] as follows: 463 o The EARO is used in the IPv6 ND exchanges over the Backbone 464 between the 6BBRs to help distinguish duplication from movement. 465 Extended Duplicate Address Messages (EDAR and EDAC) may also be 466 used between a 6LBR, if one is present, and the 6BBR. Address 467 duplication is detected using the ROVR field. Conflicting 468 registrations to different 6BBRs for the same Registered Address 469 are resolved using the TID field. 471 o The Link Layer Address (LLA) that the 6BBR advertises for the 472 Registered Address on behalf of the Registered Node over the 473 Backbone can belong to the Registering Node; in that case, the 474 6BBR (acting as a Bridging Proxy (see Section 8)) bridges the 475 unicast packets. Alternatively, the LLA can be that of the 6BBR 476 on the Backbone interface, in which case the 6BBR (acting as a 477 Routing Proxy(see Section 7)) receives the unicast packets at 478 Layer 3 and routes over. 480 3.1. Updating RFC 6775 and RFC 8505 482 This specification adds the EARO as a possible option in RS, NS(DAD) 483 and NA messages over the backbone. [RFC8505] requires that the 484 registration NS(EARO) contains an Source Link Layer Address Option 485 (SLLAO). This specification details the use of those messages over 486 the backbone. 488 Note: [RFC6775] requires that the registration NS(EARO) contains an 489 SLLAO and [RFC4862] that the NS(DAD) is sent from the unspecified 490 address for which there cannot be a SLLAO. Consequently, an NS(DAD) 491 cannot be confused with a registration. 493 This specification adds the capability to insert IPv6 ND options in 494 the EDAR and EDAC messages. In particular, a 6BBR acting as a 6LR 495 for the Registered Address can insert an SLLAO in the EDAR to the 496 6LBR in order to avoid a Lookup back. This enables the 6LBR to store 497 the MAC address associated to the Registered Address on a Link and to 498 serve as a mapping server as described in 499 [I-D.thubert-6lo-unicast-lookup]. 501 3.2. Access Link 503 The simplest Multi-Link Subnet topology from the Layer 3 perspective 504 occurs when the wireless network appears as a single hop hub-and- 505 spoke network as shown in Figure 2. The Layer 2 operation may 506 effectively be hub-and-spoke (e.g., Wi-Fi) or Mesh-Under, with a 507 Layer 2 protocol handling the complex topology. 509 | 510 +-----+ +-----+ +-----+ IPv6 511 (default) | | (Optional) | | | | Node 512 Router | | 6LBR | | | | or 513 +-----+ +-----+ +-----+ 6LN 514 | Backbone side | | 515 ----+-------+-----------------+---+-------------+----+----- 516 | | | 517 +------+ +------+ +------+ 518 | 6BBR | | 6BBR | | 6BBR | 519 | 6LR | | 6LR | | 6LR | 520 +------+ +------+ +------+ 521 (6LN) (6LN) (6LN) (6LN) (6LN) (6LN) (6LN) (6LN) 523 Figure 2: Access Link Use case 525 Figure 3 illustrates a flow where 6LN forms an IPv6 Address and 526 registers it to a 6BBR acting as a 6LR [RFC8505]. The 6BBR applies 527 ODAD (see Section 3.6) to the registered address to enable 528 connectivity while the message flow is still in progress. 530 In this example, a 6LBR is deployed on the backbone link to serve the 531 whole subnet, and EDAR / EDAC messages are used in combination with 532 DAD to enable coexistence with IPv6 ND over the backbone. 534 The RS sent initially by the 6LN(STA) is transmitted as a multicast 535 but since it is intercepted by the 6BBR, it is never effectively 536 broadcast. The multiple arrows associated to the ND messages on the 537 Backbone denote a real Layer 2 broadcast. 539 6LN(STA) 6BBR(AP) 6LBR default GW 540 | | | | 541 | LLN Access Link | IPv6 Backbone (e.g., Ethernet) | 542 | | | | 543 | RS(multicast) | | | 544 |---------------->| | | 545 | RA(PIO, Unicast)| | | 546 |<----------------| | | 547 | NS(EARO) | | | 548 |---------------->| | | 549 | | Extended DAR | | 550 | |--------------->| | 551 | | Extended DAC | | 552 | |<---------------| | 553 | | | 554 | | NS-DAD(EARO, multicast) | 555 | |--------> | 556 | |----------------------------------->| 557 | | | 558 | | RS(no SLLAO, for ODAD) | 559 | |----------------------------------->| 560 | | if (no fresher Binding) NS(Lookup) | 561 | | <----------------| 562 | |<-----------------------------------| 563 | | NA(SLLAO, not(O), EARO) | 564 | |----------------------------------->| 565 | | RA(unicast) | 566 | |<-----------------------------------| 567 | | | 568 | IPv6 Packets in optimistic mode | 569 |<---------------------------------------------------->| 570 | | | 571 | | 572 | NA(EARO) | 573 |<----------------| 574 | | 576 Figure 3: Initial Registration Flow to a 6BBR acting as Routing Proxy 578 3.3. Route-Over Mesh 580 A more complex Multi-Link Subnet topology occurs when the wireless 581 network appears as a Layer 3 Mesh network as shown in Figure 4. A 582 so-called Route-Over routing protocol exposes routes between 6LRs 583 towards both 6LRs and 6LNs, and a 6LBR acts as Root of the Layer 3 584 Mesh network and proxy-registers the LLN addresses to the 6BBR. 586 | 587 +-----+ +-----+ +-----+ IPv6 588 (default) | | (Optional) | | | | Node 589 Router | | 6LBR | | | | or 590 +-----+ +-----+ +-----+ 6LN 591 | Backbone side | | 592 ----+-------+-----------------+---+-------------+----+----- 593 | | | 594 +------+ +------+ +------+ 595 | 6BBR | | 6BBR | | 6BBR | 596 +------+ +------+ +------+ 597 | | | 598 +------+ +------+ +------+ 599 | 6LBR | | 6LBR | | 6LBR | 600 +------+ +------+ +------+ 601 (6LN) (6LR) (6LN) (6LR) (6LN) (6LR) (6LR) (6LR)(6LN) 602 (6LN)(6LR) (6LR) (6LN) (6LN) (6LR)(6LN) (6LR) (6LR) (6LR) (6LN) 603 (6LR)(6LR) (6LR) (6LR) (6LR)(6LN) (6LR) (6LR)(6LR) 604 (6LR) (6LR) (6LR) (6LR) (6LN)(6LR) (6LR) (6LR) (6LR) (6LR) 605 (6LN) (6LN)(6LN) (6LN) (6LN) (6LN) (6LN) (6LN) (6LN) (6LN) 607 Figure 4: Route-Over Mesh Use case 609 Figure 5 illustrates IPv6 signaling that enables a 6LN (the 610 Registered Node) to form a Global or a Unique-Local Address and 611 register it to the 6LBR that serves its LLN using [RFC8505]. The 612 6LBR (the Registering Node) then proxies the [RFC8505] registration 613 to the 6BBR to obtain proxy-ND services from the 6BBR. 615 As above, the RS sent initially by the 6LN(STA) is a transmitted as a 616 multicast but since it is intercepted by the 6BBR, it is never 617 effectively broadcast, and the multiple arrows associated to the ND 618 messages on the Backbone denote a real Layer 2 broadcast. 620 6LoWPAN Node 6LR 6LBR 6BBR 621 (mesh leaf) (mesh router) (mesh root) 622 | | | | 623 | 6LoWPAN ND |6LoWPAN ND | 6LoWPAN ND | IPv6 ND 624 | LLN link |Route-Over mesh|Ethernet/serial| Backbone 625 | | |/Internal call | 626 | IPv6 ND RS | | | 627 |-------------->| | | 628 |-----------> | | | 629 |------------------> | | 630 | IPv6 ND RA | | | 631 |<--------------| | | 632 | | | | 633 | NS(EARO) | | | 634 |-------------->| | | 635 | 6LoWPAN ND | Extended DAR | | 636 | |-------------->| | 637 | | | NS(EARO) | 638 | | |-------------->| 639 | | | (proxied) | NS-DAD 640 | | | |------> 641 | | | | (EARO) 642 | | | | 643 | | | NA(EARO) | 644 | | |<--------------| 645 | | Extended DAC | | 646 | |<--------------| | 647 | NA(EARO) | | | 648 |<--------------| | | 649 | | | | 651 Figure 5: Initial Registration Flow over Route-Over Mesh 653 As a non-normative example of a Route-Over Mesh, the 6TiSCH 654 architecture [I-D.ietf-6tisch-architecture] suggests using the RPL 655 [RFC6550] routing protocol and collocating the RPL root with a 6LBR 656 that serves the LLN. The 6LBR is also either collocated with or 657 directly connected to the 6BBR over an IPv6 Link. 659 3.4. The Binding Table 661 Addresses in an LLN that are reachable from the Backbone by way of 662 the 6BBR function must be registered to that 6BBR, using an NS(EARO) 663 with the R flag set [RFC8505]. A 6BBR maintains a state for its 664 active registrations in an abstract Binding Table. 666 An entry in the Binding Table is called a "Binding". A Binding may 667 be in Tentative, Reachable or Stale state. 669 The 6BBR uses a combination of [RFC8505] and IPv6 ND over the 670 Backbone to advertise the registration and avoid a duplication. 671 Conflicting registrations are solved by the 6BBRs, transparently to 672 the Registering Nodes. 674 Only one 6LN may register a given Address, but the Address may be 675 registered to Multiple 6BBRs for higher availability. 677 Over the LLN, Binding Table management is as follows: 679 o De-registrations (newer TID, same ROVR, null Lifetime) are 680 accepted with a status of 4 ("Removed"); the entry is deleted; 682 o Newer registrations (newer TID, same ROVR, non-null Lifetime) are 683 accepted with a status of 0 (Success); the Binding is updated with 684 the new TID, the Registration Lifetime and the Registering Node; 685 in Tentative state the EDAC response is held and may be 686 overwritten; in other states the Registration Lifetime timer is 687 restarted and the entry is placed in Reachable state. 689 o Identical registrations (same TID, same ROVR) from the same 690 Registering Node are accepted with a status of 0 (Success). In 691 Tentative state, the response is held and may be overwritten, but 692 the response is eventually produced, carrying the result of the 693 DAD process; 695 o Older registrations (older TID, same ROVR) from the same 696 Registering Node are discarded; 698 o Identical and older registrations (not-newer TID, same ROVR) from 700 o a different Registering Node are rejected with a status of 3 701 (Moved); this may be rate limited to avoid undue interference; 703 o Any registration for the same address but with a different ROVR is 704 rejected with a status of 1 (Duplicate). 706 The operation of the Binding Table is specified in detail in 707 Section 9. 709 3.5. Primary and Secondary 6BBRs 711 The same address may be successfully registered to more than one 712 6BBR, in which case the Registering Node uses the same EARO in all 713 the parallel registrations. To allow for this, ND(DAD) and NA 714 messages with an EARO that indicate an identical Binding in another 715 6BBR (same Registered address, same TID, same ROVR) are silently 716 ignored. 718 A 6BBR may optionally be primary or secondary. The primary is the 719 6BBR that has the highest EUI-64 Address of all the 6BBRs that share 720 a registration for the same Registered Address, with the same ROVR 721 and same Transaction ID, the EUI-64 Address being considered as an 722 unsigned 64bit integer. A given 6BBR can be primary for a given 723 Address and secondary for another Address, regardless of whether or 724 not the Addresses belong to the same 6LN. 726 In the following sections, is is expected that an NA is sent over the 727 backbone only if the node is primary or does not support the concept 728 of primary. More than one 6BBR claiming or defending an address 729 generates unwanted traffic but no reachability issue since all 6BBRs 730 provide reachability from the Backbone to the 6LN. 732 3.6. Using Optimistic DAD 734 Optimistic Duplicate Address Detection [RFC4429] (ODAD) specifies how 735 an IPv6 Address can be used before completion of Duplicate Address 736 Detection (DAD). ODAD guarantees that this behavior will not cause 737 harm if the new Address is a duplicate. 739 Support for ODAD avoids delays in installing the Neighbor Cache Entry 740 (NCE) in the 6BBRs and the default router, enabling immediate 741 connectivity to the registered node. As shown in Figure 3, if the 742 6BBR is aware of the Link-Layer Address (LLA) of a router, then the 743 6BBR sends a Router Solicitation (RS), using the Registered Address 744 as the IP Source Address, to the known router(s). The RS is sent 745 without a Source LLA Option (SLLAO), to avoid invalidating a 746 preexisting NCE in the router. 748 Following ODAD, the router may then send a unicast RA to the 749 Registered Address, and it may resolve that Address using an 750 NS(Lookup) message. In response, the 6BBR sends an NA with an EARO 751 and the Override (O) flag [RFC4861] that is not set. The router can 752 then determine the freshest EARO in case of conflicting NA(EARO) 753 messages, using the method described in section 5.2.1 of [RFC8505]. 754 If the NA(EARO) is the freshest answer, the default router creates a 755 Binding with the SLLAO of the 6BBR (in Routing Proxy mode) or that of 756 the Registering Node (in Bridging Proxy mode) so that traffic from/to 757 the Registered Address can flow immediately. 759 4. Multi-Link Subnet Considerations 761 The Backbone and the federated LLN Links are considered as different 762 links in the Multi-Link Subnet, even if multiple LLNs are attached to 763 the same 6BBR. ND messages are link-scoped and are not forwarded by 764 the 6BBR between the backbone and the LLNs though some packets may be 765 reinjected in Bridging Proxy mode (see Section 8). 767 Nodes located inside the subnet do not perform the IPv6 Path MTU 768 Discovery [RFC8201]. For that reason, the MTU MUST have the same 769 value on the Backbone and all attached LLNs. As a consequence, the 770 6BBR MUST use the same MTU value in RAs over the Backbone and in the 771 RAs that it transmits towards the LLN links. 773 5. Optional 6LBR serving the Multi-Link Subnet 775 A 6LBR can be deployed to serve the whole MLSN. It may be attached 776 to the backbone, in which case it can be discovered by its capability 777 advertisement (see section 4.3. of [RFC8505]) in RA messages. 779 This specification allows for an address to be registered to more 780 than one 6BBR. Consequently a 6LBR MUST be capable of maintaining 781 state for each of the 6BBR having registered with the same TID and 782 same ROVR. 784 When a 6LBR is present, the 6BBR uses an EDAR/EDAC message exchange 785 with the 6LBR to check if the new registration corresponds to a 786 duplication or a movement. This is done prior to the NS(DAD) 787 process, which may be avoided if the 6LBR already maintains a 788 conflicting state for the Registered Address. 790 If this registration is duplicate or not the freshest, then the 6LBR 791 replies with an EDAC message with a status code of 1 ("Duplicate 792 Address") or 3 ("Moved"), respectively. If this registration is the 793 freshest, then the 6LBR replies with a status code of 0. In that 794 case, if this registration is fresher than an existing registration 795 for another 6BBR, then the 6LBR also sends an asynchronous EDAC with 796 a status of 4 ("Removed") to that other 6BBR. 798 The EDAR message SHOULD carry the SLLAO used in NS messages by the 799 6BBR for that Binding, and the EDAC message SHOULD carry the Target 800 Link Layer Address Option (TLLAO) associated with the currently 801 accepted registration. This enables a 6BBR to locate the new 802 position of a mobile 6LN in the case of a Routing Proxy operation, 803 and opens the capability for the 6LBR to serve as a mapping server in 804 the future. 806 Note that if Link Local addresses are registered, then the scope of 807 uniqueness on which the address duplication is checked is the total 808 collection of links that the 6LBR serves as opposed to the sole link 809 on which the Link Local address is assigned. 811 6. Using IPv6 ND Over the Backbone Link 813 On the Backbone side, the 6BBR MUST join the SNMA group corresponding 814 to a Registered Address as soon as it creates a Binding for that 815 Address, and maintain that SNMA membership as long as it maintains 816 the registration. 818 The 6BBR uses either the SNMA or plain unicast to defend the 819 Registered Addresses in its Binding Table over the Backbone (as 820 specified in [RFC4862]). 822 The 6BBR advertises and defends the Registered Addresses over the 823 Backbone Link using RS, NS(DAD) and NA messages with the Registered 824 Address as the Source or Target address, respectively. 826 The 6BBR MUST place an EARO in the IPv6 ND messages that it generates 827 on behalf of the Registered Node. Note that an NS(DAD) does not 828 contain an SLLAO and cannot be confused with a proxy registration 829 such as performed by a 6LBR. 831 An NA message generated in response to an NS(DAD) MUST have the 832 Override flag set and a status of 1 (Duplicate) or 3 (Moved) in the 833 EARO. An NA message generated in response to an NS(Lookup) or an 834 NS(NUD) MUST NOT have the Override flag set. 836 This specification enables proxy operation for the IPv6 ND resolution 837 of LLN devices and a prefix that is used across a Multi-Link Subnet 838 MAY be advertised as on-link over the Backbone. This is done for 839 backward compatibility with existing IPv6 hosts by setting the L flag 840 in the Prefix Information Option (PIO) of RA messages [RFC4861]. 842 For movement involving a slow reattachment, the NUD procedure defined 843 in [RFC4861] may time out too quickly. Nodes on the backbone SHOULD 844 support [RFC7048] whenever possible. 846 7. Routing Proxy Operations 848 A Routing Proxy provides IPv6 ND proxy functions for Global and 849 Unique Local addresses between the LLN and the backbone, but not for 850 Link-Local addresses. It operates as an IPv6 border router and 851 provides a full Link-Layer isolation. 853 In this mode, it is not required that the MAC addresses of the 6LNs 854 are visible at Layer 2 over the Backbone. It is thus useful when the 855 messaging over the Backbone that is associated to wireless mobility 856 becomes expensive, e.g., when the Layer 2 topology is virtualized 857 over a wide area IP underlay. 859 This mode is definitely required when the LLN uses a MAC address 860 format that is different from that on the Backbone (e.g., EUI-64 vs. 861 EUI-48). Since a 6LN may not be able to resolve an arbitrary 862 destination in the MLSN directly, the MLSN prefix MUST NOT be 863 advertised as on-link in RA messages sent towards the LLN. 865 In order to maintain IP connectivity, the 6BBR installs a connected 866 Host route to the Registered Address on the LLN interface, via the 867 Registering Node as identified by the Source Address and the SLLA 868 option in the NS(EARO) messages. 870 When operating as a Routing Proxy, the 6BBR MUST use its Layer 2 871 Address on its Backbone Interface in the SLLAO of the RS messages and 872 the TLLAO of the NA messages that it generates to advertise the 873 Registered Addresses. 875 For each Registered Address, multiple peers on the Backbone may have 876 resolved the Address with the 6BBR MAC Address, maintaining that 877 mapping in their Neighbor Cache. The 6BBR SHOULD maintain a list of 878 the peers on the Backbone which have associated its MAC Address with 879 the Registered Address. If that Registered Address moves to a new 880 6BBR, the previous 6BBR SHOULD unicast a gratuitous NA with the 881 Override flag set to each such peer, to supply the LLA of the new 882 6BBR in the TLLA option for the Address. A 6BBR that does not 883 maintain this list MAY multicast a gratuitous NA with the Override 884 flag; this NA will possibly hit all the nodes on the Backbone, 885 whether or not they maintain an NCE for the Registered Address. 887 If a correspondent fails to receive the gratuitous NA, it will keep 888 sending traffic to a 6BBR to which the node was previously 889 registered. Since the previous 6BBR removed its Host route to the 890 Registered Address, it will look up the address over the backbone, 891 resolve the address with the LLA of the new 6BBR, and forward the 892 packet to the correct 6BBR. The previous 6BBR SHOULD also issue a 893 redirect message [RFC4861] to update the cache of the correspondent. 895 8. Bridging Proxy Operations 897 A Bridging Proxy provides IPv6 ND proxy functions between the LLN and 898 the backbone while preserving the forwarding continuity at the MAC 899 Layer. It acts as a Layer 2 Bridge for all types of unicast packets 900 including link-scoped, and appears as an IPv6 Host on the Backbone. 902 The Bridging Proxy registers any Binding including for a Link-Local 903 address to the 6LBR (if present) and defends it over the backbone in 904 IPv6 ND procedures. 906 To achieve this, the Bridging Proxy intercepts the IPv6 ND messages 907 and may reinject them on the other side, respond directly or drop 908 them. For instance, an ND(Lookup) from the backbone that matches a 909 Binding can be responded directly, or turned into a unicast on the 910 LLN side to let the 6LN respond. 912 As a Bridging Proxy, the 6BBR MUST use the Registering Node's Layer 2 913 Address in the SLLAO of the NS/RS messages and the TLLAO of the NA 914 messages that it generates to advertise the Registered Addresses. 915 The Registering Node's Layer 2 address is found in the SLLA of the 916 registration NS(EARO), and maintained in the Binding Table. 918 The Multi-Link Subnet prefix SHOULD NOT be advertised as on-link in 919 RA messages sent towards the LLN. If a destination address is seen 920 as on-link, then a 6LN may use NS(Lookup) messages to resolve that 921 address. In that case, the 6BBR MUST either answer the NS(Lookup) 922 message directly or reinject the message on the backbone, either as a 923 Layer 2 unicast or a multicast. 925 If the Registering Node owns the Registered Address, then its 926 mobility does not impact existing NCEs over the Backbone. Otherwise, 927 when the 6LN selects another Registering Node, the new Registering 928 Node SHOULD send a multicast NA with the Override flag set to fix the 929 existing NCEs across the Backbone. 931 This method can fail if the multicast message is not received; one or 932 more correspondent nodes on the Backbone might maintain an stale NCE, 933 and packets to the Registered Address may be lost. When this 934 condition happens, it is eventually discovered and resolved using NUD 935 as defined in [RFC4861]. 937 9. Creating and Maintaining a Binding 939 Upon receiving a registration for a new Address (i.e., an NS(EARO) 940 with the R flag set), the 6BBR creates a Binding and operates as a 941 6LR according to [RFC8505], interacting with the 6LBR if one is 942 present. 944 An implementation of a Routing Proxy that creates a Binding MUST also 945 create an associated Host route pointing to the registering node in 946 the LLN interface from which the registration was received. 948 The 6LR operation is modified as follows: 950 o EDAR and EDAC messages SHOULD carry a SLLAO and a TLLAO, 951 respectively. 953 o A Bridging Proxy MAY register Link Local addresses at the 6BBR and 954 proxy ND for these addresses over the backbone. 956 o An EDAC message with a status of 9 (6LBR Registry Saturated) is 957 assimilated as a status of 0 if a following DAD process protects 958 the address against duplication. 960 This specification enables nodes on a Backbone Link to co-exist along 961 with nodes implementing IPv6 ND [RFC4861] as well as other non- 962 normative specifications such as [I-D.bi-savi-wlan]. It is possible 963 that not all IPv6 addresses on the Backbone are registered and known 964 to the 6LBR, and an EDAR/EDAC echange with the 6LBR might succeed 965 even for a duplicate address. Consequently, and unless 966 administratively overridden, the 6BBR still needs to perform IPv6 ND 967 DAD over the backbone after an EDAC with a status code of 0 or 9. 969 For the DAD operation, the Binding is placed in Tentative state for a 970 duration of TENTATIVE_DURATION (Section 12), and an NS(DAD) message 971 is sent as a multicast message over the Backbone to the SNMA 972 associated with the registered Address [RFC4862]. The EARO from the 973 registration MUST be placed unchanged in the NS(DAD) message. 975 If a registration is received for an existing Binding with a non-null 976 Registration Lifetime and the registration is fresher (same ROVR, 977 fresher TID), then the Binding is updated, with the new Registration 978 Lifetime, TID, and possibly Registering Node. In Tentative state 979 (see Section 9.1), the current DAD operation continues unaltered. In 980 other states (see Section 9.2 and Section 9.3 ), the Binding is 981 placed in Reachable state for the Registration Lifetime, and the 6BBR 982 returns an NA(EARO) to the Registering Node with a status of 0 983 (Success). 985 Upon a registration that is identical (same ROVR, TID, and 986 Registering Node), the 6BBR returns an NA(EARO) back to the 987 Registering Node with a status of 0 (Success). A registration that 988 is not as fresh (same ROVR, older TID) is ignored. 990 If a registration is received for an existing Binding and a 991 registration Lifetime of zero, then the Binding is removed, and the 992 6BBR returns an NA(EARO) back to the Registering Node with a status 993 of 0 (Success). An implementation of a Routing Proxy that removes a 994 binding MUST remove the associated Host route pointing on the 995 registering node. It MAY preserve a temporary state in order to 996 forward packets in flight. The state may be a NCE formed based on a 997 received NA message, or a Binding in Stale state and pointing at the 998 new 6BBR on the backbone. 1000 The implementation should also use REDIRECT messages as specified in 1001 [RFC4861] to update the correspondents for the Registered Address, 1002 pointing the new 6BBR. 1004 9.1. Operations on a Binding in Tentative State 1006 The Tentative state covers a DAD period over the backbone during 1007 which an address being registered is checked for duplication using 1008 procedures defined in [RFC4862]. 1010 For a Binding in Tentative state: 1012 o The Binding MUST be removed if an NA message is received over the 1013 Backbone for the Registered Address with no EARO, or containing an 1014 EARO with a status of 1 (Duplicate) that indicates an existing 1015 registration owned by a different Registering Node. In that case, 1016 an NA MUST be sent back to the Registering Node with a status of 1 1017 (Duplicate) in the EARO. This behavior might be overriden by 1018 policy, in particular if the registration is trusted, e.g., based 1019 on the validation of the ROVR field (see [I-D.ietf-6lo-ap-nd]). 1021 o An NS(DAD) with no EARO or with an EARO that indicates a duplicate 1022 registration (i.e., different ROVR) MUST be answered with an NA 1023 message containing an EARO with a status of 1 (Duplicate) and the 1024 Override flag not set. This behavior might be overriden by 1025 policy, in particular if the registration is not trusted. 1027 o The Binding MUST be removed if an NA message is received over the 1028 Backbone for the Registered Address containing an EARO with a 1029 status of 3 (Moved), or an NS(DAD) with an EARO that indicates a 1030 fresher registration ([RFC8505]) for the same Registered Node 1031 (i.e., same ROVR). A status of 3 is returned in the NA(EARO) back 1032 to the Registering Node. 1034 o NS(DAD) and NA messages containing an EARO that indicates a 1035 registration for the same Registered Node that is not as fresh as 1036 this SHOULD be answered with an NA message containing an EARO with 1037 a status of 3 (Moved) in order to clean up the situation 1038 immediately. 1040 o Other NS(DAD) and NA messages from the Backbone are ignored. 1042 o NS(Lookup) and NS(NUD) messages SHOULD be optimistically answered 1043 with an NA message containing an EARO with a status of 0 and the 1044 Override flag not set (see Section 3.6). 1046 o If optimistic DAD is disabled, then they SHOULD be queued to be 1047 answered when the Binding goes to Reachable state. 1049 When the TENTATIVE_DURATION (Section 12) timer elapses, the Binding 1050 is placed in Reachable state for the Registration Lifetime, and the 1051 6BBR returns an NA(EARO) to the Registering Node with a status of 0 1052 (Success). 1054 The 6BBR also attempts to take over any existing Binding from other 1055 6BBRs and to update existing NCEs in backbone nodes. This is done by 1056 sending an NA message with an EARO and the Override flag set over the 1057 backbone (see Section 7 and Section 8). 1059 9.2. Operations on a Binding in Reachable State 1061 The Reachable state covers an active registration after a successful 1062 DAD process. 1064 If the Registration Lifetime is of a long duration, an implementation 1065 might be configured to reassess the availability of the Registering 1066 Node at a lower period, using a NUD procedure as specified in 1067 [RFC7048]. If the NUD procedure fails, the Binding SHOULD be placed 1068 in Stale state immediately. 1070 For a Binding in Reachable state: 1072 o The Binding MUST be removed if an NA or an NS(DAD) message is 1073 received over the Backbone for the Registered Address containing 1074 an EARO that indicates a fresher registration ([RFC8505]) for the 1075 same Registered Node (i.e., same ROVR). A status of 4 (Removed) 1076 is returned in an asynchronous NA(EARO) to the Registering Node. 1077 Based on configuration, an implementation may delay this operation 1078 by a timer with a short setting, e.g., a few seconds to a minute, 1079 in order to a allow for a parallel registration to reach this 1080 node, in which case the NA might be ignored. 1082 o An NS(DAD) with no EARO or with an EARO that indicates a duplicate 1083 registration (i.e., different ROVR) MUST be answered with an NA 1084 message containing an EARO with a status of 1 (Duplicate) and the 1085 Override flag not set. 1087 o NS(DAD) and NA messages containing an EARO that indicates a 1088 registration for the same Registered Node that is not as fresh as 1089 this binding MUST be answered with an NA message containing an 1090 EARO with a status of 3 (Moved). 1092 o Other NS(DAD) and NA messages from the Backbone are ignored. 1094 o NS(Lookup) and NS(NUD) messages SHOULD be answered with an NA 1095 message containing an EARO with a status of 0 and the Override 1096 flag not set. The 6BBR MAY check whether the Registering Node is 1097 still available using a NUD procedure over the LLN prior to 1098 answering; this behaviour depends on the use case and is subject 1099 to configuration. 1101 When the Registration Lifetime timer elapses, the Binding is placed 1102 in Stale state for a duration of STALE_DURATION (Section 12). 1104 9.3. Operations on a Binding in Stale State 1106 The Stale state enables tracking of the Backbone peers that have a 1107 NCE pointing to this 6BBR in case the Registered Address shows up 1108 later. 1110 If the Registered Address is claimed by another 6LN on the Backbone, 1111 with an NS(DAD) or an NA, the 6BBR does not defend the Address. 1113 For a Binding in Stale state: 1115 o The Binding MUST be removed if an NA or an NS(DAD) message is 1116 received over the Backbone for the Registered Address containing 1117 no EARO or an EARO that indicates either a fresher registration 1118 for the same Registered Node or a duplicate registration. A 1119 status of 4 (Removed) MAY be returned in an asynchronous NA(EARO) 1120 to the Registering Node. 1122 o NS(DAD) and NA messages containing an EARO that indicates a 1123 registration for the same Registered Node that is not as fresh as 1124 this MUST be answered with an NA message containing an EARO with a 1125 status of 3 (Moved). 1127 o If the 6BBR receives an NS(Lookup) or an NS(NUD) message for the 1128 Registered Address, the 6BBR MUST attempt a NUD procedure as 1129 specified in [RFC7048] to the Registering Node, targeting 1131 o the Registered Address, prior to answering. If the NUD procedure 1132 succeeds, the operation in Reachable state applies. If the NUD 1133 fails, the 6BBR refrains from answering. 1135 o Other NS(DAD) and NA messages from the Backbone are ignored. 1137 When the STALE_DURATION (Section 12) timer elapses, the Binding MUST 1138 be removed. 1140 10. Registering Node Considerations 1142 A Registering Node MUST implement [RFC8505] in order to interact with 1143 a 6BBR (which acts as a routing registrar). Following [RFC8505], the 1144 Registering Node signals that it requires IPv6 proxy-ND services from 1145 a 6BBR by registering the corresponding IPv6 Address using an 1146 NS(EARO) message with the R flag set. 1148 The Registering Node may be the 6LN owning the IPv6 Address, or a 1149 6LBR that performs the registration on its behalf in a Route-Over 1150 mesh. 1152 The Registering Node SHOULD register all of its IPv6 Addresses to its 1153 6LR, which is the 6BBR when they are connected at Layer 2. Failure 1154 to register an address may result in the address being unreachable by 1155 other parties if the 6BBR cancels the NS(Lookup) over the LLN or to 1156 selected LLN nodes that are known to register their addresses. 1158 The Registering Node MUST refrain from using multicast NS(Lookup) 1159 when the destination is not known as on-link, e.g., if the prefix is 1160 advertised in a PIO with the L flag that is not set. In that case, 1161 the Registering Node sends its packets directly to its 6LR. 1163 The Registering Node SHOULD also follow [RFC7772] in order to limit 1164 the use of multicast RAs. It SHOULD also implement Simple Procedures 1165 for Detecting Network Attachment in IPv6 [RFC6059] (DNA procedures) 1166 to detect movements, and support Packet-Loss Resiliency for Router 1167 Solicitations [RFC7559] in order to improve reliability for the 1168 unicast RS messages. 1170 11. Security Considerations 1172 This specification applies to LLNs and a backbone in which the 1173 individual links are protected against rogue access, e.g., by 1174 authenticating a node that attaches to the network and encrypting at 1175 the MAC layer the transmissions that may be overheard. 1177 In particular, the LLN MAC is required to provide secure unicast to/ 1178 from the Backbone Router and secure Broadcast from the Backbone 1179 Router in a way that prevents tampering with or replaying the RA 1180 messages. 1182 [I-D.ietf-6lo-ap-nd] guarantees the ownership of a registered address 1183 based on a proof-of-ownership encoded in the ROVR field and protects 1184 against address theft and impersonation inside the LLN, because the 1185 6LR can challenge the Registered Node for a proof-of-ownership. This 1186 method does not extend over the backbone since the 6BBR cannot 1187 provide the proof-of-ownership. A possible attack over the backbone 1188 can be done by sending an NS with an EARO and expecting the NA(EARO) 1189 back to contain the TID and ROVR fields of the existing state. With 1190 that information, the attacker can easily increase the TID and take 1191 over the Binding. 1193 12. Protocol Constants 1195 This Specification uses the following constants: 1197 TENTATIVE_DURATION: 800 milliseconds 1199 STALE_DURATION: see below 1201 In LLNs with long-lived Addresses such as LPWANs, STALE_DURATION 1202 SHOULD be configured with a relatively long value to cover an 1203 interval when the address may be reused, and before it is safe to 1204 expect that the address was definitively released. A good default 1205 value can be 24 hours. In LLNs where addresses are renewed rapidly, 1206 e.g., for privacy reasons, STALE_DURATION SHOULD be configured with a 1207 relatively shorter value, by default 5 minutes. 1209 13. IANA Considerations 1211 This document has no request to IANA. 1213 14. Acknowledgments 1215 Many thanks to Dorothy Stanley, Thomas Watteyne and Jerome Henry for 1216 their various contributions. Also many thanks to Timothy Winters and 1217 Erik Nordmark for their help, review and support in preparation to 1218 the IESG cycle, and to Kyle Rose, Elwyn Davies and Dominique Barthel 1219 for their useful contributions during the IESG review process. 1221 15. References 1223 15.1. Normative References 1225 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1226 Requirement Levels", BCP 14, RFC 2119, 1227 DOI 10.17487/RFC2119, March 1997, 1228 . 1230 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1231 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1232 2006, . 1234 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 1235 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 1236 . 1238 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1239 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1240 DOI 10.17487/RFC4861, September 2007, 1241 . 1243 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1244 Address Autoconfiguration", RFC 4862, 1245 DOI 10.17487/RFC4862, September 2007, 1246 . 1248 [RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for 1249 Detecting Network Attachment in IPv6", RFC 6059, 1250 DOI 10.17487/RFC6059, November 2010, 1251 . 1253 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1254 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1255 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1256 Low-Power and Lossy Networks", RFC 6550, 1257 DOI 10.17487/RFC6550, March 2012, 1258 . 1260 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1261 Bormann, "Neighbor Discovery Optimization for IPv6 over 1262 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1263 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1264 . 1266 [RFC7048] Nordmark, E. and I. Gashinsky, "Neighbor Unreachability 1267 Detection Is Too Impatient", RFC 7048, 1268 DOI 10.17487/RFC7048, January 2014, 1269 . 1271 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1272 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1273 May 2017, . 1275 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1276 (IPv6) Specification", STD 86, RFC 8200, 1277 DOI 10.17487/RFC8200, July 2017, 1278 . 1280 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 1281 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 1282 DOI 10.17487/RFC8201, July 2017, 1283 . 1285 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1286 Perkins, "Registration Extensions for IPv6 over Low-Power 1287 Wireless Personal Area Network (6LoWPAN) Neighbor 1288 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1289 . 1291 15.2. Informative References 1293 [I-D.bi-savi-wlan] 1294 Bi, J., Wu, J., Wang, Y., and T. Lin, "A SAVI Solution for 1295 WLAN", draft-bi-savi-wlan-18 (work in progress), November 1296 2019. 1298 [I-D.ietf-6lo-ap-nd] 1299 Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 1300 "Address Protected Neighbor Discovery for Low-power and 1301 Lossy Networks", draft-ietf-6lo-ap-nd-13 (work in 1302 progress), January 2020. 1304 [I-D.ietf-6man-rs-refresh] 1305 Nordmark, E., Yourtchenko, A., and S. Krishnan, "IPv6 1306 Neighbor Discovery Optional RS/RA Refresh", draft-ietf- 1307 6man-rs-refresh-02 (work in progress), October 2016. 1309 [I-D.ietf-6tisch-architecture] 1310 Thubert, P., "An Architecture for IPv6 over the TSCH mode 1311 of IEEE 802.15.4", draft-ietf-6tisch-architecture-28 (work 1312 in progress), October 2019. 1314 [I-D.ietf-mboned-ieee802-mcast-problems] 1315 Perkins, C., McBride, M., Stanley, D., Kumari, W., and J. 1316 Zuniga, "Multicast Considerations over IEEE 802 Wireless 1317 Media", draft-ietf-mboned-ieee802-mcast-problems-11 (work 1318 in progress), December 2019. 1320 [I-D.nordmark-6man-dad-approaches] 1321 Nordmark, E., "Possible approaches to make DAD more robust 1322 and/or efficient", draft-nordmark-6man-dad-approaches-02 1323 (work in progress), October 2015. 1325 [I-D.thubert-6lo-unicast-lookup] 1326 Thubert, P. and E. Levy-Abegnoli, "IPv6 Neighbor Discovery 1327 Unicast Lookup", draft-thubert-6lo-unicast-lookup-00 (work 1328 in progress), January 2019. 1330 [I-D.yourtchenko-6man-dad-issues] 1331 Yourtchenko, A. and E. Nordmark, "A survey of issues 1332 related to IPv6 Duplicate Address Detection", draft- 1333 yourtchenko-6man-dad-issues-01 (work in progress), March 1334 2015. 1336 [IEEEstd8021] 1337 IEEE standard for Information Technology, "IEEE Standard 1338 for Information technology -- Telecommunications and 1339 information exchange between systems Local and 1340 metropolitan area networks Part 1: Bridging and 1341 Architecture". 1343 [IEEEstd80211] 1344 IEEE standard for Information Technology, "IEEE Standard 1345 for Information technology -- Telecommunications and 1346 information exchange between systems Local and 1347 metropolitan area networks-- Specific requirements Part 1348 11: Wireless LAN Medium Access Control (MAC) and Physical 1349 Layer (PHY) Specifications". 1351 [IEEEstd802151] 1352 IEEE standard for Information Technology, "IEEE Standard 1353 for Information Technology - Telecommunications and 1354 Information Exchange Between Systems - Local and 1355 Metropolitan Area Networks - Specific Requirements. - Part 1356 15.1: Wireless Medium Access Control (MAC) and Physical 1357 Layer (PHY) Specifications for Wireless Personal Area 1358 Networks (WPANs)". 1360 [IEEEstd802154] 1361 IEEE standard for Information Technology, "IEEE Standard 1362 for Local and metropolitan area networks -- Part 15.4: 1363 Low-Rate Wireless Personal Area Networks (LR-WPANs)". 1365 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 1366 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 1367 2006, . 1369 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 1370 DOI 10.17487/RFC4903, June 2007, 1371 . 1373 [RFC5415] Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley, 1374 Ed., "Control And Provisioning of Wireless Access Points 1375 (CAPWAP) Protocol Specification", RFC 5415, 1376 DOI 10.17487/RFC5415, March 2009, 1377 . 1379 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 1380 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 1381 2011, . 1383 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1384 Statement and Requirements for IPv6 over Low-Power 1385 Wireless Personal Area Network (6LoWPAN) Routing", 1386 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1387 . 1389 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 1390 Locator/ID Separation Protocol (LISP)", RFC 6830, 1391 DOI 10.17487/RFC6830, January 2013, 1392 . 1394 [RFC7559] Krishnan, S., Anipko, D., and D. Thaler, "Packet-Loss 1395 Resiliency for Router Solicitations", RFC 7559, 1396 DOI 10.17487/RFC7559, May 2015, 1397 . 1399 [RFC7772] Yourtchenko, A. and L. Colitti, "Reducing Energy 1400 Consumption of Router Advertisements", BCP 202, RFC 7772, 1401 DOI 10.17487/RFC7772, February 2016, 1402 . 1404 [RFC8273] Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix 1405 per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017, 1406 . 1408 Appendix A. Possible Future Extensions 1410 With the current specification, the 6LBR is not leveraged to avoid 1411 multicast NS(Lookup) on the Backbone. This could be done by adding a 1412 lookup procedure in the EDAR/EDAC exchange. 1414 By default the specification does not have a trust model, e.g., 1415 whereby nodes that associate their address with a proof-of-ownership 1416 [I-D.ietf-6lo-ap-nd] should be more trusted than nodes that do not. 1417 Such a trust model and related signaling could be added in the future 1418 to override the default operation and favor trusted nodes. 1420 Future documents may extend this specification by allowing the 6BBR 1421 to redistribute Host routes in routing protocols that would operate 1422 over the Backbone, or in MIPv6, or FMIP, or the Locator/ID Separation 1423 Protocol (LISP) [RFC6830] to support mobility on behalf of the 6LNs, 1424 etc... LISP may also be used to provide an equivalent to the EDAR/ 1425 EDAC exchange using a Map Server / Map Resolver as a replacement to 1426 the 6LBR. 1428 Appendix B. Applicability and Requirements Served 1430 This document specifies proxy-ND functions that can be used to 1431 federate an IPv6 Backbone Link and multiple IPv6 LLNs into a single 1432 Multi-Link Subnet. The proxy-ND functions enable IPv6 ND services 1433 for Duplicate Address Detection (DAD) and Address Lookup that do not 1434 require broadcasts over the LLNs. 1436 The term LLN is used to cover multiple types of WLANs and WPANs, 1437 including (Low-Power) Wi-Fi, BLUETOOTH(R) Low Energy, IEEE STD 1438 802.11ah and IEEE STD.802.15.4 wireless meshes, covering the types of 1439 networks listed in Appendix B.3 of [RFC8505] "Requirements Related to 1440 Various Low-Power Link Types". 1442 Each LLN in the subnet is attached to an IPv6 Backbone Router (6BBR). 1443 The Backbone Routers interconnect the LLNs and advertise the 1444 Addresses of the 6LNs over the Backbone Link using proxy-ND 1445 operations. 1447 This specification updates IPv6 ND over the Backbone to distinguish 1448 Address movement from duplication and eliminate stale state in the 1449 Backbone routers and Backbone nodes once a 6LN has roamed. This way, 1450 mobile nodes may roam rapidly from one 6BBR to the next and 1451 requirements in Appendix B.1 of [RFC8505] "Requirements Related to 1452 Mobility" are met. 1454 A 6LN can register its IPv6 Addresses and thereby obtain proxy-ND 1455 services over the Backbone, meeting the requirements expressed in 1456 Appendix B.4 of [RFC8505], "Requirements Related to Proxy 1457 Operations". 1459 The impact if the IPv6 ND operation is limited to one of the 1460 federated LLNs, enabling the number of 6LNs to grow. The Routing 1461 Proxy operation avoids the need to expose the MAC addresses of the 1462 6LNs onto the backbone, keeping the Layer 2 topology simple and 1463 stable. This meets the requirements in Appendix B.6 of [RFC8505] 1464 "Requirements Related to Scalability", as long has the 6BBRs are 1465 dimensioned for the number of registrations that each needs to 1466 support. 1468 In the case of a Wi-Fi access link, a 6BBR may be collocated with the 1469 Access Point (AP), or with a Fabric Edge (FE) or a CAPWAP [RFC5415] 1470 Wireless LAN Controller (WLC). In those cases, the wireless client 1471 (STA) is the 6LN that makes use of [RFC8505] to register its IPv6 1472 Address(es) to the 6BBR acting as Routing Registrar. The 6LBR can be 1473 centralized and either connected to the Backbone Link or reachable 1474 over IP. 1476 The 6BBR proxy-ND operations eliminate the need for wireless nodes to 1477 respond synchronously when a Lookup is performed for their IPv6 1478 Addresses. This provides the function of a Sleep Proxy for ND 1479 [I-D.nordmark-6man-dad-approaches]. 1481 For the TimeSlotted Channel Hopping (TSCH) mode of [IEEEstd802154], 1482 the 6TiSCH architecture [I-D.ietf-6tisch-architecture] describes how 1483 a 6LoWPAN ND host could connect to the Internet via a RPL mesh 1484 Network, but doing so requires extensions to the 6LOWPAN ND protocol 1485 to support mobility and reachability in a secure and manageable 1486 environment. The extensions detailed in this document also work for 1487 the 6TiSCH architecture, serving the requirements listed in 1488 Appendix B.2 of [RFC8505] "Requirements Related to Routing 1489 Protocols". 1491 The registration mechanism may be seen as a more reliable alternate 1492 to snooping [I-D.bi-savi-wlan]. It can be noted that registration 1493 and snooping are not mutually exclusive. Snooping may be used in 1494 conjunction with the registration for nodes that do not register 1495 their IPv6 Addresses. The 6BBR assumes that if a node registers at 1496 least one IPv6 Address to it, then the node registers all of its 1497 Addresses to the 6BBR. With this assumption, the 6BBR can possibly 1498 cancel all undesirable multicast NS messages that would otherwise 1499 have been delivered to that node. 1501 Scalability of the Multi-Link Subnet [RFC4903] requires avoidance of 1502 multicast/broadcast operations as much as possible even on the 1503 Backbone [I-D.ietf-mboned-ieee802-mcast-problems]. Although hosts 1504 can connect to the Backbone using IPv6 ND operations, multicast RAs 1505 can be saved by using [I-D.ietf-6man-rs-refresh], which also requires 1506 the support of [RFC7559]. 1508 Authors' Addresses 1510 Pascal Thubert (editor) 1511 Cisco Systems, Inc 1512 Building D 1513 45 Allee des Ormes - BP1200 1514 MOUGINS - Sophia Antipolis 06254 1515 FRANCE 1517 Phone: +33 497 23 26 34 1518 Email: pthubert@cisco.com 1519 Charles E. Perkins 1520 Futurewei 1521 2330 Central Expressway 1522 Santa Clara 95050 1523 United States of America 1525 Email: charliep@computer.org 1527 Eric Levy-Abegnoli 1528 Cisco Systems, Inc 1529 Building D 1530 45 Allee des Ormes - BP1200 1531 MOUGINS - Sophia Antipolis 06254 1532 FRANCE 1534 Phone: +33 497 23 26 20 1535 Email: elevyabe@cisco.com