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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 6lo P.T. Thubert, Ed. 3 Internet-Draft Cisco Systems 4 Updates: 6775, 8505 (if approved) C.E. Perkins 5 Intended status: Standards Track Blue Meadow Networking 6 Expires: 11 August 2020 E.L.A. Levy-Abegnoli 7 Cisco Systems 8 8 February 2020 10 IPv6 Backbone Router 11 draft-ietf-6lo-backbone-router-16 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 11 August 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 (https://trustee.ietf.org/ 45 license-info) in effect on the date of publication of this document. 46 Please review these documents carefully, as they describe your rights 47 and restrictions with respect to this document. Code Components 48 extracted from this document must include Simplified BSD License text 49 as described in Section 4.e of the Trust Legal Provisions and are 50 provided without warranty as described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 56 2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 5 57 2.2. New Terms . . . . . . . . . . . . . . . . . . . . . . . . 5 58 2.3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 6 59 2.4. References . . . . . . . . . . . . . . . . . . . . . . . 7 60 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7 61 3.1. Updating RFC 6775 and RFC 8505 . . . . . . . . . . . . . 10 62 3.2. Access Link . . . . . . . . . . . . . . . . . . . . . . . 10 63 3.3. Route-Over Mesh . . . . . . . . . . . . . . . . . . . . . 12 64 3.4. The Binding Table . . . . . . . . . . . . . . . . . . . . 14 65 3.5. Primary and Secondary 6BBRs . . . . . . . . . . . . . . . 15 66 3.6. Using Optimistic DAD . . . . . . . . . . . . . . . . . . 16 67 4. Multi-Link Subnet Considerations . . . . . . . . . . . . . . 16 68 5. Optional 6LBR serving the Multi-Link Subnet . . . . . . . . . 17 69 6. Using IPv6 ND Over the Backbone Link . . . . . . . . . . . . 18 70 7. Routing Proxy Operations . . . . . . . . . . . . . . . . . . 18 71 8. Bridging Proxy Operations . . . . . . . . . . . . . . . . . . 19 72 9. Creating and Maintaining a Binding . . . . . . . . . . . . . 20 73 9.1. Operations on a Binding in Tentative State . . . . . . . 22 74 9.2. Operations on a Binding in Reachable State . . . . . . . 23 75 9.3. Operations on a Binding in Stale State . . . . . . . . . 24 76 10. Registering Node Considerations . . . . . . . . . . . . . . . 25 77 11. Security Considerations . . . . . . . . . . . . . . . . . . . 25 78 12. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 26 79 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 80 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26 81 15. Normative References . . . . . . . . . . . . . . . . . . . . 26 82 16. Informative References . . . . . . . . . . . . . . . . . . . 28 83 Appendix A. Possible Future Extensions . . . . . . . . . . . . . 30 84 Appendix B. Applicability and Requirements Served . . . . . . . 31 85 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 87 1. Introduction 89 IEEE STD. 802.1 [IEEEstd8021] Ethernet Bridging provides an efficient 90 and reliable broadcast service for wired networks; applications and 91 protocols have been built that heavily depend on that feature for 92 their core operation. Unfortunately, Low-Power Lossy Networks (LLNs) 93 and local wireless networks generally do not provide the broadcast 94 capabilities of Ethernet Bridging in an economical fashion. 96 As a result, protocols designed for bridged networks that rely on 97 multicast and broadcast often exhibit disappointing behaviours when 98 employed unmodified on a local wireless medium (see 99 [I-D.ietf-mboned-ieee802-mcast-problems]). 101 Wi-Fi [IEEEstd80211] Access Points (APs) deployed in an Extended 102 Service Set (ESS) act as Ethernet Bridges [IEEEstd8021], with the 103 property that the bridging state is established at the time of 104 association. This ensures connectivity to the end node (the Wi-Fi 105 STA) and protects the wireless medium against broadcast-intensive 106 Transparent Bridging reactive Lookups. In other words, the 107 association process is used to register the MAC Address of the STA to 108 the AP. The AP subsequently proxies the bridging operation and does 109 not need to forward the broadcast Lookups over the radio. 111 In the same way as Transparent Bridging, IPv6 [RFC8200] Neighbor 112 Discovery [RFC4861] [RFC4862] Protocol (IPv6 ND) is a reactive 113 protocol, based on multicast transmissions to locate an on-link 114 correspondent and ensure the uniqueness of an IPv6 address. The 115 mechanism for Duplicate Address Detection (DAD) [RFC4862] was 116 designed for the efficient broadcast operation of Ethernet Bridging. 117 Since broadcast can be unreliable over wireless media, DAD often 118 fails to discover duplications [I-D.yourtchenko-6man-dad-issues]. In 119 practice, the fact that IPv6 addresses very rarely conflict is mostly 120 attributable to the entropy of the 64-bit Interface IDs as opposed to 121 the succesful operation of the IPv6 ND duplicate address detection 122 and resolution mechanisms. 124 The IPv6 ND Neighbor Solicitation (NS) [RFC4861] message is used for 125 DAD and address Lookup when a node moves, or wakes up and reconnects 126 to the wireless network. The NS message is targeted to a Solicited- 127 Node Multicast Address (SNMA) [RFC4291] and should in theory only 128 reach a very small group of nodes. But in reality, IPv6 multicast 129 messages are typically broadcast on the wireless medium, and so they 130 are processed by most of the wireless nodes over the subnet (e.g., 131 the ESS fabric) regardless of how few of the nodes are subscribed to 132 the SNMA. As a result, IPv6 ND address Lookups and DADs over a large 133 wireless and/or a LowPower Lossy Network (LLN) can consume enough 134 bandwidth to cause a substantial degradation to the unicast traffic 135 service. 137 Because IPv6 ND messages sent to the SNMA group are broadcast at the 138 radio MAC Layer, wireless nodes that do not belong to the SNMA group 139 still have to keep their radio turned on to listen to multicast NS 140 messages, which is a total waste of energy for them. In order to 141 reduce their power consumption, certain battery-operated devices such 142 as IoT sensors and smartphones ignore some of the broadcasts, making 143 IPv6 ND operations even less reliable. 145 These problems can be alleviated by reducing the IPv6 ND broadcasts 146 over wireless access links. This has been done by splitting the 147 broadcast domains and routes between subnets, or even by assigning a 148 /64 prefix to each wireless node (see [RFC8273]). 150 Another way is to proxy at the boundary of the wired and wireless 151 domains the Layer 3 protocols that rely on MAC Layer broadcast 152 operations. For instance, IEEE 802.11 [IEEEstd80211] situates proxy- 153 ARP (IPv4) and proxy-ND (IPv6) functions at the Access Points (APs). 154 The 6BBR provides a proxy-ND function and can be extended for proxy- 155 ARP in a continuation specification. 157 Knowledge of which address to proxy for can be obtained by snooping 158 the IPV6 ND protocol (see [I-D.bi-savi-wlan]), but it has been found 159 to be unreliable. An IPv6 address may not be discovered immediately 160 due to a packet loss, or if a "silent" node is not currently using 161 one of its addresses. A change of state (e.g., due to movement) may 162 be missed or misordered, leading to unreliable connectivity and 163 incomplete knowledge of the state of the network. 165 This specification defines the 6BBR as a Routing Registrar [RFC8505] 166 that provides proxy services for IPv6 Neighbor Discovery. As 167 represented in Figure 1, Backbone Routers federate multiple LLNs over 168 a Backbone Link to form a Multi-Link Subnet (MLSN). The MLSN breaks 169 the Layer 2 continuity and splits the broadcast domain, in a fashion 170 that each Link, including the backbone, is its own broadcast domain. 171 This means that devices that rely on a link-scope multicast on the 172 backbone will only reach other nodes on the backbone but not LLN 173 nodes. A key property of MLSNs is that link-local traffic and 174 traffic with a hop limit of 1 will not transit to nodes in the same 175 subnet on a different link, something that may produce unexpected 176 behavior in software that expects a subnet to be entirely contained 177 within a single link. In order to enable the continuity of IPv6 ND 178 operations beyond the backbone, and enable communication using Global 179 or Unique Local Addresses between any pair of nodes in the MLSN, 180 Backbone Routers placed along the LLN edge of the Backbone handle 181 IPv6 ND on behalf of Registered Nodes and forward IPv6 packets back 182 and forth. 184 A 6LoWPAN node (6LN) registers all its IPv6 Addresses using an 185 NS(EARO) as specified in [RFC8505] to the 6BBR. The 6BBR is also a 186 Border Router that performs IPv6 Neighbor Discovery (IPv6 ND) 187 operations on its Backbone interface on behalf of the 6LNs that have 188 registered addresses on its LLN interfaces without the need of a 189 broadcast over the wireless medium. A 6LN that resides on the 190 backbone does not register to the SNMA groups associated to its 191 Registered Addresses and defers to the 6BBR to answer or preferably 192 forward to it as unicast the corresponding multicast packets. 194 Additional benefits are discussed in Appendix B. 196 2. Terminology 198 2.1. BCP 14 200 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 201 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 202 "OPTIONAL" in this document are to be interpreted as described in BCP 203 14 [RFC2119] [RFC8174] when, and only when, they appear in all 204 capitals, as shown here. 206 2.2. New Terms 208 This document introduces the following terminology: 210 Federated: A subnet that comprises a Backbone and one or more 211 (wireless) access links, is said to be federated into one Multi- 212 Link Subnet. The proxy-ND operation of 6BBRs over the Backbone 213 and the access links provides the appearance of a subnet for IPv6 214 ND. 216 Sleeping Proxy: A 6BBR acts as a Sleeping Proxy if it answers ND 217 Neighbor Solicitations over the Backbone on behalf of the 218 Registering Node which might be in a sleep state in a low power 219 network. The Sleeping Proxy that is also a Bridging Proxy will 220 preferably forward the relevant messages to the Registering Node 221 as unicast frames in accord to the duty cycle of the Registering 222 Node and let it respond. 224 Routing Proxy: A Routing Proxy provides IPv6 ND proxy functions and 225 enables the MLSN operation over federated links that may not be 226 compatible for bridging. The Routing Proxy advertises its own MAC 227 Address as the Target Link Layer Address (TLLA) in the proxied NAs 228 over the Backbone, and routes at the Network Layer between the 229 federated links. 231 Bridging Proxy: A Bridging Proxy provides IPv6 ND proxy functions 232 while preserving forwarding continuity at the MAC Layer. The 233 Bridging Proxy advertises the MAC Address of the Registering Node 234 as the TLLA in the proxied NAs over the Backbone. In that case, 235 the MAC Address and the mobility of 6LN is still visible across 236 the bridged Backbone, and the 6BBR may be configured to proxy for 237 Link Local Addresses. 239 Binding Table: The Binding Table is an abstract database that is 240 maintained by the 6BBR to store the state associated with its 241 registrations. 243 Binding: A Binding is an abstract state associated to one 244 registration, in other words one entry in the Binding Table. 246 2.3. Abbreviations 248 This document uses the following abbreviations: 250 6BBR: 6LoWPAN Backbone Router 251 6LBR: 6LoWPAN Border Router 252 6LN: 6LoWPAN Node 253 6LR: 6LoWPAN Router 254 6CIO: Capability Indication Option 255 ARO: Address Registration Option 256 DAC: Duplicate Address Confirmation 257 DAD: Duplicate Address Detection 258 DAR: Duplicate Address Request 259 EARO: Extended Address Registration Option 260 EDAC: Extended Duplicate Address Confirmation 261 EDAR: Extended Duplicate Address Request 262 DODAG: Destination-Oriented Directed Acyclic Graph 263 ID: Identifier 264 LLN: Low-Power and Lossy Network 265 NA: Neighbor Advertisement 266 MAC: Medium Access Control 267 NCE: Neighbor Cache Entry 268 ND: Neighbor Discovery 269 NDP: Neighbor Discovery Protocol 270 NS: Neighbor Solicitation 271 NS(DAD): NDP NS message used for the purpose of duplication 272 avoidance (multicast) 273 NS(Lookup): NDP NS message used for the purpose of address 274 resolution (multicast) 275 NS(NUD): NDP NS message used for the purpose of unreachability 276 detection (unicast) 277 NUD: Neighbor Unreachability Detection 278 ROVR: Registration Ownership Verifier 279 RPL: IPv6 Routing Protocol for LLNs 280 RA: Router Advertisement 281 RS: Router Solicitation 282 SNMA: Solicited-Node Multicast Address 283 LLA: Link Layer Address (aka MAC address) 284 SLLA: Source Link Layer Address 285 TLLA: Target Link Layer Address 286 TID: Transaction ID 288 2.4. References 290 In this document, readers will encounter terms and concepts that are 291 discussed in the following documents: 293 * "Neighbor Discovery for IP version 6" [RFC4861], "IPv6 Stateless 294 Address Autoconfiguration" [RFC4862] and "Optimistic Duplicate 295 Address Detection" [RFC4429], 297 * "Neighbor Discovery Proxies (proxy-ND)" [RFC4389] and "Multi-Link 298 Subnet Issues" [RFC4903], 300 * "Problem Statement and Requirements for IPv6 over Low-Power 301 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606], and 303 * Neighbor Discovery Optimization for Low-Power and Lossy Networks 304 [RFC6775] and "Registration Extensions for 6LoWPAN Neighbor 305 Discovery" [RFC8505]. 307 3. Overview 309 This section and its subsections present a non-normative high level 310 view of the operation of the 6BBR. The following sections cover the 311 normative part. Figure 1 illustrates a backbone link that federates 312 a collection of LLNs as a single IPv6 Subnet, with a number of 6BBRs 313 providing proxy-ND services to their attached LLNs. 315 The LLN may be a hub-and-spoke access link such as (Low-Power) IEEE 316 STD. 802.11 (Wi-Fi) [IEEEstd80211] and IEEE STD. 802.15.1 (Bluetooth) 317 [IEEEstd802151], or a Mesh-Under or a Route-Over network [RFC8505]. 318 The proxy state can be distributed across multiple 6BBRs attached to 319 the same Backbone. 321 | 322 +-----+ +-----+ +-----+ IPv6 323 (default) | | (Optional) | | | | Node 324 Router | | 6LBR | | | | or 325 +-----+ +-----+ +-----+ 6LN 326 | Backbone side | | 327 ----+-------+-----------------+---+-------------+----+----- 328 | | | 329 +------+ +------+ +------+ 330 | 6BBR | | 6BBR | | 6BBR | 331 | | | | | | 332 +------+ +------+ +------+ 333 o Wireless side o o o o o o 334 o o o o o o o o o o o o o o o o o o o o 335 o o o o o o o o o o o o o o o o o o o 336 o o o o o o o o o LLN o o o o o o o o o 337 o o o o o o o o o o o o o o 338 o o o 340 Figure 1: Backbone Link and Backbone Routers 342 The main features of a 6BBR are as follows: 344 * Multi-Link-subnet functions (provided by the 6BBR on the backbone) 345 performed on behalf of registered 6LNs, and 347 * Routing registrar services that reduce multicast within the LLN: 349 * Binding Table management 350 * failover, e.g., due to mobility 352 Each Backbone Router (6BBR) maintains a data structure for its 353 Registered Addresses called a Binding Table. The combined Binding 354 Tables of all the 6BBRs on a backbone form a distributed database of 355 6LNs that reside in the LLNs or on the IPv6 Backbone. 357 Unless otherwise configured, a 6BBR does the following: 359 * Create a new entry in a Binding Table for a new Registered Address 360 and ensure that the Address is not duplicated over the Backbone. 362 * Advertise a Registered Address over the Backbone using an 363 unsolicited NA message, asynchronously or as a response to a NS 364 message. This includes joining the multicast group associated to 365 the SNMA derived from the Registered Address as specified in 366 section 7.2.1. of [RFC4861] over the Backbone. 368 * The 6BBR may respond immediately as a Proxy in lieu of the 369 Registering Node, e.g., if the Registering Node has a sleeping 370 cycle that the 6BBR does not want to interrupt, or if the 6BBR has 371 a recent state that is deemed fresh enough to permit the proxied 372 response. It is preferred, though, that the 6BBR checks whether 373 the Registering Node is still responsive on the Registered 374 Address. To that effect: 376 - as a Bridging Proxy: 377 the 6BBR forwards the multicast DAD and Address Lookup messages 378 as a unicast MAC-Layer frames to the MAC address of the 379 Registering Node that matches the Target in the ND message, and 380 forwards as is the unicast Neighbor Unreachability Detection 381 (NUD) messages, so as to let the Registering Node answer with 382 the ND Message and options that it sees fit; 383 - as a Routing Proxy: 384 the 6BBR checks the liveliness of the Registering Node, e.g., 385 using a NUD verification, before answering on its behalf. 387 * Deliver packets arriving from the LLN, using Neighbor Solicitation 388 messages to look up the destination over the Backbone. 390 * Forward or bridge packets between the LLN and the Backbone. 392 * Verify liveness for a registration, when needed. 394 The first of these functions enables the 6BBR to fulfill its role as 395 a Routing Registrar for each of its attached LLNs. The remaining 396 functions fulfill the role of the 6BBRs as the border routers 397 connecting the Multi-link IPv6 subnet to the Internet. 399 The operation of IPv6 ND and of proxy-ND are not mutually exclusive 400 on the Backbone, meaning that nodes attached to the Backbone and 401 using IPv6 ND can transparently interact with 6LNs that rely on a 402 6BBR to proxy ND for them, whether the 6LNs are reachable over an LLN 403 or directly attached to the Backbone. 405 The [RFC8505] registration mechanism used to learn addresses to be 406 proxied for may co-exist in a 6BBR with a proprietary snooping or the 407 traditional bridging functionality of an Access Point, in order to 408 support legacy LLN nodes that do not support this specification. 410 The registration to a proxy service uses an NS/NA(EARO) exchange. 411 The 6BBR operation resembles that of a Mobile IPv6 (MIPv6) [RFC6275] 412 Home Agent (HA). The combination of a 6BBR and a MIPv6 HA enables 413 full mobility support for 6LNs, inside and outside the links that 414 form the subnet. 416 The 6BBRs use the Extended Address Registration Option (EARO) defined 417 in [RFC8505] as follows: 419 * The EARO is used in the IPv6 ND exchanges over the Backbone 420 between the 6BBRs to help distinguish duplication from movement. 421 Extended Duplicate Address Messages (EDAR and EDAC) may also be 422 used between a 6LBR, if one is present, and the 6BBR. Address 423 duplication is detected using the ROVR field. Conflicting 424 registrations to different 6BBRs for the same Registered Address 425 are resolved using the TID field. 427 * The Link Layer Address (LLA) that the 6BBR advertises for the 428 Registered Address on behalf of the Registered Node over the 429 Backbone can belong to the Registering Node; in that case, the 430 6BBR (acting as a Bridging Proxy (see Section 8)) bridges the 431 unicast packets. Alternatively, the LLA can be that of the 6BBR 432 on the Backbone interface, in which case the 6BBR (acting as a 433 Routing Proxy(see Section 7)) receives the unicast packets at 434 Layer 3 and routes over. 436 3.1. Updating RFC 6775 and RFC 8505 438 This specification adds the EARO as a possible option in RS, NS(DAD) 439 and NA messages over the backbone. [RFC8505] requires that the 440 registration NS(EARO) contains an Source Link Layer Address Option 441 (SLLAO). This specification details the use of those messages over 442 the backbone. 444 Note: [RFC6775] requires that the registration NS(EARO) contains an 445 SLLAO and [RFC4862] that the NS(DAD) is sent from the unspecified 446 address for which there cannot be a SLLAO. Consequently, an NS(DAD) 447 cannot be confused with a registration. 449 This specification adds the capability to insert IPv6 ND options in 450 the EDAR and EDAC messages. In particular, a 6BBR acting as a 6LR 451 for the Registered Address can insert an SLLAO in the EDAR to the 452 6LBR in order to avoid a Lookup back. This enables the 6LBR to store 453 the MAC address associated to the Registered Address on a Link and to 454 serve as a mapping server as described in 455 [I-D.thubert-6lo-unicast-lookup]. 457 3.2. Access Link 459 The simplest Multi-Link Subnet topology from the Layer 3 perspective 460 occurs when the wireless network appears as a single hop hub-and- 461 spoke network as shown in Figure 2. The Layer 2 operation may 462 effectively be hub-and-spoke (e.g., Wi-Fi) or Mesh-Under, with a 463 Layer 2 protocol handling the complex topology. 465 | 466 +-----+ +-----+ +-----+ IPv6 467 (default) | | (Optional) | | | | Node 468 Router | | 6LBR | | | | or 469 +-----+ +-----+ +-----+ 6LN 470 | Backbone side | | 471 ----+-------+-----------------+---+-------------+----+----- 472 | | | 473 +------+ +------+ +------+ 474 | 6BBR | | 6BBR | | 6BBR | 475 | 6LR | | 6LR | | 6LR | 476 +------+ +------+ +------+ 477 (6LN) (6LN) (6LN) (6LN) (6LN) (6LN) (6LN) (6LN) 479 Figure 2: Access Link Use case 481 Figure 3 illustrates a flow where 6LN forms an IPv6 Address and 482 registers it to a 6BBR acting as a 6LR [RFC8505]. The 6BBR applies 483 ODAD (see Section 3.6) to the registered address to enable 484 connectivity while the message flow is still in progress. 486 In this example, a 6LBR is deployed on the backbone link to serve the 487 whole subnet, and EDAR / EDAC messages are used in combination with 488 DAD to enable coexistence with IPv6 ND over the backbone. 490 The RS sent initially by the 6LN(STA) is transmitted as a multicast 491 but since it is intercepted by the 6BBR, it is never effectively 492 broadcast. The multiple arrows associated to the ND messages on the 493 Backbone denote a real Layer 2 broadcast. 495 6LN(STA) 6BBR(AP) 6LBR default GW 496 | | | | 497 | LLN Access Link | IPv6 Backbone (e.g., Ethernet) | 498 | | | | 499 | RS(multicast) | | | 500 |---------------->| | | 501 | RA(PIO, Unicast)| | | 502 |<----------------| | | 503 | NS(EARO) | | | 504 |---------------->| | | 505 | | Extended DAR | | 506 | |--------------->| | 507 | | Extended DAC | | 508 | |<---------------| | 509 | | | 510 | | NS-DAD(EARO, multicast) | 511 | |--------> | 512 | |----------------------------------->| 513 | | | 514 | | RS(no SLLAO, for ODAD) | 515 | |----------------------------------->| 516 | | if (no fresher Binding) NS(Lookup) | 517 | | <----------------| 518 | |<-----------------------------------| 519 | | NA(SLLAO, not(O), EARO) | 520 | |----------------------------------->| 521 | | RA(unicast) | 522 | |<-----------------------------------| 523 | | | 524 | IPv6 Packets in optimistic mode | 525 |<---------------------------------------------------->| 526 | | | 527 | | 528 | NA(EARO) | 529 |<----------------| 530 | | 532 Figure 3: Initial Registration Flow to a 6BBR acting as Routing Proxy 534 3.3. Route-Over Mesh 536 A more complex Multi-Link Subnet topology occurs when the wireless 537 network appears as a Layer 3 Mesh network as shown in Figure 4. A 538 so-called Route-Over routing protocol exposes routes between 6LRs 539 towards both 6LRs and 6LNs, and a 6LBR acts as Root of the Layer 3 540 Mesh network and proxy-registers the LLN addresses to the 6BBR. 542 | 543 +-----+ +-----+ +-----+ IPv6 544 (default) | | (Optional) | | | | Node 545 Router | | 6LBR | | | | or 546 +-----+ +-----+ +-----+ 6LN 547 | Backbone side | | 548 ----+-------+-----------------+---+-------------+----+----- 549 | | | 550 +------+ +------+ +------+ 551 | 6BBR | | 6BBR | | 6BBR | 552 +------+ +------+ +------+ 553 | | | 554 +------+ +------+ +------+ 555 | 6LBR | | 6LBR | | 6LBR | 556 +------+ +------+ +------+ 557 (6LN) (6LR) (6LN) (6LR) (6LN) (6LR) (6LR) (6LR)(6LN) 558 (6LN)(6LR) (6LR) (6LN) (6LN) (6LR)(6LN) (6LR) (6LR) (6LR) (6LN) 559 (6LR)(6LR) (6LR) (6LR) (6LR)(6LN) (6LR) (6LR)(6LR) 560 (6LR) (6LR) (6LR) (6LR) (6LN)(6LR) (6LR) (6LR) (6LR) (6LR) 561 (6LN) (6LN)(6LN) (6LN) (6LN) (6LN) (6LN) (6LN) (6LN) (6LN) 563 Figure 4: Route-Over Mesh Use case 565 Figure 5 illustrates IPv6 signaling that enables a 6LN (the 566 Registered Node) to form a Global or a Unique-Local Address and 567 register it to the 6LBR that serves its LLN using [RFC8505]. The 568 6LBR (the Registering Node) then proxies the [RFC8505] registration 569 to the 6BBR to obtain proxy-ND services from the 6BBR. 571 As above, the RS sent initially by the 6LN(STA) is a transmitted as a 572 multicast but since it is intercepted by the 6BBR, it is never 573 effectively broadcast, and the multiple arrows associated to the ND 574 messages on the Backbone denote a real Layer 2 broadcast. 576 6LoWPAN Node 6LR 6LBR 6BBR 577 (mesh leaf) (mesh router) (mesh root) 578 | | | | 579 | 6LoWPAN ND |6LoWPAN ND | 6LoWPAN ND | IPv6 ND 580 | LLN link |Route-Over mesh|Ethernet/serial| Backbone 581 | | |/Internal call | 582 | IPv6 ND RS | | | 583 |-------------->| | | 584 |-----------> | | | 585 |------------------> | | 586 | IPv6 ND RA | | | 587 |<--------------| | | 588 | | | | 589 | NS(EARO) | | | 590 |-------------->| | | 591 | 6LoWPAN ND | Extended DAR | | 592 | |-------------->| | 593 | | | NS(EARO) | 594 | | |-------------->| 595 | | | (proxied) | NS-DAD 596 | | | |------> 597 | | | | (EARO) 598 | | | | 599 | | | NA(EARO) | 600 | | |<--------------| 601 | | Extended DAC | | 602 | |<--------------| | 603 | NA(EARO) | | | 604 |<--------------| | | 605 | | | | 607 Figure 5: Initial Registration Flow over Route-Over Mesh 609 As a non-normative example of a Route-Over Mesh, the 6TiSCH 610 architecture [I-D.ietf-6tisch-architecture] suggests using the RPL 611 [RFC6550] routing protocol and collocating the RPL root with a 6LBR 612 that serves the LLN. The 6LBR is also either collocated with or 613 directly connected to the 6BBR over an IPv6 Link. 615 3.4. The Binding Table 617 Addresses in an LLN that are reachable from the Backbone by way of 618 the 6BBR function must be registered to that 6BBR, using an NS(EARO) 619 with the R flag set [RFC8505]. A 6BBR maintains a state for its 620 active registrations in an abstract Binding Table. 622 An entry in the Binding Table is called a "Binding". A Binding may 623 be in Tentative, Reachable or Stale state. 625 The 6BBR uses a combination of [RFC8505] and IPv6 ND over the 626 Backbone to advertise the registration and avoid a duplication. 627 Conflicting registrations are solved by the 6BBRs, transparently to 628 the Registering Nodes. 630 Only one 6LN may register a given Address, but the Address may be 631 registered to Multiple 6BBRs for higher availability. 633 Over the LLN, Binding Table management is as follows: 635 * De-registrations (newer TID, same ROVR, null Lifetime) are 636 accepted with a status of 4 ("Removed"); the entry is deleted; 638 * Newer registrations (newer TID, same ROVR, non-null Lifetime) are 639 accepted with a status of 0 (Success); the Binding is updated with 640 the new TID, the Registration Lifetime and the Registering Node; 641 in Tentative state the EDAC response is held and may be 642 overwritten; in other states the Registration Lifetime timer is 643 restarted and the entry is placed in Reachable state. 645 * Identical registrations (same TID, same ROVR) from the same 646 Registering Node are accepted with a status of 0 (Success). In 647 Tentative state, the response is held and may be overwritten, but 648 the response is eventually produced, carrying the result of the 649 DAD process; 651 * Older registrations (older TID, same ROVR) from the same 652 Registering Node are discarded; 654 * Identical and older registrations (not-newer TID, same ROVR) from 655 a different Registering Node are rejected with a status of 3 656 (Moved); this may be rate limited to avoid undue interference; 658 * Any registration for the same address but with a different ROVR is 659 rejected with a status of 1 (Duplicate). 661 The operation of the Binding Table is specified in detail in 662 Section 9. 664 3.5. Primary and Secondary 6BBRs 666 The same address may be successfully registered to more than one 667 6BBR, in which case the Registering Node uses the same EARO in all 668 the parallel registrations. To allow for this, ND(DAD) and NA 669 messages with an EARO that indicate an identical Binding in another 670 6BBR (same Registered address, same TID, same ROVR) are silently 671 ignored. 673 A 6BBR may optionally be primary or secondary. The primary is the 674 6BBR that has the highest EUI-64 Address of all the 6BBRs that share 675 a registration for the same Registered Address, with the same ROVR 676 and same Transaction ID, the EUI-64 Address being considered as an 677 unsigned 64bit integer. A given 6BBR can be primary for a given 678 Address and secondary for another Address, regardless of whether or 679 not the Addresses belong to the same 6LN. 681 In the following sections, is is expected that an NA is sent over the 682 backbone only if the node is primary or does not support the concept 683 of primary. More than one 6BBR claiming or defending an address 684 generates unwanted traffic but no reachability issue since all 6BBRs 685 provide reachability from the Backbone to the 6LN. 687 3.6. Using Optimistic DAD 689 Optimistic Duplicate Address Detection [RFC4429] (ODAD) specifies how 690 an IPv6 Address can be used before completion of Duplicate Address 691 Detection (DAD). ODAD guarantees that this behavior will not cause 692 harm if the new Address is a duplicate. 694 Support for ODAD avoids delays in installing the Neighbor Cache Entry 695 (NCE) in the 6BBRs and the default router, enabling immediate 696 connectivity to the registered node. As shown in Figure 3, if the 697 6BBR is aware of the Link-Layer Address (LLA) of a router, then the 698 6BBR sends a Router Solicitation (RS), using the Registered Address 699 as the IP Source Address, to the known router(s). The RS is sent 700 without a Source LLA Option (SLLAO), to avoid invalidating a 701 preexisting NCE in the router. 703 Following ODAD, the router may then send a unicast RA to the 704 Registered Address, and it may resolve that Address using an 705 NS(Lookup) message. In response, the 6BBR sends an NA with an EARO 706 and the Override (O) flag [RFC4861] that is not set. The router can 707 then determine the freshest EARO in case of conflicting NA(EARO) 708 messages, using the method described in section 5.2.1 of [RFC8505]. 709 If the NA(EARO) is the freshest answer, the default router creates a 710 Binding with the SLLAO of the 6BBR (in Routing Proxy mode) or that of 711 the Registering Node (in Bridging Proxy mode) so that traffic from/to 712 the Registered Address can flow immediately. 714 4. Multi-Link Subnet Considerations 716 The Backbone and the federated LLN Links are considered as different 717 links in the Multi-Link Subnet, even if multiple LLNs are attached to 718 the same 6BBR. ND messages are link-scoped and are not forwarded by 719 the 6BBR between the backbone and the LLNs though some packets may be 720 reinjected in Bridging Proxy mode (see Section 8). 722 Nodes located inside the subnet do not perform the IPv6 Path MTU 723 Discovery [RFC8201]. For that reason, the MTU MUST have the same 724 value on the Backbone and all attached LLNs. As a consequence, the 725 6BBR MUST use the same MTU value in RAs over the Backbone and in the 726 RAs that it transmits towards the LLN links. 728 5. Optional 6LBR serving the Multi-Link Subnet 730 A 6LBR can be deployed to serve the whole MLSN. It may be attached 731 to the backbone, in which case it can be discovered by its capability 732 advertisement (see section 4.3. of [RFC8505]) in RA messages. 734 This specification allows for an address to be registered to more 735 than one 6BBR. Consequently a 6LBR MUST be capable of maintaining 736 state for each of the 6BBR having registered with the same TID and 737 same ROVR. 739 When a 6LBR is present, the 6BBR uses an EDAR/EDAC message exchange 740 with the 6LBR to check if the new registration corresponds to a 741 duplication or a movement. This is done prior to the NS(DAD) 742 process, which may be avoided if the 6LBR already maintains a 743 conflicting state for the Registered Address. 745 If this registration is duplicate or not the freshest, then the 6LBR 746 replies with an EDAC message with a status code of 1 ("Duplicate 747 Address") or 3 ("Moved"), respectively. If this registration is the 748 freshest, then the 6LBR replies with a status code of 0. In that 749 case, if this registration is fresher than an existing registration 750 for another 6BBR, then the 6LBR also sends an asynchronous EDAC with 751 a status of 4 ("Removed") to that other 6BBR. 753 The EDAR message SHOULD carry the SLLAO used in NS messages by the 754 6BBR for that Binding, and the EDAC message SHOULD carry the Target 755 Link Layer Address Option (TLLAO) associated with the currently 756 accepted registration. This enables a 6BBR to locate the new 757 position of a mobile 6LN in the case of a Routing Proxy operation, 758 and opens the capability for the 6LBR to serve as a mapping server in 759 the future. 761 Note that if Link Local addresses are registered, then the scope of 762 uniqueness on which the address duplication is checked is the total 763 collection of links that the 6LBR serves as opposed to the sole link 764 on which the Link Local address is assigned. 766 6. Using IPv6 ND Over the Backbone Link 768 On the Backbone side, the 6BBR MUST join the SNMA group corresponding 769 to a Registered Address as soon as it creates a Binding for that 770 Address, and maintain that SNMA membership as long as it maintains 771 the registration. 773 The 6BBR uses either the SNMA or plain unicast to defend the 774 Registered Addresses in its Binding Table over the Backbone (as 775 specified in [RFC4862]). 777 The 6BBR advertises and defends the Registered Addresses over the 778 Backbone Link using RS, NS(DAD) and NA messages with the Registered 779 Address as the Source or Target address, respectively. 781 The 6BBR MUST place an EARO in the IPv6 ND messages that it generates 782 on behalf of the Registered Node. Note that an NS(DAD) does not 783 contain an SLLAO and cannot be confused with a proxy registration 784 such as performed by a 6LBR. 786 An NA message generated in response to an NS(DAD) MUST have the 787 Override flag set and a status of 1 (Duplicate) or 3 (Moved) in the 788 EARO. An NA message generated in response to an NS(Lookup) or an 789 NS(NUD) MUST NOT have the Override flag set. 791 This specification enables proxy operation for the IPv6 ND resolution 792 of LLN devices and a prefix that is used across a Multi-Link Subnet 793 MAY be advertised as on-link over the Backbone. This is done for 794 backward compatibility with existing IPv6 hosts by setting the L flag 795 in the Prefix Information Option (PIO) of RA messages [RFC4861]. 797 For movement involving a slow reattachment, the NUD procedure defined 798 in [RFC4861] may time out too quickly. Nodes on the backbone SHOULD 799 support [RFC7048] whenever possible. 801 7. Routing Proxy Operations 803 A Routing Proxy provides IPv6 ND proxy functions for Global and 804 Unique Local addresses between the LLN and the backbone, but not for 805 Link-Local addresses. It operates as an IPv6 border router and 806 provides a full Link-Layer isolation. 808 In this mode, it is not required that the MAC addresses of the 6LNs 809 are visible at Layer 2 over the Backbone. It is thus useful when the 810 messaging over the Backbone that is associated to wireless mobility 811 becomes expensive, e.g., when the Layer 2 topology is virtualized 812 over a wide area IP underlay. 814 This mode is definitely required when the LLN uses a MAC address 815 format that is different from that on the Backbone (e.g., EUI-64 vs. 816 EUI-48). Since a 6LN may not be able to resolve an arbitrary 817 destination in the MLSN directly, the MLSN prefix MUST NOT be 818 advertised as on-link in RA messages sent towards the LLN. 820 In order to maintain IP connectivity, the 6BBR installs a connected 821 Host route to the Registered Address on the LLN interface, via the 822 Registering Node as identified by the Source Address and the SLLA 823 option in the NS(EARO) messages. 825 When operating as a Routing Proxy, the 6BBR MUST use its Layer 2 826 Address on its Backbone Interface in the SLLAO of the RS messages and 827 the TLLAO of the NA messages that it generates to advertise the 828 Registered Addresses. 830 For each Registered Address, multiple peers on the Backbone may have 831 resolved the Address with the 6BBR MAC Address, maintaining that 832 mapping in their Neighbor Cache. The 6BBR SHOULD maintain a list of 833 the peers on the Backbone which have associated its MAC Address with 834 the Registered Address. If that Registered Address moves to a new 835 6BBR, the previous 6BBR SHOULD unicast a gratuitous NA with the 836 Override flag set to each such peer, to supply the LLA of the new 837 6BBR in the TLLA option for the Address. A 6BBR that does not 838 maintain this list MAY multicast a gratuitous NA with the Override 839 flag; this NA will possibly hit all the nodes on the Backbone, 840 whether or not they maintain an NCE for the Registered Address. 842 If a correspondent fails to receive the gratuitous NA, it will keep 843 sending traffic to a 6BBR to which the node was previously 844 registered. Since the previous 6BBR removed its Host route to the 845 Registered Address, it will look up the address over the backbone, 846 resolve the address with the LLA of the new 6BBR, and forward the 847 packet to the correct 6BBR. The previous 6BBR SHOULD also issue a 848 redirect message [RFC4861] to update the cache of the correspondent. 850 8. Bridging Proxy Operations 852 A Bridging Proxy provides IPv6 ND proxy functions between the LLN and 853 the backbone while preserving the forwarding continuity at the MAC 854 Layer. It acts as a Layer 2 Bridge for all types of unicast packets 855 including link-scoped, and appears as an IPv6 Host on the Backbone. 857 The Bridging Proxy registers any Binding including for a Link-Local 858 address to the 6LBR (if present) and defends it over the backbone in 859 IPv6 ND procedures. 861 To achieve this, the Bridging Proxy intercepts the IPv6 ND messages 862 and may reinject them on the other side, respond directly or drop 863 them. For instance, an ND(Lookup) from the backbone that matches a 864 Binding can be responded directly, or turned into a unicast on the 865 LLN side to let the 6LN respond. 867 As a Bridging Proxy, the 6BBR MUST use the Registering Node's Layer 2 868 Address in the SLLAO of the NS/RS messages and the TLLAO of the NA 869 messages that it generates to advertise the Registered Addresses. 870 The Registering Node's Layer 2 address is found in the SLLA of the 871 registration NS(EARO), and maintained in the Binding Table. 873 The Multi-Link Subnet prefix SHOULD NOT be advertised as on-link in 874 RA messages sent towards the LLN. If a destination address is seen 875 as on-link, then a 6LN may use NS(Lookup) messages to resolve that 876 address. In that case, the 6BBR MUST either answer the NS(Lookup) 877 message directly or reinject the message on the backbone, either as a 878 Layer 2 unicast or a multicast. 880 If the Registering Node owns the Registered Address, then its 881 mobility does not impact existing NCEs over the Backbone. Otherwise, 882 when the 6LN selects another Registering Node, the new Registering 883 Node SHOULD send a multicast NA with the Override flag set to fix the 884 existing NCEs across the Backbone. 886 This method can fail if the multicast message is not received; one or 887 more correspondent nodes on the Backbone might maintain an stale NCE, 888 and packets to the Registered Address may be lost. When this 889 condition happens, it is eventually discovered and resolved using NUD 890 as defined in [RFC4861]. 892 9. Creating and Maintaining a Binding 894 Upon receiving a registration for a new Address (i.e., an NS(EARO) 895 with the R flag set), the 6BBR creates a Binding and operates as a 896 6LR according to [RFC8505], interacting with the 6LBR if one is 897 present. 899 An implementation of a Routing Proxy that creates a Binding MUST also 900 create an associated Host route pointing to the registering node in 901 the LLN interface from which the registration was received. 903 The 6LR operation is modified as follows: 905 * EDAR and EDAC messages SHOULD carry a SLLAO and a TLLAO, 906 respectively. 908 * A Bridging Proxy MAY register Link Local addresses at the 6BBR and 909 proxy ND for these addresses over the backbone. 911 * An EDAC message with a status of 9 (6LBR Registry Saturated) is 912 assimilated as a status of 0 if a following DAD process protects 913 the address against duplication. 915 This specification enables nodes on a Backbone Link to co-exist along 916 with nodes implementing IPv6 ND [RFC4861] as well as other non- 917 normative specifications such as [I-D.bi-savi-wlan]. It is possible 918 that not all IPv6 addresses on the Backbone are registered and known 919 to the 6LBR, and an EDAR/EDAC echange with the 6LBR might succeed 920 even for a duplicate address. Consequently, and unless 921 administratively overridden, the 6BBR still needs to perform IPv6 ND 922 DAD over the backbone after an EDAC with a status code of 0 or 9. 924 For the DAD operation, the Binding is placed in Tentative state for a 925 duration of TENTATIVE_DURATION (Section 12), and an NS(DAD) message 926 is sent as a multicast message over the Backbone to the SNMA 927 associated with the registered Address [RFC4862]. The EARO from the 928 registration MUST be placed unchanged in the NS(DAD) message. 930 If a registration is received for an existing Binding with a non-null 931 Registration Lifetime and the registration is fresher (same ROVR, 932 fresher TID), then the Binding is updated, with the new Registration 933 Lifetime, TID, and possibly Registering Node. In Tentative state 934 (see Section 9.1), the current DAD operation continues unaltered. In 935 other states (see Section 9.2 and Section 9.3 ), the Binding is 936 placed in Reachable state for the Registration Lifetime, and the 6BBR 937 returns an NA(EARO) to the Registering Node with a status of 0 938 (Success). 940 Upon a registration that is identical (same ROVR, TID, and 941 Registering Node), the 6BBR returns an NA(EARO) back to the 942 Registering Node with a status of 0 (Success). A registration that 943 is not as fresh (same ROVR, older TID) is ignored. 945 If a registration is received for an existing Binding and a 946 registration Lifetime of zero, then the Binding is removed, and the 947 6BBR returns an NA(EARO) back to the Registering Node with a status 948 of 0 (Success). An implementation of a Routing Proxy that removes a 949 binding MUST remove the associated Host route pointing on the 950 registering node. It MAY preserve a temporary state in order to 951 forward packets in flight. The state may be a NCE formed based on a 952 received NA message, or a Binding in Stale state and pointing at the 953 new 6BBR on the backbone. 955 The implementation should also use REDIRECT messages as specified in 956 [RFC4861] to update the correspondents for the Registered Address, 957 pointing the new 6BBR. 959 9.1. Operations on a Binding in Tentative State 961 The Tentative state covers a DAD period over the backbone during 962 which an address being registered is checked for duplication using 963 procedures defined in [RFC4862]. 965 For a Binding in Tentative state: 967 * The Binding MUST be removed if an NA message is received over the 968 Backbone for the Registered Address with no EARO, or containing an 969 EARO with a status of 1 (Duplicate) that indicates an existing 970 registration owned by a different Registering Node. In that case, 971 an NA MUST be sent back to the Registering Node with a status of 1 972 (Duplicate) in the EARO. This behavior might be overriden by 973 policy, in particular if the registration is trusted, e.g., based 974 on the validation of the ROVR field (see [I-D.ietf-6lo-ap-nd]). 976 * An NS(DAD) with no EARO or with an EARO that indicates a duplicate 977 registration (i.e., different ROVR) MUST be answered with an NA 978 message containing an EARO with a status of 1 (Duplicate) and the 979 Override flag not set. This behavior might be overriden by 980 policy, in particular if the registration is not trusted. 982 * The Binding MUST be removed if an NA message is received over the 983 Backbone for the Registered Address containing an EARO with a 984 status of 3 (Moved), or an NS(DAD) with an EARO that indicates a 985 fresher registration ([RFC8505]) for the same Registered Node 986 (i.e., same ROVR). A status of 3 is returned in the NA(EARO) back 987 to the Registering Node. 989 * 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 SHOULD be answered with an NA message containing an EARO with 992 a status of 3 (Moved) in order to clean up the situation 993 immediately. 995 * Other NS(DAD) and NA messages from the Backbone are ignored. 997 * NS(Lookup) and NS(NUD) messages SHOULD be optimistically answered 998 with an NA message containing an EARO with a status of 0 and the 999 Override flag not set (see Section 3.6). If optimistic DAD is 1000 disabled, then they SHOULD be queued to be answered when the 1001 Binding goes to Reachable state. 1003 When the TENTATIVE_DURATION (Section 12) timer elapses, the Binding 1004 is placed in Reachable state for the Registration Lifetime, and the 1005 6BBR returns an NA(EARO) to the Registering Node with a status of 0 1006 (Success). 1008 The 6BBR also attempts to take over any existing Binding from other 1009 6BBRs and to update existing NCEs in backbone nodes. This is done by 1010 sending an NA message with an EARO and the Override flag set over the 1011 backbone (see Section 7 and Section 8). 1013 9.2. Operations on a Binding in Reachable State 1015 The Reachable state covers an active registration after a successful 1016 DAD process. 1018 If the Registration Lifetime is of a long duration, an implementation 1019 might be configured to reassess the availability of the Registering 1020 Node at a lower period, using a NUD procedure as specified in 1021 [RFC7048]. If the NUD procedure fails, the Binding SHOULD be placed 1022 in Stale state immediately. 1024 For a Binding in Reachable state: 1026 * The Binding MUST be removed if an NA or an NS(DAD) message is 1027 received over the Backbone for the Registered Address containing 1028 an EARO that indicates a fresher registration ([RFC8505]) for the 1029 same Registered Node (i.e., same ROVR). A status of 4 (Removed) 1030 is returned in an asynchronous NA(EARO) to the Registering Node. 1031 Based on configuration, an implementation may delay this operation 1032 by a timer with a short setting, e.g., a few seconds to a minute, 1033 in order to a allow for a parallel registration to reach this 1034 node, in which case the NA might be ignored. 1036 * An NS(DAD) with no EARO or with an EARO that indicates a duplicate 1037 registration (i.e., different ROVR) MUST be answered with an NA 1038 message containing an EARO with a status of 1 (Duplicate) and the 1039 Override flag not set. 1041 * NS(DAD) and NA messages containing an EARO that indicates a 1042 registration for the same Registered Node that is not as fresh as 1043 this binding MUST be answered with an NA message containing an 1044 EARO with a status of 3 (Moved). 1046 * Other NS(DAD) and NA messages from the Backbone are ignored. 1048 * NS(Lookup) and NS(NUD) messages SHOULD be answered with an NA 1049 message containing an EARO with a status of 0 and the Override 1050 flag not set. The 6BBR MAY check whether the Registering Node is 1051 still available using a NUD procedure over the LLN prior to 1052 answering; this behaviour depends on the use case and is subject 1053 to configuration. 1055 When the Registration Lifetime timer elapses, the Binding is placed 1056 in Stale state for a duration of STALE_DURATION (Section 12). 1058 9.3. Operations on a Binding in Stale State 1060 The Stale state enables tracking of the Backbone peers that have a 1061 NCE pointing to this 6BBR in case the Registered Address shows up 1062 later. 1064 If the Registered Address is claimed by another 6LN on the Backbone, 1065 with an NS(DAD) or an NA, the 6BBR does not defend the Address. 1067 For a Binding in Stale state: 1069 * The Binding MUST be removed if an NA or an NS(DAD) message is 1070 received over the Backbone for the Registered Address containing 1071 no EARO or an EARO that indicates either a fresher registration 1072 for the same Registered Node or a duplicate registration. A 1073 status of 4 (Removed) MAY be returned in an asynchronous NA(EARO) 1074 to the Registering Node. 1076 * NS(DAD) and NA messages containing an EARO that indicates a 1077 registration for the same Registered Node that is not as fresh as 1078 this MUST be answered with an NA message containing an EARO with a 1079 status of 3 (Moved). 1081 * If the 6BBR receives an NS(Lookup) or an NS(NUD) message for the 1082 Registered Address, the 6BBR MUST attempt a NUD procedure as 1083 specified in [RFC7048] to the Registering Node, targeting the 1084 Registered Address, prior to answering. If the NUD procedure 1085 succeeds, the operation in Reachable state applies. If the NUD 1086 fails, the 6BBR refrains from answering. 1088 * Other NS(DAD) and NA messages from the Backbone are ignored. 1090 When the STALE_DURATION (Section 12) timer elapses, the Binding MUST 1091 be removed. 1093 10. Registering Node Considerations 1095 A Registering Node MUST implement [RFC8505] in order to interact with 1096 a 6BBR (which acts as a routing registrar). Following [RFC8505], the 1097 Registering Node signals that it requires IPv6 proxy-ND services from 1098 a 6BBR by registering the corresponding IPv6 Address using an 1099 NS(EARO) message with the R flag set. 1101 The Registering Node may be the 6LN owning the IPv6 Address, or a 1102 6LBR that performs the registration on its behalf in a Route-Over 1103 mesh. 1105 The Registering Node SHOULD register all of its IPv6 Addresses to its 1106 6LR, which is the 6BBR when they are connected at Layer 2. Failure 1107 to register an address may result in the address being unreachable by 1108 other parties if the 6BBR cancels the NS(Lookup) over the LLN or to 1109 selected LLN nodes that are known to register their addresses. 1111 The Registering Node MUST refrain from using multicast NS(Lookup) 1112 when the destination is not known as on-link, e.g., if the prefix is 1113 advertised in a PIO with the L flag that is not set. In that case, 1114 the Registering Node sends its packets directly to its 6LR. 1116 The Registering Node SHOULD also follow [RFC7772] in order to limit 1117 the use of multicast RAs. It SHOULD also implement Simple Procedures 1118 for Detecting Network Attachment in IPv6 [RFC6059] (DNA procedures) 1119 to detect movements, and support Packet-Loss Resiliency for Router 1120 Solicitations [RFC7559] in order to improve reliability for the 1121 unicast RS messages. 1123 11. Security Considerations 1125 This specification applies to LLNs and a backbone in which the 1126 individual links are protected against rogue access, e.g., by 1127 authenticating a node that attaches to the network and encrypting at 1128 the MAC layer the transmissions that may be overheard. In 1129 particular, the LLN MAC is required to provide secure unicast to/from 1130 the Backbone Router and secure Broadcast from the Backbone Router in 1131 a way that prevents tampering with or replaying the RA messages. 1133 [I-D.ietf-6lo-ap-nd] guarantees the ownership of a registered address 1134 based on a proof-of-ownership encoded in the ROVR field and protects 1135 against address theft and impersonation inside the LLN, because the 1136 6LR can challenge the Registered Node for a proof-of-ownership. This 1137 method does not extend over the backbone since the 6BBR cannot 1138 provide the proof-of-ownership. A possible attack over the backbone 1139 can be done by sending an NS with an EARO and expecting the NA(EARO) 1140 back to contain the TID and ROVR fields of the existing state. With 1141 that information, the attacker can easily increase the TID and take 1142 over the Binding. 1144 12. Protocol Constants 1146 This Specification uses the following constants: 1148 TENTATIVE_DURATION: 800 milliseconds 1150 STALE_DURATION: see below 1152 In LLNs with long-lived Addresses such as LPWANs, STALE_DURATION 1153 SHOULD be configured with a relatively long value to cover an 1154 interval when the address may be reused, and before it is safe to 1155 expect that the address was definitively released. A good default 1156 value can be 24 hours. In LLNs where addresses are renewed rapidly, 1157 e.g., for privacy reasons, STALE_DURATION SHOULD be configured with a 1158 relatively shorter value, by default 5 minutes. 1160 13. IANA Considerations 1162 This document has no request to IANA. 1164 14. Acknowledgments 1166 Many thanks to Dorothy Stanley, Thomas Watteyne and Jerome Henry for 1167 their various contributions. Also many thanks to Timothy Winters and 1168 Erik Nordmark for their help, review and support in preparation to 1169 the IESG cycle, and to Kyle Rose, Elwyn Davies and Dominique Barthel 1170 for their useful contributions through the IETF last call and IESG 1171 process. 1173 15. Normative References 1175 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1176 Requirement Levels", BCP 14, RFC 2119, 1177 DOI 10.17487/RFC2119, March 1997, 1178 . 1180 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1181 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1182 2006, . 1184 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 1185 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 1186 . 1188 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1189 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1190 DOI 10.17487/RFC4861, September 2007, 1191 . 1193 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1194 Address Autoconfiguration", RFC 4862, 1195 DOI 10.17487/RFC4862, September 2007, 1196 . 1198 [RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for 1199 Detecting Network Attachment in IPv6", RFC 6059, 1200 DOI 10.17487/RFC6059, November 2010, 1201 . 1203 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1204 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1205 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1206 Low-Power and Lossy Networks", RFC 6550, 1207 DOI 10.17487/RFC6550, March 2012, 1208 . 1210 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1211 Bormann, "Neighbor Discovery Optimization for IPv6 over 1212 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1213 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1214 . 1216 [RFC7048] Nordmark, E. and I. Gashinsky, "Neighbor Unreachability 1217 Detection Is Too Impatient", RFC 7048, 1218 DOI 10.17487/RFC7048, January 2014, 1219 . 1221 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1222 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1223 May 2017, . 1225 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1226 (IPv6) Specification", STD 86, RFC 8200, 1227 DOI 10.17487/RFC8200, July 2017, 1228 . 1230 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 1231 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 1232 DOI 10.17487/RFC8201, July 2017, 1233 . 1235 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1236 Perkins, "Registration Extensions for IPv6 over Low-Power 1237 Wireless Personal Area Network (6LoWPAN) Neighbor 1238 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1239 . 1241 16. Informative References 1243 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 1244 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 1245 2006, . 1247 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 1248 DOI 10.17487/RFC4903, June 2007, 1249 . 1251 [RFC5415] Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley, 1252 Ed., "Control And Provisioning of Wireless Access Points 1253 (CAPWAP) Protocol Specification", RFC 5415, 1254 DOI 10.17487/RFC5415, March 2009, 1255 . 1257 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1258 Statement and Requirements for IPv6 over Low-Power 1259 Wireless Personal Area Network (6LoWPAN) Routing", 1260 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1261 . 1263 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 1264 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 1265 2011, . 1267 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 1268 Locator/ID Separation Protocol (LISP)", RFC 6830, 1269 DOI 10.17487/RFC6830, January 2013, 1270 . 1272 [RFC7559] Krishnan, S., Anipko, D., and D. Thaler, "Packet-Loss 1273 Resiliency for Router Solicitations", RFC 7559, 1274 DOI 10.17487/RFC7559, May 2015, 1275 . 1277 [RFC7772] Yourtchenko, A. and L. Colitti, "Reducing Energy 1278 Consumption of Router Advertisements", BCP 202, RFC 7772, 1279 DOI 10.17487/RFC7772, February 2016, 1280 . 1282 [RFC8273] Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix 1283 per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017, 1284 . 1286 [I-D.yourtchenko-6man-dad-issues] 1287 Yourtchenko, A. and E. Nordmark, "A survey of issues 1288 related to IPv6 Duplicate Address Detection", Work in 1289 Progress, Internet-Draft, draft-yourtchenko-6man-dad- 1290 issues-01, 3 March 2015, . 1293 [I-D.nordmark-6man-dad-approaches] 1294 Nordmark, E., "Possible approaches to make DAD more robust 1295 and/or efficient", Work in Progress, Internet-Draft, 1296 draft-nordmark-6man-dad-approaches-02, 19 October 2015, 1297 . 1300 [I-D.ietf-6man-rs-refresh] 1301 Nordmark, E., Yourtchenko, A., and S. Krishnan, "IPv6 1302 Neighbor Discovery Optional RS/RA Refresh", Work in 1303 Progress, Internet-Draft, draft-ietf-6man-rs-refresh-02, 1304 31 October 2016, . 1307 [I-D.ietf-6lo-ap-nd] 1308 Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 1309 "Address Protected Neighbor Discovery for Low-power and 1310 Lossy Networks", Work in Progress, Internet-Draft, draft- 1311 ietf-6lo-ap-nd-13, 6 January 2020, 1312 . 1314 [I-D.ietf-6tisch-architecture] 1315 Thubert, P., "An Architecture for IPv6 over the TSCH mode 1316 of IEEE 802.15.4", Work in Progress, Internet-Draft, 1317 draft-ietf-6tisch-architecture-28, 29 October 2019, 1318 . 1321 [I-D.ietf-mboned-ieee802-mcast-problems] 1322 Perkins, C., McBride, M., Stanley, D., Kumari, W., and J. 1323 Zuniga, "Multicast Considerations over IEEE 802 Wireless 1324 Media", Work in Progress, Internet-Draft, draft-ietf- 1325 mboned-ieee802-mcast-problems-11, 11 December 2019, 1326 . 1329 [I-D.bi-savi-wlan] 1330 Bi, J., Wu, J., Wang, Y., and T. Lin, "A SAVI Solution for 1331 WLAN", Work in Progress, Internet-Draft, draft-bi-savi- 1332 wlan-18, 17 November 2019, 1333 . 1335 [I-D.thubert-6lo-unicast-lookup] 1336 Thubert, P. and E. Levy-Abegnoli, "IPv6 Neighbor Discovery 1337 Unicast Lookup", Work in Progress, Internet-Draft, draft- 1338 thubert-6lo-unicast-lookup-00, 25 January 2019, 1339 . 1342 [IEEEstd8021] 1343 IEEE standard for Information Technology, "IEEE Standard 1344 for Information technology -- Telecommunications and 1345 information exchange between systems Local and 1346 metropolitan area networks Part 1: Bridging and 1347 Architecture". 1349 [IEEEstd80211] 1350 IEEE standard for Information Technology, "IEEE Standard 1351 for Information technology -- Telecommunications and 1352 information exchange between systems Local and 1353 metropolitan area networks-- Specific requirements Part 1354 11: Wireless LAN Medium Access Control (MAC) and Physical 1355 Layer (PHY) Specifications". 1357 [IEEEstd802151] 1358 IEEE standard for Information Technology, "IEEE Standard 1359 for Information Technology - Telecommunications and 1360 Information Exchange Between Systems - Local and 1361 Metropolitan Area Networks - Specific Requirements. - Part 1362 15.1: Wireless Medium Access Control (MAC) and Physical 1363 Layer (PHY) Specifications for Wireless Personal Area 1364 Networks (WPANs)". 1366 [IEEEstd802154] 1367 IEEE standard for Information Technology, "IEEE Standard 1368 for Local and metropolitan area networks -- Part 15.4: 1369 Low-Rate Wireless Personal Area Networks (LR-WPANs)". 1371 Appendix A. Possible Future Extensions 1373 With the current specification, the 6LBR is not leveraged to avoid 1374 multicast NS(Lookup) on the Backbone. This could be done by adding a 1375 lookup procedure in the EDAR/EDAC exchange. 1377 By default the specification does not have a trust model, e.g., 1378 whereby nodes that associate their address with a proof-of-ownership 1379 [I-D.ietf-6lo-ap-nd] should be more trusted than nodes that do not. 1380 Such a trust model and related signaling could be added in the future 1381 to override the default operation and favor trusted nodes. 1383 Future documents may extend this specification by allowing the 6BBR 1384 to redistribute Host routes in routing protocols that would operate 1385 over the Backbone, or in MIPv6, or FMIP, or the Locator/ID Separation 1386 Protocol (LISP) [RFC6830] to support mobility on behalf of the 6LNs, 1387 etc... LISP may also be used to provide an equivalent to the EDAR/ 1388 EDAC exchange using a Map Server / Map Resolver as a replacement to 1389 the 6LBR. 1391 Appendix B. Applicability and Requirements Served 1393 This document specifies proxy-ND functions that can be used to 1394 federate an IPv6 Backbone Link and multiple IPv6 LLNs into a single 1395 Multi-Link Subnet. The proxy-ND functions enable IPv6 ND services 1396 for Duplicate Address Detection (DAD) and Address Lookup that do not 1397 require broadcasts over the LLNs. 1399 The term LLN is used to cover multiple types of WLANs and WPANs, 1400 including (Low-Power) Wi-Fi, BLUETOOTH(R) Low Energy, IEEE STD 1401 802.11ah and IEEE STD.802.15.4 wireless meshes, covering the types of 1402 networks listed in Appendix B.3 of [RFC8505] "Requirements Related to 1403 Various Low-Power Link Types". 1405 Each LLN in the subnet is attached to an IPv6 Backbone Router (6BBR). 1406 The Backbone Routers interconnect the LLNs and advertise the 1407 Addresses of the 6LNs over the Backbone Link using proxy-ND 1408 operations. 1410 This specification updates IPv6 ND over the Backbone to distinguish 1411 Address movement from duplication and eliminate stale state in the 1412 Backbone routers and Backbone nodes once a 6LN has roamed. This way, 1413 mobile nodes may roam rapidly from one 6BBR to the next and 1414 requirements in Appendix B.1 of [RFC8505] "Requirements Related to 1415 Mobility" are met. 1417 A 6LN can register its IPv6 Addresses and thereby obtain proxy-ND 1418 services over the Backbone, meeting the requirements expressed in 1419 Appendix B.4 of [RFC8505], "Requirements Related to Proxy 1420 Operations". 1422 The impact if the IPv6 ND operation is limited to one of the 1423 federated LLNs, enabling the number of 6LNs to grow. The Routing 1424 Proxy operation avoids the need to expose the MAC addresses of the 1425 6LNs onto the backbone, keeping the Layer 2 topology simple and 1426 stable. This meets the requirements in Appendix B.6 of [RFC8505] 1427 "Requirements Related to Scalability", as long has the 6BBRs are 1428 dimensioned for the number of registrations that each needs to 1429 support. 1431 In the case of a Wi-Fi access link, a 6BBR may be collocated with the 1432 Access Point (AP), or with a Fabric Edge (FE) or a CAPWAP [RFC5415] 1433 Wireless LAN Controller (WLC). In those cases, the wireless client 1434 (STA) is the 6LN that makes use of [RFC8505] to register its IPv6 1435 Address(es) to the 6BBR acting as Routing Registrar. The 6LBR can be 1436 centralized and either connected to the Backbone Link or reachable 1437 over IP. The 6BBR proxy-ND operations eliminate the need for 1438 wireless nodes to respond synchronously when a Lookup is performed 1439 for their IPv6 Addresses. This provides the function of a Sleep 1440 Proxy for ND [I-D.nordmark-6man-dad-approaches]. 1442 For the TimeSlotted Channel Hopping (TSCH) mode of [IEEEstd802154], 1443 the 6TiSCH architecture [I-D.ietf-6tisch-architecture] describes how 1444 a 6LoWPAN ND host could connect to the Internet via a RPL mesh 1445 Network, but doing so requires extensions to the 6LOWPAN ND protocol 1446 to support mobility and reachability in a secure and manageable 1447 environment. The extensions detailed in this document also work for 1448 the 6TiSCH architecture, serving the requirements listed in 1449 Appendix B.2 of [RFC8505] "Requirements Related to Routing 1450 Protocols". 1452 The registration mechanism may be seen as a more reliable alternate 1453 to snooping [I-D.bi-savi-wlan]. It can be noted that registration 1454 and snooping are not mutually exclusive. Snooping may be used in 1455 conjunction with the registration for nodes that do not register 1456 their IPv6 Addresses. The 6BBR assumes that if a node registers at 1457 least one IPv6 Address to it, then the node registers all of its 1458 Addresses to the 6BBR. With this assumption, the 6BBR can possibly 1459 cancel all undesirable multicast NS messages that would otherwise 1460 have been delivered to that node. 1462 Scalability of the Multi-Link Subnet [RFC4903] requires avoidance of 1463 multicast/broadcast operations as much as possible even on the 1464 Backbone [I-D.ietf-mboned-ieee802-mcast-problems]. Although hosts 1465 can connect to the Backbone using IPv6 ND operations, multicast RAs 1466 can be saved by using [I-D.ietf-6man-rs-refresh], which also requires 1467 the support of [RFC7559]. 1469 Authors' Addresses 1471 Pascal Thubert (editor) 1472 Cisco Systems, Inc 1473 Building D 1474 45 Allee des Ormes - BP1200 1475 06254 MOUGINS - Sophia Antipolis 1476 France 1478 Phone: +33 497 23 26 34 1479 Email: pthubert@cisco.com 1481 Charles E. Perkins 1482 Blue Meadow Networking 1483 Saratoga, 95070 1484 United States of America 1486 Email: charliep@computer.org 1488 Eric Levy-Abegnoli 1489 Cisco Systems, Inc 1490 Building D 1491 45 Allee des Ormes - BP1200 1492 06254 MOUGINS - Sophia Antipolis 1493 France 1495 Phone: +33 497 23 26 20 1496 Email: elevyabe@cisco.com