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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 8, 2019 E. Levy-Abegnoli 7 Cisco Systems 8 February 4, 2019 10 IPv6 Backbone Router 11 draft-ietf-6lo-backbone-router-11 13 Abstract 15 This document updates RFC 4861 and RFC 8505 in order to enable proxy 16 services for IPv6 Neighbor Discovery by Routing Registrars called 17 Backbone Routers. Backbone Routers are placed along the wireless 18 edge of a Backbone, and federate multiple wireless links to form a 19 single MultiLink Subnet. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at https://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on August 8, 2019. 38 Copyright Notice 40 Copyright (c) 2019 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (https://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 57 2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 2.2. New Terms . . . . . . . . . . . . . . . . . . . . . . . . 5 59 2.3. Acronym Definitions . . . . . . . . . . . . . . . . . . . 6 60 2.4. References . . . . . . . . . . . . . . . . . . . . . . . 7 61 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7 62 3.1. Updating RFC 6775 and RFC 8505 . . . . . . . . . . . . . 9 63 3.2. Access Link . . . . . . . . . . . . . . . . . . . . . . . 10 64 3.3. Route-Over Mesh . . . . . . . . . . . . . . . . . . . . . 11 65 3.4. The Binding Table . . . . . . . . . . . . . . . . . . . . 12 66 3.5. Primary and Secondary 6BBRs . . . . . . . . . . . . . . . 13 67 3.6. Using Optimistic DAD . . . . . . . . . . . . . . . . . . 14 68 4. MultiLink Subnet Considerations . . . . . . . . . . . . . . . 14 69 5. Optional 6LBR serving the MultiLink Subnet . . . . . . . . . 15 70 6. Using IPv6 ND Over the Backbone Link . . . . . . . . . . . . 15 71 7. Routing Proxy Operations . . . . . . . . . . . . . . . . . . 16 72 8. Bridging Proxy Operations . . . . . . . . . . . . . . . . . . 17 73 9. Creating and Maintaining a Binding . . . . . . . . . . . . . 18 74 9.1. Operation on a Binding in Tentative State . . . . . . . . 19 75 9.2. Operation on a Binding in Reachable State . . . . . . . . 20 76 9.3. Operation on a Binding in Stale State . . . . . . . . . . 21 77 10. Registering Node Considerations . . . . . . . . . . . . . . . 22 78 11. Security Considerations . . . . . . . . . . . . . . . . . . . 23 79 12. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 23 80 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 81 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 82 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 83 15.1. Normative References . . . . . . . . . . . . . . . . . . 24 84 15.2. Informative References . . . . . . . . . . . . . . . . . 25 85 Appendix A. Possible Future Extensions . . . . . . . . . . . . . 28 86 Appendix B. Applicability and Requirements Served . . . . . . . 28 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30 89 1. Introduction 91 IEEE STD. 802.1 [IEEEstd8021] Ethernet Bridging provides an efficient 92 and reliable broadcast service for wired networks; applications and 93 protocols have been built that heavily depend on that feature for 94 their core operation. Unfortunately, Low-Power Lossy Networks (LLNs) 95 and local wireless networks generally do not provide the broadcast 96 capabilities of Ethernet Bridging in an economical fashion. 98 As a result, protocols designed for bridged networks that rely on 99 multicast and broadcast often exhibit disappointing behaviours when 100 employed unmodified on a local wireless medium (see 101 [I-D.ietf-mboned-ieee802-mcast-problems]). 103 Wi-Fi [IEEEstd80211] Access Points (APs) deployed in an Extended 104 Service Set (ESS) act as Ethernet Bridges [IEEEstd8021], with the 105 property that the bridging state is established at the time of 106 association. This ensures connectivity to the node (STA) and 107 protects the wireless medium against broadcast-intensive Transparent 108 Bridging reactive Lookups. In other words, the association process 109 is used to register the MAC Address of the STA to the AP. The AP 110 subsequently proxies the bridging operation and does not need to 111 forward the broadcast Lookups over the radio. 113 Like Transparent Bridging, IPv6 [RFC8200] Neighbor Discovery 114 [RFC4861] [RFC4862] Protocol (IPv6 ND) is a reactive protocol, based 115 on multicast transmissions to locate an on-link correspondent and 116 ensure the uniqueness of an IPv6 address. The mechanism for 117 Duplicate Address Detection (DAD) [RFC4862] was designed for the 118 efficient broadcast operation of Ethernet Bridging. Since broadcast 119 can be unreliable over wireless media, DAD often fails to discover 120 duplications [I-D.yourtchenko-6man-dad-issues]. In practice, IPv6 121 addresses very rarely conflict because of the entropy of the 64-bit 122 Interface IDs, not because address duplications are detected and 123 resolved. 125 The IPv6 ND Neighbor Solicitation (NS) [RFC4861] message is used for 126 DAD and address Lookup when a node moves, or wakes up and reconnects 127 to the wireless network. The NS message is targeted to a Solicited- 128 Node Multicast Address (SNMA) [RFC4291] and should in theory only 129 reach a very small group of nodes. But in reality, IPv6 multicast 130 messages are typically broadcast on the wireless medium, and so they 131 are processed by most of the wireless nodes over the subnet (e.g., 132 the ESS fabric) regardless of how few of the nodes are subscribed to 133 the SNMA. As a result, IPv6 ND address Lookups and DADs over a large 134 wireless and/or a LowPower Lossy Network (LLN) can consume enough 135 bandwidth to cause a substantial degradation to the unicast traffic 136 service. 138 Because IPv6 ND messages sent to the SNMA group are broadcasted at 139 the radio MAC Layer, wireless nodes that do not belong to the SNMA 140 group still have to keep their radio turned on to listen to multicast 141 NS messages, which is a total waste of energy for them. In order to 142 reduce their power consumption, certain battery-operated devices such 143 as IoT sensors and smartphones ignore some of the broadcasts, making 144 IPv6 ND operations even less reliable. 146 These problems can be alleviated by reducing the IPv6 ND broadcasts 147 over wireless access links. This has been done by splitting the 148 broadcast domains and routes between subnets, or even by assigning a 149 /64 prefix to each wireless node (see [RFC8273]). 151 Another way is to proxy at the boundary of the wired and wireless 152 domains the Layer-3 protocols that rely on MAC Layer broadcast 153 operations. For instance, IEEE 802.11 [IEEEstd80211] situates proxy- 154 ARP (IPv4) and proxy-ND (IPv6) functions at the Access Points (APs). 155 The 6BBR provides a proxy-ND function and can be extended for proxy- 156 ARP in a continuation specification. 158 IPv6 proxy-ND services can be obtained by snooping the IPV6 ND 159 protocol (see [I-D.bi-savi-wlan]). Proprietary techniques for IPv6 160 ND and DHCP snooping have been used; although snooping does eliminate 161 undesirable broadcast transmissions, it has been found to be 162 unreliable. An IPv6 address may not be discovered immediately due to 163 a packet loss, or if a "silent" node is not currently using one of 164 its addresses. A change of state (e.g. due to movement) may be 165 missed or misordered, leading to unreliable connectivity and 166 incomplete knowledge of the state of the network. 168 This specification defines the 6BBR as a Routing Registrar [RFC8505] 169 that provide proxy services for IPv6 Neighbor Discovery. Backbone 170 Routers federate multiple LLNs over a Backbone Link to form a 171 MultiLink Subnet (MLSN). Backbone Routers placed along the LLN edge 172 of the Backbone handle IPv6 Neighbor Discovery, and forward packets 173 on behalf of registered nodes. 175 An LLN node (6LN) registers all its IPv6 Addresses using an NS(EARO) 176 as specified in [RFC8505] to the 6BBR. The 6BBR is also a Border 177 Router that performs IPv6 Neighbor Discovery (IPv6 ND) operations on 178 its Backbone interface on behalf of the 6LNs that have registered 179 addresses on its LLN interfaces without the need of a broadcast over 180 the wireless medium. Additional benefits are discussed in 181 Appendix B. 183 2. Terminology 185 2.1. BCP 14 187 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 188 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 189 "OPTIONAL" in this document are to be interpreted as described in BCP 190 14 [RFC2119] [RFC8174] when, and only when, they appear in all 191 capitals, as shown here. 193 2.2. New Terms 195 This document introduces the following terminology: 197 Federated 199 A subnet that comprises a Backbone and one or more (wireless) 200 access links, is said to be federated into one MultiLink 201 Subnet. The proxy-ND operation of 6BBRs over the Backbone and 202 the access links provides the appearance of a subnet for IPv6 203 ND. 205 Sleeping Proxy 207 A 6BBR acts as a Sleeping Proxy if it answers ND Neighbor 208 Solicitations over the Backbone on behalf of a Registered Node. 210 Routing Proxy 212 A Routing Proxy provides IPv6 ND proxy functions and enables 213 the MLSN operation over federated links that may not be 214 compatible for bridging. The Routing Proxy advertises its own 215 MAC Address as the TLLA in the proxied NAs over the Backbone, 216 and routes at the Network Layer between the federated links. 218 Bridging Proxy 220 A Bridging Proxy provides IPv6 ND proxy functions while 221 preserving forwarding continuity at the MAC Layer. The 222 Bridging Proxy advertises the MAC Address of the Registering 223 Node as the TLLA in the proxied NAs over the Backbone. In that 224 case, the MAC Address and the mobility of 6LN is still visible 225 across the bridged Backbone, and the 6BR may be configured to 226 proxy for Link Local Addresses. 228 Binding Table 230 The Binding Table is an abstract database that is maintained by 231 the 6BBR to store the state associated with its registrations. 233 Binding 235 A Binding is an abstract state associated to one registration, 236 in other words one entry in the Binding Table. 238 2.3. Acronym Definitions 240 This document uses the following acronyms: 242 6BBR: 6LoWPAN Backbone Router 244 6LBR: 6LoWPAN Border Router 246 6LN: 6LoWPAN Node 248 6LR: 6LoWPAN Router 250 6CIO: Capability Indication Option 252 ARO: Address Registration Option 254 DAC: Duplicate Address Confirmation 256 DAD: Duplicate Address Detection 258 DAR: Duplicate Address Request 260 EDAC: Extended Duplicate Address Confirmation 262 EDAR: Extended Duplicate Address Request 264 DODAG: Destination-Oriented Directed Acyclic Graph 266 LLN: Low-Power and Lossy Network 268 NA: Neighbor Advertisement 270 NCE: Neighbor Cache Entry 272 ND: Neighbor Discovery 274 NDP: Neighbor Discovery Protocol 276 NS: Neighbor Solicitation 278 ROVR: Registration Ownership Verifier 280 RPL: IPv6 Routing Protocol for LLNs 282 RA: Router Advertisement 284 RS: Router Solicitation 285 TID: Transaction ID 287 2.4. References 289 In this document, readers will encounter terms and concepts that are 290 discussed in the following documents: 292 o "Neighbor Discovery for IP version 6" [RFC4861], "IPv6 Stateless 293 Address Autoconfiguration" [RFC4862] and "Optimistic Duplicate 294 Address Detection" [RFC4429], 296 o "Neighbor Discovery Proxies (proxy-ND)" [RFC4389] and "MultiLink 297 Subnet Issues" [RFC4903], 299 o "Problem Statement and Requirements for IPv6 over Low-Power 300 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606], and 302 o Neighbor Discovery Optimization for Low-Power and Lossy Networks 303 [RFC6775] and "Registration Extensions for 6LoWPAN Neighbor 304 Discovery" [RFC8505]. 306 3. Overview 308 Figure 1 illustrates backbone link federating a collection of LLNs as 309 a single IPv6 Subnet, with a number of 6BBRs providing proxy-ND 310 services to their attached LLNs. 312 | 313 +-----+ +-----+ +-----+ 314 (default) | | (Optional) | | | | IPv6 315 Router | | 6LBR | | | | Node 316 +-----+ +-----+ +-----+ 317 | Backbone side | | 318 ----+-------+-----------------+---+-------------+----+----- 319 | | | 320 +------+ +------+ +------+ 321 | 6BBR | | 6BBR | | 6BBR | 322 | | | | | | 323 +------+ +------+ +------+ 324 o Wireless side o o o o o 325 o o o o o o o o o o o o o o 326 o o o o o o o o o o o o o o o 327 o o o o o o o o o o 328 o o o o o o o 330 LLN LLN LLN 332 Figure 1: Backbone Link and Backbone Routers 334 The LLN may be a hub-and-spoke access link such as (Low-Power) IEEE 335 STD. 802.11 (Wi-Fi) [IEEEstd80211] and IEEE STD. 802.15.1 (Bluetooth) 336 [IEEEstd802151], or a Mesh-Under or a Route-Over network [RFC8505]. 337 The proxy state can be distributed across multiple 6BBRs attached to 338 the same Backbone. 340 The main features of a 6BBR are as follows: 342 o Multilink-subnet functions (provided by the 6BBR on the backbone) 343 performed on behalf of registered 6LNs, and 345 o Routing registrar services that reduce multicast within the LLN: 347 * Binding Table management 349 * failover, e.g., due to mobility 351 Each Backbone Router (6BBR) maintains a data structure for its 352 Registered Nodes called a Binding Table. The combined Binding Tables 353 of all the 6BBRs on a backbone form a distributed database of 6LNs 354 that reside in the LLNs or on the IPv6 Backbone. 356 Unless otherwise configured, a 6BBR does the following: 358 o Create a new entry in a Binding Table for a new Registered Address 359 and ensure that the Address is not duplicated over the Backbone 361 o Defend a Registered Address over the Backbone using NA messages on 362 behalf of the sleeping 6LN 364 o Advertise a Registered Address over the Backbone using NA 365 messages, asynchronously or as a response to a Neighbor 366 Solicitation messages. 368 o Deliver packets arriving from the LLN, using Neighbor Solicitation 369 messages to look up the destination over the Backbone. 371 o Forward or bridge packets between the LLN and the Backbone. 373 o Verify liveness for a registration, when needed. 375 The first of these functions enables the 6BBR to fulfill its role as 376 a Routing Registrar for each of its attached LLNs. The remaining 377 functions fulfill the role of the 6BBRs as the border routers 378 connecting the Multi-link IPv6 subnet to the Internet. 380 The proxy-ND operation can co-exist with IPv6 ND over the Backbone. 382 The 6BBR may co-exist with a proprietary snooping or a traditional 383 bridging functionality in an Access Point, in order to support legacy 384 nodes that do not support this specification. In the case, the co- 385 existing function may turn multicastsinto a series of unicast to the 386 legacy nodes. 388 The registration to a proxy service uses an NS/NA(EARO) exchange. 389 The 6BBR operation resembles that of a Mobile IPv6 (MIPv6) [RFC6275] 390 Home Agent (HA). The combination of a 6BBR and a MIPv6 HA enables 391 full mobility support for 6LNs, inside and outside the links that 392 form the subnet. 394 The 6BBRs use the Extended Address Registration Option (EARO) defined 395 in [RFC8505] as follows: 397 o The EARO is used in the IPv6 ND exchanges over the Backbone 398 between the 6BBRs to help distinguish duplication from movement. 399 Extended Duplicate Address Messages (EDAR and EDAC) MAY also be 400 used with a 6LBR, if one is present, and the 6BBR. Address 401 duplication is detected using the ROVR field. Conflicting 402 registrations to different 6BBRs for the same Registered Address 403 are resolved using the TID field. 405 o The Link Layer Address (LLA) that the 6BBR advertises for the 406 Registered Address on behalf of the Registered Node over the 407 Backbone can belong to the Registering Node; in that case, the 408 6BBR (acting as a Bridging Proxy (see Section 8)) bridges the 409 unicast packets. Alternatively, the LLA can be that of the 6BBR 410 on the Backbone interface, in which case the 6BBR (acting as a 411 Routing Proxy(see Section 7)) receives the unicast packets at 412 Layer-3 and routes over. 414 3.1. Updating RFC 6775 and RFC 8505 416 This specification adds the EARO as a possible option in RS, NS(DAD) 417 and NA messages over the backbone. [RFC8505] requires that the 418 registration NS(EARO) contains an SLLAO. This specification details 419 the use of those messages over the backbone. 421 Note: [RFC6775] requires that the registration NS(EARO) contains an 422 SLLAO and [RFC4862] that the NS(DAD) is sent from the unspecified 423 address for which there cannot be a SLLAO. Consequently, an NS(DAD) 424 cannot be confused with a registration. 426 This specification adds the capability to insert IPv6 ND options in 427 the EDAR and EDAC messages. In particular, a 6BBR acting as a 6LR 428 for the Registered Address can insert an SLLAO in the EDAR to the 429 6LBR in order to avoid a Lookup back. This enables the 6LBR to store 430 the MAC address associated to the Registered Address on a Link and to 431 serve as a mapping server as described in 432 [I-D.thubert-6lo-unicast-lookup]. 434 3.2. Access Link 436 Figure 2 illustrates a flow where 6LN forms an IPv6 Address and 437 registers it to a 6BBR acting as a 6LR [RFC8505]. The 6BBRs applies 438 ODAD (see Section 3.6) to the registered address to enable 439 connectivity while the message flow is still in progress. In that 440 example, a 6LBR is deployed on the backbone link to serve the whole 441 subnet, and EDAR / EDAC messages are used in combination with DAD to 442 enable coexistence with IPv6 ND over the backbone. 444 6LN(STA) 6BBR(AP) 6LBR default GW 445 | | | | 446 | LLN Access Link | IPv6 Backbone (e.g., Ethernet) | 447 | | | | 448 | RS(multicast) | | | 449 |---------------->| | | 450 | RA(PIO, Unicast)| | | 451 |<----------------| | | 452 | NS(EARO) | | | 453 |---------------->| | | 454 | | Extended DAR | | 455 | |--------------->| | 456 | | Extended DAC | | 457 | |<---------------| | 458 | | | 459 | | NS-DAD(EARO, multicast) | 460 | |--------> | 461 | |-------------------------------->| 462 | | | 463 | | RS(no SLLAO, for ODAD) | 464 | |-------------------------------->| 465 | | (if no fresher Binding) NS(Lookup) | 466 | | <-------------| 467 | |<--------------------------------| 468 | | NA(SLLAO, not(O), EARO) | 469 | |-------------------------------->| 470 | | RA(unicast) | 471 | |<--------------------------------| 472 | | | 473 | IPv6 Packets in optimistic mode | 474 |<------------------------------------------------->| 475 | | | 476 | | 477 | NA(EARO) | 478 |<----------------| 479 | | 481 Figure 2: Initial Registration Flow to a 6BBR acting as Routing Proxy 483 3.3. Route-Over Mesh 485 Figure 3 illustrates IPv6 signaling that enables a 6LN to form a 486 Global or a Unique-Local Address and register it to the 6LBR that 487 serves its LLN using [RFC8505]. The 6LBR (acting as Registering 488 Node) proxies the registration to the 6BBR, using [RFC8505] to 489 register the addresses the 6LN (Registered Node) on its behalf to the 490 6BBR, and obtain proxy-ND services from the 6BBR. 492 6LoWPAN Node 6LR 6LBR 6BBR 493 (mesh leaf) (mesh router) (mesh root) 494 | | | | 495 | 6LoWPAN ND |6LoWPAN ND | 6LoWPAN ND | IPv6 ND 496 | LLN link |Route-Over mesh|Ethernet/serial| Backbone 497 | | |/Internal call | 498 | IPv6 ND RS | | | 499 |-------------->| | | 500 |-----------> | | | 501 |------------------> | | 502 | IPv6 ND RA | | | 503 |<--------------| | | 504 | | | | 505 | NS(EARO) | | | 506 |-------------->| | | 507 | 6LoWPAN ND | Extended DAR | | 508 | |-------------->| | 509 | | | NS(EARO) | 510 | | |-------------->| 511 | | | (proxied) | NS-DAD 512 | | | |------> 513 | | | | (EARO) 514 | | | | 515 | | | NA(EARO) | 516 | | |<--------------| 517 | | Extended DAC | | 518 | |<--------------| | 519 | NA(EARO) | | | 520 |<--------------| | | 521 | | | | 523 Figure 3: Initial Registration Flow over Route-Over Mesh 525 As a non-normative example of a Route-Over Mesh, the 6TiSCH 526 architecture [I-D.ietf-6tisch-architecture] suggests using RPL 527 [RFC6550] and collocating the RPL root with a 6LBR that serves the 528 LLN, and is either collocated with or connected to the 6BBR over an 529 IPv6 Link. 531 3.4. The Binding Table 533 Addresses in a LLN that are reachable from the Backbone by way of the 534 6BBR function must be registered to that 6BBR, using an NS(EARO) with 535 the R flag set [RFC8505]. A 6BBR maintains a state for its active 536 registrations in an abstract Binding Table. 538 An entry in the Binding Table is called a "Binding". A Binding may 539 be in Tentative, Reachable or Stale state. 541 The 6BBR uses a combination of [RFC8505] and IPv6 ND over the 542 Backbone to advertise the registration and avoid a duplication. 543 Conflicting registrations are solved by the 6BBRs transparently to 544 the Registering Nodes. 546 Only one 6LN may register a given Address, but the Address may be 547 registered to Multiple 6BBRs for higher availability. 549 Over the LLN, Binding Table management is as follows: 551 o De-registrations (newer TID, same ROVR, null Lifetime) are 552 accepted with a status of 4 ("Removed"); the entry is deleted; 554 o Newer registrations (newer TID, same ROVR, non-null Lifetime) are 555 accepted with a status of 0 (Success); the Binding is updated with 556 the new TID, the Registration Lifetime and the Registering Node; 557 in Tentative state the EDAC response is held and may be 558 overwritten; in other states the Registration Lifetime timer is 559 restarted and the entry is placed in Reachable state. 561 o Identical registrations (same TID, same ROVR) from a same 562 Registering Node are accepted with a status of 0 (Success). In 563 Tentative state, the response is held and may be overwritten, but 564 the response MUST be eventually produced, carrying the result of 565 the DAD process; 567 o Older registrations (older TID, same ROVR) from the same 568 Registering Node are discarded; 570 o Identical and older registrations (not-newer TID, same ROVR) from 571 a different Registering Node are rejected with a status of 3 572 (Moved); this may be rate limited to avoid undue interference; 574 o Any registration for the same address but with a different ROVR is 575 rejected with a status of 1 (Duplicate). 577 3.5. Primary and Secondary 6BBRs 579 A same address may be successfully registered to more than one 6BBR, 580 in which case the Registering Node uses the same EARO in all the 581 parallel registrations. To allow for this, ND(DAD) and NA messages 582 with an EARO that indicate an identical Binding in another 6BBR (same 583 Registered address, same TID, same ROVR) as silently ignored. 585 A 6BBR MAY optionally be primary or secondary. The primary is the 586 6BBR that has the highest EUI-64 Address of all the 6BBRs that share 587 a registration for the same Registered Address, with the same ROVR 588 and same Transaction ID, the EUI-64 Address being considered as an 589 unsigned 64bit integer. A given 6BBR can be primary for a given 590 Address and secondary for another Address, regardless of whether or 591 not the Addresses belong to the same 6LN. 593 In the following sections, is is expected that an NA is sent over the 594 backbone only if the node is primary or does not support the concept 595 of primary. More than one 6BBR claiming or defending an address 596 generates unwanted traffic but no reachability issue since all 6BBRs 597 provide reachability from the Backbone to the 6LN. 599 3.6. Using Optimistic DAD 601 Optimistic Duplicate Address Detection [RFC4429] (ODAD) specifies how 602 an IPv6 Address can be used before completion of Duplicate Address 603 Detection (DAD). ODAD guarantees that this behavior will not cause 604 harm if the new Address is a duplicate. 606 Support for ODAD avoids delays in installing the Neighbor Cache Entry 607 (NCE) in the 6BBRs and the default router, enabling immediate 608 connectivity to the registered node. As shown in Figure 2, if the 609 6BBR is aware of the Link-Layer Address (LLA) of a router, then the 610 6BBR sends a Router Solicitation (RS), using the Registered Address 611 as the IP Source Address, to the known router(s). The RS MUST be 612 sent without a Source LLA Option (SLLAO), to avoid invalidating a 613 preexisting NCE in the router. 615 Following ODAD, the router may then send a unicast RA to the 616 Registered Address, and it may resolve that Address using an 617 NS(Lookup) message. In response, the 6BBR sends an NA with an EARO 618 and the Override (O) flag [RFC4861] that is not set. The router can 619 then determine the freshest EARO in case of a conflicting NA(EARO) 620 messages, using the method described in section 5.2.1 of [RFC8505]. 621 If the NA(EARO) is the freshest answer, the default router creates a 622 Binding with the SLLAO of the 6BBR (in Routing Proxy mode) or that of 623 the Registering Node (in Bridging Proxy mode) so that traffic from/to 624 the Registered Address can flow immediately. 626 4. MultiLink Subnet Considerations 628 The Backbone and the federated LLN Links are considered as different 629 links in the MultiLink Subnet, even if multiple LLNs are attached to 630 the same 6BBR. ND messages are link-scoped and are not forwarded by 631 the 6BBR between the backbone and the LLNs though some packets may be 632 reinjected in Bridging Proxy mode (see Section 8). 634 Nodes located inside the subnet do not perform the IPv6 Path MTU 635 Discovery [RFC8201]. For that reason, the MTU must have a same value 636 on the Backbone and all attached LLNs. To achieve this, the 6BBR 637 MUST use the same MTU value in RAs over the Backbone and in the RAs 638 that it transmits towards the LLN links. 640 5. Optional 6LBR serving the MultiLink Subnet 642 A 6LBR can be deployed to serve the whole MLSN. It may be attached 643 to the backbone, in which case it can be discovered by its capability 644 advertisement (see section 4.3. of [RFC8505]) in RA messages. 646 When a 6LBR is present, the 6BBR uses an EDAR/EDAC message exchange 647 with the 6LBR to check for duplication or movement. This is done 648 prior to the NS(DAD) process, which may be avoided of the 6LBR 649 already maintains a conflicting state for the Registered Address. 651 This specification enables an address to be registered to more than 652 one 6BBR. It results that a 6LBR MUST be capable to maintain a state 653 for each of the 6BBR having registered with a same TID and same ROVR. 655 If this registration is duplicate or not the freshest, then the 6LBR 656 replies with an EDAC message with a status code of 1 ("Duplicate 657 Address") or 3 ("Moved"), respectively. If this registration is the 658 freshest, then the 6LBR replies with a status code of 0. In that 659 case, if this registration is fresher than an existing registration 660 for another 6BBR, then the 6LBR also sends an asynchronous EDAC with 661 a status of 4 ("Removed") to that other 6BBR. 663 The EDAC message SHOULD carry the SLLAO used in NS messages by the 664 6BBR for that Binding, and the EDAR message SHOULD carry the TLLAO 665 associated with the currently accepted registration. This enables a 666 6BBR to locate the new position of a mobile 6LN in the case of a 667 Routing Proxy operation, and opens the capability for the 6LBR to 668 serve as a mapping server in the future. 670 Note that if Link Local addresses are registered, then the scope of 671 uniqueness on which the address duplication is checked is the total 672 collection of links that the 6LBR serves as opposed to the sole link 673 on which the Link Local address is assigned. 675 6. Using IPv6 ND Over the Backbone Link 677 On the Backbone side, the 6BBR MUST join the SNMA group corresponding 678 to a Registered Address as soon as it creates a Binding for that 679 Address, and maintain that SNMA membership as long as it maintains 680 the registration. 682 The 6BBR uses either the SNMA or plain unicast to defend the 683 Registered Addresses in its Binding Table over the Backbone (as 684 specified in [RFC4862]). 686 The 6BBR advertises and defends the Registered Addresses over the 687 Backbone Link using RS, NS(DAD) and NA messages with the Registered 688 Address as the Source or Target address, respectively. 690 The 6BBR MUST place an EARO in the IPv6 ND messages that it generates 691 on behalf of the Registered Node. Note that an NS(DAD) does not 692 contain an SLLAO and cannot be confused with a proxy registration 693 such as performed by a 6LBR. 695 An NA message generated in response to an NS(DAD) MUST have the 696 Override flag set and a status of 1 (Duplicate) or 3 (Moved) in the 697 EARO. An NA message generated in response to an NS(Lookup) or an 698 NS(NUD) MUST NOT have the Override flag set. 700 This specification enables proxy operation for the IPv6 ND resolution 701 of LLN devices and a prefix that is used across a MultiLink Subnet 702 MAY be advertised as on-link over the Backbone. This is done for 703 backward compatibility with existing IPv6 hosts by setting the L flag 704 in the Prefix Information Option (PIO) of RA messages [RFC4861]. 706 For movement involving a slow reattachment, the Neighbor 707 Unreachability Detection (NUD) defined in [RFC4861] may time out too 708 quickly. Nodes on the backbone SHOULD support [RFC7048] whenever 709 possible. 711 7. Routing Proxy Operations 713 A Routing Proxy provides IPv6 ND proxy functions for Global and 714 Unique Local addresses between the LLN and the backbone, but not for 715 Link-Local addresses. It operates as an IPv6 border router and 716 provides a full Link-Layer isolation. 718 In this mode, it is not required that the MAC addresses of the 6LNs 719 are visible at Layer-2 over the Backbone. It is thus useful when the 720 messaging over the Backbone that is associated to wireless mobility 721 becomes expensive, e.g., when the Layer-2 topology is virtualized 722 over a wide area IP underlay. 724 This mode is definitely required when the LLN uses a MAC address 725 format that is different from that on the Backbone (e.g., EUI-64 vs. 726 EUI-48). Since a 6LN may not be able to resolve an arbitrary 727 destination in the MLSN directly, the MLSN prefix MUST NOT be 728 advertised as on-link in RA messages sent towards the LLN. 730 In order to maintain IP connectivity, the 6BBR installs a connected 731 Host route to the Registered Address on the LLN interface, via the 732 Registering Node as identified by the Source Address and the SLLA 733 option in the NS(EARO) messages. 735 When operating as a Routing Proxy, the 6BBR MUST use its Layer-2 736 Address on its Backbone Interface in the SLLAO of the RS messages and 737 the TLLAO of the NA messages that it generates to advertise the 738 Registered Addresses. 740 For each Registered Address, multiple peers on the Backbone may have 741 resolved the Address with the 6BBR MAC Address, maintaining that 742 mapping in their Neighbor Cache. The 6BBR SHOULD maintain a list of 743 the peers on the Backbone which have associated its MAC Address with 744 the Registered Address. If that Registered Address moves to a new 745 6BBR, the previous 6BBR SHOULD unicast a gratuitous NA with the 746 Override flag set to each such peer, to supply the LLA of the new 747 6BBR in the TLLA option for the Address. A 6BBR that does not 748 maintain this list MAY multicast a gratuitous NA with the Override 749 flag; this NA will possibly hit all the nodes on the Backbone, 750 whether or not they maintain an NCE for the Registered Address. 752 If a correspondent fails to receive the gratuitous NA, it will keep 753 sending traffic to a 6BBR to which the node was previously 754 registered. Since the previous 6BBR removed its Host route to the 755 Registered Address, it will look up the address over the backbone, 756 resolve the address with the LLA of the new 6BBR, and forward the 757 packet to the correct 6BBR. The previous 6BBR SHOULD also issue a 758 redirect message [RFC4861] to update the cache of the correspondent. 760 8. Bridging Proxy Operations 762 A Bridging Proxy provides IPv6 ND proxy functions between the LLN and 763 the backbone while preserving the forwarding continuity at the MAC 764 Layer. It acts as a Layer-2 Bridge for all types unicast packets 765 including link-scoped, and appears as an IPv6 Host on the Backbone. 767 The Bridging Proxy registers any Binding including for a Link-Local 768 address to the 6LBR (if present) and defends it over the backbone in 769 IPv6 ND procedures. 771 To achieve this, the Bridging Proxy intercepts the IPv6 ND messages 772 and may reinject them on the other side, respond directly or drop 773 them. For instance, an ND(Lookup) from the backbone that matches a 774 Binding can be responded directly, or turned into a unicast on the 775 LLN side to let the 6LN respond. 777 As a Bridging Proxy, the 6BBR MUST use the Registering Node's Layer-2 778 Address in the SLLAO of the NS/RS messages and the TLLAO of the NA 779 messages that it generates to advertise the Registered Addresses. 780 The Registering Node's Layer-2 address is found in the SLLA of the 781 registration NS(EARO), and maintained in the Binding Table. 783 The MultiLink Subnet prefix SHOULD NOT be advertised as on-link in RA 784 messages sent towards the LLN. If a destination address is seen as 785 on-link, then a 6LN may use NS(Lookup) messages to resolve that 786 address. In that case, the 6BBR MUST either answer directly to the 787 NS(Lookup) message or reinject the message on the backbone, either as 788 a Layer-2 unicast or a multicast. 790 If the Registering Node owns the Registered Address, then its 791 mobility does not impact existing NCEs over the Backbone. Otherwise, 792 when the 6LN selects another Registering Node, the new Registering 793 Node SHOULD send a multicast NA with the Override flag set to fix the 794 existing NCEs across the Backbone. This method can fail if the 795 multicast message is not received; one or more correspondent nodes on 796 the Backbone might maintain an stale NCE, and packets to the 797 Registered Address may be lost. When this condition happens, it is 798 eventually be discovered and resolved using Neighbor Unreachability 799 Detection (NUD) as defined in [RFC4861]. 801 9. Creating and Maintaining a Binding 803 Upon receiving a registration for a new Address (i.e., an NS(EARO) 804 with the R flag set), the 6BBR creates a Binding and operates as a 805 6LR according to [RFC8505], interacting with the 6LBR if one is 806 present. 808 An implementation of a Routing Proxy that creates a Binding MUST also 809 create an associated Host route pointing on the registering node in 810 the LLN interface from which the registration was received. 812 The 6LR operation is modified as follows: 814 o EDAR and EDAC messages SHOULD carry a SLLAO and a TLLAO, 815 respectively. 817 o A Bridging Proxy MAY register Link Local addresses to the 6BBR and 818 proxy ND for those addresses over the backbone. 820 o An EDAC message with a status of 9 (6LBR Registry Saturated) is 821 assimilated as a status of 0 if a following DAD process protects 822 the address against duplication. 824 This specification enables nodes on a Backbone Link to co-exist along 825 with nodes implementing IPv6 ND [RFC4861] as well as other non- 826 normative specifications such as [I-D.bi-savi-wlan]. It is possible 827 that not all IPv6 addresses on the Backbone are registered and known 828 to the 6LBR, and an EDAR/EDAC echange with the 6LBR might succeed 829 even for a duplicate address. Consequently, and unless 830 administratively overridden, the 6BBR still needs to perform IPv6 ND 831 DAD over the backbone after an EDAC with a status code of 0 or 9. 833 For the DAD operation, the Binding is placed in Tentative state for a 834 duration of TENTATIVE_DURATION, and an NS(DAD) message is sent as a 835 multicast message over the Backbone to the SNMA associated with the 836 registered Address [RFC4862]. The EARO from the registration MUST be 837 placed unchanged in the NS(DAD) message. 839 If a registration is received for an existing Binding with a non-null 840 Registration Lifetime and the registration is fresher (same ROVR, 841 fresher TID), then the Binding is updated, with the new Registration 842 Lifetime, TID, and possibly Registering Node. In Tentative state 843 (see Section 9.1), the current DAD operation continues as it was. In 844 other states (see Section 9.2 and Section 9.3 ), the Binding is 845 placed in Reachable state for the Registration Lifetime, and the 6BBR 846 returns an NA(EARO) to the Registering Node with a status of 0 847 (Success). 849 Upon a registration that is identical (same ROVR, TID, and 850 Registering Node), the 6BBR returns an NA(EARO) back to the 851 Registering Node with a status of 0 (Success). A registration that 852 is not as fresh (same ROVR, older TID) is ignored. 854 If a registration is received for an existing Binding and a 855 registration Lifetime of zero, then the Binding is removed, and the 856 6BBR returns an NA(EARO) back to the Registering Node with a status 857 of 0 (Success). An implementation of a Routing Proxy that removes a 858 binding MUST remove the associated Host route pointing on the 859 registering node. It MAY preserve a temporary state in order to 860 forward packets in flight. The state may be a NCE formed based on a 861 received NA message, or a Binding in Stale state and pointing at the 862 new 6BBR on the backbone. 864 The implementation should also use REDIRECT messages as specified in 865 [RFC4861] to update the correspondents for the Registered Address, 866 pointing the new 6BBR. 868 9.1. Operation on a Binding in Tentative State 870 The Tentative state covers a DAD period over the backbone during 871 which an address being registered is checked for duplication using 872 procedures defined in [RFC4862]. 874 For a Binding in Tentative state: 876 o The Binding MUST be removed if an NA message is received over the 877 Backbone for the Registered Address with no EARO, or containing an 878 EARO with a status of 1 (Duplicate) that indicates an existing 879 registration owned by a different Registering Node. In that case, 880 an NA MUST be sent back to the Registering Node with a status of 1 881 (Duplicate) in the EARO. This behavior might be overriden by 882 policy, in particular if the registration is trusted, e.g., based 883 on the validation of the ROVR field (see [I-D.ietf-6lo-ap-nd]). 885 o An NS(DAD) with no EARO or with an EARO that indicates a duplicate 886 registration (i.e. different ROVR) MUST be answered with an NA 887 message containing an EARO with a status of 1 (Duplicate) and the 888 Override flag not set. This behavior might be overriden by 889 policy, in particular if the registration is not trusted. 891 o The Binding MUST be removed if an NA message is received over the 892 Backbone for the Registered Address containing an EARO with a 893 status of 3 (Moved), or an NS(DAD) with an EARO that indicates a 894 fresher registration ([RFC8505]) for the same Registered Node 895 (i.e. same ROVR). A status of 3 is returned in the NA(EARO) back 896 to the Registering Node. 898 o NS(DAD) and NA messages containing an EARO that indicates a 899 registration for the same Registered Node that is not as fresh as 900 this SHOULD be answered with an NA message containing an EARO with 901 a status of 3 (Moved) in order to clean up the situation 902 immediately. 904 o Other NS(DAD) and NA messages from the Backbone are ignored. 906 o NS(Lookup) and NS(NUD) messages SHOULD be optimistically answered 907 with an NA message containing an EARO with a status of 0 and the 908 Override flag not set (see Section 3.6). If optimistic DAD is 909 disabled, then they SHOULD be queued to be answered when the 910 Binding goes to Reachable state. 912 When the TENTATIVE_DURATION timer elapses, the Binding is placed in 913 Reachable state for the Registration Lifetime, and the 6BBR returns 914 an NA(EARO) to the Registering Node with a status of 0 (Success). 916 The 6BBR also attempts to take over any existing Binding from other 917 6BBRs and to update existing NCEs in backbone nodes. This is done by 918 sending an NA message with an EARO and the Override flag set over the 919 backbone (see Section 7 and Section 8). 921 9.2. Operation on a Binding in Reachable State 923 The Reachable state covers an active registration after a successful 924 DAD process. 926 An NS(DAD) with no EARO or with an EARO that indicates a duplicate If 927 the Registration Lifetime is of a long duration, an implementation 928 might be configured to reassess the availability of the Registering 929 Node at a lower period, using a NUD procedure as specified in 930 [RFC7048]. If the NUD procedure fails, the Binding SHOULD be placed 931 in Stale state immediately. 933 For a Binding in Reachable state: 935 o The Binding MUST be removed if an NA or an NS(DAD) message is 936 received over the Backbone for the Registered Address containing 937 an EARO that indicates a fresher registration ([RFC8505]) for the 938 same Registered Node (i.e. same ROVR). A status of 4 (Removed) is 939 returned in an asynchronous NA(EARO) to the Registering Node. 940 Based on configuration, an implementation may delay this operation 941 by a small timer in order to a allow for a parallel registration 942 to arrive to this node, in which case the NA might be ignored. 944 o An NS(DAD) with no EARO or with an EARO that indicates a duplicate 945 registration (i.e. different ROVR) MUST be answered with an NA 946 message containing an EARO with a status of 1 (Duplicate) and the 947 Override flag not set. 949 o NS(DAD) and NA messages containing an EARO that indicates a 950 registration for the same Registered Node that is not as fresh as 951 this MUST be answered with an NA message containing an EARO with a 952 status of 3 (Moved). 954 o Other NS(DAD) and NA messages from the Backbone are ignored. 956 o NS(Lookup) and NS(NUD) messages SHOULD be answered with an NA 957 message containing an EARO with a status of 0 and the Override 958 flag not set. The 6BBR MAY check whether the Registering Node is 959 still available using a NUD procedure over the LLN prior to 960 answering; this behaviour depends on the use case and is subject 961 to configuration. 963 When the Registration Lifetime timer elapses, the Binding is placed 964 in Stale state for a duration of STALE_DURATION. 966 9.3. Operation on a Binding in Stale State 968 The Stale state enables tracking of the Backbone peers that have a 969 NCE pointing to this 6BBR in case the Registered Address shows up 970 later. 972 If the Registered Address is claimed by another 6LN on the Backbone, 973 with an NS(DAD) or an NA, the 6BBR does not defend the Address. 975 For a Binding in Stale state: 977 o The Binding MUST be removed if an NA or an NS(DAD) message is 978 received over the Backbone for the Registered Address containing 979 no EARO or an EARO that indicates either a fresher registration 980 for the same Registered Node or a duplicate registration. A 981 status of 4 (Removed) MAY be returned in an asynchronous NA(EARO) 982 to the Registering Node. 984 o NS(DAD) and NA messages containing an EARO that indicates a 985 registration for the same Registered Node that is not as fresh as 986 this MUST be answered with an NA message containing an EARO with a 987 status of 3 (Moved). 989 o If the 6BBR receives an NS(Lookup) or an NS(NUD) message for the 990 Registered Address, the 6BBR MUST attempts a NUD procedure as 991 specified in [RFC7048] to the Registering Node, targeting the 992 Registered Address, prior to answering. If the NUD procedure 993 succeeds, the operation in Reachable state applies. If the NUD 994 fails, the 6BBR refrains from answering. 996 o Other NS(DAD) and NA messages from the Backbone are ignored. 998 When the STALE_DURATION timer elapses, the Binding MUST be removed. 1000 10. Registering Node Considerations 1002 A Registering Node MUST implement [RFC8505] in order to interact with 1003 a 6BBR (which acts as a routing registrar). Following [RFC8505], the 1004 Registering Node signals that it requires IPv6 proxy-ND services from 1005 a 6BBR by registering the corresponding IPv6 Address using an 1006 NS(EARO) message with the R flag set. 1008 The Registering Node may be the 6LN owning the IPv6 Address, or a 1009 6LBR that performs the registration on its behalf in a Route-Over 1010 mesh. 1012 The Registering Node SHOULD register all of its IPv6 Addresses to its 1013 6LR, which is the 6BBR when they are connected at Layer-2. Failure 1014 to register an address may result in the address being unreachable by 1015 other parties if the 6BBR cancels the NS(Lookup) over the LLN or to 1016 selected LLN nodes that are known to register their addresses. 1018 The Registering Node MUST refrain from using multicast NS(Lookup) 1019 when the destination is not known as on-link, e.g., if the prefix is 1020 advertised in a PIO with the L flag that is not set. In that case, 1021 the Registering Node sends its packets directly to its 6LR. 1023 The Registering Node SHOULD also follow [RFC7772] in order to limit 1024 the use of multicast RAs. It SHOULD also implement Simple Procedures 1025 for Detecting Network Attachment in IPv6 [RFC6059] (DNA procedures) 1026 to detect movements, and support Packet-Loss Resiliency for Router 1027 Solicitations [RFC7559] in order to improve reliability for the 1028 unicast RS messages. 1030 11. Security Considerations 1032 This specification applies to LLNs in which the link layer is 1033 protected, either by means of physical or IP security for the 1034 Backbone Link or MAC-layer security. In particular, the LLN MAC is 1035 required to provide secure unicast to/from the Backbone Router and 1036 secure Broadcast from the Backbone Router in a way that prevents 1037 tampering with or replaying the RA messages. 1039 A possible attack over the backbone can be done by sending an NS with 1040 an EARO and expecting the NA(EARO) back to contain the TID and ROVR 1041 fields of the existing state. With that information, the attacker 1042 can easily increase the TID and take over the Binding. 1043 [I-D.ietf-6lo-ap-nd] guarantees the ownership of a registered address 1044 based on a proof-of-ownership encoded in the ROVR field and protects 1045 against address theft and impersonation. 1047 12. Protocol Constants 1049 This Specification uses the following constants: 1051 TENTATIVE_DURATION: 800 milliseconds 1053 STALE_DURATION: see below 1055 In LLNs with long-lived Addresses such as LPWANs, STALE_DURATION 1056 SHOULD be configured with a relatively long value, by default 24 1057 hours. In LLNs where addresses are renewed rapidly, e.g. for privacy 1058 reasons, STALE_DURATION SHOULD be configured with a relatively long 1059 value, by default 5 minutes. 1061 13. IANA Considerations 1063 This document has no request to IANA. 1065 14. Acknowledgments 1067 Many thanks to Dorothy Stanley, Thomas Watteyne and Jerome Henry for 1068 their various contributions. 1070 15. References 1072 15.1. Normative References 1074 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1075 Requirement Levels", BCP 14, RFC 2119, 1076 DOI 10.17487/RFC2119, March 1997, 1077 . 1079 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1080 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1081 2006, . 1083 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 1084 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 1085 . 1087 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1088 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1089 DOI 10.17487/RFC4861, September 2007, 1090 . 1092 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1093 Address Autoconfiguration", RFC 4862, 1094 DOI 10.17487/RFC4862, September 2007, 1095 . 1097 [RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for 1098 Detecting Network Attachment in IPv6", RFC 6059, 1099 DOI 10.17487/RFC6059, November 2010, 1100 . 1102 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1103 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1104 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1105 Low-Power and Lossy Networks", RFC 6550, 1106 DOI 10.17487/RFC6550, March 2012, 1107 . 1109 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1110 Bormann, "Neighbor Discovery Optimization for IPv6 over 1111 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1112 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1113 . 1115 [RFC7048] Nordmark, E. and I. Gashinsky, "Neighbor Unreachability 1116 Detection Is Too Impatient", RFC 7048, 1117 DOI 10.17487/RFC7048, January 2014, 1118 . 1120 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1121 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1122 May 2017, . 1124 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1125 (IPv6) Specification", STD 86, RFC 8200, 1126 DOI 10.17487/RFC8200, July 2017, 1127 . 1129 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 1130 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 1131 DOI 10.17487/RFC8201, July 2017, 1132 . 1134 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1135 Perkins, "Registration Extensions for IPv6 over Low-Power 1136 Wireless Personal Area Network (6LoWPAN) Neighbor 1137 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1138 . 1140 15.2. Informative References 1142 [I-D.bi-savi-wlan] 1143 Bi, J., Wu, J., Wang, Y., and T. Lin, "A SAVI Solution for 1144 WLAN", draft-bi-savi-wlan-16 (work in progress), November 1145 2018. 1147 [I-D.ietf-6lo-ap-nd] 1148 Thubert, P., Sethi, M., Struik, R., and B. Sarikaya, 1149 "Address Protected Neighbor Discovery for Low-power and 1150 Lossy Networks", draft-ietf-6lo-ap-nd-09 (work in 1151 progress), December 2018. 1153 [I-D.ietf-6man-rs-refresh] 1154 Nordmark, E., Yourtchenko, A., and S. Krishnan, "IPv6 1155 Neighbor Discovery Optional RS/RA Refresh", draft-ietf- 1156 6man-rs-refresh-02 (work in progress), October 2016. 1158 [I-D.ietf-6tisch-architecture] 1159 Thubert, P., "An Architecture for IPv6 over the TSCH mode 1160 of IEEE 802.15.4", draft-ietf-6tisch-architecture-19 (work 1161 in progress), December 2018. 1163 [I-D.ietf-mboned-ieee802-mcast-problems] 1164 Perkins, C., McBride, M., Stanley, D., Kumari, W., and J. 1165 Zuniga, "Multicast Considerations over IEEE 802 Wireless 1166 Media", draft-ietf-mboned-ieee802-mcast-problems-04 (work 1167 in progress), November 2018. 1169 [I-D.nordmark-6man-dad-approaches] 1170 Nordmark, E., "Possible approaches to make DAD more robust 1171 and/or efficient", draft-nordmark-6man-dad-approaches-02 1172 (work in progress), October 2015. 1174 [I-D.thubert-6lo-unicast-lookup] 1175 Thubert, P. and E. Levy-Abegnoli, "IPv6 Neighbor Discovery 1176 Unicast Lookup", draft-thubert-6lo-unicast-lookup-00 (work 1177 in progress), January 2019. 1179 [I-D.yourtchenko-6man-dad-issues] 1180 Yourtchenko, A. and E. Nordmark, "A survey of issues 1181 related to IPv6 Duplicate Address Detection", draft- 1182 yourtchenko-6man-dad-issues-01 (work in progress), March 1183 2015. 1185 [IEEEstd8021] 1186 IEEE standard for Information Technology, "IEEE Standard 1187 for Information technology -- Telecommunications and 1188 information exchange between systems Local and 1189 metropolitan area networks Part 1: Bridging and 1190 Architecture". 1192 [IEEEstd80211] 1193 IEEE standard for Information Technology, "IEEE Standard 1194 for Information technology -- Telecommunications and 1195 information exchange between systems Local and 1196 metropolitan area networks-- Specific requirements Part 1197 11: Wireless LAN Medium Access Control (MAC) and Physical 1198 Layer (PHY) Specifications". 1200 [IEEEstd802151] 1201 IEEE standard for Information Technology, "IEEE Standard 1202 for Information Technology - Telecommunications and 1203 Information Exchange Between Systems - Local and 1204 Metropolitan Area Networks - Specific Requirements. - Part 1205 15.1: Wireless Medium Access Control (MAC) and Physical 1206 Layer (PHY) Specifications for Wireless Personal Area 1207 Networks (WPANs)". 1209 [IEEEstd802154] 1210 IEEE standard for Information Technology, "IEEE Standard 1211 for Local and metropolitan area networks -- Part 15.4: 1212 Low-Rate Wireless Personal Area Networks (LR-WPANs)". 1214 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 1215 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 1216 2006, . 1218 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 1219 DOI 10.17487/RFC4903, June 2007, 1220 . 1222 [RFC5415] Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley, 1223 Ed., "Control And Provisioning of Wireless Access Points 1224 (CAPWAP) Protocol Specification", RFC 5415, 1225 DOI 10.17487/RFC5415, March 2009, 1226 . 1228 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 1229 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 1230 2011, . 1232 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1233 Statement and Requirements for IPv6 over Low-Power 1234 Wireless Personal Area Network (6LoWPAN) Routing", 1235 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1236 . 1238 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 1239 Locator/ID Separation Protocol (LISP)", RFC 6830, 1240 DOI 10.17487/RFC6830, January 2013, 1241 . 1243 [RFC7559] Krishnan, S., Anipko, D., and D. Thaler, "Packet-Loss 1244 Resiliency for Router Solicitations", RFC 7559, 1245 DOI 10.17487/RFC7559, May 2015, 1246 . 1248 [RFC7772] Yourtchenko, A. and L. Colitti, "Reducing Energy 1249 Consumption of Router Advertisements", BCP 202, RFC 7772, 1250 DOI 10.17487/RFC7772, February 2016, 1251 . 1253 [RFC8273] Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix 1254 per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017, 1255 . 1257 Appendix A. Possible Future Extensions 1259 With the current specification, the 6LBR is not leveraged to avoid 1260 multicast NS(Lookup) on the Backbone. This could be done by adding a 1261 lookup procedure in the EDAR/EDAC exchange. 1263 By default the specification does not have a trust model, e.g., 1264 whereby nodes that associate their address with a proof-of-ownership 1265 [I-D.ietf-6lo-ap-nd] should be more trusted than nodes that do not. 1266 Such a trust model and related signaling could be added in the future 1267 to override the default operation and favor trusted nodes. 1269 Future documents may extend this specification by allowing the 6BBR 1270 to redistribute Host routes in routing protocols that would operate 1271 over the Backbone, or in MIPv6, or FMIP, or the Locator/ID Separation 1272 Protocol (LISP) [RFC6830] to support mobility on behalf of the 6LNs, 1273 etc... LISP may also be used to provide an equivalent to the EDAR/ 1274 EDAC exchange using a Map Server / Map Resolver as a replacement to 1275 the 6LBR. 1277 Appendix B. Applicability and Requirements Served 1279 This document specifies proxy-ND functions that can be used to 1280 federate an IPv6 Backbone Link and multiple IPv6 LLNs into a single 1281 MultiLink Subnet. The proxy-ND functions enable IPv6 ND services for 1282 Duplicate Address Detection (DAD) and Address Lookup that do not 1283 require broadcasts over the LLNs. 1285 The term LLN is used to cover multiple types of WLANs and WPANs, 1286 including (Low-Power) Wi-Fi, BLUETOOTH(R) Low Energy, IEEE STD 1287 802.11ah and IEEE STD.802.15.4 wireless meshes, meeting the 1288 requirements listed in Appendix B.3 of [RFC8505] "Requirements 1289 Related to Various Low-Power Link Types". 1291 Each LLN in the subnet is attached at an IPv6 Backbone Router (6BBR). 1292 The Backbone Routers interconnect the LLNs and advertise the 1293 Addresses of the 6LNs over the Backbone Link using proxy-ND 1294 operations. 1296 This specification updates IPv6 ND over the Backbone to distinguish 1297 Address movement from duplication and eliminate stale state in the 1298 Backbone routers and Backbone nodes once a 6LN has roamed. In this 1299 way, mobile nodes may roam rapidly from one 6BBR to the next and 1300 requirements in Appendix B.1 of [RFC8505] "Requirements Related to 1301 Mobility" are met. 1303 A 6LN can register its IPv6 Addresses and thereby obtain proxy-ND 1304 services over the Backbone, meeting the requirements expressed in 1305 Appendix B.4 of [RFC8505], "Requirements Related to Proxy 1306 Operations". 1308 The IPv6 ND operation is minimized as the number of 6LNs grows in the 1309 LLN. This meets the requirements in Appendix B.6 of [RFC8505] 1310 "Requirements Related to Scalability", as long has the 6BBRs are 1311 dimensioned for the number of registrations that each needs to 1312 support. 1314 In the case of a Wi-Fi access link, a 6BBR may be collocated with the 1315 Access Point (AP), or with a Fabric Edge (FE) or a CAPWAP [RFC5415] 1316 Wireless LAN Controller (WLC). In those cases, the wireless client 1317 (STA) is the 6LN that makes use of [RFC8505] to register its IPv6 1318 Address(es) to the 6BBR acting as Routing Registrar. The 6LBR can be 1319 centralized and either connected to the Backbone Link or reachable 1320 over IP. The 6BBR proxy-ND operations eliminate the need for 1321 wireless nodes to respond synchronously when a Lookup is performed 1322 for their IPv6 Addresses. This provides the function of a Sleep 1323 Proxy for ND [I-D.nordmark-6man-dad-approaches]. 1325 For the TimeSlotted Channel Hopping (TSCH) mode of [IEEEstd802154], 1326 the 6TiSCH architecture [I-D.ietf-6tisch-architecture] describes how 1327 a 6LoWPAN ND host could connect to the Internet via a RPL mesh 1328 Network, but doing so requires extensions to the 6LOWPAN ND protocol 1329 to support mobility and reachability in a secure and manageable 1330 environment. The extensions detailed in this document also work for 1331 the 6TiSCH architecture, serving the requirements listed in 1332 Appendix B.2 of [RFC8505] "Requirements Related to Routing 1333 Protocols". 1335 The registration mechanism may be seen as a more reliable alternate 1336 to snooping [I-D.bi-savi-wlan]. It can be noted that registration 1337 and snooping are not mutually exclusive. Snooping may be used in 1338 conjunction with the registration for nodes that do not register 1339 their IPv6 Addresses. The 6BBR assumes that if a node registers at 1340 least one IPv6 Address to it, then the node registers all of its 1341 Addresses to the 6BBR. With this assumption, the 6BBR can possibly 1342 cancel all undesirable multicast NS messages that would otherwise 1343 have been delivered to that node. 1345 Scalability of the MultiLink Subnet [RFC4903] requires avoidance of 1346 multicast/broadcast operations as much as possible even on the 1347 Backbone [I-D.ietf-mboned-ieee802-mcast-problems]. Although hosts 1348 can connect to the Backbone using IPv6 ND operations, multicast RAs 1349 can be saved by using [I-D.ietf-6man-rs-refresh], which also requires 1350 the support of [RFC7559]. 1352 Authors' Addresses 1354 Pascal Thubert (editor) 1355 Cisco Systems, Inc 1356 Building D 1357 45 Allee des Ormes - BP1200 1358 MOUGINS - Sophia Antipolis 06254 1359 FRANCE 1361 Phone: +33 497 23 26 34 1362 Email: pthubert@cisco.com 1364 Charles E. Perkins 1365 Futurewei 1366 2330 Central Expressway 1367 Santa Clara 95050 1368 United States of America 1370 Email: charliep@computer.org 1372 Eric Levy-Abegnoli 1373 Cisco Systems, Inc 1374 Building D 1375 45 Allee des Ormes - BP1200 1376 MOUGINS - Sophia Antipolis 06254 1377 FRANCE 1379 Phone: +33 497 23 26 20 1380 Email: elevyabe@cisco.com