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Savolainen 6 DarkMatter 7 M. Spoerk 8 Graz University of Technology 9 October 7, 2020 11 IPv6 Mesh over BLUETOOTH(R) Low Energy using IPSP 12 draft-ietf-6lo-blemesh-08 14 Abstract 16 RFC 7668 describes the adaptation of 6LoWPAN techniques to enable 17 IPv6 over Bluetooth low energy networks that follow the star 18 topology. However, recent Bluetooth specifications allow the 19 formation of extended topologies as well. This document specifies 20 mechanisms that are needed to enable IPv6 mesh over Bluetooth Low 21 Energy links established by using the Bluetooth Internet Protocol 22 Support Profile. This document does not specify the routing protocol 23 to be used in an IPv6 mesh over Bluetooth LE links. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on April 10, 2021. 42 Copyright Notice 44 Copyright (c) 2020 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (https://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 1.1. Terminology and Requirements Language . . . . . . . . . . 3 61 2. Bluetooth LE Networks and the IPSP . . . . . . . . . . . . . 3 62 3. Specification of IPv6 mesh over Bluetooth LE links . . . . . 4 63 3.1. Protocol stack . . . . . . . . . . . . . . . . . . . . . 4 64 3.2. Subnet model . . . . . . . . . . . . . . . . . . . . . . 5 65 3.3. Link model . . . . . . . . . . . . . . . . . . . . . . . 6 66 3.3.1. Stateless address autoconfiguration . . . . . . . . . 6 67 3.3.2. Neighbor Discovery . . . . . . . . . . . . . . . . . 6 68 3.3.3. Header compression . . . . . . . . . . . . . . . . . 7 69 3.3.4. Unicast and multicast mapping . . . . . . . . . . . . 8 70 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 71 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 72 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9 73 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 74 8. Appendix A: Bluetooth LE connection establishment example . . 10 75 9. Appendix B: Node joining procedure . . . . . . . . . . . . . 13 76 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 77 10.1. Normative References . . . . . . . . . . . . . . . . . . 13 78 10.2. Informative References . . . . . . . . . . . . . . . . . 14 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 81 1. Introduction 83 Bluetooth Low Energy (hereinafter, Bluetooth LE) was first introduced 84 in the Bluetooth 4.0 specification. Bluetooth LE (which has been 85 marketed as Bluetooth Smart) is a low-power wireless technology 86 designed for short-range control and monitoring applications. 87 Bluetooth LE is currently implemented in a wide range of consumer 88 electronics devices, such as smartphones and wearable devices. Given 89 the high potential of this technology for the Internet of Things, the 90 Bluetooth Special Interest Group (Bluetooth SIG) and the IETF have 91 produced specifications in order to enable IPv6 over Bluetooth LE, 92 such as the Internet Protocol Support Profile (IPSP) [IPSP], and RFC 93 7668, respectively. Bluetooth 4.0 only supports Bluetooth LE 94 networks that follow the star topology. As a consequence, RFC 7668 95 was specifically developed and optimized for that type of network 96 topology. However, the functionality described in RFC 7668 is not 97 sufficient and would fail to enable an IPv6 mesh over Bluetooth LE 98 links. This document specifies mechanisms that are needed to enable 99 IPv6 mesh over Bluetooth LE links. This document does not specify 100 the routing protocol to be used in an IPv6 mesh over Bluetooth LE 101 links. 103 1.1. Terminology and Requirements Language 105 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 106 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 107 document are to be interpreted as described in RFC 2119 [RFC2119]. 109 The terms 6LoWPAN Node (6LN), 6LoWPAN Router (6LR) and 6LoWPAN Border 110 Router (6LBR) are defined as in [RFC6775], with an addition that 111 Bluetooth LE central and Bluetooth LE peripheral (see Section 2) can 112 both be adopted by a 6LN, a 6LR or a 6LBR. 114 2. Bluetooth LE Networks and the IPSP 116 Bluetooth LE defines two Generic Access Profile (GAP) roles of 117 relevance herein: the Bluetooth LE central role and the Bluetooth LE 118 peripheral role. A device in the central role, which is called 119 central from now on, has traditionally been able to manage multiple 120 simultaneous connections with a number of devices in the peripheral 121 role, called peripherals hereinafter. Bluetooth 4.1 (now deprecated) 122 introduced the possibility for a peripheral to be connected to more 123 than one central simultaneously, therefore allowing extended 124 topologies beyond the star topology for a Bluetooth LE network. In 125 addition, a device may simultaneously be a central in a set of link 126 layer connections, as well as a peripheral in others. 128 On the other hand, the IPSP enables discovery of IP-enabled devices 129 and the establishment of a link layer connection for transporting 130 IPv6 packets. The IPSP defines the Node and Router roles for devices 131 that consume/originate IPv6 packets and for devices that can route 132 IPv6 packets, respectively. Consistently with Bluetooth 4.1 and 133 subsequent Bluetooth versions (e.g. Bluetooth 4.2 [BTCorev4.2] or 134 subsequent), a device may implement both roles simultaneously. 136 This document assumes a mesh network composed of Bluetooth LE links, 137 where link layer connections are established between neighboring 138 IPv6-enabled devices (see Section 3.3.2, item 3.b)). The IPv6 139 forwarding devices of the mesh have to implement both IPSP Node and 140 Router roles, while simpler leaf-only nodes can implement only the 141 Node role. In an IPv6 mesh over Bluetooth LE links, a node is a 142 neighbor of another node, and vice versa, if a link layer connection 143 has been established between both by using the IPSP functionality for 144 discovery and link layer connection establishment for IPv6 packet 145 transport. 147 3. Specification of IPv6 mesh over Bluetooth LE links 149 3.1. Protocol stack 151 Figure 1 illustrates the protocol stack for IPv6 mesh over Bluetooth 152 LE links. There are two main differences with the IPv6 over 153 Bluetooth LE stack in RFC 7668: a) the adaptation layer below IPv6 154 (labelled as "6Lo for IPv6 mesh over Bluetooth LE") is now adapted 155 for IPv6 mesh over Bluetooth LE links, and b) the protocol stack for 156 IPv6 mesh over Bluetooth LE links includes IPv6 routing 157 functionality. 159 +------------------------------------+ 160 | Application | 161 +---------+ +------------------------------------+ 162 | IPSS | | UDP/TCP/other | 163 +---------+ +------------------------------------+ 164 | GATT | | IPv6 |routing| | 165 +---------+ +------------------------------------+ 166 | ATT | | 6Lo for IPv6 mesh over Bluetooh LE | 167 +---------+--+------------------------------------+ 168 | Bluetooth LE L2CAP | 169 - - +-------------------------------------------------+- - - HCI 170 | Bluetooth LE Link Layer | 171 +-------------------------------------------------+ 172 | Bluetooth LE Physical | 173 +-------------------------------------------------+ 175 Figure 1: Protocol stack for IPv6 mesh over Bluetooth LE links. 177 Bluetooth 4.2 defines a default MTU for Bluetooth LE of 251 bytes. 178 Excluding the L2CAP header of 4 bytes, a protocol data unit (PDU) 179 size of 247 bytes is available for the layer above L2CAP. (Note: 180 earlier Bluetooth LE versions offered a maximum amount of 23 bytes 181 for the layer atop L2CAP.) The L2CAP provides a fragmentation and 182 reassembly solution for transmitting or receiving larger PDUs. At 183 each link, the IPSP defines means for negotiating a link-layer 184 connection that provides an MTU of 1280 octets or higher for the IPv6 185 layer [IPSP]. For the sake of lightweight implementation and 186 operation, an MTU of 1280 octets is RECOMMENDED for IPv6 mesh over 187 BLE links. The link-layer MTU is negotiated separately for each 188 direction. Implementations that require an equal link-layer MTU for 189 the two directions SHALL use the smallest of the possibly different 190 MTU values. 192 Note that this specification allows using different MTUs in different 193 links. If an implementation requires use of the same MTU on every 194 one of its links, and a new node with a smaller MTU is added to the 195 network, a renegotiation of one or more links can occur. In the 196 worst case, the renegotiations could cascade network-wide. In that 197 case, implementers need to assess the impact of such phenomenon. 199 Similarly to RFC 7668, fragmentation functionality from 6LoWPAN 200 standards is not used for IPv6 mesh over Bluetooth LE links. 201 Bluetooth LE's fragmentation support provided by L2CAP is used when 202 necessary. 204 3.2. Subnet model 206 For IPv6 mesh over Bluetooth LE links, a multilink model has been 207 chosen, as further illustrated in Figure 2. As IPv6 over Bluetooth 208 LE is intended for constrained nodes, and for Internet of Things use 209 cases and environments, the complexity of implementing a separate 210 subnet on each peripheral-central link and routing between the 211 subnets appears to be excessive. In this specification, the benefits 212 of treating the collection of point-to-point links between a central 213 and its connected peripherals as a single multilink subnet rather 214 than a multiplicity of separate subnets are considered to outweigh 215 the multilink model's drawbacks as described in [RFC4903]. 217 / 218 .--------------------------------. / 219 / 6LR 6LN 6LN \ / 220 / \ \ \ \ / 221 | \ \ \ | / 222 | 6LN ----- 6LR --------- 6LR ------ 6LBR ----- | Internet 223 | <--Link--> <---Link--->/<--Link->/ | | 224 \ / / / \ 225 \ 6LN ---- 6LR ----- 6LR / \ 226 '--------------------------------' \ 227 \ 229 <------------ Subnet -----------------><---- IPv6 connection --> 230 to the Internet 232 Figure 2: Example of an IPv6 mesh over a Bluetooth LE network 233 connected to the Internet 235 One or more 6LBRs are connected to the Internet. 6LNs are connected 236 to the network through a 6LR or a 6LBR. A single Global Unicast 237 prefix is used on the whole subnet. 239 IPv6 mesh over Bluetooth LE links MUST follow a route-over approach. 240 This document does not specify the routing protocol to be used in an 241 IPv6 mesh over Bluetooth LE links. 243 3.3. Link model 245 3.3.1. Stateless address autoconfiguration 247 6LN, 6LR and 6LBR IPv6 addresses in an IPv6 mesh over Bluetooth LE 248 links are configured as per section 3.2.2 of RFC 7668. 250 Multihop DAD functionality as defined in section 8.2 of RFC 6775 and 251 updated by RFC 8505, or some substitute mechanism (see section 252 3.3.2), MAY be supported. 254 3.3.2. Neighbor Discovery 256 'Neighbor Discovery Optimization for IPv6 over Low-Power Wireless 257 Personal Area Networks (6LoWPANs)' [RFC6775], subsequently updated by 258 'Registration Extensions for IPv6 over Low-Power Wireless Personal 259 Area Network (6LoWPAN) Neighbor Discovery' [RFC8505], describes the 260 neighbor discovery functionality adapted for use in several 6LoWPAN 261 topologies, including the mesh topology. The route-over 262 functionality of RFC 6775 and RFC 8505 MUST be supported. 264 The following aspects of the Neighbor Discovery optimizations for 265 6LoWPAN [RFC6775],[RFC8505] are applicable to Bluetooth LE 6LNs: 267 1. A Bluetooth LE 6LN SHOULD register its non-link-local addresses 268 with its routers by sending a Neighbor Solicitation (NS) message with 269 the Extended Address Registration Option (EARO) and process the 270 Neighbor Advertisement (NA) accordingly. Note that in some cases 271 (e.g. very short-lived connections) it may not be worthwhile for a 272 6LN to send an NS with EARO for registering its address. The EARO 273 option includes a Registration Ownership Verifier (ROVR) field 274 [RFC8505]. In the case of Bluetooth LE, by default the ROVR field is 275 filled with the 48-bit device address used by the Bluetooth LE node 276 converted into 64-bit Modified EUI-64 format [RFC4291]. Optionally, 277 a cryptographic ID (see [I-D.ietf-6lo-ap-nd] MAY be placed in the 278 ROVR field. If a cryptographic ID is used, address registration and 279 multihop DAD formats and procedures defined in [I-D.ietf-6lo-ap-nd] 280 MUST be used, unless an alternative mechanism offering equivalent 281 protection is used. As per RFC 8505, a 6LN MUST NOT register its 282 link-local address. 284 If the 6LN registers multiple addresses that are not based on 285 Bluetooth device address using the same compression context, the 286 header compression efficiency will decrease. 288 2. For sending Router Solicitations and processing Router 289 Advertisements the Bluetooth LE hosts MUST, respectively, follow 290 Sections 5.3 and 5.4 of [RFC6775], and Section 5.6 of [RFC8505]. 292 3. The router behavior for 6LRs and 6LBRs is described in Section 6 293 of RFC 6775, and updated by RFC 8505. However, as per this 294 specification: a) Routers SHALL NOT use multicast NSs to discover 295 other routers' link layer addresses. b) As per section 6.2 of RFC 296 6775, in a dynamic configuration scenario, a 6LR comes up as a non- 297 router and waits to receive a Router Advertisement for configuring 298 its own interface address first, before setting its interfaces to be 299 advertising interfaces and turning into a router. In order to 300 support such operation in an IPv6 mesh over Bluetooth LE links, a 6LR 301 first uses the IPSP Node role only. Once the 6LR has established a 302 connection with another node currently running as a router, and 303 receives a Router Advertisement from that router, the 6LR configures 304 its own interface address, it turns into a router, and it runs as an 305 IPSP Router. A 6LBR uses the IPSP Router role since the 6LBR is 306 initialized. See an example in the Appendix. 308 4. Border router behavior is described in Section 7 of RFC 6775, and 309 updated by RFC 8505. 311 RFC 6775 defines substitutable mechanisms for distributing prefixes 312 and context information (section 8.1 of RFC 6775), as well as for 313 Duplicate Address Detection across a route-over 6LoWPAN (section 8.2 314 of RFC 6775). RFC 8505 updates those mechanisms and the related 315 message formats. Implementations of this specification MAY support 316 the features described in sections 8.1 and 8.2 of RFC 6775, as 317 updated by RFC 8505, unless some alternative ("substitute") from some 318 other specification is supported by the implementation. 320 3.3.3. Header compression 322 Header compression as defined in RFC 6282 [RFC6282], which specifies 323 the compression format for IPv6 datagrams on top of IEEE 802.15.4, is 324 REQUIRED as the basis for IPv6 header compression on top of Bluetooth 325 LE. All headers MUST be compressed according to RFC 6282 [RFC6282] 326 encoding formats. 328 To enable efficient header compression, when the 6LBR sends a Router 329 Advertisement it MAY include a 6LoWPAN Context Option (6CO) [RFC6775] 330 matching each address prefix advertised via a Prefix Information 331 Option (PIO) [RFC4861] for use in stateless address 332 autoconfiguration. Note that 6CO is not needed for context-based 333 compression when a single prefix is used in the network. 335 The specific optimizations of RFC 7668 for header compression, which 336 exploited the star topology and ARO (note that the latter has been 337 updated by EARO as per RFC 8505), cannot be generalized in an IPv6 338 mesh over Bluetooth LE links. Still, a subset of those optimizations 339 can be applied in some cases in such a network. These cases comprise 340 link-local interactions, non-link-local packet transmissions 341 originated by a 6LN, and non-link-local packets intended for a 6LN 342 that are originated or forwarded by a neighbor of that 6LN. For all 343 other packet transmissions, context-based compression MAY be used. 345 When a device transmits a packet to a neighbor, the sender MUST fully 346 elide the source IID if the source IPv6 address is the link-local 347 address based on the sender's Bluetooth device address (SAC=0, 348 SAM=11). The sender also MUST fully elide the destination IPv6 349 address if it is the link-local address based on the neighbor's 350 Bluetooth device address (DAC=0, DAM=11). 352 When a 6LN transmits a packet, with a non-link-local source address 353 that the 6LN has registered with EARO in the next-hop router for the 354 indicated prefix, the source address MUST be fully elided if it is 355 the latest address that the 6LN has registered for the indicated 356 prefix (SAC=1, SAM=11). If the source non-link-local address is not 357 the latest registered by the 6LN, then the 64 bits of the IID SHALL 358 be fully carried in-line (SAC=1, SAM=01) or if the first 48 bits of 359 the IID match with the latest address registered by the 6LN, then the 360 last 16 bits of the IID SHALL be carried in-line (SAC=1, SAM=10). 362 When a router transmits a packet to a neighboring 6LN, with a non- 363 link-local destination address, the router MUST fully elide the 364 destination IPv6 address if the destination address is the latest 365 registered by the 6LN with EARO for the indicated context (DAC=1, 366 DAM=11). If the destination address is a non-link-local address and 367 not the latest registered, then the 6LN MUST either include the IID 368 part fully in-line (DAM=01) or, if the first 48 bits of the IID match 369 to the latest registered address, then elide those 48 bits (DAM=10). 371 3.3.4. Unicast and multicast mapping 373 The Bluetooth LE Link Layer does not support multicast. Hence, 374 traffic is always unicast between two Bluetooth LE neighboring nodes. 375 If a node needs to send a multicast packet to several neighbors, it 376 has to replicate the packet and unicast it on each link. However, 377 this may not be energy efficient, and particular care must be taken 378 if the node is battery powered. A router (i.e. a 6LR or a 6LBR) MUST 379 keep track of neighboring multicast listeners, and it MUST NOT 380 forward multicast packets to neighbors that have not registered as 381 listeners for multicast groups the packets belong to. 383 4. IANA Considerations 385 There are no IANA considerations related to this document. 387 5. Security Considerations 389 The security considerations in RFC 7668 apply. 391 IPv6 mesh over Bluetooth LE links requires a routing protocol to find 392 end-to-end paths. Unfortunately, the routing protocol may generate 393 additional opportunities for threats and attacks to the network. 395 RFC 7416 [RFC 7416] provides a systematic overview of threats and 396 attacks on the IPv6 Routing Protocol for Low-Power and Lossy Networks 397 (RPL), as well as countermeasures. In that document, described 398 threats and attacks comprise threats due to failures to authenticate, 399 threats due to failure to keep routing information, threats and 400 attacks on integrity, and threats and attacks on availability. 401 Reported countermeasures comprise confidentiality attack, integrity 402 attack, and availability attack countermeasures. 404 While this specification does not state the routing protocol to be 405 used in IPv6 mesh over Bluetooth LE links, the guidance of RFC 7416 406 is useful when RPL is used in such scenarios. Furthermore, such 407 guidance may partly apply for other routing protocols as well. 409 The ROVR can be derived from the Bluetooth device address. However, 410 such a ROVR can be spoofed, and therefore, any node connected to the 411 subnet and aware of a registered-address-to-ROVR mapping could 412 perform address theft and impersonation attacks. Use of Address 413 Protected Neighbor Discovery [I-D.ietf-6lo-ap-nd] provides protection 414 against such attacks. 416 6. Contributors 418 Carlo Alberto Boano (Graz University of Technology) contributed to 419 the design and validation of this document. 421 7. Acknowledgements 423 The Bluetooth, Bluetooth Smart and Bluetooth Smart Ready marks are 424 registered trademarks owned by Bluetooth SIG, Inc. 426 The authors of this document are grateful to all RFC 7668 authors, 427 since this document borrows many concepts (albeit, with necessary 428 extensions) from RFC 7668. 430 The authors also thank Alain Michaud, Mark Powell, Martin Turon, 431 Bilhanan Silverajan, Rahul Jadhav and Pascal Thubert for their 432 comments, which helped improve the document. 434 Carles Gomez has been supported in part by the Spanish Government 435 Ministerio de Economia y Competitividad through projects 436 TEC2012-32531, TEC2016-79988-P and FEDER. 438 8. Appendix A: Bluetooth LE connection establishment example 440 This appendix provides an example of Bluetooth LE connection 441 establishment and use of IPSP roles in an IPv6 mesh over Bluetooth LE 442 links that uses dynamic configuration. The example follows text in 443 Section 3.3.2, item 3.b). 445 The example assumes a network with one 6LBR, two 6LRs and three 6LNs, 446 as shown in Figure 3. Connectivity between the 6LNs and the 6LBR is 447 only possible via the 6LRs. 449 The following text describes the different steps as time evolves, in 450 the example. Note that other sequences of events that may lead to 451 the same final scenario are also possible. 453 At the beginning, the 6LBR starts running as an IPSP Router, whereas 454 the rest of devices are not yet initialized (Step 1). Next, the 6LRs 455 start running as IPSP Nodes, i.e., they use Bluetooth LE 456 advertisement packets to announce their presence and support of IPv6 457 capabilities (Step 2). The 6LBR (already running as an IPSP Router) 458 discovers the presence of the 6LRs and establishes one Bluetooth LE 459 connection with each 6LR (Step 3). After establishment of those link 460 layer connections (and after reception of Router Advertisements from 461 the 6LBR), Step 4, the 6LRs start operating as routers, and also 462 initiate the IPSP Router role (note: whether the IPSP Node role is 463 kept running simultaneously is an implementation decision). Then, 464 6LNs start running the IPSP Node role (Step 5). Finally, the 6LRs 465 discover presence of the 6LNs and establish connections with the 466 latter (Step 6). 468 Step 1 469 ****** 470 6LBR 471 (IPSP: Router) 473 6LR 6LR 474 (not initialized) (not initialized) 476 6LN 6LN 6LN 477 (not initialized) (not initialized) (not initialized) 479 Step 2 480 ****** 481 6LBR 482 (IPSP: Router) 484 6LR 6LR 485 (IPSP: Node) (IPSP: Node) 487 6LN 6LN 6LN 488 (not initialized) (not initialized) (not initialized) 490 Step 3 491 ****** 493 6LBR 494 (IPSP: Router) 495 Bluetooth LE connection --> / \ 496 / \ 497 6LR 6LR 498 (IPSP: Node) (IPSP: Node) 500 6LN 6LN 6LN 501 (not initialized) (not initialized) (not initialized) 503 Step 4 504 ****** 506 6LBR 507 (IPSP: Router) 508 / \ 510 / \ 511 6LR 6LR 512 (IPSP: Router) (IPSP: Router) 514 6LN 6LN 6LN 515 (not initialized) (not initialized) (not initialized) 517 Step 5 518 ****** 520 6LBR 521 (IPSP: Router) 522 / \ 523 / \ 524 6LR 6LR 525 (IPSP: Router) (IPSP: Router) 527 6LN 6LN 6LN 528 (IPSP: Node) (IPSP: Node) (IPSP: Node) 530 Step 6 531 ****** 533 6LBR 534 (IPSP: Router) 535 / \ 536 / \ 537 6LR 6LR 538 (IPSP: Router) (IPSP: Router) 539 / \ / \ 540 / \ / \ 541 / \ / \ 542 6LN 6LN 6LN 543 (IPSP: Node) (IPSP: Node) (IPSP: Node) 545 Figure 3: An example of connection establishment and use of IPSP 546 roles in an IPv6 mesh over Bluetooth LE links. 548 9. Appendix B: Node joining procedure 550 This appendix provides a diagram that illustrates the node joining 551 procedure. First of all, the joining node advertises its presence in 552 order to allow establishing Bluetooth LE connections with neighbors 553 that already belong to a network. The latter typically run as a 6LR 554 or as a 6LBR. After Bluetooth LE connection establishment, the 555 joining node starts acting as a 6LN. 557 Figure 4 shows the sequence of messages that are exchanged by the 6LN 558 and a neighboring 6LR that already belongs to the network, after the 559 establishment of a Bluetooth LE connection between both devices. 560 Initially, the 6LN sends an RS message (1). Then, the 6LR replies 561 with an RA, which includes the PIO (2). After discovering the non- 562 link-local prefix in use in the network, the 6LN creates its non- 563 link-local address, registers that address with EARO (3) in the 6LR, 564 and multihop DAD is performed (4). The next step is the transmission 565 of the NA message sent by the 6LR in response to the NS previously 566 sent by the 6LN (5). If the non-link-local address of the 6LN has 567 been successfully validated, the 6LN can operate as a member of the 568 network it has joined. 570 (1) 6LN ----(RS)-------> 6LR 571 (2) 6LN <---(RA-PIO)---- 6LR 572 (3) 6LN ----(NS-EARO)--> 6LR 573 (4) [Multihop DAD procedure] 574 (5) 6LN <---(NA)-------- 6LR 576 Figure 4: Message exchange diagram for a joining node 578 10. References 580 10.1. Normative References 582 [BTCorev4.2] 583 Bluetooth Special Interest Group, "Bluetooth Core 584 Specification Version 4.2", December 2014, 585 . 588 [IPSP] Bluetooth Special Interest Group, "Bluetooth Internet 589 Protocol Support Profile Specification Version 1.0.0", 590 December 2014, . 593 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 594 Requirement Levels", BCP 14, RFC 2119, 595 DOI 10.17487/RFC2119, March 1997, 596 . 598 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 599 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 600 2006, . 602 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 603 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 604 DOI 10.17487/RFC4861, September 2007, 605 . 607 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 608 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 609 DOI 10.17487/RFC6282, September 2011, 610 . 612 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 613 Bormann, "Neighbor Discovery Optimization for IPv6 over 614 Low-Power Wireless Personal Area Networks (6LoWPANs)", 615 RFC 6775, DOI 10.17487/RFC6775, November 2012, 616 . 618 [RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B., 619 Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low 620 Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015, 621 . 623 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 624 Perkins, "Registration Extensions for IPv6 over Low-Power 625 Wireless Personal Area Network (6LoWPAN) Neighbor 626 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 627 . 629 10.2. Informative References 631 [BTCorev4.1] 632 Bluetooth Special Interest Group, "Bluetooth Core 633 Specification Version 4.1", December 2013, 634 . 637 [I-D.ietf-6lo-ap-nd] 638 Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 639 "Address Protected Neighbor Discovery for Low-power and 640 Lossy Networks", draft-ietf-6lo-ap-nd-23 (work in 641 progress), April 2020. 643 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 644 DOI 10.17487/RFC4903, June 2007, 645 . 647 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 648 and M. Richardson, Ed., "A Security Threat Analysis for 649 the Routing Protocol for Low-Power and Lossy Networks 650 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 651 . 653 Authors' Addresses 655 Carles Gomez 656 Universitat Politecnica de Catalunya 657 C/Esteve Terradas, 7 658 Castelldefels 08860 659 Spain 661 Email: carlesgo@entel.upc.edu 663 Seyed Mahdi Darroudi 664 Universitat Politecnica de Catalunya 665 C/Esteve Terradas, 7 666 Castelldefels 08860 667 Spain 669 Email: sm.darroudi@entel.upc.edu 671 Teemu Savolainen 672 DarkMatter LLC 674 Email: teemu.savolainen@darkmatter.ae 675 Michael Spoerk 676 Graz University of Technology 677 Inffeldgasse 16/I 678 Graz 8010 679 Austria 681 Email: michael.spoerk@tugraz.at