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Boilerplate error? (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (April 22, 2021) is 387 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Possible downref: Non-RFC (?) normative reference: ref. 'IPSP' Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 6Lo Working Group C. Gomez 3 Internet-Draft S. Darroudi 4 Intended status: Standards Track Universitat Politecnica de Catalunya 5 Expires: October 24, 2021 T. Savolainen 6 Unaffiliated 7 M. Spoerk 8 Graz University of Technology 9 April 22, 2021 11 IPv6 Mesh over BLUETOOTH(R) Low Energy using IPSP 12 draft-ietf-6lo-blemesh-10 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 October 24, 2021. 42 Copyright Notice 44 Copyright (c) 2021 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 . . . . . . . . . . . . . . . . . 8 69 3.3.4. Unicast and multicast mapping . . . . . . . . . . . . 9 70 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 71 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 72 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 10 73 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 74 8. Appendix A: Bluetooth LE connection establishment example . . 10 75 9. Appendix B: Node joining procedure . . . . . . . . . . . . . 13 76 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 77 10.1. Normative References . . . . . . . . . . . . . . . . . . 14 78 10.2. Informative References . . . . . . . . . . . . . . . . . 15 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 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 [RFC7668], respectively. Bluetooth 4.0 only supports Bluetooth 94 LE networks that follow the star topology. As a consequence, RFC 95 7668 [RFC7668] was specifically developed and optimized for that type 96 of network topology. However, the functionality described in RFC 97 7668 [RFC7668] is not sufficient and would fail to enable an IPv6 98 mesh over Bluetooth LE links. This document specifies mechanisms 99 that are needed to enable IPv6 mesh over Bluetooth LE links. This 100 document does not specify the routing protocol to be used in an IPv6 101 mesh over Bluetooth LE links. 103 1.1. Terminology and Requirements Language 105 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 106 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 107 "OPTIONAL" in this document are to be interpreted as described in 108 BCP14 RFC 2119 [RFC2119], RFC 8174 [RFC8174], when, and only when, 109 they appear in all capitals, as shown here. 111 The terms 6LoWPAN Node (6LN), 6LoWPAN Router (6LR) and 6LoWPAN Border 112 Router (6LBR) are defined as in [RFC6775], with an addition that 113 Bluetooth LE central and Bluetooth LE peripheral (see Section 2) can 114 both be adopted by a 6LN, a 6LR or a 6LBR. 116 2. Bluetooth LE Networks and the IPSP 118 Bluetooth LE defines two Generic Access Profile (GAP) roles of 119 relevance herein: the Bluetooth LE central role and the Bluetooth LE 120 peripheral role. A device in the central role, which is called 121 central from now on, has traditionally been able to manage multiple 122 simultaneous connections with a number of devices in the peripheral 123 role, called peripherals hereinafter. Bluetooth 4.1 (now deprecated) 124 introduced the possibility for a peripheral to be connected to more 125 than one central simultaneously, therefore allowing extended 126 topologies beyond the star topology for a Bluetooth LE network. In 127 addition, a device may simultaneously be a central in a set of link 128 layer connections, as well as a peripheral in others. 130 On the other hand, the IPSP enables discovery of IP-enabled devices 131 and the establishment of a link layer connection for transporting 132 IPv6 packets. The IPSP defines the Node and Router roles for devices 133 that consume/originate IPv6 packets and for devices that can route 134 IPv6 packets, respectively. Consistently with Bluetooth 4.1 and 135 subsequent Bluetooth versions (e.g. Bluetooth 4.2 [BTCorev4.2] or 136 subsequent), a device may implement both roles simultaneously. 138 This document assumes a mesh network composed of Bluetooth LE links, 139 where link layer connections are established between neighboring 140 IPv6-enabled devices (see Section 3.3.2, item 3.b, and an example in 141 Appendix A)). The IPv6 forwarding devices of the mesh have to 142 implement both IPSP Node and Router roles, while simpler leaf-only 143 nodes can implement only the Node role. In an IPv6 mesh over 144 Bluetooth LE links, a node is a neighbor of another node, and vice 145 versa, if a link layer connection has been established between both 146 by using the IPSP functionality for discovery and link layer 147 connection establishment for IPv6 packet transport. 149 3. Specification of IPv6 mesh over Bluetooth LE links 151 3.1. Protocol stack 153 Figure 1 illustrates the protocol stack for IPv6 mesh over Bluetooth 154 LE links. The core Bluetooth LE protocol stack comprises two main 155 sections: the Controller, and the Host. The former includes the 156 Physical Layer, and the Link Layer, whereas the latter is composed of 157 the Logical Link Control and Adaptation Protocol (L2CAP), the 158 Attribute Protocol (ATT), and the Generic Attribute Profile (GATT). 159 The Host and the Controller sections are connected by means of the 160 Host-Controller Interface (HCI). A device that supports the IPSP 161 Node role instantiates one Internet Protocol Support Service (IPSS), 162 which runs atop GATT. The protocol stack shown in Figure 1 shows two 163 main differences with the IPv6 over Bluetooth LE stack in RFC 7668: 164 a) the adaptation layer below IPv6 (labelled as "6Lo for IPv6 mesh 165 over Bluetooth LE") is now adapted for IPv6 mesh over Bluetooth LE 166 links, and b) the protocol stack for IPv6 mesh over Bluetooth LE 167 links includes IPv6 routing functionality. 169 +------------------------------------+ 170 | Application | 171 +---------+ +------------------------------------+ 172 | IPSS | | UDP/TCP/other | 173 +---------+ +------------------------------------+ 174 | GATT | | IPv6 |routing| | 175 +---------+ +------------------------------------+ 176 | ATT | | 6Lo for IPv6 mesh over Bluetooh LE | 177 +---------+--+------------------------------------+ 178 | Bluetooth LE L2CAP | 179 HCI - - +-------------------------------------------------+ - - 180 | Bluetooth LE Link Layer | 181 +-------------------------------------------------+ 182 | Bluetooth LE Physical Layer | 183 +-------------------------------------------------+ 185 Figure 1: Protocol stack for IPv6 mesh over Bluetooth LE links. 187 Bluetooth 4.2 defines a default MTU for Bluetooth LE of 251 bytes. 188 Excluding the L2CAP header of 4 bytes, a protocol data unit (PDU) 189 size of 247 bytes is available for the layer above L2CAP. (Note: 190 earlier Bluetooth LE versions offered a maximum amount of 23 bytes 191 for the layer atop L2CAP.) The L2CAP provides a fragmentation and 192 reassembly solution for transmitting or receiving larger PDUs. At 193 each link, the IPSP defines means for negotiating a link-layer 194 connection that provides an MTU of 1280 octets or higher for the IPv6 195 layer [IPSP]. As per the present specification, the MTU size for 196 IPv6 mesh over BLE links is 1280 octets. 198 Similarly to RFC 7668, fragmentation functionality from 6LoWPAN 199 standards is not used for IPv6 mesh over Bluetooth LE links. 200 Bluetooth LE's fragmentation support provided by L2CAP is used. 202 3.2. Subnet model 204 For IPv6 mesh over Bluetooth LE links, a multilink model has been 205 chosen, as further illustrated in Figure 2. As IPv6 over Bluetooth 206 LE is intended for constrained nodes, and for Internet of Things use 207 cases and environments, the complexity of implementing a separate 208 subnet on each peripheral-central link and routing between the 209 subnets appears to be excessive. In this specification, the benefits 210 of treating the collection of point-to-point links between a central 211 and its connected peripherals as a single multilink subnet rather 212 than a multiplicity of separate subnets are considered to outweigh 213 the multilink model's drawbacks as described in [RFC4903]. With the 214 multilink subnet model, the routers have to take on responsibility 215 for tracking multicast state and forwarding multicast in a loop-free 216 manner. Note that the route-over functionality defined in [RFC6775] 217 is essential to enable the multilink subnet model for IPv6 mesh over 218 Bluetooth LE links. 220 / 221 / 222 6LR 6LN 6LN / 223 \ \ \ / 224 \ \ \ / 225 6LN ----- 6LR --------- 6LR ------ 6LBR ----- | Internet 226 <--Link--> <---Link--->/<--Link->/ | 227 / / \ 228 6LN ---- 6LR ----- 6LR \ 229 \ 230 \ 232 <------------ Subnet -----------------><---- IPv6 connection --> 233 to the Internet 235 Figure 2: Example of an IPv6 mesh over a Bluetooth LE network 236 connected to the Internet 238 One or more 6LBRs are connected to the Internet. 6LNs are connected 239 to the network through a 6LR or a 6LBR. Note that, in some 240 scenarios, and/or for some time intervals, a 6LR may remain at the 241 edge of the network (e.g. the top left node in Figure 2). This may 242 happen when a 6LR has no neighboring 6LNs. A single Global Unicast 243 prefix is used on the whole subnet. 245 IPv6 mesh over Bluetooth LE links MUST follow a route-over approach. 246 This document does not specify the routing protocol to be used in an 247 IPv6 mesh over Bluetooth LE links. 249 3.3. Link model 251 3.3.1. Stateless address autoconfiguration 253 6LN, 6LR, and 6LBR IPv6 addresses in an IPv6 mesh over Bluetooth LE 254 links are configured as per section 3.2.2 of RFC 7668. 256 Multihop Duplicate Address Detection (DAD) functionality as defined 257 in section 8.2 of RFC 6775 and updated by RFC 8505, or some 258 substitute mechanism (see section 3.3.2), MAY be supported. 260 3.3.2. Neighbor Discovery 262 'Neighbor Discovery Optimization for IPv6 over Low-Power Wireless 263 Personal Area Networks (6LoWPANs)' [RFC6775], subsequently updated by 264 'Registration Extensions for IPv6 over Low-Power Wireless Personal 265 Area Network (6LoWPAN) Neighbor Discovery' [RFC8505], describes the 266 neighbor discovery functionality adapted for use in several 6LoWPAN 267 topologies, including the mesh topology. The route-over 268 functionality of RFC 6775 and RFC 8505 MUST be supported. 270 The following aspects of the Neighbor Discovery optimizations for 271 6LoWPAN [RFC6775],[RFC8505] are applicable to Bluetooth LE 6LNs: 273 1. A Bluetooth LE 6LN MUST register its non-link-local addresses 274 with its routers by sending a Neighbor Solicitation (NS) message with 275 the Extended Address Registration Option (EARO) and process the 276 Neighbor Advertisement (NA) accordingly. The EARO option includes a 277 Registration Ownership Verifier (ROVR) field [RFC8505]. In the case 278 of Bluetooth LE, by default the ROVR field is filled with the 48-bit 279 device address used by the Bluetooth LE node converted into 64-bit 280 Modified EUI-64 format [RFC4291]. Optionally, a cryptographic ID 281 (see RFC 8928 [RFC8928]) MAY be placed in the ROVR field. If a 282 cryptographic ID is used, address registration and multihop DAD 283 formats and procedures defined in RFC 8928 MUST be used, unless an 284 alternative mechanism offering equivalent protection is used. 286 As per RFC 8505, a 6LN link-local address does not need to be unique 287 in the multilink subnet. A link-local address only needs to be 288 unique from the perspective of the two nodes that use it to 289 communicate (e.g., the 6LN and the 6LR in an NS/NA exchange). 290 Therefore, the exchange of EDAR and EDAC messages between the 6LR and 291 a 6LBR, which ensures that an address is unique across the domain 292 covered by the 6LBR, does not need to take place for link-local 293 addresses. 295 If the 6LN registers multiple addresses that are not based on the 296 Bluetooth device address using the same compression context, the 297 header compression efficiency may decrease, since only the last 298 registered address can be fully elided (see Section 3.2.4 of RFC 299 7668). 301 2. For sending Router Solicitations and processing Router 302 Advertisements, the hosts that participate in an IPv6 mesh over BLE 303 MUST, respectively, follow Sections 5.3 and 5.4 of [RFC6775], and 304 Section 5.6 of [RFC8505]. 306 3. The router behavior for 6LRs and 6LBRs is described in Section 6 307 of RFC 6775, and updated by RFC 8505. However, as per this 308 specification: a) Routers SHALL NOT use multicast NSs to discover 309 other routers' link layer addresses. b) As per section 6.2 of RFC 310 6775, in a dynamic configuration scenario, a 6LR comes up as a non- 311 router and waits to receive a Router Advertisement for configuring 312 its own interface address first, before setting its interfaces to be 313 advertising interfaces and turning into a router. In order to 314 support such operation in an IPv6 mesh over Bluetooth LE links, a 6LR 315 first uses the IPSP Node role only. Once the 6LR has established a 316 connection with another node currently running as a router, and 317 receives a Router Advertisement from that router, the 6LR configures 318 its own interface address, it turns into a router, and it runs as an 319 IPSP Router. In contrast with a 6LR, a 6LBR uses the IPSP Router 320 role since the 6LBR is initialized, that is, the 6LBR uses both the 321 IPSP Node and IPSP Router roles at all times. See an example in 322 Appendix B.. 324 4. Border router behavior is described in Section 7 of RFC 6775, and 325 updated by RFC 8505. 327 RFC 6775 defines substitutable mechanisms for distributing prefixes 328 and context information (section 8.1 of RFC 6775), as well as for 329 Duplicate Address Detection across a route-over 6LoWPAN (section 8.2 330 of RFC 6775). RFC 8505 updates those mechanisms and the related 331 message formats. Implementations of this specification MUST either 332 support the features described in sections 8.1 and 8.2 of RFC 6775, 333 as updated by RFC 8505, or some alternative ("substitute") mechanism. 335 3.3.3. Header compression 337 Header compression as defined in RFC 6282 [RFC6282], which specifies 338 the compression format for IPv6 datagrams on top of IEEE 802.15.4, is 339 REQUIRED as the basis for IPv6 header compression on top of Bluetooth 340 LE. All headers MUST be compressed according to RFC 6282 [RFC6282] 341 encoding formats. 343 To enable efficient header compression, when the 6LBR sends a Router 344 Advertisement it MAY include a 6LoWPAN Context Option (6CO) [RFC6775] 345 matching each address prefix advertised via a Prefix Information 346 Option (PIO) [RFC4861] for use in stateless address 347 autoconfiguration. Note that 6CO is not needed for context-based 348 compression when context is pre-provisioned or provided by out-of- 349 band means, as in these cases the in-band indication (6CO) becomes 350 superfluous. 352 The specific optimizations of RFC 7668 for header compression, which 353 exploited the star topology and ARO (note that the latter has been 354 updated by EARO as per RFC 8505), cannot be generalized in an IPv6 355 mesh over Bluetooth LE links. Still, a subset of those optimizations 356 can be applied in some cases in such a network. These cases comprise 357 link-local interactions, non-link-local packet transmissions 358 originated by a 6LN (i.e. the first hop from a 6LN), and non-link- 359 local packets intended for a 6LN that are originated or forwarded by 360 a neighbor of that 6LN (i.e. the last hop toward a 6LN). For all 361 other packet transmissions, context-based compression MAY be used. 363 When a device transmits a packet to a neighbor, the sender MUST fully 364 elide the source IID if the source IPv6 address is the link-local 365 address based on the sender's Bluetooth device address (SAC=0, 366 SAM=11). The sender also MUST fully elide the destination IPv6 367 address if it is the link-local address based on the neighbor's 368 Bluetooth device address (DAC=0, DAM=11). 370 When a 6LN transmits a packet, with a non-link-local source address 371 that the 6LN has registered with EARO in the next-hop router for the 372 indicated prefix, the source address MUST be fully elided if it is 373 the latest address that the 6LN has registered for the indicated 374 prefix (SAC=1, SAM=11). If the source non-link-local address is not 375 the latest registered by the 6LN, and the first 48 bits of the IID 376 match with the latest address registered by the 6LN, then the last 16 377 bits of the IID SHALL be carried in-line (SAC=1, SAM=10). Otherwise, 378 if the first 48 bits of the IID do not match, then the 64 bits of the 379 IID SHALL be fully carried in-line (SAC=1, SAM=01). 381 When a router transmits a packet to a neighboring 6LN, with a non- 382 link-local destination address, the router MUST fully elide the 383 destination IPv6 address if the destination address is the latest 384 registered by the 6LN with EARO for the indicated context (DAC=1, 385 DAM=11). If the destination address is a non-link-local address and 386 not the latest registered, and the first 48 bits of the IID match to 387 those of the latest registered address, then the last 16 bits of the 388 IID SHALL be carried in-line (DAC=1, DAM=10). Otherwise, if the 389 first 48 bits of the IID do not match, then the 64 bits of the IID 390 SHALL be fully carried in-line (DAC=1, DAM=01). 392 3.3.4. Unicast and multicast mapping 394 The Bluetooth LE Link Layer does not support multicast. Hence, 395 traffic is always unicast between two Bluetooth LE neighboring nodes. 396 If a node needs to send a multicast packet to several neighbors, it 397 has to replicate the packet and unicast it on each link. However, 398 this may not be energy efficient, and particular care must be taken 399 if the node is battery powered. A router (i.e., a 6LR or a 6LBR) 400 MUST keep track of neighboring multicast listeners, and it MUST NOT 401 forward multicast packets to neighbors that have not registered as 402 listeners for multicast groups to which the packets are destined. 404 4. IANA Considerations 406 There are no IANA considerations related to this document. 408 5. Security Considerations 410 The security considerations in RFC 7668 apply. 412 IPv6 mesh over Bluetooth LE links requires a routing protocol to find 413 end-to-end paths. Unfortunately, the routing protocol may generate 414 additional opportunities for threats and attacks to the network. 416 RFC 7416 [RFC7416] provides a systematic overview of threats and 417 attacks on the IPv6 Routing Protocol for Low-Power and Lossy Networks 418 (RPL), as well as countermeasures. In that document, described 419 threats and attacks comprise threats due to failures to authenticate, 420 threats due to failure to keep routing information, threats and 421 attacks on integrity, and threats and attacks on availability. 422 Reported countermeasures comprise confidentiality attack, integrity 423 attack, and availability attack countermeasures. 425 While this specification does not state the routing protocol to be 426 used in IPv6 mesh over Bluetooth LE links, the guidance of RFC 7416 427 is useful when RPL is used in such scenarios. Furthermore, such 428 guidance may partly apply for other routing protocols as well. 430 The ROVR can be derived from the Bluetooth device address. However, 431 such a ROVR can be spoofed, and therefore, any node connected to the 432 subnet and aware of a registered-address-to-ROVR mapping could 433 perform address theft and impersonation attacks. Use of Address 434 Protected Neighbor Discovery RFC 8928 [RFC8928] provides protection 435 against such attacks. 437 6. Contributors 439 Carlo Alberto Boano (Graz University of Technology) contributed to 440 the design and validation of this document. 442 7. Acknowledgements 444 The Bluetooth, Bluetooth Smart and Bluetooth Smart Ready marks are 445 registered trademarks owned by Bluetooth SIG, Inc. 447 The authors of this document are grateful to all RFC 7668 authors, 448 since this document borrows many concepts (albeit, with necessary 449 extensions) from RFC 7668. 451 The authors also thank Alain Michaud, Mark Powell, Martin Turon, 452 Bilhanan Silverajan, Rahul Jadhav, Pascal Thubert, Acee Lindem, 453 Catherine Meadows, and Dominique Barthel for their reviews and 454 comments, which helped improve the document. 456 Carles Gomez has been supported in part by the Spanish Government 457 Ministerio de Economia y Competitividad through projects 458 TEC2012-32531, TEC2016-79988-P, PID2019-106808RA-I00 and FEDER, and 459 Secretaria d'Universitats i Recerca del Departament d'Empresa i 460 Coneixement de la Generalitat de Catalunya 2017 through grant SGR 461 376. 463 8. Appendix A: Bluetooth LE connection establishment example 465 This appendix provides an example of Bluetooth LE connection 466 establishment and use of IPSP roles in an IPv6 mesh over Bluetooth LE 467 links that uses dynamic configuration. The example follows text in 468 Section 3.3.2, item 3.b). 470 The example assumes a network with one 6LBR, two 6LRs and three 6LNs, 471 as shown in Figure 3. Connectivity between the 6LNs and the 6LBR is 472 only possible via the 6LRs. 474 The following text describes the different steps as time evolves, in 475 the example. Note that other sequences of events that may lead to 476 the same final scenario are also possible. 478 At the beginning, the 6LBR starts running as an IPSP Router, whereas 479 the rest of devices are not yet initialized (Step 1). Next, the 6LRs 480 start running as IPSP Nodes, i.e., they use Bluetooth LE 481 advertisement packets to announce their presence and support of IPv6 482 capabilities (Step 2). The 6LBR (already running as an IPSP Router) 483 discovers the presence of the 6LRs and establishes one Bluetooth LE 484 connection with each 6LR (Step 3). After establishment of those link 485 layer connections (and after reception of Router Advertisements from 486 the 6LBR), the 6LRs start operating as routers, and also initiate the 487 IPSP Router role (Step 4) (note: whether the IPSP Node role is kept 488 running simultaneously is an implementation decision). Then, 6LNs 489 start running the IPSP Node role (Step 5). Finally, the 6LRs 490 discover presence of the 6LNs and establish connections with the 491 latter (Step 6). 493 Step 1 494 ****** 495 6LBR 496 (IPSP: Router) 498 6LR 6LR 499 (not initialized) (not initialized) 501 6LN 6LN 6LN 502 (not initialized) (not initialized) (not initialized) 504 Step 2 505 ****** 506 6LBR 507 (IPSP: Router) 509 6LR 6LR 510 (IPSP: Node) (IPSP: Node) 512 6LN 6LN 6LN 513 (not initialized) (not initialized) (not initialized) 515 Step 3 516 ****** 518 6LBR 519 (IPSP: Router) 520 Bluetooth LE connection --> / \ 521 / \ 522 6LR 6LR 523 (IPSP: Node) (IPSP: Node) 525 6LN 6LN 6LN 526 (not initialized) (not initialized) (not initialized) 528 Step 4 529 ****** 531 6LBR 532 (IPSP: Router) 533 / \ 534 / \ 535 6LR 6LR 536 (IPSP: Router) (IPSP: Router) 538 6LN 6LN 6LN 539 (not initialized) (not initialized) (not initialized) 541 Step 5 542 ****** 544 6LBR 545 (IPSP: Router) 546 / \ 547 / \ 548 6LR 6LR 549 (IPSP: Router) (IPSP: Router) 551 6LN 6LN 6LN 552 (IPSP: Node) (IPSP: Node) (IPSP: Node) 554 Step 6 555 ****** 557 6LBR 558 (IPSP: Router) 559 / \ 560 / \ 561 6LR 6LR 562 (IPSP: Router) (IPSP: Router) 563 / \ / \ 564 / \ / \ 565 / \ / \ 566 6LN 6LN 6LN 567 (IPSP: Node) (IPSP: Node) (IPSP: Node) 569 Figure 3: An example of connection establishment and use of IPSP 570 roles in an IPv6 mesh over Bluetooth LE links. 572 9. Appendix B: Node joining procedure 574 This appendix provides a diagram that illustrates the node joining 575 procedure. First of all, the joining node advertises its presence in 576 order to allow establishing Bluetooth LE connections with neighbors 577 that already belong to a network. The latter typically run as a 6LR 578 or as a 6LBR. After Bluetooth LE connection establishment, the 579 joining node starts acting as a 6LN. 581 Figure 4 shows the sequence of messages that are exchanged by the 6LN 582 and a neighboring 6LR that already belongs to the network, after the 583 establishment of a Bluetooth LE connection between both devices. 584 Initially, the 6LN sends an RS message (1). Then, the 6LR replies 585 with an RA, which includes the PIO (2). After discovering the non- 586 link-local prefix in use in the network, the 6LN creates its non- 587 link-local address, registers that address with EARO (3) in the 6LR, 588 and multihop DAD is performed (4). The next step is the transmission 589 of the NA message sent by the 6LR in response to the NS previously 590 sent by the 6LN (5). If the non-link-local address of the 6LN has 591 been successfully validated, the 6LN can operate as a member of the 592 network it has joined. 594 (1) 6LN ----(RS)-------> 6LR 595 (2) 6LN <---(RA-PIO)---- 6LR 596 (3) 6LN ----(NS-EARO)--> 6LR 597 (4) [Multihop DAD procedure] 598 (5) 6LN <---(NA)-------- 6LR 600 Figure 4: Message exchange diagram for a joining node 602 10. References 604 10.1. Normative References 606 [BTCorev4.2] 607 Bluetooth Special Interest Group, "Bluetooth Core 608 Specification Version 4.2", December 2014, 609 . 612 [IPSP] Bluetooth Special Interest Group, "Bluetooth Internet 613 Protocol Support Profile Specification Version 1.0.0", 614 December 2014, . 617 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 618 Requirement Levels", BCP 14, RFC 2119, 619 DOI 10.17487/RFC2119, March 1997, 620 . 622 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 623 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 624 2006, . 626 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 627 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 628 DOI 10.17487/RFC4861, September 2007, 629 . 631 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 632 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 633 DOI 10.17487/RFC6282, September 2011, 634 . 636 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 637 Bormann, "Neighbor Discovery Optimization for IPv6 over 638 Low-Power Wireless Personal Area Networks (6LoWPANs)", 639 RFC 6775, DOI 10.17487/RFC6775, November 2012, 640 . 642 [RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B., 643 Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low 644 Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015, 645 . 647 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 648 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 649 May 2017, . 651 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 652 Perkins, "Registration Extensions for IPv6 over Low-Power 653 Wireless Personal Area Network (6LoWPAN) Neighbor 654 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 655 . 657 [RFC8928] Thubert, P., Ed., Sarikaya, B., Sethi, M., and R. Struik, 658 "Address-Protected Neighbor Discovery for Low-Power and 659 Lossy Networks", RFC 8928, DOI 10.17487/RFC8928, November 660 2020, . 662 10.2. Informative References 664 [BTCorev4.1] 665 Bluetooth Special Interest Group, "Bluetooth Core 666 Specification Version 4.1", December 2013, 667 . 670 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 671 DOI 10.17487/RFC4903, June 2007, 672 . 674 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 675 and M. Richardson, Ed., "A Security Threat Analysis for 676 the Routing Protocol for Low-Power and Lossy Networks 677 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 678 . 680 Authors' Addresses 682 Carles Gomez 683 Universitat Politecnica de Catalunya 684 C/Esteve Terradas, 7 685 Castelldefels 08860 686 Spain 688 Email: carlesgo@entel.upc.edu 690 Seyed Mahdi Darroudi 691 Universitat Politecnica de Catalunya 692 C/Esteve Terradas, 7 693 Castelldefels 08860 694 Spain 696 Email: sm.darroudi@entel.upc.edu 698 Teemu Savolainen 699 Unaffiliated 701 Email: tsavo.stds@gmail.com 703 Michael Spoerk 704 Graz University of Technology 705 Inffeldgasse 16/I 706 Graz 8010 707 Austria 709 Email: michael.spoerk@tugraz.at