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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 4 Updates: 6775 (if approved) E. Nordmark 5 Intended status: Standards Track 6 Expires: November 2, 2017 S. Chakrabarti 7 May 1, 2017 9 An Update to 6LoWPAN ND 10 draft-ietf-6lo-rfc6775-update-04 12 Abstract 14 This specification updates RFC 6775 - 6LoWPAN Neighbor Discovery, to 15 clarify the role of the protocol as a registration technique, 16 simplify the registration operation in 6LoWPAN routers, and provide 17 enhancements to the registration capabilities, in particular for the 18 registration to a Backbone Router for proxy ND operations. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on November 2, 2017. 37 Copyright Notice 39 Copyright (c) 2017 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 55 2. Considerations On Registration Rejection . . . . . . . . . . 3 56 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 57 4. Extending RFC 7400 . . . . . . . . . . . . . . . . . . . . . 5 58 5. Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . . 5 59 5.1. Extended Address Registration Option . . . . . . . . . . 6 60 5.2. Transaction ID . . . . . . . . . . . . . . . . . . . . . 6 61 5.3. Owner Unique ID . . . . . . . . . . . . . . . . . . . . . 7 62 5.4. Registering the Target Address . . . . . . . . . . . . . 8 63 5.5. Link-Local Addresses and Registration . . . . . . . . . . 8 64 5.6. Maintaining the Registration States . . . . . . . . . . . 10 65 6. Updated ND Options . . . . . . . . . . . . . . . . . . . . . 11 66 6.1. New 6LoWPAN capability Bits in the Capability Indication 67 Option . . . . . . . . . . . . . . . . . . . . . . . . . 11 68 6.2. The Enhanced Address Registration Option (EARO) . . . . . 12 69 7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 14 70 7.1. Discovering the capabilities of an ND peer . . . . . . . 14 71 7.1.1. Using the E Flag in the CIO . . . . . . . . . . . . . 14 72 7.1.2. Using the T Flag in the EARO . . . . . . . . . . . . 15 73 7.2. Legacy 6LoWPAN Node . . . . . . . . . . . . . . . . . . . 15 74 7.3. Legacy 6LoWPAN Router . . . . . . . . . . . . . . . . . . 16 75 7.4. Legacy 6LoWPAN Border Router . . . . . . . . . . . . . . 16 76 8. Security Considerations . . . . . . . . . . . . . . . . . . . 16 77 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 78 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19 79 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 80 11.1. Normative References . . . . . . . . . . . . . . . . . . 20 81 11.2. Informative References . . . . . . . . . . . . . . . . . 21 82 11.3. External Informative References . . . . . . . . . . . . 23 83 Appendix A. Applicability and Requirements Served . . . . . . . 24 84 Appendix B. Requirements . . . . . . . . . . . . . . . . . . . . 24 85 B.1. Requirements Related to Mobility . . . . . . . . . . . . 25 86 B.2. Requirements Related to Routing Protocols . . . . . . . . 25 87 B.3. Requirements Related to the Variety of Low-Power Link 88 types . . . . . . . . . . . . . . . . . . . . . . . . . . 26 89 B.4. Requirements Related to Proxy Operations . . . . . . . . 27 90 B.5. Requirements Related to Security . . . . . . . . . . . . 27 91 B.6. Requirements Related to Scalability . . . . . . . . . . . 28 92 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29 94 1. Introduction 96 RFC 6775, the "Neighbor Discovery Optimization for IPv6 over Low- 97 Power Wireless Personal Area Networks (6LoWPANs)" [RFC6775] 98 introduced a proactive registration mechanism to IPv6 Neighbor 99 Discovery (ND) services that is well suited to nodes belonging to a 100 Low Power Lossy Network (LLN). 102 The scope of this draft is an IPv6 LLN, which can be a simple star or 103 a more complex mesh topology. The LLN may be anchored at an IPv6 104 Backbone Router (6BBR) [I-D.ietf-6lo-backbone-router]. The 6BBRs 105 interconnect the LLNs over a Backbone Link and emulate that the LLN 106 nodes are present on the Backbone using proxy-ND operations. 108 This specification modifies and extends the behavior and protocol 109 elements of RFC 6775 [RFC6775] to enable additional capabilities, in 110 particular the registration to a 6BBR for proxy ND operations. 112 2. Considerations On Registration Rejection 114 The purpose of the Address Registration Option (ARO) RFC 6775 115 [RFC6775] and of the Extended ARO (EARO) that is introduced in this 116 document is to facilitate duplicate address detection (DAD) for hosts 117 and pre-populate Neighbor Cache Entries (NCE) [RFC4861] in the 118 routers to reduce the need for sending multicast neighbor 119 solicitations and also to be able to support IPv6 Backbone Routers. 121 In some cases the address registration can fail or be useless for 122 reasons other than a duplicate address. Examples are the router 123 having run out of space, a registration bearing a stale sequence 124 number (e.g. denoting a movement of the host after this registration 125 was placed), a host misbehaving and attempting to register an invalid 126 address such as the unspecified address [RFC4291], or the host using 127 an address which is not topologically correct on that link. In such 128 cases the host will receive an error to help diagnose the issue and 129 may retry, possibly with a different address, and possibly 130 registering to a different 6LR, depending on the returned error. 132 However, the ability to return errors to address registrations MUST 133 NOT be used to restrict the ability of hosts to form and use 134 addresses as recommended in "Host Address Availability 135 Recommendations" [RFC7934]. In particular, this is needed for 136 enhanced privacy, which implies that each host will register a 137 multiplicity of address as part mechanisms like "Privacy Extensions 138 for Stateless Address Autoconfiguration (SLAAC) in IPv6" [RFC4941]. 139 This implies that the capabilities of 6LR and 6LBRs in terms of 140 number of registrations must be clearly announced in the router 141 documentation, and that a network administrator should deploy adapted 142 6LR/6LBRs to support the number and type of devices in his network, 143 based on the number of IPv6 addresses that those devices require. 145 3. Terminology 147 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 148 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 149 document are to be interpreted as described in RFC 2119 [RFC2119]. 151 Readers are expected to be familiar with all the terms and concepts 152 that are discussed in 154 "Neighbor Discovery for IP version 6" [RFC4861], 156 "IPv6 Stateless Address Autoconfiguration" [RFC4862], 158 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 159 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 161 "Neighbor Discovery Optimization for Low-power and Lossy Networks" 162 [RFC6775] and 164 "Multi-link Subnet Support in IPv6" 165 [I-D.ietf-ipv6-multilink-subnets]. 167 Additionally, this document uses terminology from 169 "Terms Used in Routing for Low-Power and Lossy Networks" [RFC7102] 170 and 172 the "6TiSCH Terminology" [I-D.ietf-6tisch-terminology], 174 as well as this additional terminology: 176 Backbone This is an IPv6 transit link that interconnects 2 or more 177 Backbone Routers. It is expected to be deployed as a high 178 speed backbone in order to federate a potentially large set of 179 LLNS. Also referred to as a LLN backbone or Backbone network. 181 Backbone Router An IPv6 router that federates the LLN using a 182 Backbone link as a backbone. A 6BBR acts as a 6LoWPAN Border 183 Routers (6LBR) and an Energy Aware Default Router (NEAR). 185 Extended LLN This is the aggregation of multiple LLNs as defined in 186 RFC 4919 [RFC4919], interconnected by a Backbone Link via 187 Backbone Routers, and forming a single IPv6 MultiLink Subnet. 189 Registration The process during which a wireless Node registers its 190 address(es) with the Border Router so the 6BBR can proxy ND for 191 it over the backbone. 193 Binding The state in the 6BBR that associates an IP address with a 194 MAC address, a port and some other information about the node 195 that owns the IP address. 197 Registered Node The node for which the registration is performed, 198 which owns the fields in the EARO option. 200 Registering Node The node that performs the registration to the 201 6BBR, either for one of its own addresses, in which case it is 202 Registered Node and indicates its own MAC Address as Source 203 Link Layer Address (SLLA) in the NS(EARO), or on behalf of a 204 Registered Node that is reachable over a LLN mesh. In the 205 latter case, if the Registered Node is reachable from the 6BBR 206 over a Mesh-Under mesh, the Registering Node indicates the MAC 207 Address of the Registered Node as SLLA in the NS(EARO). 208 Otherwise, it is expected that the Registered Device is 209 reachable over a Route-Over mesh from the Registering Node, in 210 which case the SLLA in the NS(ARO) is that of the Registering 211 Node, which causes it to attract the packets from the 6BBR to 212 the Registered Node and route them over the LLN. 214 Registered Address The address owned by the Registered Node node 215 that is being registered. 217 4. Extending RFC 7400 219 RFC 7400 [RFC7400] introduces the 6LoWPAN Capability Indication 220 Option (6CIO) to indicate a node's capabilities to its peers. This 221 specification extends the format defined in RFC 7400 to signal the 222 support for EARO, as well as the capability to act as a 6LR, 6LBR and 223 6BBR. 225 With RFC 7400 [RFC7400], the 6CIO is typically sent Router 226 Solicitation (RS) messages. When used to signal the capabilities 227 above per this specification, the 6CIO is typically present Router 228 Advertisement (RA) messages but can also be present in RS, Neighbor 229 Solicitation (NS) and Neighbor Advertisement (NA) messages. 231 5. Updating RFC 6775 233 This specification extends the Address Registration Option (ARO) 234 defined in RFC 6775 [RFC6775]; in particular a "T" flag is added that 235 must be set is NS messages when this specification is used, and 236 echo'ed in NA messages to confirm that the protocol effectively 237 supported. Support for this specification can thus be inferred from 238 the presence of the Extended ARO ("T" flag set) in ND messages. 240 In order to support various types of link layers, this specification 241 also adds recommendation to allow multiple registrations, including 242 for privacy / temporary addresses, and provides new mechanisms to 243 help clean up stale registration states as soon as possible. 245 A Registering Node that supports this specification will favor 246 registering to a 6LR that indicates support for this specification 247 over that of RFC 6775 [RFC6775]. 249 5.1. Extended Address Registration Option 251 This specification extends the ARO option that is used for the 252 process of address registration. The new ARO is referred to as 253 Extended ARO (EARO), and its semantics are modified as follows: 255 The address that is being registered with a Neighbor Solicitation 256 (NS) with an EARO is now the Target Address, as opposed to the Source 257 Address as specified in RFC 6775 [RFC6775] (see Section 5.4 for 258 more). This change enables a 6LBR to use an address of his as source 259 to the proxy-registration of an address that belongs to a LLN Node to 260 a 6BBR. This also limits the use of an address as source address 261 before it is registered and the associated Duplicate Address 262 Detection (DAD) is complete. 264 The Unique ID in the EARO option does no more have to be a MAC 265 address (see Section 5.3 for more). This enables in particular the 266 use of a Provable Temporary UID (PT-UID) as opposed to burn-in MAC 267 address, the PT-UID providing a trusted anchor by the 6LR and 6LBR to 268 protect the state associated to the node. 270 The specification introduces a Transaction ID (TID) field in the EARO 271 (see Section 5.2 for more on TID). The TID MUST be provided by a 272 node that supports this specification and a new T flag MUST be set to 273 indicate so. The T bit can be used to determine whether the peer 274 supports this specification. 276 Finally, this specification introduces a number of new Status codes 277 to help diagnose the cause of a registration failure (more in 278 Table 1). 280 5.2. Transaction ID 282 The specification expects that the Registered Node can provide a 283 sequence number called Transaction ID (TID) that is incremented with 284 each re-registration. The TID essentially obeys the same rules as 285 the Path Sequence field in the Transit Information Option (TIO) found 286 in the RPL Destination Advertisement Object (DAO) [RFC6550]. This 287 way, the LLN node can use the same counter for ND and RPL, and a 6LBR 288 acting as RPL root may easily maintain the registration on behalf of 289 a RPL node deep inside the mesh by simply using the RPL TIO Path 290 Sequence as TID for EARO. 292 When a Registered Node is registered to multiple BBRs in parallel, it 293 is expected that the same TID is used, to enable the 6BBRs to 294 correlate the registrations as being a single one, and differentiate 295 that situation from a movement. 297 If the TIDs are different, a conflict resolution inherited from RPL 298 sorts out the most recent registration and other ones are removed. 299 The operation for computing and comparing the Path Sequence is 300 detailed in section 7 of RFC 6550 [RFC6550] and applies to the TID in 301 the exact same fashion. The resolution is used to determine the 302 freshest registration for a particular address, and an EARO is 303 processed only if it is the freshest, otherwise a Status code 3 304 "Moved" is returned. 306 5.3. Owner Unique ID 308 The Owner Unique ID (OUID) enables to differentiate a real duplicate 309 address registration from a double registration or a movement. An ND 310 message from the 6BBR over the backbone that is proxied on behalf of 311 a Registered Node must carry the most recent EARO option seen for 312 that node. A NS/NA with an EARO and a NS/NA without a EARO thus 313 represent different nodes and if they relate to a same target then 314 they reflect an address duplication. The Owner Unique ID can be as 315 simple as a EUI-64 burn-in address, if duplicate EUI-64 addresses are 316 avoided. 318 Alternatively, the unique ID can be a cryptographic string that can 319 can be used to prove the ownership of the registration as discussed 320 in "Address Protected Neighbor Discovery for Low-power and Lossy 321 Networks" [I-D.ietf-6lo-ap-nd]. 323 In any fashion, it is recommended that the node stores the unique Id 324 or the keys used to generate that ID in persistent memory. 325 Otherwise, it will be prevented to re-register after a reboot that 326 would cause a loss of memory until the Backbone Router times out the 327 registration. 329 5.4. Registering the Target Address 331 This specification changes the behavior of the 6LN and the 6LR so 332 that the Registered Address is found in the Target Address field of 333 the NS and NA messages as opposed to the Source Address. 335 The reason for this change is to enable proxy-registrations on behalf 336 of other nodes in Route-Over meshes, for instance to enable that a 337 RPL root registers addresses on behalf LLN nodes that are deeper in a 338 6TiSCH mesh, as discussed in Appendix B.4. In that case, the 339 Registering Node MUST indicate its own address as source of the ND 340 message and its MAC address in the Source Link-Layer Address Option 341 (SLLAO), since it still expects to get the packets and route them 342 down the mesh. But the Registered Address belongs to another node, 343 the Registered Node, and that address is indicated in the Target 344 Address field of the NS message. 346 With this convention, a TLLA option indicates the link-layer address 347 of the 6LN that owns the address, whereas the SLLA Option in a NS 348 message indicates that of the Registering Node, which can be the 349 owner device, or a proxy. 351 Since the Registering Node is the one that has reachability with the 352 6LR, and is the one expecting packets for the 6LN, it makes sense to 353 maintain compatibility with RFC 6775 [RFC6775], and it is REQUIRED 354 that an SLLA Option is always placed in a registration NS(EARO) 355 message. 357 5.5. Link-Local Addresses and Registration 359 Considering that LLN nodes are often not wired and may move, there is 360 no guarantee that a Link-Local address stays unique between a 361 potentially variable and unbounded set of neighboring nodes. 362 Compared to RFC 6775 [RFC6775], this specification only requires that 363 a Link-Local address is unique from the perspective of the peering 364 nodes. This simplifies the Duplicate Address Detection (DAD) for 365 Link-Local addresses, and there is no DAR/DAC exchange between the 366 6LR and a 6LBR for Link-Local addresses. 368 Additionally, RFC 6775 [RFC6775] requires that a 6LoWPAN Node (6LN) 369 uses an address being registered as the source of the registration 370 message. This generates complexities in the 6LR to be able to cope 371 with a potential duplication, in particular for global addresses. To 372 simplify this, a 6LN and a 6LR that conform this specification always 373 use Link-Local addresses as source and destination addresses for the 374 registration NS/NA exchange. As a result, the registration is 375 globally faster, and some of the complexity is removed. 377 In more details: 379 An exchange between two nodes using Link-Local addresses implies that 380 they are reachable over one hop and that at least one of the 2 nodes 381 acts as a 6LR. A node MUST register a Link-Local address to a 6LR in 382 order to obtain reachability from that 6LR beyond the current 383 exchange, and in particular to use the Link-Local address as source 384 address to register other addresses, e.g. global addresses. 386 If there is no collision with an address previously registered to 387 this 6LR by another 6LN, then, from the standpoint of this 6LR, this 388 Link-Local address is unique and the registration is acceptable. 389 Conversely, it may possibly happen that two different 6LRs expose a 390 same Link-Local address but different link-layer addresses. In that 391 case, a 6LN may only interact with one of the 6LR so as to avoid 392 confusion in the 6LN neighbor cache. 394 The DAD process between the 6LR and a 6LoWPAN Border Router (6LBR), 395 which is based on a Duplicate Address Request (DAR) / Duplicate 396 Address Confirmation (DAC) exchange as described in RFC 6775 397 [RFC6775], does not need to take place for Link-Local addresses. 399 It is desired that a 6LR does not need to modify its state associated 400 to the Source Address of an NS(EARO) message. For that reason, when 401 possible, it is RECOMMENDED to use an address that is already 402 registered with a 6LR 404 When registering to a 6LR that conforms this specification, a node 405 MUST use a Link-Local address as the source address of the 406 registration, whatever the type of IPv6 address that is being 407 registered. That Link-Local Address MUST be either already 408 registered, or the address that is being registered. 410 When a Registering Node does not have an already-registered address, 411 it MUST register a Link-Local address, using it as both the Source 412 and the Target Address of an NS(EARO) message. In that case, it is 413 RECOMMENDED to use a Link-Local address that is (expected to be) 414 globally unique, e.g. derived from a burn-in MAC address. An EARO 415 option in the response NA indicates that the 6LR supports this 416 specification. 418 Since there is no DAR/DAC exchange for Link-Local addresses, the 6LR 419 may answer immediately to the registration of a Link-Local address, 420 based solely on its existing state and the Source Link-Layer Option 421 that MUST be placed in the NS(EARO) message as required in RFC 6775 422 [RFC6775]. 424 A node needs to register its IPv6 Global Unicast IPv6 Addresses (GUA) 425 to a 6LR in order to obtain a global reachability for these addresses 426 via that 6LR. As opposed to a node that complies to RFC 6775 427 [RFC6775], a Registering Node registering a GUA does not use that GUA 428 as Source Address for the registration to a 6LR that conforms this 429 specification. The DAR/DAC exchange MUST take place for non-Link- 430 Local addresses as prescribed by RFC 6775 [RFC6775]. 432 5.6. Maintaining the Registration States 434 This section discusses protocol actions that involve the registering 435 node, the 6LR and the 6LBR. It must be noted that the portion that 436 deals with a 6LBR only applies to those addresses that are registered 437 to it, which, as discussed in Section 5.5, is not the case for Link- 438 Local addresses. The registration state includes all data that is 439 stored in the router relative to that registration, in particular, 440 but not limited to, an NCE in a 6LR. 6LBRs and 6BBRs may store 441 additional registration information in more complex data structures 442 and use protocols that are out of scope of this document to keep them 443 synchonized when they are distributed. 445 When its Neighbor Cache is full, a 6LR cannot accept a new 446 registration. In that situation, the EARO is returned in a NA 447 message with a Status of 2, and the registering node may attempt to 448 register to another 6LR. Conversely the registry in the 6LBR may be 449 saturated, in which case the 6LBR cannot guarantee that a new address 450 is effectively not a duplicate. In that case, the 6LBR replies to a 451 DAR message with a DAC message that carries a Status code 9 452 indicating "6LBR Registry saturated", and the address stays in 453 TENTATIVE state. 455 A node renews an existing registration by repeatedly sending NS(EARO) 456 messages for the registered address. In order to refresh the 457 registration state in the 6LBR, these registrations MUST be reported 458 to the 6LBR. This is normally done through a DAR/DAC exchange, but 459 the refresh MAY alternatively be piggy-backed in another protocol 460 such as RPL [RFC6550], as long as the semantics of the EARO are fully 461 carried in the alternate protocol. In the particular case of RPL, 462 the TID MUST be used as the Path Sequence in the TIO, and the 463 Registration Lifetime MUST be used as Path Lifetime. It is also 464 REQUIRED that the root of the RPL DODAG passes that information to 465 the 6LBR on behalf of the 6LR, either through a DAR/DAC exchange, or 466 through internal methods if they are collocated. 468 A node that ceases to use an address SHOULD attempt to deregister 469 that address from all the 6LRs to which it has registered the 470 address, which is achieved using an NS(EARO) message with a 471 Registration Lifetime of 0. 473 A node that moves away from a particular 6LR SHOULD attempt to 474 deregister all of its addresses registered to that 6LR. 476 Upon receiving a NS(EARO) message with a Registration Lifetime of 0 477 and determining that this EARO is the freshest for a given NCE (see 478 Section 5.2), a 6LR cleans up its NCE. If the address was registered 479 to the 6LBR, then the 6LR MUST report to the 6LBR, through a DAR/DAC 480 exchange with the 6LBR, or an alternate protocol, indicating the null 481 Registration Lifetime and the latest TID that this 6LR is aware of. 483 Upon the DAR message, the 6LBR evaluates if this is the freshest EARO 484 it has received for that particular registry entry. If it is, then 485 the entry is scheduled to be removed, and the DAR is answered with a 486 DAC message bearing a Status of 0 "Success". If it is not the 487 freshest, then a Status 2 "Moved" is returned instead, and the 488 existing entry is conserved. The 6LBR SHOULD conserve the address in 489 a DELAY state for a configurable period of time, so as to protect a 490 mobile node that deregistered from one 6LR and did not register yet 491 to a new one. 493 6. Updated ND Options 495 This specification does not introduce new options, but it modifies 496 existing ones and updates the associated behaviors as follow: 498 6.1. New 6LoWPAN capability Bits in the Capability Indication Option 500 This specification defines a number of capability bits in the CIO 501 that was introduced by RFC 7400 [RFC7400]. 503 Support for this specification is indicated by setting the "E" flag 504 in a CIO option. Routers that are capable of acting as 6LR, 6LBR and 505 6BBR SHOULD set the L, B and P flags, respectively. 507 Those flags are not mutually exclusive and if a router is capable of 508 multiple roles, it SHOULD set all the related flags. 510 0 1 2 3 511 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 512 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 513 | Type | Length = 1 |_____________________|L|B|P|E|G| 514 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |_______________________________________________________________| 515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 517 Figure 1: New capability Bits L, B, P, E in the CIO 519 Option Fields 520 Type: 36 522 L: Node is a 6LR, it can take registrations. 524 B: Node is a 6LBR. 526 P: Node is a 6BBR, proxying for nodes on this link. 528 E: This specification is supported and applied. 530 6.2. The Enhanced Address Registration Option (EARO) 532 The Enhanced Address Registration Option (EARO) is intended to be 533 used as a replacement to the ARO option within Neighbor Discovery NS 534 and NA messages between a LLN node and its 6LoWPAN Router (6LR), as 535 well as in Duplicate Address Request (DAR) and the Duplicate Address 536 Confirmation (DAC) messages between 6LRs and 6LBRs in LLNs meshes 537 such as 6TiSCH networks. 539 An NS message with an EARO option is a registration if and only if it 540 also carries an SLLAO option. The AERO option also used in NS and NA 541 messages between Backbone Routers over the backbone link to sort out 542 the distributed registration state, and in that case, it does not 543 carry the SLLAO option and is not confused with a registration. 545 The EARO extends the ARO and is recognized by the "T" flag set. 547 When using the EARO option, the address being registered is found in 548 the Target Address field of the NS and NA messages. This differs 549 from 6LoWPAN ND RFC 6775 [RFC6775] which specifies that the address 550 being registered is the source of the NS. 552 The format of the EARO option is as follows: 554 0 1 2 3 555 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 556 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 557 | Type | Length = 2 | Status | Reserved | 558 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 559 | Reserved |T| TID | Registration Lifetime | 560 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 561 | | 562 + Owner Unique ID (EUI-64 or equivalent) + 563 | | 564 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 566 Figure 2: EARO 568 Option Fields 570 Type: 33 572 Length: 8-bit unsigned integer. 574 Status: 8-bit unsigned integer. Indicates the status of a 575 registration in the NA response. MUST be set to 0 in NS messages. 576 See Table 1 below. 578 Reserved: This field is unused. It MUST be initialized to zero by 579 the sender and MUST be ignored by the receiver. 581 T: One bit flag. Set if the next octet is a used as a TID. 583 TID: 1-byte integer; a transaction id that is maintained by the node 584 and incremented with each transaction. it is recommended that the 585 node maintains the TID in a persistent storage. 587 Registration Lifetime: 16-bit integer; expressed in minutes. 0 588 means that the registration has ended and the associated state 589 should be removed. 591 Owner Unique Identifier (OUI): A globally unique identifier for the 592 node associated. This can be the EUI-64 derived IID of an 593 interface, or some provable ID obtained cryptographically. 595 +-------+-----------------------------------------------------------+ 596 | Value | Description | 597 +-------+-----------------------------------------------------------+ 598 | 0..2 | See RFC 6775 [RFC6775]. Note that a Status of 1 | 599 | | "Duplicate Address" applies to the Registered Address. If | 600 | | the Source Address conflicts with an existing | 601 | | registration, "Duplicate Source Address" should be used | 602 | | instead | 603 | | | 604 | 3 | Moved: The registration fails because it is not the | 605 | | freshest. This Status indicates that the registration is | 606 | | rejected because another more recent registration was | 607 | | done, as indicated by a same OUI and a more recent TID. | 608 | | One possible cause is a stale registration that has | 609 | | progressed slowly in the network and was passed by a more | 610 | | recent one. It could also indicate a OUI collision. | 611 | | | 612 | 4 | Removed: The binding state was removed. This may be | 613 | | placed in an asynchronous NS(ARO) message, or as the | 614 | | rejection of a proxy registration to a Backbone Router | 615 | | | 616 | 5 | Proof requested: The registering node is challenged for | 617 | | owning the registered address or for being an acceptable | 618 | | proxy for the registration. This Status is expected in | 619 | | asynchronous messages from a registrar (6LR, 6LBR, 6BBR) | 620 | | to indicate that the registration state is removed, for | 621 | | instance due to time out of a lifetime, or a movement. It | 622 | | is used for instance by a 6BBR in a NA(ARO) message to | 623 | | indicate that the ownership of the proxy state on the | 624 | | backbone was transferred to another 6BBR, which is | 625 | | indicative of a movement of the device. The receiver of | 626 | | the NA is the device that has performed a registration | 627 | | that is now stale and it should clean up its state. | 628 | | | 629 | 6 | Duplicate Source Address: The address used as source of | 630 | | the NS(ARO) conflicts with an existing registration. | 631 | | | 632 | 7 | Invalid Source Address: The address used as source of the | 633 | | NS(ARO) is not a Link-Local address as prescribed by this | 634 | | document. | 635 | | | 636 | 8 | Registered Address topologically incorrect: The address | 637 | | being registered is not usable on this link, e.g. it is | 638 | | not topologically correct | 639 | | | 640 | 9 | 6LBR Registry saturated: A new registration cannot be | 641 | | accepted because the 6LBR Registry is saturated. This | 642 | | code is used by 6LBRs instead of Status 2 when responding | 643 | | to a DAR/DAC exchange and passed on to the registering | 644 | | node by the 6LR. There is no point for the node to retry | 645 | | this registration immediately via another 6LR, since the | 646 | | problem is global to the network. The node may either | 647 | | abandon that address, deregister other addresses first to | 648 | | make room, or keep the address in TENTATIVE state and | 649 | | retry later. | 650 +-------+-----------------------------------------------------------+ 652 Table 1: EARO Status 654 7. Backward Compatibility 656 7.1. Discovering the capabilities of an ND peer 658 7.1.1. Using the E Flag in the CIO 660 If the CIO is used in an ND message, then the "E" Flag MUST be set by 661 the sending node if supports this specification. 663 It is RECOMMENDED that a router that supports this specification 664 indicates so with a CIO option, but this might not be practical if 665 the link-layer MTU is too small. 667 If the registering node receives a CIO in a RA, then the setting of 668 the E" Flag indicates whether or not this specification is supported. 670 7.1.2. Using the T Flag in the EARO 672 One alternate way for a 6LN to discover the router's capabilities to 673 first register a Link Local address, placing the same address in the 674 Source and Target Address fields of the NS message, and setting the 675 "T" Flag. The node may for instance register an address that is 676 based on EUI-64. For such address, DAD is not required and using the 677 SLLAO option in the NS is actually more amenable with existing ND 678 specifications such as the "Optimistic Duplicate Address Detection 679 (DAD) for IPv6" [RFC4429]. Once that first registration is complete, 680 the node knows from the setting of the "T" Flag in the response 681 whether the router supports this specification. If this is verified, 682 the node may register other addresses that it owns, or proxy-register 683 addresses on behalf some another node, indicating those addresses 684 being registered in the Target Address field of the NS messages, 685 while using one of its own, already registered, addresses as source. 687 A node that supports this specification MUST always use an EARO as a 688 replacement to an ARO in its registration to a router. This is 689 harmless since the "T" flag and TID field are reserved in RFC 6775 690 [RFC6775] are ignored by a legacy router. A router that supports 691 this specification answers to an ARO with an ARO and to an EARO with 692 an EARO. 694 This specification changes the behavior of the peers in a 695 registration flows. To enable backward compatibility, a node that 696 registers to a router that is not known to support this specification 697 MUST behave as prescribed by RFC 6775 [RFC6775]. Once the router is 698 known to support this specification, the node MUST obey this 699 specification. 701 7.2. Legacy 6LoWPAN Node 703 A legacy 6LN will use the registered address as source and will not 704 use an EARO option. In order to be backward compatible, an updated 705 6LR needs to accept that registration if it is valid per the 706 "Cryptographically Generated Addresses (CGA)" [RFC3972] 707 specification, and manage the binding cache accordingly. 709 The main difference with RFC 3972 [RFC3972] is that DAR/DAC exchange 710 for DAD may be avoided for Link-Local addresses. Additionally, the 711 6LR SHOULD use an EARO in the reply, and may use any of the Status 712 codes defined in this specification. 714 7.3. Legacy 6LoWPAN Router 716 The first registration by a an updated 6LN is for a Link-Local 717 address, using that Link-Local address as source. A legacy 6LN will 718 not makes a difference and accept -or reject- that registration as if 719 the 6LN was a legacy node. 721 An updated 6LN will always use an EARO option in the registration NS 722 message, whereas a legacy 6LN will always areply with an ARO option 723 in the NA message. So from that first registration, the updated 6LN 724 can figure whether the 6LR supports this specification or not. 726 When facing a legacy 6LR, an updated 6LN may attempt to find an 727 alternate 6LR that is updated. In order to be backward compatible, 728 based on the discovery that a 6LR is legacy, the 6LN needs to 729 fallback to legacy behavior and source the packet with the registered 730 address. 732 The main difference is that the updated 6LN SHOULD use an EARO in the 733 request regardless of the type of 6LN, legacy or updated 735 7.4. Legacy 6LoWPAN Border Router 737 With this specification, the DAR/DAC transports an EARO option as 738 opposed to an ARO option. As described for the NS/NA exchange, 739 devices that support this specification always use an EARO option and 740 all the associated behavior. 742 8. Security Considerations 744 This specification extends RFC 6775 [RFC6775], and the security 745 section of that draft also applies to this as well. In particular, 746 it is expected that the link layer is sufficiently protected to 747 prevent a rogue access, either by means of physical or IP security on 748 the Backbone Link and link layer cryptography on the LLN. This 749 specification also expects that the LLN MAC provides secure unicast 750 to/from the Backbone Router and secure Broadcast from the Backbone 751 Router in a way that prevents tempering with or replaying the RA 752 messages. 754 This specification does not mandate any particular way for forming 755 IPv6 addresses, but it recognizes that use of EUI-64 for forming the 756 Interface ID in the Link-Local address prevents the usage of "SEcure 757 Neighbor Discovery (SEND)" [RFC3971] and CGA [RFC3972], and that of 758 address privacy techniques. This specification RECOMMENDS the use of 759 additional protection against address theft such as provided by 760 "Address Protected Neighbor Discovery for Low-power and Lossy 761 Networks" [I-D.ietf-6lo-ap-nd], which guarantees the ownership of the 762 OUID. 764 As indicated in section Section 2, this protocol does not aim at 765 limiting the number of IPv6 addresses that a device can form, either. 766 A host should be able to register any address that is topologically 767 correct in the subnet(s) advertised by the 6LR/6LBR. 769 On the other hand, the registration mechanism may be used by a rogue 770 node to attack the 6LR or the 6LBR with a Denial-of-Service attack 771 against the registry. It may also happen that the registry of a 6LR 772 or a 6LBR is saturated and cannot take any more registration, which 773 effectively denies the requesting a node the capability to use a new 774 address. In order to alleviate those concerns, Section 5.6 provides 775 a number of recommendations that ensure that a stale registration is 776 removed as soon as possible from the 6LR and 6LBR. In particular, 777 this specification recommends that: 779 o A node that ceases to use an address should attempt to deregister 780 that address from all the 6LRs to which it is registered. The 781 flow is propagated to the 6LBR when needed, and a sequence number 782 is used to make sure that only the freshest command is acted upon. 784 o The nodes should be configured with a Registration Lifetime that 785 reflects their expectation of how long they will use the address 786 with the 6LR to which it is registered. In particular, use cases 787 that involve mobility or rapid address changes should use 788 lifetimes that are homogeneous with the expectation of presence. 790 o The router (6LR or 6LBR) should be configurable so as to limit the 791 number of addresses that can be registered by a single node, as 792 identified at least by MAC address and preferably by security 793 credentials. When that maximum is reached, the router should use 794 a Least-Recently-Used (LRU) logic so as to clean up the addresses 795 that were not used for the longest time, keeping at least one 796 Link-Local address, and attempting to keep one or more stable 797 addresses if such can be recognized, e.g. from the way the IID is 798 formed or because they are used over a much longer time span than 799 other (privacy, shorter-lived) addresses. 801 o Administrators should take great care to deploy adequate numbers 802 of 6LR to cover the needs of the nodes in their range, so as to 803 avoid a situation of starving nodes. It is expected that the 6LBR 804 that serves a LLN is a more capable node then the average 6LR, but 805 in a network condition where it may become saturated, a particular 806 deployment should distribute the 6LBR functionality, for instance 807 by leveraging a high speed backbone and Backbone Routers to 808 aggregate multiple LLNs into a larger subnet. 810 When the ownership of the OUID cannot be assessed, this specification 811 limits the cases where the OUID and the TID are multicasted, and 812 obfuscates them in responses to attempts to take over an address. 814 The LLN nodes depend on the 6LBR and the 6BBR for their operation. A 815 trust model must be put in place to ensure that the right devices are 816 acting in these roles, so as to avoid threats such as black-holing, 817 or bombing attack whereby an impersonated 6LBR would destroy state in 818 the network by using the "Removed" Status code. 820 9. IANA Considerations 822 IANA is requested to create a new subregistry for "ARO Flags" under 823 the "Internet Control Message Protocol version 6 (ICMPv6) 824 Parameters". This specification defines 8 positions, bit 0 to bit 7, 825 and assigns bit 7 for the "T" flag in Section 6.2. The policy is 826 "IETF Review" or "IESG Approval" [RFC5226]. The initial content of 827 the registry is as shown in Table 2. 829 New subregistry for ARO Flags under the "Internet Control Message 830 Protocol version 6 (ICMPv6) Parameters" 832 +------------+--------------+-----------+ 833 | ARO Status | Description | Document | 834 +------------+--------------+-----------+ 835 | 0..6 | Unassigned | | 836 | | | | 837 | 7 | "T" Flag | RFC This | 838 +------------+--------------+-----------+ 840 Table 2: new ARO Flags 842 IANA is requested to make additions to existing registries as 843 follows: 845 Address Registration Option Status Values Registry 847 +------------+------------------------------------------+-----------+ 848 | ARO Status | Description | Document | 849 +------------+------------------------------------------+-----------+ 850 | 3 | Moved | RFC This | 851 | | | | 852 | 4 | Removed | RFC This | 853 | | | | 854 | 5 | Proof requested | RFC This | 855 | | | | 856 | 6 | Duplicate Source Address | RFC This | 857 | | | | 858 | 7 | Invalid Source Address | RFC This | 859 | | | | 860 | 8 | Registered Address topologically | RFC This | 861 | | incorrect | | 862 | | | | 863 | 9 | 6LBR registry saturated | RFC This | 864 +------------+------------------------------------------+-----------+ 866 Table 3: New ARO Status values 868 Subregistry for "6LoWPAN capability Bits" under the "Internet Control 869 Message Protocol version 6 (ICMPv6) Parameters" 871 +----------------+----------------------+-----------+ 872 | capability Bit | Description | Document | 873 +----------------+----------------------+-----------+ 874 | 11 | 6LR capable (L bit) | RFC This | 875 | | | | 876 | 12 | 6LBR capable (B bit) | RFC This | 877 | | | | 878 | 13 | 6BBR capable (P bit) | RFC This | 879 | | | | 880 | 14 | EARO support (E bit) | RFC This | 881 +----------------+----------------------+-----------+ 883 Table 4: New 6LoWPAN capability Bits 885 10. Acknowledgments 887 Kudos to Eric Levy-Abegnoli who designed the First Hop Security 888 infrastructure at Cisco. 890 11. References 892 11.1. Normative References 894 [I-D.ietf-6lo-backbone-router] 895 Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo- 896 backbone-router-03 (work in progress), January 2017. 898 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 899 Requirement Levels", BCP 14, RFC 2119, 900 DOI 10.17487/RFC2119, March 1997, 901 . 903 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 904 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 905 2006, . 907 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 908 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 909 DOI 10.17487/RFC4861, September 2007, 910 . 912 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 913 Address Autoconfiguration", RFC 4862, 914 DOI 10.17487/RFC4862, September 2007, 915 . 917 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 918 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 919 DOI 10.17487/RFC5226, May 2008, 920 . 922 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 923 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 924 DOI 10.17487/RFC6282, September 2011, 925 . 927 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 928 Bormann, "Neighbor Discovery Optimization for IPv6 over 929 Low-Power Wireless Personal Area Networks (6LoWPANs)", 930 RFC 6775, DOI 10.17487/RFC6775, November 2012, 931 . 933 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 934 IPv6 over Low-Power Wireless Personal Area Networks 935 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 936 2014, . 938 11.2. Informative References 940 [I-D.chakrabarti-nordmark-6man-efficient-nd] 941 Chakrabarti, S., Nordmark, E., Thubert, P., and M. 942 Wasserman, "IPv6 Neighbor Discovery Optimizations for 943 Wired and Wireless Networks", draft-chakrabarti-nordmark- 944 6man-efficient-nd-07 (work in progress), February 2015. 946 [I-D.delcarpio-6lo-wlanah] 947 Vega, L., Robles, I., and R. Morabito, "IPv6 over 948 802.11ah", draft-delcarpio-6lo-wlanah-01 (work in 949 progress), October 2015. 951 [I-D.ietf-6lo-6lobac] 952 Lynn, K., Martocci, J., Neilson, C., and S. Donaldson, 953 "Transmission of IPv6 over MS/TP Networks", draft-ietf- 954 6lo-6lobac-08 (work in progress), March 2017. 956 [I-D.ietf-6lo-ap-nd] 957 Sarikaya, B., Thubert, P., and M. Sethi, "Address 958 Protected Neighbor Discovery for Low-power and Lossy 959 Networks", draft-ietf-6lo-ap-nd-00 (work in progress), 960 November 2016. 962 [I-D.ietf-6lo-dect-ule] 963 Mariager, P., Petersen, J., Shelby, Z., Logt, M., and D. 964 Barthel, "Transmission of IPv6 Packets over DECT Ultra Low 965 Energy", draft-ietf-6lo-dect-ule-09 (work in progress), 966 December 2016. 968 [I-D.ietf-6lo-nfc] 969 Choi, Y., Hong, Y., Youn, J., Kim, D., and J. Choi, 970 "Transmission of IPv6 Packets over Near Field 971 Communication", draft-ietf-6lo-nfc-06 (work in progress), 972 March 2017. 974 [I-D.ietf-6tisch-architecture] 975 Thubert, P., "An Architecture for IPv6 over the TSCH mode 976 of IEEE 802.15.4", draft-ietf-6tisch-architecture-11 (work 977 in progress), January 2017. 979 [I-D.ietf-6tisch-terminology] 980 Palattella, M., Thubert, P., Watteyne, T., and Q. Wang, 981 "Terminology in IPv6 over the TSCH mode of IEEE 982 802.15.4e", draft-ietf-6tisch-terminology-08 (work in 983 progress), December 2016. 985 [I-D.ietf-bier-architecture] 986 Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and 987 S. Aldrin, "Multicast using Bit Index Explicit 988 Replication", draft-ietf-bier-architecture-06 (work in 989 progress), April 2017. 991 [I-D.ietf-ipv6-multilink-subnets] 992 Thaler, D. and C. Huitema, "Multi-link Subnet Support in 993 IPv6", draft-ietf-ipv6-multilink-subnets-00 (work in 994 progress), July 2002. 996 [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] 997 Popa, D. and J. Hui, "6LoPLC: Transmission of IPv6 Packets 998 over IEEE 1901.2 Narrowband Powerline Communication 999 Networks", draft-popa-6lo-6loplc-ipv6-over- 1000 ieee19012-networks-00 (work in progress), March 2014. 1002 [RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with 1003 CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September 1004 2003, . 1006 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1007 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1008 DOI 10.17487/RFC3810, June 2004, 1009 . 1011 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 1012 "SEcure Neighbor Discovery (SEND)", RFC 3971, 1013 DOI 10.17487/RFC3971, March 2005, 1014 . 1016 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 1017 RFC 3972, DOI 10.17487/RFC3972, March 2005, 1018 . 1020 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 1021 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 1022 . 1024 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1025 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1026 Overview, Assumptions, Problem Statement, and Goals", 1027 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1028 . 1030 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 1031 Extensions for Stateless Address Autoconfiguration in 1032 IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, 1033 . 1035 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1036 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1037 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1038 Low-Power and Lossy Networks", RFC 6550, 1039 DOI 10.17487/RFC6550, March 2012, 1040 . 1042 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1043 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1044 2014, . 1046 [RFC7217] Gont, F., "A Method for Generating Semantically Opaque 1047 Interface Identifiers with IPv6 Stateless Address 1048 Autoconfiguration (SLAAC)", RFC 7217, 1049 DOI 10.17487/RFC7217, April 2014, 1050 . 1052 [RFC7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets 1053 over ITU-T G.9959 Networks", RFC 7428, 1054 DOI 10.17487/RFC7428, February 2015, 1055 . 1057 [RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B., 1058 Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low 1059 Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015, 1060 . 1062 [RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi, 1063 "Host Address Availability Recommendations", BCP 204, 1064 RFC 7934, DOI 10.17487/RFC7934, July 2016, 1065 . 1067 11.3. External Informative References 1069 [IEEEstd802154] 1070 IEEE, "IEEE Standard for Low-Rate Wireless Networks", 1071 IEEE Standard 802.15.4, DOI 10.1109/IEEESTD.2016.7460875, 1072 . 1074 Appendix A. Applicability and Requirements Served 1076 This specification extends 6LoWPAN ND to sequence the registration 1077 and serves the requirements expressed Appendix B.1 by enabling the 1078 mobility of devices from one LLN to the next based on the 1079 complementary work in the "IPv6 Backbone Router" 1080 [I-D.ietf-6lo-backbone-router] specification. 1082 In the context of the the TimeSlotted Channel Hopping (TSCH) mode of 1083 IEEE Std. 802.15.4 [IEEEstd802154], the "6TiSCH architecture" 1084 [I-D.ietf-6tisch-architecture] introduces how a 6LoWPAN ND host could 1085 connect to the Internet via a RPL mesh Network, but this requires 1086 additions to the 6LOWPAN ND protocol to support mobility and 1087 reachability in a secured and manageable environment. This 1088 specification details the new operations that are required to 1089 implement the 6TiSCH architecture and serves the requirements listed 1090 in Appendix B.2. 1092 The term LLN is used loosely in this specification to cover multiple 1093 types of WLANs and WPANs, including Low-Power Wi-Fi, BLUETOOTH(R) Low 1094 Energy, IEEE Std.802.11AH and IEEE Std.802.15.4 wireless meshes, so 1095 as to address the requirements discussed in Appendix B.3 1097 This specification can be used by any wireless node to associate at 1098 Layer-3 with a 6BBR and register its IPv6 addresses to obtain routing 1099 services including proxy-ND operations over the backbone, effectively 1100 providing a solution to the requirements expressed in Appendix B.4. 1102 "Efficiency aware IPv6 Neighbor Discovery Optimizations" 1103 [I-D.chakrabarti-nordmark-6man-efficient-nd] suggests that 6LoWPAN ND 1104 [RFC6775] can be extended to other types of links beyond IEEE Std. 1105 802.15.4 for which it was defined. The registration technique is 1106 beneficial when the Link-Layer technique used to carry IPv6 multicast 1107 packets is not sufficiently efficient in terms of delivery ratio or 1108 energy consumption in the end devices, in particular to enable 1109 energy-constrained sleeping nodes. The value of such extension is 1110 especially apparent in the case of mobile wireless nodes, to reduce 1111 the multicast operations that are related to classical ND ([RFC4861], 1112 [RFC4862]) and plague the wireless medium. This serves scalability 1113 requirements listed in Appendix B.6. 1115 Appendix B. Requirements 1117 This section lists requirements that were discussed at 6lo for an 1118 update to 6LoWPAN ND. This specification meets most of them, but 1119 those listed in Appendix B.5 which are deferred to a different 1120 specification such as [I-D.ietf-6lo-ap-nd], and those related to 1121 multicast. 1123 B.1. Requirements Related to Mobility 1125 Due to the unstable nature of LLN links, even in a LLN of immobile 1126 nodes a 6LN may change its point of attachment to a 6LR, say 6LR-a, 1127 and may not be able to notify 6LR-a. Consequently, 6LR-a may still 1128 attract traffic that it cannot deliver any more. When links to a 6LR 1129 change state, there is thus a need to identify stale states in a 6LR 1130 and restore reachability in a timely fashion. 1132 Req1.1: Upon a change of point of attachment, connectivity via a new 1133 6LR MUST be restored timely without the need to de-register from the 1134 previous 6LR. 1136 Req1.2: For that purpose, the protocol MUST enable to differentiate 1137 between multiple registrations from one 6LoWPAN Node and 1138 registrations from different 6LoWPAN Nodes claiming the same address. 1140 Req1.3: Stale states MUST be cleaned up in 6LRs. 1142 Req1.4: A 6LoWPAN Node SHOULD also be capable to register its Address 1143 to multiple 6LRs, and this, concurrently. 1145 B.2. Requirements Related to Routing Protocols 1147 The point of attachment of a 6LN may be a 6LR in an LLN mesh. IPv6 1148 routing in a LLN can be based on RPL, which is the routing protocol 1149 that was defined at the IETF for this particular purpose. Other 1150 routing protocols than RPL are also considered by Standard Defining 1151 Organizations (SDO) on the basis of the expected network 1152 characteristics. It is required that a 6LoWPAN Node attached via ND 1153 to a 6LR would need to participate in the selected routing protocol 1154 to obtain reachability via the 6LR. 1156 Next to the 6LBR unicast address registered by ND, other addresses 1157 including multicast addresses are needed as well. For example a 1158 routing protocol often uses a multicast address to register changes 1159 to established paths. ND needs to register such a multicast address 1160 to enable routing concurrently with discovery. 1162 Multicast is needed for groups. Groups MAY be formed by device type 1163 (e.g. routers, street lamps), location (Geography, RPL sub-tree), or 1164 both. 1166 The Bit Index Explicit Replication (BIER) Architecture 1167 [I-D.ietf-bier-architecture] proposes an optimized technique to 1168 enable multicast in a LLN with a very limited requirement for routing 1169 state in the nodes. 1171 Related requirements are: 1173 Req2.1: The ND registration method SHOULD be extended in such a 1174 fashion that the 6LR MAY advertise the Address of a 6LoWPAN Node over 1175 the selected routing protocol and obtain reachability to that Address 1176 using the selected routing protocol. 1178 Req2.2: Considering RPL, the Address Registration Option that is used 1179 in the ND registration SHOULD be extended to carry enough information 1180 to generate a DAO message as specified in [RFC6550] section 6.4, in 1181 particular the capability to compute a Path Sequence and, as an 1182 option, a RPLInstanceID. 1184 Req2.3: Multicast operations SHOULD be supported and optimized, for 1185 instance using BIER or MPL. Whether ND is appropriate for the 1186 registration to the 6BBR is to be defined, considering the additional 1187 burden of supporting the Multicast Listener Discovery Version 2 1188 [RFC3810] (MLDv2) for IPv6. 1190 B.3. Requirements Related to the Variety of Low-Power Link types 1192 6LoWPAN ND [RFC6775] was defined with a focus on IEEE Std.802.15.4 1193 and in particular the capability to derive a unique Identifier from a 1194 globally unique MAC-64 address. At this point, the 6lo Working Group 1195 is extending the 6LoWPAN Header Compression (HC) [RFC6282] technique 1196 to other link types ITU-T G.9959 [RFC7428], Master-Slave/Token- 1197 Passing [I-D.ietf-6lo-6lobac], DECT Ultra Low Energy 1198 [I-D.ietf-6lo-dect-ule], Near Field Communication [I-D.ietf-6lo-nfc], 1199 IEEE Std.802.11ah [I-D.delcarpio-6lo-wlanah], as well as IEEE1901.2 1200 Narrowband Powerline Communication Networks 1201 [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] and BLUETOOTH(R) 1202 Low Energy [RFC7668]. 1204 Related requirements are: 1206 Req3.1: The support of the registration mechanism SHOULD be extended 1207 to more LLN links than IEEE Std.802.15.4, matching at least the LLN 1208 links for which an "IPv6 over foo" specification exists, as well as 1209 Low-Power Wi-Fi. 1211 Req3.2: As part of this extension, a mechanism to compute a unique 1212 Identifier should be provided, with the capability to form a Link- 1213 Local Address that SHOULD be unique at least within the LLN connected 1214 to a 6LBR discovered by ND in each node within the LLN. 1216 Req3.3: The Address Registration Option used in the ND registration 1217 SHOULD be extended to carry the relevant forms of unique Identifier. 1219 Req3.4: The Neighbour Discovery should specify the formation of a 1220 site-local address that follows the security recommendations from 1221 [RFC7217]. 1223 B.4. Requirements Related to Proxy Operations 1225 Duty-cycled devices may not be able to answer themselves to a lookup 1226 from a node that uses classical ND on a backbone and may need a 1227 proxy. Additionally, the duty-cycled device may need to rely on the 1228 6LBR to perform registration to the 6BBR. 1230 The ND registration method SHOULD defend the addresses of duty-cycled 1231 devices that are sleeping most of the time and not capable to defend 1232 their own Addresses. 1234 Related requirements are: 1236 Req4.1: The registration mechanism SHOULD enable a third party to 1237 proxy register an Address on behalf of a 6LoWPAN node that may be 1238 sleeping or located deeper in an LLN mesh. 1240 Req4.2: The registration mechanism SHOULD be applicable to a duty- 1241 cycled device regardless of the link type, and enable a 6BBR to 1242 operate as a proxy to defend the registered Addresses on its behalf. 1244 Req4.3: The registration mechanism SHOULD enable long sleep 1245 durations, in the order of multiple days to a month. 1247 B.5. Requirements Related to Security 1249 In order to guarantee the operations of the 6LoWPAN ND flows, the 1250 spoofing of the 6LR, 6LBR and 6BBRs roles should be avoided. Once a 1251 node successfully registers an address, 6LoWPAN ND should provide 1252 energy-efficient means for the 6LBR to protect that ownership even 1253 when the node that registered the address is sleeping. 1255 In particular, the 6LR and the 6LBR then should be able to verify 1256 whether a subsequent registration for a given Address comes from the 1257 original node. 1259 In a LLN it makes sense to base security on layer-2 security. During 1260 bootstrap of the LLN, nodes join the network after authorization by a 1261 Joining Assistant (JA) or a Commissioning Tool (CT). After joining 1262 nodes communicate with each other via secured links. The keys for 1263 the layer-2 security are distributed by the JA/CT. The JA/CT can be 1264 part of the LLN or be outside the LLN. In both cases it is needed 1265 that packets are routed between JA/CT and the joining node. 1267 Related requirements are: 1269 Req5.1: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for 1270 the 6LR, 6LBR and 6BBR to authenticate and authorize one another for 1271 their respective roles, as well as with the 6LoWPAN Node for the role 1272 of 6LR. 1274 Req5.2: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for 1275 the 6LR and the 6LBR to validate new registration of authorized 1276 nodes. Joining of unauthorized nodes MUST be impossible. 1278 Req5.3: 6LoWPAN ND security mechanisms SHOULD lead to small packet 1279 sizes. In particular, the NS, NA, DAR and DAC messages for a re- 1280 registration flow SHOULD NOT exceed 80 octets so as to fit in a 1281 secured IEEE Std.802.15.4 [IEEEstd802154] frame. 1283 Req5.4: Recurrent 6LoWPAN ND security operations MUST NOT be 1284 computationally intensive on the LoWPAN Node CPU. When a Key hash 1285 calculation is employed, a mechanism lighter than SHA-1 SHOULD be 1286 preferred. 1288 Req5.5: The number of Keys that the 6LoWPAN Node needs to manipulate 1289 SHOULD be minimized. 1291 Req5.6: The 6LoWPAN ND security mechanisms SHOULD enable the 1292 variation of CCM [RFC3610] called CCM* for use at both Layer 2 and 1293 Layer 3, and SHOULD enable the reuse of security code that has to be 1294 present on the device for upper layer security such as TLS. 1296 Req5.7: Public key and signature sizes SHOULD be minimized while 1297 maintaining adequate confidentiality and data origin authentication 1298 for multiple types of applications with various degrees of 1299 criticality. 1301 Req5.8: Routing of packets should continue when links pass from the 1302 unsecured to the secured state. 1304 Req5.9: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for 1305 the 6LR and the 6LBR to validate whether a new registration for a 1306 given address corresponds to the same 6LoWPAN Node that registered it 1307 initially, and, if not, determine the rightful owner, and deny or 1308 clean-up the registration that is duplicate. 1310 B.6. Requirements Related to Scalability 1312 Use cases from Automatic Meter Reading (AMR, collection tree 1313 operations) and Advanced Metering Infrastructure (AMI, bi-directional 1314 communication to the meters) indicate the needs for a large number of 1315 LLN nodes pertaining to a single RPL DODAG (e.g. 5000) and connected 1316 to the 6LBR over a large number of LLN hops (e.g. 15). 1318 Related requirements are: 1320 Req6.1: The registration mechanism SHOULD enable a single 6LBR to 1321 register multiple thousands of devices. 1323 Req6.2: The timing of the registration operation should allow for a 1324 large latency such as found in LLNs with ten and more hops. 1326 Authors' Addresses 1328 Pascal Thubert (editor) 1329 Cisco Systems, Inc 1330 Sophia Antipolis 1331 FRANCE 1333 Email: pthubert@cisco.com 1335 Erik Nordmark 1336 Santa Clara, CA 1337 USA 1339 Email: nordmark@sonic.net 1341 Samita Chakrabarti 1342 San Jose, CA 1343 USA 1345 Email: samitac.ietf@gmail.com