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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 13, 2017 S. Chakrabarti 7 May 12, 2017 9 An Update to 6LoWPAN ND 10 draft-ietf-6lo-rfc6775-update-05 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 13, 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. Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . . 5 58 4.1. Extended Address Registration Option . . . . . . . . . . 5 59 4.2. Transaction ID . . . . . . . . . . . . . . . . . . . . . 6 60 4.3. Owner Unique ID . . . . . . . . . . . . . . . . . . . . . 7 61 4.4. Registering the Target Address . . . . . . . . . . . . . 7 62 4.5. Link-Local Addresses and Registration . . . . . . . . . . 8 63 4.6. Maintaining the Registration States . . . . . . . . . . . 9 64 5. Extending RFC 7400 . . . . . . . . . . . . . . . . . . . . . 11 65 6. Updated ND Options . . . . . . . . . . . . . . . . . . . . . 11 66 6.1. The Enhanced Address Registration Option (EARO) . . . . . 11 67 6.2. New 6LoWPAN capability Bits in the Capability Indication 68 Option . . . . . . . . . . . . . . . . . . . . . . . . . 14 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 . . . . . . . . . . . . 24 83 Appendix A. Applicability and Requirements Served . . . . . . . 24 84 Appendix B. Requirements . . . . . . . . . . . . . . . . . . . . 25 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 . . . . . . . . . . . 29 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]. This 105 specification modifies and extends the behavior and protocol elements 106 of RFC 6775 [RFC6775] to enable additional capabilities, in 107 particular the registration to a 6BBR for proxy ND operations. 109 2. Considerations On Registration Rejection 111 The purpose of the Address Registration Option (ARO) [RFC6775] and of 112 the Extended ARO (EARO) that is introduced in this document is to 113 facilitate duplicate address detection (DAD) for hosts and pre- 114 populate Neighbor Cache Entries (NCE) [RFC4861] in the routers to 115 reduce the need for sending multicast neighbor solicitations and also 116 to be able to support IPv6 Backbone Routers. 118 In some cases the address registration can fail or be useless for 119 reasons other than a duplicate address. Examples are the router 120 having run out of space, a registration bearing a stale sequence 121 number (e.g. denoting a movement of the host after this registration 122 was placed), a host misbehaving and attempting to register an invalid 123 address such as the unspecified address [RFC4291], or the host using 124 an address which is not topologically correct on that link. In such 125 cases the host will receive an error to help diagnose the issue and 126 may retry, possibly with a different address, and possibly 127 registering to a different 6LR, depending on the returned error. 129 However, the ability to return errors to address registrations MUST 130 NOT be used to restrict the ability of hosts to form and use 131 addresses as recommended in "Host Address Availability 132 Recommendations" [RFC7934]. In particular, this is needed for 133 enhanced privacy, which implies that each host will register a 134 multiplicity of address as part mechanisms like "Privacy Extensions 135 for Stateless Address Autoconfiguration (SLAAC) in IPv6" [RFC4941]. 136 This implies that the capabilities of 6LR and 6LBRs in terms of 137 number of registrations must be clearly announced in the router 138 documentation, and that a network administrator should deploy adapted 139 6LR/6LBRs to support the number and type of devices in his network, 140 based on the number of IPv6 addresses that those devices require. 142 3. Terminology 144 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 145 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 146 document are to be interpreted as described in RFC 2119 [RFC2119]. 148 Readers are expected to be familiar with all the terms and concepts 149 that are discussed in 151 "Neighbor Discovery for IP version 6" [RFC4861], 153 "IPv6 Stateless Address Autoconfiguration" [RFC4862], 155 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 156 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 158 "Neighbor Discovery Optimization for Low-power and Lossy Networks" 159 [RFC6775] and 161 "Multi-link Subnet Support in IPv6" 162 [I-D.ietf-ipv6-multilink-subnets]. 164 Additionally, this document uses terminology from 166 "Terms Used in Routing for Low-Power and Lossy Networks" [RFC7102] 167 and 169 the "6TiSCH Terminology" [I-D.ietf-6tisch-terminology], 171 as well as this additional terminology: 173 Backbone This is an IPv6 transit link that interconnects 2 or more 174 Backbone Routers. It is expected to be deployed as a high 175 speed Backbone in order to federate a potentially large set of 176 LLNS. Also referred to as a LLN Backbone or Backbone network. 178 Backbone Router An IPv6 router that federates the LLN using a 179 Backbone link as a Backbone. A 6BBR acts as a 6LoWPAN Border 180 Routers (6LBR) and an Energy Aware Default Router (NEAR). 182 Extended LLN This is the aggregation of multiple LLNs as defined in 183 RFC 4919 [RFC4919], interconnected by a Backbone Link via 184 Backbone Routers, and forming a single IPv6 MultiLink Subnet. 186 Registration The process during which a wireless Node registers its 187 address(es) with the Border Router so the 6BBR can proxy ND for 188 it over the Backbone. 190 Binding The state in the 6BBR that associates an IP address with a 191 MAC address, a port and some other information about the node 192 that owns the IP address. 194 Registered Node The node for which the registration is performed, 195 which owns the fields in the EARO option. 197 Registering Node The node that performs the registration to the 198 6BBR, either for one of its own addresses, in which case it is 199 Registered Node and indicates its own MAC Address as Source 200 Link Layer Address (SLLA) in the NS(EARO), or on behalf of a 201 Registered Node that is reachable over a LLN mesh. In the 202 latter case, if the Registered Node is reachable from the 6BBR 203 over a Mesh-Under mesh, the Registering Node indicates the MAC 204 Address of the Registered Node as SLLA in the NS(EARO). 205 Otherwise, it is expected that the Registered Device is 206 reachable over a Route-Over mesh from the Registering Node, in 207 which case the SLLA in the NS(ARO) is that of the Registering 208 Node, which causes it to attract the packets from the 6BBR to 209 the Registered Node and route them over the LLN. 211 Registered Address The address owned by the Registered Node node 212 that is being registered. 214 4. Updating RFC 6775 216 This specification extends the Address Registration Option (ARO) 217 defined in RFC 6775 [RFC6775]; in particular a "T" flag is added that 218 must be set is NS messages when this specification is used, and 219 echo'ed in NA messages to confirm that the protocol effectively 220 supported. Support for this specification can thus be inferred from 221 the presence of the Extended ARO ("T" flag set) in ND messages. 223 In order to support various types of link layers, this specification 224 also adds recommendation to allow multiple registrations, including 225 for privacy / temporary addresses, and provides new mechanisms to 226 help clean up stale registration states as soon as possible. 228 A Registering Node that supports this specification will favor 229 registering to a 6LR that indicates support for this specification 230 over that of RFC 6775 [RFC6775]. 232 4.1. Extended Address Registration Option 234 This specification extends the ARO option that is used for the 235 process of address registration. The new ARO is referred to as 236 Extended ARO (EARO), and its semantics are modified as follows: 238 The address that is being registered with a Neighbor Solicitation 239 (NS) with an EARO is now the Target Address, as opposed to the Source 240 Address as specified in RFC 6775 [RFC6775] (see Section 4.4 for 241 more). This change enables a 6LBR to use an address of his as source 242 to the proxy-registration of an address that belongs to a LLN Node to 243 a 6BBR. This also limits the use of an address as source address 244 before it is registered and the associated Duplicate Address 245 Detection (DAD) is complete. 247 The Unique ID in the EARO option does no more have to be a MAC 248 address (see Section 4.3 for more). This enables in particular the 249 use of a Provable Temporary UID (PT-UID) as opposed to burn-in MAC 250 address, the PT-UID providing a trusted anchor by the 6LR and 6LBR to 251 protect the state associated to the node. 253 The specification introduces a Transaction ID (TID) field in the EARO 254 (see Section 4.2 for more on TID). The TID MUST be provided by a 255 node that supports this specification and a new T flag MUST be set to 256 indicate so. The T bit can be used to determine whether the peer 257 supports this specification. 259 Finally, this specification introduces a number of new Status codes 260 to help diagnose the cause of a registration failure (more in 261 Table 1). 263 4.2. Transaction ID 265 The specification expects that the Registered Node can provide a 266 sequence number called Transaction ID (TID) that is incremented with 267 each re-registration. The TID essentially obeys the same rules as 268 the Path Sequence field in the Transit Information Option (TIO) found 269 in the RPL Destination Advertisement Object (DAO) [RFC6550]. This 270 way, the LLN node can use the same counter for ND and RPL, and a 6LBR 271 acting as RPL root may easily maintain the registration on behalf of 272 a RPL node deep inside the mesh by simply using the RPL TIO Path 273 Sequence as TID for EARO. 275 When a Registered Node is registered to multiple BBRs in parallel, it 276 is expected that the same TID is used, to enable the 6BBRs to 277 correlate the registrations as being a single one, and differentiate 278 that situation from a movement. 280 If the TIDs are different, a conflict resolution inherited from RPL 281 sorts out the most recent registration and other ones are removed. 282 The operation for computing and comparing the Path Sequence is 283 detailed in section 7 of RFC 6550 [RFC6550] and applies to the TID in 284 the exact same fashion. The resolution is used to determine the 285 freshest registration for a particular address, and an EARO is 286 processed only if it is the freshest, otherwise a Status code 3 287 "Moved" is returned. 289 4.3. Owner Unique ID 291 The Owner Unique ID (OUID) enables to differentiate a real duplicate 292 address registration from a double registration or a movement. An ND 293 message from the 6BBR over the Backbone that is proxied on behalf of 294 a Registered Node must carry the most recent EARO option seen for 295 that node. A NS/NA with an EARO and a NS/NA without a EARO thus 296 represent different nodes and if they relate to a same target then 297 they reflect an address duplication. The Owner Unique ID can be as 298 simple as a EUI-64 burn-in address, if duplicate EUI-64 addresses are 299 avoided. 301 Alternatively, the unique ID can be a cryptographic string that can 302 can be used to prove the ownership of the registration as discussed 303 in "Address Protected Neighbor Discovery for Low-power and Lossy 304 Networks" [I-D.ietf-6lo-ap-nd]. 306 In any fashion, it is recommended that the node stores the unique Id 307 or the keys used to generate that ID in persistent memory. 308 Otherwise, it will be prevented to re-register after a reboot that 309 would cause a loss of memory until the Backbone Router times out the 310 registration. 312 4.4. Registering the Target Address 314 This specification changes the behavior of the 6LN and the 6LR so 315 that the Registered Address is found in the Target Address field of 316 the NS and NA messages as opposed to the Source Address. 318 The reason for this change is to enable proxy-registrations on behalf 319 of other nodes in Route-Over meshes, for instance to enable that a 320 RPL root registers addresses on behalf LLN nodes that are deeper in a 321 6TiSCH mesh, as discussed in Appendix B.4. In that case, the 322 Registering Node MUST indicate its own address as source of the ND 323 message and its MAC address in the Source Link-Layer Address Option 324 (SLLAO), since it still expects to get the packets and route them 325 down the mesh. But the Registered Address belongs to another node, 326 the Registered Node, and that address is indicated in the Target 327 Address field of the NS message. 329 With this convention, a TLLA option indicates the link-layer address 330 of the 6LN that owns the address, whereas the SLLA Option in a NS 331 message indicates that of the Registering Node, which can be the 332 owner device, or a proxy. 334 Since the Registering Node is the one that has reachability with the 335 6LR, and is the one expecting packets for the 6LN, it makes sense to 336 maintain compatibility with RFC 6775 [RFC6775], and it is REQUIRED 337 that an SLLA Option is always placed in a registration NS(EARO) 338 message. 340 4.5. Link-Local Addresses and Registration 342 Considering that LLN nodes are often not wired and may move, there is 343 no guarantee that a Link-Local address stays unique between a 344 potentially variable and unbounded set of neighboring nodes. 345 Compared to RFC 6775 [RFC6775], this specification only requires that 346 a Link-Local address is unique from the perspective of the peering 347 nodes. This simplifies the Duplicate Address Detection (DAD) for 348 Link-Local addresses, and there is no DAR/DAC exchange between the 349 6LR and a 6LBR for Link-Local addresses. 351 Additionally, RFC 6775 [RFC6775] requires that a 6LoWPAN Node (6LN) 352 uses an address being registered as the source of the registration 353 message. This generates complexities in the 6LR to be able to cope 354 with a potential duplication, in particular for global addresses. To 355 simplify this, a 6LN and a 6LR that conform this specification always 356 use Link-Local addresses as source and destination addresses for the 357 registration NS/NA exchange. As a result, the registration is 358 globally faster, and some of the complexity is removed. 360 In more details: 362 An exchange between two nodes using Link-Local addresses implies that 363 they are reachable over one hop and that at least one of the 2 nodes 364 acts as a 6LR. A node MUST register a Link-Local address to a 6LR in 365 order to obtain reachability from that 6LR beyond the current 366 exchange, and in particular to use the Link-Local address as source 367 address to register other addresses, e.g. global addresses. 369 If there is no collision with an address previously registered to 370 this 6LR by another 6LN, then, from the standpoint of this 6LR, this 371 Link-Local address is unique and the registration is acceptable. 372 Conversely, it may possibly happen that two different 6LRs expose a 373 same Link-Local address but different link-layer addresses. In that 374 case, a 6LN may only interact with one of the 6LR so as to avoid 375 confusion in the 6LN neighbor cache. 377 The DAD process between the 6LR and a 6LoWPAN Border Router (6LBR), 378 which is based on a Duplicate Address Request (DAR) / Duplicate 379 Address Confirmation (DAC) exchange as described in RFC 6775 380 [RFC6775], does not need to take place for Link-Local addresses. 382 It is desired that a 6LR does not need to modify its state associated 383 to the Source Address of an NS(EARO) message. For that reason, when 384 possible, it is RECOMMENDED to use an address that is already 385 registered with a 6LR 387 When registering to a 6LR that conforms this specification, a node 388 MUST use a Link-Local address as the source address of the 389 registration, whatever the type of IPv6 address that is being 390 registered. That Link-Local Address MUST be either already 391 registered, or the address that is being registered. 393 When a Registering Node does not have an already-Registered Address, 394 it MUST register a Link-Local address, using it as both the Source 395 and the Target Address of an NS(EARO) message. In that case, it is 396 RECOMMENDED to use a Link-Local address that is (expected to be) 397 globally unique, e.g. derived from a burn-in MAC address. An EARO 398 option in the response NA indicates that the 6LR supports this 399 specification. 401 Since there is no DAR/DAC exchange for Link-Local addresses, the 6LR 402 may answer immediately to the registration of a Link-Local address, 403 based solely on its existing state and the Source Link-Layer Option 404 that MUST be placed in the NS(EARO) message as required in RFC 6775 405 [RFC6775]. 407 A node needs to register its IPv6 Global Unicast IPv6 Addresses (GUA) 408 to a 6LR in order to obtain a global reachability for these addresses 409 via that 6LR. As opposed to a node that complies to RFC 6775 410 [RFC6775], a Registering Node registering a GUA does not use that GUA 411 as Source Address for the registration to a 6LR that conforms this 412 specification. The DAR/DAC exchange MUST take place for non-Link- 413 Local addresses as prescribed by RFC 6775 [RFC6775]. 415 4.6. Maintaining the Registration States 417 This section discusses protocol actions that involve the Registering 418 Node, the 6LR and the 6LBR. It must be noted that the portion that 419 deals with a 6LBR only applies to those addresses that are registered 420 to it, which, as discussed in Section 4.5, is not the case for Link- 421 Local addresses. The registration state includes all data that is 422 stored in the router relative to that registration, in particular, 423 but not limited to, an NCE in a 6LR. 6LBRs and 6BBRs may store 424 additional registration information in more complex data structures 425 and use protocols that are out of scope of this document to keep them 426 synchonized when they are distributed. 428 When its Neighbor Cache is full, a 6LR cannot accept a new 429 registration. In that situation, the EARO is returned in a NA 430 message with a Status of 2, and the Registering Node may attempt to 431 register to another 6LR. Conversely the registry in the 6LBR may be 432 saturated, in which case the 6LBR cannot guarantee that a new address 433 is effectively not a duplicate. In that case, the 6LBR replies to a 434 DAR message with a DAC message that carries a Status code 9 435 indicating "6LBR Registry saturated", and the address stays in 436 TENTATIVE state. 438 A node renews an existing registration by repeatedly sending NS(EARO) 439 messages for the Registered Address. In order to refresh the 440 registration state in the 6LBR, these registrations MUST be reported 441 to the 6LBR. This is normally done through a DAR/DAC exchange, but 442 the refresh MAY alternatively be piggy-backed in another protocol 443 such as RPL [RFC6550], as long as the semantics of the EARO are fully 444 carried in the alternate protocol. In the particular case of RPL, 445 the TID MUST be used as the Path Sequence in the TIO, and the 446 Registration Lifetime MUST be used as Path Lifetime. It is also 447 REQUIRED that the root of the RPL DODAG passes that information to 448 the 6LBR on behalf of the 6LR, either through a DAR/DAC exchange, or 449 through internal methods if they are collocated. 451 A node that ceases to use an address SHOULD attempt to deregister 452 that address from all the 6LRs to which it has registered the 453 address, which is achieved using an NS(EARO) message with a 454 Registration Lifetime of 0. 456 A node that moves away from a particular 6LR SHOULD attempt to 457 deregister all of its addresses registered to that 6LR. 459 Upon receiving a NS(EARO) message with a Registration Lifetime of 0 460 and determining that this EARO is the freshest for a given NCE (see 461 Section 4.2), a 6LR cleans up its NCE. If the address was registered 462 to the 6LBR, then the 6LR MUST report to the 6LBR, through a DAR/DAC 463 exchange with the 6LBR, or an alternate protocol, indicating the null 464 Registration Lifetime and the latest TID that this 6LR is aware of. 466 Upon the DAR message, the 6LBR evaluates if this is the freshest EARO 467 it has received for that particular registry entry. If it is, then 468 the entry is scheduled to be removed, and the DAR is answered with a 469 DAC message bearing a Status of 0 "Success". If it is not the 470 freshest, then a Status 2 "Moved" is returned instead, and the 471 existing entry is conserved. The 6LBR SHOULD conserve the address in 472 a DELAY state for a configurable period of time, so as to protect a 473 mobile node that deregistered from one 6LR and did not register yet 474 to a new one. 476 5. Extending RFC 7400 478 RFC 7400 [RFC7400] introduces the 6LoWPAN Capability Indication 479 Option (6CIO) to indicate a node's capabilities to its peers. This 480 specification extends the format defined in RFC 7400 to signal the 481 support for EARO, as well as the capability to act as a 6LR, 6LBR and 482 6BBR. 484 With RFC 7400 [RFC7400], the 6CIO is typically sent Router 485 Solicitation (RS) messages. When used to signal the capabilities 486 above per this specification, the 6CIO is typically present Router 487 Advertisement (RA) messages but can also be present in RS, Neighbor 488 Solicitation (NS) and Neighbor Advertisement (NA) messages. 490 6. Updated ND Options 492 This specification does not introduce new options, but it modifies 493 existing ones and updates the associated behaviors as follow: 495 6.1. The Enhanced Address Registration Option (EARO) 497 The Enhanced Address Registration Option (EARO) is intended to be 498 used as a replacement to the ARO option within Neighbor Discovery NS 499 and NA messages between a LLN node and its 6LoWPAN Router (6LR), as 500 well as in Duplicate Address Request (DAR) and the Duplicate Address 501 Confirmation (DAC) messages between 6LRs and 6LBRs in LLNs meshes 502 such as 6TiSCH networks. 504 An NS message with an EARO option is a registration if and only if it 505 also carries an SLLAO option. The AERO option also used in NS and NA 506 messages between Backbone Routers over the Backbone link to sort out 507 the distributed registration state, and in that case, it does not 508 carry the SLLAO option and is not confused with a registration. 510 The EARO extends the ARO and is recognized by the "T" flag set. 512 When using the EARO option, the address being registered is found in 513 the Target Address field of the NS and NA messages. This differs 514 from 6LoWPAN ND RFC 6775 [RFC6775] which specifies that the address 515 being registered is the source of the NS. 517 The format of the EARO option is as follows: 519 0 1 2 3 520 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 1 521 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 522 | Type | Length = 2 | Status | Reserved | 523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 524 | Reserved |T| TID | Registration Lifetime | 525 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 526 | | 527 + Owner Unique ID (EUI-64 or equivalent) + 528 | | 529 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 531 Figure 1: EARO 533 Option Fields 535 Type: 33 537 Length: 8-bit unsigned integer. 539 Status: 8-bit unsigned integer. Indicates the status of a 540 registration in the NA response. MUST be set to 0 in NS messages. 541 See Table 1 below. 543 Reserved: This field is unused. It MUST be initialized to zero by 544 the sender and MUST be ignored by the receiver. 546 T: One bit flag. Set if the next octet is a used as a TID. 548 TID: 1-byte integer; a transaction id that is maintained by the node 549 and incremented with each transaction. it is recommended that the 550 node maintains the TID in a persistent storage. 552 Registration Lifetime: 16-bit integer; expressed in minutes. 0 553 means that the registration has ended and the associated state 554 should be removed. 556 Owner Unique Identifier (OUI): A globally unique identifier for the 557 node associated. This can be the EUI-64 derived IID of an 558 interface, or some provable ID obtained cryptographically. 560 +-------+-----------------------------------------------------------+ 561 | Value | Description | 562 +-------+-----------------------------------------------------------+ 563 | 0..2 | See RFC 6775 [RFC6775]. Note that a Status of 1 | 564 | | "Duplicate Address" applies to the Registered Address. If | 565 | | the Source Address conflicts with an existing | 566 | | registration, "Duplicate Source Address" should be used. | 567 | | | 568 | 3 | Moved: The registration fails because it is not the | 569 | | freshest. This Status indicates that the registration is | 570 | | rejected because another more recent registration was | 571 | | done, as indicated by a same OUI and a more recent TID. | 572 | | One possible cause is a stale registration that has | 573 | | progressed slowly in the network and was passed by a more | 574 | | recent one. It could also indicate a OUI collision. | 575 | | | 576 | 4 | Removed: The binding state was removed. This may be | 577 | | placed in an asynchronous NS(ARO) message, or as the | 578 | | rejection of a proxy registration to a Backbone Router | 579 | | | 580 | 5 | Proof requested: The Registering Node is challenged for | 581 | | owning the Registered Address or for being an acceptable | 582 | | proxy for the registration. This Status is expected in | 583 | | asynchronous messages from a registrar (6LR, 6LBR, 6BBR) | 584 | | to indicate that the registration state is removed, for | 585 | | instance due to time out of a lifetime, or a movement. | 586 | | The receiver of the NA is the device that has performed a | 587 | | registration that is now stale and it should clean up its | 588 | | state. | 589 | | | 590 | 6 | Duplicate Source Address: The address used as source of | 591 | | the NS(ARO) conflicts with an existing registration. | 592 | | | 593 | 7 | Invalid Source Address: The address used as source of the | 594 | | NS(ARO) is not a Link-Local address as prescribed by this | 595 | | document. | 596 | | | 597 | 8 | Registered Address topologically incorrect: The address | 598 | | being registered is not usable on this link, e.g. it is | 599 | | not topologically correct | 600 | | | 601 | 9 | 6LBR Registry saturated: A new registration cannot be | 602 | | accepted because the 6LBR Registry is saturated. This | 603 | | code is used by 6LBRs instead of Status 2 when responding | 604 | | to a DAR/DAC exchange and passed on to the Registering | 605 | | Node by the 6LR. There is no point for the node to retry | 606 | | this registration immediately via another 6LR, since the | 607 | | problem is global to the network. The node may either | 608 | | abandon that address, deregister other addresses first to | 609 | | make room, or keep the address in TENTATIVE state and | 610 | | retry later. | 611 +-------+-----------------------------------------------------------+ 613 Table 1: EARO Status 615 6.2. New 6LoWPAN capability Bits in the Capability Indication Option 617 This specification defines a number of capability bits in the CIO 618 that was introduced by RFC 7400 [RFC7400]. 620 Support for this specification is indicated by setting the "E" flag 621 in a CIO option. Routers that are capable of acting as 6LR, 6LBR and 622 6BBR SHOULD set the L, B and P flags, respectively. 624 Those flags are not mutually exclusive and if a router is capable of 625 multiple roles, it SHOULD set all the related flags. 627 0 1 2 3 628 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 1 629 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 630 | Type | Length = 1 |_____________________|L|B|P|E|G| 631 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 632 |_______________________________________________________________| 633 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 635 Figure 2: New capability Bits L, B, P, E in the CIO 637 Option Fields 639 Type: 36 641 L: Node is a 6LR, it can take registrations. 643 B: Node is a 6LBR. 645 P: Node is a 6BBR, proxying for nodes on this link. 647 E: This specification is supported and applied. 649 7. Backward Compatibility 651 7.1. Discovering the capabilities of an ND peer 653 7.1.1. Using the E Flag in the CIO 655 If the CIO is used in an ND message, then the "E" Flag MUST be set by 656 the sending node if supports this specification. 658 It is RECOMMENDED that a router that supports this specification 659 indicates so with a CIO option, but this might not be practical if 660 the link-layer MTU is too small. 662 If the Registering Node receives a CIO in a RA, then the setting of 663 the E" Flag indicates whether or not this specification is supported. 665 7.1.2. Using the T Flag in the EARO 667 One alternate way for a 6LN to discover the router's capabilities to 668 first register a Link Local address, placing the same address in the 669 Source and Target Address fields of the NS message, and setting the 670 "T" Flag. The node may for instance register an address that is 671 based on EUI-64. For such address, DAD is not required and using the 672 SLLAO option in the NS is actually more amenable with existing ND 673 specifications such as the "Optimistic Duplicate Address Detection 674 (DAD) for IPv6" [RFC4429]. Once that first registration is complete, 675 the node knows from the setting of the "T" Flag in the response 676 whether the router supports this specification. If this is verified, 677 the node may register other addresses that it owns, or proxy-register 678 addresses on behalf some another node, indicating those addresses 679 being registered in the Target Address field of the NS messages, 680 while using one of its own, already registered, addresses as source. 682 A node that supports this specification MUST always use an EARO as a 683 replacement to an ARO in its registration to a router. This is 684 harmless since the "T" flag and TID field are reserved in RFC 6775 685 [RFC6775] are ignored by a legacy router. A router that supports 686 this specification answers to an ARO with an ARO and to an EARO with 687 an EARO. 689 This specification changes the behavior of the peers in a 690 registration flows. To enable backward compatibility, a node that 691 registers to a router that is not known to support this specification 692 MUST behave as prescribed by RFC 6775. Once the router is known to 693 support this specification, the node MUST obey this specification. 695 7.2. Legacy 6LoWPAN Node 697 A legacy 6LN will use the Registered Address as source and will not 698 use an EARO option. In order to be backward compatible, an updated 699 6LR needs to accept that registration if it is valid per the RFC 6775 700 [RFC6775] specification, and manage the binding cache accordingly. 702 The main difference with RFC 6775 is that DAR/DAC exchange for DAD 703 may be avoided for Link-Local addresses. Additionally, the 6LR 704 SHOULD use an EARO in the reply, and may use any of the Status codes 705 defined in this specification. 707 7.3. Legacy 6LoWPAN Router 709 The first registration by a an updated 6LN is for a Link-Local 710 address, using that Link-Local address as source. A legacy 6LN will 711 not makes a difference and accept -or reject- that registration as if 712 the 6LN was a legacy node. 714 An updated 6LN will always use an EARO option in the registration NS 715 message, whereas a legacy 6LN will always areply with an ARO option 716 in the NA message. So from that first registration, the updated 6LN 717 can figure whether the 6LR supports this specification or not. 719 When facing a legacy 6LR, an updated 6LN may attempt to find an 720 alternate 6LR that is updated. In order to be backward compatible, 721 based on the discovery that a 6LR is legacy, the 6LN needs to 722 fallback to legacy behavior and source the packet with the Registered 723 Address. 725 The main difference is that the updated 6LN SHOULD use an EARO in the 726 request regardless of the type of 6LN, legacy or updated 728 7.4. Legacy 6LoWPAN Border Router 730 With this specification, the DAR/DAC transports an EARO option as 731 opposed to an ARO option. As described for the NS/NA exchange, 732 devices that support this specification always use an EARO option and 733 all the associated behavior. 735 8. Security Considerations 737 This specification extends RFC 6775 [RFC6775], and the security 738 section of that draft also applies to this as well. In particular, 739 it is expected that the link layer is sufficiently protected to 740 prevent a rogue access, either by means of physical or IP security on 741 the Backbone Link and link layer cryptography on the LLN. This 742 specification also expects that the LLN MAC provides secure unicast 743 to/from the Backbone Router and secure Broadcast from the Backbone 744 Router in a way that prevents tempering with or replaying the RA 745 messages. 747 This specification does not mandate any particular way for forming 748 IPv6 addresses, but it recognizes that use of EUI-64 for forming the 749 Interface ID in the Link-Local address prevents the usage of "SEcure 750 Neighbor Discovery (SEND)" [RFC3971] and "Cryptographically Generated 751 Addresses (CGA)" [RFC3972], and that of address privacy techniques, 752 such as recommended in "Privacy Considerations for IPv6 Adaptation- 753 Layer Mechanisms" [RFC8065]. This specification RECOMMENDS the use 754 of privacy techniques, and that of additional protection against 755 address theft such as provided by "Address Protected Neighbor 756 Discovery for Low-power and Lossy Networks" [I-D.ietf-6lo-ap-nd], 757 which guarantees the ownership of the Registered Address using a 758 cryptographic OUID. 760 As indicated in section Section 2, this protocol does not aim at 761 limiting the number of IPv6 addresses that a device can form, either. 762 A host should be able to register any address that is topologically 763 correct in the subnet(s) advertised by the 6LR/6LBR. 765 On the other hand, the registration mechanism may be used by a rogue 766 node to attack the 6LR or the 6LBR with a Denial-of-Service attack 767 against the registry. It may also happen that the registry of a 6LR 768 or a 6LBR is saturated and cannot take any more registration, which 769 effectively denies the requesting a node the capability to use a new 770 address. In order to alleviate those concerns, Section 4.6 provides 771 a number of recommendations that ensure that a stale registration is 772 removed as soon as possible from the 6LR and 6LBR. In particular, 773 this specification recommends that: 775 o A node that ceases to use an address should attempt to deregister 776 that address from all the 6LRs to which it is registered. The 777 flow is propagated to the 6LBR when needed, and a sequence number 778 is used to make sure that only the freshest command is acted upon. 780 o The nodes should be configured with a Registration Lifetime that 781 reflects their expectation of how long they will use the address 782 with the 6LR to which it is registered. In particular, use cases 783 that involve mobility or rapid address changes should use 784 lifetimes that are homogeneous with the expectation of presence. 786 o The router (6LR or 6LBR) should be configurable so as to limit the 787 number of addresses that can be registered by a single node, as 788 identified at least by MAC address and preferably by security 789 credentials. When that maximum is reached, the router should use 790 a Least-Recently-Used (LRU) logic so as to clean up the addresses 791 that were not used for the longest time, keeping at least one 792 Link-Local address, and attempting to keep one or more stable 793 addresses if such can be recognized, e.g. from the way the IID is 794 formed or because they are used over a much longer time span than 795 other (privacy, shorter-lived) addresses. 797 o Administrators should take great care to deploy adequate numbers 798 of 6LR to cover the needs of the nodes in their range, so as to 799 avoid a situation of starving nodes. It is expected that the 6LBR 800 that serves a LLN is a more capable node then the average 6LR, but 801 in a network condition where it may become saturated, a particular 802 deployment should distribute the 6LBR functionality, for instance 803 by leveraging a high speed Backbone and Backbone Routers to 804 aggregate multiple LLNs into a larger subnet. 806 When the ownership of the OUID cannot be assessed, this specification 807 limits the cases where the OUID and the TID are multicasted, and 808 obfuscates them in responses to attempts to take over an address. 810 The LLN nodes depend on the 6LBR and the 6BBR for their operation. A 811 trust model must be put in place to ensure that the right devices are 812 acting in these roles, so as to avoid threats such as black-holing, 813 or bombing attack whereby an impersonated 6LBR would destroy state in 814 the network by using the "Removed" Status code. 816 9. IANA Considerations 818 IANA is requested to create a new subregistry for "ARO Flags" under 819 the "Internet Control Message Protocol version 6 (ICMPv6) 820 Parameters". This specification defines 8 positions, bit 0 to bit 7, 821 and assigns bit 7 for the "T" flag in Section 6.1. The policy is 822 "IETF Review" or "IESG Approval" [RFC5226]. The initial content of 823 the registry is as shown in Table 2. 825 New subregistry for ARO Flags under the "Internet Control Message 826 Protocol version 6 (ICMPv6) Parameters" 828 +------------+--------------+-----------+ 829 | ARO Status | Description | Document | 830 +------------+--------------+-----------+ 831 | 0..6 | Unassigned | | 832 | | | | 833 | 7 | "T" Flag | RFC This | 834 +------------+--------------+-----------+ 836 Table 2: new ARO Flags 838 IANA is requested to make additions to existing registries as 839 follows: 841 Address Registration Option Status Values Registry 843 +------------+------------------------------------------+-----------+ 844 | ARO Status | Description | Document | 845 +------------+------------------------------------------+-----------+ 846 | 3 | Moved | RFC This | 847 | | | | 848 | 4 | Removed | RFC This | 849 | | | | 850 | 5 | Proof requested | RFC This | 851 | | | | 852 | 6 | Duplicate Source Address | RFC This | 853 | | | | 854 | 7 | Invalid Source Address | RFC This | 855 | | | | 856 | 8 | Registered Address topologically | RFC This | 857 | | incorrect | | 858 | | | | 859 | 9 | 6LBR registry saturated | RFC This | 860 +------------+------------------------------------------+-----------+ 862 Table 3: New ARO Status values 864 Subregistry for "6LoWPAN capability Bits" under the "Internet Control 865 Message Protocol version 6 (ICMPv6) Parameters" 867 +----------------+----------------------+-----------+ 868 | capability Bit | Description | Document | 869 +----------------+----------------------+-----------+ 870 | 11 | 6LR capable (L bit) | RFC This | 871 | | | | 872 | 12 | 6LBR capable (B bit) | RFC This | 873 | | | | 874 | 13 | 6BBR capable (P bit) | RFC This | 875 | | | | 876 | 14 | EARO support (E bit) | RFC This | 877 +----------------+----------------------+-----------+ 879 Table 4: New 6LoWPAN capability Bits 881 10. Acknowledgments 883 Kudos to Eric Levy-Abegnoli who designed the First Hop Security 884 infrastructure at Cisco. 886 11. References 888 11.1. Normative References 890 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 891 Requirement Levels", BCP 14, RFC 2119, 892 DOI 10.17487/RFC2119, March 1997, 893 . 895 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 896 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 897 2006, . 899 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 900 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 901 DOI 10.17487/RFC4861, September 2007, 902 . 904 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 905 Address Autoconfiguration", RFC 4862, 906 DOI 10.17487/RFC4862, September 2007, 907 . 909 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 910 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 911 DOI 10.17487/RFC5226, May 2008, 912 . 914 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 915 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 916 DOI 10.17487/RFC6282, September 2011, 917 . 919 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 920 Bormann, "Neighbor Discovery Optimization for IPv6 over 921 Low-Power Wireless Personal Area Networks (6LoWPANs)", 922 RFC 6775, DOI 10.17487/RFC6775, November 2012, 923 . 925 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 926 IPv6 over Low-Power Wireless Personal Area Networks 927 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 928 2014, . 930 11.2. Informative References 932 [I-D.chakrabarti-nordmark-6man-efficient-nd] 933 Chakrabarti, S., Nordmark, E., Thubert, P., and M. 934 Wasserman, "IPv6 Neighbor Discovery Optimizations for 935 Wired and Wireless Networks", draft-chakrabarti-nordmark- 936 6man-efficient-nd-07 (work in progress), February 2015. 938 [I-D.delcarpio-6lo-wlanah] 939 Vega, L., Robles, I., and R. Morabito, "IPv6 over 940 802.11ah", draft-delcarpio-6lo-wlanah-01 (work in 941 progress), October 2015. 943 [I-D.ietf-6lo-ap-nd] 944 Sarikaya, B., Thubert, P., and M. Sethi, "Address 945 Protected Neighbor Discovery for Low-power and Lossy 946 Networks", draft-ietf-6lo-ap-nd-00 (work in progress), 947 November 2016. 949 [I-D.ietf-6lo-backbone-router] 950 Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo- 951 backbone-router-03 (work in progress), January 2017. 953 [I-D.ietf-6lo-nfc] 954 Choi, Y., Hong, Y., Youn, J., Kim, D., and J. Choi, 955 "Transmission of IPv6 Packets over Near Field 956 Communication", draft-ietf-6lo-nfc-06 (work in progress), 957 March 2017. 959 [I-D.ietf-6tisch-architecture] 960 Thubert, P., "An Architecture for IPv6 over the TSCH mode 961 of IEEE 802.15.4", draft-ietf-6tisch-architecture-11 (work 962 in progress), January 2017. 964 [I-D.ietf-6tisch-terminology] 965 Palattella, M., Thubert, P., Watteyne, T., and Q. Wang, 966 "Terminology in IPv6 over the TSCH mode of IEEE 967 802.15.4e", draft-ietf-6tisch-terminology-08 (work in 968 progress), December 2016. 970 [I-D.ietf-bier-architecture] 971 Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and 972 S. Aldrin, "Multicast using Bit Index Explicit 973 Replication", draft-ietf-bier-architecture-06 (work in 974 progress), April 2017. 976 [I-D.ietf-ipv6-multilink-subnets] 977 Thaler, D. and C. Huitema, "Multi-link Subnet Support in 978 IPv6", draft-ietf-ipv6-multilink-subnets-00 (work in 979 progress), July 2002. 981 [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] 982 Popa, D. and J. Hui, "6LoPLC: Transmission of IPv6 Packets 983 over IEEE 1901.2 Narrowband Powerline Communication 984 Networks", draft-popa-6lo-6loplc-ipv6-over- 985 ieee19012-networks-00 (work in progress), March 2014. 987 [RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with 988 CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September 989 2003, . 991 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 992 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 993 DOI 10.17487/RFC3810, June 2004, 994 . 996 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 997 "SEcure Neighbor Discovery (SEND)", RFC 3971, 998 DOI 10.17487/RFC3971, March 2005, 999 . 1001 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 1002 RFC 3972, DOI 10.17487/RFC3972, March 2005, 1003 . 1005 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 1006 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 1007 . 1009 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1010 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1011 Overview, Assumptions, Problem Statement, and Goals", 1012 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1013 . 1015 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 1016 Extensions for Stateless Address Autoconfiguration in 1017 IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, 1018 . 1020 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1021 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1022 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1023 Low-Power and Lossy Networks", RFC 6550, 1024 DOI 10.17487/RFC6550, March 2012, 1025 . 1027 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1028 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1029 2014, . 1031 [RFC7217] Gont, F., "A Method for Generating Semantically Opaque 1032 Interface Identifiers with IPv6 Stateless Address 1033 Autoconfiguration (SLAAC)", RFC 7217, 1034 DOI 10.17487/RFC7217, April 2014, 1035 . 1037 [RFC7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets 1038 over ITU-T G.9959 Networks", RFC 7428, 1039 DOI 10.17487/RFC7428, February 2015, 1040 . 1042 [RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B., 1043 Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low 1044 Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015, 1045 . 1047 [RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi, 1048 "Host Address Availability Recommendations", BCP 204, 1049 RFC 7934, DOI 10.17487/RFC7934, July 2016, 1050 . 1052 [RFC8065] Thaler, D., "Privacy Considerations for IPv6 Adaptation- 1053 Layer Mechanisms", RFC 8065, DOI 10.17487/RFC8065, 1054 February 2017, . 1056 [RFC8105] Mariager, P., Petersen, J., Ed., Shelby, Z., Van de Logt, 1057 M., and D. Barthel, "Transmission of IPv6 Packets over 1058 Digital Enhanced Cordless Telecommunications (DECT) Ultra 1059 Low Energy (ULE)", RFC 8105, DOI 10.17487/RFC8105, May 1060 2017, . 1062 [RFC8163] Lynn, K., Ed., Martocci, J., Neilson, C., and S. 1063 Donaldson, "Transmission of IPv6 over Master-Slave/Token- 1064 Passing (MS/TP) Networks", RFC 8163, DOI 10.17487/RFC8163, 1065 May 2017, . 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 [RFC8163], DECT Ultra Low Energy [RFC8105], Near Field 1198 Communication [I-D.ietf-6lo-nfc], IEEE Std. 802.11ah 1199 [I-D.delcarpio-6lo-wlanah], as well as IEEE1901.2 Narrowband 1200 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