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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: December 23, 2017 S. Chakrabarti 7 June 21, 2017 9 An Update to 6LoWPAN ND 10 draft-ietf-6lo-rfc6775-update-06 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, as well as to 17 provide enhancements to the registration capabilities and mobility 18 detection for different network topologies including the backbone 19 routers performing proxy Neighbor Discovery in a low power network. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on December 23, 2017. 38 Copyright Notice 40 Copyright (c) 2017 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. Applicability of Address Registration Options . . . . . . . . 3 57 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 4. Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . . 5 59 4.1. Extended Address Registration Option . . . . . . . . . . 6 60 4.2. Transaction ID . . . . . . . . . . . . . . . . . . . . . 6 61 4.3. Owner Unique ID . . . . . . . . . . . . . . . . . . . . . 7 62 4.4. Registering the Target Address . . . . . . . . . . . . . 7 63 4.5. Link-Local Addresses and Registration . . . . . . . . . . 8 64 4.6. Maintaining the Registration States . . . . . . . . . . . 9 65 5. Detecting Enhanced ARO Capability Support . . . . . . . . . . 10 66 6. Updated ND Options . . . . . . . . . . . . . . . . . . . . . 11 67 6.1. The Enhanced Address Registration Option (EARO) . . . . . 11 68 6.2. New 6LoWPAN capability Bits in the Capability Indication 69 Option . . . . . . . . . . . . . . . . . . . . . . . . . 14 70 7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 14 71 7.1. Discovering the capabilities of an ND peer . . . . . . . 14 72 7.1.1. Using the E Flag in the CIO . . . . . . . . . . . . . 14 73 7.1.2. Using the T Flag in the EARO . . . . . . . . . . . . 15 74 7.2. Legacy 6LoWPAN Node . . . . . . . . . . . . . . . . . . . 15 75 7.3. Legacy 6LoWPAN Router . . . . . . . . . . . . . . . . . . 16 76 7.4. Legacy 6LoWPAN Border Router . . . . . . . . . . . . . . 16 77 8. Security Considerations . . . . . . . . . . . . . . . . . . . 16 78 9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18 79 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 80 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20 81 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 82 12.1. Normative References . . . . . . . . . . . . . . . . . . 20 83 12.2. Informative References . . . . . . . . . . . . . . . . . 21 84 12.3. External Informative References . . . . . . . . . . . . 23 85 Appendix A. Applicability and Requirements Served . . . . . . . 24 86 Appendix B. Requirements . . . . . . . . . . . . . . . . . . . . 24 87 B.1. Requirements Related to Mobility . . . . . . . . . . . . 25 88 B.2. Requirements Related to Routing Protocols . . . . . . . . 25 89 B.3. Requirements Related to the Variety of Low-Power Link 90 types . . . . . . . . . . . . . . . . . . . . . . . . . . 26 91 B.4. Requirements Related to Proxy Operations . . . . . . . . 27 92 B.5. Requirements Related to Security . . . . . . . . . . . . 27 93 B.6. Requirements Related to Scalability . . . . . . . . . . . 28 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29 96 1. Introduction 98 The scope of this draft is an IPv6 Low Power Networks including star 99 and mesh topologies. This specification modifies and extends the 100 behavior and protocol elements of RFC 6775 "Neighbor Discovery 101 Optimization for IPv6 over Low-Power Wireless Personal Area Networks 102 (6LoWPANs)" [RFC6775] to enable additional capabilities such as: 104 * Support the indication of mobility vs retry (T-bit) 106 * Ease up requirement of registration for link-local addresses 108 * Introducing Enhancement to Address Registration Option (ARO) 110 * Permitting regitration of target address 112 * Clarification of support of privacy and temporary addresses 114 The following sections will discuss applicability of 6LoWPAN ND 115 registration, new extensions and updates to RFC 6775. Finally, we 116 will discuss how the extensions of registration framework can be 117 useful for a scenario such as Backbone router(6BBR) proxy ND 118 operations. 120 2. Applicability of Address Registration Options 122 The purpose of the Address Registration Option (ARO) [RFC6775] and of 123 the Extended ARO (EARO) that is introduced in this document is to 124 facilitate duplicate address detection (DAD) for hosts and pre- 125 populate Neighbor Cache Entries (NCE) [RFC4861] in the routers to 126 reduce the need for sending 'multicast neighbor solicitations' which 127 may be harmful in low power constrained nodes networks where 128 multicast is most often treated as broadcasts. 130 In some cases the address registration can fail or becomes useless 131 for reasons other than a duplicate address. Examples are the router 132 having run out of space, a registration bearing a stale sequence 133 number (e.g. denoting a movement of the host after this registration 134 was placed), a host misbehaving and attempting to register an invalid 135 address such as the unspecified address [RFC4291], or the host using 136 an address which is not topologically correct on that link. In such 137 cases the host will receive an error to help diagnose the issue and 138 may retry, possibly with a different address, and possibly 139 registering to a different 6LR, depending on the returned error. 141 However, the ability to return errors to address registrations MUST 142 NOT be used to restrict the ability of hosts to form and use 143 addresses as recommended in "Host Address Availability 144 Recommendations" [RFC7934]. In particular, this is needed for 145 enhanced privacy, which implies that each host will register a 146 multiplicity of address as part mechanisms like "Privacy Extensions 147 for Stateless Address Autoconfiguration (SLAAC) in IPv6" [RFC4941]. 148 This implies that the capabilities of 6LR and 6LBRs in terms of 149 number of registrations must be clearly announced in the router 150 documentation, and that a network administrator should deploy adapted 151 6LR/6LBRs to support the number and type of devices in his network, 152 based on the number of IPv6 addresses that those devices require. 154 3. Terminology 156 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 157 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 158 document are to be interpreted as described in RFC 2119 [RFC2119]. 160 Readers are expected to be familiar with all the terms and concepts 161 that are discussed in 163 "Neighbor Discovery for IP version 6" [RFC4861], 165 "IPv6 Stateless Address Autoconfiguration" [RFC4862], 167 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 168 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 170 "Neighbor Discovery Optimization for Low-power and Lossy Networks" 171 [RFC6775] and 173 "Multi-link Subnet Support in IPv6" 174 [I-D.ietf-ipv6-multilink-subnets]. 176 as well as this additional terminology: 178 Backbone This is an IPv6 transit link that interconnects 2 or more 179 Backbone Routers. It is expected to be deployed as a high 180 speed Backbone in order to federate a potentially large set of 181 LLNS. Also referred to as a LLN Backbone or Backbone network. 183 Backbone Router An IPv6 router that federates the LLN using a 184 Backbone link as a Backbone. A 6BBR acts as a 6LoWPAN Border 185 Routers (6LBR) and an Energy Aware Default Router (NEAR). 187 Extended LLN This is the aggregation of multiple LLNs as defined in 188 RFC 4919 [RFC4919], interconnected by a Backbone Link via 189 Backbone Routers, and forming a single IPv6 MultiLink Subnet. 191 Registration The process during which a wireless Node registers its 192 address(es) with the Border Router so the 6BBR can proxy ND for 193 it over the Backbone. 195 Binding The state in the 6BBR that associates an IP address with a 196 MAC address, a port and some other information about the node 197 that owns the IP address. 199 Registered Node The node for which the registration is performed, 200 which owns the fields in the EARO option. 202 Registering Node The node that performs the registration to the 203 6BBR, either for one of its own addresses, in which case it is 204 Registered Node and indicates its own MAC Address as Source 205 Link Layer Address (SLLA) in the NS(EARO), or on behalf of a 206 Registered Node that is reachable over a LLN mesh. In the 207 latter case, if the Registered Node is reachable from the 6BBR 208 over a Mesh-Under mesh, the Registering Node indicates the MAC 209 Address of the Registered Node as SLLA in the NS(EARO). 210 Otherwise, it is expected that the Registered Device is 211 reachable over a Route-Over mesh from the Registering Node, in 212 which case the SLLA in the NS(ARO) is that of the Registering 213 Node, which causes it to attract the packets from the 6BBR to 214 the Registered Node and route them over the LLN. 216 Registered Address The address owned by the Registered Node node 217 that is being registered. 219 4. Updating RFC 6775 221 This specification extends the Address Registration Option (ARO) 222 defined in RFC 6775 [RFC6775]; in particular a "T" flag is added that 223 must be set is NS messages when this specification is used, and 224 echo'ed in NA messages to confirm that the protocol effectively 225 supported. Support for this specification can thus be inferred from 226 the presence of the Extended ARO ("T" flag set) in ND messages. 228 In order to support various types of link layers, this specification 229 also adds recommendation to allow multiple registrations, including 230 for privacy / temporary addresses, and provides new mechanisms to 231 help clean up stale registration states as soon as possible. 233 A Registering Node that supports this specification will favor 234 registering to a 6LR that indicates support for this specification 235 over that of RFC 6775 [RFC6775]. 237 4.1. Extended Address Registration Option 239 This specification extends the ARO option that is used for the 240 process of address registration. The new ARO is referred to as 241 Extended ARO (EARO), and its semantics are modified as follows: 243 The address that is being registered with a Neighbor Solicitation 244 (NS) with an EARO is now the Target Address, as opposed to the Source 245 Address as specified in RFC 6775 [RFC6775] (see Section 4.4 for 246 more). This change enables a 6LBR to use an address of his as source 247 to the proxy-registration of an address that belongs to a LLN Node to 248 a 6BBR. This also limits the use of an address as source address 249 before it is registered and the associated Duplicate Address 250 Detection (DAD) is complete. 252 The Unique ID in the EARO option does no more have to be a MAC 253 address (see Section 4.3 for more). This enables in particular the 254 use of a Provable Temporary UID (PT-UID) as opposed to burn-in MAC 255 address, the PT-UID providing a trusted anchor by the 6LR and 6LBR to 256 protect the state associated to the node. 258 The specification introduces a Transaction ID (TID) field in the EARO 259 (see Section 4.2 for more on TID). The TID MUST be provided by a 260 node that supports this specification and a new T flag MUST be set to 261 indicate so. The T bit can be used to determine whether the peer 262 supports this specification. 264 Finally, this specification introduces a number of new Status codes 265 to help diagnose the cause of a registration failure (more in 266 Table 1). 268 4.2. Transaction ID 270 The specification expects that the Registered Node can provide a 271 sequence number called Transaction ID (TID) that is incremented with 272 each re-registration. The TID is used to detect the freshness of the 273 registration request and useful to detect one single registration by 274 multiple 6LOWPAN border routers supporting the same large 6LOWPAN, as 275 is the case for backbone routers (BBR). 277 For example, when a Registered Node is registered with multiple BBRs 278 in parallel, it is expected that the same TID is used, to enable the 279 6BBRs to correlate the registrations as being a single one, and 280 differentiate that situation from a movement. 282 Thus TID could be tracked to follow the sequence of mobility of a 283 node. The details protocols of mobility verification by the border 284 routers is not part of this specification. 286 4.3. Owner Unique ID 288 The Owner Unique ID (OUID) enables to differentiate a real duplicate 289 address registration from a double registration or a movement. An ND 290 message from the 6BBR over the Backbone that is proxied on behalf of 291 a Registered Node must carry the most recent EARO option seen for 292 that node. A NS/NA with an EARO and a NS/NA without a EARO thus 293 represent different nodes and if they relate to a same target then 294 they reflect an address duplication. The Owner Unique ID can be as 295 simple as a EUI-64 burn-in address, if duplicate EUI-64 addresses are 296 avoided. 298 Alternatively, the unique ID can be a cryptographic string that can 299 can be used to prove the ownership of the registration as discussed 300 in "Address Protected Neighbor Discovery for Low-power and Lossy 301 Networks" [I-D.ietf-6lo-ap-nd]. 303 In any fashion, it is recommended that the node stores the unique Id 304 or the keys used to generate that ID in persistent memory. 305 Otherwise, it will be prevented to re-register after a reboot that 306 would cause a loss of memory until the Backbone Router times out the 307 registration. 309 4.4. Registering the Target Address 311 This specification changes the behavior of the 6LN and the 6LR so 312 that the Registered Address is found in the Target Address field of 313 the NS and NA messages as opposed to the Source Address. 315 The reason for this change is to enable proxy-registrations on behalf 316 of other nodes in Route-Over meshes, for instance to enable that a 317 RPL root registers addresses on behalf LLN nodes that are deeper in a 318 6TiSCH mesh, as discussed in Appendix B.4. In that case, the 319 Registering Node MUST indicate its own address as source of the ND 320 message and its MAC address in the Source Link-Layer Address Option 321 (SLLAO), since it still expects to get the packets and route them 322 down the mesh. But the Registered Address belongs to another node, 323 the Registered Node, and that address is indicated in the Target 324 Address field of the NS message. 326 With this convention, a TLLA option indicates the link-layer address 327 of the 6LN that owns the address, whereas the SLLA Option in a NS 328 message indicates that of the Registering Node, which can be the 329 owner device, or a proxy. 331 Since the Registering Node is the one that has reachability with the 332 6LR, and is the one expecting packets for the 6LN, it makes sense to 333 maintain compatibility with RFC 6775 [RFC6775], and it is REQUIRED 334 that an SLLA Option is always placed in a registration NS(EARO) 335 message. 337 4.5. Link-Local Addresses and Registration 339 Considering that LLN nodes are often not wired and may move, there is 340 no guarantee that a Link-Local address stays unique between a 341 potentially variable and unbounded set of neighboring nodes. 342 Compared to RFC 6775 [RFC6775], this specification only requires that 343 a Link-Local address is unique from the perspective of the peering 344 nodes. This simplifies the Duplicate Address Detection (DAD) for 345 Link-Local addresses, and there is no Duplicate Address Request (DAR) 346 / Duplicate Address Confirmation (DAC) exchange between the 6LR and a 347 6LBR for Link-Local addresses. 349 Additionally, RFC 6775 [RFC6775] requires that a 6LoWPAN Node (6LN) 350 uses an address being registered as the source of the registration 351 message. This generates complexities in the 6LR to be able to cope 352 with a potential duplication, in particular for global addresses. To 353 simplify this, a 6LN and a 6LR that conform this specification always 354 use Link-Local addresses as source and destination addresses for the 355 registration NS/NA exchange. As a result, the registration is 356 globally faster, and some of the complexity is removed. 358 In more details: 360 An exchange between two nodes using Link-Local addresses implies that 361 they are reachable over one hop and that at least one of the 2 nodes 362 acts as a 6LR. A node MUST register a Link-Local address to a 6LR in 363 order to obtain reachability from that 6LR beyond the current 364 exchange, and in particular to use the Link-Local address as source 365 address to register other addresses, e.g. global addresses. 367 If there is no collision with an address previously registered to 368 this 6LR by another 6LN, then, from the standpoint of this 6LR, this 369 Link-Local address is unique and the registration is acceptable. 370 Conversely, it may possibly happen that two different 6LRs expose a 371 same Link-Local address but different link-layer addresses. In that 372 case, a 6LN may only interact with one of the 6LR so as to avoid 373 confusion in the 6LN neighbor cache. 375 The DAD process between the 6LR and a 6LoWPAN Border Router (6LBR), 376 which is based on a Duplicate Address Request (DAR) / Duplicate 377 Address Confirmation (DAC) exchange as described in RFC 6775 378 [RFC6775], does not need to take place for Link-Local addresses. 380 It is desired that a 6LR does not need to modify its state associated 381 to the Source Address of an NS(EARO) message. For that reason, when 382 possible, it is RECOMMENDED to use an address that is already 383 registered with a 6LR 385 When registering to a 6LR that conforms this specification, a node 386 MUST use a Link-Local address as the source address of the 387 registration, whatever the type of IPv6 address that is being 388 registered. That Link-Local Address MUST be either already 389 registered, or the address that is being registered. 391 When a Registering Node does not have an already-Registered Address, 392 it MUST register a Link-Local address, using it as both the Source 393 and the Target Address of an NS(EARO) message. In that case, it is 394 RECOMMENDED to use a Link-Local address that is (expected to be) 395 globally unique, e.g. derived from a burn-in MAC address. An EARO 396 option in the response NA indicates that the 6LR supports this 397 specification. 399 Since there is no DAR/DAC exchange for Link-Local addresses, the 6LR 400 may answer immediately to the registration of a Link-Local address, 401 based solely on its existing state and the Source Link-Layer Option 402 that MUST be placed in the NS(EARO) message as required in RFC 6775 403 [RFC6775]. 405 A node needs to register its IPv6 Global Unicast IPv6 Addresses (GUA) 406 to a 6LR in order to obtain a global reachability for these addresses 407 via that 6LR. As opposed to a node that complies to RFC 6775 408 [RFC6775], a Registering Node registering a GUA does not use that GUA 409 as Source Address for the registration to a 6LR that conforms this 410 specification. The DAR/DAC exchange MUST take place for non-Link- 411 Local addresses as prescribed by RFC 6775 [RFC6775]. 413 4.6. Maintaining the Registration States 415 This section discusses protocol actions that involve the Registering 416 Node, the 6LR and the 6LBR. It must be noted that the portion that 417 deals with a 6LBR only applies to those addresses that are registered 418 to it, which, as discussed in Section 4.5, is not the case for Link- 419 Local addresses. The registration state includes all data that is 420 stored in the router relative to that registration, in particular, 421 but not limited to, an NCE in a 6LR. 6LBRs and 6BBRs may store 422 additional registration information in more complex data structures 423 and use protocols that are out of scope of this document to keep them 424 synchonized when they are distributed. 426 When its Neighbor Cache is full, a 6LR cannot accept a new 427 registration. In that situation, the EARO is returned in a NA 428 message with a Status of 2, and the Registering Node may attempt to 429 register to another 6LR. Conversely the registry in the 6LBR may be 430 saturated, in which case the 6LBR cannot guarantee that a new address 431 is effectively not a duplicate. In that case, the 6LBR replies to a 432 DAR message with a DAC message that carries a Status code 9 433 indicating "6LBR Registry saturated", and the address stays in 434 TENTATIVE state. 436 A node renews an existing registration by repeatedly sending NS(EARO) 437 messages for the Registered Address. In order to refresh the 438 registration state in the 6LBR, these registrations MUST be reported 439 to the 6LBR. 441 A node that ceases to use an address SHOULD attempt to deregister 442 that address from all the 6LRs to which it has registered the 443 address, which is achieved using an NS(EARO) message with a 444 Registration Lifetime of 0. 446 A node that moves away from a particular 6LR SHOULD attempt to 447 deregister all of its addresses registered to that 6LR. 449 Upon receiving a NS(EARO) message with a Registration Lifetime of 0 450 and determining that this EARO is the freshest for a given NCE (see 451 Section 4.2), a 6LR cleans up its NCE. If the address was registered 452 to the 6LBR, then the 6LR MUST report to the 6LBR, through a DAR/DAC 453 exchange with the 6LBR, or an alternate protocol, indicating the null 454 Registration Lifetime and the latest TID that this 6LR is aware of. 456 Upon the DAR message, the 6LBR evaluates if this is the freshest EARO 457 it has received for that particular registry entry. If it is, then 458 the entry is scheduled to be removed, and the DAR is answered with a 459 DAC message bearing a Status of 0 "Success". If it is not the 460 freshest, then a Status 2 "Moved" is returned instead, and the 461 existing entry is conserved. The 6LBR SHOULD conserve the address in 462 a DELAY state for a configurable period of time, so as to protect a 463 mobile node that deregistered from one 6LR and did not register yet 464 to a new one. 466 5. Detecting Enhanced ARO Capability Support 468 The nodes and routers in a network may be mixed and if a node wants 469 to use EARO feature for address registration, it has to find a router 470 which supports it. Thus all implementations with EARO option MUST 471 provide the capability detection method using 6CIO option to support 472 both types of registrations (ARO and EARO) as described in later 473 sections. Moreover, any new implementation of 6LOWPAN is also 474 RECOMMENDED to support 6LoWPAN Capability Indication option(6CIO)in 475 general. 477 RFC 7400 [RFC7400] introduces the 6LoWPAN Capability Indication 478 Option (6CIO) to indicate a node's capabilities to its peers. This 479 specification extends the format defined in RFC 7400 to signal the 480 support for EARO, as well as the capability to act as a 6LR, 6LBR and 481 6BBR. 483 With RFC 7400 [RFC7400], the 6CIO is typically sent Router 484 Solicitation (RS) messages. When used to signal the capabilities 485 above per this specification, the 6CIO is typically present Router 486 Advertisement (RA) messages but can also be present in RS, Neighbor 487 Solicitation (NS) and Neighbor Advertisement (NA) messages. 489 6. Updated ND Options 491 This specification does not introduce new options, but it modifies 492 existing ones and updates the associated behaviors as follow: 494 6.1. The Enhanced Address Registration Option (EARO) 496 The Enhanced Address Registration Option (EARO) is intended to be 497 used as a replacement to the ARO option within Neighbor Discovery NS 498 and NA messages between a LLN node and its 6LoWPAN Router (6LR), as 499 well as in Duplicate Address Request (DAR) and the Duplicate Address 500 Confirmation (DAC) messages between 6LRs and 6LBRs in LLNs meshes 501 such as 6TiSCH networks. 503 An NS message with an EARO option is a registration if and only if it 504 also carries an SLLAO option. The AERO option also used in NS and NA 505 messages between Backbone Routers over the Backbone link to sort out 506 the distributed registration state, and in that case, it does not 507 carry the SLLAO option and is not confused with a registration. 509 The EARO extends the ARO and is recognized by the "T" flag set. 511 When using the EARO option, the address being registered is found in 512 the Target Address field of the NS and NA messages. This differs 513 from 6LoWPAN ND RFC 6775 [RFC6775] which specifies that the address 514 being registered is the source of the NS. 516 The format of the EARO option is as follows: 518 0 1 2 3 519 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 1 520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 521 | Type | Length = 2 | Status | Reserved | 522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 523 | Reserved |T| TID | Registration Lifetime | 524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 525 | | 526 + Owner Unique ID (EUI-64 or equivalent) + 527 | | 528 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 530 Figure 1: EARO 532 Option Fields 534 Type: 33 536 Length: 8-bit unsigned integer. 538 Status: 8-bit unsigned integer. Indicates the status of a 539 registration in the NA response. MUST be set to 0 in NS messages. 540 See Table 1 below. 542 Reserved: This field is unused. It MUST be initialized to zero by 543 the sender and MUST be ignored by the receiver. 545 T: One bit flag. Set if the next octet is a used as a TID. 547 TID: 1-byte integer; a transaction id that is maintained by the node 548 and incremented with each transaction. it is recommended that the 549 node maintains the TID in a persistent storage. 551 Registration Lifetime: 16-bit integer; expressed in minutes. 0 552 means that the registration has ended and the associated state 553 should be removed. 555 Owner Unique Identifier (OUI): A globally unique identifier for the 556 node associated. This can be the EUI-64 derived IID of an 557 interface, or some provable ID obtained cryptographically. 559 +-------+-----------------------------------------------------------+ 560 | Value | Description | 561 +-------+-----------------------------------------------------------+ 562 | 0..2 | See RFC 6775 [RFC6775]. Note that a Status of 1 | 563 | | "Duplicate Address" applies to the Registered Address. If | 564 | | the Source Address conflicts with an existing | 565 | | registration, "Duplicate Source Address" should be used. | 566 | | | 567 | 3 | Moved: The registration fails because it is not the | 568 | | freshest. This Status indicates that the registration is | 569 | | rejected because another more recent registration was | 570 | | done, as indicated by a same OUI and a more recent TID. | 571 | | One possible cause is a stale registration that has | 572 | | progressed slowly in the network and was passed by a more | 573 | | recent one. It could also indicate a OUI collision. | 574 | | | 575 | 4 | Removed: The binding state was removed. This may be | 576 | | placed in an asynchronous NS(ARO) message, or as the | 577 | | rejection of a proxy registration to a Backbone Router | 578 | | | 579 | 5 | Proof requested: The Registering Node is challenged for | 580 | | owning the Registered Address or for being an acceptable | 581 | | proxy for the registration. This Status is expected in | 582 | | asynchronous messages from a registrar (6LR, 6LBR, 6BBR) | 583 | | to indicate that the registration state is removed, for | 584 | | instance due to time out of a lifetime, or a movement. | 585 | | The receiver of the NA is the device that has performed a | 586 | | registration that is now stale and it should clean up its | 587 | | state. | 588 | | | 589 | 6 | Duplicate Source Address: The address used as source of | 590 | | the NS(ARO) conflicts with an existing registration. | 591 | | | 592 | 7 | Invalid Source Address: The address used as source of the | 593 | | NS(ARO) is not a Link-Local address as prescribed by this | 594 | | document. | 595 | | | 596 | 8 | Registered Address topologically incorrect: The address | 597 | | being registered is not usable on this link, e.g. it is | 598 | | not topologically correct | 599 | | | 600 | 9 | 6LBR Registry saturated: A new registration cannot be | 601 | | accepted because the 6LBR Registry is saturated. | 602 | | | 603 | 10 | Incorrect proof: The proof of ownership of the registered | 604 | | address is not correct. | 605 +-------+-----------------------------------------------------------+ 607 Table 1: EARO Status 609 Note: the code "6LBR Registry saturated" is used by 6LBRs instead of 610 Status 2 when responding to a DAR/DAC exchange and passed on to the 611 Registering Node by the 6LR. There is no point for the node to retry 612 this registration immediately via another 6LR, since the problem is 613 global to the network. The node may either abandon that address, 614 deregister other addresses first to make room, or keep the address in 615 TENTATIVE state and retry later. 617 6.2. New 6LoWPAN capability Bits in the Capability Indication Option 619 This specification defines a number of capability bits in the CIO 620 that was introduced by RFC 7400 [RFC7400]. 622 Support for this specification is indicated by setting the "E" flag 623 in a CIO option. Routers that are capable of acting as 6LR, 6LBR and 624 6BBR SHOULD set the L, B and P flags, respectively. 626 Those flags are not mutually exclusive and if a router is capable of 627 multiple roles, it SHOULD set all the related flags. 629 0 1 2 3 630 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 1 631 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 632 | Type | Length = 1 |_____________________|L|B|P|E|G| 633 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 634 |_______________________________________________________________| 635 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 637 Figure 2: New capability Bits L, B, P, E in the CIO 639 Option Fields 641 Type: 36 643 L: Node is a 6LR, it can take registrations. 645 B: Node is a 6LBR. 647 P: Node is a 6BBR, proxying for nodes on this link. 649 E: This specification is supported and applied. 651 7. Backward Compatibility 653 7.1. Discovering the capabilities of an ND peer 655 7.1.1. Using the E Flag in the CIO 657 If the CIO is used in an ND message, then the "E" Flag MUST be set by 658 the sending node if supports this specification. 660 It is RECOMMENDED that a router that supports this specification 661 indicates so with a CIO option, but this might not be practical if 662 the link-layer MTU is too small. 664 If the Registering Node receives a CIO in a RA, then the setting of 665 the E" Flag indicates whether or not this specification is supported. 667 A node which does not implement this draft or parse 6CIO option, MUST 668 ignore the packet and the sender of option SHOULD use legacy 669 registration method according to RFC 6775 [RFC6775] after a timeout 670 period. 672 7.1.2. Using the T Flag in the EARO 674 One alternate way for a 6LN to discover the router's capabilities to 675 first register a Link Local address, placing the same address in the 676 Source and Target Address fields of the NS message, and setting the 677 "T" Flag. The node may for instance register an address that is 678 based on EUI-64. For such address, DAD is not required and using the 679 SLLAO option in the NS is actually more amenable with existing ND 680 specifications such as the "Optimistic Duplicate Address Detection 681 (DAD) for IPv6" [RFC4429]. Once that first registration is complete, 682 the node knows from the setting of the "T" Flag in the response 683 whether the router supports this specification. If this is verified, 684 the node may register other addresses that it owns, or proxy-register 685 addresses on behalf some another node, indicating those addresses 686 being registered in the Target Address field of the NS messages, 687 while using one of its own, already registered, addresses as source. 689 A node that supports this specification MUST always use an EARO as a 690 replacement to an ARO in its registration to a router. This is 691 harmless since the "T" flag and TID field are reserved in RFC 6775 692 [RFC6775] are ignored by a legacy router. A router that supports 693 this specification answers to an ARO with an ARO and to an EARO with 694 an EARO. 696 This specification changes the behavior of the peers in a 697 registration flows. To enable backward compatibility, a node that 698 registers to a router that is not known to support this specification 699 MUST behave as prescribed by RFC 6775. Once the router is known to 700 support this specification, the node MUST obey this specification. 702 7.2. Legacy 6LoWPAN Node 704 A legacy 6LN will use the Registered Address as source and will not 705 use an EARO option. In order to be backward compatible, an updated 706 6LR needs to accept that registration if it is valid per the RFC 6775 707 [RFC6775] specification, and manage the binding cache accordingly. 709 The main difference with RFC 6775 is that DAR/DAC exchange for DAD 710 may be avoided for Link-Local addresses. Additionally, the 6LR 711 SHOULD use an EARO in the reply, and may use any of the Status codes 712 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 recommends to using privacy techniques (more in 755 section Section 9, and protection against address theft such as 756 provided by "Address Protected Neighbor Discovery for Low-power and 757 Lossy Networks" [I-D.ietf-6lo-ap-nd], which guarantees the ownership 758 of the Registered Address using a cryptographic OUID. 760 The registration mechanism may be used by a rogue node to attack the 761 6LR or the 6LBR with a Denial-of-Service attack against the registry. 762 It may also happen that the registry of a 6LR or a 6LBR is saturated 763 and cannot take any more registration, which effectively denies the 764 requesting a node the capability to use a new address. In order to 765 alleviate those concerns, Section 4.6 provides a number of 766 recommendations that ensure that a stale registration is removed as 767 soon as possible from the 6LR and 6LBR. In particular, this 768 specification recommends that: 770 o A node that ceases to use an address should attempt to deregister 771 that address from all the 6LRs to which it is registered. The 772 flow is propagated to the 6LBR when needed, and a sequence number 773 is used to make sure that only the freshest command is acted upon. 775 o The nodes should be configured with a Registration Lifetime that 776 reflects their expectation of how long they will use the address 777 with the 6LR to which it is registered. In particular, use cases 778 that involve mobility or rapid address changes should use 779 lifetimes that are homogeneous with the expectation of presence. 781 o The router (6LR or 6LBR) should be configurable so as to limit the 782 number of addresses that can be registered by a single node, as 783 identified at least by MAC address and preferably by security 784 credentials. When that maximum is reached, the router should use 785 a Least-Recently-Used (LRU) logic so as to clean up the addresses 786 that were not used for the longest time, keeping at least one 787 Link-Local address, and attempting to keep one or more stable 788 addresses if such can be recognized, e.g. from the way the IID is 789 formed or because they are used over a much longer time span than 790 other (privacy, shorter-lived) addresses. 792 o Administrators should take great care to deploy adequate numbers 793 of 6LR to cover the needs of the nodes in their range, so as to 794 avoid a situation of starving nodes. It is expected that the 6LBR 795 that serves a LLN is a more capable node then the average 6LR, but 796 in a network condition where it may become saturated, a particular 797 deployment should distribute the 6LBR functionality, for instance 798 by leveraging a high speed Backbone and Backbone Routers to 799 aggregate multiple LLNs into a larger subnet. 801 When the ownership of the OUID cannot be assessed, this specification 802 limits the cases where the OUID and the TID are multicasted, and 803 obfuscates them in responses to attempts to take over an address. 805 The LLN nodes depend on the 6LBR and the 6BBR for their operation. A 806 trust model must be put in place to ensure that the right devices are 807 acting in these roles, so as to avoid threats such as black-holing, 808 or bombing attack whereby an impersonated 6LBR would destroy state in 809 the network by using the "Removed" Status code. 811 9. Privacy Considerations 813 As indicated in section Section 2, this protocol does not aim at 814 limiting the number of IPv6 addresses that a device can form. A host 815 should be able to form and register any address that is topologically 816 correct in the subnet(s) advertised by the 6LR/6LBR. 818 This specification does not mandate any particular way for forming 819 IPv6 addresses, but it recognizes that use of EUI-64 for forming the 820 Interface ID in the Link-Local address prevents the usage of "SEcure 821 Neighbor Discovery (SEND)" [RFC3971] and "Cryptographically Generated 822 Addresses (CGA)" [RFC3972], and that of address privacy techniques. 824 "Privacy Considerations for IPv6 Adaptation-Layer Mechanisms" 825 [RFC8065] addresses why privacy is important and how to form such 826 addresses. All implementations and deployment must consider the 827 option of privacy addresses in their own environment. Also future 828 specifications involving 6LOWPAN Neighbor Discovery should consult 829 "Recommendation on Stable IPv6 Interface Identifiers" [RFC8064] for 830 default interface identifaction. 832 10. IANA Considerations 834 IANA is requested to create a new subregistry for "ARO Flags" under 835 the "Internet Control Message Protocol version 6 (ICMPv6) 836 Parameters". This specification defines 8 positions, bit 0 to bit 7, 837 and assigns bit 7 for the "T" flag in Section 6.1. The policy is 838 "IETF Review" or "IESG Approval" [RFC5226]. The initial content of 839 the registry is as shown in Table 2. 841 New subregistry for ARO Flags under the "Internet Control Message 842 Protocol version 6 (ICMPv6) Parameters" 844 +------------+--------------+-----------+ 845 | ARO Status | Description | Document | 846 +------------+--------------+-----------+ 847 | 0..6 | Unassigned | | 848 | | | | 849 | 7 | "T" Flag | RFC This | 850 +------------+--------------+-----------+ 852 Table 2: new ARO Flags 854 IANA is requested to make additions to existing registries as 855 follows: 857 Address Registration Option Status Values Registry 859 +------------+------------------------------------------+-----------+ 860 | ARO Status | Description | Document | 861 +------------+------------------------------------------+-----------+ 862 | 3 | Moved | RFC This | 863 | | | | 864 | 4 | Removed | RFC This | 865 | | | | 866 | 5 | Proof requested | RFC This | 867 | | | | 868 | 6 | Duplicate Source Address | RFC This | 869 | | | | 870 | 7 | Invalid Source Address | RFC This | 871 | | | | 872 | 8 | Registered Address topologically | RFC This | 873 | | incorrect | | 874 | | | | 875 | 9 | 6LBR registry saturated | RFC This | 876 | | | | 877 | 10 | Incorrect proof | RFC This | 878 +------------+------------------------------------------+-----------+ 880 Table 3: New ARO Status values 882 Subregistry for "6LoWPAN capability Bits" under the "Internet Control 883 Message Protocol version 6 (ICMPv6) Parameters" 885 +----------------+----------------------+-----------+ 886 | capability Bit | Description | Document | 887 +----------------+----------------------+-----------+ 888 | 11 | 6LR capable (L bit) | RFC This | 889 | | | | 890 | 12 | 6LBR capable (B bit) | RFC This | 891 | | | | 892 | 13 | 6BBR capable (P bit) | RFC This | 893 | | | | 894 | 14 | EARO support (E bit) | RFC This | 895 +----------------+----------------------+-----------+ 897 Table 4: New 6LoWPAN capability Bits 899 11. Acknowledgments 901 Kudos to Eric Levy-Abegnoli who designed the First Hop Security 902 infrastructure at Cisco. 904 12. References 906 12.1. Normative References 908 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 909 Requirement Levels", BCP 14, RFC 2119, 910 DOI 10.17487/RFC2119, March 1997, 911 . 913 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 914 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 915 2006, . 917 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 918 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 919 DOI 10.17487/RFC4861, September 2007, 920 . 922 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 923 Address Autoconfiguration", RFC 4862, 924 DOI 10.17487/RFC4862, September 2007, 925 . 927 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 928 IANA Considerations Section in RFCs", RFC 5226, 929 DOI 10.17487/RFC5226, May 2008, 930 . 932 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 933 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 934 DOI 10.17487/RFC6282, September 2011, 935 . 937 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 938 Bormann, "Neighbor Discovery Optimization for IPv6 over 939 Low-Power Wireless Personal Area Networks (6LoWPANs)", 940 RFC 6775, DOI 10.17487/RFC6775, November 2012, 941 . 943 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 944 IPv6 over Low-Power Wireless Personal Area Networks 945 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 946 2014, . 948 12.2. Informative References 950 [I-D.chakrabarti-nordmark-6man-efficient-nd] 951 Chakrabarti, S., Nordmark, E., Thubert, P., and M. 952 Wasserman, "IPv6 Neighbor Discovery Optimizations for 953 Wired and Wireless Networks", draft-chakrabarti-nordmark- 954 6man-efficient-nd-07 (work in progress), February 2015. 956 [I-D.delcarpio-6lo-wlanah] 957 Vega, L., Robles, I., and R. Morabito, "IPv6 over 958 802.11ah", draft-delcarpio-6lo-wlanah-01 (work in 959 progress), October 2015. 961 [I-D.ietf-6lo-ap-nd] 962 Sarikaya, B., Thubert, P., and M. Sethi, "Address 963 Protected Neighbor Discovery for Low-power and Lossy 964 Networks", draft-ietf-6lo-ap-nd-02 (work in progress), May 965 2017. 967 [I-D.ietf-6lo-backbone-router] 968 Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo- 969 backbone-router-03 (work in progress), January 2017. 971 [I-D.ietf-6lo-nfc] 972 Choi, Y., Hong, Y., Youn, J., Kim, D., and J. Choi, 973 "Transmission of IPv6 Packets over Near Field 974 Communication", draft-ietf-6lo-nfc-07 (work in progress), 975 June 2017. 977 [I-D.ietf-6tisch-architecture] 978 Thubert, P., "An Architecture for IPv6 over the TSCH mode 979 of IEEE 802.15.4", draft-ietf-6tisch-architecture-11 (work 980 in progress), January 2017. 982 [I-D.ietf-bier-architecture] 983 Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and 984 S. Aldrin, "Multicast using Bit Index Explicit 985 Replication", draft-ietf-bier-architecture-07 (work in 986 progress), June 2017. 988 [I-D.ietf-ipv6-multilink-subnets] 989 Thaler, D. and C. Huitema, "Multi-link Subnet Support in 990 IPv6", draft-ietf-ipv6-multilink-subnets-00 (work in 991 progress), July 2002. 993 [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] 994 Popa, D. and J. Hui, "6LoPLC: Transmission of IPv6 Packets 995 over IEEE 1901.2 Narrowband Powerline Communication 996 Networks", draft-popa-6lo-6loplc-ipv6-over- 997 ieee19012-networks-00 (work in progress), March 2014. 999 [RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with 1000 CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September 1001 2003, . 1003 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1004 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1005 DOI 10.17487/RFC3810, June 2004, 1006 . 1008 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 1009 "SEcure Neighbor Discovery (SEND)", RFC 3971, 1010 DOI 10.17487/RFC3971, March 2005, 1011 . 1013 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 1014 RFC 3972, DOI 10.17487/RFC3972, March 2005, 1015 . 1017 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 1018 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 1019 . 1021 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1022 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1023 Overview, Assumptions, Problem Statement, and Goals", 1024 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1025 . 1027 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 1028 Extensions for Stateless Address Autoconfiguration in 1029 IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, 1030 . 1032 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1033 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1034 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1035 Low-Power and Lossy Networks", RFC 6550, 1036 DOI 10.17487/RFC6550, March 2012, 1037 . 1039 [RFC7217] Gont, F., "A Method for Generating Semantically Opaque 1040 Interface Identifiers with IPv6 Stateless Address 1041 Autoconfiguration (SLAAC)", RFC 7217, 1042 DOI 10.17487/RFC7217, April 2014, 1043 . 1045 [RFC7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets 1046 over ITU-T G.9959 Networks", RFC 7428, 1047 DOI 10.17487/RFC7428, February 2015, 1048 . 1050 [RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B., 1051 Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low 1052 Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015, 1053 . 1055 [RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi, 1056 "Host Address Availability Recommendations", BCP 204, 1057 RFC 7934, DOI 10.17487/RFC7934, July 2016, 1058 . 1060 [RFC8064] Gont, F., Cooper, A., Thaler, D., and W. Liu, 1061 "Recommendation on Stable IPv6 Interface Identifiers", 1062 RFC 8064, DOI 10.17487/RFC8064, February 2017, 1063 . 1065 [RFC8065] Thaler, D., "Privacy Considerations for IPv6 Adaptation- 1066 Layer Mechanisms", RFC 8065, DOI 10.17487/RFC8065, 1067 February 2017, . 1069 [RFC8105] Mariager, P., Petersen, J., Ed., Shelby, Z., Van de Logt, 1070 M., and D. Barthel, "Transmission of IPv6 Packets over 1071 Digital Enhanced Cordless Telecommunications (DECT) Ultra 1072 Low Energy (ULE)", RFC 8105, DOI 10.17487/RFC8105, May 1073 2017, . 1075 [RFC8163] Lynn, K., Ed., Martocci, J., Neilson, C., and S. 1076 Donaldson, "Transmission of IPv6 over Master-Slave/Token- 1077 Passing (MS/TP) Networks", RFC 8163, DOI 10.17487/RFC8163, 1078 May 2017, . 1080 12.3. External Informative References 1082 [IEEEstd802154] 1083 IEEE, "IEEE Standard for Low-Rate Wireless Networks", 1084 IEEE Standard 802.15.4, DOI 10.1109/IEEESTD.2016.7460875, 1085 . 1087 Appendix A. Applicability and Requirements Served 1089 This specification extends 6LoWPAN ND to sequence the registration 1090 and serves the requirements expressed Appendix B.1 by enabling the 1091 mobility of devices from one LLN to the next based on the 1092 complementary work in the "IPv6 Backbone Router" 1093 [I-D.ietf-6lo-backbone-router] specification. 1095 In the context of the the TimeSlotted Channel Hopping (TSCH) mode of 1096 IEEE Std. 802.15.4 [IEEEstd802154], the "6TiSCH architecture" 1097 [I-D.ietf-6tisch-architecture] introduces how a 6LoWPAN ND host could 1098 connect to the Internet via a RPL mesh Network, but this requires 1099 additions to the 6LOWPAN ND protocol to support mobility and 1100 reachability in a secured and manageable environment. This 1101 specification details the new operations that are required to 1102 implement the 6TiSCH architecture and serves the requirements listed 1103 in Appendix B.2. 1105 The term LLN is used loosely in this specification to cover multiple 1106 types of WLANs and WPANs, including Low-Power Wi-Fi, BLUETOOTH(R) Low 1107 Energy, IEEE Std.802.11AH and IEEE Std.802.15.4 wireless meshes, so 1108 as to address the requirements discussed in Appendix B.3 1110 This specification can be used by any wireless node to associate at 1111 Layer-3 with a 6BBR and register its IPv6 addresses to obtain routing 1112 services including proxy-ND operations over the Backbone, effectively 1113 providing a solution to the requirements expressed in Appendix B.4. 1115 "Efficiency aware IPv6 Neighbor Discovery Optimizations" 1116 [I-D.chakrabarti-nordmark-6man-efficient-nd] suggests that 6LoWPAN ND 1117 [RFC6775] can be extended to other types of links beyond IEEE Std. 1118 802.15.4 for which it was defined. The registration technique is 1119 beneficial when the Link-Layer technique used to carry IPv6 multicast 1120 packets is not sufficiently efficient in terms of delivery ratio or 1121 energy consumption in the end devices, in particular to enable 1122 energy-constrained sleeping nodes. The value of such extension is 1123 especially apparent in the case of mobile wireless nodes, to reduce 1124 the multicast operations that are related to classical ND ([RFC4861], 1125 [RFC4862]) and plague the wireless medium. This serves scalability 1126 requirements listed in Appendix B.6. 1128 Appendix B. Requirements 1130 This section lists requirements that were discussed at 6lo for an 1131 update to 6LoWPAN ND. This specification meets most of them, but 1132 those listed in Appendix B.5 which are deferred to a different 1133 specification such as [I-D.ietf-6lo-ap-nd], and those related to 1134 multicast. 1136 B.1. Requirements Related to Mobility 1138 Due to the unstable nature of LLN links, even in a LLN of immobile 1139 nodes a 6LN may change its point of attachment to a 6LR, say 6LR-a, 1140 and may not be able to notify 6LR-a. Consequently, 6LR-a may still 1141 attract traffic that it cannot deliver any more. When links to a 6LR 1142 change state, there is thus a need to identify stale states in a 6LR 1143 and restore reachability in a timely fashion. 1145 Req1.1: Upon a change of point of attachment, connectivity via a new 1146 6LR MUST be restored timely without the need to de-register from the 1147 previous 6LR. 1149 Req1.2: For that purpose, the protocol MUST enable to differentiate 1150 between multiple registrations from one 6LoWPAN Node and 1151 registrations from different 6LoWPAN Nodes claiming the same address. 1153 Req1.3: Stale states MUST be cleaned up in 6LRs. 1155 Req1.4: A 6LoWPAN Node SHOULD also be capable to register its Address 1156 to multiple 6LRs, and this, concurrently. 1158 B.2. Requirements Related to Routing Protocols 1160 The point of attachment of a 6LN may be a 6LR in an LLN mesh. IPv6 1161 routing in a LLN can be based on RPL, which is the routing protocol 1162 that was defined at the IETF for this particular purpose. Other 1163 routing protocols than RPL are also considered by Standard Defining 1164 Organizations (SDO) on the basis of the expected network 1165 characteristics. It is required that a 6LoWPAN Node attached via ND 1166 to a 6LR would need to participate in the selected routing protocol 1167 to obtain reachability via the 6LR. 1169 Next to the 6LBR unicast address registered by ND, other addresses 1170 including multicast addresses are needed as well. For example a 1171 routing protocol often uses a multicast address to register changes 1172 to established paths. ND needs to register such a multicast address 1173 to enable routing concurrently with discovery. 1175 Multicast is needed for groups. Groups MAY be formed by device type 1176 (e.g. routers, street lamps), location (Geography, RPL sub-tree), or 1177 both. 1179 The Bit Index Explicit Replication (BIER) Architecture 1180 [I-D.ietf-bier-architecture] proposes an optimized technique to 1181 enable multicast in a LLN with a very limited requirement for routing 1182 state in the nodes. 1184 Related requirements are: 1186 Req2.1: The ND registration method SHOULD be extended in such a 1187 fashion that the 6LR MAY advertise the Address of a 6LoWPAN Node over 1188 the selected routing protocol and obtain reachability to that Address 1189 using the selected routing protocol. 1191 Req2.2: Considering RPL, the Address Registration Option that is used 1192 in the ND registration SHOULD be extended to carry enough information 1193 to generate a DAO message as specified in [RFC6550] section 6.4, in 1194 particular the capability to compute a Path Sequence and, as an 1195 option, a RPLInstanceID. 1197 Req2.3: Multicast operations SHOULD be supported and optimized, for 1198 instance using BIER or MPL. Whether ND is appropriate for the 1199 registration to the 6BBR is to be defined, considering the additional 1200 burden of supporting the Multicast Listener Discovery Version 2 1201 [RFC3810] (MLDv2) for IPv6. 1203 B.3. Requirements Related to the Variety of Low-Power Link types 1205 6LoWPAN ND [RFC6775] was defined with a focus on IEEE Std.802.15.4 1206 and in particular the capability to derive a unique Identifier from a 1207 globally unique MAC-64 address. At this point, the 6lo Working Group 1208 is extending the 6LoWPAN Header Compression (HC) [RFC6282] technique 1209 to other link types ITU-T G.9959 [RFC7428], Master-Slave/Token- 1210 Passing [RFC8163], DECT Ultra Low Energy [RFC8105], Near Field 1211 Communication [I-D.ietf-6lo-nfc], IEEE Std. 802.11ah 1212 [I-D.delcarpio-6lo-wlanah], as well as IEEE1901.2 Narrowband 1213 Powerline Communication Networks 1214 [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] and BLUETOOTH(R) 1215 Low Energy [RFC7668]. 1217 Related requirements are: 1219 Req3.1: The support of the registration mechanism SHOULD be extended 1220 to more LLN links than IEEE Std.802.15.4, matching at least the LLN 1221 links for which an "IPv6 over foo" specification exists, as well as 1222 Low-Power Wi-Fi. 1224 Req3.2: As part of this extension, a mechanism to compute a unique 1225 Identifier should be provided, with the capability to form a Link- 1226 Local Address that SHOULD be unique at least within the LLN connected 1227 to a 6LBR discovered by ND in each node within the LLN. 1229 Req3.3: The Address Registration Option used in the ND registration 1230 SHOULD be extended to carry the relevant forms of unique Identifier. 1232 Req3.4: The Neighbour Discovery should specify the formation of a 1233 site-local address that follows the security recommendations from 1234 [RFC7217]. 1236 B.4. Requirements Related to Proxy Operations 1238 Duty-cycled devices may not be able to answer themselves to a lookup 1239 from a node that uses classical ND on a Backbone and may need a 1240 proxy. Additionally, the duty-cycled device may need to rely on the 1241 6LBR to perform registration to the 6BBR. 1243 The ND registration method SHOULD defend the addresses of duty-cycled 1244 devices that are sleeping most of the time and not capable to defend 1245 their own Addresses. 1247 Related requirements are: 1249 Req4.1: The registration mechanism SHOULD enable a third party to 1250 proxy register an Address on behalf of a 6LoWPAN node that may be 1251 sleeping or located deeper in an LLN mesh. 1253 Req4.2: The registration mechanism SHOULD be applicable to a duty- 1254 cycled device regardless of the link type, and enable a 6BBR to 1255 operate as a proxy to defend the Registered Addresses on its behalf. 1257 Req4.3: The registration mechanism SHOULD enable long sleep 1258 durations, in the order of multiple days to a month. 1260 B.5. Requirements Related to Security 1262 In order to guarantee the operations of the 6LoWPAN ND flows, the 1263 spoofing of the 6LR, 6LBR and 6BBRs roles should be avoided. Once a 1264 node successfully registers an address, 6LoWPAN ND should provide 1265 energy-efficient means for the 6LBR to protect that ownership even 1266 when the node that registered the address is sleeping. 1268 In particular, the 6LR and the 6LBR then should be able to verify 1269 whether a subsequent registration for a given Address comes from the 1270 original node. 1272 In a LLN it makes sense to base security on layer-2 security. During 1273 bootstrap of the LLN, nodes join the network after authorization by a 1274 Joining Assistant (JA) or a Commissioning Tool (CT). After joining 1275 nodes communicate with each other via secured links. The keys for 1276 the layer-2 security are distributed by the JA/CT. The JA/CT can be 1277 part of the LLN or be outside the LLN. In both cases it is needed 1278 that packets are routed between JA/CT and the joining node. 1280 Related requirements are: 1282 Req5.1: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for 1283 the 6LR, 6LBR and 6BBR to authenticate and authorize one another for 1284 their respective roles, as well as with the 6LoWPAN Node for the role 1285 of 6LR. 1287 Req5.2: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for 1288 the 6LR and the 6LBR to validate new registration of authorized 1289 nodes. Joining of unauthorized nodes MUST be impossible. 1291 Req5.3: 6LoWPAN ND security mechanisms SHOULD lead to small packet 1292 sizes. In particular, the NS, NA, DAR and DAC messages for a re- 1293 registration flow SHOULD NOT exceed 80 octets so as to fit in a 1294 secured IEEE Std.802.15.4 [IEEEstd802154] frame. 1296 Req5.4: Recurrent 6LoWPAN ND security operations MUST NOT be 1297 computationally intensive on the LoWPAN Node CPU. When a Key hash 1298 calculation is employed, a mechanism lighter than SHA-1 SHOULD be 1299 preferred. 1301 Req5.5: The number of Keys that the 6LoWPAN Node needs to manipulate 1302 SHOULD be minimized. 1304 Req5.6: The 6LoWPAN ND security mechanisms SHOULD enable the 1305 variation of CCM [RFC3610] called CCM* for use at both Layer 2 and 1306 Layer 3, and SHOULD enable the reuse of security code that has to be 1307 present on the device for upper layer security such as TLS. 1309 Req5.7: Public key and signature sizes SHOULD be minimized while 1310 maintaining adequate confidentiality and data origin authentication 1311 for multiple types of applications with various degrees of 1312 criticality. 1314 Req5.8: Routing of packets should continue when links pass from the 1315 unsecured to the secured state. 1317 Req5.9: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for 1318 the 6LR and the 6LBR to validate whether a new registration for a 1319 given address corresponds to the same 6LoWPAN Node that registered it 1320 initially, and, if not, determine the rightful owner, and deny or 1321 clean-up the registration that is duplicate. 1323 B.6. Requirements Related to Scalability 1325 Use cases from Automatic Meter Reading (AMR, collection tree 1326 operations) and Advanced Metering Infrastructure (AMI, bi-directional 1327 communication to the meters) indicate the needs for a large number of 1328 LLN nodes pertaining to a single RPL DODAG (e.g. 5000) and connected 1329 to the 6LBR over a large number of LLN hops (e.g. 15). 1331 Related requirements are: 1333 Req6.1: The registration mechanism SHOULD enable a single 6LBR to 1334 register multiple thousands of devices. 1336 Req6.2: The timing of the registration operation should allow for a 1337 large latency such as found in LLNs with ten and more hops. 1339 Authors' Addresses 1341 Pascal Thubert (editor) 1342 Cisco Systems, Inc 1343 Sophia Antipolis 1344 FRANCE 1346 Email: pthubert@cisco.com 1348 Erik Nordmark 1349 Santa Clara, CA 1350 USA 1352 Email: nordmark@sonic.net 1354 Samita Chakrabarti 1355 San Jose, CA 1356 USA 1358 Email: samitac.ietf@gmail.com