idnits 2.17.00 (12 Aug 2021) /tmp/idnits32989/draft-ietf-6lo-rfc6775-update-08.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (September 20, 2017) is 1704 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'Perlman83' is mentioned on line 1393, but not defined == Missing Reference: 'IEEEstd802154' is mentioned on line 1606, but not defined == Outdated reference: draft-ietf-6lo-ap-nd has been published as RFC 8928 == Outdated reference: draft-ietf-6lo-backbone-router has been published as RFC 8929 == Outdated reference: A later version (-17) exists of draft-ietf-6lo-nfc-07 == Outdated reference: draft-ietf-6tisch-architecture has been published as RFC 9030 == Outdated reference: draft-ietf-bier-architecture has been published as RFC 8279 -- Obsolete informational reference (is this intentional?): RFC 4941 (Obsoleted by RFC 8981) Summary: 0 errors (**), 0 flaws (~~), 8 warnings (==), 2 comments (--). 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: March 24, 2018 S. Chakrabarti 7 September 20, 2017 9 An Update to 6LoWPAN ND 10 draft-ietf-6lo-rfc6775-update-08 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 https://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 March 24, 2018. 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 (https://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 (EARO . . . . . . . 7 60 4.2. Transaction ID . . . . . . . . . . . . . . . . . . . . . 7 61 4.2.1. Comparing TID values . . . . . . . . . . . . . . . . 8 62 4.3. Owner Unique ID . . . . . . . . . . . . . . . . . . . . . 9 63 4.4. Extended Duplicate Address Messages . . . . . . . . . . . 10 64 4.5. Registering the Target Address . . . . . . . . . . . . . 10 65 4.6. Link-Local Addresses and Registration . . . . . . . . . . 11 66 4.7. Maintaining the Registration States . . . . . . . . . . . 13 67 5. Detecting Enhanced ARO Capability Support . . . . . . . . . . 14 68 6. Extended ND Options And Messages . . . . . . . . . . . . . . 15 69 6.1. Enhanced Address Registration Option (EARO) . . . . . . . 15 70 6.2. Extended Duplicate Address Message Formats . . . . . . . 18 71 6.3. New 6LoWPAN Capability Bits in the Capability Indication 72 Option . . . . . . . . . . . . . . . . . . . . . . . . . 19 73 7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 19 74 7.1. Discovering the capabilities of an ND peer . . . . . . . 19 75 7.1.1. Using the E Flag in the 6CIO Option . . . . . . . . . 19 76 7.1.2. Using the T Flag in the EARO . . . . . . . . . . . . 20 77 7.2. Legacy 6LoWPAN Node . . . . . . . . . . . . . . . . . . . 21 78 7.3. Legacy 6LoWPAN Router . . . . . . . . . . . . . . . . . . 21 79 7.4. Legacy 6LoWPAN Border Router . . . . . . . . . . . . . . 22 80 8. Security Considerations . . . . . . . . . . . . . . . . . . . 22 81 9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 23 82 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 83 10.1. ARO Flags . . . . . . . . . . . . . . . . . . . . . . . 24 84 10.2. ICMP Codes . . . . . . . . . . . . . . . . . . . . . . . 24 85 10.3. New ARO Status values . . . . . . . . . . . . . . . . . 25 86 10.4. New 6LoWPAN capability Bits . . . . . . . . . . . . . . 26 87 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26 88 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 26 89 12.1. Normative References . . . . . . . . . . . . . . . . . . 26 90 12.2. Informative References . . . . . . . . . . . . . . . . . 27 91 12.3. External Informative References . . . . . . . . . . . . 30 92 Appendix A. Applicability and Requirements Served . . . . . . . 30 93 Appendix B. Requirements . . . . . . . . . . . . . . . . . . . . 31 94 B.1. Requirements Related to Mobility . . . . . . . . . . . . 32 95 B.2. Requirements Related to Routing Protocols . . . . . . . . 32 96 B.3. Requirements Related to the Variety of Low-Power Link 97 types . . . . . . . . . . . . . . . . . . . . . . . . . . 33 98 B.4. Requirements Related to Proxy Operations . . . . . . . . 34 99 B.5. Requirements Related to Security . . . . . . . . . . . . 34 100 B.6. Requirements Related to Scalability . . . . . . . . . . . 35 101 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36 103 1. Introduction 105 The scope of this draft is an IPv6 Low Power Networks including star 106 and mesh topologies. This specification modifies and extends the 107 behavior and protocol elements of "Neighbor Discovery Optimization 108 for IPv6 over Low-Power Wireless Personal Area Networks" (6LoWPAN ND) 109 [RFC6775] to enable additional capabilities such as: 111 o Support for indicating mobility vs retry (T-bit) 113 o Ease up requirement of registration for link-local addresses 115 o Enhancement to Address Registration Option (ARO) 117 o Permitting registration of target address 119 o Clarification of support of privacy and temporary addresses 121 The applicability of 6LoWPAN ND registration is discussed in 122 Section 2, and new extensions and updates to RFC 6775 are presented 123 in Section 4. Considerations on Backward Compatibility, Security and 124 Privacy are also elaborated upon in Section 7, Section 8 and in 125 Section 9, respectively. 127 2. Applicability of Address Registration Options 129 The original purpose of the Address Registration Option (ARO) in the 130 original 6LoWPAN ND specification is to facilitate duplicate address 131 detection (DAD) for hosts as well as populate Neighbor Cache Entries 132 (NCE) [RFC4861] in the routers. This reduces the reliance on 133 multicast operations, which are often as intrusive as broadcast, in 134 IPv6 ND operations. 136 With this specification, a registration can fail or become useless 137 for reasons other than address duplication. Examples include: the 138 router having run out of space; a registration bearing a stale 139 sequence number perhaps denoting a movement of the host after the 140 registration was placed; a host misbehaving and attempting to 141 register an invalid address such as the unspecified address 142 [RFC4291]; or a host using an address which is not topologically 143 correct on that link. 145 In such cases the host will receive an error to help diagnose the 146 issue and may retry, possibly with a different address, and possibly 147 registering to a different router, depending on the returned error. 148 However, the ability to return errors to address registrations is not 149 intended to be used to restrict the ability of hosts to form and use 150 addresses, as recommended in "Host Address Availability 151 Recommendations" [RFC7934]. 153 In particular, the freedom to form and register addresses is needed 154 for enhanced privacy; each host may register a multiplicity of 155 address using mechanisms such as "Privacy Extensions for Stateless 156 Address Autoconfiguration (SLAAC) in IPv6" [RFC4941]. 158 In the classical IPv6 ND [RFC4861], a router must have enough storage 159 to hold neighbor cache entries for all the addresses to which it may 160 forward. A router using the Address Registration mechanism needs 161 enough storage to hold NCEs for all the addresses that may be 162 registered to it, regardless of whether or not they are actively 163 communicating. For this reason, the number of registrations 164 supported by a 6LoWPAN Router (6LR) or 6LoWPAN Border Router (6LBR) 165 must be clearly documented. 167 A network administrator should deploy adapted 6LR/6LBRs to support 168 the number and type of devices in his network, based on the number of 169 IPv6 addresses that those devices require and their renewal rate and 170 behaviour. 172 3. Terminology 174 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 175 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 176 document are to be interpreted as described in RFC 2119 [RFC2119]. 178 Readers are expected to be familiar with all the terms and concepts 179 that are discussed in 181 o "Neighbor Discovery for IP version 6" [RFC4861], 183 o "IPv6 Stateless Address Autoconfiguration" [RFC4862], 185 o "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 186 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 188 o "Neighbor Discovery Optimization for Low-power and Lossy Networks" 189 [RFC6775] and 191 o "Multi-link Subnet Support in IPv6" 192 [I-D.ietf-ipv6-multilink-subnets], 194 as well as the following terminology: 196 Backbone Link An IPv6 transit link that interconnects two or more 197 Backbone Routers. It is expected to be of a relatively high 198 speed compared to the LLN in order to support the trafic that 199 is required to federate multiple segments of the potentially 200 large LLN into a single IPv6 subnet. Also referred to as a to 201 as a Backbone, a LLN Backbone, and a Backbone Network. 203 Backbone Router A logical network function in an IPv6 router that 204 federates a LLN over a Backbone Link. In order to do so, the 205 Backbone Router (6BBR) proxies the 6LoWPAN ND operations 206 detailed in the document onto the matching operations that run 207 over the backbone, typically classical IPv6 ND. Note that 6BBR 208 is a logical function, just like 6LR and 6LBR, and that a same 209 physical router may operate all three. 211 Extended LLN The aggregation of multiple LLNs as defined in RFC 4919 212 [RFC4919], interconnected by a Backbone Link via Backbone 213 Routers, and forming a single IPv6 MultiLink Subnet. 215 Registration The process during which a wireless Node registers its 216 address(es) with the Border Router so the 6BBR can serve as 217 proxy for ND operations over the Backbone. 219 Binding The association between an IP address with a MAC address, a 220 port and/or other information about the node that owns the IP 221 address. 223 Registered Node The node for which the registration is performed, 224 and which owns the fields in the EARO option. 226 Registering Node The node that performs the registration to the 227 6BBR, which may proxy for the registered node. 229 Registered Address An address owned by the Registered Node node that 230 was or is being registered. 232 legacy and original vs. updated In the context of this 233 specification, the terms "legacy" and "original" relate to the 234 support of the RFC 6775 by a 6LN, a 6LR or a 6LBR, whereas the 235 term "updated" refers to the support of this specification. 237 4. Updating RFC 6775 239 This specification introduces the Extended Address Registration 240 Option (EARO) based on the ARO as defined in RFC 6775 [RFC6775]; in 241 particular a "T" flag is added that must be set is NS messages when 242 this specification is used, and echoed in NA messages to confirm that 243 the protocol is supported. 245 Support for this specification can thus be inferred from the presence 246 of the Extended ARO ("T" flag set) in 6LoWPAN ND messages. 248 The extensions to the ARO option are reported to the Duplicate 249 Address Request (DAR) and Duplicate Address Confirmation (DAC) 250 messages, so as to convey the additional information all the way to 251 the 6LBR, and in turn the 6LBR may proxy the registration using 252 classical ND over a backbone as illustrated in Figure 1. 254 6LN 6LR 6LBR 6BBR 255 | | | | 256 | NS(EARO) | | | 257 |--------------->| | | 258 | | Extended DAR | | 259 | |-------------->| | 260 | | | | 261 | | | proxy NS(EARO) | 262 | | |--------------->| 263 | | | | NS(DAD) 264 | | | | ------> 265 | | | | 266 | | | | 267 | | | | 268 | | | proxy NA(EARO) | 269 | | |<---------------| 270 | | Extended DAC | | 271 | |<--------------| | 272 | NA(EARO) | | | 273 |<---------------| | | 274 | | | | 276 Figure 1: (Re-)Registration Flow 278 In order to support various types of link layers, this specification 279 also RECOMMENDS to allow multiple registrations, including for 280 privacy / temporary addresses, and provides new mechanisms to help 281 clean up stale registration states as soon as possible. 283 A Registering Node that supports this specification SHOULD prefer 284 registering to a 6LR that is found to support this specification, as 285 discussed in Section 7.1, over a legacy one. 287 4.1. Extended Address Registration Option (EARO 289 This specification extends the ARO option that is used for the 290 process of address registration. The new ARO is referred to as 291 Extended ARO (EARO), and it is backward compatible with the ARO. 292 More details on backward compatibility can be found in Section 7. 294 The semantics of the ARO are modified as follows: 296 o The address that is being registered with a Neighbor Solicitation 297 (NS) with an EARO is now the Target Address, as opposed to the 298 Source Address as specified in RFC 6775 [RFC6775] (see 299 Section 4.5). This change enables a 6LBR to use one of its 300 addresses as source to the proxy-registration of an address that 301 belongs to a LLN Node to a 6BBR. This also limits the use of an 302 address as source address before it is registered and the 303 associated DAD process is complete. 305 o The Unique ID in the EARO Option is no longer required to be a MAC 306 address (see Section 4.3). This enables in particular the use of 307 a Provable Temporary UID (PT-UID) as opposed to burn-in MAC 308 address; the PT-UID provides an anchor trusted by the 6LR and 6LBR 309 to protect the state associated to the node. 311 o The specification introduces a Transaction ID (TID) field in the 312 EARO (see Section 4.2). The TID MUST be provided by a node that 313 supports this specification and a new "T" flag MUST be set to 314 indicate so. 316 o Finally, this specification introduces new status codes to help 317 diagnose the cause of a registration failure (see Table 1). 319 4.2. Transaction ID 321 sequence number that is incremented with each re-registration. The 322 TID is used to detect the freshness of the registration request and 323 useful to detect one single registration by multiple 6LOWPAN border 324 routers (e.g., 6LBRs and 6BBRs) supporting the same 6LOWPAN. The TID 325 may also be used by the network to track the sequence of movements of 326 a node in order to route to the current (freshest known) location of 327 a moving node. 329 When a Registered Node is registered with multiple BBRs in parallel, 330 the same TID SHOULD be used, to enable the 6BBRs to determine that 331 the registrations are the same, and distinguish that situation from a 332 movement. 334 4.2.1. Comparing TID values 336 The TID is a sequence counter and its operation is the exact match of 337 the path sequence specified in RPL, the IPv6 Routing Protocol for 338 Low-Power and Lossy Networks [RFC6550] specification. 340 In order to keep this document self-contained and yet compatible, the 341 text below is an exact copy from section 7.2. "Sequence Counter 342 Operation" of [RFC6550]. 344 A TID is deemed to be fresher than another when its value is greater 345 per the operations detailed in this section. 347 The TID range is subdivided in a 'lollipop' fashion ([Perlman83]), 348 where the values from 128 and greater are used as a linear sequence 349 to indicate a restart and bootstrap the counter, and the values less 350 than or equal to 127 used as a circular sequence number space of size 351 128 as in [RFC1982]. Consideration is given to the mode of operation 352 when transitioning from the linear region to the circular region. 353 Finally, when operating in the circular region, if sequence numbers 354 are detected to be too far apart then they are not comparable, as 355 detailed below. 357 A window of comparison, SEQUENCE_WINDOW = 16, is configured based on 358 a value of 2^N, where N is defined to be 4 in this specification. 360 For a given sequence counter, 362 1. The sequence counter SHOULD be initialized to an implementation 363 defined value which is 128 or greater prior to use. A 364 recommended value is 240 (256 - SEQUENCE_WINDOW). 366 2. When a sequence counter increment would cause the sequence 367 counter to increment beyond its maximum value, the sequence 368 counter MUST wrap back to zero. When incrementing a sequence 369 counter greater than or equal to 128, the maximum value is 255. 370 When incrementing a sequence counter less than 128, the maximum 371 value is 127. 373 3. When comparing two sequence counters, the following rules MUST be 374 applied: 376 1. When a first sequence counter A is in the interval [128..255] 377 and a second sequence counter B is in [0..127]: 379 1. If (256 + B - A) is less than or equal to 380 SEQUENCE_WINDOW, then B is greater than A, A is less than 381 B, and the two are not equal. 383 2. If (256 + B - A) is greater than SEQUENCE_WINDOW, then A 384 is greater than B, B is less than A, and the two are not 385 equal. 387 For example, if A is 240, and B is 5, then (256 + 5 - 240) is 388 21. 21 is greater than SEQUENCE_WINDOW (16), thus 240 is 389 greater than 5. As another example, if A is 250 and B is 5, 390 then (256 + 5 - 250) is 11. 11 is less than SEQUENCE_WINDOW 391 (16), thus 250 is less than 5. 393 2. In the case where both sequence counters to be compared are 394 less than or equal to 127, and in the case where both 395 sequence counters to be compared are greater than or equal to 396 128: 398 1. If the absolute magnitude of difference between the two 399 sequence counters is less than or equal to 400 SEQUENCE_WINDOW, then a comparison as described in 401 [RFC1982] is used to determine the relationships greater 402 than, less than, and equal. 404 2. If the absolute magnitude of difference of the two 405 sequence counters is greater than SEQUENCE_WINDOW, then a 406 desynchronization has occurred and the two sequence 407 numbers are not comparable. 409 4. If two sequence numbers are determined to be not comparable, i.e. 410 the results of the comparison are not defined, then a node should 411 consider the comparison as if it has evaluated in such a way so 412 as to give precedence to the sequence number that has most 413 recently been observed to increment. Failing this, the node 414 should consider the comparison as if it has evaluated in such a 415 way so as to minimize the resulting changes to its own state. 417 4.3. Owner Unique ID 419 The Owner Unique ID (OUID) enables a duplicate address registration 420 to be distinguished from a double registration or a movement. An ND 421 message from the 6BBR over the Backbone that is proxied on behalf of 422 a Registered Node must carry the most recent EARO option seen for 423 that node. A NS/NA with an EARO and a NS/NA without a EARO thus 424 represent different nodes; if they relate to a same target then an 425 address duplication is likely. 427 With RFC 6775, the Owner Unique ID carries an EUI-64 burn-in address, 428 which implies that duplicate EUI-64 addresses are avoided. With this 429 specification, the Owner Unique ID is allowed to be extended to 430 different types of identifier, as long as the type is clearly 431 indicated. For instance, the type can be a cryptographic string and 432 used to prove the ownership of the registration as discussed in 433 "Address Protected Neighbor Discovery for Low-power and Lossy 434 Networks" [I-D.ietf-6lo-ap-nd]. 436 In any fashion, it is recommended that the node stores the unique Id 437 or the keys used to generate that ID in persistent memory. 438 Otherwise, it will be prevented to re-register a same address after a 439 reboot that would cause a loss of memory until the 6LBR times out the 440 registration. 442 4.4. Extended Duplicate Address Messages 444 In order to map the new EARO content in the DAR/DAC messages, a new 445 TID field is added to the Extended DAR (EDAR) and the Extended DAC 446 (EDAC) messages as a replacement to a Reserved field, and an odd 447 value of the ICMP Code indicates support for the TID, to transport 448 the "T" flag. 450 In order to prepare for new extensions, and though no option had been 451 earlier defined for the Duplicate Address messages, implementations 452 SHOULD expect ND options after the main body, and SHOULD ignore them. 454 As for the EARO, the Extended Duplicate Address messages are backward 455 compatible with the original versions, and remarks concerning 456 backwards compatibility between the 6LN and the 6LR apply similarly 457 between a 6LR and a 6LBR. 459 4.5. Registering the Target Address 461 The Registering Node is the node that performs the registration to 462 the 6BBR. As inherited from RFC 6775, it may be the Registered Node 463 as well, in which case it registers one of its own addresses, and 464 indicates its own MAC Address as Source Link Layer Address (SLLA) in 465 the NS(EARO). 467 This specification adds the capability to proxy the registration 468 operation on behalf of a Registered Node that is reachable over a LLN 469 mesh. In that case, if the Registered Node is reachable from the 470 6BBR over a Mesh-Under mesh, the Registering Node indicates the MAC 471 Address of the Registered Node as SLLA in the NS(EARO). If the 472 Registered Node is reachable over a Route-Over mesh from the 473 Registering Node, the SLLA in the NS(ARO) is that of the Registering 474 Node. This enables the Registering Node to attract the packets from 475 the 6BBR and route them over the LLN to the Registered Node . 477 In order to enable the latter operation, this specification changes 478 the behavior of the 6LN and the 6LR so that the Registered Address is 479 found in the Target Address field of the NS and NA messages as 480 opposed to the Source Address. 482 The reason for this change is to enable proxy-registrations on behalf 483 of other nodes, for instance to enable a RPL root to register 484 addresses on behalf of other LLN nodes, as discussed in Appendix B.4. 485 In that case, the Registering Node MUST indicate its own address as 486 source of the ND message and its MAC address in the Source Link-Layer 487 Address Option (SLLAO), since it still expects to receive and route 488 the packets. Since the Registered Address belongs to the Registered 489 Node, that address is indicated in the Target Address field of the NS 490 message. 492 With this convention, a TLLA option indicates the link-layer address 493 of the 6LN that owns the address, whereas the SLLA Option in a NS 494 message indicates that of the Registering Node, which can be the 495 owner device, or a proxy. 497 The Registering Node is reachable from the 6LR, and is also the one 498 expecting packets for the 6LN. Therefore, it MUST place its own Link 499 Layer Address in the SLLA Option that MUST always be placed in a 500 registration NS(EARO) message. This maintains compatibility with the 501 original 6LoWPAN ND [RFC6775]. 503 4.6. Link-Local Addresses and Registration 505 Considering that LLN nodes are often not wired and may move, there is 506 no guarantee that a Link-Local address stays unique between a 507 potentially variable and unbounded set of neighboring nodes. 509 Compared to RFC 6775, this specification only requires that a Link- 510 Local address is unique from the perspective of the nodes that use it 511 to communicate (e.g. the 6LN and the 6LR in an NS/NA exchange). This 512 simplifies the DAD process for Link-Local addresses, and there is no 513 exchange of Duplicate Address messages between the 6LR and a 6LBR for 514 Link-Local addresses. 516 According to RFC 6775, a 6LoWPAN Node (6LN) uses the an address being 517 registered as the source of the registration message. This generates 518 complexities in the 6LR to be able to cope with a potential 519 duplication, in particular for global addresses. 521 To simplify this, a 6LN and a 6LR that conform this specification 522 MUST always use Link-Local addresses as source and destination 523 addresses for the registration NS/NA exchange. As a result, the 524 registration is globally faster, and some of the complexity is 525 removed. 527 In more details: 529 An exchange between two nodes using Link-Local addresses implies that 530 they are reachable over one hop and that at least one of the 2 nodes 531 acts as a 6LR. A node MUST register a Link-Local address to a 6LR in 532 order to obtain reachability from that 6LR beyond the current 533 exchange, and in particular to use the Link-Local address as source 534 address to register other addresses, e.g. global addresses. 536 If there is no collision with an address previously registered to 537 this 6LR by another 6LN, then, from the standpoint of this 6LR, this 538 Link-Local address is unique and the registration is acceptable. 539 Conversely, it may possibly happen that two different 6LRs expose the 540 same Link-Local address but different link-layer addresses. In that 541 case, a 6LN may only interact with one of the 6LRs so as to avoid 542 confusion in the 6LN neighbor cache. 544 The DAD process between the 6LR and a 6LBR, which is based on an 545 exchange of Duplicate Address messages, does not need to take place 546 for Link-Local addresses. 548 It is desired that a 6LR does not need to modify its state associated 549 to the Source Address of an NS(EARO) message. For that reason, when 550 possible, it is RECOMMENDED to use an address that is already 551 registered with a 6LR 553 When registering to a 6LR that conforms this specification, a node 554 MUST use a Link-Local address as the source address of the 555 registration, whatever the type of IPv6 address that is being 556 registered. That Link-Local Address MUST be either already 557 registered, or the address that is being registered. 559 When a Registering Node does not have an already-Registered Address, 560 it MUST register a Link-Local address, using it as both the Source 561 and the Target Address of an NS(EARO) message. In that case, it is 562 RECOMMENDED to use a Link-Local address that is (expected to be) 563 globally unique, e.g. derived from a burn-in MAC address. An EARO 564 option in the response NA indicates that the 6LR supports this 565 specification. 567 Since there is no Duplicate Address exchange for Link-Local 568 addresses, the 6LR may answer immediately to the registration of a 569 Link-Local address, based solely on its existing state and the Source 570 Link-Layer Option that MUST be placed in the NS(EARO) message as 571 required in RFC 6775 [RFC6775]. 573 A node needs to register its IPv6 Global Unicast IPv6 Addresses 574 (GUAs) to a 6LR in order to establish global reachability for these 575 addresses via that 6LR. When registering with a 6LR that conforms 576 this specification, a Registering Node does not use its GUA as Source 577 Address, in contrast to a node that complies to RFC 6775 [RFC6775]. 578 For non-Link-Local addresses, the Duplicate Address exchange MUST 579 conform to RFC 6775, but the extended formats described in this 580 specification for the DAR and the DAC are used to relay the extended 581 information in the case of an EARO. 583 4.7. Maintaining the Registration States 585 This section discusses protocol actions that involve the Registering 586 Node, the 6LR and the 6LBR. It must be noted that the portion that 587 deals with a 6LBR only applies to those addresses that are registered 588 to it, which, as discussed in Section 4.6, is not the case for Link- 589 Local addresses. The registration state includes all data that is 590 stored in the router relative to that registration, in particular, 591 but not limited to, an NCE in a 6LR. 6LBRs and 6BBRs may store 592 additional registration information in more complex data structures 593 and use protocols that are out of scope of this document to keep them 594 synchonized when they are distributed. 596 When its Neighbor Cache is full, a 6LR cannot accept a new 597 registration. In that situation, the EARO is returned in a NA 598 message with a Status of 2, and the Registering Node may attempt to 599 register to another 6LR. 601 Conversely the registry in the 6LBR may be saturated, in which case 602 the LBR cannot guarantee that a new address is effectively not a 603 duplicate. In that case, the 6LBR replies to a EDAR message with a 604 EDAC message that carries a Status code 9 indicating "6LBR Registry 605 saturated", and the address stays in TENTATIVE state. Note: this 606 code is used by 6LBRs instead of Status 2 when responding to a 607 Duplicate Address message exchange and passed on to the Registering 608 Node by the 6LR. There is no point for the node to retry this 609 registration immediately via another 6LR, since the problem is global 610 to the network. The node may either abandon that address, deregister 611 other addresses first to make room, or keep the address in TENTATIVE 612 state and retry later. 614 A node renews an existing registration by repeatedly sending NS(EARO) 615 messages for the Registered Address. In order to refresh the 616 registration state in the 6LBR, these registrations MUST be reported 617 to the 6LBR. 619 A node that ceases to use an address SHOULD attempt to deregister 620 that address from all the 6LRs to which it has registered the 621 address, which is achieved using an NS(EARO) message with a 622 Registration Lifetime of 0. 624 A node that moves away from a particular 6LR SHOULD attempt to 625 deregister all of its addresses registered to that 6LR and register 626 to a new 6LR with an incremented TID. When/if the node shows up 627 elsewhere, an used to clean up the state in the previous location. 628 For instance, the "Moved" status can be used by a 6BBR in a NA(EARO) 629 message to indicate that the ownership of the proxy state on the 630 Backbone was transferred to another 6BBR, as the consequence of a 631 movement of the device. The receiver of the message SHOULD propagate 632 the status down the chain towards the Registered node and clean up 633 its state. 635 Upon receiving a NS(EARO) message with a Registration Lifetime of 0 636 and determining that this EARO is the freshest for a given NCE (see 637 Section 4.2), a 6LR cleans up its NCE. If the address was registered 638 to the 6LBR, then the 6LR MUST report to the 6LBR, through a 639 Duplicate Address exchange with the 6LBR, or an alternate protocol, 640 indicating the null Registration Lifetime and the latest TID that 641 this 6LR is aware of. 643 Upon the Extended DAR message, the 6LBR evaluates if this is the 644 freshest TID it has received for that particular registry entry. If 645 it is, then the entry is scheduled to be removed, and the EDAR is 646 answered with a EDAC message bearing a Status of 0 "Success". If it 647 is not the freshest, then a Status 3 "Moved" is returned instead, and 648 the existing entry is conserved. 650 Upon timing out a registration, a 6LR removes silently its binding 651 cache entry, and a 6LBR schedules its entry to be removed. 653 When an address is scheduled to be removed, the 6LBR SHOULD keep its 654 entry in a DELAY state for a configurable period of time, so as to 655 protect a mobile node that deregistered from one 6LR and did not 656 register yet to a new one, or the new registration did not reach yet 657 the 6LBR due to propagation delays in the network. Once the DELAY 658 time is passed, the 6LBR removes silently its entry. 660 5. Detecting Enhanced ARO Capability Support 662 The "Generic Header Compression for IPv6 over 6LoWPANs" [RFC7400] 663 introduces the 6LoWPAN Capability Indication Option (6CIO) to 664 indicate a node's capabilities to its peers. This specification 665 extends the format defined in RFC 7400 to signal the support for 666 EARO, as well as the node's capability to act as a 6LR, 6LBR and 667 6BBR. 669 With RFC 7400, the 6CIO is typically sent in a Router Solicitation 670 (RS) message. When used to signal the capabilities above per this 671 specification, the 6CIO is typically present in Router Advertisement 672 (RA) messages but can also be present in RS, Neighbor Solicitation 673 (NS) and Neighbor Advertisement (NA) messages. 675 6. Extended ND Options And Messages 677 This specification does not introduce new options, but it modifies 678 existing ones and updates the associated behaviors as specified in 679 the following subsections. 681 6.1. Enhanced Address Registration Option (EARO) 683 The Address Registration Option (ARO) is defined in section 4.1. of 684 [RFC6775]. 686 The Enhanced Address Registration Option (EARO) is intended to be 687 used as a replacement to the ARO option within Neighbor Discovery NS 688 and NA messages between a 6LN and its 6LR. Conversely, the Extended 689 Duplicate Address messages, EDAR and EDAC, are to be used in 690 replacement of the DAR and DAC messages so as to transport the new 691 information between 6LRs and 6LBRs across LLNs meshes such as 6TiSCH 692 networks. 694 An NS message with an EARO option is a registration if and only if it 695 also carries an SLLAO option. The EARO option also used in NS and NA 696 messages between Backbone Routers over the Backbone link to sort out 697 the distributed registration state; in that case, it does not carry 698 the SLLAO option and is not confused with a registration. 700 When using the EARO option, the address being registered is found in 701 the Target Address field of the NS and NA messages. This differs 702 from 6LoWPAN ND RFC 6775 [RFC6775] which specifies that the address 703 being registered is the source of the NS. 705 The EARO extends the ARO and is recognized by the "T" flag set. The 706 format of the EARO option is as follows: 708 0 1 2 3 709 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 1 710 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 711 | Type | Length = 2 | Status | Reserved | 712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 713 | Reserved |T| TID | Registration Lifetime | 714 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 715 | | 716 + Owner Unique ID (EUI-64 or equivalent) + 717 | | 718 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 720 Figure 2: EARO 722 Option Fields 724 Type: 33 726 Length: 8-bit unsigned integer. The length of the option in 727 units of 8 bytes. Always 2. 729 Status: 8-bit unsigned integer. Indicates the status of a 730 registration in the NA response. MUST be set to 0 in 731 NS messages. See Table 1 below. 733 +-------+-----------------------------------------------------------+ 734 | Value | Description | 735 +-------+-----------------------------------------------------------+ 736 | 0..2 | See RFC 6775 [RFC6775]. Note: a Status of 1 "Duplicate | 737 | | Address" applies to the Registered Address. If the Source | 738 | | Address conflicts with an existing registration, | 739 | | "Duplicate Source Address" should be used. | 740 | | | 741 | 3 | Moved: The registration fails because it is not the | 742 | | freshest. This Status indicates that the registration is | 743 | | rejected because another more recent registration was | 744 | | done, as indicated by a same OUI and a more recent TID. | 745 | | One possible cause is a stale registration that has | 746 | | progressed slowly in the network and was passed by a more | 747 | | recent one. It could also indicate a OUI collision. | 748 | | | 749 | 4 | Removed: The binding state was removed. This may be | 750 | | placed in an asynchronous NS(ARO) message, or as the | 751 | | rejection of a proxy registration to a Backbone Router | 752 | | | 753 | 5 | Validation Requested: The Registering Node is challenged | 754 | | for owning the Registered Address or for being an | 755 | | acceptable proxy for the registration. This Status is | 756 | | expected in asynchronous messages from a registrar (6LR, | 757 | | 6LBR, 6BBR) to indicate that the registration state is | 758 | | removed, for instance due to a movement of the device. | 759 | | | 760 | 6 | Duplicate Source Address: The address used as source of | 761 | | the NS(ARO) conflicts with an existing registration. | 762 | | | 763 | 7 | Invalid Source Address: The address used as source of the | 764 | | NS(ARO) is not a Link-Local address as prescribed by this | 765 | | document. | 766 | | | 767 | 8 | Registered Address topologically incorrect: The address | 768 | | being registered is not usable on this link, e.g. it is | 769 | | not topologically correct | 770 | | | 771 | 9 | 6LBR Registry saturated: A new registration cannot be | 772 | | accepted because the 6LBR Registry is saturated. Note: | 773 | | this code is used by 6LBRs instead of Status 2 when | 774 | | responding to a Duplicate Address message exchange and | 775 | | passed on to the Registering Node by the 6LR. | 776 | | | 777 | 10 | Validation Failed: The proof of ownership of the | 778 | | registered address is not correct. | 779 +-------+-----------------------------------------------------------+ 781 Table 1: EARO Status 783 Reserved: This field is unused. It MUST be initialized to zero 784 by the sender and MUST be ignored by the receiver. 786 T: One bit flag. Set if the next octet is a used as a 787 TID. 789 TID: 1-byte integer; a transaction id that is maintained 790 by the node and incremented with each transaction. 791 The node SHOULD maintain the TID in a persistent 792 storage. 794 Registration Lifetime: 16-bit integer; expressed in minutes. 0 795 means that the registration has ended and the 796 associated state should be removed. 798 Owner Unique Identifier (OUI): A globally unique identifier for the 799 node associated. This can be the EUI-64 derived IID 800 of an interface, or some provable ID obtained 801 cryptographically. 803 6.2. Extended Duplicate Address Message Formats 805 The Duplicate Address Request (DAR) and the Duplicate Address 806 Confirmation (DAC) messages are defined in section 4.4. of [RFC6775]. 807 Those messages follow a common base format, which enables information 808 from the ARO to be transported over multiple hops. 810 The Duplicate Address Messages are extended to adapt to the Extended 811 ARO format, as follows: 813 0 1 2 3 814 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 1 815 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 816 | Type | Code | Checksum | 817 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 818 | Status | TID | Registration Lifetime | 819 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 820 | | 821 + Owner Unique ID (EUI-64 or equivalent) + 822 | | 823 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 824 | | 825 + + 826 | | 827 + Registered Address + 828 | | 829 + + 830 | | 831 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 833 Figure 3: Duplicate Address Messages Format 835 Modified Message Fields 837 Code: The ICMP Code as defined in [RFC4443]. The ICMP Code 838 MUST be set to 1 with this specification. An odd 839 value of the ICMP Code indicates that the TID field 840 is present and obeys this specification. 842 TID: 1-byte integer; same definition and processing as the 843 TID in the EARO option as defined in Section 6.1. 845 Owner Unique Identifier (OUI): 8 bytes; same definition and 846 processing as the OUI in the EARO option as defined 847 in Section 6.1. 849 6.3. New 6LoWPAN Capability Bits in the Capability Indication Option 851 This specification defines a number of capability bits in the 6CIO 852 that was introduced by RFC 7400 for use in IPv6 ND RA messages. 854 Routers that support this specification SHOULD set the "E" flag and 855 6LN SHOULD favor 6LR routers that support this specification over 856 those that do not. Routers that are capable of acting as 6LR, 6LBR 857 and 6BBR SHOULD set the "L", "B" and "P" flags, respectively. In 858 particular, the function 6LR is usually collocated with that of 6LBR. 860 Those flags are not mutually exclusive and if a router is capable of 861 running multiple functions, it SHOULD set all the related flags. 863 0 1 2 3 864 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 1 865 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 866 | Type | Length = 1 | Reserved |L|B|P|E|G| 867 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 868 | Reserved | 869 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 871 Figure 4: New capability Bits L, B, P, E in the 6CIO 873 Option Fields 875 Type: 36 877 L: Node is a 6LR, it can take registrations. 879 B: Node is a 6LBR. 881 P: Node is a 6BBR, proxying for nodes on this link. 883 E: This specification is supported and applied. 885 7. Backward Compatibility 887 7.1. Discovering the capabilities of an ND peer 889 7.1.1. Using the E Flag in the 6CIO Option 891 If the 6CIO is used in an ND message and the sending node supports 892 this specification, then the "E" Flag MUST be set. 894 A router that supports this specification SHOULD indicate that with a 895 6CIO Option, but this might not be practical if the link-layer MTU is 896 too small. 898 If the Registering Node (RN) receives a CIO in a Router Advertisement 899 message, then the setting of the "E" Flag indicates whether or not 900 this specification is supported. RN SHOULD favor a router that 901 supports this specification over those that do not. 903 7.1.2. Using the T Flag in the EARO 905 One alternate way for a 6LN to discover the router's capabilities to 906 first register a Link Local address, placing the same address in the 907 Source and Target Address fields of the NS message, and setting the 908 "T" Flag. The node may for instance register an address that is 909 based on EUI-64. For such address, DAD is not required and using the 910 SLLAO option in the NS is actually more consistent with existing ND 911 specifications such as the "Optimistic Duplicate Address Detection 912 (DAD) for IPv6" [RFC4429]. 914 Once that first registration is complete, the node knows from the 915 setting of the "T" Flag in the response whether the router supports 916 this specification. If support is verified, the node may register 917 other addresses that it owns, or proxy-register addresses on behalf 918 some another node, indicating those addresses being registered in the 919 Target Address field of the NS messages, while using one of its own 920 previously registered addresses as source. 922 A node that supports this specification MUST always use an EARO as a 923 replacement to an ARO in its registration to a router. This is 924 harmless since the "T" flag and TID field are reserved in RFC 6775 925 are ignored by a legacy router. A router that supports this 926 specification answers an ARO with an ARO and answers an EARO with an 927 EARO. 929 This specification changes the behavior of the peers in a 930 registration flows. To enable backward compatibility, a 6LB that 931 registers to a 6LR that is not known to support this specification 932 MUST behave in a manner that is compatible with RFC 6775. A 6LN can 933 achieve that by sending a NS(EARO) message with a Link-Local Address 934 used as both Source and Target Address, as described in Section 4.6. 935 Once the 6LR is known to support this specification, the 6LN MUST 936 obey this specification. 938 7.2. Legacy 6LoWPAN Node 940 A legacy 6LN will use the Registered Address as source and will not 941 use an EARO option. An updated 6LR MUST accept that registration if 942 it is valid per RFC 6775, and it MUST manage the binding cache 943 accordingly. The updated 6LR MUST then use the original Duplicate 944 Address messages as specified in RFC 6775 to indicate to the 6LBR 945 that the TID is not present in the messages. 947 The main difference with RFC 6775 is that Duplicate Address exchange 948 for DAD is avoided for Link-Local addresses. In any case, the 6LR 949 SHOULD use an EARO in the reply, and may use any of the Status codes 950 defined in this specification. 952 7.3. Legacy 6LoWPAN Router 954 The first registration by an updated 6LN MUST be for a Link-Local 955 address, using that Link-Local address as source. A legacy 6LR will 956 not make a difference and accept -or reject- that registration as if 957 the 6LN was a legacy node. 959 An updated 6LN will always use an EARO option in the registration NS 960 message, whereas a legacy 6LR will always reply with an ARO option in 961 the NA message. So from that first registration, the updated 6LN can 962 figure whether the 6LR supports this specification or not. 964 After detecting a legacy 6LR, an updated 6LN may attempt to find an 965 alternate 6LR that is updated. In order to be backward compatible, 966 after detecting that a 6LR is legacy, the 6LN MUST adhere to RFC 6775 967 in future protocol exchanges with that 6LR, and source the packet 968 with the Registered Address. 970 Note that the updated 6LN SHOULD use an EARO in the request 971 regardless of the type of 6LR, legacy or updated, which implies that 972 the 'T' flag is set. 974 If an updated 6LN moves from an updated 6LR to a legacy 6LR, the 975 legacy 6LR will send a legacy DAR message, which can not be compared 976 with an updated one for freshness. 978 Allowing legacy DAR messages to replace a state established by the 979 updated protocol in the 6LBR would be an attack vector and that 980 cannot be the default behavior. 982 But if legacy and updated 6LRs coexist temporarily in a network, then 983 it makes sense for an administrator to install a policy that allows 984 so, and the capability to install such a policy should be 985 configurable in a 6LBR though it is out of scope for this document. 987 7.4. Legacy 6LoWPAN Border Router 989 With this specification, the Duplicate Address messages are extended 990 to transport the EARO information. Similarly to the NS/NA exchange, 991 updated 6LBR devices always use the Extended Duplicate Address 992 messages and all the associated behavior so they can amlways be 993 differentiated from legacy ones. 995 Note that a legacy 6LBR will accept and process an EDAR message as if 996 it was an original one, so the original support of DAD is preserved. 998 8. Security Considerations 1000 This specification extends RFC 6775 [RFC6775], and the security 1001 section of that draft also applies to this as well. In particular, 1002 it is expected that the link layer is sufficiently protected to 1003 prevent a rogue access, either by means of physical or IP security on 1004 the Backbone Link and link layer cryptography on the LLN. This 1005 specification also expects that the LLN MAC provides secure unicast 1006 to/from the Backbone Router and secure Broadcast from the Backbone 1007 Router in a way that prevents tempering with or replaying the RA 1008 messages. 1010 This specification recommends to using privacy techniques (see 1011 Section 9, and protection against address theft such as provided by 1012 "Address Protected Neighbor Discovery for Low-power and Lossy 1013 Networks" [I-D.ietf-6lo-ap-nd], which guarantees the ownership of the 1014 Registered Address using a cryptographic OUID. 1016 The registration mechanism may be used by a rogue node to attack the 1017 6LR or the 6LBR with a Denial-of-Service attack against the registry. 1018 It may also happen that the registry of a 6LR or a 6LBR is saturated 1019 and cannot take any more registration, which effectively denies the 1020 requesting a node the capability to use a new address. In order to 1021 alleviate those concerns, Section 4.7 provides a number of 1022 recommendations that ensure that a stale registration is removed as 1023 soon as possible from the 6LR and 6LBR. In particular, this 1024 specification recommends that: 1026 o A node that ceases to use an address SHOULD attempt to deregister 1027 that address from all the 6LRs to which it is registered. The 1028 flow is propagated to the 6LBR when needed, and a sequence number 1029 is used to make sure that only the freshest command is acted upon. 1031 o The Registration lifetimes SHOULD be individually configurable for 1032 each address or group of addresses. The nodes SHOULD be 1033 configured with a Registration Lifetime that reflects their 1034 expectation of how long they will use the address with the 6LR to 1035 which it is registered. In particular, use cases that involve 1036 mobility or rapid address changes SHOULD use lifetimes that are 1037 larger yet of a same order as the duration of the expectation of 1038 presence. 1040 o The router (6LR or 6LBR) SHOULD be configurable so as to limit the 1041 number of addresses that can be registered by a single node, as 1042 identified at least by MAC address and preferably by security 1043 credentials. When that maximum is reached, the router should use 1044 a Least-Recently-Used (LRU) logic so as to clean up the addresses 1045 that were not used for the longest time, keeping at least one 1046 Link-Local address, and attempting to keep one or more stable 1047 addresses if such can be recognized, e.g. from the way the IID is 1048 formed or because they are used over a much longer time span than 1049 other (privacy, shorter-lived) addresses. The address lifetimes 1050 SHOULD be individually configurable. 1052 o In order to avoid denial of registration for the lack of 1053 resources, administrators SHOULD take great care to deploy 1054 adequate numbers of 6LRs to cover the needs of the nodes in their 1055 range, so as to avoid a situation of starving nodes. It is 1056 expected that the 6LBR that serves a LLN is a more capable node 1057 then the average 6LR, but in a network condition where it may 1058 become saturated, a particular deployment SHOULD distribute the 1059 6LBR functionality, for instance by leveraging a high speed 1060 Backbone and Backbone Routers to aggregate multiple LLNs into a 1061 larger subnet. 1063 The LLN nodes depend on the 6LBR and the 6BBR for their operation. A 1064 trust model must be put in place to ensure that the right devices are 1065 acting in these roles, so as to avoid threats such as black-holing, 1066 or bombing attack whereby an impersonated 6LBR would destroy state in 1067 the network by using the "Removed" Status code. 1069 9. Privacy Considerations 1071 As indicated in section Section 2, this protocol does not aim at 1072 limiting the number of IPv6 addresses that a device can form. A host 1073 should be able to form and register any address that is topologically 1074 correct in the subnet(s) advertised by the 6LR/6LBR. 1076 This specification does not mandate any particular way for forming 1077 IPv6 addresses, but it discourages using EUI-64 for forming the 1078 Interface ID in the Link-Local address because this method prevents 1079 the usage of "SEcure Neighbor Discovery (SEND)" [RFC3971] and 1080 "Cryptographically Generated Addresses (CGA)" [RFC3972], and that of 1081 address privacy techniques. 1083 "Privacy Considerations for IPv6 Adaptation-Layer Mechanisms" 1084 [RFC8065] explains why privacy is important and how to form such 1085 addresses. All implementations and deployment must consider the 1086 option of privacy addresses in their own environment. Also future 1087 specifications involving 6LOWPAN Neighbor Discovery should consult 1088 "Recommendation on Stable IPv6 Interface Identifiers" [RFC8064] for 1089 default interface identifaction. 1091 10. IANA Considerations 1093 IANA is requested to make a number of changes under the "Internet 1094 Control Message Protocol version 6 (ICMPv6) Parameters" registry, as 1095 follows. 1097 10.1. ARO Flags 1099 IANA is requested to create a new subregistry for "ARO Flags". This 1100 specification defines 8 positions, bit 0 to bit 7, and assigns bit 7 1101 for the 'T' flag in Section 6.1. The policy is "IETF Review" or 1102 "IESG Approval" [RFC8126]. The initial content of the registry is as 1103 shown in Table 2. 1105 New subregistry for ARO Flags under the "Internet Control Message 1106 Protocol version 6 (ICMPv6) [RFC4443] Parameters" 1108 +------------+--------------+-----------+ 1109 | ARO Status | Description | Document | 1110 +------------+--------------+-----------+ 1111 | 0..6 | Unassigned | | 1112 | 7 | 'T' Flag | RFC This | 1113 +------------+--------------+-----------+ 1115 Table 2: new ARO Flags 1117 10.2. ICMP Codes 1119 IANA is requested to create a new entry in the ICMPv6 "Code" Fields 1120 subregistry of the Internet Control Message Protocol version 6 1121 (ICMPv6) Parameters for the ICMP codes related to the ICMP type 157 1122 and 158 Duplicate Address Request (shown in Table 3) and Confirmation 1123 (shown in Table 4), respectively, as follows: 1125 New entries for ICMP types 157 DAR message 1127 +------+----------------------+------------+ 1128 | Code | Name | Reference | 1129 +------+----------------------+------------+ 1130 | 0 | Original DAR message | RFC 6775 | 1131 | 1 | Extended DAR message | RFC This | 1132 +------+----------------------+------------+ 1134 Table 3: new ICMPv6 Code Fields 1136 New entries for ICMP types 158 DAC message 1138 +------+----------------------+------------+ 1139 | Code | Name | Reference | 1140 +------+----------------------+------------+ 1141 | 0 | Original DAC message | RFC 6775 | 1142 | 1 | Extended DAC message | RFC This | 1143 +------+----------------------+------------+ 1145 Table 4: new ICMPv6 Code Fields 1147 10.3. New ARO Status values 1149 IANA is requested to make additions to the Address Registration 1150 Option Status Values Registry as follows: 1152 Address Registration Option Status Values Registry 1154 +------------+------------------------------------------+-----------+ 1155 | ARO Status | Description | Document | 1156 +------------+------------------------------------------+-----------+ 1157 | 3 | Moved | RFC This | 1158 | 4 | Removed | RFC This | 1159 | 5 | Validation Requested | RFC This | 1160 | 6 | Duplicate Source Address | RFC This | 1161 | 7 | Invalid Source Address | RFC This | 1162 | 8 | Registered Address topologically | RFC This | 1163 | | incorrect | | 1164 | 9 | 6LBR registry saturated | RFC This | 1165 | 10 | Validation Failed | RFC This | 1166 +------------+------------------------------------------+-----------+ 1168 Table 5: New ARO Status values 1170 10.4. New 6LoWPAN capability Bits 1172 IANA is requested to make additions to the Subregistry for "6LoWPAN 1173 capability Bits" as follows: 1175 Subregistry for "6LoWPAN capability Bits" under the "Internet Control 1176 Message Protocol version 6 (ICMPv6) Parameters" 1178 +----------------+----------------------+-----------+ 1179 | capability Bit | Description | Document | 1180 +----------------+----------------------+-----------+ 1181 | 11 | 6LR capable (L bit) | RFC This | 1182 | 12 | 6LBR capable (B bit) | RFC This | 1183 | 13 | 6BBR capable (P bit) | RFC This | 1184 | 14 | EARO support (E bit) | RFC This | 1185 +----------------+----------------------+-----------+ 1187 Table 6: New 6LoWPAN capability Bits 1189 11. Acknowledgments 1191 Kudos to Eric Levy-Abegnoli who designed the First Hop Security 1192 infrastructure upon which the first backbone router was implemented; 1193 many thanks to Charlie Perkins for his in-depth reviews and 1194 constructive suggestions, as well as to Sedat Gormus, Rahul Jadhav 1195 and Lorenzo Colitti for their various contributions and reviews. 1196 Also many thanks to Thomas Watteyne for his early implementation of a 1197 6LN that was instrumental to the early tests of the 6LR, 6LBR and 1198 Backbone Router. 1200 12. References 1202 12.1. Normative References 1204 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1205 Requirement Levels", BCP 14, RFC 2119, 1206 DOI 10.17487/RFC2119, March 1997, 1207 . 1209 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1210 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1211 2006, . 1213 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 1214 Control Message Protocol (ICMPv6) for the Internet 1215 Protocol Version 6 (IPv6) Specification", STD 89, 1216 RFC 4443, DOI 10.17487/RFC4443, March 2006, 1217 . 1219 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1220 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1221 DOI 10.17487/RFC4861, September 2007, 1222 . 1224 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1225 Address Autoconfiguration", RFC 4862, 1226 DOI 10.17487/RFC4862, September 2007, 1227 . 1229 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1230 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1231 DOI 10.17487/RFC6282, September 2011, 1232 . 1234 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1235 Bormann, "Neighbor Discovery Optimization for IPv6 over 1236 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1237 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1238 . 1240 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 1241 IPv6 over Low-Power Wireless Personal Area Networks 1242 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 1243 2014, . 1245 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1246 Writing an IANA Considerations Section in RFCs", BCP 26, 1247 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1248 . 1250 12.2. Informative References 1252 [I-D.chakrabarti-nordmark-6man-efficient-nd] 1253 Chakrabarti, S., Nordmark, E., Thubert, P., and M. 1254 Wasserman, "IPv6 Neighbor Discovery Optimizations for 1255 Wired and Wireless Networks", draft-chakrabarti-nordmark- 1256 6man-efficient-nd-07 (work in progress), February 2015. 1258 [I-D.delcarpio-6lo-wlanah] 1259 Vega, L., Robles, I., and R. Morabito, "IPv6 over 1260 802.11ah", draft-delcarpio-6lo-wlanah-01 (work in 1261 progress), October 2015. 1263 [I-D.ietf-6lo-ap-nd] 1264 Sarikaya, B., Thubert, P., and M. Sethi, "Address 1265 Protected Neighbor Discovery for Low-power and Lossy 1266 Networks", draft-ietf-6lo-ap-nd-02 (work in progress), May 1267 2017. 1269 [I-D.ietf-6lo-backbone-router] 1270 Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo- 1271 backbone-router-04 (work in progress), July 2017. 1273 [I-D.ietf-6lo-nfc] 1274 Choi, Y., Hong, Y., Youn, J., Kim, D., and J. Choi, 1275 "Transmission of IPv6 Packets over Near Field 1276 Communication", draft-ietf-6lo-nfc-07 (work in progress), 1277 June 2017. 1279 [I-D.ietf-6tisch-architecture] 1280 Thubert, P., "An Architecture for IPv6 over the TSCH mode 1281 of IEEE 802.15.4", draft-ietf-6tisch-architecture-12 (work 1282 in progress), August 2017. 1284 [I-D.ietf-bier-architecture] 1285 Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and 1286 S. Aldrin, "Multicast using Bit Index Explicit 1287 Replication", draft-ietf-bier-architecture-08 (work in 1288 progress), September 2017. 1290 [I-D.ietf-ipv6-multilink-subnets] 1291 Thaler, D. and C. Huitema, "Multi-link Subnet Support in 1292 IPv6", draft-ietf-ipv6-multilink-subnets-00 (work in 1293 progress), July 2002. 1295 [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] 1296 Popa, D. and J. Hui, "6LoPLC: Transmission of IPv6 Packets 1297 over IEEE 1901.2 Narrowband Powerline Communication 1298 Networks", draft-popa-6lo-6loplc-ipv6-over- 1299 ieee19012-networks-00 (work in progress), March 2014. 1301 [RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, 1302 DOI 10.17487/RFC1982, August 1996, 1303 . 1305 [RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with 1306 CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September 1307 2003, . 1309 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1310 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1311 DOI 10.17487/RFC3810, June 2004, 1312 . 1314 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 1315 "SEcure Neighbor Discovery (SEND)", RFC 3971, 1316 DOI 10.17487/RFC3971, March 2005, 1317 . 1319 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 1320 RFC 3972, DOI 10.17487/RFC3972, March 2005, 1321 . 1323 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 1324 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 1325 . 1327 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1328 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1329 Overview, Assumptions, Problem Statement, and Goals", 1330 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1331 . 1333 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 1334 Extensions for Stateless Address Autoconfiguration in 1335 IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, 1336 . 1338 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1339 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1340 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1341 Low-Power and Lossy Networks", RFC 6550, 1342 DOI 10.17487/RFC6550, March 2012, 1343 . 1345 [RFC7217] Gont, F., "A Method for Generating Semantically Opaque 1346 Interface Identifiers with IPv6 Stateless Address 1347 Autoconfiguration (SLAAC)", RFC 7217, 1348 DOI 10.17487/RFC7217, April 2014, 1349 . 1351 [RFC7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets 1352 over ITU-T G.9959 Networks", RFC 7428, 1353 DOI 10.17487/RFC7428, February 2015, 1354 . 1356 [RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B., 1357 Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low 1358 Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015, 1359 . 1361 [RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi, 1362 "Host Address Availability Recommendations", BCP 204, 1363 RFC 7934, DOI 10.17487/RFC7934, July 2016, 1364 . 1366 [RFC8064] Gont, F., Cooper, A., Thaler, D., and W. Liu, 1367 "Recommendation on Stable IPv6 Interface Identifiers", 1368 RFC 8064, DOI 10.17487/RFC8064, February 2017, 1369 . 1371 [RFC8065] Thaler, D., "Privacy Considerations for IPv6 Adaptation- 1372 Layer Mechanisms", RFC 8065, DOI 10.17487/RFC8065, 1373 February 2017, . 1375 [RFC8105] Mariager, P., Petersen, J., Ed., Shelby, Z., Van de Logt, 1376 M., and D. Barthel, "Transmission of IPv6 Packets over 1377 Digital Enhanced Cordless Telecommunications (DECT) Ultra 1378 Low Energy (ULE)", RFC 8105, DOI 10.17487/RFC8105, May 1379 2017, . 1381 [RFC8163] Lynn, K., Ed., Martocci, J., Neilson, C., and S. 1382 Donaldson, "Transmission of IPv6 over Master-Slave/Token- 1383 Passing (MS/TP) Networks", RFC 8163, DOI 10.17487/RFC8163, 1384 May 2017, . 1386 12.3. External Informative References 1388 [IEEEstd802154] 1389 IEEE, "IEEE Standard for Low-Rate Wireless Networks", 1390 IEEE Standard 802.15.4, DOI 10.1109/IEEESTD.2016.7460875, 1391 . 1393 [Perlman83] 1394 Perlman, R., "Fault-Tolerant Broadcast of Routing 1395 Information", North-Holland Computer Networks 7: 395-405, 1396 1983, . 1399 Appendix A. Applicability and Requirements Served 1401 This specification extends 6LoWPAN ND to sequence the registration 1402 and serves the requirements expressed Appendix B.1 by enabling the 1403 mobility of devices from one LLN to the next based on the 1404 complementary work in the "IPv6 Backbone Router" 1405 [I-D.ietf-6lo-backbone-router] specification. 1407 In the context of the the TimeSlotted Channel Hopping (TSCH) mode of 1408 IEEE Std. 802.15.4 [IEEEstd802154], the "6TiSCH architecture" 1409 [I-D.ietf-6tisch-architecture] introduces how a 6LoWPAN ND host could 1410 connect to the Internet via a RPL mesh Network, but this requires 1411 additions to the 6LOWPAN ND protocol to support mobility and 1412 reachability in a secured and manageable environment. This 1413 specification details the new operations that are required to 1414 implement the 6TiSCH architecture and serves the requirements listed 1415 in Appendix B.2. 1417 The term LLN is used loosely in this specification to cover multiple 1418 types of WLANs and WPANs, including Low-Power Wi-Fi, BLUETOOTH(R) Low 1419 Energy, IEEE Std.802.11AH and IEEE Std.802.15.4 wireless meshes, so 1420 as to address the requirements discussed in Appendix B.3 1422 This specification can be used by any wireless node to associate at 1423 Layer-3 with a 6BBR and register its IPv6 addresses to obtain routing 1424 services including proxy-ND operations over the Backbone, effectively 1425 providing a solution to the requirements expressed in Appendix B.4. 1427 "Efficiency aware IPv6 Neighbor Discovery Optimizations" 1428 [I-D.chakrabarti-nordmark-6man-efficient-nd] suggests that 6LoWPAN ND 1429 [RFC6775] can be extended to other types of links beyond IEEE Std. 1430 802.15.4 for which it was defined. The registration technique is 1431 beneficial when the Link-Layer technique used to carry IPv6 multicast 1432 packets is not sufficiently efficient in terms of delivery ratio or 1433 energy consumption in the end devices, in particular to enable 1434 energy-constrained sleeping nodes. The value of such extension is 1435 especially apparent in the case of mobile wireless nodes, to reduce 1436 the multicast operations that are related to classical ND ([RFC4861], 1437 [RFC4862]) and plague the wireless medium. This serves scalability 1438 requirements listed in Appendix B.6. 1440 Appendix B. Requirements 1442 This section lists requirements that were discussed at 6lo for an 1443 update to 6LoWPAN ND. This specification meets most of them, but 1444 those listed in Appendix B.5 which are deferred to a different 1445 specification such as [I-D.ietf-6lo-ap-nd], and those related to 1446 multicast. 1448 B.1. Requirements Related to Mobility 1450 Due to the unstable nature of LLN links, even in a LLN of immobile 1451 nodes a 6LN may change its point of attachment to a 6LR, say 6LR-a, 1452 and may not be able to notify 6LR-a. Consequently, 6LR-a may still 1453 attract traffic that it cannot deliver any more. When links to a 6LR 1454 change state, there is thus a need to identify stale states in a 6LR 1455 and restore reachability in a timely fashion. 1457 Req1.1: Upon a change of point of attachment, connectivity via a new 1458 6LR MUST be restored timely without the need to de-register from the 1459 previous 6LR. 1461 Req1.2: For that purpose, the protocol MUST enable to differentiate 1462 between multiple registrations from one 6LoWPAN Node and 1463 registrations from different 6LoWPAN Nodes claiming the same address. 1465 Req1.3: Stale states MUST be cleaned up in 6LRs. 1467 Req1.4: A 6LoWPAN Node SHOULD also be capable to register its Address 1468 to multiple 6LRs, and this, concurrently. 1470 B.2. Requirements Related to Routing Protocols 1472 The point of attachment of a 6LN may be a 6LR in an LLN mesh. IPv6 1473 routing in a LLN can be based on RPL, which is the routing protocol 1474 that was defined at the IETF for this particular purpose. Other 1475 routing protocols than RPL are also considered by Standard Defining 1476 Organizations (SDO) on the basis of the expected network 1477 characteristics. It is required that a 6LoWPAN Node attached via ND 1478 to a 6LR would need to participate in the selected routing protocol 1479 to obtain reachability via the 6LR. 1481 Next to the 6LBR unicast address registered by ND, other addresses 1482 including multicast addresses are needed as well. For example a 1483 routing protocol often uses a multicast address to register changes 1484 to established paths. ND needs to register such a multicast address 1485 to enable routing concurrently with discovery. 1487 Multicast is needed for groups. Groups MAY be formed by device type 1488 (e.g. routers, street lamps), location (Geography, RPL sub-tree), or 1489 both. 1491 The Bit Index Explicit Replication (BIER) Architecture 1492 [I-D.ietf-bier-architecture] proposes an optimized technique to 1493 enable multicast in a LLN with a very limited requirement for routing 1494 state in the nodes. 1496 Related requirements are: 1498 Req2.1: The ND registration method SHOULD be extended in such a 1499 fashion that the 6LR MAY advertise the Address of a 6LoWPAN Node over 1500 the selected routing protocol and obtain reachability to that Address 1501 using the selected routing protocol. 1503 Req2.2: Considering RPL, the Address Registration Option that is used 1504 in the ND registration SHOULD be extended to carry enough information 1505 to generate a DAO message as specified in [RFC6550] section 6.4, in 1506 particular the capability to compute a Path Sequence and, as an 1507 option, a RPLInstanceID. 1509 Req2.3: Multicast operations SHOULD be supported and optimized, for 1510 instance using BIER or MPL. Whether ND is appropriate for the 1511 registration to the 6BBR is to be defined, considering the additional 1512 burden of supporting the Multicast Listener Discovery Version 2 1513 [RFC3810] (MLDv2) for IPv6. 1515 B.3. Requirements Related to the Variety of Low-Power Link types 1517 6LoWPAN ND [RFC6775] was defined with a focus on IEEE Std.802.15.4 1518 and in particular the capability to derive a unique Identifier from a 1519 globally unique MAC-64 address. At this point, the 6lo Working Group 1520 is extending the 6LoWPAN Header Compression (HC) [RFC6282] technique 1521 to other link types ITU-T G.9959 [RFC7428], Master-Slave/Token- 1522 Passing [RFC8163], DECT Ultra Low Energy [RFC8105], Near Field 1523 Communication [I-D.ietf-6lo-nfc], IEEE Std. 802.11ah 1524 [I-D.delcarpio-6lo-wlanah], as well as IEEE1901.2 Narrowband 1525 Powerline Communication Networks 1526 [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] and BLUETOOTH(R) 1527 Low Energy [RFC7668]. 1529 Related requirements are: 1531 Req3.1: The support of the registration mechanism SHOULD be extended 1532 to more LLN links than IEEE Std.802.15.4, matching at least the LLN 1533 links for which an "IPv6 over foo" specification exists, as well as 1534 Low-Power Wi-Fi. 1536 Req3.2: As part of this extension, a mechanism to compute a unique 1537 Identifier should be provided, with the capability to form a Link- 1538 Local Address that SHOULD be unique at least within the LLN connected 1539 to a 6LBR discovered by ND in each node within the LLN. 1541 Req3.3: The Address Registration Option used in the ND registration 1542 SHOULD be extended to carry the relevant forms of unique Identifier. 1544 Req3.4: The Neighbour Discovery should specify the formation of a 1545 site-local address that follows the security recommendations from 1546 [RFC7217]. 1548 B.4. Requirements Related to Proxy Operations 1550 Duty-cycled devices may not be able to answer themselves to a lookup 1551 from a node that uses classical ND on a Backbone and may need a 1552 proxy. Additionally, the duty-cycled device may need to rely on the 1553 6LBR to perform registration to the 6BBR. 1555 The ND registration method SHOULD defend the addresses of duty-cycled 1556 devices that are sleeping most of the time and not capable to defend 1557 their own Addresses. 1559 Related requirements are: 1561 Req4.1: The registration mechanism SHOULD enable a third party to 1562 proxy register an Address on behalf of a 6LoWPAN node that may be 1563 sleeping or located deeper in an LLN mesh. 1565 Req4.2: The registration mechanism SHOULD be applicable to a duty- 1566 cycled device regardless of the link type, and enable a 6BBR to 1567 operate as a proxy to defend the Registered Addresses on its behalf. 1569 Req4.3: The registration mechanism SHOULD enable long sleep 1570 durations, in the order of multiple days to a month. 1572 B.5. Requirements Related to Security 1574 In order to guarantee the operations of the 6LoWPAN ND flows, the 1575 spoofing of the 6LR, 6LBR and 6BBRs roles should be avoided. Once a 1576 node successfully registers an address, 6LoWPAN ND should provide 1577 energy-efficient means for the 6LBR to protect that ownership even 1578 when the node that registered the address is sleeping. 1580 In particular, the 6LR and the 6LBR then should be able to verify 1581 whether a subsequent registration for a given Address comes from the 1582 original node. 1584 In a LLN it makes sense to base security on layer-2 security. During 1585 bootstrap of the LLN, nodes join the network after authorization by a 1586 Joining Assistant (JA) or a Commissioning Tool (CT). After joining 1587 nodes communicate with each other via secured links. The keys for 1588 the layer-2 security are distributed by the JA/CT. The JA/CT can be 1589 part of the LLN or be outside the LLN. In both cases it is needed 1590 that packets are routed between JA/CT and the joining node. 1592 Related requirements are: 1594 Req5.1: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for 1595 the 6LR, 6LBR and 6BBR to authenticate and authorize one another for 1596 their respective roles, as well as with the 6LoWPAN Node for the role 1597 of 6LR. 1599 Req5.2: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for 1600 the 6LR and the 6LBR to validate new registration of authorized 1601 nodes. Joining of unauthorized nodes MUST be impossible. 1603 Req5.3: 6LoWPAN ND security mechanisms SHOULD lead to small packet 1604 sizes. In particular, the NS, NA, DAR and DAC messages for a re- 1605 registration flow SHOULD NOT exceed 80 octets so as to fit in a 1606 secured IEEE Std.802.15.4 [IEEEstd802154] frame. 1608 Req5.4: Recurrent 6LoWPAN ND security operations MUST NOT be 1609 computationally intensive on the LoWPAN Node CPU. When a Key hash 1610 calculation is employed, a mechanism lighter than SHA-1 SHOULD be 1611 preferred. 1613 Req5.5: The number of Keys that the 6LoWPAN Node needs to manipulate 1614 SHOULD be minimized. 1616 Req5.6: The 6LoWPAN ND security mechanisms SHOULD enable the 1617 variation of CCM [RFC3610] called CCM* for use at both Layer 2 and 1618 Layer 3, and SHOULD enable the reuse of security code that has to be 1619 present on the device for upper layer security such as TLS. 1621 Req5.7: Public key and signature sizes SHOULD be minimized while 1622 maintaining adequate confidentiality and data origin authentication 1623 for multiple types of applications with various degrees of 1624 criticality. 1626 Req5.8: Routing of packets should continue when links pass from the 1627 unsecured to the secured state. 1629 Req5.9: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for 1630 the 6LR and the 6LBR to validate whether a new registration for a 1631 given address corresponds to the same 6LoWPAN Node that registered it 1632 initially, and, if not, determine the rightful owner, and deny or 1633 clean-up the registration that is duplicate. 1635 B.6. Requirements Related to Scalability 1637 Use cases from Automatic Meter Reading (AMR, collection tree 1638 operations) and Advanced Metering Infrastructure (AMI, bi-directional 1639 communication to the meters) indicate the needs for a large number of 1640 LLN nodes pertaining to a single RPL DODAG (e.g. 5000) and connected 1641 to the 6LBR over a large number of LLN hops (e.g. 15). 1643 Related requirements are: 1645 Req6.1: The registration mechanism SHOULD enable a single 6LBR to 1646 register multiple thousands of devices. 1648 Req6.2: The timing of the registration operation should allow for a 1649 large latency such as found in LLNs with ten and more hops. 1651 Authors' Addresses 1653 Pascal Thubert (editor) 1654 Cisco Systems, Inc 1655 Sophia Antipolis 1656 FRANCE 1658 Email: pthubert@cisco.com 1660 Erik Nordmark 1661 Santa Clara, CA 1662 USA 1664 Email: nordmark@sonic.net 1666 Samita Chakrabarti 1667 San Jose, CA 1668 USA 1670 Email: samitac.ietf@gmail.com