idnits 2.17.1 draft-ietf-6lo-backbone-router-02.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 19, 2016) is 2777 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. 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: 'IEEE80211' is mentioned on line 1307, but not defined == Missing Reference: 'IEEE802154' is mentioned on line 1324, but not defined == Missing Reference: 'IEEE802151' is mentioned on line 1315, but not defined ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) == Outdated reference: A later version (-08) exists of draft-ietf-6lo-6lobac-05 == Outdated reference: A later version (-09) exists of draft-ietf-6lo-dect-ule-05 == Outdated reference: A later version (-22) exists of draft-ietf-6lo-nfc-04 == Outdated reference: A later version (-02) exists of draft-ietf-6man-rs-refresh-01 == Outdated reference: A later version (-30) exists of draft-ietf-6tisch-architecture-10 == Outdated reference: A later version (-10) exists of draft-ietf-6tisch-terminology-07 == Outdated reference: A later version (-08) exists of draft-ietf-bier-architecture-04 == Outdated reference: A later version (-01) exists of draft-thubert-6lo-rfc6775-update-00 -- Obsolete informational reference (is this intentional?): RFC 3315 (Obsoleted by RFC 8415) -- Obsolete informational reference (is this intentional?): RFC 6830 (Obsoleted by RFC 9300, RFC 9301) Summary: 1 error (**), 0 flaws (~~), 12 warnings (==), 4 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 Intended status: Standards Track September 19, 2016 5 Expires: March 23, 2017 7 IPv6 Backbone Router 8 draft-ietf-6lo-backbone-router-02 10 Abstract 12 This specification proposes an update to IPv6 Neighbor Discovery, to 13 enhance the operation of IPv6 over wireless links that exhibit lossy 14 multicast support, and enable a large degree of scalability by 15 splitting the broadcast domains. A higher speed backbone federates 16 multiple wireless links to form a large MultiLink Subnet. Backbone 17 Routers acting as Layer-3 Access Point route packets to registered 18 nodes, where an classical Layer-2 Access Point would bridge. 19 Conversely, wireless nodes register to the Backbone Router to setup 20 routing services in a fashion that is essentially similar to a 21 classical Layer-2 association. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on March 23, 2017. 40 Copyright Notice 42 Copyright (c) 2016 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 58 2. Applicability and Requirements Served . . . . . . . . . . . . 5 59 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7 60 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 9 61 5. New Types And Formats . . . . . . . . . . . . . . . . . . . . 11 62 5.1. Transaction ID . . . . . . . . . . . . . . . . . . . . . 11 63 5.2. Owner Unique ID . . . . . . . . . . . . . . . . . . . . . 11 64 5.3. The Enhanced Address Registration Option (EARO) . . . . . 12 65 6. Backbone Router Routing Operations . . . . . . . . . . . . . 14 66 6.1. Over the Backbone Link . . . . . . . . . . . . . . . . . 14 67 6.2. Over the LLN Link . . . . . . . . . . . . . . . . . . . . 16 68 7. BackBone Router Proxy Operations . . . . . . . . . . . . . . 17 69 7.1. Registration and Binding State Creation . . . . . . . . . 20 70 7.2. Defending Addresses . . . . . . . . . . . . . . . . . . . 21 71 8. Security Considerations . . . . . . . . . . . . . . . . . . . 22 72 9. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 23 73 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 74 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 75 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 23 76 12.1. Normative References . . . . . . . . . . . . . . . . . . 23 77 12.2. Informative References . . . . . . . . . . . . . . . . . 24 78 12.3. External Informative References . . . . . . . . . . . . 28 79 Appendix A. Requirements . . . . . . . . . . . . . . . . . . . . 29 80 A.1. Requirements Related to Mobility . . . . . . . . . . . . 29 81 A.2. Requirements Related to Routing Protocols . . . . . . . . 29 82 A.3. Requirements Related to the Variety of Low-Power Link 83 types . . . . . . . . . . . . . . . . . . . . . . . . . . 30 84 A.4. Requirements Related to Proxy Operations . . . . . . . . 31 85 A.5. Requirements Related to Security . . . . . . . . . . . . 31 86 A.6. Requirements Related to Scalability . . . . . . . . . . . 33 87 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 33 89 1. Introduction 91 Classical IPv6 Neighbor Discovery [RFC4862] operations are reactive 92 and rely heavily on multicast operations to locate a correspondent. 93 When this was designed, it was a natural match for the transparent 94 bridging operation of Ethernet. IEEE 802.11 Access Points IEEE802.11 95 [IEEE80211] effectively act as bridges, but, in order to protect the 96 medium, they do not implement transparent bridging. Instead, a so- 97 called association process is used to register proactively the MAC 98 addresses of the wireless STAs to the APs. Sadly, the IPv6 ND 99 operation was not adapted to match that model. 101 Though in most cases, including Low-Power ones, IEEE802.11 is 102 operated as a wireless extension to an Ethernet bridged domain, the 103 impact of radio broadcasts for IPv6 [RFC2460] multicast operations, 104 in particular related to the power consumption of battery-operated 105 devices, lead the community to rethink the plain layer-2 approach and 106 consider splitting the broadcast domain between the wired and the 107 wireless access links. To that effect, the current IEEE802.11 108 specifications require the capability to perform ARP and ND proxy 109 [RFC4389] functions at the Access Points (APs), but rely on snooping 110 for acquiring the related state, which is unsatisfactory in a lossy 111 and mobile environments. 113 Without a proxy, any IP multicast that circulates in the bridged 114 domain ends up broadcasted by the Access Points to all STAs, 115 including Low-Power battery-operated ones. With an incorrect or 116 missing state in the proxy, a packet may not be delivered to the 117 destination, which may have operational impacts depending on the 118 criticality of the packet. 120 Some messages are lost for the lack of retries, regardless of their 121 degree of criticality; it results for instance that Duplicate Address 122 Detection (DAD) as defined in [RFC4862] is mostly broken over Wi-Fi 123 [I-D.yourtchenko-6man-dad-issues]. 125 On the other hand, IPv6 multicast messages are processed by most if 126 not all wireless nodes over the fabric even when very few if any of 127 the nodes is effectively listening to the multicast address. It 128 results that a simple Neighbor Solicitation (NS) message [RFC4861], 129 that is supposedly targeted to a very small group of nodes, ends up 130 polluting the whole wireless bandwidth across the fabric 131 [I-D.vyncke-6man-mcast-not-efficient]. 133 It appears that in a variety of Wireless Local Area Networks (WLANs) 134 and Wireless Personal Area Networks (WPANs), the decision to leverage 135 the broadcast support of a particular link should be left to Layer-3 136 based on the criticality of the message and the number of interested 137 listeners on that link, for the lack of capability to indicate that 138 criticality to the lower layer. To achieve this, the operation at 139 the Access Point cannot be a Layer-2 bridge operation, but that of a 140 Layer-3 router; the concept of MultiLink Subnet (MLSN) must be 141 reintroduced, with IPv6 backbone routers (6BBRs) interconnecting the 142 various links and routing within the subnet. For link-scope 143 multicast operations, a 6BBR participates to MLD on its access links 144 and a multicast routing protocol is setup between the 6BBRs over the 145 backbone of the MLSN. 147 As the network scales up, none of the approaches of using either 148 broadcast or N*unicast for a multicast packet is really satisfying 149 and the protocols themselves need to be adapted to reduce their use 150 of multicast. 152 One degree of improvement can be achieved by changing the tuning of 153 the protocol parameters and operational practices, such as suggested 154 in Reducing energy consumption of Router Advertisements [RFC7772] 155 (RA). This works enables to lower the rate of RA messages but does 156 not solve the problem associated with multicast NS and NA messages, 157 which are a lot more frequent in large-scale radio environments with 158 mobile devices which exhibit intermittent access patterns and short- 159 lived IPv6 addresses. 161 In the context of IEEE802.15.4 [IEEE802154], the more drastic step of 162 considering the radio as a medium that is different from Ethernet 163 because of the impact of multicast, was already taken with the 164 adoption of Neighbor Discovery Optimization for IPv6 over Low-Power 165 Wireless Personal Area Networks (6LoWPANs) [RFC6775]. This 166 specification applies that same thinking to other wireless links such 167 as Low-Power IEEE802.11 (Wi-Fi) and IEEE802.15.1 (Bluetooth) 168 [IEEE802151], and extends [RFC6775] to enable proxy operation by the 169 6BBR so as to decouple the broadcast domain in the backbone from the 170 wireless links. The proxy operation can be maintained asynchronous 171 so that low-power nodes or nodes that are deep in a mesh do not need 172 to be bothered synchronously when a lookup is performed for their 173 addresses, effectively implementing the ND contribution to the 174 concept of a Sleep Proxy [I-D.nordmark-6man-dad-approaches]. 176 RFC 6775 is now being updated as [I-D.thubert-6lo-rfc6775-update]; 177 this upodate duplicates some text from this document, and the intent 178 to migrate what is common to the update document once it is adopted. 180 DHCPv6 [RFC3315] is still a viable option in Low power and Lossy 181 Network (LLN) to assign IPv6 global addresses. However, the IETF 182 standard that supports address assignment specifically for LLNs is 183 6LoWPAN ND [RFC6775], which is a mix of IPv6 stateless 184 autoconfiguration mechanism (SLAAC) [RFC4862] and a new registration 185 process for ND. This specification introduces a Layer-3 association 186 process based on 6LoWPAN ND that maintains a proxy state in the 6BBR 187 to keep the LLN nodes reachable and protect their addresses through 188 sleeping periods. 190 A number of use cases, including the Industrial Internet, require a 191 large scale deployment of monitoring sensors that can only be 192 realized in a cost-effective fashion with wireless technologies. 193 Mesh networks are deployed when simpler hub-and-spoke topologies are 194 not sufficient for the expected size, throughput, and density. 195 Meshes imply the routing of packets, operated at either Layer-2 or 196 Layer-3. For routing over a mesh at Layer-3, the IETF has designed 197 the IPv6 Routing Protocol over LLN (RPL) [RFC6550]. 6LoWPAN ND was 198 designed as a stand-alone mechanism separately from RPL, and the 199 interaction between the 2 protocols was not defined. This 200 specification details how periodic updates from RPL can be used by 201 the RPL root to renew the association of the RPL node to the 6BBR on 202 its behalf so as to maintain the proxy operation active for that 203 node. 205 This document suggests a limited evolution to [RFC6775] so as to 206 allow operation of a 6LoWPAN ND node while a routing protocol (in 207 first instance RPL) is present and operational. It also suggests a 208 more generalized use of the information in the ARO option of the ND 209 messages outside the strict LLN domain, for instance over a 210 federating backbone. 212 2. Applicability and Requirements Served 214 Efficiency aware IPv6 Neighbor Discovery Optimizations 215 [I-D.chakrabarti-nordmark-6man-efficient-nd] suggests that 6LoWPAN ND 216 [RFC6775] can be extended to other types of links beyond IEEE802.15.4 217 for which it was defined. The registration technique is beneficial 218 when the Link-Layer technique used to carry IPv6 multicast packets is 219 not sufficiently efficient in terms of delivery ratio or energy 220 consumption in the end devices, in particular to enable energy- 221 constrained sleeping nodes. The value of such extension is 222 especially apparent in the case of mobile wireless nodes, to reduce 223 the multicast operations that are related to classical ND ([RFC4861], 224 [RFC4862]) and plague the wireless medium. 226 This specification updates and generalizes 6LoWPAN ND to a broader 227 range of Low power and Lossy Networks (LLNs) with a solid support for 228 Duplicate Address Detection (DAD) and address lookup that does not 229 require broadcasts over the LLNs. The term LLN is used loosely in 230 this specification to cover multiple types of WLANs and WPANs, 231 including Low-Power Wi-Fi, BLUETOOTH(R) Low Energy, IEEE802.11AH and 232 IEEE802.15.4 wireless meshes, so as to address the requirements 233 listed in Appendix A.3 235 The scope of this draft is a Backbone Link that federates multiple 236 LLNs as a single IPv6 MultiLink Subnet. Each LLN in the subnet is 237 anchored at an IPv6 Backbone Router (6BBR). The Backbone Routers 238 interconnect the LLNs over the Backbone Link and emulate that the LLN 239 nodes are present on the Backbone using proxy-ND operations. This 240 specification extends IPv6 ND over the backbone to discriminate 241 address movement from duplication and eliminate stale state in the 242 backbone routers and backbone nodes once a LLN node has roamed. This 243 way, mobile nodes may roam rapidly from a 6BBR to the next and 244 requirements in Appendix A.1 are met. 246 This specification can be used by any wireless node to associate at 247 Layer-3 with a 6BBR and register its IPv6 addresses to obtain routing 248 services including proxy-ND operations over the backbone, effectively 249 providing a solution to the requirements expressed in Appendix A.4. 251 The Link Layer Address (LLA) that is returned as Target LLA (TLLA) in 252 Neighbor Advertisements (NA) messages by the 6BBR on behalf of the 253 Registered Node over the backbone may be that of the Registering 254 Node, in which case the 6BBR needs to bridge the unicast packets 255 (Bridging proxy), or that of the 6BBR on the backbone, in which case 256 the 6BBRs needs to route the unicast packets (Routing proxy). In the 257 latter case, the 6BBR may maintain the list of correspondents to 258 which it has advertised its own MAC address on behalf of the LLN node 259 and the IPv6 ND operation is minimized as the number of nodes scale 260 up in the LLN. This enables to meet the requirements in Appendix A.6 261 as long has the 6BBRs are dimensioned for the number of registration 262 that each needs to support. 264 In the context of the the TimeSlotted Channel Hopping (TSCH) mode of 265 [IEEE802154], the 6TiSCH architecture [I-D.ietf-6tisch-architecture] 266 introduces how a 6LoWPAN ND host could connect to the Internet via a 267 RPL mesh Network, but this requires additions to the 6LOWPAN ND 268 protocol to support mobility and reachability in a secured and 269 manageable environment. This specification details the new 270 operations that are required to implement the 6TiSCH architecture and 271 serves the requirements listed in Appendix A.2. 273 In the case of Low-Power IEEE802.11, a 6BBR may be collocated with a 274 standalone AP or a CAPWAP [RFC5415] wireless controller, and the 275 wireless client (STA) leverages this specification to register its 276 IPv6 address(es) to the 6BBR over the wireless medium. In the case 277 of a 6TiSCH LLN mesh, the RPL root is collocated with a 6LoWPAN 278 Border Router (6LBR), and either collocated with or connected to the 279 6BBR over an IPv6 Link. The 6LBR leverages this specification to 280 register the LLN nodes on their behalf to the 6BBR. In the case of 281 BTLE, the 6BBR is collocated with the router that implements the BTLE 282 central role as discussed in section 2.2 of [RFC7668]. 284 3. Terminology 286 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 287 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 288 document are to be interpreted as described in [RFC2119]. 290 Readers are expected to be familiar with all the terms and concepts 291 that are discussed in "Neighbor Discovery for IP version 6" 292 [RFC4861], "IPv6 Stateless Address Autoconfiguration" [RFC4862], 293 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 294 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 295 Neighbor Discovery Optimization for Low-power and Lossy Networks 296 [RFC6775] and "Multi-link Subnet Support in IPv6" 297 [I-D.ietf-ipv6-multilink-subnets]. 299 Readers would benefit from reading "Multi-Link Subnet Issues" 300 [RFC4903], ,"Mobility Support in IPv6" [RFC6275], "Neighbor Discovery 301 Proxies (ND Proxy)" [RFC4389] and "Optimistic Duplicate Address 302 Detection" [RFC4429] prior to this specification for a clear 303 understanding of the art in ND-proxying and binding. 305 Additionally, this document uses terminology from [RFC7102] and 306 [I-D.ietf-6tisch-terminology], and introduces the following 307 terminology: 309 LLN Low Power Lossy Network. Used loosely in this specification to 310 represent WLANs and WPANs. See [RFC4919] 312 Backbone This is an IPv6 transit link that interconnects 2 or more 313 Backbone Routers. It is expected to be deployed as a high 314 speed backbone in order to federate a potentially large set of 315 LLNS. Also referred to as a LLN backbone or Backbone network. 317 Backbone Router An IPv6 router that federates the LLN using a 318 Backbone link as a backbone. A BBR acts as a 6LoWPAN Border 319 Routers (6LBR) and an Energy Aware Default Router (NEAR). 321 Extended LLN This is the aggregation of multiple LLNs as defined in 322 [RFC4919], interconnected by a Backbone Link via Backbone 323 Routers, and forming a single IPv6 MultiLink Subnet. 325 Registration The process during which a wireless Node registers its 326 address(es) with the Border Router so the 6BBR can proxy ND for 327 it over the backbone. 329 Binding The state in the 6BBR that associates an IP address with a 330 MAC address, a port and some other information about the node 331 that owns the IP address. 333 Registered Node The node for which the registration is performed, 334 which owns the fields in the EARO option. 336 Registering Node The node that performs the registration to the 337 6BBR, either for one of its own addresses, in which case it is 338 Registered Node and indicates its own MAC Address as SLLA in 339 the NS(ARO), or on behalf of a Registered Node that is 340 reachable over a LLN mesh. In the latter case, if the 341 Registered Node is reachable from the 6BBR over a Mesh-Under 342 mesh, the Registering Node indicates the MAC Address of the 343 Registered Node as SLLA in the NS(ARO). Otherwise, it is 344 expected that the Registered Device is reachable over a Route- 345 Over mesh from the Registering Node, in which case the SLLA in 346 the NS(ARO) is that of the Registering Node, which causes it to 347 attract the packets from the 6BBR to the Registered Node and 348 route them over the LLN. 350 Registered Address The address owned by the Registered Node node 351 that is being registered. 353 Sleeping Proxy A 6BBR acts as a Sleeping Proxy if it answers ND 354 Neighbor Solicitation over the backbone on behalf of the 355 Registered Node whenever possible. This is the default mode 356 for this specification but it may be overridden, for instance 357 by configuration, into Unicasting Proxy. 359 Unicasting Proxy As a Unicasting Proxy, the 6BBR forwards NS 360 messages to the Registering Node, transforming Layer-2 361 multicast into unicast whenever possible. 363 Routing proxy A 6BBR acts as a routing proxy if it advertises its 364 own MAC address, as opposed to that of the node that performs 365 the registration, as the TLLA in the proxied NAs over the 366 backbone. In that case, the MAC address of the node is not 367 visible at Layer-2 over the backbone and the bridging fabric is 368 not aware of the addresses of the LLN devices and their 369 mobility. The 6BBR installs a connected host route towards the 370 registered node over the interface to the node, and acts as a 371 Layer-3 router for unicast packets to the node. The 6BBR 372 updates the ND Neighbor Cache Entries (NCE) in correspondent 373 nodes if the wireless node moves and registers to another 6BBR, 374 either with a single broadcast, or with a series of unicast 375 NA(O) messages, indicating the TLLA of the new router. 377 Bridging proxy A 6BBR acts as a bridging proxy if it advertises the 378 MAC address of the node that performs the registration as the 379 TLLA in the proxied NAs over the backbone. In that case, the 380 MAC address and the mobility of the node is still visible 381 across the bridged backbone fabric, as is traditionally the 382 case with Layer-2 APs. The 6BBR acts as a Layer-2 bridge for 383 unicast packets to the registered node. The MAC address 384 exposed in the S/TLLA is that of the Registering Node, which is 385 not necessarily the Registered Device. When a device moves 386 within a LLN mesh, it may end up attached to a different 6LBR 387 acting as Registering Node, and the LLA that is exposed over 388 the backbone will change. 390 Primary BBR The BBR that will defend a Registered Address for the 391 purpose of DAD over the backbone. 393 Secondary BBR A BBR to which the address is registered. A Secondary 394 Router MAY advertise the address over the backbone and proxy 395 for it. 397 4. Overview 399 An LLN node can move freely from an LLN anchored at a Backbone Router 400 to an LLN anchored at another Backbone Router on the same backbone 401 and conserve any of the IPv6 addresses that it has formed, 402 transparently. 404 | 405 +-----+ 406 | | Other (default) Router 407 | | 408 +-----+ 409 | 410 | Backbone Link 411 +--------------------+------------------+ 412 | | | 413 +-----+ +-----+ +-----+ 414 | | Backbone | | Backbone | | Backbone 415 | | router | | router | | router 416 +-----+ +-----+ +-----+ 417 o o o o o o 418 o o o o o o o o o o o o o o 419 o o o o o o o o o o o o o o o 420 o o o o o o o o o o 421 o o o o o o o 423 LLN LLN LLN 425 Figure 1: Backbone Link and Backbone Routers 427 The Backbone Routers maintain an abstract Binding Table of their 428 Registered Nodes. The Binding Table operates as a distributed 429 database of all the wireless Nodes whether they reside on the LLNs or 430 on the backbone, and use an extension to the Neighbor Discovery 431 Protocol to exchange that information across the Backbone in the 432 classical ND reactive fashion. 434 The Address Registration Option (ARO) defined in [RFC6775] is 435 extended to enable the registration for routing and proxy Neighbor 436 Discovery operations by the 6BBR, and the Extended ARO (EARO) option 437 is included in the ND exchanges over the backbone between the 6BBRs 438 to sort out duplication from movement. 440 Address duplication is sorted out with the Owner Unique-ID field in 441 the EARO, which is a generalization of the EUI-64 that allows 442 different types of unique IDs beyond the name space derived from the 443 MAC addresses. First-Come First-Serve rules apply, whether the 444 duplication happens between LLN nodes as represented by their 445 respective 6BBRs, or between an LLN node and a classical node that 446 defends its address over the backbone with classical ND and does not 447 include the EARO option. 449 In case of conflicting registrations to multiple 6BBRs from a same 450 node, a sequence counter called Transaction ID (TID) is introduced 451 that enables 6BBRs to sort out the latest anchor for that node. 452 Registrations with a same TID are compatible and maintained, but, in 453 case of different TIDs, only the freshest registration is maintained 454 and the stale state is eliminated. 456 With this specification, Backbone Routers perform ND proxy over the 457 Backbone Link on behalf of their Registered Nodes. The Backbone 458 Router operation is essentially similar to that of a Mobile IPv6 459 (MIPv6) [RFC6275] Home Agent. This enables mobility support for LLN 460 nodes that would move outside of the network delimited by the 461 Backbone link attach to a Home Agent from that point on. This also 462 enables collocation of Home Agent functionality within Backbone 463 Router functionality on the same backbone interface of a router. 464 Further specification may extend this be allowing the 6BBR to 465 redistribute host routes in routing protocols that would operate over 466 the backbone, or in MIPv6 or the Locator/ID Separation Protocol 467 (LISP) [RFC6830] to support mobility on behalf of the nodes, etc... 469 The Optimistic Duplicate Address Detection [RFC4429] (ODAD) 470 specification details how an address can be used before a Duplicate 471 Address Detection (DAD) is complete, and insists that an address that 472 is TENTATIVE should not be associated to a Source Link-Layer Address 473 Option in a Neighbor Solicitation message. This specification 474 leverages ODAD to create a temporary proxy state in the 6BBR till DAD 475 is completed over the backbone. This way, the specification enables 476 to distribute proxy states across multiple 6BBR and co-exist with 477 classical ND over the backbone. 479 5. New Types And Formats 481 5.1. Transaction ID 483 The specification expects that the Registered Node can provide a 484 sequence number called Transaction ID (TID) that is incremented with 485 each re-registration. The TID essentially obeys the same rules as 486 the Path Sequence field in the Transit Information Option (TIO) found 487 in RPL's Destination Advertisement Object (DAO). This way, the LLN 488 node can use the same counter for ND and RPL, and a 6LBR acting as 489 RPL root may easily maintain the registration on behalf of a RPL node 490 deep inside the mesh by simply using the RPL TIO Path Sequence as TID 491 for EARO. 493 When a Registered Node is registered to multiple BBRs in parallel, it 494 is expected that the same TID is used, to enable the 6BBRs to 495 correlate the registrations as being a single one, and differentiate 496 that situation from a movement. 498 If the TIDs are different, the resolution inherited from RPL sorts 499 out the most recent registration and other ones are removed. The 500 operation for computing and comparing the Path Sequence is detailed 501 in section 7 of [RFC6550] and applies to the TID in the exact same 502 fashion. 504 5.2. Owner Unique ID 506 The Owner Unique ID (OUID) enables to differentiate a real duplicate 507 address registration from a double registration or a movement. An ND 508 message from the 6BBR over the backbone that is proxied on behalf of 509 a Registered Node must carry the most recent EARO option seen for 510 that node. A NS/NA with an EARO and a NS/NA without a EARO thus 511 represent different nodes and if they relate to a same target then 512 they reflect an address duplication. The Owner Unique ID can be as 513 simple as a EUI-64 burn-in address, if duplicate EUI-64 addresses are 514 avoided. 516 Alternatively, the unique ID can be a cryptographic string that can 517 can be used to prove the ownership of the registration as discussed 518 in Address Protected Neighbor Discovery for Low-power and Lossy 519 Networks [I-D.sarikaya-6lo-ap-nd]. 521 In any fashion, it is recommended that the node stores the unique Id 522 or the keys used to generate that ID in persistent memory. 524 Otherwise, it will be prevented to re-register after a reboot that 525 would cause a loss of memory until the Backbone Router times out the 526 registration. 528 5.3. The Enhanced Address Registration Option (EARO) 530 With the ARO option defined in 6LoWPAN ND [RFC6775], the address 531 being registered and its owner can be uniquely identified and matched 532 with the Binding Table entries of each Backbone Router. 534 The Enhanced Address Registration Option (EARO) is intended to be 535 used as a replacement to the ARO option within Neighbor Discovery NS 536 and NA messages between a LLN node and its 6LoWPAN Router (6LR), as 537 well as in Duplicate Address Request (DAR) and the Duplicate Address 538 Confirmation (DAC) messages between 6LRs and 6LBRs in LLNs meshes 539 such as 6TiSCH networks. 541 An NS message with an EARO option is a registration if and only if it 542 also carries an SLLAO option. The AERO option also used in NS and NA 543 messages between Backbone Routers over the backbone link to sort out 544 the distributed registration state, and in that case, it does not 545 carry the SLLAO option and is not confused with a registration. 547 The EARO extends the ARO and is recognized by the setting of the TID 548 bit. A node that supports this specification MUST always use an EARO 549 as a replacement to an ARO in its registration to a router. This is 550 harmless since the TID bit and fields are reserved in [RFC6775] are 551 ignored by a legacy router. A router that supports this 552 specification answers to an ARO with an ARO and to an EARO with an 553 EARO. 555 This specification changes the behavior of the peers in a 556 registration flows. To enable backward compatibility, a node that 557 registers to a router that is not known to support this specification 558 MUST behave as prescribed by [RFC6775]. Once the router is known to 559 support this specification, the node MUST obey this specification. 561 When using the EARO option, the address being registered is found in 562 the Target Address field of the NS and NA messages. This differs 563 from 6LoWPAN ND [RFC6775] which specifies that the address being 564 registered is the source of the NS. 566 The reason for this change is to enable proxy-registrations on behalf 567 of other nodes in Route-Over meshes, for instance to enable that a 568 RPL root registers addresses on behalf LLN nodes that are deeper in a 569 6TiSCH mesh. In that case, the Registering Node MUST indicate its 570 own address as source of the ND message and its MAC address in the 571 Source Link-Layer Address Option (SLLAO), since it still expects to 572 get the packets and route them down the mesh. But the Registered 573 Address belongs to another node, the Registered Node, and that 574 address is indicated in the Target Address field of the NS message. 576 One way of achieving all the above is for a node to first register an 577 address that it owns in order to validate that the router supports 578 this specification, placing the same address in the Source and Target 579 Address fields of the NS message. The node may for instance register 580 an address that is based on EUI-64. For such address, DAD is not 581 required and using the SLLAO option in the NS is actually more 582 amenable with older ND specifications such as ODAD [RFC4429]. 584 Once that first registration is complete, the node knows from the 585 setting of the TID in the response whether the router supports this 586 specification. If this is verified, the node may register other 587 addresses that it owns, or proxy-register addresses on behalf some 588 another node, indicating those addresses being registered in the 589 Target Address field of the NS messages, while using one of its own, 590 already registered, addresses as source. 592 The format of the EARO option is as follows: 594 0 1 2 3 595 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 1 596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 597 | Type | Length = 2 | Status | Reserved | 598 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 599 | Reserved |T| TID | Registration Lifetime | 600 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 601 | | 602 + Owner Unique ID (EUI-64 or equivalent) + 603 | | 604 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 606 Figure 2: EARO 608 Option Fields 610 Type: 612 Length: 2 614 Status: OK=0; Duplicate=1; Full=2; Moved=3; Removed=4; 616 Reserved: This field is unused. It MUST be initialized to zero by 617 the sender and MUST be ignored by the receiver. 619 T: One bit flag. Set if the next octet is a used as a TID. 621 TID: 1-byte integer; a transaction id that is maintained by the node 622 and incremented with each transaction. it is recommended that the 623 node maintains the TID in a persistent storage. 625 Registration Lifetime: 16-bit integer; expressed in minutes. 0 626 means that the registration has ended and the state should be 627 removed. 629 Owner Unique Identifier: A globally unique identifier for the node 630 associated. This can be the EUI-64 derived IID of an interface, 631 or some provable ID obtained cryptographically. 633 6. Backbone Router Routing Operations 635 | 636 +-----+ 637 | | Other (default) Router 638 | | 639 +-----+ 640 | /64 641 | Backbone Link 642 +-------------------+-------------------+ 643 | /64 | /64 | /64 644 +-----+ +-----+ +-----+ 645 | | Backbone | | Backbone | | Backbone 646 | | router | | router | | router 647 +-----+ +-----+ +-----+ 648 o N*/128 o o o M*/128 o o P*/128 649 o o o o o o o o o o o o o o 650 o o o o o o o o o o o o o o o 651 o o o o o o o o o o 652 o o o o o o o 654 LLN LLN LLN 656 Figure 3: Routing Configuration in the ML Subnet 658 6.1. Over the Backbone Link 660 The Backbone Router is a specific kind of Border Router that performs 661 proxy Neighbor Discovery on its backbone interface on behalf of the 662 nodes that it has discovered on its LLN interfaces. 664 The backbone is expected to be a high speed, reliable Backbone link, 665 with affordable and reliable multicast capabilities, such as a 666 bridged Ethernet Network, and to allow a full support of classical ND 667 as specified in [RFC4861] and subsequent RFCs. In other words, the 668 backbone is not a LLN. 670 Still, some restrictions of the attached LLNs will apply to the 671 backbone. In particular, it is expected that the MTU is set to the 672 same value on the backbone and all attached LLNs, and the scalability 673 of the whole subnet requires that broadcast operations are avoided as 674 much as possible on the backbone as well. Unless configured 675 otherwise, the Backbone Router MUST echo the MTU that it learns in 676 RAs over the backbone in the RAs that it sends towards the LLN links. 678 As a router, the Backbone Router behaves like any other IPv6 router 679 on the backbone side. It has a connected route installed towards the 680 backbone for the prefixes that are present on that backbone and that 681 it proxies for on the LLN interfaces. 683 As a proxy, the 6BBR uses an EARO option in the NS-DAD and the 684 multicast NA messages that it generates on behalf of a Registered 685 Node, and it places an EARO in its unicast NA messages if and only if 686 the NS/NA that stimulates it had an EARO in it. 688 When possible, the 6BBR SHOULD use unicast or solicited-node 689 multicast address (SNMA) [RFC4291] to defend its Registered Addresses 690 over the backbone. In particular, the 6BBR MUST join the SNMA group 691 that corresponds to a Registered Address as soon as it creates an 692 entry for that address and as long as it maintains that entry, 693 whatever the state of the entry. The expectation is that it is 694 possible to get a message delivered to all the nodes on the backbone 695 that listen to a particular address and support this specification - 696 which includes all the 6BBRs in the MultiLink Subnet - by sending a 697 multicast message to the associated SNMA over the backbone. 699 The support of Optimistic DAD (ODAD) [RFC4429] is recommended for all 700 nodes in the backbone and followed by the 6BBRs in their proxy 701 activity over the backbone. With ODAD, any optimistic node MUST join 702 the SNMA of a Tentative address, which interacts better with this 703 specification. 705 This specification allows the 6BBR in Routing Proxy mode to advertise 706 the Registered IPv6 Address with the 6BBR Link Layer Address, and 707 attempts to update Neighbor Cache Entries (NCE) in correspondent 708 nodes over the backbone, using gratuitous NA(Override). This method 709 may fail of the multicast message is not properly received, and 710 correspondent nodes may maintain an incorrect neighbor state, which 711 they will eventually discover through Neighbor Unreachability 712 Detection (NUD). Because mobility may be slow, the NUD procedure 713 defined in [RFC4861] may be too impatient, and the support of 714 [RFC7048] is recommended in all nodes in the network. 716 Since the MultiLink Subnet may grow very large in terms of individual 717 IPv6 addresses, multicasts should be avoided as much as possible even 718 on the backbone. Though it is possible for plain hosts to 719 participate with legacy IPv6 ND support, the support by all nodes 720 connected to the backbone of [I-D.ietf-6man-rs-refresh] is 721 recommended, and this implies the support of [RFC7559] as well. 723 6.2. Over the LLN Link 725 As a router, the Nodes and Backbone Router operation on the LLN 726 follows [RFC6775]. Per that specification, LLN Hosts generally do 727 not depend on multicast RAs to discover routers. It is still 728 generally required for LLN nodes to accept multicast RAs [RFC7772], 729 but those are rare on the LLN link. Nodes are expected to follow the 730 Simple Procedures for Detecting Network Attachment in IPv6 [RFC6059] 731 (DNA procedures) to assert movements, and to support the Packet-Loss 732 Resiliency for Router Solicitations [RFC7559] to make the unicast RS 733 more reliable. 735 The Backbone Router acquires its states about the addresses on the 736 LLN side through a registration process from either the nodes 737 themselves, or from a node such as a RPL root / 6LBR (the Registering 738 Node) that performs the registration on behalf of the address owner 739 (the Registered Node). 741 When operating as a Routing Proxy, the router installs hosts routes 742 (/128) to the Registered Addresses over the LLN links, via the 743 Registering Node as identified by the Source Address and the SLLAO 744 option in the NS(EARO) messages. 746 In that mode, the 6BBR handles the ND protocol over the backbone on 747 behalf of the Registered Nodes, using its own MAC address in the TLLA 748 and SLLA options in proxyed NS and NA messages. It results that for 749 each Registered Address, a number of peer Nodes on the backbone have 750 resolved the address with the 6BBR MAC address and keep that mapping 751 stored in their Neighbor cache. 753 The 6BBR SHOULD maintain, per Registered Address, the list of the 754 peers on the backbone to which it answered with it MAC address, and 755 when a binding moves to a different 6BBR, it SHOULD send a unicast 756 gratuitous NA(O) individually to each of them to inform them that the 757 address has moved and pass the MAC address of the new 6BBR in the 758 TLLAO option. If the 6BBR can not maintain that list, then it SHOULD 759 remember whether that list is empty or not and if not, send a 760 multicast NA(O) to all nodes to update the impacted Neighbor Caches 761 with the information from the new 6BBR. 763 The Bridging Proxy is a variation where the BBR function is 764 implemented in a Layer-3 switch or an wireless Access Point that acts 765 as a Host from the IPv6 standpoint, and, in particular, does not 766 operate the routing of IPv6 packets. In that case, the SLLAO in the 767 proxied NA messages is that of the Registering Node and classical 768 bridging operations take place on data frames. 770 If a registration moves from one 6BBR to the next, but the 771 Registering Node does not change, as indicated by the S/TLLAO option 772 in the ND exchanges, there is no need to update the Neighbor Caches 773 in the peers Nodes on the backbone. On the other hand, if the LLAO 774 changes, the 6BBR SHOULD inform all the relevant peers as described 775 above, to update the impacted Neighbor Caches. In the same fashion, 776 if the Registering Node changes with a new registration, the 6BBR 777 SHOULD also update the impacted Neighbor Caches over the backbone. 779 7. BackBone Router Proxy Operations 781 This specification enables a Backbone Router to proxy Neighbor 782 Discovery operations over the backbone on behalf of the nodes that 783 are registered to it, allowing any node on the backbone to reach a 784 Registered Node as if it was on-link. The backbone and the LLNs are 785 considered different Links in a MultiLink subnet but the prefix that 786 is used may still be advertised as on-link on the backbone to support 787 legacy nodes; multicast ND messages are link-scoped and not forwarded 788 across the backbone routers. 790 ND Messages on the backbone side that do not match to a registration 791 on the LLN side are not acted upon on the LLN side, which stands 792 protected. On the LLN side, the prefixes associated to the MultiLink 793 Subnet are presented as not on-link, so address resolution for other 794 hosts do not occur. 796 The default operation in this specification is Sleeping proxy which 797 means: 799 o creating a new entry in an abstract Binding Table for a new 800 Registered Address and validating that the address is not a 801 duplicate over the backbone 803 o defending a Registered Address over the backbone using NA messages 804 with the Override bit set on behalf of the sleeping node whenever 805 possible 807 o advertising a Registered Address over the backbone using NA 808 messages, asynchronously or as a response to a Neighbor 809 Solicitation messages. 811 o Looking up a destination over the backbone in order to deliver 812 packets arriving from the LLN using Neighbor Solicitation 813 messages. 815 o Forwarding packets from the LLN over the backbone, and the other 816 way around. 818 o Eventually triggering a liveliness verification of a stale 819 registration. 821 A 6BBR may act as a Sleeping Proxy only if the state of the binding 822 entry is REACHABLE, or TENTATIVE in which case the answer is delayed. 823 In any other state, the Sleeping Proxy operates as a Unicasting 824 Proxy. 826 As a Unicasting Proxy, the 6BBR forwards NS messages to the 827 Registering Node, transforming Layer-2 multicast into unicast 828 whenever possible. This is not possible in UNREACHABLE state, so the 829 NS messages are multicasted, and rate-limited to protect the medium 830 with an exponential back-off. In other states, The messages are 831 forwarded to the Registering Node as unicast Layer-2 messages. In 832 TENTATIVE state, the NS message is either held till DAD completes, or 833 dropped. 835 The draft introduces the optional concept of primary and secondary 836 BBRs. The primary is the backbone router that has the highest EUI-64 837 address of all the 6BBRs that share a registration for a same 838 Registered Address, with the same Owner Unique ID and same 839 Transaction ID, the EUI-64 address being considered as an unsigned 840 64bit integer. The concept is defined with the granularity of an 841 address, that is a given 6BBR can be primary for a given address and 842 secondary or another one, regardless on whether the addresses belong 843 to the same node or not. The primary Backbone Router is in charge of 844 protecting the address for DAD over the Backbone. Any of the Primary 845 and Secondary 6BBR may claim the address over the backbone, since 846 they are all capable to route from the backbone to the LLN node, and 847 the address appears on the backbone as an anycast address. 849 The Backbone Routers maintain a distributed binding table, using 850 classical ND over the backbone to detect duplication. This 851 specification requires that: 853 1. All addresses that can be reachable from the backbone, including 854 IPv6 addresses based on burn-in EUI64 addresses MUST be 855 registered to the 6BBR. 857 2. A Registered Node MUST include the EARO option in an NS message 858 that used to register an addresses to a 6LR; the 6LR MUST 859 propagate that option unchanged to the 6LBR in the DAR/DAC 860 exchange, and the 6LBR MUST propagate that option unchanged in 861 proxy registrations. 863 3. The 6LR MUST echo the same EARO option in the NA that it uses to 864 respond, but for the status filed which is not used in NS 865 messages, and significant in NA. 867 A false positive duplicate detection may arise over the backbone, for 868 instance if the Registered Address is registered to more than one 869 LBR, or if the node has moved. Both situations are handled 870 gracefully unbeknownst to the node. In the former case, one LBR 871 becomes primary to defend the address over the backbone while the 872 others become secondary and may still forward packets back and forth. 873 In the latter case the LBR that receives the newest registration wins 874 and becomes primary. 876 The expectation in this specification is that there is a single 877 Registering Node at a time per Backbone Router for a given Registered 878 Address, but that a Registered Address may be registered to Multiple 879 6BBRs for higher availability. 881 Over the LLN, and for any given Registered Address, it is REQUIRED 882 that: 884 de-registrations (newer TID, same OUID, null Lifetime) are 885 accepted and responded immediately with a status of 4; the entry 886 is deleted; 888 newer registrations (newer TID, same OUID, non-null Lifetime) are 889 accepted and responded with a status of 0 (success); the entry is 890 updated with the new TID, the new Registration Lifetime and the 891 new Registering Node, if any has changed; in TENTATIVE state the 892 response is held and may be overwritten; in other states the 893 Registration-Lifetime timer is restarted and the entry is placed 894 in REACHABLE state. 896 identical registrations (same TID, same OUID) from a same 897 Registering Node are not processed but responded with a status of 898 0 (success); they are expected to be identical and an error may be 899 logged if not; in TENTATIVE state, the response is held and may be 900 overwritten, but it MUST be eventually produced and it carries the 901 result of the DAD process; 903 older registrations (not(newer or equal) TID, same OUID) from a 904 same Registering Node are ignored; 906 identical and older registrations (not-newer TID, same OUID) from 907 a different Registering Node are responded immediately with a 908 status of 3 (moved); this may be rate limited to protect the 909 medium; 911 and any registration for a different Registered Node (different 912 OUID) are responded immediately with a status of 1 (duplicate). 914 7.1. Registration and Binding State Creation 916 Upon a registration for a new address with an NS(EARO), the 6BBR 917 performs a DAD operation over the backbone placing the new address as 918 target in the NS-DAD message. The EARO from the registration MUST be 919 placed unchanged in the NS-DAD message, and an entry is created in 920 TENTATIVE state for a duration of TENTATIVE_DURATION. The NS-DAD 921 message is sent multicast over the backbone to the SNMA address 922 associated with the registered address. If that operation is known 923 to be costly, and the 6BBR has an indication from another source 924 (such as a NCE) that the Registered Address was present on the 925 backbone, that information may be leveraged to send the NS-DAD 926 message as a Layer-2 unicast to the MAC that was associated with the 927 Registered Address. 929 In TENTATIVE state: 931 o the entry is removed if an NA is received over the backbone for 932 the Registered Address with no EARO option, or with an EARO option 933 with a status of 1 (duplicate) that indicates an existing 934 registration for another LLN node. The OUID and TID fields in the 935 EARO option received over the backbone are ignored. A status of 1 936 is returned in the EARO option of the NA back to the Registering 937 Node; 939 o the entry is also removed if an NA with an ARO option with a 940 status of 3 (moved), or a NS-DAD with an ARO option that indicates 941 a newer registration for the same Registered Node, is received 942 over the backbone for the Registered Address. A status of 3 is 943 returned in the NA(EARO) back to the Registering Node; 945 o when a registration is updated but not deleted, e.g. from a newer 946 registration, the DAD process on the backbone continues and the 947 running timers are not restarted; 949 o Other NS (including DAD with no EARO option) and NA from the 950 backbone are not responded in TENTATIVE state, but the list of 951 their origins may be kept in memory and if so, the 6BBR may send 952 them each a unicast NA with eventually an EARO option when the 953 TENTATIVE_DURATION timer elapses, so as to cover legacy nodes that 954 do not support ODAD. 956 o When the TENTATIVE_DURATION timer elapses, a status 0 (success) is 957 returned in a NA(EARO) back to the Registering Node(s), and the 958 entry goes to REACHABLE state for the Registration Lifetime; the 959 DAD process is successful and the 6BBR MUST send a multicast 960 NA(EARO) to the SNMA associated to the Registered Address over the 961 backbone with the Override bit set so as to take over the binding 962 from other 6BBRs. 964 7.2. Defending Addresses 966 If a 6BBR has an entry in REACHABLE state for a Registered Address: 968 o If the 6BBR is primary, or does not support the concept, it MUST 969 defend that address over the backbone upon an incoming NS-DAD, 970 either if the NS does not carry an EARO, or if an EARO is present 971 that indicates a different Registering Node (different OUID). The 972 6BBR sends a NA message with the Override bit set and the NA 973 carries an EARO option if and only if the NS-DAD did so. When 974 present, the EARO in the NA(O) that is sent in response to the NS- 975 DAD(EARO) carries a status of 1 (duplicate), and the OUID and TID 976 fields in the EARO option are obfuscated with null or random 977 values to avoid network scanning and impersonation attacks. 979 o If the 6BBR receives an NS-DAD(EARO) that reflect a newer 980 registration, the 6BBR updates the entry and the routing state to 981 forward packets to the new 6BBR, but keeps the entry REACHABLE. 982 In that phase, it MAY use REDIRECT messages to reroute traffic for 983 the Registered Address to the new 6BBR. 985 o If the 6BBR receives an NA(EARO) that reflect a newer 986 registration, the 6BBR removes its entry and sends a NA(AERO) with 987 a status of 3 (moved) to the Registering Node, if the Registering 988 Node is different from the Registered Node. If necessary, the 989 6BBR cleans up ND cache in peers nodes as discussed in 990 Section 6.1, by sending a series of unicast to the impacted nodes, 991 or one broadcast NA(O) to all-nodes. 993 o If the 6BBR received a NS(LOOKUP) for a Registered Address, it 994 answers immediately with an NA on behalf of the Registered Node, 995 without polling it. There is no need of an EARO in that exchange. 997 o When the Registration-Lifetime timer elapses, the entry goes to 998 STALE state for a duration of STABLE_STALE_DURATION in LLNs that 999 keep stable addresses such as LWPANs, and UNSTABLE_STALE_DURATION 1000 in LLNs where addresses are renewed rapidly, e.g. for privacy 1001 reasons. 1003 The STALE state is a chance to keep track of the backbone peers that 1004 may have an ND cache pointing on this 6BBR in case the Registered 1005 Address shows back up on this or a different 6BBR at a later time. 1006 In STALE state: 1008 o If the Registered Address is claimed by another node on the 1009 backbone, with an NS-DAD or an NA, the 6BBR does not defend the 1010 address. Upon an NA(O), or the stale time elapses, the 6BBR 1011 removes its entry and sends a NA(AERO) with a status of 4 1012 (removed) to the Registering Node. 1014 o If the 6BBR received a NS(LOOKUP) for a Registered Address, the 1015 6BBR MUST send an NS(NUD) following rules in [RFC7048] to the 1016 registering Node targeting the Registered Address prior to 1017 answering. If the NUD succeeds, the operation in REACHABLE state 1018 applies. If the NUD fails, the 6BBR refrains from answering the 1019 lookup. The NUD expected to be mapped by the Registering Node 1020 into a liveliness validation of the Registered Node if they are in 1021 fact different nodes. 1023 8. Security Considerations 1025 This specification expects that the link layer is sufficiently 1026 protected, either by means of physical or IP security for the 1027 Backbone Link or MAC sublayer cryptography. In particular, it is 1028 expected that the LLN MAC provides secure unicast to/from the 1029 Backbone Router and secure Broadcast from the Backbone Router in a 1030 way that prevents tempering with or replaying the RA messages. 1032 The use of EUI-64 for forming the Interface ID in the link local 1033 address prevents the usage of Secure ND ([RFC3971] and [RFC3972]) and 1034 address privacy techniques. This specification RECOMMENDS the use of 1035 additional protection against address theft such as provided by 1036 [I-D.sarikaya-6lo-ap-nd], which guarantees the ownership of the OUID. 1038 When the ownership of the OUID cannot be assessed, this specification 1039 limits the cases where the OUID and the TID are multicasted, and 1040 obfuscates them in responses to attempts to take over an address. 1042 9. Protocol Constants 1044 This Specification uses the following constants: 1046 TENTATIVE_DURATION: 800 milliseconds 1048 STABLE_STALE_DURATION: 24 hours 1050 UNSTABLE_STALE_DURATION: 5 minutes 1052 DEFAULT_NS_POLLING: 3 times 1054 10. IANA Considerations 1056 This document requires the following additions: 1058 Address Registration Option Status Values Registry 1060 +--------+----------------------------------------------------------+ 1061 | Status | Description | 1062 +--------+----------------------------------------------------------+ 1063 | 3 | Moved: The registration fails because it is not the | 1064 | | freshest. | 1065 | | | 1066 | 4 | Removed: The binding state was removed | 1067 +--------+----------------------------------------------------------+ 1069 IANA is required to change the registry accordingly 1071 Table 1: New ARO Status values 1073 11. Acknowledgments 1075 Kudos to Eric Levy-Abegnoli who designed the First Hop Security 1076 infrastructure at Cisco. 1078 12. References 1080 12.1. Normative References 1082 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1083 Requirement Levels", BCP 14, RFC 2119, 1084 DOI 10.17487/RFC2119, March 1997, 1085 . 1087 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1088 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 1089 December 1998, . 1091 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1092 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1093 2006, . 1095 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 1096 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 1097 . 1099 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1100 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1101 DOI 10.17487/RFC4861, September 2007, 1102 . 1104 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1105 Address Autoconfiguration", RFC 4862, 1106 DOI 10.17487/RFC4862, September 2007, 1107 . 1109 [RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for 1110 Detecting Network Attachment in IPv6", RFC 6059, 1111 DOI 10.17487/RFC6059, November 2010, 1112 . 1114 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1115 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1116 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1117 Low-Power and Lossy Networks", RFC 6550, 1118 DOI 10.17487/RFC6550, March 2012, 1119 . 1121 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1122 Bormann, "Neighbor Discovery Optimization for IPv6 over 1123 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1124 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1125 . 1127 12.2. Informative References 1129 [I-D.chakrabarti-nordmark-6man-efficient-nd] 1130 Chakrabarti, S., Nordmark, E., Thubert, P., and M. 1131 Wasserman, "IPv6 Neighbor Discovery Optimizations for 1132 Wired and Wireless Networks", draft-chakrabarti-nordmark- 1133 6man-efficient-nd-07 (work in progress), February 2015. 1135 [I-D.delcarpio-6lo-wlanah] 1136 Vega, L., Robles, I., and R. Morabito, "IPv6 over 1137 802.11ah", draft-delcarpio-6lo-wlanah-01 (work in 1138 progress), October 2015. 1140 [I-D.ietf-6lo-6lobac] 1141 Lynn, K., Martocci, J., Neilson, C., and S. Donaldson, 1142 "Transmission of IPv6 over MS/TP Networks", draft-ietf- 1143 6lo-6lobac-05 (work in progress), June 2016. 1145 [I-D.ietf-6lo-dect-ule] 1146 Mariager, P., Petersen, J., Shelby, Z., Logt, M., and D. 1147 Barthel, "Transmission of IPv6 Packets over DECT Ultra Low 1148 Energy", draft-ietf-6lo-dect-ule-05 (work in progress), 1149 May 2016. 1151 [I-D.ietf-6lo-nfc] 1152 Hong, Y. and J. Youn, "Transmission of IPv6 Packets over 1153 Near Field Communication", draft-ietf-6lo-nfc-04 (work in 1154 progress), July 2016. 1156 [I-D.ietf-6man-rs-refresh] 1157 Nordmark, E., Yourtchenko, A., and S. Krishnan, "IPv6 1158 Neighbor Discovery Optional RS/RA Refresh", draft-ietf- 1159 6man-rs-refresh-01 (work in progress), March 2016. 1161 [I-D.ietf-6tisch-architecture] 1162 Thubert, P., "An Architecture for IPv6 over the TSCH mode 1163 of IEEE 802.15.4", draft-ietf-6tisch-architecture-10 (work 1164 in progress), June 2016. 1166 [I-D.ietf-6tisch-terminology] 1167 Palattella, M., Thubert, P., Watteyne, T., and Q. Wang, 1168 "Terminology in IPv6 over the TSCH mode of IEEE 1169 802.15.4e", draft-ietf-6tisch-terminology-07 (work in 1170 progress), March 2016. 1172 [I-D.ietf-bier-architecture] 1173 Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and 1174 S. Aldrin, "Multicast using Bit Index Explicit 1175 Replication", draft-ietf-bier-architecture-04 (work in 1176 progress), July 2016. 1178 [I-D.ietf-ipv6-multilink-subnets] 1179 Thaler, D. and C. Huitema, "Multi-link Subnet Support in 1180 IPv6", draft-ietf-ipv6-multilink-subnets-00 (work in 1181 progress), July 2002. 1183 [I-D.nordmark-6man-dad-approaches] 1184 Nordmark, E., "Possible approaches to make DAD more robust 1185 and/or efficient", draft-nordmark-6man-dad-approaches-02 1186 (work in progress), October 2015. 1188 [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] 1189 Popa, D. and J. Hui, "6LoPLC: Transmission of IPv6 Packets 1190 over IEEE 1901.2 Narrowband Powerline Communication 1191 Networks", draft-popa-6lo-6loplc-ipv6-over- 1192 ieee19012-networks-00 (work in progress), March 2014. 1194 [I-D.sarikaya-6lo-ap-nd] 1195 Sethi, M., Thubert, P., and B. Sarikaya, "Address 1196 Protected Neighbor Discovery for Low-power and Lossy 1197 Networks", draft-sarikaya-6lo-ap-nd-04 (work in progress), 1198 August 2016. 1200 [I-D.thubert-6lo-rfc6775-update] 1201 Thubert, P., Nordmark, E., and S. Chakrabarti, "An Update 1202 to 6LoWPAN ND", draft-thubert-6lo-rfc6775-update-00 (work 1203 in progress), May 2016. 1205 [I-D.vyncke-6man-mcast-not-efficient] 1206 Vyncke, E., Thubert, P., Levy-Abegnoli, E., and A. 1207 Yourtchenko, "Why Network-Layer Multicast is Not Always 1208 Efficient At Datalink Layer", draft-vyncke-6man-mcast-not- 1209 efficient-01 (work in progress), February 2014. 1211 [I-D.yourtchenko-6man-dad-issues] 1212 Yourtchenko, A. and E. Nordmark, "A survey of issues 1213 related to IPv6 Duplicate Address Detection", draft- 1214 yourtchenko-6man-dad-issues-01 (work in progress), March 1215 2015. 1217 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 1218 C., and M. Carney, "Dynamic Host Configuration Protocol 1219 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 1220 2003, . 1222 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1223 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1224 DOI 10.17487/RFC3810, June 2004, 1225 . 1227 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 1228 "SEcure Neighbor Discovery (SEND)", RFC 3971, 1229 DOI 10.17487/RFC3971, March 2005, 1230 . 1232 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 1233 RFC 3972, DOI 10.17487/RFC3972, March 2005, 1234 . 1236 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 1237 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 1238 2006, . 1240 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 1241 DOI 10.17487/RFC4903, June 2007, 1242 . 1244 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1245 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1246 Overview, Assumptions, Problem Statement, and Goals", 1247 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1248 . 1250 [RFC5415] Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley, 1251 Ed., "Control And Provisioning of Wireless Access Points 1252 (CAPWAP) Protocol Specification", RFC 5415, 1253 DOI 10.17487/RFC5415, March 2009, 1254 . 1256 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 1257 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 1258 2011, . 1260 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1261 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1262 DOI 10.17487/RFC6282, September 2011, 1263 . 1265 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 1266 Locator/ID Separation Protocol (LISP)", RFC 6830, 1267 DOI 10.17487/RFC6830, January 2013, 1268 . 1270 [RFC7048] Nordmark, E. and I. Gashinsky, "Neighbor Unreachability 1271 Detection Is Too Impatient", RFC 7048, 1272 DOI 10.17487/RFC7048, January 2014, 1273 . 1275 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1276 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1277 2014, . 1279 [RFC7217] Gont, F., "A Method for Generating Semantically Opaque 1280 Interface Identifiers with IPv6 Stateless Address 1281 Autoconfiguration (SLAAC)", RFC 7217, 1282 DOI 10.17487/RFC7217, April 2014, 1283 . 1285 [RFC7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets 1286 over ITU-T G.9959 Networks", RFC 7428, 1287 DOI 10.17487/RFC7428, February 2015, 1288 . 1290 [RFC7559] Krishnan, S., Anipko, D., and D. Thaler, "Packet-Loss 1291 Resiliency for Router Solicitations", RFC 7559, 1292 DOI 10.17487/RFC7559, May 2015, 1293 . 1295 [RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B., 1296 Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low 1297 Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015, 1298 . 1300 [RFC7772] Yourtchenko, A. and L. Colitti, "Reducing Energy 1301 Consumption of Router Advertisements", BCP 202, RFC 7772, 1302 DOI 10.17487/RFC7772, February 2016, 1303 . 1305 12.3. External Informative References 1307 [IEEE80211] 1308 IEEE standard for Information Technology, "IEEE Standard 1309 for Information technology-- Telecommunications and 1310 information exchange between systems Local and 1311 metropolitan area networks-- Specific requirements Part 1312 11: Wireless LAN Medium Access Control (MAC) and Physical 1313 Layer (PHY) Specifications". 1315 [IEEE802151] 1316 IEEE standard for Information Technology, "IEEE Standard 1317 for Information Technology - Telecommunications and 1318 Information Exchange Between Systems - Local and 1319 Metropolitan Area Networks - Specific Requirements. - Part 1320 15.1: Wireless Medium Access Control (MAC) and Physical 1321 Layer (PHY) Specifications for Wireless Personal Area 1322 Networks (WPANs)". 1324 [IEEE802154] 1325 IEEE standard for Information Technology, "IEEE Standard 1326 for Local and metropolitan area networks-- Part 15.4: Low- 1327 Rate Wireless Personal Area Networks (LR-WPANs)". 1329 Appendix A. Requirements 1331 This section lists requirements that were discussed at 6lo for an 1332 update to 6LoWPAN ND. This specification meets most of them, but 1333 those listed in Appendix A.5 which are deferred to a different 1334 specification such as [I-D.sarikaya-6lo-ap-nd]. 1336 A.1. Requirements Related to Mobility 1338 Due to the unstable nature of LLN links, even in a LLN of immobile 1339 nodes a 6LoWPAN Node may change its point of attachment to a 6LR, say 1340 6LR-a, and may not be able to notify 6LR-a. Consequently, 6LR-a may 1341 still attract traffic that it cannot deliver any more. When links to 1342 a 6LR change state, there is thus a need to identify stale states in 1343 a 6LR and restore reachability in a timely fashion. 1345 Req1.1: Upon a change of point of attachment, connectivity via a new 1346 6LR MUST be restored timely without the need to de-register from the 1347 previous 6LR. 1349 Req1.2: For that purpose, the protocol MUST enable to differentiate 1350 between multiple registrations from one 6LoWPAN Node and 1351 registrations from different 6LoWPAN Nodes claiming the same address. 1353 Req1.3: Stale states MUST be cleaned up in 6LRs. 1355 Req1.4: A 6LoWPAN Node SHOULD also be capable to register its Address 1356 to multiple 6LRs, and this, concurrently. 1358 A.2. Requirements Related to Routing Protocols 1360 The point of attachment of a 6LoWPAN Node may be a 6LR in an LLN 1361 mesh. IPv6 routing in a LLN can be based on RPL, which is the 1362 routing protocol that was defined at the IETF for this particular 1363 purpose. Other routing protocols than RPL are also considered by 1364 Standard Defining Organizations (SDO) on the basis of the expected 1365 network characteristics. It is required that a 6LoWPAN Node attached 1366 via ND to a 6LR would need to participate in the selected routing 1367 protocol to obtain reachability via the 6LR. 1369 Next to the 6LBR unicast address registered by ND, other addresses 1370 including multicast addresses are needed as well. For example a 1371 routing protocol often uses a multicast address to register changes 1372 to established paths. ND needs to register such a multicast address 1373 to enable routing concurrently with discovery. 1375 Multicast is needed for groups. Groups MAY be formed by device type 1376 (e.g. routers, street lamps), location (Geography, RPL sub-tree), or 1377 both. 1379 The Bit Index Explicit Replication (BIER) Architecture 1380 [I-D.ietf-bier-architecture] proposes an optimized technique to 1381 enable multicast in a LLN with a very limited requirement for routing 1382 state in the nodes. 1384 Related requirements are: 1386 Req2.1: The ND registration method SHOULD be extended in such a 1387 fashion that the 6LR MAY advertise the Address of a 6LoWPAN Node over 1388 the selected routing protocol and obtain reachability to that Address 1389 using the selected routing protocol. 1391 Req2.2: Considering RPL, the Address Registration Option that is used 1392 in the ND registration SHOULD be extended to carry enough information 1393 to generate a DAO message as specified in [RFC6550] section 6.4, in 1394 particular the capability to compute a Path Sequence and, as an 1395 option, a RPLInstanceID. 1397 Req2.3: Multicast operations SHOULD be supported and optimized, for 1398 instance using BIER or MPL. Whether ND is appropriate for the 1399 registration to the 6BBR is to be defined, considering the additional 1400 burden of supporting the Multicast Listener Discovery Version 2 1401 [RFC3810] (MLDv2) for IPv6. 1403 A.3. Requirements Related to the Variety of Low-Power Link types 1405 6LoWPAN ND [RFC6775] was defined with a focus on IEEE802.15.4 and in 1406 particular the capability to derive a unique Identifier from a 1407 globally unique MAC-64 address. At this point, the 6lo Working Group 1408 is extending the 6LoWPAN Header Compression (HC) [RFC6282] technique 1409 to other link types ITU-T G.9959 [RFC7428], Master-Slave/Token- 1410 Passing [I-D.ietf-6lo-6lobac], DECT Ultra Low Energy 1411 [I-D.ietf-6lo-dect-ule], Near Field Communication [I-D.ietf-6lo-nfc], 1412 IEEE802.11ah [I-D.delcarpio-6lo-wlanah], as well as IEEE1901.2 1413 Narrowband Powerline Communication Networks 1414 [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] and BLUETOOTH(R) 1415 Low Energy [RFC7668]. 1417 Related requirements are: 1419 Req3.1: The support of the registration mechanism SHOULD be extended 1420 to more LLN links than IEEE 802.15.4, matching at least the LLN links 1421 for which an "IPv6 over foo" specification exists, as well as Low- 1422 Power Wi-Fi. 1424 Req3.2: As part of this extension, a mechanism to compute a unique 1425 Identifier should be provided, with the capability to form a Link- 1426 Local Address that SHOULD be unique at least within the LLN connected 1427 to a 6LBR discovered by ND in each node within the LLN. 1429 Req3.3: The Address Registration Option used in the ND registration 1430 SHOULD be extended to carry the relevant forms of unique Identifier. 1432 Req3.4: The Neighbour Discovery should specify the formation of a 1433 site-local address that follows the security recommendations from 1434 [RFC7217]. 1436 A.4. Requirements Related to Proxy Operations 1438 Duty-cycled devices may not be able to answer themselves to a lookup 1439 from a node that uses classical ND on a backbone and may need a 1440 proxy. Additionally, the duty-cycled device may need to rely on the 1441 6LBR to perform registration to the 6BBR. 1443 The ND registration method SHOULD defend the addresses of duty-cycled 1444 devices that are sleeping most of the time and not capable to defend 1445 their own Addresses. 1447 Related requirements are: 1449 Req4.1: The registration mechanism SHOULD enable a third party to 1450 proxy register an Address on behalf of a 6LoWPAN node that may be 1451 sleeping or located deeper in an LLN mesh. 1453 Req4.2: The registration mechanism SHOULD be applicable to a duty- 1454 cycled device regardless of the link type, and enable a 6BBR to 1455 operate as a proxy to defend the registered Addresses on its behalf. 1457 Req4.3: The registration mechanism SHOULD enable long sleep 1458 durations, in the order of multiple days to a month. 1460 A.5. Requirements Related to Security 1462 In order to guarantee the operations of the 6LoWPAN ND flows, the 1463 spoofing of the 6LR, 6LBR and 6BBRs roles should be avoided. Once a 1464 node successfully registers an address, 6LoWPAN ND should provide 1465 energy-efficient means for the 6LBR to protect that ownership even 1466 when the node that registered the address is sleeping. 1468 In particular, the 6LR and the 6LBR then should be able to verify 1469 whether a subsequent registration for a given Address comes from the 1470 original node. 1472 In a LLN it makes sense to base security on layer-2 security. During 1473 bootstrap of the LLN, nodes join the network after authorization by a 1474 Joining Assistant (JA) or a Commissioning Tool (CT). After joining 1475 nodes communicate with each other via secured links. The keys for 1476 the layer-2 security are distributed by the JA/CT. The JA/CT can be 1477 part of the LLN or be outside the LLN. In both cases it is needed 1478 that packets are routed between JA/CT and the joining node. 1480 Related requirements are: 1482 Req5.1: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for 1483 the 6LR, 6LBR and 6BBR to authenticate and authorize one another for 1484 their respective roles, as well as with the 6LoWPAN Node for the role 1485 of 6LR. 1487 Req5.2: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for 1488 the 6LR and the 6LBR to validate new registration of authorized 1489 nodes. Joining of unauthorized nodes MUST be impossible. 1491 Req5.3: 6LoWPAN ND security mechanisms SHOULD lead to small packet 1492 sizes. In particular, the NS, NA, DAR and DAC messages for a re- 1493 registration flow SHOULD NOT exceed 80 octets so as to fit in a 1494 secured IEEE802.15.4 frame. 1496 Req5.4: Recurrent 6LoWPAN ND security operations MUST NOT be 1497 computationally intensive on the LoWPAN Node CPU. When a Key hash 1498 calculation is employed, a mechanism lighter than SHA-1 SHOULD be 1499 preferred. 1501 Req5.5: The number of Keys that the 6LoWPAN Node needs to manipulate 1502 SHOULD be minimized. 1504 Req5.6: The 6LoWPAN ND security mechanisms SHOULD enable CCM* for use 1505 at both Layer 2 and Layer 3, and SHOULD enable the reuse of security 1506 code that has to be present on the device for upper layer security 1507 such as TLS. 1509 Req5.7: Public key and signature sizes SHOULD be minimized while 1510 maintaining adequate confidentiality and data origin authentication 1511 for multiple types of applications with various degrees of 1512 criticality. 1514 Req5.8: Routing of packets should continue when links pass from the 1515 unsecured to the secured state. 1517 Req5.9: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for 1518 the 6LR and the 6LBR to validate whether a new registration for a 1519 given address corresponds to the same 6LoWPAN Node that registered it 1520 initially, and, if not, determine the rightful owner, and deny or 1521 clean-up the registration that is duplicate. 1523 A.6. Requirements Related to Scalability 1525 Use cases from Automatic Meter Reading (AMR, collection tree 1526 operations) and Advanced Metering Infrastructure (AMI, bi-directional 1527 communication to the meters) indicate the needs for a large number of 1528 LLN nodes pertaining to a single RPL DODAG (e.g. 5000) and connected 1529 to the 6LBR over a large number of LLN hops (e.g. 15). 1531 Related requirements are: 1533 Req6.1: The registration mechanism SHOULD enable a single 6LBR to 1534 register multiple thousands of devices. 1536 Req6.2: The timing of the registration operation should allow for a 1537 large latency such as found in LLNs with ten and more hops. 1539 Author's Address 1541 Pascal Thubert (editor) 1542 Cisco Systems, Inc 1543 Building D 1544 45 Allee des Ormes - BP1200 1545 MOUGINS - Sophia Antipolis 06254 1546 FRANCE 1548 Phone: +33 497 23 26 34 1549 Email: pthubert@cisco.com