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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 6LoWPAN Working Group Z. Shelby, Ed. 3 Internet-Draft Sensinode 4 Updates: 4944 (if approved) S. Chakrabarti 5 Intended status: Standards Track Ericsson 6 Expires: December 15, 2011 E. Nordmark 7 Cisco Systems 8 June 13, 2011 10 Neighbor Discovery Optimization for Low Power and Lossy Networks 11 (6LoWPAN) 12 draft-ietf-6lowpan-nd-17 14 Abstract 16 The IETF 6LoWPAN working group defines IPv6 over Low-power Wireless 17 Personal Area Networks such as IEEE 802.15.4. This and other similar 18 link technologies have limited or no usage of multicast signaling due 19 to energy conservation. In addition, the wireless network may not 20 strictly follow traditional concept of IP subnets and IP links. IPv6 21 Neighbor Discovery was not designed for non-transitive wireless 22 links. The traditional IPv6 link concept and heavy use of multicast 23 make the protocol inefficient and sometimes impractical in a low 24 power and lossy network. This document describes simple 25 optimizations to IPv6 Neighbor Discovery, addressing mechanisms and 26 duplicate address detection for 6LoWPAN and similar networks. 28 Status of this Memo 30 This Internet-Draft is submitted to IETF in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF), its areas, and its working groups. Note that 35 other groups may also distribute working documents as Internet- 36 Drafts. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 The list of current Internet-Drafts can be accessed at 44 http://www.ietf.org/ietf/1id-abstracts.txt. 46 The list of Internet-Draft Shadow Directories can be accessed at 47 http://www.ietf.org/shadow.html. 49 This Internet-Draft will expire on December 15, 2011. 51 Copyright Notice 53 Copyright (c) 2011 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (http://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the BSD License. 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 1.1. The Shortcomings of IPv6 Neighbor Discovery . . . . . . . 5 70 1.2. Mesh-under and Route-over Concepts . . . . . . . . . . . . 6 71 1.3. Applicability . . . . . . . . . . . . . . . . . . . . . . 7 72 1.4. Goals and Assumptions . . . . . . . . . . . . . . . . . . 7 73 1.5. Optional Features . . . . . . . . . . . . . . . . . . . . 9 74 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 9 75 3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 11 76 3.1. Extensions to RFC4861 . . . . . . . . . . . . . . . . . . 11 77 3.2. Address Assignment . . . . . . . . . . . . . . . . . . . . 12 78 3.3. Host-to-Router Interaction . . . . . . . . . . . . . . . . 12 79 3.4. Router-to-Router Interaction . . . . . . . . . . . . . . . 13 80 3.5. Neighbor Cache Management . . . . . . . . . . . . . . . . 14 81 4. New Neighbor Discovery Options and Messages . . . . . . . . . 15 82 4.1. Address Registration Option . . . . . . . . . . . . . . . 15 83 4.2. 6LoWPAN Context Option . . . . . . . . . . . . . . . . . . 17 84 4.3. Authoritative Border Router Option . . . . . . . . . . . . 18 85 4.4. Duplicate Address messages . . . . . . . . . . . . . . . . 20 86 5. Host Behavior . . . . . . . . . . . . . . . . . . . . . . . . 21 87 5.1. Forbidden Actions . . . . . . . . . . . . . . . . . . . . 21 88 5.2. Interface Initialization . . . . . . . . . . . . . . . . . 21 89 5.3. Sending a Router Solicitation . . . . . . . . . . . . . . 22 90 5.4. Processing a Router Advertisement . . . . . . . . . . . . 22 91 5.4.1. Address configuration . . . . . . . . . . . . . . . . 23 92 5.4.2. Storing Contexts . . . . . . . . . . . . . . . . . . . 23 93 5.4.3. Maintaining Prefix and Context Information . . . . . . 23 94 5.5. Registration and Neighbor Unreachability Detection . . . . 24 95 5.5.1. Sending a Neighbor Solicitation . . . . . . . . . . . 24 96 5.5.2. Processing a Neighbor Advertisement . . . . . . . . . 25 97 5.5.3. Recovering from Failures . . . . . . . . . . . . . . . 25 98 5.6. Next-hop Determination . . . . . . . . . . . . . . . . . . 26 99 5.7. Address Resolution . . . . . . . . . . . . . . . . . . . . 26 100 5.8. Sleeping . . . . . . . . . . . . . . . . . . . . . . . . . 26 101 5.8.1. Picking an Appropriate Registration Lifetime . . . . . 27 102 5.8.2. Behavior on Wakeup . . . . . . . . . . . . . . . . . . 27 103 6. Router Behavior for 6LR and 6LBR . . . . . . . . . . . . . . . 27 104 6.1. Forbidden Actions . . . . . . . . . . . . . . . . . . . . 28 105 6.2. Interface Initialization . . . . . . . . . . . . . . . . . 28 106 6.3. Processing a Router Solicitation . . . . . . . . . . . . . 28 107 6.4. Periodic Router Advertisements . . . . . . . . . . . . . . 29 108 6.5. Processing a Neighbor Solicitation . . . . . . . . . . . . 29 109 6.5.1. Checking for Duplicates . . . . . . . . . . . . . . . 30 110 6.5.2. Returning Address Registration Errors . . . . . . . . 30 111 6.5.3. Updating the Neighbor Cache . . . . . . . . . . . . . 30 112 6.5.4. Next-hop Determination . . . . . . . . . . . . . . . . 31 113 6.5.5. Address Resolution between Routers . . . . . . . . . . 31 115 7. Border Router Behavior . . . . . . . . . . . . . . . . . . . . 31 116 7.1. Prefix Determination . . . . . . . . . . . . . . . . . . . 32 117 7.2. Context Configuration and Management . . . . . . . . . . . 32 118 8. Optional Behavior . . . . . . . . . . . . . . . . . . . . . . 33 119 8.1. Multihop Prefix and Context Distribution . . . . . . . . . 33 120 8.1.1. 6LBRs Sending Router Advertisements . . . . . . . . . 34 121 8.1.2. Routers Sending Router Solicitations . . . . . . . . . 34 122 8.1.3. Routers Processing Router Advertisements . . . . . . . 34 123 8.1.4. Storing the Information . . . . . . . . . . . . . . . 35 124 8.1.5. Sending Router Advertisements . . . . . . . . . . . . 35 125 8.2. Multihop Duplicate Address Detection . . . . . . . . . . . 36 126 8.2.1. Message Validation for DAR and DAC . . . . . . . . . . 37 127 8.2.2. Conceptual Data Structures . . . . . . . . . . . . . . 38 128 8.2.3. 6LR Sending a Duplicate Address Request . . . . . . . 38 129 8.2.4. 6LBR Receiving a Duplicate Address Request . . . . . . 39 130 8.2.5. Processing a Duplicate Address Confirmation . . . . . 39 131 8.2.6. Recovering from Failures . . . . . . . . . . . . . . . 40 132 9. Protocol Constants . . . . . . . . . . . . . . . . . . . . . . 40 133 10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 134 10.1. Message Examples . . . . . . . . . . . . . . . . . . . . . 41 135 10.2. Host Bootstrapping Example . . . . . . . . . . . . . . . . 42 136 10.2.1. Host Bootstrapping Messages . . . . . . . . . . . . . 43 137 10.3. Router Interaction Example . . . . . . . . . . . . . . . . 46 138 10.3.1. Bootstrapping a Router . . . . . . . . . . . . . . . . 46 139 10.3.2. Updating the Neighbor Cache . . . . . . . . . . . . . 46 140 11. Security Considerations . . . . . . . . . . . . . . . . . . . 47 141 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47 142 13. Guideline for New Features . . . . . . . . . . . . . . . . . . 48 143 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 50 144 15. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 50 145 16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 56 146 16.1. Normative References . . . . . . . . . . . . . . . . . . . 56 147 16.2. Informative References . . . . . . . . . . . . . . . . . . 57 148 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 58 150 1. Introduction 152 The IPv6-over-IEEE 802.15.4 [RFC4944] document specifies how IPv6 is 153 carried over an IEEE 802.15.4 network with the help of an adaptation 154 layer which sits between the MAC layer and the IP network layer. A 155 link in a LoWPAN is characterized as lossy, low-power, low bit-rate, 156 short range, with many nodes saving energy with long sleep periods. 157 Multicast as used in IPv6 Neighbor Discovery [RFC4861] is not 158 desirable in such a wireless low-power and lossy network. Moreover, 159 LoWPAN links are asymmetric and non-transitive in nature. A LoWPAN 160 is potentially composed of a large number of overlapping radio 161 ranges. Although a given radio range has broadcast capabilities, the 162 aggregation of these is a complex Non-Broadcast MultiAccess (NBMA, 163 [RFC2491]) structure with generally no LoWPAN-wide multicast 164 capabilities. Link-local scope is in reality defined by reachability 165 and radio strength. Thus we can consider a LoWPAN to be made up of 166 links with undetermined connectivity properties as in [RFC5889], 167 along with the corresponding address model assumptions defined 168 therein. 170 This specification introduces the following optimizations to IPv6 171 Neighbor Discovery [RFC4861] specifically aimed at low-power and 172 lossy networks such as LoWPANs: 174 o Host-initiated interactions to allow for sleeping hosts. 176 o Elimination of multicast-based address resolution for hosts. 178 o A host address registration feature using a new option in unicast 179 Neighbor Solicitation and Neighbor Advertisement messages. 181 o A new Neighbor Discovery option to distribute 6LoWPAN header 182 compression context to hosts. 184 o Optional multihop distribution of prefix and 6LoWPAN header 185 compression context. 187 o Optional multihop duplicate address detection which uses two new 188 ICMPv6 message types. 190 The document defines three new ICMPv6 message options: the required 191 Address Registration option and the optional Authoritative Border 192 Router and 6LoWPAN Context options. It also defines two new ICMPv6 193 message types: the Duplicate Address Request and Duplicate Address 194 Confirmation. 196 1.1. The Shortcomings of IPv6 Neighbor Discovery 198 IPv6 Neighbor Discovery [RFC4861] provides several important 199 mechanisms used for Router Discovery, Address Resolution, Duplicate 200 Address Detection, Redirect, along with Prefix and Parameter 201 Discovery. 203 Following power-on and initialization of the network in IPv6 Ethernet 204 networks, a node joins the solicited-node multicast address on the 205 interface and then performs Duplicate Address Detection (DAD) for the 206 acquired link-local address by sending a solicited-node multicast 207 message to the link. After that it sends multicast messages to the 208 all-router address to solicit router advertisements. If the host 209 receives a valid Router Advertisement with the "A" flag, it 210 autoconfigures the IPv6 address with the advertised prefix in the 211 Router Advertisement (RA) message. Besides this, the IPv6 routers 212 usually send router advertisements periodically on the network. RAs 213 are sent to the all-node multicast address. Nodes send Neighbor 214 Solicitation/Neighbor Advertisement messages to resolve the IPv6 215 address of the destination on the link. The Neighbor Solicitation 216 messages used for address resolution are multicast. The Duplicate 217 Address Detection procedure and the use of periodic Router 218 Advertisement messages assumes that the nodes are powered on and 219 reachable most of the time. 221 In Neighbor Discovery the routers find the hosts by assuming that a 222 subnet prefix maps to one broadcast domain, and then multicast 223 Neighbor Solicitation messages to find the host and its link-layer 224 address. Furthermore, the DAD use of multicast assumes that all 225 hosts that autoconfigure IPv6 addresses from the same prefix can be 226 reached using link-local multicast messages. 228 Note that the 'L' (on-link) bit in the Prefix Information option can 229 be set to zero in Neighbor Discovery, which makes the host not use 230 multicast Neighbor Solicitation (NS) messages for address resolution 231 of other hosts, but routers still use multicast NS messages to find 232 the hosts. 234 In a LoWPAN, primarily two types of network topologies are found - 235 star networks and mesh networks. A star network is similar to a 236 regular IPv6 subnet with a router and a set of nodes connected to it 237 via the same non-transitive link. But in Mesh networks, the nodes 238 are capable of routing and forwarding packets. Due to the lossy 239 nature of wireless communication and a changing radio environment, 240 the IPv6-link node-set may change due to external physical factors. 241 Thus the link is often unstable and the nodes appear to be moving 242 without necessarily moving physically. 244 A LoWPAN can use two types of link-layer addresses; 16-bit short 245 addresses and 64-bit unique addresses as defined in [RFC4944]. 246 Moreover, the available link-layer payload size is on the order of 247 less than 100 bytes thus header compression is very useful. 249 Considering the above characteristics in a LoWPAN, and the IPv6 250 Neighbor Discovery [RFC4861] protocol design center, some 251 optimizations and extensions to Neighbor Discovery are useful for the 252 wide deployment of IPv6 over low-powered and lossy networks such as 253 6LoWPANs. 255 1.2. Mesh-under and Route-over Concepts 257 In the 6LoWPAN context, often a link-layer mesh routing mechanism is 258 referred to as "mesh-under" while routing/forwarding packets using 259 IP-layer addresses is referred to as "route-over". The difference 260 between mesh-under and route-over is similar to a bridged-network 261 versus IP-routing using Ethernet. In a mesh-under network all nodes 262 are on the same link which is served by one or more routers, which we 263 call 6LoWPAN Border Routers (6LBR). In a route-over network, there 264 are multiple links in the 6LoWPAN. Unlike fixed IP links, these 265 link's members may be changing due to the nature of the low-power and 266 lossy behavior of wireless technology. Thus a route-over network is 267 made up of a flexible set of links interconnected by interior 268 routers, which we call 6LoWPAN Routers (6LR). 270 This specification is applicable to both mesh-under and route-over 271 networks. However, in route-over networks, we have two types of 272 routers - 6LBRs and 6LRs. 6LoWPAN Border Routers sit at the boundary 273 of the 6LoWPAN and the rest of the network while 6LoWPAN Routers are 274 inside the LoWPAN. 6LoWPAN Routers are assumed to be running a 275 routing protocol. 277 In a mesh-under configuration a 6LBR is acting as the IPv6 router 278 where all the hosts in the LoWPAN are on the same link, thus they are 279 only one IP hop away. No 6LoWPAN Routers exist in this topology as 280 forwarding is handled by a link-layer mesh routing protocol. 282 In a route-over configuration, Neighbor Discovery operations take 283 place between hosts and 6LRs or 6LBRs. The 6LR nodes are able to 284 send and receive Router Advertisements, Router Solicitations as well 285 as forward and route IPv6 packets. Here packet forwarding happens at 286 the IP layer. 288 In both types of configurations, hosts do not take part in routing 289 and forwarding packets and they act as simple IPv6 hosts. 291 1.3. Applicability 293 In its Section 1, [RFC4861] foresees a document that covers operating 294 IP over a particular link type and defines an exception to the 295 otherwise general applicability of unmodified RFC 4861. The present 296 specification optimizes the usage of IPv6 Neighbor Discovery for 297 LoWPANs in order to save energy and processing power of such nodes. 298 The document, thus updates RFC 4944 to specify the use of the 299 optimizations defined here. 301 The applicability of this specification is limited to LoWPANs where 302 all nodes on the subnet implement these optimizations in a 303 homogeneous way. Although it is noted that some of these 304 optimizations may be useful outside of 6LoWPAN, for example in 305 general IPv6 low-power and lossy networks and possibly even in 306 combination with [RFC4861], the usage of such combinations is out of 307 scope of this document. 309 In this document, we specify a set of behaviors between hosts and 310 routers in LoWPANs. An implementation that adheres to this document 311 MUST implement those behaviors. The document also specifies a set of 312 behaviors (multihop prefix or context dissemination, and separately 313 multihop duplicate address detection) which are OPTIONAL to use. An 314 implementation of this specification SHOULD implement those optional 315 to use pieces. 317 The optimizations described in this document apply to different 318 topologies. They are most useful for route-over and mesh-under 319 configurations in Mesh topologies. However, Star topology 320 configurations will also benefit from the optimizations due to 321 minimized signaling, robust handling of the non-transitive link, and 322 header compression context information. 324 1.4. Goals and Assumptions 326 The document has the following main goals and assumptions. 328 Goals: 330 o Optimize Neighbor Discovery with a mechanism that is minimal yet 331 sufficient for the operation in both mesh-under and route-over 332 configurations. 334 o Minimize signaling by avoiding the use of multicast flooding and 335 reducing the use of link-scope multicast messages. 337 o Optimize the interfaces between hosts and their default routers. 339 o Support for sleeping hosts. 341 o Disseminate context information to hosts as needed by 342 [I-D.ietf-6lowpan-hc]. 344 o Optionally disseminate context information and prefix information 345 from the border to all routers in a LoWPAN. 347 o Optional duplicate address detection mechanism suitable for route- 348 over LoWPANs. 350 Assumptions: 352 o EUI-64 addresses are globally unique. 354 o All nodes in the network have an EUI-64 interface identifier in 355 order to do address auto-configuration and detect duplicate 356 addresses. 358 o The link layer technology is assumed to be low-power and lossy, 359 exhibiting undetermined connectivity, such as IEEE 802.15.4 360 [RFC4944]. However, the Address Registration mechanism might be 361 useful for other link layer technologies. 363 o A 6LoWPAN is configured to share one or more global IPv6 address 364 prefixes to enable hosts to move between routers in the 6LoWPAN 365 without changing their IPv6 addresses. 367 o When using the optional DAD mechanism of Section 8.2 it is assumed 368 that 6LRs register with all the 6LBRs. 370 o If IEEE 802.15.4 16-bit short addresses are used, then some 371 technique is used to ensure uniqueness of those link-layer 372 addresses. That could be done using DHCPv6, the Address 373 Registration Option based duplicate address detection (specified 374 in Section 8.2) or other techniques outside of the scope of this 375 document. 377 o In order to preserve the uniqueness of addresses not derived from 378 an EUI-64, they must be either assigned or checked for duplicates 379 in the same way throughout the LoWPAN. This can be done using 380 DHCPv6 for assignment and/or using the duplicate address detection 381 mechanism specified in Section 8.2 (or any other protocols 382 developed for that purpose). 384 o In order for [I-D.ietf-6lowpan-hc] to operate correctly, the 385 compression context must match for all the hosts, 6LRs, and 6LBRs 386 that can send, receive, or forward a given packet. If Section 8.1 387 is used to distribute context information this implies that all 388 the 6LBRs must coordinate the context information they distribute 389 within a single 6LoWPAN. 391 o This specification describes the operation of ND within a single 392 LoWPAN. The participation of a node in multiple LoWPANs 393 simultaneously may be possible, but is out of scope of this 394 document. 396 o Since the 6LoWPAN shares one single prefix throughout the network, 397 mobility of nodes within the LoWPAN is transparent. Inter-LoWPAN 398 mobility is out-of-scope of this document. 400 1.5. Optional Features 402 This document defines the optimization of Neighbor Discovery messages 403 host-router interfaces and introduces the communication in case of 404 Route-over topology. The multihop prefix distribution by the 6LBR 405 and multihop Duplicate Address Detection mechanisms, as well as 406 6LoWPAN context option are optional features for a 6LoWPAN 407 deployment. A guideline for feature implementation and deployment is 408 provided at the end of the document. 410 2. Terminology 412 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 413 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 414 document are to be interpreted as described in [RFC2119]. 416 This specification requires readers to be familiar with all the terms 417 and concepts that are discussed in "Neighbor Discovery for IP version 418 6" [RFC4861] "IPv6 Stateless Address Autoconfiguration" [RFC4862], 419 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 420 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 421 "Transmission of IPv6 Packets over IEEE 802.15.4 Networks" [RFC4944] 422 and "IP Addressing Model in Ad Hoc Networks" [RFC5889]. 424 This specification makes extensive use of the same terminology 425 defined in [RFC4861] unless otherwise defined below. 427 6LoWPAN link: 428 A wireless link determined by single IP hop reachability of 429 neighboring nodes. These are considered links with undetermined 430 connectivity properties as in [RFC5889]. 432 6LoWPAN Node (6LN): 433 A 6LoWPAN Node is any host or router participating in a LoWPAN. 434 This term is used when referring to situations in which either a 435 host or router can play the role described. 437 6LoWPAN Router (6LR): 438 An intermediate router in the LoWPAN who can communicate with 439 other 6LoWPAN routers in the same LoWPAN. 6LoWPAN routers are 440 present only in route-over topologies. 442 6LoWPAN Border Router (6LBR): 443 A border router located at the junction of separate 6LoWPAN 444 networks or between a 6LoWPAN network and another IP network. 445 There may be one or more 6LBRs at the 6LoWPAN network boundary. A 446 6LBR is the responsible authority for IPv6 Prefix propagation for 447 the 6LoWPAN network it is serving. An isolated LoWPAN also 448 contains a 6LBR in the network, which provides the prefix(es) for 449 the isolated network. 451 Router: 452 Either a 6LR or a 6LBR. Note that nothing in this document 453 precludes a node being a router on some interfaces and a host on 454 other interfaces as allowed by [RFC2460]. 456 Mesh-under: 457 A topology where hosts are connected to a 6LBR through a mesh 458 using link-layer forwarding. Thus in a mesh-under configuration 459 all IPv6 hosts in a LoWPAN are only one IP hop away from the 6LBR. 460 This topology simulates the typical IP-subnet topology with one 461 router with multiple nodes in the same subnet. 463 Route-over: 464 A topology where hosts are connected to the 6LBR through the use 465 of intermediate layer-3 (IP) routing. Here hosts are typically 466 multiple IP hops away from a 6LBR. The route-over topology 467 typically consists of a 6LBR, a set of 6LRs and hosts. 469 Registration: 470 The process during which a LoWPAN node sends an Neighbor 471 Solicitation message with an Address Registration option to a 472 Router creating a Neighbor Cache entry for the LoWPAN node with a 473 specific timeout. Thus for 6LoWPAN Routers the Neighbor Cache 474 doesn't behave like a cache. Instead it behaves as a registry of 475 all the host addresses that are attached to the Router. 477 3. Protocol Overview 479 These Neighbor Discovery optimizations are applicable to both mesh- 480 under and route-over configurations. In a mesh-under configuration 481 only 6LoWPAN Border Routers and hosts exist; there are no 6LoWPAN 482 routers in mesh-under topologies. 484 The most important part of the optimizations is the evolved host-to- 485 router interaction that allows for sleeping nodes and avoids using 486 multicast Neighbor Discovery messages except for the case of a host 487 finding an initial set of default routers, and redoing such 488 determination when that set of routers have become unreachable. 490 The protocol also provides for header compression 491 [I-D.ietf-6lowpan-hc] by carrying header compression information in a 492 new option in Router Advertisement messages. 494 In addition, there are optional and separate mechanisms that can be 495 used between 6LRs and 6LBRs to perform multihop Duplicate Address 496 Detection and distribution of the Prefix and compression Context 497 information from the 6LBRs to all the 6LRs, which in turn use normal 498 Neighbor Discovery mechanisms to convey this information to the 499 hosts. 501 The protocol is designed so that the host-to-router interaction is 502 not affected by the configuration of the 6LoWPAN; the host-to-router 503 interaction is the same in a mesh-under and route-over configuration. 505 3.1. Extensions to RFC4861 507 This document specifies the following optimizations and extensions to 508 IPv6 Neighbor Discovery [RFC4861]: 510 o Host initiated refresh of Router Advertisement information. This 511 removes the need for periodic or unsolicited Router Advertisements 512 from routers to hosts. 514 o No Duplicate Address Detection (DAD) is performed if EUI-64 based 515 IPv6 addresses are used (as these addresses are assumed to be 516 globally unique). 518 o DAD is optional if DHCPv6 is used to assign addresses. 520 o A New Address Registration mechanism using a new Address 521 Registration option between hosts and routers. This removes the 522 need for Routers to use multicast Neighbor Solicitations to find 523 hosts, and supports sleeping hosts. This also enables the same 524 IPv6 address prefix(es) to be used across a route-over 6LoWPAN. 526 It provides the host-to-router interface for Duplicate Address 527 Detection. 529 o A new optional Router Advertisement option for Context information 530 used by 6LoWPAN header compression. 532 o A new optional mechanism to perform Duplicate Address Detection 533 across a route-over 6LoWPAN using the new Duplicate Address 534 Request and Confirmation messages. 536 o New optional mechanisms to distribute Prefixes and Context 537 information across a route-over network which uses a new 538 Authoritative Border Router option to control the flooding of 539 configuration changes. 541 o A few new default protocol constants are introduced and some 542 existing Neighbor Discovery protocol constants are tuned. 544 3.2. Address Assignment 546 Hosts in a 6LoWPAN configure their IPv6 address as specified in 547 [RFC4861] and [RFC4862] based on the information received in Router 548 Advertisement messages. The use of the M flag in this optimization 549 is however more restrictive than in [RFC4861]. When the M flag is 550 set a host is required to use DHCPv6 to assign any non-EUI-64 551 addresses. When the M flag is not set, the LoWPAN is required to 552 support duplicate address detection, thus a host can then safely use 553 the address registration mechanism to check non-EUI-64 addresses for 554 uniqueness. 556 6LRs MAY use the same mechanisms to configure their IPv6 addresses. 558 The 6LBRs are responsible for managing the prefix(es) assigned to the 559 6LoWPAN, using manual configuration, DHCPv6 Prefix Delegation 560 [RFC3633], or other mechanisms. In an isolated LoWPAN a ULA 561 [RFC4193] prefix SHOULD be generated by the 6LBR. 563 3.3. Host-to-Router Interaction 565 A host sends Router Solicitation messages at startup and also when it 566 suspects that one of its default routers has become unreachable 567 (after Neighbor Unreachability Detection towards the router fails). 569 Hosts receive Router Advertisement messages typically containing the 570 Authoritative Border Router option (ABRO) and may optionally contain 571 one or more 6LoWPAN Context options (6CO) in addition to the existing 572 Prefix Information options (PIO) as described in [RFC4861]. 574 When a host has configured a non-link-local IPv6 address, it 575 registers that address with one or more of its default routers using 576 the Address Registration option (ARO) in an NS message. The host 577 chooses a lifetime of the registration and repeats the ARO option 578 periodically (before the lifetime runs out) to maintain the 579 registration. The lifetime should be chosen in such a way as to 580 maintain the registration even while a host is sleeping. Likewise, 581 mobile nodes that change their point of attachment often, should use 582 a suitably short lifetime. 584 The registration can fail (an ARO option returned to the host with a 585 non-zero Status) if the router determines that the IPv6 address is 586 already used by another host, that is, is used by a host with a 587 different EUI-64. This can be used to support non-EUI-64 based 588 addresses such as temporary IPv6 addresses [RFC4941] or addresses 589 based on an Interface ID that is a IEEE 802.15.4 16-bit short 590 addresses. Failure can also occur if the Neighbor Cache on that 591 router is full. 593 The re-registration of an address can be combined with Neighbor 594 Unreachability Detection (NUD) of the router since both use unicast 595 Neighbor Solicitation messages. This makes things efficient when a 596 host wakes up to send a packet and both need to perform NUD to check 597 that the router is still reachable, and refresh its registration with 598 the router. 600 The response to an address registration might not be immediate since 601 in route-over configurations the 6LR might perform Duplicate Address 602 Detection against the 6LBR. A host retransmits the Address 603 Registration option until it is acknowledged by the receipt of a 604 Address Registration option. 606 As part of the optimizations, Address Resolution is not performed by 607 multicasting Neighbor Solicitation messages as in [RFC4861]. 608 Instead, the routers maintain Neighbor Cache entries for all 609 registered IPv6 addresses. If the address is not in the Neighbor 610 Cache in the router, then the address either doesn't exist, or is 611 assigned to a host attached to some other router in the 6LoWPAN, or 612 is external to the 6LoWPAN. In a route-over configuration the 613 routing protocol is used to route such packets toward the 614 destination. 616 3.4. Router-to-Router Interaction 618 The optional new router-to-router interaction is only for the route- 619 over configuration where 6LRs are present. It is optional in this 620 protocol since the functions it provides might be better provided by 621 other protocol mechanisms, be it DHCPv6, link-layer mechanisms, the 622 routing protocol, or something else. It is however assumed that all 623 6LRs in a network are configured to perform these functions 624 homogeneously. Some mechanisms from this protocol might be used for 625 router-to-router interaction, while others are provided by other 626 protocols. For instance, context information and/or prefix 627 information might be disseminated using this protocol, while 628 Duplicate Address Detection is done using some other protocol. 630 6LRs MAY act like a host during system startup and prefix 631 configuration by sending Router Solicitation messages and 632 autoconfiguring their IPv6 addresses unlike routers in [RFC4861]. 634 When multihop prefix or context dissemination is used then the 6LRs 635 store the ABRO, 6CO and Prefix Information received (directly or 636 indirectly) from the 6LBRs and redistribute this information in the 637 Router Advertisement they send to other 6LRs or send to hosts in 638 response to a Router Solicitations. There is a version number field 639 in the ABRO which is used to limit the flooding of updated 640 information between the 6LRs. 642 Optionally the 6LRs can perform Duplicate Address Detection against 643 one or more 6LBRs using the new Duplicate Address Request (DAR) and 644 Confirmation (DAC) messages, which carry the information from the 645 Address Registration option. The DAR and DAC messages will be 646 forwarded between the 6LR and 6LBRs thus the [RFC4861] rule for 647 checking hop limit=255 does not apply to the DAR and DAC messages. 648 Those multihop DAD messages MUST NOT modify any Neighbor Cache 649 entries on the routers since we do not have the security benefits 650 provided by the hop limit=255 check. 652 3.5. Neighbor Cache Management 654 The use of explicit registrations with lifetimes plus the desire to 655 not multicast Neighbor Solicitation messages for hosts imply that we 656 manage the Neighbor Cache entries (NCE) slightly differently than in 657 [RFC4861]. This results in three different types of NCEs and the 658 types specify how those entries can be removed: 660 Garbage-collectible: Entries that are subject to the normal rules in 661 [RFC4861] that allow for garbage collection 662 when low on memory. 664 Registered: Entries that have an explicit registered 665 lifetime and are kept until this lifetime 666 expires or they are explicitly unregistered. 668 Tentative: Entries that are temporary with a short 669 lifetime, which typically get converted to 670 Registered entries. 672 Note that the type of the NCE is orthogonal to the states specified 673 in [RFC4861]. 675 When a host interacts with a router by sending Router Solicitations 676 this results in a Tentative NCE. Once a node successfully registers 677 with a Router the result is a Registered NCE. When Routers send RAs 678 to hosts, and when routers optionally receive RA messages or receive 679 multicast NS messages from other Routers, the result is Garbage- 680 collectible NCEs. There can only be one kind of NCE for an IP 681 address at a time. 683 Neighbor Cache entries on Routers can additionally be added or 684 deleted by a routing protocol used in the 6LoWPAN. This is useful if 685 the routing protocol carries the link-layer addresses of the 686 neighboring routers. Depending on the details of such routing 687 protocols such NCEs could be either Registered or Garbage- 688 collectible. 690 4. New Neighbor Discovery Options and Messages 692 This section defines new Neighbor Discovery message options used by 693 this specification. The Address Registration Option is mandatory, 694 whereas the Authoritative Border Router Option and 6LoWPAN Context 695 Option are optional. This section also defines the optional and new 696 Duplicate Address Request and Confirmation messages. 698 4.1. Address Registration Option 700 The routers need to know the set of host IP addresses that are 701 directly reachable and their corresponding link-layer addresses. 702 This needs to be maintained as the radio reachability changes. For 703 this purpose an Address Registration Option (ARO) is introduced, 704 which can be included in unicast Neighbor Solicitation (NS) messages 705 sent by hosts. Thus it can be included in the unicast NS messages 706 that a host sends as part of Neighbor Unreachability Detection to 707 determine that it can still reach a default router. The ARO is used 708 by the receiving router to reliably maintain its Neighbor Cache. The 709 same option is included in corresponding Neighbor Advertisement (NA) 710 messages with a Status field indicating the success or failure of the 711 registration. This option is always host initiated. 713 The information contained in the ARO is also included in optional 714 multihop DAR and DAC messages used between 6LRs to 6LBRs, but the 715 option itself is not used in those messages. 717 The ARO is required for reliability and power saving. The lifetime 718 field provides flexibility to the host to register an address which 719 should be usable (continue to be advertised by the 6LR in the routing 720 protocol etc.) during its intended sleep schedule. 722 The sender of the NS also includes the EUI-64 [EUI64] of the 723 interface it is registering an address from. This is used as a 724 unique ID for the detection of duplicate addresses. It is used to 725 tell the difference between the same node re-registering its address 726 and a different node (with a different EUI-64) registering an address 727 that is already in use by someone else. The EUI-64 is also used to 728 deliver an NA carrying an error Status code to the EUI-64 based link- 729 local IPv6 address of the host (see Section 6.5.2). 731 When the ARO is used by hosts an SLLA (Source Link-layer Address) 732 option [RFC4861] MUST be included and the address that is to be 733 registered MUST be the IPv6 source address of the Neighbor 734 Solicitation message. 736 0 1 2 3 737 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 1 738 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 739 | Type | Length = 2 | Status | Reserved | 740 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 741 | Reserved | Registration Lifetime | 742 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 743 | | 744 + EUI-64 + 745 | | 746 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 748 Fields: 750 Type: TBD1 752 Length: 8-bit unsigned integer. The length of the option in 753 units of 8 bytes. Always 2. 755 Status: 8-bit unsigned integer. Indicates the status of a 756 registration in the NA response. MUST be set to 0 in 757 NS messages. See below. 759 Reserved: This field is unused. It MUST be initialized to zero 760 by the sender and MUST be ignored by the receiver. 762 Registration Lifetime: 16-bit unsigned integer. The amount of time 763 in a unit of 60 seconds that the router should retain 764 the Neighbor Cache entry for the sender of the NS that 765 includes this option. 767 EUI-64: 64 bits. This field is used to uniquely identify the 768 interface of the registered address by including the 769 EUI-64 identifier [EUI64] assigned to it unmodified. 771 The Status values used in Neighbor Advertisements are: 773 +--------+--------------------------------------------+ 774 | Status | Description | 775 +--------+--------------------------------------------+ 776 | 0 | Success | 777 | 1 | Duplicate Address | 778 | 2 | Neighbor Cache Full | 779 | 3-255 | Allocated using Standards Action [RFC2434] | 780 +--------+--------------------------------------------+ 782 Table 1 784 4.2. 6LoWPAN Context Option 786 The optional 6LoWPAN Context Option (6CO) carries prefix information 787 for LoWPAN header compression, and is similar to the Prefix 788 Information Option of [RFC4861]. However, the prefixes can be remote 789 as well as local to the LoWPAN since header compression potentially 790 applies to all IPv6 addresses. This option allows for the 791 dissemination of multiple contexts identified by a Context Identifier 792 (CID) for use as specified in [I-D.ietf-6lowpan-hc]. A context may 793 be a prefix of any length or an address (/128), and up to 16 6LoWPAN 794 Context options may be carried in an Router Advertisement message. 796 0 1 2 3 797 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 1 798 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 799 | Type | Length |Context Length | Res |C| CID | 800 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 801 | Reserved | Valid Lifetime | 802 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 803 . . 804 . Context Prefix . 805 . . 806 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 808 Figure 1: 6LoWPAN Context Option format 810 Type: TBD2 812 Length: 8-bit unsigned integer. The length of the option (including 813 the type and length fields) in units of 8 bytes. May be 2 or 3 814 depending on the length of the Context Prefix field. 816 Context Length: 8-bit unsigned integer. The number of leading bits 817 in the Context Prefix field that are valid. The value ranges from 818 0 to 128. If it is more than 64 then the Length MUST be 3. 820 C: 1-bit context compression flag. This flag indicates if the 821 context is valid for use in compression. A context that is not 822 valid MUST NOT be used for compression, but SHOULD be used in 823 decompression in case another compressor has not yet received the 824 updated context information. This flag is used to manage the 825 context lifecycle based on the recommendations in Section 7.2. 827 CID: 4-bit Context Identifier for this prefix information. CID is 828 used by context based header compression specified in 829 [I-D.ietf-6lowpan-hc]. The list of CIDs for a LoWPAN is 830 configured by on the 6LBR that originates the context information 831 for the 6LoWPAN. 833 Res, Reserved: This field is unused. It MUST be initialized to zero 834 by the sender and MUST be ignored by the receiver. 836 Valid Lifetime: 16-bit unsigned integer. The length of time in a 837 unit of 60 seconds (relative to the time the packet is received) 838 that the context is valid for the purpose of header compression or 839 decompression. A value of all zero bits (0x0) indicates that this 840 context entry MUST be removed immediately. 842 Context Prefix: The IPv6 prefix or address corresponding to the 843 Context ID (CID) field. The valid length of this field is 844 included in the Context Length field. This field is padded with 845 zeros in order to make the option a multiple of 8-bytes. 847 4.3. Authoritative Border Router Option 849 The optional Authoritative Border Router Option (ABRO) is needed when 850 Router Advertisement (RA) messages are used to disseminate prefixes 851 and context information across a route-over topology. In this case 852 6LRs receive Prefix Information options from other 6LRs. This 853 implies that a 6LR can't just let the most recently received RA win. 854 In order to be able to reliably add and remove prefixes from the 855 6LoWPAN we need to carry information from the authoritative 6LBR. 856 This is done by introducing a version number which the 6LBR sets and 857 6LRs propagate as they propagate the prefix and context information 858 with this Authoritative Border Router Option. When there are 859 multiple 6LBRs they would have separate version number spaces. Thus 860 this option needs to carry the IP address of the 6LBR that originated 861 that set of information. 863 The Authoritative Border Router option MUST be included in all Router 864 Advertisement messages in the case when Router Advertisements are 865 used to propagate information between routers (as described in 866 Section 8.2). 868 0 1 2 3 869 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 1 870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 871 | Type | Length = 3 | Version Number | 872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 873 | Reserved | 874 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 875 | | 876 + + 877 | | 878 + 6LBR Address + 879 | | 880 + + 881 | | 882 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 884 Fields: 886 Type: TBD3 888 Length: 8-bit unsigned integer. The length of the option in 889 units of 8 bytes. Always 3. 891 Version Number: 16-bit unsigned integer. The version number 892 corresponding to this set of information contained in 893 the RA message. The authoritative 6LBR originating 894 the prefix increases this version number each time its 895 set of prefix or context information changes. This 896 version number uses sequence number arithmetic as it 897 may wrap around. 899 Reserved: This field is unused. It MUST be initialized to zero 900 by the sender and MUST be ignored by the receiver. 902 6LBR Address: IPv6 address of the 6LBR that is the origin of the 903 included version number. 905 4.4. Duplicate Address messages 907 For the optional multihop DAD exchanges between 6LR and 6LBR 908 specified in Section 8.2 there are two new ICMPv6 message types 909 called the Duplicate Address Request (DAR) and Duplicate Address 910 Confirmation (DAC). We avoid reusing the Neighbor Solicitation and 911 Neighbor Advertisement messages for this purpose since these messages 912 are not subject to the hop limit=255 check as they are forwarded by 913 intermediate 6LRs. The information contained in the messages are 914 otherwise the same as would be in a Neighbor Solicitation carrying a 915 Address Registration option, with the message format inlining the 916 fields that are in the ARO. 918 The DAR and DAC use the same message format with different ICMPv6 919 type values, and the Status field is only meaningful in the DAC 920 message. 922 0 1 2 3 923 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 1 924 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 925 | Type | Code | Checksum | 926 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 927 | Status | Reserved | Registration Lifetime | 928 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 929 | | 930 + EUI-64 + 931 | | 932 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 933 | | 934 + + 935 | | 936 + Registered Address + 937 | | 938 + + 939 | | 940 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 942 IP fields: 944 IPv6 source: A non link-local address of the sending router. 946 IPv6 destination: A non link-local address of the sending router. 947 In a DAC this is just the source from the DAR. 949 Hop Limit: Set to MULTIHOP_HOPLIMIT on transmit. MUST be ignored 950 on receipt. 952 ICMP Fields: 954 Type: TBD4 for DAR and TBD5 for DAC 956 Code: Set to zero on transmit. MUST be ignored on receipt. 958 Checksum: The ICMP checksum. See [RFC4443]. 960 Status: 8-bit unsigned integer. Indicates the status of a 961 registration in the DAC. MUST be set to 0 in DAR. 962 See Table 1. 964 Reserved: This field is unused. It MUST be initialized to zero 965 by the sender and MUST be ignored by the receiver. 967 Registration Lifetime: 16-bit unsigned integer. The amount of time 968 in a unit of 60 seconds that the router should retain 969 the Neighbor Cache entry for the sender of the NS that 970 includes this option. A value of 0 indicates in an NS 971 that the neighbor cache entry should be removed. 973 EUI-64: 64 bits. This field is used to uniquely identify the 974 interface of the registered address by including the 975 EUI-64 identifier [EUI64] assigned to it unmodified. 977 Registered Address: 128-bit field. Carries the host address, which 978 was contained in the IPv6 Source field in the NS that 979 contained the ARO option sent by the host. 981 5. Host Behavior 983 Hosts in a LoWPAN use the Address Registration option in the Neighbor 984 Solicitation messages they send as a way to maintain the Neighbor 985 Cache in the routers thereby removing the need for multicast Neighbor 986 Solicitations to do address resolution. Unlike in [RFC4861] the 987 hosts initiate updating the information they receive in Router 988 Advertisements by sending Router Solicitations before the information 989 expires. Finally, when Neighbor Unreachability Detection indicates 990 that one or all default routers have become unreachable, then the 991 host uses Router Solicitations to find a new set of default routers. 993 5.1. Forbidden Actions 995 A host MUST NOT multicast a Neighbor Solicitation message. 997 5.2. Interface Initialization 999 When the interface on a host is initialized it follows the 1000 specification in [RFC4861]. A link-local address is formed based on 1001 the EUI-64 identifier [EUI64] assigned to the interface as per 1002 [RFC4944] or the appropriate IP-over-foo document for the link, and 1003 then the host sends Router Solicitation messages as described in 1004 [RFC4861] Section 6.3.7. 1006 There is no need to join the Solicited-Node multicast address since 1007 nobody multicasts Neighbor Solicitations in this type of network. A 1008 host MUST join the all-nodes multicast address. 1010 5.3. Sending a Router Solicitation 1012 The Router Solicitation is formatted as specified in [RFC4861] and 1013 sent to the IPv6 All-Routers multicast address (see [RFC4861] Section 1014 6.3.7 for details). An SLLA option MUST be included to enable 1015 unicast Router Advertisements in response. An unspecified source 1016 address MUST NOT be used in RS messages. 1018 If the link layer supports a way to send packets to some kind of all- 1019 routers anycast link-layer address, then that MAY be used to convey 1020 theses packets to a router. 1022 Since hosts do not depend on multicast Router Advertisements to 1023 discover routers, the hosts need to intelligently retransmit Router 1024 Solicitations whenever the default router list is empty, one of its 1025 default routers becomes unreachable, or the lifetime of the prefixes 1026 and contexts in the previous RA are about to expire. The RECOMMENDED 1027 retransmissions is to initially send up to 3 (MAX_RTR_SOLICITATIONS) 1028 RS messages separated by at least 10 seconds 1029 (RTR_SOLICITATION_INTERVAL) as specified in [RFC4861], and then 1030 switch to slower retransmissions. After the initial retransmissions 1031 the host SHOULD do binary exponential backoff of the retransmission 1032 timer for each subsequent retransmission. However, it is useful to 1033 have a maximum retransmission timer of 60 seconds 1034 (MAX_RTR_SOLICITATION_INTERVAL). In all cases the RS retransmissions 1035 are terminated when a RA is received. 1037 5.4. Processing a Router Advertisement 1039 The processing of Router Advertisements is as in [RFC4861] with the 1040 addition of handling the 6LoWPAN Context option and triggering 1041 address registration when a new address has been configured. 1042 Furthermore, the SLLA option MUST be included in the RA. Unlike in 1043 [RFC4861], the maximum value of the RA Router Lifetime field MAY be 1044 up to 0xFFFF (approximately 18 hours). 1046 Should the host erroneously receive a Prefix Information option with 1047 the 'L' (on-link) flag set, then that Prefix Information Option (PIO) 1048 MUST be ignored. 1050 5.4.1. Address configuration 1052 Address configuration follows [RFC4862]. For an address not derived 1053 from an EUI-64, the M flag of the RA determines how the address can 1054 be configured. If the M flag is set in the RA, then DHCPv6 MUST be 1055 used to assign the address. If the M flag is not set, then the 1056 address can be configured by any other means (and duplicate detection 1057 is performed as part of the registration process). 1059 Once an address has been configured it will be registered by 1060 unicasting a Neighbor Solicitation with the Address Registration 1061 option to one or more routers. 1063 5.4.2. Storing Contexts 1065 The host maintains a conceptual data structure for the context 1066 information it receives from the routers, which is called the Context 1067 Table. This includes the Context ID, the prefix (from the Context 1068 Prefix field in the 6CO), the Compression bit, and the Valid 1069 Lifetime. A Context Table entry that has the Compression bit clear 1070 is used for decompression when receiving packets, but MUST NOT be 1071 used for compression when sending packets. 1073 When a 6CO option is received in a Router Advertisement it is used to 1074 add or update the information in the Context Table. If the Context 1075 ID field in the 6CO matches an existing Context Table entry, then 1076 that entry is updated with the information in the 6CO. If the Valid 1077 Lifetime field in the 6CO is zero, then the entry is immediately 1078 deleted. 1080 If there is no matching entry in the Context Table, and the Valid 1081 Lifetime field is non-zero, then a new context is added to the 1082 Context Table. The 6CO is used to update the created entry. 1084 When the 6LBR changes the context information a host might not 1085 immediately notice. And in the worst case a host might have stale 1086 context information. For this reason 6LBRs use the recommendations 1087 in Section 7.2 for carefully managing the context lifecycle. Nodes 1088 should be careful about using header compression in RA messages that 1089 include 6COs. 1091 5.4.3. Maintaining Prefix and Context Information 1093 The prefix information is timed out as specified in [RFC4861]. When 1094 the Valid Lifetime for a Context Table entry expires the entry is 1095 placed in a receive-only mode, which is the equivalent of receiving a 1096 6CO for that context with C=0. The entry is held in receive-only 1097 mode for a period of twice the Default Router Lifetime, after which 1098 the entry is removed. 1100 A host should inspect the various lifetimes to determine when it 1101 should next initiate sending a Router Solicitation to ask for any 1102 updates to the information. The lifetimes that matter are the 1103 Default Router lifetime, the Valid Lifetime in the Prefix Information 1104 options, and the Valid Lifetime in the 6CO. The host SHOULD unicast 1105 one or more Router Solicitations to the router well before the 1106 minimum of those lifetimes (across all the prefixes and all the 1107 contexts) expire, and switch to multicast RS messages if there is no 1108 response to the unicasts. The retransmission behavior for the Router 1109 Solicitations is specified in Section 5.3. 1111 5.5. Registration and Neighbor Unreachability Detection 1113 Hosts send Unicast Neighbor Solicitation (NS) messages to register 1114 their IPv6 addresses, and also to do NUD to verify that their default 1115 routers are still reachable. The registration is performed by the 1116 host including an ARO in the Neighbor Solicitation it sends. Even if 1117 the host doesn't have data to send, but is expecting others to try to 1118 send packets to the host, the host needs to maintain its Neighbor 1119 Cache entries in the routers. This is done by sending NS messages 1120 with the ARO to the router well in advance of the registration 1121 lifetime expiring. NS messages are retransmitted up to 1122 MAX_UNICAST_SOLICIT times using a minimum timeout of RETRANS_TIMER 1123 until the host receives an Neighbor Advertisement message with an ARO 1124 option. 1126 Hosts that receive Router Advertisement messages from multiple 1127 default routers SHOULD attempt to register with more than one of them 1128 in order to increase the robustness of the network. 1130 Note that Neighbor Unreachability Detection probes can be suppressed 1131 by Reachability Confirmations from transport protocols or 1132 applications as specified in [RFC4861]. 1134 When a host knows it will no longer use a router it is registered to, 1135 it SHOULD de-register with the router by sending an NS with an ARO 1136 containing a lifetime of 0. To handle the case when a host loses 1137 connectivity with the default router involuntarily, the host SHOULD 1138 use a suitably low registration lifetime. 1140 5.5.1. Sending a Neighbor Solicitation 1142 The host triggers sending Neighbor Solicitation (NS) messages 1143 containing an ARO when a new address is configured, when it discovers 1144 a new default router, or well before the Registration Lifetime 1145 expires. Such an NS MUST include a Source Link-Layer Address (SLLA) 1146 option, since the router needs to record the link-layer address of 1147 the host. An unspecified source address MUST NOT be used in NS 1148 messages. 1150 5.5.2. Processing a Neighbor Advertisement 1152 A host handles Neighbor Advertisement messages as specified in 1153 [RFC4861], with added logic described in this section for handling 1154 the Address Registration option. 1156 In addition to the normal validation of a Neighbor Advertisement and 1157 its options, the Address Registration option is verified as follows 1158 (if present). If the Length field is not two, the option is silently 1159 ignored. If the EUI-64 field does not match the EUI-64 of the 1160 interface, the option is silently ignored. 1162 If the status field is zero, then the address registration was 1163 successful. The host saves the Registration Lifetime from the 1164 Address Registration option for use to trigger a new NS well before 1165 the lifetime expires. If the Status field is not equal to zero, the 1166 address registration has failed. 1168 5.5.3. Recovering from Failures 1170 The procedure for maintaining reachability information about a 1171 neighbor is the same as in [RFC4861] Section 7.3 with the exception 1172 that address resolution is not performed. 1174 The address registration procedure may fail for two reasons: no 1175 response to Neighbor Solicitations is received (NUD failure), or an 1176 Address Registration option with a failure Status (Status > 0) is 1177 received. In the case of NUD failure the entry for that router will 1178 be removed thus address registration is no longer of importance. 1179 When an Address Registration option with a non-zero Status field is 1180 received this indicates that registration for that address has 1181 failed. A failure Status of one indicates that a duplicate address 1182 was detected and the procedure described in [RFC4862] Section 5.4.5 1183 is followed. The host MUST NOT use the address it tried to register. 1184 If the host has valid registrations with other routers, these MUST be 1185 removed by registering with each using a zero ARO lifetime. 1187 A Status code of two indicates that the Neighbor Cache of that router 1188 is full. In this case the host SHOULD remove this router from its 1189 default router list and attempt to register with another router. If 1190 the host has no more default routers it needs to revert to sending 1191 Router Solicitations as specified in Section 5.3. 1193 Other failure codes may be defined in future documents. 1195 5.6. Next-hop Determination 1197 The IP address of the next-hop for a destination is determined as 1198 follows. Destinations to the link-local prefix (FE80::) are always 1199 sent on the link to that destination. It is assumed that link-local 1200 addresses are formed as specified in Section 5.2 from the EUI-64, and 1201 address resolution is not performed. 1203 Multicast addresses are considered to be on-link and are resolved as 1204 specified in [RFC4944] or the appropriate IP-over-foo document. Note 1205 that [RFC4944] only defines how to represent a multicast destination 1206 address in the LoWPAN header. Support for multicast scopes larger 1207 than link-local needs an appropriate multicast routing algorithm. 1209 All other prefixes are assumed to be off-link [RFC5889]. Anycast 1210 addresses are always considered to be off-link. They are therefore 1211 sent to one of the routers in the Default Router List. 1213 A LoWPAN Node is not required to maintain a minimum of one buffer per 1214 neighbor as specified in [RFC4861], since packets are never queued 1215 while waiting for address resolution. 1217 5.7. Address Resolution 1219 The address registration mechanism and the SLLA option in Router 1220 Advertisement messages provide sufficient a priori state in routers 1221 and hosts to resolve an IPv6 address to its associated link-layer 1222 address. As all prefixes, except the link-local prefix and multicast 1223 addresses, are always assumed to be off-link, multicast-based address 1224 resolution between neighbors is not needed. 1226 Link-layer addresses for neighbors are stored in Neighbor Cache 1227 entries [RFC4861]. In order to achieve LoWPAN compression, most 1228 global addresses are formed using a link-layer address. Thus a host 1229 can minimize memory usage by optimizing for this case and only 1230 storing link-layer address information if it differs from the link- 1231 layer address corresponding to the Interface ID of the IPv6 address 1232 (i.e., differs in more than the on-link/global bit being inverted). 1234 5.8. Sleeping 1236 It is often advantageous for battery-powered hosts in LoWPANs to keep 1237 a low duty cycle. The optimizations described in this document 1238 enable hosts to sleep as described further in this section. Routers 1239 may want to cache traffic destined to a host which is sleeping, but 1240 such functionality is out of the scope of this document. 1242 5.8.1. Picking an Appropriate Registration Lifetime 1244 As all Neighbor Discovery messages are initiated by the hosts, this 1245 allows a host to sleep or otherwise be unreachable between NS/NA 1246 message exchanges. The Address Registration option attached to NS 1247 messages indicates to a router to keep the Neighbor Cache entry for 1248 that address valid for the period in the Registration Lifetime field. 1249 A host should choose a sleep time appropriate for its energy 1250 characteristics, and set a registration lifetime larger than the 1251 sleep time to ensure the registration is renewed successfully 1252 (considering e.g. clock drift and additional time for potential 1253 retransmissions of the re-registration). A host should also consider 1254 the stability of the network (how quickly the topology changes) when 1255 choosing its sleep time (and thus registration lifetime). A dynamic 1256 network requires a shorter sleep time so that routers don't keep 1257 invalid neighbor cache entries for nodes longer than necessary. 1259 5.8.2. Behavior on Wakeup 1261 When a host wakes up from a sleep period it SHOULD maintain its 1262 current address registrations that will timeout before the next 1263 wakeup. This is done by sending Neighbor Solicitation messages with 1264 the Address Registration option as described in Section 5.5.1. The 1265 host may also need to refresh its prefix and context information by 1266 sending a new unicast Router Solicitation (the maximum Router 1267 Lifetime is about 18 hours whereas the maximum Registration lifetime 1268 is about 45.5 days). If after wakeup the host (using NUD) determines 1269 that some or all previous default routers have become unreachable, 1270 then the host will send multicast Router Solicitations to discover 1271 new default router(s) and restart the address registration process. 1273 6. Router Behavior for 6LR and 6LBR 1275 Both 6LRs and 6LBRs maintain the Neighbor Cache [RFC4861] based on 1276 the Address Registration Options they receive in Neighbor 1277 Advertisement messages from hosts, Neighbor Discovery packets from 1278 other nodes, and potentially a routing protocol used in the 6LoWPAN 1279 as outlined in Section 3.5. 1281 The routers SHOULD NOT garbage collect Registered Neighbor Cache 1282 entries (see Section 3.4) since they need to retain them until the 1283 Registration Lifetime expires. Similarly, if Neighbor Unreachability 1284 Detection on the router determines that the host is UNREACHABLE 1285 (based on the logic in [RFC4861]), the Neighbor Cache entry SHOULD 1286 NOT be deleted but be retained until the Registration Lifetime 1287 expires. A renewed ARO should mark the cache entry as STALE. Thus 1288 for 6LoWPAN Routers the Neighbor Cache doesn't behave like a cache. 1290 Instead it behaves as a registry of all the host addresses that are 1291 attached to the Router. 1293 Routers MAY implement the Default Router Preferences [RFC4191] and 1294 use that to indicate to the host whether the router is a 6LBR or a 1295 6LR. If this is implemented then 6LRs with no route to a border 1296 router MUST set Prf to (11) for low preference, other 6LRs MUST set 1297 Prf to (00) for normal preference, and 6LBRs MUST set Prf to (01) for 1298 high preference. 1300 6.1. Forbidden Actions 1302 A router SHOULD NOT send Redirect messages in a route-over topology, 1303 but MAY send Redirect messages in a mesh-under topology. In route- 1304 over the link has non-transitive reachability and the router has no 1305 way to determine that the recipient of a Redirect message can reach 1306 the link-layer address. 1308 A router MUST NOT set the 'L' (on-link) flag in the Prefix 1309 Information options, since that might trigger hosts to send multicast 1310 Neighbor Solicitations. 1312 6.2. Interface Initialization 1314 A router initializes its interface more or less as in [RFC4861]. 1315 However, a 6LR might want to wait to make its interfaces advertising 1316 (implicitly keeping the AdvSendAdvertisements flag clear) until it 1317 has received the prefix(es) and context information from its 6LBR. 1318 That is independent of whether prefixes and context information is 1319 disseminated using the methods specified in this document, or using 1320 some other method. 1322 6.3. Processing a Router Solicitation 1324 A router processes Router Solicitation messages as specified in 1325 [RFC4861]. The differences relate to the inclusion of Authoritative 1326 Border Router options in the Router Advertisement (RA) messages, and 1327 the exclusive use of unicast Router Advertisements. If a 6LR has 1328 received an ABRO from a 6LBR, then it will include that option 1329 unmodified in the Router Advertisement messages it sends. And if the 1330 6LR has received RAs, whether with the same prefixes and context 1331 information or different, from a different 6LBR, then it will need to 1332 keep those prefixes and context information separately so that the 1333 RAs the 6LR sends will maintain the association between the ABRO and 1334 the prefixes and context information. The router can tell which 6LBR 1335 originated the prefixes and context information from the 6LBR Address 1336 field in the ABRO. When a router has information tied to multiple 1337 ABROs, a single RS will result in multiple RAs each containing a 1338 different ABRO. 1340 A Router Solicitation might be received from a host that has not yet 1341 registered its address with the router. Thus the router MUST NOT 1342 modify an existing Neighbor Cache entry based on the SLLA option from 1343 the Router Solicitation. However, a router MAY create a Tentative 1344 Neighbor Cache entry based on the SLLA option. Such a Tentative 1345 Neighbor Cache entry SHOULD be timed out in TENTATIVE_NCE_LIFETIME 1346 seconds unless a registration converts it into a Registered NCE. 1348 A 6LR or 6LBR MUST include a Source Link-layer address option in the 1349 Router Advertisements it sends. That is required so that the hosts 1350 will know the link-layer address of the router. Unlike in [RFC4861], 1351 the maximum value of the RA Router Lifetime field MAY be up to 0xFFFF 1352 (approximately 18 hours). 1354 Unlike [RFC4861] which suggests multicast Router Advertisements, this 1355 specification optimizes the exchange by always unicasting RAs in 1356 response to RSs. This is possible since the RS always includes a 1357 SLLA option, which is used by the router to unicast the RA. 1359 6.4. Periodic Router Advertisements 1361 A router does not need to send any periodic Router Advertisement 1362 messages since the hosts will solicit updated information by sending 1363 Router Solicitations before the lifetimes expire. 1365 However, if the routers use Router Advertisements to optionally 1366 distribute prefix and/or context information across a route-over 1367 topology, that might require periodic Router Advertisement messages. 1368 Such RAs are sent using the configurable MinRtrAdvInterval and 1369 MaxRtrAdvInterval as per [RFC4861]. 1371 6.5. Processing a Neighbor Solicitation 1373 A router handles Neighbor Solicitation messages as specified in 1374 [RFC4861], with added logic described in this section for handling 1375 the Address Registration option. 1377 In addition to the normal validation of a Neighbor Solicitation and 1378 its options, the Address Registration option is verified as follows 1379 (if present). If the Length field is not two, or if the Status field 1380 is not zero, then the Neighbor Solicitation is silently ignored. 1382 If the source address of the NS is the unspecified address, or if no 1383 SLLA option is included, then any included ARO is ignored, that is, 1384 the NS is processed as if it did not contain an ARO. 1386 6.5.1. Checking for Duplicates 1388 If the NS contains a valid ARO, then the router inspects its Neighbor 1389 Cache on the arriving interface to see if it is a duplicate. If 1390 there is no Neighbor Cache entry for the IPv6 source address of the 1391 NS, then it isn't a duplicate. If there is such a Neighbor Cache 1392 entry and the EUI-64 is the same, then it isn't a duplicate either. 1393 Otherwise it is a duplicate address. Note that if multihop DAD 1394 (Section 8.2) is used then the checks are slightly different to take 1395 into account Tentative Neighbor Cache entries. In the case it is a 1396 duplicate address then the router responds with a unicast Neighbor 1397 Advertisement (NA) message with the ARO Status field set to one (to 1398 indicate the address is a duplicate) as described in Section 6.5.2. 1399 In this case there is no modification to the Neighbor Cache. 1401 6.5.2. Returning Address Registration Errors 1403 Address registration errors are not sent back to the source address 1404 of the NS due to a possible risk of L2 address collision. Instead 1405 the NA is sent to the link-local IPv6 address with the IID part 1406 derived from the EUI-64 field of the ARO as per [RFC4944]. In 1407 particular, this means that the universal/local bit needs to be 1408 inverted. The NA is formatted with a copy of the ARO from the NS, 1409 but with the Status field set to indicate the appropriate error. 1411 6.5.3. Updating the Neighbor Cache 1413 If ARO did not result in a duplicate address being detected as above, 1414 then if the Registration Lifetime is non-zero the router creates (if 1415 it didn't exist) or updates (otherwise) a Neighbor Cache entry for 1416 the IPv6 source address of the NS. If the Neighbor Cache is full and 1417 a new entry needs to be created, then the router responds with a 1418 unicast NA with the ARO Status field set to two (to indicate the 1419 router's Neighbor Cache is full) as described in Section 6.5.2. 1421 The Registration Lifetime and the EUI-64 are recorded in the Neighbor 1422 Cache entry. A unicast Neighbor Advertisement (NA) is then sent in 1423 response to the NS. This NA SHOULD include a copy of the ARO, with 1424 the Status field set to zero. A TLLA (Target Link-layer Address) 1425 option [RFC4861] is not required in the NA, since the host already 1426 knows the router's link-layer address from Router Advertisements. 1428 If the ARO contains a zero Registration Lifetime then any existing 1429 Neighbor Cache entry for the IPv6 source address of the NS MUST be 1430 deleted, and a NA sent as above. 1432 Should the Registration Lifetime in a Neighbor Cache entry expire, 1433 then the router MUST delete the cache entry. 1435 The addition and removal of Registered Neighbor Cache entries would 1436 result in notifying the routing protocol. 1438 Note: If the optional multihop DAD (Section 8.2) is used, then the 1439 updating of the Neighbor Cache is slightly different due to Tentative 1440 NCEs. 1442 6.5.4. Next-hop Determination 1444 In order to deliver a packet destined for a 6LN registered with a 1445 router, next-hop determination is slightly different for routers than 1446 hosts (see Section 5.6. The routing table is checked to determine 1447 the next hop IP address. A registered Neighbor Cache Entry (NCE) 1448 determines if the next hop IP-address is on-link. It is the 1449 responsibility of the routing protocol of the router to maintain on- 1450 link information about its registered neighbors. Tentative NCEs MUST 1451 NOT be used to determine on-link status of the registered nodes. 1453 6.5.5. Address Resolution between Routers 1455 There needs to be a mechanism somewhere for the routers to discover 1456 each others' link-layer addresses. If the routing protocol used 1457 between the routers provides this, then there is no need for the 1458 routers to use the Address Registration option between each other. 1459 Otherwise, the routers MAY use the ARO. When routers use ARO to 1460 register with each other and the optional multihop DAD Section 8.2 is 1461 in use, then care should be taken to ensure that there isn't a flood 1462 of ARO-carrying messages sent to the 6LBR as each router hears an ARO 1463 from their neighboring routers. The details for this is out of scope 1464 of this document. 1466 Optionally Routers can use multicast Neighbor Solicitations as in 1467 [RFC4861] to resolve each others link-layer addresses. Thus Routers 1468 MAY multicast Neighbor Solicitations for other routers, for example 1469 as a result of receiving some routing protocol update. Routers MUST 1470 respond to multicast Neighbor Solicitations. This implies that 1471 Routers MUST join the Solicited-node multicast addresses as specified 1472 in [RFC4861]. 1474 7. Border Router Behavior 1476 A 6LBR handles sending of Router Advertisements and processing of 1477 Neighbor Solicitations from hosts as specified above in section 1478 Section 6. A 6LBR SHOULD always include an Authoritative Border 1479 Router option in the Router Advertisements it sends, listing itself 1480 as the 6LBR Address. That requires that the 6LBR maintain the 1481 version number in stable storage, and increases the version number 1482 when some information in its Router Advertisements change. The 1483 information whose change affects the version are in the Prefix 1484 Information options (the prefixes or their lifetimes) and in the 6CO 1485 option (the prefixes, Context IDs, or lifetimes.) 1487 In addition, a 6LBR is somehow configured with the prefix or prefixes 1488 that are assigned to the LoWPAN, and advertises those in Router 1489 Advertisements as in [RFC4861]. Optionally, in the case of route- 1490 over, those prefixes can be disseminated to all the 6LRs using the 1491 technique in Section 8.1. However, there might be mechanisms outside 1492 of the scope of this document that can be used instead for prefix 1493 dissemination with route-over. 1495 If the 6LoWPAN uses Header Compression [I-D.ietf-6lowpan-hc] with 1496 context then the 6LBR needs to manage the context IDs, and advertise 1497 those in Router Advertisements by including 6CO options in its Router 1498 Advertisements so that directly attached hosts are informed about the 1499 context IDs. Below we specify things to consider when the 6LBR needs 1500 to add, remove, or change the context information. Optionally, in 1501 the case of route-over, the context information can be disseminated 1502 to all the 6LRs using the technique in Section 8. However, there 1503 might be mechanisms outside of the scope of this document that can be 1504 used instead for disseminating context information with route-over. 1506 7.1. Prefix Determination 1508 The prefix or prefixes used in a LoWPAN can be manually configured, 1509 or can be acquired using DHCPv6 Prefix Delegation [RFC3633]. For a 1510 LoWPAN that is isolated from the network, either permanently or 1511 occasionally, the 6LBR can assign a ULA prefix using [RFC4193]. The 1512 ULA prefix should be stored in stable storage so that the same prefix 1513 is used after a failure of the 6LBR. If the LoWPAN has multiple 1514 6LBRs, then they should be configured with the same set of prefixes. 1515 The set of prefixes are included in the Router Advertisement messages 1516 as specified in [RFC4861]. 1518 7.2. Context Configuration and Management 1520 If the LoWPAN uses Header Compression [I-D.ietf-6lowpan-hc] with 1521 context then the 6LBR may be configured with context information and 1522 related context IDs. If the LoWPAN has multiple 6LBRs, then they 1523 MUST be configured with the same context information and context IDs. 1525 The context information carried in Router Advertisement (RA) messages 1526 originate at 6LBRs and must be disseminated to all the routers and 1527 hosts within the LoWPAN. RAs include one 6CO for each context. 1529 For the dissemination of context information using the 6CO, a strict 1530 lifecycle SHOULD be used in order to ensure the context information 1531 stays synchronized throughout the LoWPAN. New context information 1532 SHOULD be introduced into the LoWPAN with C=0, to ensure it is known 1533 by all nodes that may have to decompress based on this context 1534 information. Only when it is reasonable to assume that this 1535 information was successfully disseminated SHOULD an option with C=1 1536 be sent, enabling the actual use of the context information for 1537 compression. 1539 Conversely, to avoid that nodes send packets making use of previous 1540 values of contexts, resulting in ambiguity when receiving a packet 1541 that uses a recently changed context, old values of a context SHOULD 1542 be taken out of use for a while before new values are assigned to 1543 this specific context. That is, in preparation for a change of 1544 context information, its dissemination SHOULD continue for at least 1545 MIN_CONTEXT_CHANGE_DELAY with C=0. Only when it is reasonable to 1546 assume that the fact that the context is now invalid was successfully 1547 disseminated, should the context ID be taken out of dissemination or 1548 reused with a different Context Prefix field. In the latter case, 1549 dissemination of the new value again SHOULD start with C=0, as above. 1551 8. Optional Behavior 1553 Optionally the Router Advertisement messages can be used to 1554 disseminate prefixes and context information to all the 6LRs in a 1555 route-over topology. If all routers are configured to use another 1556 mechanism for such information distribution, this mechanism MAY stay 1557 unused. 1559 There is also the option for a 6LR to perform multihop DAD (for non- 1560 EUI-64 derived IPv6 addresses) against a 6LBR in a route-over 1561 topology by using the DAR and DAC messages. This is optional because 1562 there might be other ways to either allocate unique address, such as 1563 DHCPv6 [RFC3315], or other future mechanisms for multihop DAD. 1565 8.1. Multihop Prefix and Context Distribution 1567 The multihop distribution relies on Router Solicitation messages and 1568 Router Advertisement (RA) messages sent between routers, and using 1569 the ABRO version number to control the propagation of the information 1570 (prefixes and context information) that is being sent in the RAs. 1572 This multihop distribution mechanism can handle arbitrary information 1573 from an arbitrary number of 6LBRs. However, the semantics of the 1574 context information requires that all the 6LNs use the same 1575 information, whether they send, forward, or receive compressed 1576 packets. Thus the manager of the 6LBRs need to somehow ensure that 1577 the context information is in synchrony across the 6LBRs. This can 1578 be handled in different ways. One possible way to ensure it is to 1579 treat the context and prefix information as originating from some 1580 logical or virtual source, which in essence means that it looks like 1581 the information is distributed from a single source. 1583 If a set of 6LBRs behave as a single one (using mechanisms out of 1584 scope of this document) so that the prefixes and contexts and ABRO 1585 version number will be the same from all the 6LBRs, then those 6LBRs 1586 can pick a single IP address to use in the ABRO option. 1588 8.1.1. 6LBRs Sending Router Advertisements 1590 6LBRs supporting multihop prefix and context distribution MUST 1591 include an ABRO in each of its RAs. The ABRO Version Number field is 1592 used to keep prefix and context information consistent throughout the 1593 LoWPAN along with the guidelines in Section 7.2. Each time any 1594 information in the set of PIO or 6CO options change, the ABRO Version 1595 is increased by one. 1597 This requires that the 6LBR maintain the PIO, 6CO, and ABRO Version 1598 Number in stable storage, since an old version number will be 1599 silently ignored by the 6LRs. 1601 8.1.2. Routers Sending Router Solicitations 1603 If multihop distribution is done using Router Advertisement (RA) 1604 messages, then on interface initialization a router SHOULD send some 1605 Router Solicitation messages similarly to how hosts do this in 1606 [RFC4861]. That will cause the routers to respond with RA messages 1607 which then can be used to initially seed the prefix and context 1608 information. 1610 8.1.3. Routers Processing Router Advertisements 1612 If multihop distribution is not done using RA messages, then the 1613 routers follow [RFC4861] which states that they merely do some 1614 consistency checks and nothing in Section 8.1 applies. Otherwise the 1615 routers will check and record the prefix and context information from 1616 the receive RAs, and use that information as follows. 1618 If a received RA does not contain a Authoritative Border Router 1619 option, then the RA MUST be silently ignored. 1621 The router uses the 6LBR Address field in the ABRO to check if it has 1622 previously received information from the 6LBR. If it finds no such 1623 information, then it just records the 6LBR Address and Version and 1624 the associated prefixes and context information. If the 6LBR is 1625 previously known, then the Version number field MUST be compared 1626 against the recorded version number for that 6LBR. The comparison 1627 MUST be done the same way as TCP sequence number comparisons to 1628 handle the case when the version number wraps around. If the version 1629 number received in the packet is less than the stored version number 1630 (following [RFC1982] Section 3.2), then the information in the RA is 1631 silently ignored. Otherwise the recorded information and version 1632 number are updated. 1634 By TCP sequence number comparison we mean that half of the version 1635 number space is "old" and half is "new". For example, if the current 1636 version number is 0x2, then anything between 0x80000003 (0x2- 1637 0x7fffffff) and 0x1 is old, and anything between 0x3 and 0x80000002 1638 (0x2+0x8000000) is new. 1640 8.1.4. Storing the Information 1642 The router keeps state for each 6LBR that it sees with an ABRO. This 1643 includes the version number, and the complete set of Prefix 1644 Information options and 6LoWPAN Context options. The prefixes are 1645 timed out based on the Valid lifetime in the Prefix Information 1646 Option. The Context Prefix is timed out based on the Valid lifetime 1647 in the 6LoWPAN Context option. 1649 While the prefixes and context information are stored in the router 1650 their valid and preferred lifetimes are decremented as time passes. 1651 This ensures that when the router is in turn later advertising that 1652 information in the Router Advertisements it sends, the 'expiry time' 1653 doesn't accidentally move further into the future. For example, if a 1654 6CO with a Valid lifetime of 10 minutes is received at time T, and 1655 the router includes this in a RA it sends at time T+5 minutes, the 1656 Valid lifetime in the 6CO it sends will be only 5 minutes. 1658 8.1.5. Sending Router Advertisements 1660 If multihop distribution is performed using RA messages, then the 1661 routers MUST ensure that the ABRO always stay together with the 1662 prefixes and context information received with that ABRO. Thus if 1663 the router has received prefix P1 with ABRO saying it is from one 1664 6LBR, and prefix P2 from another 6LBR, then the router MUST NOT 1665 include the two prefixes in the same RA message. Prefix P1 MUST be 1666 in a RA that include a ABRO from the first 6LBR etc. Note that 1667 multiple 6LBRs might advertise the same prefix and context 1668 information, but they still need to be associated with the 6LBRs that 1669 advertised them. 1671 The routers periodically send Router Advertisements as in [RFC4861]. 1672 This is for the benefit of the other routers receiving the prefixes 1673 and context information. And the routers also respond to Router 1674 Solicitations by unicasting RA messages. In both cases the above 1675 constraint of keeping the ABRO together with 'its' prefixes and 1676 context information apply. 1678 When a router receives new information from a 6LBR, that is, either 1679 it hears from a new 6LBR (a new 6LBR Address in the ABRO) or the ABRO 1680 version number of an existing 6LBR has increased, then it is useful 1681 to send out a few triggered updates. The recommendation is to behave 1682 the same as when an interface has become an advertising interface in 1683 [RFC4861], that is, send up to three RA messages. This ensures rapid 1684 propagation of new information to all the 6LRs. 1686 8.2. Multihop Duplicate Address Detection 1688 The ARO can be used, in addition to registering an address in a 6LR, 1689 to have the 6LR verify that the address isn't used by some other host 1690 known to the 6LR. However, that isn't sufficient in a route-over 1691 topology (or in a LoWPAN with multiple 6LBRs) since some host 1692 attached to another 6LR could be using the same address. There might 1693 be different ways for the 6LRs to coordinate such Duplicate Address 1694 Detection in the future, or addresses could be assigned using a 1695 DHCPv6 server that verifies uniqueness as part of the assignment. 1697 This specification offers an optional and simple technique for 6LRs 1698 and 6LBRs to perform Duplicate Address Detection that reuses the 1699 information from Address Registration option in the DAR and DAC 1700 messages. This technique is not needed when the Interface ID in the 1701 address is based on an EUI-64, since those are assumed to be globally 1702 unique. The technique assumes that the 6LRs either register with all 1703 the 6LBRs, or that the network uses some out-of-scope mechanism to 1704 keep the DAD tables in the 6LBRs synchronized. 1706 The multihop DAD mechanism is used synchronously the first time an 1707 address is registered with a particular 6LR. That is, the ARO option 1708 is not returned to the host until multihop DAD has been completed 1709 against the 6LBRs. For existing registrations in the 6LR the 1710 multihop DAD needs to be repeated against the 6LBRs to ensure that 1711 the entry for the address in the 6LBRs does not time out, but that 1712 can be done asynchronously with the response to the hosts. For 1713 instance, by tracking how much is left of the lifetime the 6LR 1714 registered with the 6LBRs and re-registering with the 6LBR when this 1715 lifetime is about to run out. 1717 For the synchronous multihop DAD the 6LR performs some additional 1718 checks to ensure that it has a Neighbor Cache entry it can use to 1719 respond to the host when it receives a response from a 6LBR. This 1720 consists of checking for an already existing (Tentative or 1721 Registered) Neighbor Cache entry for the registered address with a 1722 different EUI-64. If such a Registered NCE exists, then the 6LR 1723 SHOULD respond that the address is a duplicate. If such a Tentative 1724 NCE exists, then the 6LR SHOULD silently ignore the ARO thereby 1725 relying on the host retransmitting the ARO. This is needed to handle 1726 the case when multiple hosts try to register the same IPv6 address at 1727 the same time. If no Neighbor Cache entry exists, then the 6LR MUST 1728 create a Tentative Neighbor Cache entry with the EUI-64 and the SLLA 1729 option. This entry will be used to send the response to the host 1730 when the 6LBR responds positively. 1732 When a 6LR receives a Neighbor Solicitation containing an Address 1733 Registration option with a non-zero Registration Lifetime and it has 1734 no existing Registered Neighbor Cache entry, then with this mechanism 1735 the 6LR will invoke synchronous multihop DAD. 1737 The 6LR will unicast a Duplicate Address Request message to one or 1738 more 6LBRs, where the DAR contains the host's address in the 1739 Registered Address field. The DAR will be forwarded by 6LRs until it 1740 reaches the 6LBR, hence its IPv6 hop limit field will not be 255 when 1741 received by the 6LBR. The 6LBR will respond with a Duplicate Address 1742 Confirmation message, which will have a hop limit less than 255 when 1743 it reaches the 6LR. 1745 When the 6LR receives the DAC from the 6LBR, it will look for a 1746 matching (same IP address and EUI-64) (Tentative or Registered) 1747 Neighbor Cache entry. If no such entry is found then the DAC is 1748 silently ignored. If an entry is found and the DAC had Status=0 then 1749 the 6LR will mark the Tentative Neighbor Cache entry as Registered. 1750 In all cases when an entry is found then the 6LR will respond to the 1751 host with an NA, copying the Status and EUI-64 fields from the DAC to 1752 an ARO option in the NA. In case the status is an error, then the 1753 destination IP address of the NA is derived from the EUI-64 field of 1754 the DAC. 1756 A Tentative Neighbor Cache entry SHOULD be timed out 1757 TENTATIVE_NCE_LIFETIME seconds after it was created in order to allow 1758 for another host to attempt to register the IPv6 address. 1760 8.2.1. Message Validation for DAR and DAC 1762 A node MUST silently discard any received Duplicate Address Request 1763 and Confirmation messages that do not satisfy all of the following 1764 validity checks: 1766 o If the message includes an IP Authentication Header, the message 1767 authenticates correctly. 1769 o ICMP Checksum is valid. 1771 o ICMP Code is 0. 1773 o ICMP length (derived from the IP length) is 32 or more bytes. 1775 o The Registered Address is not a multicast address. 1777 o All included options have a length that is greater than zero. 1779 o The IP source address is not the unspecified address, nor a 1780 multicast address. 1782 The contents of the Reserved field, and of any unrecognized options, 1783 MUST be ignored. Future, backward-compatible changes to the protocol 1784 may specify the contents of the Reserved field or add new options; 1785 backward-incompatible changes may use different Code values. 1787 Note that due to the forwarding of the DAR and DAC messages between 1788 the 6LR and 6LBR there is no hop limit check on receipt for these 1789 ICMPv6 message types. 1791 8.2.2. Conceptual Data Structures 1793 A 6LBR implementing the optional multihop DAD needs to maintain some 1794 state separate from the Neighbor Cache. We call this conceptual data 1795 structure the DAD table. It is indexed by the IPv6 address - the 1796 Registered Address in the DAR - and contains the EUI-64 and the 1797 registration lifetime of the host that is using that address. 1799 8.2.3. 6LR Sending a Duplicate Address Request 1801 When a 6LR that implements the optional multihop DAD receives an NS 1802 from a host and subject to the above checks, the 6LR forms and sends 1803 a DAR to at least one 6LBR. The DAR contains the following 1804 information: 1806 o In the IPv6 source address, a global address of the 6LR. 1808 o In the IPv6 destination address, the address of the 6LBR. 1810 o In the IPv6 hop limit, MULTIHOP_HOPLIMIT. 1812 o The Status field MUST be set to zero 1814 o The EUI-64 and Registration lifetime are copied from the ARO 1815 received from the host. 1817 o The Registered Address set to the IPv6 address of the host, that 1818 is, the sender of the triggering NS. 1820 When a 6LR receives an NS from a host with a zero Registration 1821 Lifetime then, in addition to removing the Neighbor Cache entry for 1822 the host as specified in Section 6, an DAR is sent to the 6LBRs as 1823 above. 1825 A router MUST NOT modify the Neighbor Cache as a result of receiving 1826 a Duplicate Address Request. 1828 8.2.4. 6LBR Receiving a Duplicate Address Request 1830 When a 6LBR that implements the optional multihop DAD receives an DAR 1831 from a 6LR, it performs the message validation specified in 1832 Section 8.2.1. If the DAR is valid the 6LBR proceeds to look for the 1833 Registration Address in the DAD Table. If an entry is found and the 1834 recorded EUI-64 is different than the EUI-64 in the DAR, then it 1835 returns a DAC NA with the Status set to 1 ('Duplicate Address'). 1836 Otherwise it returns a DAC with Status set to zero and updates the 1837 lifetime. 1839 If no entry is found in the DAD Table and the Registration Lifetime 1840 is non-zero, then an entry is created and the EUI-64 and Registered 1841 Address from the DAR are stored in that entry. 1843 If an entry is found in the DAD Table, the EUI-64 matches, and the 1844 Registration Lifetime is zero then the entry is deleted from the 1845 table. 1847 In both of the above cases the 6LBR forms an DAC with the information 1848 copied from the DAR and the Status field is set to zero. The DAC is 1849 sent back to the 6LR i.e., back to the source of the DAR. The IPv6 1850 hop limit is set to MULTIHOP_HOPLIMIT 1852 8.2.5. Processing a Duplicate Address Confirmation 1854 When a 6LR that implements the optional multihop DAD receives a DAC 1855 message, then it first validates the message per Section 8.2.1. For 1856 a valid DAC, if there is no Tentative Neighbor Cache entry matching 1857 the Registered address and EUI-64, then the DAC is silently ignored. 1858 Otherwise, the information in the DAC and in the Tentative Neighbor 1859 Cache entry is used to form an NA to send to the host. The Status 1860 code is copied from the DAC to the ARO that is sent to the host. In 1861 case of the DAC indicates an error (the Status is non-zero), the NA 1862 is returned to the host as described in Section 6.5.2 and the 1863 Tentative Neighbor Cache entry for the Registered Address is removed. 1864 Otherwise it is made into a Registered Neighbor Cache entry. 1866 A router MUST NOT modify the Neighbor Cache as a result of receiving 1867 a Duplicate Address Confirmation, unless there is a Tentative 1868 Neighbor Cache entry matching the IPv6 address and EUI-64. 1870 8.2.6. Recovering from Failures 1872 If there is no response from a 6LBR after RETRANS_TIMER [RFC4861] 1873 then the 6LR would retransmit the DAR to the 6LBR up to 1874 MAX_UNICAST_SOLICIT [RFC4861] times. After this the 6LR SHOULD 1875 respond to the host with an ARO Status of zero. 1877 9. Protocol Constants 1879 This section defines the relevant protocol constants used in this 1880 document based on a subset of [RFC4861] constants. (*) indicates 1881 constants modified from [RFC4861] and (+) indicates new constants. 1883 Additional protocol constants are defined in Section 4. 1885 6LBR Constants: 1887 MIN_CONTEXT_CHANGE_DELAY+ 300 seconds 1889 6LR Constants: 1891 MAX_RTR_ADVERTISEMENTS 3 transmissions 1893 MIN_DELAY_BETWEEN_RAS* 10 seconds 1895 MAX_RA_DELAY_TIME* 2 seconds 1897 TENTATIVE_NCE_LIFETIME+ 20 seconds 1899 Router Constants: 1901 MULTIHOP_HOPLIMIT+ 64 1903 Host Constants: 1905 RTR_SOLICITATION_INTERVAL* 10 seconds 1907 MAX_RTR_SOLICITATIONS 3 transmissions 1909 MAX_RTR_SOLICITATION_INTERVAL+ 60 seconds 1911 10. Examples 1913 10.1. Message Examples 1915 STEP 1917 6LN 6LR 1919 | | 1921 1. | ---------- Router Solicitation --------> | 1923 | [SLLAO] | 1925 | | 1927 2. | <-------- Router Advertisement --------- | 1929 | [PIO + 6CO + ABRO + SLLAO] | 1931 Figure 2: Basic Router Solicitation/Router Advertisement exchange 1932 between a node and 6LR or 6LBR 1934 6LN 6LR 1936 | | 1938 1. | ------- NS with Address Registration ------> | 1940 | [ARO + SLLAO] | 1942 | | 1944 2. | <----- NA with Address Registration -------- | 1946 | [ARO with Status] | 1948 Figure 3: Neighbor Discovery Address Registration 1950 6LN 6LR 6LBR 1952 | | | 1954 1. | --- NS with Address Reg --> | | 1956 | [ARO + SLLAO] | | 1958 | | | 1960 2. | | ----------- DAR ----------> | 1962 | | | 1964 3. | | <---------- DAC ----------- | 1966 | | | 1968 4. | <-- NA with Address Reg --- | | 1970 | [ARO with Status] | 1972 Figure 4: Neighbor Discovery Address Registration with Multi-Hop DAD 1974 10.2. Host Bootstrapping Example 1976 The following example describes the address bootstrapping scenarios 1977 using the optimized ND mechanisms specified in this document. It is 1978 assumed that the 6LN first performs a sequence of operations in order 1979 to get secure access at the link-layer of the LoWPAN and obtain a key 1980 for link-layer security. The methods of how to establish the link- 1981 layer security is out of scope of this document. In this example an 1982 IEEE 802.15.4 6LN forms a 16-bit short-address based IPv6 addresses 1983 without using DHCPv6 (i.e., the M flag is not set in the Router 1984 Advertisements). 1986 1. After obtaining link-level security, a 6LN assigns a link-local 1987 IPv6 address to itself. A link-local IPv6 address is configured 1988 based on the 6LN's EUI-64 link-layer address formed as per [RFC4944]. 1990 2. Next the 6LN determines one or more default routers in the 1991 network by sending an RS to the all-routers multicast address with 1992 the SLLA Option set to its EUI-64 link-local address. If the 6LN was 1993 able to obtain the link-layer address of a router through its link- 1994 layer operations then the 6LN may form a link-local destination IPv6 1995 address for the router and send it a unicast RS. The 6LR responds 1996 with a unicast RA to the IP source using the SLLA option from the RS 1997 (it may have created a tentative NCE). See Figure 2. 1999 3. In order to communicate more than one IP hop away the 6LN 2000 configures a global IPv6 address. In order to save overhead, this 2001 6LN wishes to configure its IPv6 address based on a 16-bit short 2002 address as per [RFC4944]. As the network is unmanaged (M flag not 2003 set in RA), the 6LN randomly chooses a 16-bit link-layer address and 2004 forms a tentative IPv6 address from it. 2006 4. Next the 6LN registers that address with one or more of its 2007 default routers by sending a unicast NS message with an ARO 2008 containing its tentative global IPv6 address to register, the 2009 registration lifetime and its EUI-64. An SLLA option is also 2010 included with the link-layer address corresponding to the address 2011 being registered. If a successful (status 0) NA message is received 2012 the address can then be used and the 6LN assumes it has been 2013 successfully checked for duplicates. If a duplicate address (status 2014 1) NA message is received, the 6LN then removes the temporary IPv6 2015 address and 16-bit link-layer address and goes back to step 3. If a 2016 neighbor cache full (status 2) message is received, the 6LN attempts 2017 to register with another default router, or if none, goes back to 2018 step 2. See Figure 3. Note that an NA message returning an error 2019 would be sent back to the link-local EUI-64 based IPv6 address of the 2020 6LN instead of the 16-bit (duplicate) address. 2022 5. The 6LN now performs maintenance by sending a new NS address 2023 registration before the lifetime expires. 2025 If multihop DAD and multihop prefix and context distribution is used, 2026 the effect of the 6LRs and hosts following the above bootstrapping is 2027 a "wavefront" of 6LRs and host being configured spreading from the 2028 6LBRs. First the hosts and 6LRs that can directly reach a 6LBR would 2029 receive one or more RAs and configure and register their IPv6 2030 addresses. Once that is done they would enable the routing protocol 2031 and start sending out Router Advertisements. That would result in a 2032 new set of 6LRs and hosts to receive responses to their Router 2033 Solicitations, form and register their addresses, etc. That repeats 2034 until all of the 6LRs and hosts have been configured. 2036 10.2.1. Host Bootstrapping Messages 2038 This section brings specific message examples to the previous 2039 bootstrapping process. When discussing messages, the following 2040 notation is used: 2042 LL64: Link-Local Address based on the EUI-64, which is also the 2043 802.15.4 Long Address. 2045 GP16: Global Address based on the 802.15.4 Short Address. This 2046 address may not be unique. 2048 GP64: Global addresses derived from the EUI-64 address as specified 2049 in RFC 4944. 2051 MAC64: EUI-64 address used as the link-layer address. 2053 MAC16: IEEE 802.15.4 16-bit short address. 2055 Note that some implementations may use LL64 and GP16 style addresses 2056 instead of LL64 and GP64. In the following, we will show an example 2057 message flow as to how a node uses LL64 to register a GP16 address 2058 for multihop DAD verification. 2060 6LN-----RS-------->6LR 2061 Src= LL64 (6LN) 2062 Dst= All-router-link-scope-multicast 2063 SLLAO= MAC64 (6LN) 2065 6LR------RA--------->6LN 2066 Src= LL64 (6LR) 2067 Dst= LL64 (6LN) 2069 Note: Source address of RA must be a link-local 2070 address (Section 4.2, RFC 4861). 2072 6LN-------NS Reg------>6LR 2073 Src= GP16 (6LN) 2074 Dst= LL64 (6LR) 2075 ARO 2076 SLLAO= MAC16 (6LN) 2078 6LR---------DAR----->6LBR 2079 Src= GP64 or GP16 (6LR) 2080 Dst= GP64 or GP16 (6LBR) 2081 Registered Address= GP16 (6LN) and EUI-64 (6LN) 2083 6LBR-------DAC--------->6LR 2084 Src= GP64 or GP16 (6LBR) 2085 Dst= GP64 or GP16 (6LR) 2086 Copy of information from DAR 2088 If Status is a Success: 2090 6LR ---------NA-Reg------->6LN 2091 Src= LL64 (6LR) 2092 Dst= GP16 (6LN) 2093 ARO with Status = 0 2095 If Status is not a success: 2097 6LR ---------NA-Reg-------->6LN 2098 Src= LL64 (6LR) 2099 Dst= LL64 (6LN) --> Derived from the EUI-64 of ARO 2100 ARO with Status > 0 2102 Figure 5: Detailed Message Address Examples 2104 10.3. Router Interaction Example 2106 In the Route-over topology, when a routing protocol is run across 2107 6LRs the bootstrapping and neighbor cache management are handled a 2108 little differently. The description in this paragraph provides only 2109 a guideline for an implementation. 2111 At the initialization of a 6LR, it may choose to bootstrap as a host 2112 with the help of a parent 6LR if the optional multihop DAD is 2113 performed with the 6LBR. The neighbor cache management of a router 2114 and address resolution among the neighboring routers are described in 2115 Section 6.5.3 and Section 6.5.5, respectively. In this example, we 2116 assume that the neighboring 6LoWPAN link is secure. 2118 10.3.1. Bootstrapping a Router 2120 In this scenario, the bootstrapping 6LR, 'R1', is multiple hops away 2121 from the 6LBR and surrounded by other 6LR neighbors. Initially R1 2122 behaves as a host. It sends multicast RS and receives an RA from one 2123 or more neighboring 6LRs. R1 picks one 6LR as its temporary default 2124 router and performs address resolution via this default router. 2125 Note, if multihop DAD is not required (e.g. in a managed network or 2126 using EUI-64 based addresses) then it does not need to pick a 2127 temporary default router, however it may still want to send the 2128 initial RS message if it wants to autoconfigure its address with the 2129 global prefix disseminated by the 6LBR. 2131 Based on the information received in the RAs, R1 updates its cache 2132 with entries for all the neighboring 6LRs. Upon completion of the 2133 address registration, the bootstrapping router deletes the temporary 2134 entry of the default router and the routing protocol is started. 2136 Also note that R1 may refresh its multihop DAD registration directly 2137 with the 6LBR (using the next hop neighboring 6LR determined by the 2138 routing protocol for reaching the 6LBR). 2140 10.3.2. Updating the Neighbor Cache 2142 In this example, there are three 6LRs, R1, R2, R3. Initially when R2 2143 boots it sees only R1, and accordingly R2 creates a neighbor cache 2144 entry for R1. Now assume R2 receives a valid routing update from 2145 router R3. R2 does not have any neighbor cache entry for R3. If the 2146 implementation of R2 supports detecting link-layer address from the 2147 routing information packets then it directly updates the its neighbor 2148 cache using that link-layer information. If this is not possible, 2149 then R2 should perform multicast NS with source set with its link- 2150 local or global address depending on the scope of the source IP- 2151 address received in the routing update packet. The target address of 2152 the NS message is the source IPv6 address of the received routing 2153 update packet. The format of the NS message is as described in 2154 Section 4.3 of [RFC4861]. 2156 More generally any 6LR that receives a valid route-update from a 2157 neighboring router for which it does not have any neighbor cache 2158 entry is required to update its neighbor cache as described above. 2160 The router (6LR and 6LBR) IP-addresses learned via Neighbor Discovery 2161 are not redistributed to the routing protocol. 2163 11. Security Considerations 2165 The security considerations of IPv6 Neighbor Discovery [RFC4861] 2166 apply. Additional considerations can be found in [RFC3756]. 2168 This specification expects that the link layer is sufficiently 2169 protected, for instance using MAC sublayer cryptography. In other 2170 words, model 1 from [RFC3756] applies. In particular, it is expected 2171 that the LoWPAN MAC provides secure unicast to/from Routers and 2172 secure broadcast from the Routers in a way that prevents tampering 2173 with or replaying the Router Advertisement messages. However, any 2174 future 6LoWPAN security protocol that applies to Neighbor Discovery 2175 for 6LoWPAN protocol, is out of scope of this document. 2177 The multihop DAD mechanisms rely on DAR and DAC messages that are 2178 forwarded by 6LRs, and as a result the hop_limit=255 check on the 2179 receiver does not apply to those messages. This implies that any 2180 node on the Internet could successfully send such messages. We avoid 2181 any additional security issues due to this by requiring that the 2182 routers never modify the Neighbor Cache entry due to such messages, 2183 and that they reject them unless they are received on an interface 2184 that has been explicitly configured to use these optimizations. 2186 In some future deployments one might want to use SEcure Neighbor 2187 Discovery [RFC3971] [RFC3972]. This is possible with the Address 2188 Registration option as sent between hosts and routers, since the 2189 address that is being registered is the IPv6 source address of the 2190 Neighbor Solicitation and SeND verifies the IPv6 source address of 2191 the packet. Applying SeND to the optional router-to-router 2192 communication in this document is out of scope. 2194 12. IANA Considerations 2196 The document requires three new Neighbor Discovery option types under 2197 the subregistry "IPv6 Neighbor Discovery Option Formats": 2199 o Address Registration Option (TBD1) 2201 o 6LoWPAN Context Option (TBD2) 2203 o Authoritative Border Router Option (TBD3) 2205 The document requires two new ICMPv6 types under the subregistry 2206 "ICMPv6 type Numbers": 2208 o Duplicate Address Request (TBD4) 2210 o Duplicate Address Confirmation (TBD5) 2212 For the purpose of protocol interoperability testing of this 2213 specification, the following values are being used temporarily: 2215 o TBD1 = 31 2217 o TBD2 = 32 2219 o TBD3 = 33 2221 o TBD4 = 155 XXX 2223 o TBD3 = 156 XXX 2225 This document also requests IANA to create a new registry for the 2226 Status values of the Address Registration Option. 2228 [TO BE REMOVED: This registration should take place at the following 2229 location: http://www.iana.org/assignments/icmpv6-parameters] 2231 13. Guideline for New Features 2233 This section discusses a guideline of new features for implementation 2234 and deployment. 2236 +----------+---------------------------------+----------+-----------+ 2237 | Section | Description | deploy | implement | 2238 +----------+---------------------------------+----------+-----------+ 2239 | 3.1 | Host initiated RA | MUST | MUST | 2240 | 3.2 | EUI-64 based IPv6-address | MUST | MUST | 2241 | | 16bit-MAC based address | MAY | SHOULD | 2242 | | Other non-unique addresses | MAY | MAY | 2243 | 3.3 | Host Initiated RS | MUST | MUST | 2244 | | ABRO Processing | SHOULD | MUST | 2245 | 4.1 | Registration with ARO | MUST | MUST | 2246 | 4.2, 5.4 | 6lowpan Context Option | SHOULD | SHOULD | 2247 | 5.1 | Re-direct Message Acceptance | MUST NOT | MUST NOT | 2248 | | Joining Solicited Node | N/A | N/A | 2249 | | Multicast | | | 2250 | | Joining all-node Multicast | MUST | MUST | 2251 | | Using link-layer indication for | SHOULD | MAY | 2252 | | NUD | | | 2253 | 5.5 | 6lowpan-ND NUD | MUST | MUST | 2254 | 5.8.2 | Behavior on wake-up | SHOULD | SHOULD | 2255 +----------+---------------------------------+----------+-----------+ 2257 Table 2: Guideline for 6LoWPAN-ND features for hosts 2259 +---------------+-------------------------+------------+------------+ 2260 | Section | Description | deploy | implement | 2261 +---------------+-------------------------+------------+------------+ 2262 | 3.1 | Periodic RA | SHOULD NOT | SHOULD NOT | 2263 | 3.2 | Address assignment | SHOULD | MUST | 2264 | | during Startup | | | 2265 | 3.3 | Supporting EUI-64 based | MUST | MUST | 2266 | | MAC Hosts | | | 2267 | | Supporting 16-bit MAC | MAY | SHOULD | 2268 | | hosts | | | 2269 | 3.4, 4.3, | ABRO Processing/sending | MAY | SHOULD | 2270 | 8.1.3, 8.1.4 | | | | 2271 | 8.1 | Multihop Prefix storing | MAY | SHOULD | 2272 | | and re-distribution | | | 2273 | 3.5 | Tentative NCE | MUST | MUST | 2274 | 8.2 | Multihop DAD | MAY | SHOULD | 2275 | 4.1, 6.5, | ARO Support | MUST | MUST | 2276 | 6.5.1 - 6.5.5 | | | | 2277 | 4.2 | 6LoWPAN Context Option | SHOULD | SHOULD | 2278 | 6.3 | Process RS/ARO | MUST | MUST | 2279 +---------------+-------------------------+------------+------------+ 2281 Table 3: Guideline for 6LR features in 6LoWPAN-ND 2283 +--------------+--------------------------+------------+------------+ 2284 | Section | Description | deploy | implement | 2285 +--------------+--------------------------+------------+------------+ 2286 | 3.1 | Periodic RA | SHOULD NOT | SHOULD NOT | 2287 | 3.2 | Address autoconf on | MUST NOT | MUST NOT | 2288 | | Router interface | | | 2289 | 3.3 | EUI-64 MAC support on | MUST | MUST | 2290 | | 6lowpan interface | | | 2291 | 8.1 - 8.1.1, | Multihop Prefix | MAY | SHOULD | 2292 | 8.1.5 | distribution | | | 2293 | 8.2 | Multihop DAD | MAY | SHOULD | 2294 +--------------+--------------------------+------------+------------+ 2296 Table 4: Guideline for 6LBR features in 6LoWPAN-ND 2298 14. Acknowledgments 2300 The authors thank Pascal Thubert, Jonathan Hui, Carsten Bormann, 2301 Richard Kelsey, Geoff Mulligan, Julien Abeille, Alexandru Petrescu, 2302 Peter Siklosi, Pieter De Mil, Fred Baker, Anthony Schoofs, Phil 2303 Roberts, Daniel Gavelle, Joseph Reddy, Robert Cragie, Mathilde Durvy, 2304 Colin O'Flynn, Dario Tedeschi, Esko Dijk and Joakim Eriksson for 2305 useful discussions and comments that have helped shaped and improve 2306 this document. 2308 Additionally, the authors would like to recognize Carsten Bormann for 2309 the suggestions on the Context Prefix Option and contribution to 2310 earlier version of the draft, Pascal Thubert for contribution of the 2311 original registration idea and extensive contributions to earlier 2312 versions of the draft, Jonathan Hui for original ideas on prefix/ 2313 context distribution and extensive contributions to earlier versions 2314 of the draft, Colin O'Flynn for useful Error-to suggestions and 2315 contributions to the Examples section, Geoff Mulligan for suggesting 2316 the use of Address Registration as part of existing IPv6 Neighbor 2317 Discovery messages, and Mathilde Durvy for helping to clarify router 2318 interaction. 2320 15. Changelog 2322 Changes from -16 to -17: 2324 o Removed unnecessary normative text from Assumptions. 2326 o Clarified the next-hop determination of multicast addresses. 2328 o Editorial improvements from WGLC review. 2330 Changes from -15 to -16: 2332 o Added an applicability section (#133) 2334 o Updated document title to align with HC 2336 o Minor editing as result of WGLC review (#134) 2338 Changes from -14 to -15: 2340 o Changed use of redirect to SHOULD NOT for route-over and MAY for 2341 mesh-under. (#130) 2343 o Changed the 16-bit lifetimes to a unit of 60 seconds (#131) 2345 o Added text to Section 5.4.2 adding a receive-only state to 2346 context entries that timeout. (#132) 2348 Changes from -13 to -14: 2350 o Introduced the new DAR and DAC ICMPv6 message types for multihop 2351 DAD to avoid relying on the Length=4 checks for the ARO. This 2352 simplifies implementing the hop limit check. 2354 o Clarified the hop limit values for the multihop DAD messages by 2355 introducing the MULTIHOP_HOPLIMIT constant set to 64. 2357 o Clarified when a host should de-register from a router. 2359 o Added a section on next-hop determination for routers. 2361 o Removed the infinite lifetime from 6CO. 2363 o Increased MIN_CONTEXT_CHANGE_DELAY to 300 seconds. 2365 Changes from -12 to -13: 2367 o Error-to solution added for returning NA messages carrying an 2368 error ARO option to the link-local EUI-64 based IPv6 address of 2369 the host (#126). 2371 o New examples added. 2373 Changes from -11 to -12: 2375 o Version field of ABRO moved after Length for 32-bit alignment of 2376 the reserved space (#90). 2378 o Several clarifications were made on router interaction, 2379 including a new section with router interaction examples (#91). 2381 o Temporary Neighbor Cache Entry created upon host sending NS+ARO, 2382 and SLLAO removed from multihop DAD NS/NA messages (#87). 2384 Changes from -10 to -11: 2386 o Reference to RFC1982 for version number comparison (#80) 2388 o RA Router Lifetime field use clarified (#81) 2390 o Make fields 16-bit rather than 32-bit where possible (#83) 2392 o Unicast RA clarification (#84) 2394 o Temporary ND option types (#85) 2396 o SLLA/TLLA clarification (#86) 2398 o GP16 as source address in initial NS clarification (#87) 2400 Changes from -09 to -10: 2402 o Clarifications made to Section 8.2 (#66) 2404 o Explained behavior of Neighbor Cache (#67) 2406 o Clarified use of SLLAO in RS and NS messages (#68) 2408 o Added new term 6LN (#69) 2410 o Small clarification on 6CO flag (#70) 2412 o Defined host behavior on ARO failure better (#72) 2414 o Added bootstrapping example for a host (#73) 2416 o Added new Neighbor Cache Full ARO error (#74) 2418 o Added rule on the use of the M flag (#75) 2420 Changes from -08 to -09: 2422 o Clean re-write of the draft (re-use of some introductory 2423 material) 2425 o Merged in draft-chakrabarti-6lowpan-ipv6-nd-simple-00 2427 o Changed address registration to an option piggybacked on NS/NA 2429 o New Authoritative Border Router option 2431 o New Address Registration Option 2433 o Separated Prefix Information and Content Information 2435 o Optional DAD to the edge 2437 Changes from -07 to -08: 2439 o Removed Extended LoWPAN and Whiteboard related sections. 2441 o Included reference to the autoconf addressing model. 2443 o Added Optimistic Flag to 6AO. 2445 o Added guidelines on routers performing DAD. 2447 o Removed the NR/NC Advertising Interval. 2449 o Added assumption of uniform IID formation and DAD throughout a 2450 LoWPAN. 2452 Changes from -06 to -07: 2454 o Updated addressing and address resolution (#60). 2456 o Changed the Address Option to 6LoWPAN Address Option, fixed S 2457 values (#61). 2459 o Added support for classic RFC4861 RA Prefix Information messages 2460 to be processed (#62). 2462 o Added a section on using 6LoWPAN-ND under a hard-wired RFC4861 2463 stack (#63). 2465 o Updated the NR/NC message with a new Router flag, combined the 2466 Code and Status fields into one byte, and added the capability to 2467 carry 6IOs (#64). 2469 o Made co-existence with other ND mechanisms clear (#59). 2471 o Added a new Protocol Specification section with all mechanisms 2472 specified there (#59). 2474 o Removed dependencies and conflicts with RFC4861 wherever 2475 possible (#59). 2477 o Some editorial cleanup. 2479 Changes from -05 to -06: 2481 o Fixed the Prf codes (#52). 2483 o Corrected the OIIO TID field to 8-bits. Changed the Nonce/OII 2484 order in both the OIIO and the NR/NC. (#53) 2486 o Corrected an error in Table 1 (#54). 2488 o Fixed asymmetric and a misplaced transient in the 6LoWPAN 2489 terminology section. 2491 o Added Updates RFC4861 to header 2493 Changes from -04 to -05: 2495 o Meaning of the RA's M-bit changed to original [RFC4861] meaning 2496 (#46). 2498 o Terms "on-link" and "off-link" used in place of "on-link" and 2499 "off-link". 2501 o Next-hop determination text simplified (#49). 2503 o Neighbor cache and destination cache removed. 2505 o IID to link-layer address requirement relaxed. 2507 o NR/NC changes to enable on-link refresh with routers (#48). 2509 o Modified 6LoWPAN Information Option (#47). 2511 o Added a Protocol Constants section (#24) 2513 o Added the NR processing table (#51) 2515 o Considered the use of SeND on backbone NS/NA messages (#50) 2517 Changes from -03 to -04: 2519 o Moved Ad-hoc LoWPAN operation to Section 7 and made ULA prefix 2520 generation a features useful also in Simple and Extended LoWPANs. 2521 (#41) 2523 o Added a 32-bit Owner Nonce to the NR/NC messages and the 2524 Whiteboard, removed the TID history. (#39) 2526 o Improved the duplicate OII detection algorithm using the Owner 2527 Nonce. (#39) 2529 o Clarified the use of Source and Target link-layer options in 2530 NR/NC. (#43) 2532 o Included text on the use of alternative methods to acquire 2533 addresses. (#38) 2535 o Removed S=2 from Address Option (not needed). (#36) 2537 o Added a section on router dissemination consistency. (#44) 2539 o Small improvements and extensive editing. (#42, #37, #35) 2541 Changes from -02 to -03: 2543 o Updated terminology, with RFC4861 non-transitive link model. 2545 o 6LoWPAN and ND terminology separated. 2547 o Protocol overview explains RFC4861 diff in detail. 2549 o RR/RC is now Node Registration/Confirmation (NR/NC). 2551 o Added NR failure codes. 2553 o ER Metric now included in 6LoWPAN Summary Option for use in 2554 default router determination by hosts. 2556 o Examples of host data structures, and the Whiteboard given. 2558 o Whiteboard is supported by all Edge Routers for option 2559 simplicity. 2561 o Edge Router Specification chapter re-structured, clarifying 2562 optional Extended LoWPAN operation. 2564 o NS/NA now completely optional for nodes. No address resolution 2565 or NS/NA NUD required. 2567 o link-local operation now compatible with oDAD (was broken). 2569 o Exception to hop limit = 255 for NR/NC messages. 2571 o Security considerations improved. 2573 o ICMPv6 destination unreachable supported. 2575 Changes from -01 to -02: 2577 o Fixed 16 != 0xff bug (ticket closed). 2579 o Specified use of ULAs in ad-hoc LoWPAN section 9 (ticket 2580 closed). 2582 o Terminology cleanup based on Alex's comments. 2584 o General editing improvements. 2586 Changes from -00 to -01: 2588 o Specified the duplicate owner interface identifier procedures. 2589 A TID lollipop algorithm was sufficient (nonce unnecessary). 2591 o Defined fault tolerance using secondary bindings. 2593 o Defined ad-hoc network operation. 2595 o Removed the E flag from RA and the X flag from RR/RC. 2597 o Completed message examples. 2599 o Lots of improvements in text quality and consistency were made. 2601 16. References 2603 16.1. Normative References 2605 [EUI64] "GUIDELINES FOR 64-BIT GLOBAL IDENTIFIER (EUI-64) 2606 REGISTRATION AUTHORITY", . 2609 [RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, 2610 August 1996. 2612 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2613 Requirement Levels", BCP 14, RFC 2119, March 1997. 2615 [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an 2616 IANA Considerations Section in RFCs", BCP 26, RFC 2434, 2617 October 1998. 2619 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2620 (IPv6) Specification", RFC 2460, December 1998. 2622 [RFC2491] Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6 2623 over Non-Broadcast Multiple Access (NBMA) networks", 2624 RFC 2491, January 1999. 2626 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 2627 More-Specific Routes", RFC 4191, November 2005. 2629 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 2630 Addresses", RFC 4193, October 2005. 2632 [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control 2633 Message Protocol (ICMPv6) for the Internet Protocol 2634 Version 6 (IPv6) Specification", RFC 4443, March 2006. 2636 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2637 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2638 September 2007. 2640 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2641 Address Autoconfiguration", RFC 4862, September 2007. 2643 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 2644 "Transmission of IPv6 Packets over IEEE 802.15.4 2645 Networks", RFC 4944, September 2007. 2647 [RFC5889] Baccelli, E. and M. Townsley, "IP Addressing Model in Ad 2648 Hoc Networks", RFC 5889, September 2010. 2650 16.2. Informative References 2652 [I-D.ietf-6lowpan-hc] 2653 Hui, J. and P. Thubert, "Compression Format for IPv6 2654 Datagrams in Low Power and Lossy Networks (6LoWPAN)", 2655 draft-ietf-6lowpan-hc-15 (work in progress), 2656 February 2011. 2658 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 2659 and M. Carney, "Dynamic Host Configuration Protocol for 2660 IPv6 (DHCPv6)", RFC 3315, July 2003. 2662 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 2663 Host Configuration Protocol (DHCP) version 6", RFC 3633, 2664 December 2003. 2666 [RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor 2667 Discovery (ND) Trust Models and Threats", RFC 3756, 2668 May 2004. 2670 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 2671 Neighbor Discovery (SEND)", RFC 3971, March 2005. 2673 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 2674 RFC 3972, March 2005. 2676 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 2677 over Low-Power Wireless Personal Area Networks (6LoWPANs): 2678 Overview, Assumptions, Problem Statement, and Goals", 2679 RFC 4919, August 2007. 2681 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 2682 Extensions for Stateless Address Autoconfiguration in 2683 IPv6", RFC 4941, September 2007. 2685 Authors' Addresses 2687 Zach Shelby (editor) 2688 Sensinode 2689 Hallituskatu 13-17D 2690 Oulu 90100 2691 FINLAND 2693 Phone: +358407796297 2694 Email: zach@sensinode.com 2696 Samita Chakrabarti 2697 Ericsson 2699 Email: samita.chakrabarti@ericsson.com 2700 Erik Nordmark 2701 Cisco Systems 2703 Email: nordmark@cisco.com