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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'SLLAO' is mentioned on line 1917, but not defined ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) -- Obsolete informational reference (is this intentional?): RFC 3315 (Obsoleted by RFC 8415) -- Obsolete informational reference (is this intentional?): RFC 3633 (Obsoleted by RFC 8415) -- Obsolete informational reference (is this intentional?): RFC 4941 (Obsoleted by RFC 8981) Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 5 comments (--). 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: April 26, 2012 E. Nordmark 7 Cisco Systems 8 October 24, 2011 10 Neighbor Discovery Optimization for Low Power and Lossy Networks 11 (6LoWPAN) 12 draft-ietf-6lowpan-nd-18 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. The 27 document, thus updates RFC 4944 to specify the use of the 28 optimizations defined here. 30 Status of this Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on April 26, 2012. 47 Copyright Notice 48 Copyright (c) 2011 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 1.1. The Shortcomings of IPv6 Neighbor Discovery . . . . . . . 5 65 1.2. Mesh-under and Route-over Concepts . . . . . . . . . . . . 6 66 1.3. Applicability . . . . . . . . . . . . . . . . . . . . . . 7 67 1.4. Goals and Assumptions . . . . . . . . . . . . . . . . . . 7 68 1.5. Optional Features . . . . . . . . . . . . . . . . . . . . 9 69 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 9 70 3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 11 71 3.1. Extensions to RFC4861 . . . . . . . . . . . . . . . . . . 11 72 3.2. Address Assignment . . . . . . . . . . . . . . . . . . . . 12 73 3.3. Host-to-Router Interaction . . . . . . . . . . . . . . . . 12 74 3.4. Router-to-Router Interaction . . . . . . . . . . . . . . . 13 75 3.5. Neighbor Cache Management . . . . . . . . . . . . . . . . 14 76 4. New Neighbor Discovery Options and Messages . . . . . . . . . 15 77 4.1. Address Registration Option . . . . . . . . . . . . . . . 15 78 4.2. 6LoWPAN Context Option . . . . . . . . . . . . . . . . . . 17 79 4.3. Authoritative Border Router Option . . . . . . . . . . . . 18 80 4.4. Duplicate Address messages . . . . . . . . . . . . . . . . 20 81 5. Host Behavior . . . . . . . . . . . . . . . . . . . . . . . . 21 82 5.1. Forbidden Actions . . . . . . . . . . . . . . . . . . . . 21 83 5.2. Interface Initialization . . . . . . . . . . . . . . . . . 21 84 5.3. Sending a Router Solicitation . . . . . . . . . . . . . . 22 85 5.4. Processing a Router Advertisement . . . . . . . . . . . . 22 86 5.4.1. Address configuration . . . . . . . . . . . . . . . . 23 87 5.4.2. Storing Contexts . . . . . . . . . . . . . . . . . . . 23 88 5.4.3. Maintaining Prefix and Context Information . . . . . . 23 89 5.5. Registration and Neighbor Unreachability Detection . . . . 24 90 5.5.1. Sending a Neighbor Solicitation . . . . . . . . . . . 24 91 5.5.2. Processing a Neighbor Advertisement . . . . . . . . . 25 92 5.5.3. Recovering from Failures . . . . . . . . . . . . . . . 25 93 5.6. Next-hop Determination . . . . . . . . . . . . . . . . . . 26 94 5.7. Address Resolution . . . . . . . . . . . . . . . . . . . . 26 95 5.8. Sleeping . . . . . . . . . . . . . . . . . . . . . . . . . 26 96 5.8.1. Picking an Appropriate Registration Lifetime . . . . . 27 97 5.8.2. Behavior on Wakeup . . . . . . . . . . . . . . . . . . 27 98 6. Router Behavior for 6LR and 6LBR . . . . . . . . . . . . . . . 27 99 6.1. Forbidden Actions . . . . . . . . . . . . . . . . . . . . 28 100 6.2. Interface Initialization . . . . . . . . . . . . . . . . . 28 101 6.3. Processing a Router Solicitation . . . . . . . . . . . . . 28 102 6.4. Periodic Router Advertisements . . . . . . . . . . . . . . 29 103 6.5. Processing a Neighbor Solicitation . . . . . . . . . . . . 29 104 6.5.1. Checking for Duplicates . . . . . . . . . . . . . . . 30 105 6.5.2. Returning Address Registration Errors . . . . . . . . 30 106 6.5.3. Updating the Neighbor Cache . . . . . . . . . . . . . 30 107 6.5.4. Next-hop Determination . . . . . . . . . . . . . . . . 31 108 6.5.5. Address Resolution between Routers . . . . . . . . . . 31 109 7. Border Router Behavior . . . . . . . . . . . . . . . . . . . . 31 110 7.1. Prefix Determination . . . . . . . . . . . . . . . . . . . 32 111 7.2. Context Configuration and Management . . . . . . . . . . . 32 112 8. Optional Behavior . . . . . . . . . . . . . . . . . . . . . . 33 113 8.1. Multihop Prefix and Context Distribution . . . . . . . . . 33 114 8.1.1. 6LBRs Sending Router Advertisements . . . . . . . . . 34 115 8.1.2. Routers Sending Router Solicitations . . . . . . . . . 34 116 8.1.3. Routers Processing Router Advertisements . . . . . . . 34 117 8.1.4. Storing the Information . . . . . . . . . . . . . . . 35 118 8.1.5. Sending Router Advertisements . . . . . . . . . . . . 35 119 8.2. Multihop Duplicate Address Detection . . . . . . . . . . . 36 120 8.2.1. Message Validation for DAR and DAC . . . . . . . . . . 37 121 8.2.2. Conceptual Data Structures . . . . . . . . . . . . . . 38 122 8.2.3. 6LR Sending a Duplicate Address Request . . . . . . . 38 123 8.2.4. 6LBR Receiving a Duplicate Address Request . . . . . . 39 124 8.2.5. Processing a Duplicate Address Confirmation . . . . . 39 125 8.2.6. Recovering from Failures . . . . . . . . . . . . . . . 40 126 9. Protocol Constants . . . . . . . . . . . . . . . . . . . . . . 40 127 10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 128 10.1. Message Examples . . . . . . . . . . . . . . . . . . . . . 41 129 10.2. Host Bootstrapping Example . . . . . . . . . . . . . . . . 42 130 10.2.1. Host Bootstrapping Messages . . . . . . . . . . . . . 43 131 10.3. Router Interaction Example . . . . . . . . . . . . . . . . 46 132 10.3.1. Bootstrapping a Router . . . . . . . . . . . . . . . . 46 133 10.3.2. Updating the Neighbor Cache . . . . . . . . . . . . . 46 134 11. Security Considerations . . . . . . . . . . . . . . . . . . . 47 135 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47 136 13. Guideline for New Features . . . . . . . . . . . . . . . . . . 48 137 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 50 138 15. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 50 139 16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 56 140 16.1. Normative References . . . . . . . . . . . . . . . . . . . 56 141 16.2. Informative References . . . . . . . . . . . . . . . . . . 57 142 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 58 144 1. Introduction 146 The IPv6-over-IEEE 802.15.4 [RFC4944] document specifies how IPv6 is 147 carried over an IEEE 802.15.4 network with the help of an adaptation 148 layer which sits between the MAC layer and the IP network layer. A 149 link in a LoWPAN is characterized as lossy, low-power, low bit-rate, 150 short range, with many nodes saving energy with long sleep periods. 151 Multicast as used in IPv6 Neighbor Discovery [RFC4861] is not 152 desirable in such a wireless low-power and lossy network. Moreover, 153 LoWPAN links are asymmetric and non-transitive in nature. A LoWPAN 154 is potentially composed of a large number of overlapping radio 155 ranges. Although a given radio range has broadcast capabilities, the 156 aggregation of these is a complex Non-Broadcast MultiAccess (NBMA, 157 [RFC2491]) structure with generally no LoWPAN-wide multicast 158 capabilities. Link-local scope is in reality defined by reachability 159 and radio strength. Thus we can consider a LoWPAN to be made up of 160 links with undetermined connectivity properties as in [RFC5889], 161 along with the corresponding address model assumptions defined 162 therein. 164 This specification introduces the following optimizations to IPv6 165 Neighbor Discovery [RFC4861] specifically aimed at low-power and 166 lossy networks such as LoWPANs: 168 o Host-initiated interactions to allow for sleeping hosts. 170 o Elimination of multicast-based address resolution for hosts. 172 o A host address registration feature using a new option in unicast 173 Neighbor Solicitation and Neighbor Advertisement messages. 175 o A new Neighbor Discovery option to distribute 6LoWPAN header 176 compression context to hosts. 178 o Optional multihop distribution of prefix and 6LoWPAN header 179 compression context. 181 o Optional multihop duplicate address detection which uses two new 182 ICMPv6 message types. 184 The document defines three new ICMPv6 message options: the required 185 Address Registration option and the optional Authoritative Border 186 Router and 6LoWPAN Context options. It also defines two new ICMPv6 187 message types: the Duplicate Address Request and Duplicate Address 188 Confirmation. 190 1.1. The Shortcomings of IPv6 Neighbor Discovery 192 IPv6 Neighbor Discovery [RFC4861] provides several important 193 mechanisms used for Router Discovery, Address Resolution, Duplicate 194 Address Detection, Redirect, along with Prefix and Parameter 195 Discovery. 197 Following power-on and initialization of the network in IPv6 Ethernet 198 networks, a node joins the solicited-node multicast address on the 199 interface and then performs Duplicate Address Detection (DAD) for the 200 acquired link-local address by sending a solicited-node multicast 201 message to the link. After that it sends multicast messages to the 202 all-router address to solicit router advertisements. If the host 203 receives a valid Router Advertisement with the "A" flag, it 204 autoconfigures the IPv6 address with the advertised prefix in the 205 Router Advertisement (RA) message. Besides this, the IPv6 routers 206 usually send router advertisements periodically on the network. RAs 207 are sent to the all-node multicast address. Nodes send Neighbor 208 Solicitation/Neighbor Advertisement messages to resolve the IPv6 209 address of the destination on the link. The Neighbor Solicitation 210 messages used for address resolution are multicast. The Duplicate 211 Address Detection procedure and the use of periodic Router 212 Advertisement messages assumes that the nodes are powered on and 213 reachable most of the time. 215 In Neighbor Discovery the routers find the hosts by assuming that a 216 subnet prefix maps to one broadcast domain, and then multicast 217 Neighbor Solicitation messages to find the host and its link-layer 218 address. Furthermore, the DAD use of multicast assumes that all 219 hosts that autoconfigure IPv6 addresses from the same prefix can be 220 reached using link-local multicast messages. 222 Note that the 'L' (on-link) bit in the Prefix Information option can 223 be set to zero in Neighbor Discovery, which makes the host not use 224 multicast Neighbor Solicitation (NS) messages for address resolution 225 of other hosts, but routers still use multicast NS messages to find 226 the hosts. 228 In a LoWPAN, primarily two types of network topologies are found - 229 star networks and mesh networks. A star network is similar to a 230 regular IPv6 subnet with a router and a set of nodes connected to it 231 via the same non-transitive link. But in Mesh networks, the nodes 232 are capable of routing and forwarding packets. Due to the lossy 233 nature of wireless communication and a changing radio environment, 234 the IPv6-link node-set may change due to external physical factors. 235 Thus the link is often unstable and the nodes appear to be moving 236 without necessarily moving physically. 238 A LoWPAN can use two types of link-layer addresses; 16-bit short 239 addresses and 64-bit unique addresses as defined in [RFC4944]. 240 Moreover, the available link-layer payload size is on the order of 241 less than 100 bytes thus header compression is very useful. 243 Considering the above characteristics in a LoWPAN, and the IPv6 244 Neighbor Discovery [RFC4861] protocol design center, some 245 optimizations and extensions to Neighbor Discovery are useful for the 246 wide deployment of IPv6 over low-powered and lossy networks such as 247 6LoWPANs. 249 1.2. Mesh-under and Route-over Concepts 251 In the 6LoWPAN context, often a link-layer mesh routing mechanism is 252 referred to as "mesh-under" while routing/forwarding packets using 253 IP-layer addresses is referred to as "route-over". The difference 254 between mesh-under and route-over is similar to a bridged-network 255 versus IP-routing using Ethernet. In a mesh-under network all nodes 256 are on the same link which is served by one or more routers, which we 257 call 6LoWPAN Border Routers (6LBR). In a route-over network, there 258 are multiple links in the 6LoWPAN. Unlike fixed IP links, these 259 link's members may be changing due to the nature of the low-power and 260 lossy behavior of wireless technology. Thus a route-over network is 261 made up of a flexible set of links interconnected by interior 262 routers, which we call 6LoWPAN Routers (6LR). 264 This specification is applicable to both mesh-under and route-over 265 networks. However, in route-over networks, we have two types of 266 routers - 6LBRs and 6LRs. 6LoWPAN Border Routers sit at the boundary 267 of the 6LoWPAN and the rest of the network while 6LoWPAN Routers are 268 inside the LoWPAN. 6LoWPAN Routers are assumed to be running a 269 routing protocol. 271 In a mesh-under configuration a 6LBR is acting as the IPv6 router 272 where all the hosts in the LoWPAN are on the same link, thus they are 273 only one IP hop away. No 6LoWPAN Routers exist in this topology as 274 forwarding is handled by a link-layer mesh routing protocol. 276 In a route-over configuration, Neighbor Discovery operations take 277 place between hosts and 6LRs or 6LBRs. The 6LR nodes are able to 278 send and receive Router Advertisements, Router Solicitations as well 279 as forward and route IPv6 packets. Here packet forwarding happens at 280 the IP layer. 282 In both types of configurations, hosts do not take part in routing 283 and forwarding packets and they act as simple IPv6 hosts. 285 1.3. Applicability 287 In its Section 1, [RFC4861] foresees a document that covers operating 288 IP over a particular link type and defines an exception to the 289 otherwise general applicability of unmodified RFC 4861. The present 290 specification optimizes the usage of IPv6 Neighbor Discovery for 291 LoWPANs in order to save energy and processing power of such nodes. 292 The document, thus updates RFC 4944 to specify the use of the 293 optimizations defined here. 295 The applicability of this specification is limited to LoWPANs where 296 all nodes on the subnet implement these optimizations in a 297 homogeneous way. Although it is noted that some of these 298 optimizations may be useful outside of 6LoWPAN, for example in 299 general IPv6 low-power and lossy networks and possibly even in 300 combination with [RFC4861], the usage of such combinations is out of 301 scope of this document. 303 In this document, we specify a set of behaviors between hosts and 304 routers in LoWPANs. An implementation that adheres to this document 305 MUST implement those behaviors. The document also specifies a set of 306 behaviors (multihop prefix or context dissemination, and separately 307 multihop duplicate address detection) which are OPTIONAL to use. An 308 implementation of this specification SHOULD implement those optional 309 to use pieces. 311 The optimizations described in this document apply to different 312 topologies. They are most useful for route-over and mesh-under 313 configurations in Mesh topologies. However, Star topology 314 configurations will also benefit from the optimizations due to 315 minimized signaling, robust handling of the non-transitive link, and 316 header compression context information. 318 1.4. Goals and Assumptions 320 The document has the following main goals and assumptions. 322 Goals: 324 o Optimize Neighbor Discovery with a mechanism that is minimal yet 325 sufficient for the operation in both mesh-under and route-over 326 configurations. 328 o Minimize signaling by avoiding the use of multicast flooding and 329 reducing the use of link-scope multicast messages. 331 o Optimize the interfaces between hosts and their default routers. 333 o Support for sleeping hosts. 335 o Disseminate context information to hosts as needed by 336 [I-D.ietf-6lowpan-hc]. 338 o Optionally disseminate context information and prefix information 339 from the border to all routers in a LoWPAN. 341 o Optional duplicate address detection mechanism suitable for route- 342 over LoWPANs. 344 Assumptions: 346 o EUI-64 addresses are globally unique. 348 o All nodes in the network have an EUI-64 interface identifier in 349 order to do address auto-configuration and detect duplicate 350 addresses. 352 o The link layer technology is assumed to be low-power and lossy, 353 exhibiting undetermined connectivity, such as IEEE 802.15.4 354 [RFC4944]. However, the Address Registration mechanism might be 355 useful for other link layer technologies. 357 o A 6LoWPAN is configured to share one or more global IPv6 address 358 prefixes to enable hosts to move between routers in the 6LoWPAN 359 without changing their IPv6 addresses. 361 o When using the optional DAD mechanism of Section 8.2 it is assumed 362 that 6LRs register with all the 6LBRs. 364 o If IEEE 802.15.4 16-bit short addresses are used, then some 365 technique is used to ensure uniqueness of those link-layer 366 addresses. That could be done using DHCPv6, the Address 367 Registration Option based duplicate address detection (specified 368 in Section 8.2) or other techniques outside of the scope of this 369 document. 371 o In order to preserve the uniqueness of addresses not derived from 372 an EUI-64, they must be either assigned or checked for duplicates 373 in the same way throughout the LoWPAN. This can be done using 374 DHCPv6 for assignment and/or using the duplicate address detection 375 mechanism specified in Section 8.2 (or any other protocols 376 developed for that purpose). 378 o In order for [I-D.ietf-6lowpan-hc] to operate correctly, the 379 compression context must match for all the hosts, 6LRs, and 6LBRs 380 that can send, receive, or forward a given packet. If Section 8.1 381 is used to distribute context information this implies that all 382 the 6LBRs must coordinate the context information they distribute 383 within a single 6LoWPAN. 385 o This specification describes the operation of ND within a single 386 LoWPAN. The participation of a node in multiple LoWPANs 387 simultaneously may be possible, but is out of scope of this 388 document. 390 o Since the 6LoWPAN shares one single prefix throughout the network, 391 mobility of nodes within the LoWPAN is transparent. Inter-LoWPAN 392 mobility is out-of-scope of this document. 394 1.5. Optional Features 396 This document defines the optimization of Neighbor Discovery messages 397 host-router interfaces and introduces the communication in case of 398 Route-over topology. The multihop prefix distribution by the 6LBR 399 and multihop Duplicate Address Detection mechanisms, as well as 400 6LoWPAN context option are optional features for a 6LoWPAN 401 deployment. A guideline for feature implementation and deployment is 402 provided at the end of the document. 404 2. Terminology 406 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 407 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 408 document are to be interpreted as described in [RFC2119]. 410 This specification requires readers to be familiar with all the terms 411 and concepts that are discussed in "Neighbor Discovery for IP version 412 6" [RFC4861] "IPv6 Stateless Address Autoconfiguration" [RFC4862], 413 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 414 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 415 "Transmission of IPv6 Packets over IEEE 802.15.4 Networks" [RFC4944] 416 and "IP Addressing Model in Ad Hoc Networks" [RFC5889]. 418 This specification makes extensive use of the same terminology 419 defined in [RFC4861] unless otherwise defined below. 421 6LoWPAN link: 422 A wireless link determined by single IP hop reachability of 423 neighboring nodes. These are considered links with undetermined 424 connectivity properties as in [RFC5889]. 426 6LoWPAN Node (6LN): 427 A 6LoWPAN Node is any host or router participating in a LoWPAN. 428 This term is used when referring to situations in which either a 429 host or router can play the role described. 431 6LoWPAN Router (6LR): 432 An intermediate router in the LoWPAN who can communicate with 433 other 6LoWPAN routers in the same LoWPAN. 6LoWPAN routers are 434 present only in route-over topologies. 436 6LoWPAN Border Router (6LBR): 437 A border router located at the junction of separate 6LoWPAN 438 networks or between a 6LoWPAN network and another IP network. 439 There may be one or more 6LBRs at the 6LoWPAN network boundary. A 440 6LBR is the responsible authority for IPv6 Prefix propagation for 441 the 6LoWPAN network it is serving. An isolated LoWPAN also 442 contains a 6LBR in the network, which provides the prefix(es) for 443 the isolated network. 445 Router: 446 Either a 6LR or a 6LBR. Note that nothing in this document 447 precludes a node being a router on some interfaces and a host on 448 other interfaces as allowed by [RFC2460]. 450 Mesh-under: 451 A topology where hosts are connected to a 6LBR through a mesh 452 using link-layer forwarding. Thus in a mesh-under configuration 453 all IPv6 hosts in a LoWPAN are only one IP hop away from the 6LBR. 454 This topology simulates the typical IP-subnet topology with one 455 router with multiple nodes in the same subnet. 457 Route-over: 458 A topology where hosts are connected to the 6LBR through the use 459 of intermediate layer-3 (IP) routing. Here hosts are typically 460 multiple IP hops away from a 6LBR. The route-over topology 461 typically consists of a 6LBR, a set of 6LRs and hosts. 463 Registration: 464 The process during which a LoWPAN node sends an Neighbor 465 Solicitation message with an Address Registration option to a 466 Router creating a Neighbor Cache entry for the LoWPAN node with a 467 specific timeout. Thus for 6LoWPAN Routers the Neighbor Cache 468 doesn't behave like a cache. Instead it behaves as a registry of 469 all the host addresses that are attached to the Router. 471 3. Protocol Overview 473 These Neighbor Discovery optimizations are applicable to both mesh- 474 under and route-over configurations. In a mesh-under configuration 475 only 6LoWPAN Border Routers and hosts exist; there are no 6LoWPAN 476 routers in mesh-under topologies. 478 The most important part of the optimizations is the evolved host-to- 479 router interaction that allows for sleeping nodes and avoids using 480 multicast Neighbor Discovery messages except for the case of a host 481 finding an initial set of default routers, and redoing such 482 determination when that set of routers have become unreachable. 484 The protocol also provides for header compression 485 [I-D.ietf-6lowpan-hc] by carrying header compression information in a 486 new option in Router Advertisement messages. 488 In addition, there are optional and separate mechanisms that can be 489 used between 6LRs and 6LBRs to perform multihop Duplicate Address 490 Detection and distribution of the Prefix and compression Context 491 information from the 6LBRs to all the 6LRs, which in turn use normal 492 Neighbor Discovery mechanisms to convey this information to the 493 hosts. 495 The protocol is designed so that the host-to-router interaction is 496 not affected by the configuration of the 6LoWPAN; the host-to-router 497 interaction is the same in a mesh-under and route-over configuration. 499 3.1. Extensions to RFC4861 501 This document specifies the following optimizations and extensions to 502 IPv6 Neighbor Discovery [RFC4861]: 504 o Host initiated refresh of Router Advertisement information. This 505 removes the need for periodic or unsolicited Router Advertisements 506 from routers to hosts. 508 o No Duplicate Address Detection (DAD) is performed if EUI-64 based 509 IPv6 addresses are used (as these addresses are assumed to be 510 globally unique). 512 o DAD is optional if DHCPv6 is used to assign addresses. 514 o A New Address Registration mechanism using a new Address 515 Registration option between hosts and routers. This removes the 516 need for Routers to use multicast Neighbor Solicitations to find 517 hosts, and supports sleeping hosts. This also enables the same 518 IPv6 address prefix(es) to be used across a route-over 6LoWPAN. 520 It provides the host-to-router interface for Duplicate Address 521 Detection. 523 o A new optional Router Advertisement option for Context information 524 used by 6LoWPAN header compression. 526 o A new optional mechanism to perform Duplicate Address Detection 527 across a route-over 6LoWPAN using the new Duplicate Address 528 Request and Confirmation messages. 530 o New optional mechanisms to distribute Prefixes and Context 531 information across a route-over network which uses a new 532 Authoritative Border Router option to control the flooding of 533 configuration changes. 535 o A few new default protocol constants are introduced and some 536 existing Neighbor Discovery protocol constants are tuned. 538 3.2. Address Assignment 540 Hosts in a 6LoWPAN configure their IPv6 address as specified in 541 [RFC4861] and [RFC4862] based on the information received in Router 542 Advertisement messages. The use of the M flag in this optimization 543 is however more restrictive than in [RFC4861]. When the M flag is 544 set a host is required to use DHCPv6 to assign any non-EUI-64 545 addresses. When the M flag is not set, the LoWPAN is required to 546 support duplicate address detection, thus a host can then safely use 547 the address registration mechanism to check non-EUI-64 addresses for 548 uniqueness. 550 6LRs MAY use the same mechanisms to configure their IPv6 addresses. 552 The 6LBRs are responsible for managing the prefix(es) assigned to the 553 6LoWPAN, using manual configuration, DHCPv6 Prefix Delegation 554 [RFC3633], or other mechanisms. In an isolated LoWPAN a ULA 555 [RFC4193] prefix SHOULD be generated by the 6LBR. 557 3.3. Host-to-Router Interaction 559 A host sends Router Solicitation messages at startup and also when it 560 suspects that one of its default routers has become unreachable 561 (after Neighbor Unreachability Detection towards the router fails). 563 Hosts receive Router Advertisement messages typically containing the 564 Authoritative Border Router option (ABRO) and may optionally contain 565 one or more 6LoWPAN Context options (6CO) in addition to the existing 566 Prefix Information options (PIO) as described in [RFC4861]. 568 When a host has configured a non-link-local IPv6 address, it 569 registers that address with one or more of its default routers using 570 the Address Registration option (ARO) in an NS message. The host 571 chooses a lifetime of the registration and repeats the ARO option 572 periodically (before the lifetime runs out) to maintain the 573 registration. The lifetime should be chosen in such a way as to 574 maintain the registration even while a host is sleeping. Likewise, 575 mobile nodes that change their point of attachment often, should use 576 a suitably short lifetime. 578 The registration can fail (an ARO option returned to the host with a 579 non-zero Status) if the router determines that the IPv6 address is 580 already used by another host, that is, is used by a host with a 581 different EUI-64. This can be used to support non-EUI-64 based 582 addresses such as temporary IPv6 addresses [RFC4941] or addresses 583 based on an Interface ID that is a IEEE 802.15.4 16-bit short 584 addresses. Failure can also occur if the Neighbor Cache on that 585 router is full. 587 The re-registration of an address can be combined with Neighbor 588 Unreachability Detection (NUD) of the router since both use unicast 589 Neighbor Solicitation messages. This makes things efficient when a 590 host wakes up to send a packet and both need to perform NUD to check 591 that the router is still reachable, and refresh its registration with 592 the router. 594 The response to an address registration might not be immediate since 595 in route-over configurations the 6LR might perform Duplicate Address 596 Detection against the 6LBR. A host retransmits the Address 597 Registration option until it is acknowledged by the receipt of a 598 Address Registration option. 600 As part of the optimizations, Address Resolution is not performed by 601 multicasting Neighbor Solicitation messages as in [RFC4861]. 602 Instead, the routers maintain Neighbor Cache entries for all 603 registered IPv6 addresses. If the address is not in the Neighbor 604 Cache in the router, then the address either doesn't exist, or is 605 assigned to a host attached to some other router in the 6LoWPAN, or 606 is external to the 6LoWPAN. In a route-over configuration the 607 routing protocol is used to route such packets toward the 608 destination. 610 3.4. Router-to-Router Interaction 612 The optional new router-to-router interaction is only for the route- 613 over configuration where 6LRs are present. It is optional in this 614 protocol since the functions it provides might be better provided by 615 other protocol mechanisms, be it DHCPv6, link-layer mechanisms, the 616 routing protocol, or something else. It is however assumed that all 617 6LRs in a network are configured to perform these functions 618 homogeneously. Some mechanisms from this protocol might be used for 619 router-to-router interaction, while others are provided by other 620 protocols. For instance, context information and/or prefix 621 information might be disseminated using this protocol, while 622 Duplicate Address Detection is done using some other protocol. 624 6LRs MAY act like a host during system startup and prefix 625 configuration by sending Router Solicitation messages and 626 autoconfiguring their IPv6 addresses unlike routers in [RFC4861]. 628 When multihop prefix or context dissemination is used then the 6LRs 629 store the ABRO, 6CO and Prefix Information received (directly or 630 indirectly) from the 6LBRs and redistribute this information in the 631 Router Advertisement they send to other 6LRs or send to hosts in 632 response to a Router Solicitations. There is a version number field 633 in the ABRO which is used to limit the flooding of updated 634 information between the 6LRs. 636 Optionally the 6LRs can perform Duplicate Address Detection against 637 one or more 6LBRs using the new Duplicate Address Request (DAR) and 638 Confirmation (DAC) messages, which carry the information from the 639 Address Registration option. The DAR and DAC messages will be 640 forwarded between the 6LR and 6LBRs thus the [RFC4861] rule for 641 checking hop limit=255 does not apply to the DAR and DAC messages. 642 Those multihop DAD messages MUST NOT modify any Neighbor Cache 643 entries on the routers since we do not have the security benefits 644 provided by the hop limit=255 check. 646 3.5. Neighbor Cache Management 648 The use of explicit registrations with lifetimes plus the desire to 649 not multicast Neighbor Solicitation messages for hosts imply that we 650 manage the Neighbor Cache entries (NCE) slightly differently than in 651 [RFC4861]. This results in three different types of NCEs and the 652 types specify how those entries can be removed: 654 Garbage-collectible: Entries that are subject to the normal rules in 655 [RFC4861] that allow for garbage collection 656 when low on memory. 658 Registered: Entries that have an explicit registered 659 lifetime and are kept until this lifetime 660 expires or they are explicitly unregistered. 662 Tentative: Entries that are temporary with a short 663 lifetime, which typically get converted to 664 Registered entries. 666 Note that the type of the NCE is orthogonal to the states specified 667 in [RFC4861]. 669 When a host interacts with a router by sending Router Solicitations 670 this results in a Tentative NCE. Once a node successfully registers 671 with a Router the result is a Registered NCE. When Routers send RAs 672 to hosts, and when routers optionally receive RA messages or receive 673 multicast NS messages from other Routers, the result is Garbage- 674 collectible NCEs. There can only be one kind of NCE for an IP 675 address at a time. 677 Neighbor Cache entries on Routers can additionally be added or 678 deleted by a routing protocol used in the 6LoWPAN. This is useful if 679 the routing protocol carries the link-layer addresses of the 680 neighboring routers. Depending on the details of such routing 681 protocols such NCEs could be either Registered or Garbage- 682 collectible. 684 4. New Neighbor Discovery Options and Messages 686 This section defines new Neighbor Discovery message options used by 687 this specification. The Address Registration Option is mandatory, 688 whereas the Authoritative Border Router Option and 6LoWPAN Context 689 Option are optional. This section also defines the optional and new 690 Duplicate Address Request and Confirmation messages. 692 4.1. Address Registration Option 694 The routers need to know the set of host IP addresses that are 695 directly reachable and their corresponding link-layer addresses. 696 This needs to be maintained as the radio reachability changes. For 697 this purpose an Address Registration Option (ARO) is introduced, 698 which can be included in unicast Neighbor Solicitation (NS) messages 699 sent by hosts. Thus it can be included in the unicast NS messages 700 that a host sends as part of Neighbor Unreachability Detection to 701 determine that it can still reach a default router. The ARO is used 702 by the receiving router to reliably maintain its Neighbor Cache. The 703 same option is included in corresponding Neighbor Advertisement (NA) 704 messages with a Status field indicating the success or failure of the 705 registration. This option is always host initiated. 707 The information contained in the ARO is also included in optional 708 multihop DAR and DAC messages used between 6LRs to 6LBRs, but the 709 option itself is not used in those messages. 711 The ARO is required for reliability and power saving. The lifetime 712 field provides flexibility to the host to register an address which 713 should be usable (continue to be advertised by the 6LR in the routing 714 protocol etc.) during its intended sleep schedule. 716 The sender of the NS also includes the EUI-64 [EUI64] of the 717 interface it is registering an address from. This is used as a 718 unique ID for the detection of duplicate addresses. It is used to 719 tell the difference between the same node re-registering its address 720 and a different node (with a different EUI-64) registering an address 721 that is already in use by someone else. The EUI-64 is also used to 722 deliver an NA carrying an error Status code to the EUI-64 based link- 723 local IPv6 address of the host (see Section 6.5.2). 725 When the ARO is used by hosts an SLLA (Source Link-layer Address) 726 option [RFC4861] MUST be included and the address that is to be 727 registered MUST be the IPv6 source address of the Neighbor 728 Solicitation message. 730 0 1 2 3 731 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 1 732 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 733 | Type | Length = 2 | Status | Reserved | 734 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 735 | Reserved | Registration Lifetime | 736 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 737 | | 738 + EUI-64 + 739 | | 740 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 742 Fields: 744 Type: TBD1 746 Length: 8-bit unsigned integer. The length of the option in 747 units of 8 bytes. Always 2. 749 Status: 8-bit unsigned integer. Indicates the status of a 750 registration in the NA response. MUST be set to 0 in 751 NS messages. See below. 753 Reserved: This field is unused. It MUST be initialized to zero 754 by the sender and MUST be ignored by the receiver. 756 Registration Lifetime: 16-bit unsigned integer. The amount of time 757 in a unit of 60 seconds that the router should retain 758 the Neighbor Cache entry for the sender of the NS that 759 includes this option. 761 EUI-64: 64 bits. This field is used to uniquely identify the 762 interface of the registered address by including the 763 EUI-64 identifier [EUI64] assigned to it unmodified. 765 The Status values used in Neighbor Advertisements are: 767 +--------+--------------------------------------------+ 768 | Status | Description | 769 +--------+--------------------------------------------+ 770 | 0 | Success | 771 | 1 | Duplicate Address | 772 | 2 | Neighbor Cache Full | 773 | 3-255 | Allocated using Standards Action [RFC5226] | 774 +--------+--------------------------------------------+ 776 Table 1 778 4.2. 6LoWPAN Context Option 780 The optional 6LoWPAN Context Option (6CO) carries prefix information 781 for LoWPAN header compression, and is similar to the Prefix 782 Information Option of [RFC4861]. However, the prefixes can be remote 783 as well as local to the LoWPAN since header compression potentially 784 applies to all IPv6 addresses. This option allows for the 785 dissemination of multiple contexts identified by a Context Identifier 786 (CID) for use as specified in [I-D.ietf-6lowpan-hc]. A context may 787 be a prefix of any length or an address (/128), and up to 16 6LoWPAN 788 Context options may be carried in an Router Advertisement message. 790 0 1 2 3 791 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 1 792 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 793 | Type | Length |Context Length | Res |C| CID | 794 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 795 | Reserved | Valid Lifetime | 796 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 797 . . 798 . Context Prefix . 799 . . 800 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 802 Figure 1: 6LoWPAN Context Option format 804 Type: TBD2 806 Length: 8-bit unsigned integer. The length of the option (including 807 the type and length fields) in units of 8 bytes. May be 2 or 3 808 depending on the length of the Context Prefix field. 810 Context Length: 8-bit unsigned integer. The number of leading bits 811 in the Context Prefix field that are valid. The value ranges from 812 0 to 128. If it is more than 64 then the Length MUST be 3. 814 C: 1-bit context compression flag. This flag indicates if the 815 context is valid for use in compression. A context that is not 816 valid MUST NOT be used for compression, but SHOULD be used in 817 decompression in case another compressor has not yet received the 818 updated context information. This flag is used to manage the 819 context lifecycle based on the recommendations in Section 7.2. 821 CID: 4-bit Context Identifier for this prefix information. CID is 822 used by context based header compression specified in 823 [I-D.ietf-6lowpan-hc]. The list of CIDs for a LoWPAN is 824 configured by on the 6LBR that originates the context information 825 for the 6LoWPAN. 827 Res, Reserved: This field is unused. It MUST be initialized to zero 828 by the sender and MUST be ignored by the receiver. 830 Valid Lifetime: 16-bit unsigned integer. The length of time in a 831 unit of 60 seconds (relative to the time the packet is received) 832 that the context is valid for the purpose of header compression or 833 decompression. A value of all zero bits (0x0) indicates that this 834 context entry MUST be removed immediately. 836 Context Prefix: The IPv6 prefix or address corresponding to the 837 Context ID (CID) field. The valid length of this field is 838 included in the Context Length field. This field is padded with 839 zeros in order to make the option a multiple of 8-bytes. 841 4.3. Authoritative Border Router Option 843 The optional Authoritative Border Router Option (ABRO) is needed when 844 Router Advertisement (RA) messages are used to disseminate prefixes 845 and context information across a route-over topology. In this case 846 6LRs receive Prefix Information options from other 6LRs. This 847 implies that a 6LR can't just let the most recently received RA win. 848 In order to be able to reliably add and remove prefixes from the 849 6LoWPAN we need to carry information from the authoritative 6LBR. 850 This is done by introducing a version number which the 6LBR sets and 851 6LRs propagate as they propagate the prefix and context information 852 with this Authoritative Border Router Option. When there are 853 multiple 6LBRs they would have separate version number spaces. Thus 854 this option needs to carry the IP address of the 6LBR that originated 855 that set of information. 857 The Authoritative Border Router option MUST be included in all Router 858 Advertisement messages in the case when Router Advertisements are 859 used to propagate information between routers (as described in 860 Section 8.2). 862 0 1 2 3 863 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 1 864 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 865 | Type | Length = 3 | Version Number | 866 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 867 | Reserved | 868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 869 | | 870 + + 871 | | 872 + 6LBR Address + 873 | | 874 + + 875 | | 876 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 878 Fields: 880 Type: TBD3 882 Length: 8-bit unsigned integer. The length of the option in 883 units of 8 bytes. Always 3. 885 Version Number: 16-bit unsigned integer. The version number 886 corresponding to this set of information contained in 887 the RA message. The authoritative 6LBR originating 888 the prefix increases this version number each time its 889 set of prefix or context information changes. This 890 version number uses sequence number arithmetic as it 891 may wrap around. 893 Reserved: This field is unused. It MUST be initialized to zero 894 by the sender and MUST be ignored by the receiver. 896 6LBR Address: IPv6 address of the 6LBR that is the origin of the 897 included version number. 899 4.4. Duplicate Address messages 901 For the optional multihop DAD exchanges between 6LR and 6LBR 902 specified in Section 8.2 there are two new ICMPv6 message types 903 called the Duplicate Address Request (DAR) and Duplicate Address 904 Confirmation (DAC). We avoid reusing the Neighbor Solicitation and 905 Neighbor Advertisement messages for this purpose since these messages 906 are not subject to the hop limit=255 check as they are forwarded by 907 intermediate 6LRs. The information contained in the messages are 908 otherwise the same as would be in a Neighbor Solicitation carrying a 909 Address Registration option, with the message format inlining the 910 fields that are in the ARO. 912 The DAR and DAC use the same message format with different ICMPv6 913 type values, and the Status field is only meaningful in the DAC 914 message. 916 0 1 2 3 917 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 1 918 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 919 | Type | Code | Checksum | 920 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 921 | Status | Reserved | Registration Lifetime | 922 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 923 | | 924 + EUI-64 + 925 | | 926 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 927 | | 928 + + 929 | | 930 + Registered Address + 931 | | 932 + + 933 | | 934 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 936 IP fields: 938 IPv6 source: A non link-local address of the sending router. 940 IPv6 destination: A non link-local address of the sending router. 941 In a DAC this is just the source from the DAR. 943 Hop Limit: Set to MULTIHOP_HOPLIMIT on transmit. MUST be ignored 944 on receipt. 946 ICMP Fields: 948 Type: TBD4 for DAR and TBD5 for DAC 950 Code: Set to zero on transmit. MUST be ignored on receipt. 952 Checksum: The ICMP checksum. See [RFC4443]. 954 Status: 8-bit unsigned integer. Indicates the status of a 955 registration in the DAC. MUST be set to 0 in DAR. 956 See Table 1. 958 Reserved: This field is unused. It MUST be initialized to zero 959 by the sender and MUST be ignored by the receiver. 961 Registration Lifetime: 16-bit unsigned integer. The amount of time 962 in a unit of 60 seconds that the router should retain 963 the Neighbor Cache entry for the sender of the NS that 964 includes this option. A value of 0 indicates in an NS 965 that the neighbor cache entry should be removed. 967 EUI-64: 64 bits. This field is used to uniquely identify the 968 interface of the registered address by including the 969 EUI-64 identifier [EUI64] assigned to it unmodified. 971 Registered Address: 128-bit field. Carries the host address, which 972 was contained in the IPv6 Source field in the NS that 973 contained the ARO option sent by the host. 975 5. Host Behavior 977 Hosts in a LoWPAN use the Address Registration option in the Neighbor 978 Solicitation messages they send as a way to maintain the Neighbor 979 Cache in the routers thereby removing the need for multicast Neighbor 980 Solicitations to do address resolution. Unlike in [RFC4861] the 981 hosts initiate updating the information they receive in Router 982 Advertisements by sending Router Solicitations before the information 983 expires. Finally, when Neighbor Unreachability Detection indicates 984 that one or all default routers have become unreachable, then the 985 host uses Router Solicitations to find a new set of default routers. 987 5.1. Forbidden Actions 989 A host MUST NOT multicast a Neighbor Solicitation message. 991 5.2. Interface Initialization 993 When the interface on a host is initialized it follows the 994 specification in [RFC4861]. A link-local address is formed based on 995 the EUI-64 identifier [EUI64] assigned to the interface as per 996 [RFC4944] or the appropriate IP-over-foo document for the link, and 997 then the host sends Router Solicitation messages as described in 998 [RFC4861] Section 6.3.7. 1000 There is no need to join the Solicited-Node multicast address since 1001 nobody multicasts Neighbor Solicitations in this type of network. A 1002 host MUST join the all-nodes multicast address. 1004 5.3. Sending a Router Solicitation 1006 The Router Solicitation is formatted as specified in [RFC4861] and 1007 sent to the IPv6 All-Routers multicast address (see [RFC4861] Section 1008 6.3.7 for details). An SLLA option MUST be included to enable 1009 unicast Router Advertisements in response. An unspecified source 1010 address MUST NOT be used in RS messages. 1012 If the link layer supports a way to send packets to some kind of all- 1013 routers anycast link-layer address, then that MAY be used to convey 1014 theses packets to a router. 1016 Since hosts do not depend on multicast Router Advertisements to 1017 discover routers, the hosts need to intelligently retransmit Router 1018 Solicitations whenever the default router list is empty, one of its 1019 default routers becomes unreachable, or the lifetime of the prefixes 1020 and contexts in the previous RA are about to expire. The RECOMMENDED 1021 retransmissions is to initially send up to 3 (MAX_RTR_SOLICITATIONS) 1022 RS messages separated by at least 10 seconds 1023 (RTR_SOLICITATION_INTERVAL) as specified in [RFC4861], and then 1024 switch to slower retransmissions. After the initial retransmissions 1025 the host SHOULD do binary exponential backoff of the retransmission 1026 timer for each subsequent retransmission. However, it is useful to 1027 have a maximum retransmission timer of 60 seconds 1028 (MAX_RTR_SOLICITATION_INTERVAL). In all cases the RS retransmissions 1029 are terminated when a RA is received. 1031 5.4. Processing a Router Advertisement 1033 The processing of Router Advertisements is as in [RFC4861] with the 1034 addition of handling the 6LoWPAN Context option and triggering 1035 address registration when a new address has been configured. 1036 Furthermore, the SLLA option MUST be included in the RA. Unlike in 1037 [RFC4861], the maximum value of the RA Router Lifetime field MAY be 1038 up to 0xFFFF (approximately 18 hours). 1040 Should the host erroneously receive a Prefix Information option with 1041 the 'L' (on-link) flag set, then that Prefix Information Option (PIO) 1042 MUST be ignored. 1044 5.4.1. Address configuration 1046 Address configuration follows [RFC4862]. For an address not derived 1047 from an EUI-64, the M flag of the RA determines how the address can 1048 be configured. If the M flag is set in the RA, then DHCPv6 MUST be 1049 used to assign the address. If the M flag is not set, then the 1050 address can be configured by any other means (and duplicate detection 1051 is performed as part of the registration process). 1053 Once an address has been configured it will be registered by 1054 unicasting a Neighbor Solicitation with the Address Registration 1055 option to one or more routers. 1057 5.4.2. Storing Contexts 1059 The host maintains a conceptual data structure for the context 1060 information it receives from the routers, which is called the Context 1061 Table. This includes the Context ID, the prefix (from the Context 1062 Prefix field in the 6CO), the Compression bit, and the Valid 1063 Lifetime. A Context Table entry that has the Compression bit clear 1064 is used for decompression when receiving packets, but MUST NOT be 1065 used for compression when sending packets. 1067 When a 6CO option is received in a Router Advertisement it is used to 1068 add or update the information in the Context Table. If the Context 1069 ID field in the 6CO matches an existing Context Table entry, then 1070 that entry is updated with the information in the 6CO. If the Valid 1071 Lifetime field in the 6CO is zero, then the entry is immediately 1072 deleted. 1074 If there is no matching entry in the Context Table, and the Valid 1075 Lifetime field is non-zero, then a new context is added to the 1076 Context Table. The 6CO is used to update the created entry. 1078 When the 6LBR changes the context information a host might not 1079 immediately notice. And in the worst case a host might have stale 1080 context information. For this reason 6LBRs use the recommendations 1081 in Section 7.2 for carefully managing the context lifecycle. Nodes 1082 should be careful about using header compression in RA messages that 1083 include 6COs. 1085 5.4.3. Maintaining Prefix and Context Information 1087 The prefix information is timed out as specified in [RFC4861]. When 1088 the Valid Lifetime for a Context Table entry expires the entry is 1089 placed in a receive-only mode, which is the equivalent of receiving a 1090 6CO for that context with C=0. The entry is held in receive-only 1091 mode for a period of twice the Default Router Lifetime, after which 1092 the entry is removed. 1094 A host should inspect the various lifetimes to determine when it 1095 should next initiate sending a Router Solicitation to ask for any 1096 updates to the information. The lifetimes that matter are the 1097 Default Router lifetime, the Valid Lifetime in the Prefix Information 1098 options, and the Valid Lifetime in the 6CO. The host SHOULD unicast 1099 one or more Router Solicitations to the router well before the 1100 minimum of those lifetimes (across all the prefixes and all the 1101 contexts) expire, and switch to multicast RS messages if there is no 1102 response to the unicasts. The retransmission behavior for the Router 1103 Solicitations is specified in Section 5.3. 1105 5.5. Registration and Neighbor Unreachability Detection 1107 Hosts send Unicast Neighbor Solicitation (NS) messages to register 1108 their IPv6 addresses, and also to do NUD to verify that their default 1109 routers are still reachable. The registration is performed by the 1110 host including an ARO in the Neighbor Solicitation it sends. Even if 1111 the host doesn't have data to send, but is expecting others to try to 1112 send packets to the host, the host needs to maintain its Neighbor 1113 Cache entries in the routers. This is done by sending NS messages 1114 with the ARO to the router well in advance of the registration 1115 lifetime expiring. NS messages are retransmitted up to 1116 MAX_UNICAST_SOLICIT times using a minimum timeout of RETRANS_TIMER 1117 until the host receives an Neighbor Advertisement message with an ARO 1118 option. 1120 Hosts that receive Router Advertisement messages from multiple 1121 default routers SHOULD attempt to register with more than one of them 1122 in order to increase the robustness of the network. 1124 Note that Neighbor Unreachability Detection probes can be suppressed 1125 by Reachability Confirmations from transport protocols or 1126 applications as specified in [RFC4861]. 1128 When a host knows it will no longer use a router it is registered to, 1129 it SHOULD de-register with the router by sending an NS with an ARO 1130 containing a lifetime of 0. To handle the case when a host loses 1131 connectivity with the default router involuntarily, the host SHOULD 1132 use a suitably low registration lifetime. 1134 5.5.1. Sending a Neighbor Solicitation 1136 The host triggers sending Neighbor Solicitation (NS) messages 1137 containing an ARO when a new address is configured, when it discovers 1138 a new default router, or well before the Registration Lifetime 1139 expires. Such an NS MUST include a Source Link-Layer Address (SLLA) 1140 option, since the router needs to record the link-layer address of 1141 the host. An unspecified source address MUST NOT be used in NS 1142 messages. 1144 5.5.2. Processing a Neighbor Advertisement 1146 A host handles Neighbor Advertisement messages as specified in 1147 [RFC4861], with added logic described in this section for handling 1148 the Address Registration option. 1150 In addition to the normal validation of a Neighbor Advertisement and 1151 its options, the Address Registration option is verified as follows 1152 (if present). If the Length field is not two, the option is silently 1153 ignored. If the EUI-64 field does not match the EUI-64 of the 1154 interface, the option is silently ignored. 1156 If the status field is zero, then the address registration was 1157 successful. The host saves the Registration Lifetime from the 1158 Address Registration option for use to trigger a new NS well before 1159 the lifetime expires. If the Status field is not equal to zero, the 1160 address registration has failed. 1162 5.5.3. Recovering from Failures 1164 The procedure for maintaining reachability information about a 1165 neighbor is the same as in [RFC4861] Section 7.3 with the exception 1166 that address resolution is not performed. 1168 The address registration procedure may fail for two reasons: no 1169 response to Neighbor Solicitations is received (NUD failure), or an 1170 Address Registration option with a failure Status (Status > 0) is 1171 received. In the case of NUD failure the entry for that router will 1172 be removed thus address registration is no longer of importance. 1173 When an Address Registration option with a non-zero Status field is 1174 received this indicates that registration for that address has 1175 failed. A failure Status of one indicates that a duplicate address 1176 was detected and the procedure described in [RFC4862] Section 5.4.5 1177 is followed. The host MUST NOT use the address it tried to register. 1178 If the host has valid registrations with other routers, these MUST be 1179 removed by registering with each using a zero ARO lifetime. 1181 A Status code of two indicates that the Neighbor Cache of that router 1182 is full. In this case the host SHOULD remove this router from its 1183 default router list and attempt to register with another router. If 1184 the host has no more default routers it needs to revert to sending 1185 Router Solicitations as specified in Section 5.3. 1187 Other failure codes may be defined in future documents. 1189 5.6. Next-hop Determination 1191 The IP address of the next-hop for a destination is determined as 1192 follows. Destinations to the link-local prefix (FE80::) are always 1193 sent on the link to that destination. It is assumed that link-local 1194 addresses are formed as specified in Section 5.2 from the EUI-64, and 1195 address resolution is not performed. 1197 Multicast addresses are considered to be on-link and are resolved as 1198 specified in [RFC4944] or the appropriate IP-over-foo document. Note 1199 that [RFC4944] only defines how to represent a multicast destination 1200 address in the LoWPAN header. Support for multicast scopes larger 1201 than link-local needs an appropriate multicast routing algorithm. 1203 All other prefixes are assumed to be off-link [RFC5889]. Anycast 1204 addresses are always considered to be off-link. They are therefore 1205 sent to one of the routers in the Default Router List. 1207 A LoWPAN Node is not required to maintain a minimum of one buffer per 1208 neighbor as specified in [RFC4861], since packets are never queued 1209 while waiting for address resolution. 1211 5.7. Address Resolution 1213 The address registration mechanism and the SLLA option in Router 1214 Advertisement messages provide sufficient a priori state in routers 1215 and hosts to resolve an IPv6 address to its associated link-layer 1216 address. As all prefixes, except the link-local prefix and multicast 1217 addresses, are always assumed to be off-link, multicast-based address 1218 resolution between neighbors is not needed. 1220 Link-layer addresses for neighbors are stored in Neighbor Cache 1221 entries [RFC4861]. In order to achieve LoWPAN compression, most 1222 global addresses are formed using a link-layer address. Thus a host 1223 can minimize memory usage by optimizing for this case and only 1224 storing link-layer address information if it differs from the link- 1225 layer address corresponding to the Interface ID of the IPv6 address 1226 (i.e., differs in more than the on-link/global bit being inverted). 1228 5.8. Sleeping 1230 It is often advantageous for battery-powered hosts in LoWPANs to keep 1231 a low duty cycle. The optimizations described in this document 1232 enable hosts to sleep as described further in this section. Routers 1233 may want to cache traffic destined to a host which is sleeping, but 1234 such functionality is out of the scope of this document. 1236 5.8.1. Picking an Appropriate Registration Lifetime 1238 As all Neighbor Discovery messages are initiated by the hosts, this 1239 allows a host to sleep or otherwise be unreachable between NS/NA 1240 message exchanges. The Address Registration option attached to NS 1241 messages indicates to a router to keep the Neighbor Cache entry for 1242 that address valid for the period in the Registration Lifetime field. 1243 A host should choose a sleep time appropriate for its energy 1244 characteristics, and set a registration lifetime larger than the 1245 sleep time to ensure the registration is renewed successfully 1246 (considering e.g. clock drift and additional time for potential 1247 retransmissions of the re-registration). A host should also consider 1248 the stability of the network (how quickly the topology changes) when 1249 choosing its sleep time (and thus registration lifetime). A dynamic 1250 network requires a shorter sleep time so that routers don't keep 1251 invalid neighbor cache entries for nodes longer than necessary. 1253 5.8.2. Behavior on Wakeup 1255 When a host wakes up from a sleep period it SHOULD maintain its 1256 current address registrations that will timeout before the next 1257 wakeup. This is done by sending Neighbor Solicitation messages with 1258 the Address Registration option as described in Section 5.5.1. The 1259 host may also need to refresh its prefix and context information by 1260 sending a new unicast Router Solicitation (the maximum Router 1261 Lifetime is about 18 hours whereas the maximum Registration lifetime 1262 is about 45.5 days). If after wakeup the host (using NUD) determines 1263 that some or all previous default routers have become unreachable, 1264 then the host will send multicast Router Solicitations to discover 1265 new default router(s) and restart the address registration process. 1267 6. Router Behavior for 6LR and 6LBR 1269 Both 6LRs and 6LBRs maintain the Neighbor Cache [RFC4861] based on 1270 the Address Registration Options they receive in Neighbor 1271 Advertisement messages from hosts, Neighbor Discovery packets from 1272 other nodes, and potentially a routing protocol used in the 6LoWPAN 1273 as outlined in Section 3.5. 1275 The routers SHOULD NOT garbage collect Registered Neighbor Cache 1276 entries (see Section 3.4) since they need to retain them until the 1277 Registration Lifetime expires. Similarly, if Neighbor Unreachability 1278 Detection on the router determines that the host is UNREACHABLE 1279 (based on the logic in [RFC4861]), the Neighbor Cache entry SHOULD 1280 NOT be deleted but be retained until the Registration Lifetime 1281 expires. A renewed ARO should mark the cache entry as STALE. Thus 1282 for 6LoWPAN Routers the Neighbor Cache doesn't behave like a cache. 1284 Instead it behaves as a registry of all the host addresses that are 1285 attached to the Router. 1287 Routers MAY implement the Default Router Preferences [RFC4191] and 1288 use that to indicate to the host whether the router is a 6LBR or a 1289 6LR. If this is implemented then 6LRs with no route to a border 1290 router MUST set Prf to (11) for low preference, other 6LRs MUST set 1291 Prf to (00) for normal preference, and 6LBRs MUST set Prf to (01) for 1292 high preference. 1294 6.1. Forbidden Actions 1296 A router SHOULD NOT send Redirect messages in a route-over topology, 1297 but MAY send Redirect messages in a mesh-under topology. In route- 1298 over the link has non-transitive reachability and the router has no 1299 way to determine that the recipient of a Redirect message can reach 1300 the link-layer address. 1302 A router MUST NOT set the 'L' (on-link) flag in the Prefix 1303 Information options, since that might trigger hosts to send multicast 1304 Neighbor Solicitations. 1306 6.2. Interface Initialization 1308 A router initializes its interface more or less as in [RFC4861]. 1309 However, a 6LR might want to wait to make its interfaces advertising 1310 (implicitly keeping the AdvSendAdvertisements flag clear) until it 1311 has received the prefix(es) and context information from its 6LBR. 1312 That is independent of whether prefixes and context information is 1313 disseminated using the methods specified in this document, or using 1314 some other method. 1316 6.3. Processing a Router Solicitation 1318 A router processes Router Solicitation messages as specified in 1319 [RFC4861]. The differences relate to the inclusion of Authoritative 1320 Border Router options in the Router Advertisement (RA) messages, and 1321 the exclusive use of unicast Router Advertisements. If a 6LR has 1322 received an ABRO from a 6LBR, then it will include that option 1323 unmodified in the Router Advertisement messages it sends. And if the 1324 6LR has received RAs, whether with the same prefixes and context 1325 information or different, from a different 6LBR, then it will need to 1326 keep those prefixes and context information separately so that the 1327 RAs the 6LR sends will maintain the association between the ABRO and 1328 the prefixes and context information. The router can tell which 6LBR 1329 originated the prefixes and context information from the 6LBR Address 1330 field in the ABRO. When a router has information tied to multiple 1331 ABROs, a single RS will result in multiple RAs each containing a 1332 different ABRO. 1334 A Router Solicitation might be received from a host that has not yet 1335 registered its address with the router. Thus the router MUST NOT 1336 modify an existing Neighbor Cache entry based on the SLLA option from 1337 the Router Solicitation. However, a router MAY create a Tentative 1338 Neighbor Cache entry based on the SLLA option. Such a Tentative 1339 Neighbor Cache entry SHOULD be timed out in TENTATIVE_NCE_LIFETIME 1340 seconds unless a registration converts it into a Registered NCE. 1342 A 6LR or 6LBR MUST include a Source Link-layer address option in the 1343 Router Advertisements it sends. That is required so that the hosts 1344 will know the link-layer address of the router. Unlike in [RFC4861], 1345 the maximum value of the RA Router Lifetime field MAY be up to 0xFFFF 1346 (approximately 18 hours). 1348 Unlike [RFC4861] which suggests multicast Router Advertisements, this 1349 specification optimizes the exchange by always unicasting RAs in 1350 response to RSs. This is possible since the RS always includes a 1351 SLLA option, which is used by the router to unicast the RA. 1353 6.4. Periodic Router Advertisements 1355 A router does not need to send any periodic Router Advertisement 1356 messages since the hosts will solicit updated information by sending 1357 Router Solicitations before the lifetimes expire. 1359 However, if the routers use Router Advertisements to optionally 1360 distribute prefix and/or context information across a route-over 1361 topology, that might require periodic Router Advertisement messages. 1362 Such RAs are sent using the configurable MinRtrAdvInterval and 1363 MaxRtrAdvInterval as per [RFC4861]. 1365 6.5. Processing a Neighbor Solicitation 1367 A router handles Neighbor Solicitation messages as specified in 1368 [RFC4861], with added logic described in this section for handling 1369 the Address Registration option. 1371 In addition to the normal validation of a Neighbor Solicitation and 1372 its options, the Address Registration option is verified as follows 1373 (if present). If the Length field is not two, or if the Status field 1374 is not zero, then the Neighbor Solicitation is silently ignored. 1376 If the source address of the NS is the unspecified address, or if no 1377 SLLA option is included, then any included ARO is ignored, that is, 1378 the NS is processed as if it did not contain an ARO. 1380 6.5.1. Checking for Duplicates 1382 If the NS contains a valid ARO, then the router inspects its Neighbor 1383 Cache on the arriving interface to see if it is a duplicate. If 1384 there is no Neighbor Cache entry for the IPv6 source address of the 1385 NS, then it isn't a duplicate. If there is such a Neighbor Cache 1386 entry and the EUI-64 is the same, then it isn't a duplicate either. 1387 Otherwise it is a duplicate address. Note that if multihop DAD 1388 (Section 8.2) is used then the checks are slightly different to take 1389 into account Tentative Neighbor Cache entries. In the case it is a 1390 duplicate address then the router responds with a unicast Neighbor 1391 Advertisement (NA) message with the ARO Status field set to one (to 1392 indicate the address is a duplicate) as described in Section 6.5.2. 1393 In this case there is no modification to the Neighbor Cache. 1395 6.5.2. Returning Address Registration Errors 1397 Address registration errors are not sent back to the source address 1398 of the NS due to a possible risk of L2 address collision. Instead 1399 the NA is sent to the link-local IPv6 address with the IID part 1400 derived from the EUI-64 field of the ARO as per [RFC4944]. In 1401 particular, this means that the universal/local bit needs to be 1402 inverted. The NA is formatted with a copy of the ARO from the NS, 1403 but with the Status field set to indicate the appropriate error. 1405 6.5.3. Updating the Neighbor Cache 1407 If ARO did not result in a duplicate address being detected as above, 1408 then if the Registration Lifetime is non-zero the router creates (if 1409 it didn't exist) or updates (otherwise) a Neighbor Cache entry for 1410 the IPv6 source address of the NS. If the Neighbor Cache is full and 1411 a new entry needs to be created, then the router responds with a 1412 unicast NA with the ARO Status field set to two (to indicate the 1413 router's Neighbor Cache is full) as described in Section 6.5.2. 1415 The Registration Lifetime and the EUI-64 are recorded in the Neighbor 1416 Cache entry. A unicast Neighbor Advertisement (NA) is then sent in 1417 response to the NS. This NA SHOULD include a copy of the ARO, with 1418 the Status field set to zero. A TLLA (Target Link-layer Address) 1419 option [RFC4861] is not required in the NA, since the host already 1420 knows the router's link-layer address from Router Advertisements. 1422 If the ARO contains a zero Registration Lifetime then any existing 1423 Neighbor Cache entry for the IPv6 source address of the NS MUST be 1424 deleted, and a NA sent as above. 1426 Should the Registration Lifetime in a Neighbor Cache entry expire, 1427 then the router MUST delete the cache entry. 1429 The addition and removal of Registered Neighbor Cache entries would 1430 result in notifying the routing protocol. 1432 Note: If the optional multihop DAD (Section 8.2) is used, then the 1433 updating of the Neighbor Cache is slightly different due to Tentative 1434 NCEs. 1436 6.5.4. Next-hop Determination 1438 In order to deliver a packet destined for a 6LN registered with a 1439 router, next-hop determination is slightly different for routers than 1440 hosts (see Section 5.6. The routing table is checked to determine 1441 the next hop IP address. A registered Neighbor Cache Entry (NCE) 1442 determines if the next hop IP-address is on-link. It is the 1443 responsibility of the routing protocol of the router to maintain on- 1444 link information about its registered neighbors. Tentative NCEs MUST 1445 NOT be used to determine on-link status of the registered nodes. 1447 6.5.5. Address Resolution between Routers 1449 There needs to be a mechanism somewhere for the routers to discover 1450 each others' link-layer addresses. If the routing protocol used 1451 between the routers provides this, then there is no need for the 1452 routers to use the Address Registration option between each other. 1453 Otherwise, the routers MAY use the ARO. When routers use ARO to 1454 register with each other and the optional multihop DAD Section 8.2 is 1455 in use, then care should be taken to ensure that there isn't a flood 1456 of ARO-carrying messages sent to the 6LBR as each router hears an ARO 1457 from their neighboring routers. The details for this is out of scope 1458 of this document. 1460 Optionally Routers can use multicast Neighbor Solicitations as in 1461 [RFC4861] to resolve each others link-layer addresses. Thus Routers 1462 MAY multicast Neighbor Solicitations for other routers, for example 1463 as a result of receiving some routing protocol update. Routers MUST 1464 respond to multicast Neighbor Solicitations. This implies that 1465 Routers MUST join the Solicited-node multicast addresses as specified 1466 in [RFC4861]. 1468 7. Border Router Behavior 1470 A 6LBR handles sending of Router Advertisements and processing of 1471 Neighbor Solicitations from hosts as specified above in section 1472 Section 6. A 6LBR SHOULD always include an Authoritative Border 1473 Router option in the Router Advertisements it sends, listing itself 1474 as the 6LBR Address. That requires that the 6LBR maintain the 1475 version number in stable storage, and increases the version number 1476 when some information in its Router Advertisements change. The 1477 information whose change affects the version are in the Prefix 1478 Information options (the prefixes or their lifetimes) and in the 6CO 1479 option (the prefixes, Context IDs, or lifetimes.) 1481 In addition, a 6LBR is somehow configured with the prefix or prefixes 1482 that are assigned to the LoWPAN, and advertises those in Router 1483 Advertisements as in [RFC4861]. Optionally, in the case of route- 1484 over, those prefixes can be disseminated to all the 6LRs using the 1485 technique in Section 8.1. However, there might be mechanisms outside 1486 of the scope of this document that can be used instead for prefix 1487 dissemination with route-over. 1489 If the 6LoWPAN uses Header Compression [I-D.ietf-6lowpan-hc] with 1490 context then the 6LBR needs to manage the context IDs, and advertise 1491 those in Router Advertisements by including 6CO options in its Router 1492 Advertisements so that directly attached hosts are informed about the 1493 context IDs. Below we specify things to consider when the 6LBR needs 1494 to add, remove, or change the context information. Optionally, in 1495 the case of route-over, the context information can be disseminated 1496 to all the 6LRs using the technique in Section 8. However, there 1497 might be mechanisms outside of the scope of this document that can be 1498 used instead for disseminating context information with route-over. 1500 7.1. Prefix Determination 1502 The prefix or prefixes used in a LoWPAN can be manually configured, 1503 or can be acquired using DHCPv6 Prefix Delegation [RFC3633]. For a 1504 LoWPAN that is isolated from the network, either permanently or 1505 occasionally, the 6LBR can assign a ULA prefix using [RFC4193]. The 1506 ULA prefix should be stored in stable storage so that the same prefix 1507 is used after a failure of the 6LBR. If the LoWPAN has multiple 1508 6LBRs, then they should be configured with the same set of prefixes. 1509 The set of prefixes are included in the Router Advertisement messages 1510 as specified in [RFC4861]. 1512 7.2. Context Configuration and Management 1514 If the LoWPAN uses Header Compression [I-D.ietf-6lowpan-hc] with 1515 context then the 6LBR may be configured with context information and 1516 related context IDs. If the LoWPAN has multiple 6LBRs, then they 1517 MUST be configured with the same context information and context IDs. 1519 The context information carried in Router Advertisement (RA) messages 1520 originate at 6LBRs and must be disseminated to all the routers and 1521 hosts within the LoWPAN. RAs include one 6CO for each context. 1523 For the dissemination of context information using the 6CO, a strict 1524 lifecycle SHOULD be used in order to ensure the context information 1525 stays synchronized throughout the LoWPAN. New context information 1526 SHOULD be introduced into the LoWPAN with C=0, to ensure it is known 1527 by all nodes that may have to decompress based on this context 1528 information. Only when it is reasonable to assume that this 1529 information was successfully disseminated SHOULD an option with C=1 1530 be sent, enabling the actual use of the context information for 1531 compression. 1533 Conversely, to avoid that nodes send packets making use of previous 1534 values of contexts, resulting in ambiguity when receiving a packet 1535 that uses a recently changed context, old values of a context SHOULD 1536 be taken out of use for a while before new values are assigned to 1537 this specific context. That is, in preparation for a change of 1538 context information, its dissemination SHOULD continue for at least 1539 MIN_CONTEXT_CHANGE_DELAY with C=0. Only when it is reasonable to 1540 assume that the fact that the context is now invalid was successfully 1541 disseminated, should the context ID be taken out of dissemination or 1542 reused with a different Context Prefix field. In the latter case, 1543 dissemination of the new value again SHOULD start with C=0, as above. 1545 8. Optional Behavior 1547 Optionally the Router Advertisement messages can be used to 1548 disseminate prefixes and context information to all the 6LRs in a 1549 route-over topology. If all routers are configured to use another 1550 mechanism for such information distribution, this mechanism MAY stay 1551 unused. 1553 There is also the option for a 6LR to perform multihop DAD (for non- 1554 EUI-64 derived IPv6 addresses) against a 6LBR in a route-over 1555 topology by using the DAR and DAC messages. This is optional because 1556 there might be other ways to either allocate unique address, such as 1557 DHCPv6 [RFC3315], or other future mechanisms for multihop DAD. 1559 8.1. Multihop Prefix and Context Distribution 1561 The multihop distribution relies on Router Solicitation messages and 1562 Router Advertisement (RA) messages sent between routers, and using 1563 the ABRO version number to control the propagation of the information 1564 (prefixes and context information) that is being sent in the RAs. 1566 This multihop distribution mechanism can handle arbitrary information 1567 from an arbitrary number of 6LBRs. However, the semantics of the 1568 context information requires that all the 6LNs use the same 1569 information, whether they send, forward, or receive compressed 1570 packets. Thus the manager of the 6LBRs need to somehow ensure that 1571 the context information is in synchrony across the 6LBRs. This can 1572 be handled in different ways. One possible way to ensure it is to 1573 treat the context and prefix information as originating from some 1574 logical or virtual source, which in essence means that it looks like 1575 the information is distributed from a single source. 1577 If a set of 6LBRs behave as a single one (using mechanisms out of 1578 scope of this document) so that the prefixes and contexts and ABRO 1579 version number will be the same from all the 6LBRs, then those 6LBRs 1580 can pick a single IP address to use in the ABRO option. 1582 8.1.1. 6LBRs Sending Router Advertisements 1584 6LBRs supporting multihop prefix and context distribution MUST 1585 include an ABRO in each of its RAs. The ABRO Version Number field is 1586 used to keep prefix and context information consistent throughout the 1587 LoWPAN along with the guidelines in Section 7.2. Each time any 1588 information in the set of PIO or 6CO options change, the ABRO Version 1589 is increased by one. 1591 This requires that the 6LBR maintain the PIO, 6CO, and ABRO Version 1592 Number in stable storage, since an old version number will be 1593 silently ignored by the 6LRs. 1595 8.1.2. Routers Sending Router Solicitations 1597 If multihop distribution is done using Router Advertisement (RA) 1598 messages, then on interface initialization a router SHOULD send some 1599 Router Solicitation messages similarly to how hosts do this in 1600 [RFC4861]. That will cause the routers to respond with RA messages 1601 which then can be used to initially seed the prefix and context 1602 information. 1604 8.1.3. Routers Processing Router Advertisements 1606 If multihop distribution is not done using RA messages, then the 1607 routers follow [RFC4861] which states that they merely do some 1608 consistency checks and nothing in Section 8.1 applies. Otherwise the 1609 routers will check and record the prefix and context information from 1610 the receive RAs, and use that information as follows. 1612 If a received RA does not contain a Authoritative Border Router 1613 option, then the RA MUST be silently ignored. 1615 The router uses the 6LBR Address field in the ABRO to check if it has 1616 previously received information from the 6LBR. If it finds no such 1617 information, then it just records the 6LBR Address and Version and 1618 the associated prefixes and context information. If the 6LBR is 1619 previously known, then the Version number field MUST be compared 1620 against the recorded version number for that 6LBR. The comparison 1621 MUST be done the same way as TCP sequence number comparisons to 1622 handle the case when the version number wraps around. If the version 1623 number received in the packet is less than the stored version number 1624 (following [RFC1982] Section 3.2), then the information in the RA is 1625 silently ignored. Otherwise the recorded information and version 1626 number are updated. 1628 By TCP sequence number comparison we mean that half of the version 1629 number space is "old" and half is "new". For example, if the current 1630 version number is 0x2, then anything between 0x80000003 (0x2- 1631 0x7fffffff) and 0x1 is old, and anything between 0x3 and 0x80000002 1632 (0x2+0x8000000) is new. 1634 8.1.4. Storing the Information 1636 The router keeps state for each 6LBR that it sees with an ABRO. This 1637 includes the version number, and the complete set of Prefix 1638 Information options and 6LoWPAN Context options. The prefixes are 1639 timed out based on the Valid lifetime in the Prefix Information 1640 Option. The Context Prefix is timed out based on the Valid lifetime 1641 in the 6LoWPAN Context option. 1643 While the prefixes and context information are stored in the router 1644 their valid and preferred lifetimes are decremented as time passes. 1645 This ensures that when the router is in turn later advertising that 1646 information in the Router Advertisements it sends, the 'expiry time' 1647 doesn't accidentally move further into the future. For example, if a 1648 6CO with a Valid lifetime of 10 minutes is received at time T, and 1649 the router includes this in a RA it sends at time T+5 minutes, the 1650 Valid lifetime in the 6CO it sends will be only 5 minutes. 1652 8.1.5. Sending Router Advertisements 1654 If multihop distribution is performed using RA messages, then the 1655 routers MUST ensure that the ABRO always stay together with the 1656 prefixes and context information received with that ABRO. Thus if 1657 the router has received prefix P1 with ABRO saying it is from one 1658 6LBR, and prefix P2 from another 6LBR, then the router MUST NOT 1659 include the two prefixes in the same RA message. Prefix P1 MUST be 1660 in a RA that include a ABRO from the first 6LBR etc. Note that 1661 multiple 6LBRs might advertise the same prefix and context 1662 information, but they still need to be associated with the 6LBRs that 1663 advertised them. 1665 The routers periodically send Router Advertisements as in [RFC4861]. 1666 This is for the benefit of the other routers receiving the prefixes 1667 and context information. And the routers also respond to Router 1668 Solicitations by unicasting RA messages. In both cases the above 1669 constraint of keeping the ABRO together with 'its' prefixes and 1670 context information apply. 1672 When a router receives new information from a 6LBR, that is, either 1673 it hears from a new 6LBR (a new 6LBR Address in the ABRO) or the ABRO 1674 version number of an existing 6LBR has increased, then it is useful 1675 to send out a few triggered updates. The recommendation is to behave 1676 the same as when an interface has become an advertising interface in 1677 [RFC4861], that is, send up to three RA messages. This ensures rapid 1678 propagation of new information to all the 6LRs. 1680 8.2. Multihop Duplicate Address Detection 1682 The ARO can be used, in addition to registering an address in a 6LR, 1683 to have the 6LR verify that the address isn't used by some other host 1684 known to the 6LR. However, that isn't sufficient in a route-over 1685 topology (or in a LoWPAN with multiple 6LBRs) since some host 1686 attached to another 6LR could be using the same address. There might 1687 be different ways for the 6LRs to coordinate such Duplicate Address 1688 Detection in the future, or addresses could be assigned using a 1689 DHCPv6 server that verifies uniqueness as part of the assignment. 1691 This specification offers an optional and simple technique for 6LRs 1692 and 6LBRs to perform Duplicate Address Detection that reuses the 1693 information from Address Registration option in the DAR and DAC 1694 messages. This technique is not needed when the Interface ID in the 1695 address is based on an EUI-64, since those are assumed to be globally 1696 unique. The technique assumes that the 6LRs either register with all 1697 the 6LBRs, or that the network uses some out-of-scope mechanism to 1698 keep the DAD tables in the 6LBRs synchronized. 1700 The multihop DAD mechanism is used synchronously the first time an 1701 address is registered with a particular 6LR. That is, the ARO option 1702 is not returned to the host until multihop DAD has been completed 1703 against the 6LBRs. For existing registrations in the 6LR the 1704 multihop DAD needs to be repeated against the 6LBRs to ensure that 1705 the entry for the address in the 6LBRs does not time out, but that 1706 can be done asynchronously with the response to the hosts. For 1707 instance, by tracking how much is left of the lifetime the 6LR 1708 registered with the 6LBRs and re-registering with the 6LBR when this 1709 lifetime is about to run out. 1711 For the synchronous multihop DAD the 6LR performs some additional 1712 checks to ensure that it has a Neighbor Cache entry it can use to 1713 respond to the host when it receives a response from a 6LBR. This 1714 consists of checking for an already existing (Tentative or 1715 Registered) Neighbor Cache entry for the registered address with a 1716 different EUI-64. If such a Registered NCE exists, then the 6LR 1717 SHOULD respond that the address is a duplicate. If such a Tentative 1718 NCE exists, then the 6LR SHOULD silently ignore the ARO thereby 1719 relying on the host retransmitting the ARO. This is needed to handle 1720 the case when multiple hosts try to register the same IPv6 address at 1721 the same time. If no Neighbor Cache entry exists, then the 6LR MUST 1722 create a Tentative Neighbor Cache entry with the EUI-64 and the SLLA 1723 option. This entry will be used to send the response to the host 1724 when the 6LBR responds positively. 1726 When a 6LR receives a Neighbor Solicitation containing an Address 1727 Registration option with a non-zero Registration Lifetime and it has 1728 no existing Registered Neighbor Cache entry, then with this mechanism 1729 the 6LR will invoke synchronous multihop DAD. 1731 The 6LR will unicast a Duplicate Address Request message to one or 1732 more 6LBRs, where the DAR contains the host's address in the 1733 Registered Address field. The DAR will be forwarded by 6LRs until it 1734 reaches the 6LBR, hence its IPv6 hop limit field will not be 255 when 1735 received by the 6LBR. The 6LBR will respond with a Duplicate Address 1736 Confirmation message, which will have a hop limit less than 255 when 1737 it reaches the 6LR. 1739 When the 6LR receives the DAC from the 6LBR, it will look for a 1740 matching (same IP address and EUI-64) (Tentative or Registered) 1741 Neighbor Cache entry. If no such entry is found then the DAC is 1742 silently ignored. If an entry is found and the DAC had Status=0 then 1743 the 6LR will mark the Tentative Neighbor Cache entry as Registered. 1744 In all cases when an entry is found then the 6LR will respond to the 1745 host with an NA, copying the Status and EUI-64 fields from the DAC to 1746 an ARO option in the NA. In case the status is an error, then the 1747 destination IP address of the NA is derived from the EUI-64 field of 1748 the DAC. 1750 A Tentative Neighbor Cache entry SHOULD be timed out 1751 TENTATIVE_NCE_LIFETIME seconds after it was created in order to allow 1752 for another host to attempt to register the IPv6 address. 1754 8.2.1. Message Validation for DAR and DAC 1756 A node MUST silently discard any received Duplicate Address Request 1757 and Confirmation messages that do not satisfy all of the following 1758 validity checks: 1760 o If the message includes an IP Authentication Header, the message 1761 authenticates correctly. 1763 o ICMP Checksum is valid. 1765 o ICMP Code is 0. 1767 o ICMP length (derived from the IP length) is 32 or more bytes. 1769 o The Registered Address is not a multicast address. 1771 o All included options have a length that is greater than zero. 1773 o The IP source address is not the unspecified address, nor a 1774 multicast address. 1776 The contents of the Reserved field, and of any unrecognized options, 1777 MUST be ignored. Future, backward-compatible changes to the protocol 1778 may specify the contents of the Reserved field or add new options; 1779 backward-incompatible changes may use different Code values. 1781 Note that due to the forwarding of the DAR and DAC messages between 1782 the 6LR and 6LBR there is no hop limit check on receipt for these 1783 ICMPv6 message types. 1785 8.2.2. Conceptual Data Structures 1787 A 6LBR implementing the optional multihop DAD needs to maintain some 1788 state separate from the Neighbor Cache. We call this conceptual data 1789 structure the DAD table. It is indexed by the IPv6 address - the 1790 Registered Address in the DAR - and contains the EUI-64 and the 1791 registration lifetime of the host that is using that address. 1793 8.2.3. 6LR Sending a Duplicate Address Request 1795 When a 6LR that implements the optional multihop DAD receives an NS 1796 from a host and subject to the above checks, the 6LR forms and sends 1797 a DAR to at least one 6LBR. The DAR contains the following 1798 information: 1800 o In the IPv6 source address, a global address of the 6LR. 1802 o In the IPv6 destination address, the address of the 6LBR. 1804 o In the IPv6 hop limit, MULTIHOP_HOPLIMIT. 1806 o The Status field MUST be set to zero 1808 o The EUI-64 and Registration lifetime are copied from the ARO 1809 received from the host. 1811 o The Registered Address set to the IPv6 address of the host, that 1812 is, the sender of the triggering NS. 1814 When a 6LR receives an NS from a host with a zero Registration 1815 Lifetime then, in addition to removing the Neighbor Cache entry for 1816 the host as specified in Section 6, an DAR is sent to the 6LBRs as 1817 above. 1819 A router MUST NOT modify the Neighbor Cache as a result of receiving 1820 a Duplicate Address Request. 1822 8.2.4. 6LBR Receiving a Duplicate Address Request 1824 When a 6LBR that implements the optional multihop DAD receives an DAR 1825 from a 6LR, it performs the message validation specified in 1826 Section 8.2.1. If the DAR is valid the 6LBR proceeds to look for the 1827 Registration Address in the DAD Table. If an entry is found and the 1828 recorded EUI-64 is different than the EUI-64 in the DAR, then it 1829 returns a DAC NA with the Status set to 1 ('Duplicate Address'). 1830 Otherwise it returns a DAC with Status set to zero and updates the 1831 lifetime. 1833 If no entry is found in the DAD Table and the Registration Lifetime 1834 is non-zero, then an entry is created and the EUI-64 and Registered 1835 Address from the DAR are stored in that entry. 1837 If an entry is found in the DAD Table, the EUI-64 matches, and the 1838 Registration Lifetime is zero then the entry is deleted from the 1839 table. 1841 In both of the above cases the 6LBR forms an DAC with the information 1842 copied from the DAR and the Status field is set to zero. The DAC is 1843 sent back to the 6LR i.e., back to the source of the DAR. The IPv6 1844 hop limit is set to MULTIHOP_HOPLIMIT 1846 8.2.5. Processing a Duplicate Address Confirmation 1848 When a 6LR that implements the optional multihop DAD receives a DAC 1849 message, then it first validates the message per Section 8.2.1. For 1850 a valid DAC, if there is no Tentative Neighbor Cache entry matching 1851 the Registered address and EUI-64, then the DAC is silently ignored. 1852 Otherwise, the information in the DAC and in the Tentative Neighbor 1853 Cache entry is used to form an NA to send to the host. The Status 1854 code is copied from the DAC to the ARO that is sent to the host. In 1855 case of the DAC indicates an error (the Status is non-zero), the NA 1856 is returned to the host as described in Section 6.5.2 and the 1857 Tentative Neighbor Cache entry for the Registered Address is removed. 1858 Otherwise it is made into a Registered Neighbor Cache entry. 1860 A router MUST NOT modify the Neighbor Cache as a result of receiving 1861 a Duplicate Address Confirmation, unless there is a Tentative 1862 Neighbor Cache entry matching the IPv6 address and EUI-64. 1864 8.2.6. Recovering from Failures 1866 If there is no response from a 6LBR after RETRANS_TIMER [RFC4861] 1867 then the 6LR would retransmit the DAR to the 6LBR up to 1868 MAX_UNICAST_SOLICIT [RFC4861] times. After this the 6LR SHOULD 1869 respond to the host with an ARO Status of zero. 1871 9. Protocol Constants 1873 This section defines the relevant protocol constants used in this 1874 document based on a subset of [RFC4861] constants. (*) indicates 1875 constants modified from [RFC4861] and (+) indicates new constants. 1877 Additional protocol constants are defined in Section 4. 1879 6LBR Constants: 1881 MIN_CONTEXT_CHANGE_DELAY+ 300 seconds 1883 6LR Constants: 1885 MAX_RTR_ADVERTISEMENTS 3 transmissions 1887 MIN_DELAY_BETWEEN_RAS* 10 seconds 1889 MAX_RA_DELAY_TIME* 2 seconds 1891 TENTATIVE_NCE_LIFETIME+ 20 seconds 1893 Router Constants: 1895 MULTIHOP_HOPLIMIT+ 64 1897 Host Constants: 1899 RTR_SOLICITATION_INTERVAL* 10 seconds 1901 MAX_RTR_SOLICITATIONS 3 transmissions 1903 MAX_RTR_SOLICITATION_INTERVAL+ 60 seconds 1905 10. Examples 1907 10.1. Message Examples 1909 STEP 1911 6LN 6LR 1913 | | 1915 1. | ---------- Router Solicitation --------> | 1917 | [SLLAO] | 1919 | | 1921 2. | <-------- Router Advertisement --------- | 1923 | [PIO + 6CO + ABRO + SLLAO] | 1925 Figure 2: Basic Router Solicitation/Router Advertisement exchange 1926 between a node and 6LR or 6LBR 1928 6LN 6LR 1930 | | 1932 1. | ------- NS with Address Registration ------> | 1934 | [ARO + SLLAO] | 1936 | | 1938 2. | <----- NA with Address Registration -------- | 1940 | [ARO with Status] | 1942 Figure 3: Neighbor Discovery Address Registration 1944 6LN 6LR 6LBR 1946 | | | 1948 1. | --- NS with Address Reg --> | | 1950 | [ARO + SLLAO] | | 1952 | | | 1954 2. | | ----------- DAR ----------> | 1956 | | | 1958 3. | | <---------- DAC ----------- | 1960 | | | 1962 4. | <-- NA with Address Reg --- | | 1964 | [ARO with Status] | 1966 Figure 4: Neighbor Discovery Address Registration with Multi-Hop DAD 1968 10.2. Host Bootstrapping Example 1970 The following example describes the address bootstrapping scenarios 1971 using the optimized ND mechanisms specified in this document. It is 1972 assumed that the 6LN first performs a sequence of operations in order 1973 to get secure access at the link-layer of the LoWPAN and obtain a key 1974 for link-layer security. The methods of how to establish the link- 1975 layer security is out of scope of this document. In this example an 1976 IEEE 802.15.4 6LN forms a 16-bit short-address based IPv6 addresses 1977 without using DHCPv6 (i.e., the M flag is not set in the Router 1978 Advertisements). 1980 1. After obtaining link-level security, a 6LN assigns a link-local 1981 IPv6 address to itself. A link-local IPv6 address is configured 1982 based on the 6LN's EUI-64 link-layer address formed as per [RFC4944]. 1984 2. Next the 6LN determines one or more default routers in the 1985 network by sending an RS to the all-routers multicast address with 1986 the SLLA Option set to its EUI-64 link-local address. If the 6LN was 1987 able to obtain the link-layer address of a router through its link- 1988 layer operations then the 6LN may form a link-local destination IPv6 1989 address for the router and send it a unicast RS. The 6LR responds 1990 with a unicast RA to the IP source using the SLLA option from the RS 1991 (it may have created a tentative NCE). See Figure 2. 1993 3. In order to communicate more than one IP hop away the 6LN 1994 configures a global IPv6 address. In order to save overhead, this 1995 6LN wishes to configure its IPv6 address based on a 16-bit short 1996 address as per [RFC4944]. As the network is unmanaged (M flag not 1997 set in RA), the 6LN randomly chooses a 16-bit link-layer address and 1998 forms a tentative IPv6 address from it. 2000 4. Next the 6LN registers that address with one or more of its 2001 default routers by sending a unicast NS message with an ARO 2002 containing its tentative global IPv6 address to register, the 2003 registration lifetime and its EUI-64. An SLLA option is also 2004 included with the link-layer address corresponding to the address 2005 being registered. If a successful (status 0) NA message is received 2006 the address can then be used and the 6LN assumes it has been 2007 successfully checked for duplicates. If a duplicate address (status 2008 1) NA message is received, the 6LN then removes the temporary IPv6 2009 address and 16-bit link-layer address and goes back to step 3. If a 2010 neighbor cache full (status 2) message is received, the 6LN attempts 2011 to register with another default router, or if none, goes back to 2012 step 2. See Figure 3. Note that an NA message returning an error 2013 would be sent back to the link-local EUI-64 based IPv6 address of the 2014 6LN instead of the 16-bit (duplicate) address. 2016 5. The 6LN now performs maintenance by sending a new NS address 2017 registration before the lifetime expires. 2019 If multihop DAD and multihop prefix and context distribution is used, 2020 the effect of the 6LRs and hosts following the above bootstrapping is 2021 a "wavefront" of 6LRs and host being configured spreading from the 2022 6LBRs. First the hosts and 6LRs that can directly reach a 6LBR would 2023 receive one or more RAs and configure and register their IPv6 2024 addresses. Once that is done they would enable the routing protocol 2025 and start sending out Router Advertisements. That would result in a 2026 new set of 6LRs and hosts to receive responses to their Router 2027 Solicitations, form and register their addresses, etc. That repeats 2028 until all of the 6LRs and hosts have been configured. 2030 10.2.1. Host Bootstrapping Messages 2032 This section brings specific message examples to the previous 2033 bootstrapping process. When discussing messages, the following 2034 notation is used: 2036 LL64: Link-Local Address based on the EUI-64, which is also the 2037 802.15.4 Long Address. 2039 GP16: Global Address based on the 802.15.4 Short Address. This 2040 address may not be unique. 2042 GP64: Global addresses derived from the EUI-64 address as specified 2043 in RFC 4944. 2045 MAC64: EUI-64 address used as the link-layer address. 2047 MAC16: IEEE 802.15.4 16-bit short address. 2049 Note that some implementations may use LL64 and GP16 style addresses 2050 instead of LL64 and GP64. In the following, we will show an example 2051 message flow as to how a node uses LL64 to register a GP16 address 2052 for multihop DAD verification. 2054 6LN-----RS-------->6LR 2055 Src= LL64 (6LN) 2056 Dst= All-router-link-scope-multicast 2057 SLLAO= MAC64 (6LN) 2059 6LR------RA--------->6LN 2060 Src= LL64 (6LR) 2061 Dst= LL64 (6LN) 2063 Note: Source address of RA must be a link-local 2064 address (Section 4.2, RFC 4861). 2066 6LN-------NS Reg------>6LR 2067 Src= GP16 (6LN) 2068 Dst= LL64 (6LR) 2069 ARO 2070 SLLAO= MAC16 (6LN) 2072 6LR---------DAR----->6LBR 2073 Src= GP64 or GP16 (6LR) 2074 Dst= GP64 or GP16 (6LBR) 2075 Registered Address= GP16 (6LN) and EUI-64 (6LN) 2077 6LBR-------DAC--------->6LR 2078 Src= GP64 or GP16 (6LBR) 2079 Dst= GP64 or GP16 (6LR) 2080 Copy of information from DAR 2082 If Status is a Success: 2084 6LR ---------NA-Reg------->6LN 2085 Src= LL64 (6LR) 2086 Dst= GP16 (6LN) 2087 ARO with Status = 0 2089 If Status is not a success: 2091 6LR ---------NA-Reg-------->6LN 2092 Src= LL64 (6LR) 2093 Dst= LL64 (6LN) --> Derived from the EUI-64 of ARO 2094 ARO with Status > 0 2096 Figure 5: Detailed Message Address Examples 2098 10.3. Router Interaction Example 2100 In the Route-over topology, when a routing protocol is run across 2101 6LRs the bootstrapping and neighbor cache management are handled a 2102 little differently. The description in this paragraph provides only 2103 a guideline for an implementation. 2105 At the initialization of a 6LR, it may choose to bootstrap as a host 2106 with the help of a parent 6LR if the optional multihop DAD is 2107 performed with the 6LBR. The neighbor cache management of a router 2108 and address resolution among the neighboring routers are described in 2109 Section 6.5.3 and Section 6.5.5, respectively. In this example, we 2110 assume that the neighboring 6LoWPAN link is secure. 2112 10.3.1. Bootstrapping a Router 2114 In this scenario, the bootstrapping 6LR, 'R1', is multiple hops away 2115 from the 6LBR and surrounded by other 6LR neighbors. Initially R1 2116 behaves as a host. It sends multicast RS and receives an RA from one 2117 or more neighboring 6LRs. R1 picks one 6LR as its temporary default 2118 router and performs address resolution via this default router. 2119 Note, if multihop DAD is not required (e.g. in a managed network or 2120 using EUI-64 based addresses) then it does not need to pick a 2121 temporary default router, however it may still want to send the 2122 initial RS message if it wants to autoconfigure its address with the 2123 global prefix disseminated by the 6LBR. 2125 Based on the information received in the RAs, R1 updates its cache 2126 with entries for all the neighboring 6LRs. Upon completion of the 2127 address registration, the bootstrapping router deletes the temporary 2128 entry of the default router and the routing protocol is started. 2130 Also note that R1 may refresh its multihop DAD registration directly 2131 with the 6LBR (using the next hop neighboring 6LR determined by the 2132 routing protocol for reaching the 6LBR). 2134 10.3.2. Updating the Neighbor Cache 2136 In this example, there are three 6LRs, R1, R2, R3. Initially when R2 2137 boots it sees only R1, and accordingly R2 creates a neighbor cache 2138 entry for R1. Now assume R2 receives a valid routing update from 2139 router R3. R2 does not have any neighbor cache entry for R3. If the 2140 implementation of R2 supports detecting link-layer address from the 2141 routing information packets then it directly updates the its neighbor 2142 cache using that link-layer information. If this is not possible, 2143 then R2 should perform multicast NS with source set with its link- 2144 local or global address depending on the scope of the source IP- 2145 address received in the routing update packet. The target address of 2146 the NS message is the source IPv6 address of the received routing 2147 update packet. The format of the NS message is as described in 2148 Section 4.3 of [RFC4861]. 2150 More generally any 6LR that receives a valid route-update from a 2151 neighboring router for which it does not have any neighbor cache 2152 entry is required to update its neighbor cache as described above. 2154 The router (6LR and 6LBR) IP-addresses learned via Neighbor Discovery 2155 are not redistributed to the routing protocol. 2157 11. Security Considerations 2159 The security considerations of IPv6 Neighbor Discovery [RFC4861] 2160 apply. Additional considerations can be found in [RFC3756]. 2162 This specification expects that the link layer is sufficiently 2163 protected, for instance using MAC sublayer cryptography. In other 2164 words, model 1 from [RFC3756] applies. In particular, it is expected 2165 that the LoWPAN MAC provides secure unicast to/from Routers and 2166 secure broadcast from the Routers in a way that prevents tampering 2167 with or replaying the Router Advertisement messages. However, any 2168 future 6LoWPAN security protocol that applies to Neighbor Discovery 2169 for 6LoWPAN protocol, is out of scope of this document. 2171 The multihop DAD mechanisms rely on DAR and DAC messages that are 2172 forwarded by 6LRs, and as a result the hop_limit=255 check on the 2173 receiver does not apply to those messages. This implies that any 2174 node on the Internet could successfully send such messages. We avoid 2175 any additional security issues due to this by requiring that the 2176 routers never modify the Neighbor Cache entry due to such messages, 2177 and that they reject them unless they are received on an interface 2178 that has been explicitly configured to use these optimizations. 2180 In some future deployments one might want to use SEcure Neighbor 2181 Discovery [RFC3971] [RFC3972]. This is possible with the Address 2182 Registration option as sent between hosts and routers, since the 2183 address that is being registered is the IPv6 source address of the 2184 Neighbor Solicitation and SeND verifies the IPv6 source address of 2185 the packet. Applying SeND to the optional router-to-router 2186 communication in this document is out of scope. 2188 12. IANA Considerations 2190 The document requires three new Neighbor Discovery option types under 2191 the subregistry "IPv6 Neighbor Discovery Option Formats": 2193 o Address Registration Option (TBD1) 2195 o 6LoWPAN Context Option (TBD2) 2197 o Authoritative Border Router Option (TBD3) 2199 The document requires two new ICMPv6 types under the subregistry 2200 "ICMPv6 type Numbers": 2202 o Duplicate Address Request (TBD4) 2204 o Duplicate Address Confirmation (TBD5) 2206 For the purpose of protocol interoperability testing of this 2207 specification, the following values are being used temporarily: 2209 o TBD1 = 31 2211 o TBD2 = 32 2213 o TBD3 = 33 2215 o TBD4 = 155 XXX 2217 o TBD3 = 156 XXX 2219 This document also requests IANA to create a new registry for the 2220 Status values of the Address Registration Option. 2222 [TO BE REMOVED: This registration should take place at the following 2223 location: http://www.iana.org/assignments/icmpv6-parameters] 2225 13. Guideline for New Features 2227 This section discusses a guideline of new features for implementation 2228 and deployment. 2230 +----------+---------------------------------+----------+-----------+ 2231 | Section | Description | deploy | implement | 2232 +----------+---------------------------------+----------+-----------+ 2233 | 3.1 | Host initiated RA | MUST | MUST | 2234 | 3.2 | EUI-64 based IPv6-address | MUST | MUST | 2235 | | 16bit-MAC based address | MAY | SHOULD | 2236 | | Other non-unique addresses | MAY | MAY | 2237 | 3.3 | Host Initiated RS | MUST | MUST | 2238 | | ABRO Processing | SHOULD | MUST | 2239 | 4.1 | Registration with ARO | MUST | MUST | 2240 | 4.2, 5.4 | 6lowpan Context Option | SHOULD | SHOULD | 2241 | 5.1 | Re-direct Message Acceptance | MUST NOT | MUST NOT | 2242 | | Joining Solicited Node | N/A | N/A | 2243 | | Multicast | | | 2244 | | Joining all-node Multicast | MUST | MUST | 2245 | | Using link-layer indication for | SHOULD | MAY | 2246 | | NUD | | | 2247 | 5.5 | 6lowpan-ND NUD | MUST | MUST | 2248 | 5.8.2 | Behavior on wake-up | SHOULD | SHOULD | 2249 +----------+---------------------------------+----------+-----------+ 2251 Table 2: Guideline for 6LoWPAN-ND features for hosts 2253 +---------------+-------------------------+------------+------------+ 2254 | Section | Description | deploy | implement | 2255 +---------------+-------------------------+------------+------------+ 2256 | 3.1 | Periodic RA | SHOULD NOT | SHOULD NOT | 2257 | 3.2 | Address assignment | SHOULD | MUST | 2258 | | during Startup | | | 2259 | 3.3 | Supporting EUI-64 based | MUST | MUST | 2260 | | MAC Hosts | | | 2261 | | Supporting 16-bit MAC | MAY | SHOULD | 2262 | | hosts | | | 2263 | 3.4, 4.3, | ABRO Processing/sending | MAY | SHOULD | 2264 | 8.1.3, 8.1.4 | | | | 2265 | 8.1 | Multihop Prefix storing | MAY | SHOULD | 2266 | | and re-distribution | | | 2267 | 3.5 | Tentative NCE | MUST | MUST | 2268 | 8.2 | Multihop DAD | MAY | SHOULD | 2269 | 4.1, 6.5, | ARO Support | MUST | MUST | 2270 | 6.5.1 - 6.5.5 | | | | 2271 | 4.2 | 6LoWPAN Context Option | SHOULD | SHOULD | 2272 | 6.3 | Process RS/ARO | MUST | MUST | 2273 +---------------+-------------------------+------------+------------+ 2275 Table 3: Guideline for 6LR features in 6LoWPAN-ND 2277 +--------------+--------------------------+------------+------------+ 2278 | Section | Description | deploy | implement | 2279 +--------------+--------------------------+------------+------------+ 2280 | 3.1 | Periodic RA | SHOULD NOT | SHOULD NOT | 2281 | 3.2 | Address autoconf on | MUST NOT | MUST NOT | 2282 | | Router interface | | | 2283 | 3.3 | EUI-64 MAC support on | MUST | MUST | 2284 | | 6lowpan interface | | | 2285 | 8.1 - 8.1.1, | Multihop Prefix | MAY | SHOULD | 2286 | 8.1.5 | distribution | | | 2287 | 8.2 | Multihop DAD | MAY | SHOULD | 2288 +--------------+--------------------------+------------+------------+ 2290 Table 4: Guideline for 6LBR features in 6LoWPAN-ND 2292 14. Acknowledgments 2294 The authors thank Pascal Thubert, Jonathan Hui, Carsten Bormann, 2295 Richard Kelsey, Geoff Mulligan, Julien Abeille, Alexandru Petrescu, 2296 Peter Siklosi, Pieter De Mil, Fred Baker, Anthony Schoofs, Phil 2297 Roberts, Daniel Gavelle, Joseph Reddy, Robert Cragie, Mathilde Durvy, 2298 Colin O'Flynn, Dario Tedeschi, Esko Dijk and Joakim Eriksson for 2299 useful discussions and comments that have helped shaped and improve 2300 this document. 2302 Additionally, the authors would like to recognize Carsten Bormann for 2303 the suggestions on the Context Prefix Option and contribution to 2304 earlier version of the draft, Pascal Thubert for contribution of the 2305 original registration idea and extensive contributions to earlier 2306 versions of the draft, Jonathan Hui for original ideas on prefix/ 2307 context distribution and extensive contributions to earlier versions 2308 of the draft, Colin O'Flynn for useful Error-to suggestions and 2309 contributions to the Examples section, Geoff Mulligan for suggesting 2310 the use of Address Registration as part of existing IPv6 Neighbor 2311 Discovery messages, and Mathilde Durvy for helping to clarify router 2312 interaction. 2314 15. Changelog 2316 Changes from -17 to -18: 2318 o Fixed nits related to IESG submission. 2320 Changes from -16 to -17: 2322 o Removed unnecessary normative text from Assumptions. 2324 o Clarified the next-hop determination of multicast addresses. 2326 o Editorial improvements from WGLC review. 2328 Changes from -15 to -16: 2330 o Added an applicability section (#133) 2332 o Updated document title to align with HC 2334 o Minor editing as result of WGLC review (#134) 2336 Changes from -14 to -15: 2338 o Changed use of redirect to SHOULD NOT for route-over and MAY for 2339 mesh-under. (#130) 2341 o Changed the 16-bit lifetimes to a unit of 60 seconds (#131) 2343 o Added text to Section 5.4.2 adding a receive-only state to 2344 context entries that timeout. (#132) 2346 Changes from -13 to -14: 2348 o Introduced the new DAR and DAC ICMPv6 message types for multihop 2349 DAD to avoid relying on the Length=4 checks for the ARO. This 2350 simplifies implementing the hop limit check. 2352 o Clarified the hop limit values for the multihop DAD messages by 2353 introducing the MULTIHOP_HOPLIMIT constant set to 64. 2355 o Clarified when a host should de-register from a router. 2357 o Added a section on next-hop determination for routers. 2359 o Removed the infinite lifetime from 6CO. 2361 o Increased MIN_CONTEXT_CHANGE_DELAY to 300 seconds. 2363 Changes from -12 to -13: 2365 o Error-to solution added for returning NA messages carrying an 2366 error ARO option to the link-local EUI-64 based IPv6 address of 2367 the host (#126). 2369 o New examples added. 2371 Changes from -11 to -12: 2373 o Version field of ABRO moved after Length for 32-bit alignment of 2374 the reserved space (#90). 2376 o Several clarifications were made on router interaction, 2377 including a new section with router interaction examples (#91). 2379 o Temporary Neighbor Cache Entry created upon host sending NS+ARO, 2380 and SLLAO removed from multihop DAD NS/NA messages (#87). 2382 Changes from -10 to -11: 2384 o Reference to RFC1982 for version number comparison (#80) 2386 o RA Router Lifetime field use clarified (#81) 2388 o Make fields 16-bit rather than 32-bit where possible (#83) 2390 o Unicast RA clarification (#84) 2392 o Temporary ND option types (#85) 2394 o SLLA/TLLA clarification (#86) 2396 o GP16 as source address in initial NS clarification (#87) 2398 Changes from -09 to -10: 2400 o Clarifications made to Section 8.2 (#66) 2402 o Explained behavior of Neighbor Cache (#67) 2404 o Clarified use of SLLAO in RS and NS messages (#68) 2406 o Added new term 6LN (#69) 2408 o Small clarification on 6CO flag (#70) 2410 o Defined host behavior on ARO failure better (#72) 2412 o Added bootstrapping example for a host (#73) 2414 o Added new Neighbor Cache Full ARO error (#74) 2415 o Added rule on the use of the M flag (#75) 2417 Changes from -08 to -09: 2419 o Clean re-write of the draft (re-use of some introductory 2420 material) 2422 o Merged in draft-chakrabarti-6lowpan-ipv6-nd-simple-00 2424 o Changed address registration to an option piggybacked on NS/NA 2426 o New Authoritative Border Router option 2428 o New Address Registration Option 2430 o Separated Prefix Information and Content Information 2432 o Optional DAD to the edge 2434 Changes from -07 to -08: 2436 o Removed Extended LoWPAN and Whiteboard related sections. 2438 o Included reference to the autoconf addressing model. 2440 o Added Optimistic Flag to 6AO. 2442 o Added guidelines on routers performing DAD. 2444 o Removed the NR/NC Advertising Interval. 2446 o Added assumption of uniform IID formation and DAD throughout a 2447 LoWPAN. 2449 Changes from -06 to -07: 2451 o Updated addressing and address resolution (#60). 2453 o Changed the Address Option to 6LoWPAN Address Option, fixed S 2454 values (#61). 2456 o Added support for classic RFC4861 RA Prefix Information messages 2457 to be processed (#62). 2459 o Added a section on using 6LoWPAN-ND under a hard-wired RFC4861 2460 stack (#63). 2462 o Updated the NR/NC message with a new Router flag, combined the 2463 Code and Status fields into one byte, and added the capability to 2464 carry 6IOs (#64). 2466 o Made co-existence with other ND mechanisms clear (#59). 2468 o Added a new Protocol Specification section with all mechanisms 2469 specified there (#59). 2471 o Removed dependencies and conflicts with RFC4861 wherever 2472 possible (#59). 2474 o Some editorial cleanup. 2476 Changes from -05 to -06: 2478 o Fixed the Prf codes (#52). 2480 o Corrected the OIIO TID field to 8-bits. Changed the Nonce/OII 2481 order in both the OIIO and the NR/NC. (#53) 2483 o Corrected an error in Table 1 (#54). 2485 o Fixed asymmetric and a misplaced transient in the 6LoWPAN 2486 terminology section. 2488 o Added Updates RFC4861 to header 2490 Changes from -04 to -05: 2492 o Meaning of the RA's M-bit changed to original [RFC4861] meaning 2493 (#46). 2495 o Terms "on-link" and "off-link" used in place of "on-link" and 2496 "off-link". 2498 o Next-hop determination text simplified (#49). 2500 o Neighbor cache and destination cache removed. 2502 o IID to link-layer address requirement relaxed. 2504 o NR/NC changes to enable on-link refresh with routers (#48). 2506 o Modified 6LoWPAN Information Option (#47). 2508 o Added a Protocol Constants section (#24) 2509 o Added the NR processing table (#51) 2511 o Considered the use of SeND on backbone NS/NA messages (#50) 2513 Changes from -03 to -04: 2515 o Moved Ad-hoc LoWPAN operation to Section 7 and made ULA prefix 2516 generation a features useful also in Simple and Extended LoWPANs. 2517 (#41) 2519 o Added a 32-bit Owner Nonce to the NR/NC messages and the 2520 Whiteboard, removed the TID history. (#39) 2522 o Improved the duplicate OII detection algorithm using the Owner 2523 Nonce. (#39) 2525 o Clarified the use of Source and Target link-layer options in 2526 NR/NC. (#43) 2528 o Included text on the use of alternative methods to acquire 2529 addresses. (#38) 2531 o Removed S=2 from Address Option (not needed). (#36) 2533 o Added a section on router dissemination consistency. (#44) 2535 o Small improvements and extensive editing. (#42, #37, #35) 2537 Changes from -02 to -03: 2539 o Updated terminology, with RFC4861 non-transitive link model. 2541 o 6LoWPAN and ND terminology separated. 2543 o Protocol overview explains RFC4861 diff in detail. 2545 o RR/RC is now Node Registration/Confirmation (NR/NC). 2547 o Added NR failure codes. 2549 o ER Metric now included in 6LoWPAN Summary Option for use in 2550 default router determination by hosts. 2552 o Examples of host data structures, and the Whiteboard given. 2554 o Whiteboard is supported by all Edge Routers for option 2555 simplicity. 2557 o Edge Router Specification chapter re-structured, clarifying 2558 optional Extended LoWPAN operation. 2560 o NS/NA now completely optional for nodes. No address resolution 2561 or NS/NA NUD required. 2563 o link-local operation now compatible with oDAD (was broken). 2565 o Exception to hop limit = 255 for NR/NC messages. 2567 o Security considerations improved. 2569 o ICMPv6 destination unreachable supported. 2571 Changes from -01 to -02: 2573 o Fixed 16 != 0xff bug (ticket closed). 2575 o Specified use of ULAs in ad-hoc LoWPAN section 9 (ticket 2576 closed). 2578 o Terminology cleanup based on Alex's comments. 2580 o General editing improvements. 2582 Changes from -00 to -01: 2584 o Specified the duplicate owner interface identifier procedures. 2585 A TID lollipop algorithm was sufficient (nonce unnecessary). 2587 o Defined fault tolerance using secondary bindings. 2589 o Defined ad-hoc network operation. 2591 o Removed the E flag from RA and the X flag from RR/RC. 2593 o Completed message examples. 2595 o Lots of improvements in text quality and consistency were made. 2597 16. References 2599 16.1. Normative References 2601 [RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, 2602 August 1996. 2604 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2605 Requirement Levels", BCP 14, RFC 2119, March 1997. 2607 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2608 (IPv6) Specification", RFC 2460, December 1998. 2610 [RFC2491] Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6 2611 over Non-Broadcast Multiple Access (NBMA) networks", 2612 RFC 2491, January 1999. 2614 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 2615 More-Specific Routes", RFC 4191, November 2005. 2617 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 2618 Addresses", RFC 4193, October 2005. 2620 [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control 2621 Message Protocol (ICMPv6) for the Internet Protocol 2622 Version 6 (IPv6) Specification", RFC 4443, March 2006. 2624 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2625 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2626 September 2007. 2628 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2629 Address Autoconfiguration", RFC 4862, September 2007. 2631 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 2632 "Transmission of IPv6 Packets over IEEE 802.15.4 2633 Networks", RFC 4944, September 2007. 2635 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 2636 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 2637 May 2008. 2639 16.2. Informative References 2641 [EUI64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64) 2642 Registration Authority", . 2645 [I-D.ietf-6lowpan-hc] 2646 Hui, J. and P. Thubert, "Compression Format for IPv6 2647 Datagrams in Low Power and Lossy Networks (6LoWPAN)", 2648 draft-ietf-6lowpan-hc-15 (work in progress), 2649 February 2011. 2651 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 2652 and M. Carney, "Dynamic Host Configuration Protocol for 2653 IPv6 (DHCPv6)", RFC 3315, July 2003. 2655 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 2656 Host Configuration Protocol (DHCP) version 6", RFC 3633, 2657 December 2003. 2659 [RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor 2660 Discovery (ND) Trust Models and Threats", RFC 3756, 2661 May 2004. 2663 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 2664 Neighbor Discovery (SEND)", RFC 3971, March 2005. 2666 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 2667 RFC 3972, March 2005. 2669 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 2670 over Low-Power Wireless Personal Area Networks (6LoWPANs): 2671 Overview, Assumptions, Problem Statement, and Goals", 2672 RFC 4919, August 2007. 2674 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 2675 Extensions for Stateless Address Autoconfiguration in 2676 IPv6", RFC 4941, September 2007. 2678 [RFC5889] Baccelli, E. and M. Townsley, "IP Addressing Model in Ad 2679 Hoc Networks", RFC 5889, September 2010. 2681 Authors' Addresses 2683 Zach Shelby (editor) 2684 Sensinode 2685 Hallituskatu 13-17D 2686 Oulu 90100 2687 FINLAND 2689 Phone: +358407796297 2690 Email: zach@sensinode.com 2692 Samita Chakrabarti 2693 Ericsson 2695 Email: samita.chakrabarti@ericsson.com 2696 Erik Nordmark 2697 Cisco Systems 2699 Email: nordmark@cisco.com