idnits 2.17.1 draft-ietf-6lowpan-nd-21.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year (Using the creation date from RFC4944, updated by this document, for RFC5378 checks: 2005-07-13) -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (August 24, 2012) is 4255 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'SLLAO' is mentioned on line 1929, but not defined -- Possible downref: Non-RFC (?) normative reference: ref. 'ETHERNET' ** 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) -- Obsolete informational reference (is this intentional?): RFC 5006 (Obsoleted by RFC 6106) Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 8 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: February 25, 2013 E. Nordmark 7 Cisco Systems 8 August 24, 2012 10 Neighbor Discovery Optimization for Low Power and Lossy Networks 11 (6LoWPAN) 12 draft-ietf-6lowpan-nd-21 14 Abstract 16 The IETF 6LoWPAN work defines IPv6 over Low-power Wireless Personal 17 Area Networks such as IEEE 802.15.4. This and other similar link 18 technologies have limited or no usage of multicast signaling due to 19 energy conservation. In addition, the wireless network may not 20 strictly follow the traditional concept of IP subnets and IP links. 21 IPv6 Neighbor Discovery was not designed for non-transitive wireless 22 links, as its reliance on the traditional IPv6 link concept and its 23 heavy use of multicast make it inefficient and sometimes impractical 24 in a low-power and lossy network. This document describes simple 25 optimizations to IPv6 Neighbor Discovery, its addressing mechanisms 26 and duplicate address detection for Low-power Wireless Personal Area 27 Networks and similar networks. The document thus updates RFC 4944 to 28 specify the use of the 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 February 25, 2013. 47 Copyright Notice 48 Copyright (c) 2012 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. Applicability . . . . . . . . . . . . . . . . . . . . . . 6 66 1.3. Goals and Assumptions . . . . . . . . . . . . . . . . . . 6 67 1.4. Substitutable Features . . . . . . . . . . . . . . . . . . 8 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 9 69 3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 10 70 3.1. Extensions to RFC4861 . . . . . . . . . . . . . . . . . . 11 71 3.2. Address Assignment . . . . . . . . . . . . . . . . . . . . 12 72 3.3. Host-to-Router Interaction . . . . . . . . . . . . . . . . 12 73 3.4. Router-to-Router Interaction . . . . . . . . . . . . . . . 13 74 3.5. Neighbor Cache Management . . . . . . . . . . . . . . . . 14 75 4. New Neighbor Discovery Options and Messages . . . . . . . . . 15 76 4.1. Address Registration Option . . . . . . . . . . . . . . . 15 77 4.2. 6LoWPAN Context Option . . . . . . . . . . . . . . . . . . 17 78 4.3. Authoritative Border Router Option . . . . . . . . . . . . 18 79 4.4. Duplicate Address messages . . . . . . . . . . . . . . . . 20 80 5. Host Behavior . . . . . . . . . . . . . . . . . . . . . . . . 21 81 5.1. Forbidden Actions . . . . . . . . . . . . . . . . . . . . 21 82 5.2. Interface Initialization . . . . . . . . . . . . . . . . . 21 83 5.3. Sending a Router Solicitation . . . . . . . . . . . . . . 22 84 5.4. Processing a Router Advertisement . . . . . . . . . . . . 22 85 5.4.1. Address configuration . . . . . . . . . . . . . . . . 23 86 5.4.2. Storing Contexts . . . . . . . . . . . . . . . . . . . 23 87 5.4.3. Maintaining Prefix and Context Information . . . . . . 23 88 5.5. Registration and Neighbor Unreachability Detection . . . . 24 89 5.5.1. Sending a Neighbor Solicitation . . . . . . . . . . . 24 90 5.5.2. Processing a Neighbor Advertisement . . . . . . . . . 25 91 5.5.3. Recovering from Failures . . . . . . . . . . . . . . . 25 92 5.6. Next-hop Determination . . . . . . . . . . . . . . . . . . 26 93 5.7. Address Resolution . . . . . . . . . . . . . . . . . . . . 26 94 5.8. Sleeping . . . . . . . . . . . . . . . . . . . . . . . . . 26 95 5.8.1. Picking an Appropriate Registration Lifetime . . . . . 27 96 5.8.2. Behavior on Wakeup . . . . . . . . . . . . . . . . . . 27 97 6. Router Behavior for 6LR and 6LBR . . . . . . . . . . . . . . . 27 98 6.1. Forbidden Actions . . . . . . . . . . . . . . . . . . . . 28 99 6.2. Interface Initialization . . . . . . . . . . . . . . . . . 28 100 6.3. Processing a Router Solicitation . . . . . . . . . . . . . 28 101 6.4. Periodic Router Advertisements . . . . . . . . . . . . . . 29 102 6.5. Processing a Neighbor Solicitation . . . . . . . . . . . . 30 103 6.5.1. Checking for Duplicates . . . . . . . . . . . . . . . 30 104 6.5.2. Returning Address Registration Errors . . . . . . . . 30 105 6.5.3. Updating the Neighbor Cache . . . . . . . . . . . . . 31 106 6.5.4. Next-hop Determination . . . . . . . . . . . . . . . . 31 107 6.5.5. Address Resolution between Routers . . . . . . . . . . 31 108 7. Border Router Behavior . . . . . . . . . . . . . . . . . . . . 32 109 7.1. Prefix Determination . . . . . . . . . . . . . . . . . . . 33 110 7.2. Context Configuration and Management . . . . . . . . . . . 33 111 8. Substitutable Feature Behavior . . . . . . . . . . . . . . . . 34 112 8.1. Multihop Prefix and Context Distribution . . . . . . . . . 34 113 8.1.1. 6LBRs Sending Router Advertisements . . . . . . . . . 34 114 8.1.2. Routers Sending Router Solicitations . . . . . . . . . 35 115 8.1.3. Routers Processing Router Advertisements . . . . . . . 35 116 8.1.4. Storing the Information . . . . . . . . . . . . . . . 35 117 8.1.5. Sending Router Advertisements . . . . . . . . . . . . 36 118 8.2. Multihop Duplicate Address Detection . . . . . . . . . . . 36 119 8.2.1. Message Validation for DAR and DAC . . . . . . . . . . 38 120 8.2.2. Conceptual Data Structures . . . . . . . . . . . . . . 39 121 8.2.3. 6LR Sending a Duplicate Address Request . . . . . . . 39 122 8.2.4. 6LBR Receiving a Duplicate Address Request . . . . . . 39 123 8.2.5. Processing a Duplicate Address Confirmation . . . . . 40 124 8.2.6. Recovering from Failures . . . . . . . . . . . . . . . 40 125 9. Protocol Constants . . . . . . . . . . . . . . . . . . . . . . 40 126 10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 127 10.1. Message Examples . . . . . . . . . . . . . . . . . . . . . 41 128 10.2. Host Bootstrapping Example . . . . . . . . . . . . . . . . 43 129 10.2.1. Host Bootstrapping Messages . . . . . . . . . . . . . 44 130 10.3. Router Interaction Example . . . . . . . . . . . . . . . . 47 131 10.3.1. Bootstrapping a Router . . . . . . . . . . . . . . . . 47 132 10.3.2. Updating the Neighbor Cache . . . . . . . . . . . . . 47 133 11. Security Considerations . . . . . . . . . . . . . . . . . . . 48 134 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 49 135 13. Interaction with other Neighbor Discovery Extensions . . . . . 50 136 14. Guideline for New Features . . . . . . . . . . . . . . . . . . 50 137 15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 52 138 16. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 52 139 17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 59 140 17.1. Normative References . . . . . . . . . . . . . . . . . . . 59 141 17.2. Informative References . . . . . . . . . . . . . . . . . . 60 142 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 61 144 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 Low-power Wireless Personal Area Network (LoWPAN) is 150 characterized as lossy, low-power, low bit-rate, short range, with 151 many nodes saving energy with long sleep periods. Multicast as used 152 in IPv6 Neighbor Discovery [RFC4861] is not desirable in such a 153 wireless low-power and lossy network. Moreover, LoWPAN links are 154 asymmetric and non-transitive in nature. A LoWPAN is potentially 155 composed of a large number of overlapping radio ranges. Although a 156 given radio range has broadcast capabilities, the aggregation of 157 these is a complex Non-Broadcast MultiAccess (NBMA, [RFC2491]) 158 structure with generally no LoWPAN-wide multicast capabilities. 159 Link-local scope is in reality defined by reachability and radio 160 strength. Thus we can consider a LoWPAN to be made up of links with 161 undetermined connectivity properties as in [RFC5889], along with the 162 corresponding address model assumptions defined 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 optional Neighbor Discovery option to distribute 6LoWPAN 176 header compression context to hosts. 178 o Multihop distribution of prefix and 6LoWPAN header compression 179 context. 181 o Multihop duplicate address detection which uses two new ICMPv6 182 message types. 184 The two multihop items can be substituted by a routing protocol 185 mechanism if that is desired, see Section 1.4. 187 The document defines three new ICMPv6 message options: the Address 188 Registration, Authoritative Border Router, and 6LoWPAN Context 189 options. It also defines two new ICMPv6 message types: the Duplicate 190 Address Request and Duplicate Address Confirmation. 192 1.1. The Shortcomings of IPv6 Neighbor Discovery 194 IPv6 Neighbor Discovery [RFC4861] provides several important 195 mechanisms used for Router Discovery, Address Resolution, Duplicate 196 Address Detection, Redirect, along with Prefix and Parameter 197 Discovery. 199 Following power-on and initialization of the network in IPv6 Ethernet 200 networks, a node joins the solicited-node multicast address on the 201 interface and then performs Duplicate Address Detection (DAD) for the 202 acquired link-local address by sending a solicited-node multicast 203 message to the link. After that it sends multicast messages to the 204 all-router address to solicit router advertisements. If the host 205 receives a valid Router Advertisement with the "A" flag, it 206 autoconfigures the IPv6 address with the advertised prefix in the 207 Router Advertisement (RA) message. Besides this, the IPv6 routers 208 usually send router advertisements periodically on the network. RAs 209 are sent to the all-node multicast address. Nodes send Neighbor 210 Solicitation/Neighbor Advertisement messages to resolve the IPv6 211 address of the destination on the link. The Neighbor Solicitation 212 messages used for address resolution are multicast. The Duplicate 213 Address Detection procedure and the use of periodic Router 214 Advertisement messages assumes that the nodes are powered on and 215 reachable most of the time. 217 In Neighbor Discovery the routers find the hosts by assuming that a 218 subnet prefix maps to one broadcast domain, and then multicast 219 Neighbor Solicitation messages to find the host and its link-layer 220 address. Furthermore, the DAD use of multicast assumes that all 221 hosts that autoconfigure IPv6 addresses from the same prefix can be 222 reached using link-local multicast messages. 224 Note that the 'L' (on-link) bit in the Prefix Information option can 225 be set to zero in Neighbor Discovery, which makes the host not use 226 multicast Neighbor Solicitation (NS) messages for address resolution 227 of other hosts, but routers still use multicast NS messages to find 228 the hosts. 230 Due to the lossy nature of wireless communication and a changing 231 radio environment, the IPv6-link node-set may change due to external 232 physical factors. Thus the link is often unstable and the nodes 233 appear to be moving without necessarily moving physically. 235 A LoWPAN can use two types of link-layer addresses; 16-bit short 236 addresses and 64-bit unique addresses as defined in [RFC4944]. 237 Moreover, the available link-layer payload size is on the order of 238 less than 100 bytes thus header compression is very useful. 240 Considering the above characteristics in a LoWPAN, and the IPv6 241 Neighbor Discovery [RFC4861] protocol design, some optimizations and 242 extensions to Neighbor Discovery are useful for the wide deployment 243 of IPv6 over low-powered and lossy networks (example: 6LoWPAN and 244 other homogeneous low-power networks). 246 1.2. Applicability 248 In its Section 1, [RFC4861] foresees a document that covers operating 249 IP over a particular link type and defines an exception to the 250 otherwise general applicability of unmodified [RFC4861]. The present 251 specification improves the usage of IPv6 Neighbor Discovery for 252 LoWPANs in order to save energy and processing power of such nodes. 253 The document, thus updates [RFC4944] to specify the use of the 254 optimizations defined here. 256 The applicability of this specification is limited to LoWPANs where 257 all nodes on the subnet implement these optimizations in a 258 homogeneous way. Although it is noted that some of these 259 optimizations may be useful outside of 6LoWPAN, for example in 260 general IPv6 low-power and lossy networks and possibly even in 261 combination with [RFC4861], the usage of such combinations is out of 262 scope of this document. 264 In this document, we specify a set of behaviors between hosts and 265 routers in LoWPANs. An implementation that adheres to this document 266 MUST implement those behaviors. The document also specifies a set of 267 behaviors (multihop prefix or context dissemination, and separately 268 multihop duplicate address detection) which are needed in route-over 269 configurations. An implementation of this specification MUST support 270 those pieces, unless the implementation supports some alternative 271 ("substitute") from some some other specification. 273 The optimizations described in this document apply to different 274 topologies. They are most useful for route-over and mesh-under 275 configurations in Mesh topologies. However, Star topology 276 configurations will also benefit from the optimizations due to 277 reduced signaling, robust handling of the non-transitive link, and 278 header compression context information. 280 1.3. Goals and Assumptions 282 The document has the following main goals and assumptions. 284 Goals: 286 o Optimize Neighbor Discovery with a mechanism that is minimal yet 287 sufficient for the operation in both mesh-under and route-over 288 configurations. 290 o Minimize signaling by avoiding the use of multicast flooding and 291 reducing the use of link-scope multicast messages. 293 o Optimize the interfaces between hosts and their default routers. 295 o Support for sleeping hosts. 297 o Disseminate context information to hosts as needed by 6LoWPAN 298 Header Compression [RFC6282]. 300 o Disseminate context information and prefix information from the 301 border to all routers in a LoWPAN. 303 o Multihop duplicate address detection mechanism suitable for route- 304 over LoWPANs. 306 Assumptions: 308 o EUI-64 addresses are globally unique and the LoWPAN is 309 homogeneous. 311 o All nodes in the network have an EUI-64 interface identifier in 312 order to do address auto-configuration and detect duplicate 313 addresses. 315 o The link layer technology is assumed to be low-power and lossy, 316 exhibiting undetermined connectivity, such as IEEE 802.15.4 317 [RFC4944]. However, the Address Registration mechanism might be 318 useful for other link layer technologies. 320 o A 6LoWPAN is configured to share one or more global IPv6 address 321 prefixes to enable hosts to move between routers in the LoWPAN 322 without changing their IPv6 addresses. 324 o When using the multihop DAD mechanism of Section 8.2 each 6LR 325 registers with all the 6LBRs available in the LoWPAN. 327 o If IEEE 802.15.4 16-bit short addresses are used, then some 328 technique is used to ensure uniqueness of those link-layer 329 addresses. That could be done using DHCPv6, the Address 330 Registration Option based duplicate address detection (specified 331 in Section 8.2) or other techniques outside of the scope of this 332 document. 334 o In order to preserve the uniqueness of addresses (see Section 5.4, 335 [RFC4862]) not derived from an EUI-64, they must be either 336 assigned or checked for duplicates in the same way throughout the 337 LoWPAN. This can be done using DHCPv6 for assignment and/or using 338 the duplicate address detection mechanism specified in Section 8.2 339 (or any other protocols developed for that purpose). 341 o In order for 6LoWPAN Header Compression [RFC6282] to operate 342 correctly, the compression context must match for all the hosts, 343 6LRs, and 6LBRs that can send, receive, or forward a given packet. 344 If Section 8.1 is used to distribute context information this 345 implies that all the 6LBRs must coordinate the context information 346 they distribute within a single LoWPAN. 348 o This specification describes the operation of ND within a single 349 LoWPAN. The participation of a node in multiple LoWPANs 350 simultaneously may be possible, but is out of scope of this 351 document. 353 o Since the LoWPAN shares its prefix(es) throughout the network, 354 mobility of nodes within the LoWPAN is transparent. Inter-LoWPAN 355 mobility is out-of-scope of this document. 357 1.4. Substitutable Features 359 This document defines the optimization of Neighbor Discovery messages 360 for the host-router interface and introduces two new mechanisms in a 361 Route-over topology. 363 Unless specified otherwise (in a document that defines a routing 364 protocol that is used in a 6LoWPAN) this document applies to networks 365 with any routing protocol. However, because the routing protocol may 366 provide good alternate mechanisms, this document defines certain 367 features as "substitutable", meaning they can be substituted by a 368 routing protocol specification that provides mechanisms achieving the 369 same overall effect. 371 The features that are substitutable (individually or in a group): 373 o Multihop distribution of prefix and 6LoWPAN header compression 374 context 376 o Multihop duplicate address detection 378 Thus Multihop prefix distribution (ABRO option) and 6LoWPAN Context 379 Option (6CO, for distributing Header Compression Contexts) go hand- 380 in-hand. If substitution is intended for one of them, then both of 381 them MUST be substituted. 383 A guideline for feature implementation and deployment is provided at 384 the end of the document. 386 2. Terminology 388 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 389 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 390 document are to be interpreted as described in [RFC2119]. 392 This specification requires readers to be familiar with all the terms 393 and concepts that are discussed in "Neighbor Discovery for IP version 394 6" [RFC4861] "IPv6 Stateless Address Autoconfiguration" [RFC4862], 395 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 396 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 397 "Transmission of IPv6 Packets over IEEE 802.15.4 Networks" [RFC4944] 398 and "IP Addressing Model in Ad Hoc Networks" [RFC5889]. 400 This specification makes extensive use of the same terminology 401 defined in [RFC4861] unless otherwise defined below. 403 6LoWPAN link: 404 A wireless link determined by single IP hop reachability of 405 neighboring nodes. These are considered links with undetermined 406 connectivity properties as in [RFC5889]. 408 6LoWPAN Node (6LN): 409 A 6LoWPAN Node is any host or router participating in a LoWPAN. 410 This term is used when referring to situations in which either a 411 host or router can play the role described. 413 6LoWPAN Router (6LR): 414 An intermediate router in the LoWPAN that is able to send and 415 receive Router Advertisements, Router Solicitations as well as 416 forward and route IPv6 packets. 6LoWPAN routers are present only 417 in route-over topologies. 419 6LoWPAN Border Router (6LBR): 420 A border router located at the junction of separate 6LoWPAN 421 networks or between a 6LoWPAN network and another IP network. 422 There may be one or more 6LBRs at the 6LoWPAN network boundary. A 423 6LBR is the responsible authority for IPv6 Prefix propagation for 424 the 6LoWPAN network it is serving. An isolated LoWPAN also 425 contains a 6LBR in the network, which provides the prefix(es) for 426 the isolated network. 428 Router: 429 Either a 6LR or a 6LBR. Note that nothing in this document 430 precludes a node being a router on some interfaces and a host on 431 other interfaces as allowed by [RFC2460]. 433 Mesh-under: 434 A topology where nodes are connected to a 6LBR through a mesh 435 using link-layer forwarding. Thus in a mesh-under configuration 436 all IPv6 hosts in a LoWPAN are only one IP hop away from the 6LBR. 437 This topology simulates the typical IP-subnet topology with one 438 router with multiple nodes in the same subnet. 440 Route-over: 441 A topology where hosts are connected to the 6LBR through the use 442 of intermediate layer-3 (IP) routing. Here hosts are typically 443 multiple IP hops away from a 6LBR. The route-over topology 444 typically consists of a 6LBR, a set of 6LRs and hosts. 446 Non-Transitive Link: 447 A link which exhibits asymmetric reachability as defined in 448 Section 2.2 of [RFC4861]. 450 IP-over-foo Document: 451 A specification that covers operating IP over a particular link 452 type, for example [RFC4944] "Transmission of IPv6 Packets over 453 IEEE 802.15.4 Networks". 455 Header Compression Context: 456 Address information shared across a LoWPAN and used by 6LoWPAN 457 Header Compression [RFC6282] to enable the elision of information 458 that would otherwise be sent repeatedly. In a "context", a 459 (potentially partial) address is associated with a Context 460 Identifier, which is then used in header compression as a shortcut 461 for (parts of) a source or destination address. 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 [RFC6282] by 485 carrying header compression information in a new option in Router 486 Advertisement messages. 488 In addition, there are separate mechanisms that between 6LRs and 489 6LBRs to perform multihop Duplicate Address Detection and 490 distribution of the Prefix and compression Context information from 491 the 6LBRs to all the 6LRs, which in turn use normal Neighbor 492 Discovery mechanisms to convey this information to the hosts. 494 The protocol is designed so that the host-to-router interaction is 495 not affected by the configuration of the 6LoWPAN; the host-to-router 496 interaction is the same in a mesh-under and route-over configuration. 498 3.1. Extensions to RFC4861 500 This document specifies the following optimizations and extensions to 501 IPv6 Neighbor Discovery [RFC4861]: 503 o Host initiated refresh of Router Advertisement information. This 504 removes the need for periodic or unsolicited Router Advertisements 505 from routers to hosts. 507 o No Duplicate Address Detection (DAD) is performed if EUI-64 based 508 IPv6 addresses are used (as these addresses are assumed to be 509 globally unique). 511 o DAD is optional if DHCPv6 is used to assign addresses. 513 o A New Address Registration mechanism using a new Address 514 Registration option between hosts and routers. This removes the 515 need for Routers to use multicast Neighbor Solicitations to find 516 hosts, and supports sleeping hosts. This also enables the same 517 IPv6 address prefix(es) to be used across a route-over 6LoWPAN. 518 It provides the host-to-router interface for Duplicate Address 519 Detection. 521 o A new Router Advertisement option for Context information used by 522 6LoWPAN header compression. 524 o A new mechanism to perform Duplicate Address Detection across a 525 route-over 6LoWPAN using the new Duplicate Address Request and 526 Confirmation messages. 528 o New mechanisms to distribute Prefixes and Context information 529 across a route-over network which uses a new Authoritative Border 530 Router option to control the flooding of configuration changes. 532 o A few new default protocol constants are introduced and some 533 existing Neighbor Discovery protocol constants are tuned. 535 3.2. Address Assignment 537 Hosts in a 6LoWPAN configure their IPv6 address as specified in 538 [RFC4861] and [RFC4862] based on the information received in Router 539 Advertisement messages. The use of the M flag in this optimization 540 is however more restrictive than in [RFC4861]. When the M flag is 541 set a host is assumed to use DHCPv6 to assign any non-EUI-64 542 addresses. When the M flag is not set, the nodes in the LoWPAN 543 support duplicate address detection, thus a host can then safely use 544 the address registration mechanism to check non-EUI-64 addresses for 545 uniqueness. 547 6LRs MAY use the same mechanisms to configure their IPv6 addresses. 549 The 6LBRs are responsible for managing the prefix(es) assigned to the 550 6LoWPAN, using manual configuration, DHCPv6 Prefix Delegation 551 [RFC3633], or other mechanisms. In an isolated LoWPAN a ULA 552 [RFC4193] prefix SHOULD be generated by the 6LBR. 554 3.3. Host-to-Router Interaction 556 A host sends Router Solicitation messages at startup and also when 557 Neighbor Unreachability Detection towards one of its default routers 558 fails. 560 Hosts receive Router Advertisement messages typically containing the 561 Authoritative Border Router option (ABRO) and may optionally contain 562 one or more 6LoWPAN Context options (6CO) in addition to the existing 563 Prefix Information options (PIO) as described in [RFC4861]. 565 When a host has configured a non-link-local IPv6 address, it 566 registers that address with one or more of its default routers using 567 the Address Registration option (ARO) in an NS message. The host 568 chooses a lifetime of the registration and repeats the ARO option 569 periodically (before the lifetime runs out) to maintain the 570 registration. The lifetime should be chosen in such a way as to 571 maintain the registration even while a host is sleeping. Likewise, 572 mobile nodes that change their point of attachment often, should use 573 a suitably short lifetime. See Section 5.5 for registration details 574 and Section 9 for protocol constants. 576 The registration fails when an ARO option is returned to the host 577 with a non-zero Status. One reason may be that the router determines 578 that the IPv6 address is already used by another host, that is, is 579 used by a host with a different EUI-64. This can be used to support 580 non-EUI-64 based addresses such as temporary IPv6 addresses [RFC4941] 581 or addresses based on an Interface ID that is a IEEE 802.15.4 16-bit 582 short addresses. Failure can also occur if the Neighbor Cache on 583 that router is full. 585 The re-registration of an address can be combined with Neighbor 586 Unreachability Detection (NUD) of the router since both use unicast 587 Neighbor Solicitation messages. This makes things efficient when a 588 host wakes up to send a packet and both need to perform NUD to check 589 that the router is still reachable, and refresh its registration with 590 the router. 592 The response to an address registration might not be immediate since 593 in route-over configurations the 6LR might perform Duplicate Address 594 Detection against the 6LBR. A host retransmits the Address 595 Registration option until it is acknowledged by the receipt of a 596 Address Registration option. 598 As part of the optimizations, Address Resolution is not performed by 599 multicasting Neighbor Solicitation messages as in [RFC4861]. 600 Instead, the routers maintain Neighbor Cache entries for all 601 registered IPv6 addresses. If the address is not in the Neighbor 602 Cache in the router, then the address either doesn't exist, or is 603 assigned to a host attached to some other router in the 6LoWPAN, or 604 is external to the 6LoWPAN. In a route-over configuration the 605 routing protocol is used to route such packets toward the 606 destination. 608 3.4. Router-to-Router Interaction 610 The new router-to-router interaction is only for the route-over 611 configuration where 6LRs are present. See also Section 1.4. 613 6LRs MUST act like a host during system startup and prefix 614 configuration by sending Router Solicitation messages and 615 autoconfiguring their IPv6 addresses unlike routers in [RFC4861]. 617 When multihop prefix and context dissemination are used then the 6LRs 618 store the ABRO, 6CO and Prefix Information received (directly or 619 indirectly) from the 6LBRs and redistribute this information in the 620 Router Advertisement they send to other 6LRs or send to hosts in 621 response to a Router Solicitations. There is a version number field 622 in the ABRO which is used to limit the flooding of updated 623 information between the 6LRs. 625 A 6LR can perform Duplicate Address Detection against one or more 626 6LBRs using the new Duplicate Address Request (DAR) and Confirmation 627 (DAC) messages, which carry the information from the Address 628 Registration option. The DAR and DAC messages will be forwarded 629 between the 6LR and 6LBRs thus the [RFC4861] rule for checking hop 630 limit=255 does not apply to the DAR and DAC messages. Those multihop 631 DAD messages MUST NOT modify any Neighbor Cache entries on the 632 routers since we do not have the security benefits provided by the 633 hop limit=255 check. 635 3.5. Neighbor Cache Management 637 The use of explicit registrations with lifetimes plus the desire to 638 not multicast Neighbor Solicitation messages for hosts imply that we 639 manage the Neighbor Cache entries (NCE) slightly differently than in 640 [RFC4861]. This results in three different types of NCEs and the 641 types specify how those entries can be removed: 643 Garbage-collectible: Entries that are subject to the normal rules in 644 [RFC4861] that allow for garbage collection 645 when low on memory. 647 Registered: Entries that have an explicit registered 648 lifetime and are kept until this lifetime 649 expires or they are explicitly unregistered. 651 Tentative: Entries that are temporary with a short 652 lifetime, which typically get converted to 653 Registered entries. 655 Note that the type of the NCE is orthogonal to the states specified 656 in [RFC4861]. 658 When a host interacts with a router by sending Router Solicitations 659 this results in a Tentative NCE. Once a router has successfully had 660 a node register with it, the result is a Registered NCE. When 661 Routers send RAs to hosts, and when routers receive RA messages or 662 receive multicast NS messages from other Routers, the result is 663 Garbage-collectible NCEs. There can only be one kind of NCE for an 664 IP address at a time. 666 Neighbor Cache entries on Routers can additionally be added or 667 deleted by a routing protocol used in the 6LoWPAN. This is useful if 668 the routing protocol carries the link-layer addresses of the 669 neighboring routers. Depending on the details of such routing 670 protocols such NCEs could be either Registered or Garbage- 671 collectible. 673 4. New Neighbor Discovery Options and Messages 675 This section defines new Neighbor Discovery message options used by 676 this specification. The Address Registration Option is used by 677 hosts, whereas the Authoritative Border Router Option and 6LoWPAN 678 Context Option are used in the substitable router-to-router 679 interaction. This section also defines the new router-to-router 680 Duplicate Address Request and Confirmation messages. 682 4.1. Address Registration Option 684 The routers need to know the set of host IP addresses that are 685 directly reachable and their corresponding link-layer addresses. 686 This needs to be maintained as the radio reachability changes. For 687 this purpose an Address Registration Option (ARO) is introduced, 688 which can be included in unicast Neighbor Solicitation (NS) messages 689 sent by hosts. Thus it can be included in the unicast NS messages 690 that a host sends as part of Neighbor Unreachability Detection to 691 determine that it can still reach a default router. The ARO is used 692 by the receiving router to reliably maintain its Neighbor Cache. The 693 same option is included in corresponding Neighbor Advertisement (NA) 694 messages with a Status field indicating the success or failure of the 695 registration. This option is always host initiated. 697 The information contained in the ARO is also included in the multihop 698 DAR and DAC messages used between 6LRs to 6LBRs, but the option 699 itself is not used in those messages. 701 The ARO is required for reliability and power saving. The lifetime 702 field provides flexibility to the host to register an address which 703 should be usable (continue to be advertised by the 6LR in the routing 704 protocol etc.) during its intended sleep schedule. 706 The sender of the NS also includes the EUI-64 [EUI64] of the 707 interface it is registering an address from. This is used as a 708 unique ID for the detection of duplicate addresses. It is used to 709 tell the difference between the same node re-registering its address 710 and a different node (with a different EUI-64) registering an address 711 that is already in use by someone else. The EUI-64 is also used to 712 deliver an NA carrying an error Status code to the EUI-64 based link- 713 local IPv6 address of the host (see Section 6.5.2). 715 When the ARO is used by hosts an SLLA (Source Link-layer Address) 716 option [RFC4861] MUST be included and the address that is to be 717 registered MUST be the IPv6 source address of the Neighbor 718 Solicitation message. 720 0 1 2 3 721 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 1 722 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 723 | Type | Length = 2 | Status | Reserved | 724 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 725 | Reserved | Registration Lifetime | 726 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 727 | | 728 + EUI-64 + 729 | | 730 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 732 Fields: 734 Type: TBD1 736 Length: 8-bit unsigned integer. The length of the option in 737 units of 8 bytes. Always 2. 739 Status: 8-bit unsigned integer. Indicates the status of a 740 registration in the NA response. MUST be set to 0 in 741 NS messages. See below. 743 Reserved: This field is unused. It MUST be initialized to zero 744 by the sender and MUST be ignored by the receiver. 746 Registration Lifetime: 16-bit unsigned integer. The amount of time 747 in a unit of 60 seconds that the router should retain 748 the Neighbor Cache entry for the sender of the NS that 749 includes this option. 751 EUI-64: 64 bits. This field is used to uniquely identify the 752 interface of the registered address by including the 753 EUI-64 identifier [EUI64] assigned to it unmodified. 755 The Status values used in Neighbor Advertisements are: 757 +--------+--------------------------------------------+ 758 | Status | Description | 759 +--------+--------------------------------------------+ 760 | 0 | Success | 761 | 1 | Duplicate Address | 762 | 2 | Neighbor Cache Full | 763 | 3-255 | Allocated using Standards Action [RFC5226] | 764 +--------+--------------------------------------------+ 766 Table 1 768 4.2. 6LoWPAN Context Option 770 The optional 6LoWPAN Context Option (6CO) carries prefix information 771 for LoWPAN header compression, and is similar to the Prefix 772 Information Option of [RFC4861]. However, the prefixes can be remote 773 as well as local to the LoWPAN since header compression potentially 774 applies to all IPv6 addresses. This option allows for the 775 dissemination of multiple contexts identified by a Context Identifier 776 (CID) for use as specified in [RFC6282]. A context may be a prefix 777 of any length or an address (/128), and up to 16 6LoWPAN Context 778 options may be carried in an Router Advertisement message. 780 0 1 2 3 781 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 1 782 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 783 | Type | Length |Context Length | Res |C| CID | 784 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 785 | Reserved | Valid Lifetime | 786 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 787 . . 788 . Context Prefix . 789 . . 790 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 792 Figure 1: 6LoWPAN Context Option format 794 Type: TBD2 796 Length: 8-bit unsigned integer. The length of the option (including 797 the type and length fields) in units of 8 bytes. May be 2 or 3 798 depending on the length of the Context Prefix field. 800 Context Length: 8-bit unsigned integer. The number of leading bits 801 in the Context Prefix field that are valid. The value ranges from 802 0 to 128. If it is more than 64 then the Length MUST be 3. 804 C: 1-bit context compression flag. This flag indicates if the 805 context is valid for use in compression. A context that is not 806 valid MUST NOT be used for compression, but SHOULD be used in 807 decompression in case another compressor has not yet received the 808 updated context information. This flag is used to manage the 809 context lifecycle based on the recommendations in Section 7.2. 811 CID: 4-bit Context Identifier for this prefix information. CID is 812 used by context based header compression specified in [RFC6282]. 813 The list of CIDs for a LoWPAN is configured by on the 6LBR that 814 originates the context information for the 6LoWPAN. 816 Res, Reserved: This field is unused. It MUST be initialized to zero 817 by the sender and MUST be ignored by the receiver. 819 Valid Lifetime: 16-bit unsigned integer. The length of time in a 820 unit of 60 seconds (relative to the time the packet is received) 821 that the context is valid for the purpose of header compression or 822 decompression. A value of all zero bits (0x0) indicates that this 823 context entry MUST be removed immediately. 825 Context Prefix: The IPv6 prefix or address corresponding to the 826 Context ID (CID) field. The valid length of this field is 827 included in the Context Length field. This field is padded with 828 zeros in order to make the option a multiple of 8-bytes. 830 4.3. Authoritative Border Router Option 832 The Authoritative Border Router Option (ABRO) is needed when Router 833 Advertisement (RA) messages are used to disseminate prefixes and 834 context information across a route-over topology. In this case 6LRs 835 receive Prefix Information options from other 6LRs. This implies 836 that a 6LR can't just let the most recently received RA win. In 837 order to be able to reliably add and remove prefixes from the 6LoWPAN 838 we need to carry information from the authoritative 6LBR. This is 839 done by introducing a version number which the 6LBR sets and 6LRs 840 propagate as they propagate the prefix and context information with 841 this Authoritative Border Router Option. When there are multiple 842 6LBRs they would have separate version number spaces. Thus this 843 option needs to carry the IP address of the 6LBR that originated that 844 set of information. 846 The Authoritative Border Router option MUST be included in all Router 847 Advertisement messages in the case when Router Advertisements are 848 used to propagate information between routers (as described in 849 Section 8.2). 851 0 1 2 3 852 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 1 853 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 854 | Type | Length = 3 | Version Low | 855 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 856 | Version High | Valid Lifetime | 857 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 858 | | 859 + + 860 | | 861 + 6LBR Address + 862 | | 863 + + 864 | | 865 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 867 Fields: 869 Type: TBD3 871 Length: 8-bit unsigned integer. The length of the option in 872 units of 8 bytes. Always 3. 874 Version Low, Version High: Together, Version Low and Version High 875 are a 32-bit unsigned integer, where Version Low is 876 the least significant 16 bits and Version High is the 877 most significant 16 bits. The version number 878 corresponding to this set of information contained in 879 the RA message. The authoritative 6LBR originating 880 the prefix increases this version number each time its 881 set of prefix or context information changes. 883 Valid Lifetime: 16-bit unsigned integer. The length of time in a 884 unit of 60 seconds (relative to the time the packet is 885 received) that this set of border router information 886 is valid. A value of all zero bits (0x0) assumes a 887 default value of 10,000 (~ one week). 889 Reserved: This field is unused. It MUST be initialized to zero 890 by the sender and MUST be ignored by the receiver. 892 6LBR Address: IPv6 address of the 6LBR that is the origin of the 893 included version number. 895 4.4. Duplicate Address messages 897 For the multihop DAD exchanges between 6LR and 6LBR specified in 898 Section 8.2 there are two new ICMPv6 message types called the 899 Duplicate Address Request (DAR) and Duplicate Address Confirmation 900 (DAC). We avoid reusing the Neighbor Solicitation and Neighbor 901 Advertisement messages for this purpose since these messages are not 902 subject to the hop limit=255 check as they are forwarded by 903 intermediate 6LRs. The information contained in the messages are 904 otherwise the same as would be in a Neighbor Solicitation carrying a 905 Address Registration option, with the message format inlining the 906 fields that are in the ARO. 908 The DAR and DAC use the same message format with different ICMPv6 909 type values, and the Status field is only meaningful in the DAC 910 message. 912 0 1 2 3 913 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 1 914 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 915 | Type | Code | Checksum | 916 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 917 | Status | Reserved | Registration Lifetime | 918 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 919 | | 920 + EUI-64 + 921 | | 922 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 923 | | 924 + + 925 | | 926 + Registered Address + 927 | | 928 + + 929 | | 930 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 932 IP fields: 934 IPv6 source: A non link-local address of the sending router. 936 IPv6 destination: A non link-local address of the sending router. 937 In a DAC this is just the source from the DAR. 939 Hop Limit: Set to MULTIHOP_HOPLIMIT on transmit. MUST be ignored 940 on receipt. 942 ICMP Fields: 944 Type: TBD4 for DAR and TBD5 for DAC 946 Code: Set to zero on transmit. MUST be ignored on receipt. 948 Checksum: The ICMP checksum. See [RFC4443]. 950 Status: 8-bit unsigned integer. Indicates the status of a 951 registration in the DAC. MUST be set to 0 in DAR. 952 See Table 1. 954 Reserved: This field is unused. It MUST be initialized to zero 955 by the sender and MUST be ignored by the receiver. 957 Registration Lifetime: 16-bit unsigned integer. The amount of time 958 in a unit of 60 seconds that the router should retain 959 the Neighbor Cache entry for the sender of the NS that 960 includes this option. A value of 0 indicates in an NS 961 that the neighbor cache entry should be removed. 963 EUI-64: 64 bits. This field is used to uniquely identify the 964 interface of the registered address by including the 965 EUI-64 identifier [EUI64] assigned to it unmodified. 967 Registered Address: 128-bit field. Carries the host address, which 968 was contained in the IPv6 Source field in the NS that 969 contained the ARO option sent by the host. 971 5. Host Behavior 973 Hosts in a LoWPAN use the Address Registration option in the Neighbor 974 Solicitation messages they send as a way to maintain the Neighbor 975 Cache in the routers thereby removing the need for multicast Neighbor 976 Solicitations to do address resolution. Unlike in [RFC4861] the 977 hosts initiate updating the information they receive in Router 978 Advertisements by sending Router Solicitations before the information 979 expires. Finally, when Neighbor Unreachability Detection indicates 980 that one or all default routers have become unreachable, then the 981 host uses Router Solicitations to find a new set of default routers. 983 5.1. Forbidden Actions 985 A host MUST NOT multicast a Neighbor Solicitation message. 987 5.2. Interface Initialization 989 When the interface on a host is initialized it follows the 990 specification in [RFC4861]. A link-local address is formed based on 991 the EUI-64 identifier [EUI64] assigned to the interface as per 992 [RFC4944] or the appropriate IP-over-foo document for the link, and 993 then the host sends Router Solicitation messages as described in 994 [RFC4861] Section 6.3.7. 996 There is no need to join the Solicited-Node multicast address since 997 nobody multicasts Neighbor Solicitations in this type of network. A 998 host MUST join the all-nodes multicast address. 1000 5.3. Sending a Router Solicitation 1002 The Router Solicitation is formatted as specified in [RFC4861] and 1003 sent to the IPv6 All-Routers multicast address (see [RFC4861] Section 1004 6.3.7 for details). An SLLA option MUST be included to enable 1005 unicast Router Advertisements in response. An unspecified source 1006 address MUST NOT be used in RS messages. 1008 If the link layer supports a way to send packets to some kind of all- 1009 routers anycast link-layer address, then that MAY be used to convey 1010 these packets to a router. 1012 Since hosts do not depend on multicast Router Advertisements to 1013 discover routers, the hosts need to intelligently retransmit Router 1014 Solicitations whenever the default router list is empty, one of its 1015 default routers becomes unreachable, or the lifetime of the prefixes 1016 and contexts in the previous RA are about to expire. The RECOMMENDED 1017 retransmissions is to initially send up to 3 (MAX_RTR_SOLICITATIONS) 1018 RS messages separated by at least 10 seconds 1019 (RTR_SOLICITATION_INTERVAL) as specified in [RFC4861], and then 1020 switch to slower retransmissions. After the initial retransmissions 1021 the host SHOULD do truncated binary exponential backoff [ETHERNET] of 1022 the retransmission timer for each subsequent retransmission, 1023 truncating the increase of the retransmission timer at 60 seconds 1024 (MAX_RTR_SOLICITATION_INTERVAL). In all cases the RS retransmissions 1025 are terminated when a RA is received. See Section 9 for protocol 1026 constants. 1028 5.4. Processing a Router Advertisement 1030 The processing of Router Advertisements is as in [RFC4861] with the 1031 addition of handling the 6LoWPAN Context option and triggering 1032 address registration when a new address has been configured. 1033 Furthermore, the SLLA option MUST be included in the RA. Unlike in 1034 [RFC4861], the maximum value of the RA Router Lifetime field MAY be 1035 up to 0xFFFF (approximately 18 hours). 1037 Should the host erroneously receive a Prefix Information option with 1038 the 'L' (on-link) flag set, then that Prefix Information Option (PIO) 1039 MUST be ignored. 1041 5.4.1. Address configuration 1043 Address configuration follows [RFC4862]. For an address not derived 1044 from an EUI-64, the M flag of the RA determines how the address can 1045 be configured. If the M flag is set in the RA, then DHCPv6 MUST be 1046 used to assign the address. If the M flag is not set, then the 1047 address can be configured by any other means (and duplicate detection 1048 is performed as part of the registration process). 1050 Once an address has been configured it will be registered by 1051 unicasting a Neighbor Solicitation with the Address Registration 1052 option to one or more routers. 1054 5.4.2. Storing Contexts 1056 The host maintains a conceptual data structure for the context 1057 information it receives from the routers, which is called the Context 1058 Table. This includes the Context ID, the prefix (from the Context 1059 Prefix field in the 6CO), the Compression bit, and the Valid 1060 Lifetime. A Context Table entry that has the Compression bit clear 1061 is used for decompression when receiving packets, but MUST NOT be 1062 used for compression when sending packets. 1064 When a 6CO option is received in a Router Advertisement it is used to 1065 add or update the information in the Context Table. If the Context 1066 ID field in the 6CO matches an existing Context Table entry, then 1067 that entry is updated with the information in the 6CO. If the Valid 1068 Lifetime field in the 6CO is zero, then the entry is immediately 1069 deleted. 1071 If there is no matching entry in the Context Table, and the Valid 1072 Lifetime field is non-zero, then a new context is added to the 1073 Context Table. The 6CO is used to update the created entry. 1075 When the 6LBR changes the context information a host might not 1076 immediately notice. And in the worst case a host might have stale 1077 context information. For this reason 6LBRs use the recommendations 1078 in Section 7.2 for carefully managing the context lifecycle. Nodes 1079 should be careful about using header compression in RA messages that 1080 include 6COs. 1082 5.4.3. Maintaining Prefix and Context Information 1084 The prefix information is timed out as specified in [RFC4861]. When 1085 the Valid Lifetime for a Context Table entry expires the entry is 1086 placed in a receive-only mode, which is the equivalent of receiving a 1087 6CO for that context with C=0. The entry is held in receive-only 1088 mode for a period of twice the Default Router Lifetime, after which 1089 the entry is removed. 1091 A host should inspect the various lifetimes to determine when it 1092 should next initiate sending a Router Solicitation to ask for any 1093 updates to the information. The lifetimes that matter are the 1094 Default Router lifetime, the Valid Lifetime in the Prefix Information 1095 options, and the Valid Lifetime in the 6CO. The host SHOULD unicast 1096 one or more Router Solicitations to the router well before the 1097 minimum of those lifetimes (across all the prefixes and all the 1098 contexts) expire, and switch to multicast RS messages if there is no 1099 response to the unicasts. The retransmission behavior for the Router 1100 Solicitations is specified in Section 5.3. 1102 5.5. Registration and Neighbor Unreachability Detection 1104 Hosts send Unicast Neighbor Solicitation (NS) messages to register 1105 their IPv6 addresses, and also to do NUD to verify that their default 1106 routers are still reachable. The registration is performed by the 1107 host including an ARO in the Neighbor Solicitation it sends. Even if 1108 the host doesn't have data to send, but is expecting others to try to 1109 send packets to the host, the host needs to maintain its Neighbor 1110 Cache entries in the routers. This is done by sending NS messages 1111 with the ARO to the router well in advance of the registration 1112 lifetime expiring. NS messages are retransmitted up to 1113 MAX_UNICAST_SOLICIT times using a minimum timeout of RETRANS_TIMER 1114 until the host receives an Neighbor Advertisement message with an ARO 1115 option. 1117 Hosts that receive Router Advertisement messages from multiple 1118 default routers SHOULD attempt to register with more than one of them 1119 in order to increase the robustness of the network. 1121 Note that Neighbor Unreachability Detection probes can be suppressed 1122 by Reachability Confirmations from transport protocols or 1123 applications as specified in [RFC4861]. 1125 When a host knows it will no longer use a router it is registered to, 1126 it SHOULD de-register with the router by sending an NS with an ARO 1127 containing a lifetime of 0. To handle the case when a host loses 1128 connectivity with the default router involuntarily, the host SHOULD 1129 use a suitably low registration lifetime. 1131 5.5.1. Sending a Neighbor Solicitation 1133 The host triggers sending Neighbor Solicitation (NS) messages 1134 containing an ARO when a new address is configured, when it discovers 1135 a new default router, or well before the Registration Lifetime 1136 expires. Such an NS MUST include a Source Link-Layer Address (SLLA) 1137 option, since the router needs to record the link-layer address of 1138 the host. An unspecified source address MUST NOT be used in NS 1139 messages. 1141 5.5.2. Processing a Neighbor Advertisement 1143 A host handles Neighbor Advertisement messages as specified in 1144 [RFC4861], with added logic described in this section for handling 1145 the Address Registration option. 1147 In addition to the normal validation of a Neighbor Advertisement and 1148 its options, the Address Registration option is verified as follows 1149 (if present). If the Length field is not two, the option is silently 1150 ignored. If the EUI-64 field does not match the EUI-64 of the 1151 interface, the option is silently ignored. 1153 If the status field is zero, then the address registration was 1154 successful. The host saves the Registration Lifetime from the 1155 Address Registration option for use to trigger a new NS well before 1156 the lifetime expires. If the Status field is not equal to zero, the 1157 address registration has failed. 1159 5.5.3. Recovering from Failures 1161 The procedure for maintaining reachability information about a 1162 neighbor is the same as in [RFC4861] Section 7.3 with the exception 1163 that address resolution is not performed. 1165 The address registration procedure may fail for two reasons: no 1166 response to Neighbor Solicitations is received (NUD failure), or an 1167 Address Registration option with a failure Status (Status > 0) is 1168 received. In the case of NUD failure the entry for that router will 1169 be removed thus address registration is no longer of importance. 1170 When an Address Registration option with a non-zero Status field is 1171 received this indicates that registration for that address has 1172 failed. A failure Status of one indicates that a duplicate address 1173 was detected and the procedure described in [RFC4862] Section 5.4.5 1174 is followed. The host MUST NOT use the address it tried to register. 1175 If the host has valid registrations with other routers, these MUST be 1176 removed by registering with each using a zero ARO lifetime. 1178 A Status code of two indicates that the Neighbor Cache of that router 1179 is full. In this case the host SHOULD remove this router from its 1180 default router list and attempt to register with another router. If 1181 the host's default router list is empty, it needs to revert to 1182 sending Router Solicitations as specified in Section 5.3. 1184 Other failure codes may be defined in future documents. 1186 5.6. Next-hop Determination 1188 The IP address of the next-hop for a destination is determined as 1189 follows. Destinations to the link-local prefix (FE80::) are always 1190 sent on the link to that destination. It is assumed that link-local 1191 addresses are formed as specified in Section 5.2 from the EUI-64, and 1192 address resolution is not performed. Packets are sent to link local 1193 destinations by reversing the procedure in Appendix A of [RFC4291]. 1195 Multicast addresses are considered to be on-link and are resolved as 1196 specified in [RFC4944] or the appropriate IP-over-foo document. Note 1197 that [RFC4944] only defines how to represent a multicast destination 1198 address in the LoWPAN header. Support for multicast scopes larger 1199 than link-local needs an appropriate multicast routing algorithm. 1201 All other prefixes are assumed to be off-link [RFC5889]. Anycast 1202 addresses are always considered to be off-link. They are therefore 1203 sent to one of the routers in the Default Router List. 1205 A LoWPAN Node is not required to maintain a minimum of one buffer per 1206 neighbor as specified in [RFC4861], since packets are never queued 1207 while waiting for address resolution. 1209 5.7. Address Resolution 1211 The address registration mechanism and the SLLA option in Router 1212 Advertisement messages provide sufficient a priori state in routers 1213 and hosts to resolve an IPv6 address to its associated link-layer 1214 address. As all prefixes, except the link-local prefix and multicast 1215 addresses, are always assumed to be off-link, multicast-based address 1216 resolution between neighbors is not needed. 1218 Link-layer addresses for neighbors are stored in Neighbor Cache 1219 entries [RFC4861]. In order to achieve LoWPAN compression, most 1220 global addresses are formed using a link-layer address. Thus a host 1221 can reduce memory usage by optimizing for this case and only storing 1222 link-layer address information if it differs from the link-layer 1223 address corresponding to the Interface ID of the IPv6 address (i.e., 1224 differs in more than the on-link/global bit being inverted). 1226 5.8. Sleeping 1228 It is often advantageous for battery-powered hosts in LoWPANs to keep 1229 a low duty cycle. The optimizations described in this document 1230 enable hosts to sleep as described further in this section. Routers 1231 may want to cache traffic destined to a host which is sleeping, but 1232 such functionality is out of the scope of this document. 1234 5.8.1. Picking an Appropriate Registration Lifetime 1236 As all Neighbor Discovery messages are initiated by the hosts, this 1237 allows a host to sleep or otherwise be unreachable between NS/NA 1238 message exchanges. The Address Registration option attached to NS 1239 messages indicates to a router to keep the Neighbor Cache entry for 1240 that address valid for the period in the Registration Lifetime field. 1241 A host should choose a sleep time appropriate for its energy 1242 characteristics, and set a registration lifetime larger than the 1243 sleep time to ensure the registration is renewed successfully 1244 (considering e.g. clock drift and additional time for potential 1245 retransmissions of the re-registration). External configuration of a 1246 host should also consider the stability of the network (how quickly 1247 the topology changes) when choosing its sleep time (and thus 1248 registration lifetime). A dynamic network requires a shorter sleep 1249 time so that routers don't keep invalid neighbor cache entries for 1250 nodes longer than necessary. 1252 5.8.2. Behavior on Wakeup 1254 When a host wakes up from a sleep period it SHOULD refresh its 1255 current address registrations that will timeout before the next 1256 wakeup. This is done by sending Neighbor Solicitation messages with 1257 the Address Registration option as described in Section 5.5.1. The 1258 host may also need to refresh its prefix and context information by 1259 sending a new unicast Router Solicitation (the maximum Router 1260 Lifetime is about 18 hours whereas the maximum Registration lifetime 1261 is about 45.5 days). If after wakeup the host (using NUD) determines 1262 that some or all previous default routers have become unreachable, 1263 then the host will send multicast Router Solicitations to discover 1264 new default router(s) and restart the address registration process. 1266 6. Router Behavior for 6LR and 6LBR 1268 Both 6LRs and 6LBRs maintain the Neighbor Cache [RFC4861] based on 1269 the Address Registration Options they receive in Neighbor 1270 Advertisement messages from hosts, Neighbor Discovery packets from 1271 other nodes, and potentially a routing protocol used in the 6LoWPAN 1272 as outlined in Section 3.5. 1274 The routers SHOULD NOT garbage collect Registered Neighbor Cache 1275 entries (see Section 3.4) since they need to retain them until the 1276 Registration Lifetime expires. Similarly, if Neighbor Unreachability 1277 Detection on the router determines that the host is UNREACHABLE 1278 (based on the logic in [RFC4861]), the Neighbor Cache entry SHOULD 1279 NOT be deleted but be retained until the Registration Lifetime 1280 expires. A renewed ARO should mark the cache entry as STALE. Thus 1281 for 6LoWPAN Routers the Neighbor Cache doesn't behave like a cache. 1282 Instead it behaves as a registry of all the host addresses that are 1283 attached to the Router. 1285 Routers MAY implement the Default Router Preferences [RFC4191] and 1286 use that to indicate to the host whether the router is a 6LBR or a 1287 6LR. If this is implemented then 6LRs with no route to a border 1288 router MUST set Prf to (11) for low preference, other 6LRs MUST set 1289 Prf to (00) for normal preference, and 6LBRs MUST set Prf to (01) for 1290 high preference. 1292 6.1. Forbidden Actions 1294 Even if a router in a route-over topology can reach both a host and 1295 another target, because of radio propagation it generally cannot know 1296 whether the host can directly reach the other target. Therefore it 1297 cannot assume that redirect will actually work from one host to 1298 another. Therefore it SHOULD NOT send Redirect messages. The only 1299 potential exception to this "SHOULD NOT" is when the deployment/ 1300 implementation has a way to know how the host can reach the intended 1301 target. Hence it is RECOMMENDED that the implementation by default 1302 does not send redirect messages but can be configurable when the 1303 deployment calls for this. In contrast, for mesh-under topologies, 1304 the same considerations about Redirects apply as in 4861. 1306 A router MUST NOT set the 'L' (on-link) flag in the Prefix 1307 Information options, since that might trigger hosts to send multicast 1308 Neighbor Solicitations. 1310 6.2. Interface Initialization 1312 The 6LBR router interface initialization behavior is the same as in 1313 [RFC4861]. However, in dynamic configuration scenario (see 1314 Section 8.1), a 6LR comes up as a non-router and waits to receive the 1315 advertisement for configuring its own interface address first before 1316 making its interfaces advertising and turning into a router. 1318 6.3. Processing a Router Solicitation 1320 A router processes Router Solicitation messages as specified in 1321 [RFC4861]. The differences relate to the inclusion of Authoritative 1322 Border Router options in the Router Advertisement (RA) messages, and 1323 the exclusive use of unicast Router Advertisements. If a 6LR has 1324 received an ABRO from a 6LBR, then it will include that option 1325 unmodified in the Router Advertisement messages it sends. And if the 1326 6LR has received RAs, whether with the same prefixes and context 1327 information or different, from a different 6LBR, then it will need to 1328 keep those prefixes and context information separately so that the 1329 RAs the 6LR sends will maintain the association between the ABRO and 1330 the prefixes and context information. The router can tell which 6LBR 1331 originated the prefixes and context information from the 6LBR Address 1332 field in the ABRO. When a router has information tied to multiple 1333 ABROs, a single RS will result in multiple RAs each containing a 1334 different ABRO. 1336 When the ABRO Valid Lifetime associated with a 6LBR times out, all 1337 information related to that 6LBR MUST be removed. As an 1338 implementation note, it is recommend that RAs are sent sufficiently 1339 more frequently than the ABRO Valid Lifetime so that missing an RA 1340 does not result in removing all information related to a 6LBR. 1342 A Router Solicitation might be received from a host that has not yet 1343 registered its address with the router. Thus the router MUST NOT 1344 modify an existing Neighbor Cache entry based on the SLLA option from 1345 the Router Solicitation. However, a router MAY create a Tentative 1346 Neighbor Cache entry based on the SLLA option. Such a Tentative 1347 Neighbor Cache entry SHOULD be timed out in TENTATIVE_NCE_LIFETIME 1348 seconds unless a registration converts it into a Registered NCE. 1350 A 6LR or 6LBR MUST include a Source Link-layer address option in the 1351 Router Advertisements it sends. That is required so that the hosts 1352 will know the link-layer address of the router. Unlike in [RFC4861], 1353 the maximum value of the RA Router Lifetime field MAY be up to 0xFFFF 1354 (approximately 18 hours). 1356 Unlike [RFC4861] which suggests multicast Router Advertisements, this 1357 specification improves the exchange by always unicasting RAs in 1358 response to RSs. This is possible since the RS always includes a 1359 SLLA option, which is used by the router to unicast the RA. 1361 6.4. Periodic Router Advertisements 1363 A router does not need to send any periodic Router Advertisement 1364 messages since the hosts will solicit updated information by sending 1365 Router Solicitations before the lifetimes expire. 1367 However, if the routers use Router Advertisements to distribute 1368 prefix and/or context information across a route-over topology, that 1369 might require periodic Router Advertisement messages. Such RAs are 1370 sent using the configurable MinRtrAdvInterval and MaxRtrAdvInterval 1371 as per [RFC4861]. 1373 6.5. Processing a Neighbor Solicitation 1375 A router handles Neighbor Solicitation messages as specified in 1376 [RFC4861], with added logic described in this section for handling 1377 the Address Registration option. 1379 In addition to the normal validation of a Neighbor Solicitation and 1380 its options, the Address Registration option is verified as follows 1381 (if present). If the Length field is not two, or if the Status field 1382 is not zero, then the Neighbor Solicitation is silently ignored. 1384 If the source address of the NS is the unspecified address, or if no 1385 SLLA option is included, then any included ARO is ignored, that is, 1386 the NS is processed as if it did not contain an ARO. 1388 6.5.1. Checking for Duplicates 1390 If the NS contains a valid ARO, then the router inspects its Neighbor 1391 Cache on the arriving interface to see if it is a duplicate. If 1392 there is no Neighbor Cache entry for the IPv6 source address of the 1393 NS, then it isn't a duplicate. If there is such a Neighbor Cache 1394 entry and the EUI-64 is the same, then it isn't a duplicate either. 1395 Otherwise it is a duplicate address. Note that if multihop DAD 1396 (Section 8.2) is used then the checks are slightly different to take 1397 into account Tentative Neighbor Cache entries. In the case it is a 1398 duplicate address then the router responds with a unicast Neighbor 1399 Advertisement (NA) message with the ARO Status field set to one (to 1400 indicate the address is a duplicate) as described in Section 6.5.2. 1401 In this case there is no modification to the Neighbor Cache. 1403 6.5.2. Returning Address Registration Errors 1405 Address registration errors are not sent back to the source address 1406 of the NS due to a possible risk of L2 address collision. Instead 1407 the NA is sent to the link-local IPv6 address with the IID part 1408 derived from the EUI-64 field of the ARO as per [RFC4944]. In 1409 particular, this means that the universal/local bit needs to be 1410 inverted. The NA is formatted with a copy of the ARO from the NS, 1411 but with the Status field set to indicate the appropriate error. 1413 The error is sent to the link-local address with the IID derived from 1414 the EUI-64. Thus if the ARO was from and for a short address, the L2 1415 destination address for the NA with the ARO error will be the 64-bit 1416 unique addresses. 1418 6.5.3. Updating the Neighbor Cache 1420 If ARO did not result in a duplicate address being detected as above, 1421 then if the Registration Lifetime is non-zero the router creates (if 1422 it didn't exist) or updates (otherwise) a Neighbor Cache entry for 1423 the IPv6 source address of the NS. If the Neighbor Cache is full and 1424 a new entry needs to be created, then the router responds with a 1425 unicast NA with the ARO Status field set to two (to indicate the 1426 router's Neighbor Cache is full) as described in Section 6.5.2. 1428 The Registration Lifetime and the EUI-64 are recorded in the Neighbor 1429 Cache entry. A unicast Neighbor Advertisement (NA) is then sent in 1430 response to the NS. This NA SHOULD include a copy of the ARO, with 1431 the Status field set to zero. A TLLA (Target Link-layer Address) 1432 option [RFC4861] is not required in the NA, since the host already 1433 knows the router's link-layer address from Router Advertisements. 1435 If the ARO contains a zero Registration Lifetime then any existing 1436 Neighbor Cache entry for the IPv6 source address of the NS MUST be 1437 deleted, and a NA sent as above. 1439 Should the Registration Lifetime in a Neighbor Cache entry expire, 1440 then the router MUST delete the cache entry. 1442 The addition and removal of Registered Neighbor Cache entries would 1443 result in notifying the routing protocol. 1445 Note: If the substitutable multihop DAD (Section 8.2) is used, then 1446 the updating of the Neighbor Cache is slightly different due to 1447 Tentative NCEs. 1449 6.5.4. Next-hop Determination 1451 In order to deliver a packet destined for a 6LN registered with a 1452 router, next-hop determination is slightly different for routers than 1453 hosts (see Section 5.6. The routing table is checked to determine 1454 the next hop IP address. A registered Neighbor Cache Entry (NCE) 1455 determines if the next hop IP-address is on-link. It is the 1456 responsibility of the routing protocol of the router to maintain on- 1457 link information about its registered neighbors. Tentative NCEs MUST 1458 NOT be used to determine on-link status of the registered nodes. 1460 6.5.5. Address Resolution between Routers 1462 There needs to be a mechanism somewhere for the routers to discover 1463 each others' link-layer addresses. If the routing protocol used 1464 between the routers provides this, then there is no need for the 1465 routers to use the Address Registration option between each other. 1467 Otherwise, the routers SHOULD use the ARO. When routers use ARO to 1468 register with each other and the multihop DAD Section 8.2 is in use, 1469 then care must be taken to ensure that there isn't a flood of ARO- 1470 carrying messages sent to the 6LBR as each router hears an ARO from 1471 their neighboring routers. The details for this is out of scope of 1472 this document. 1474 Routers MAY also use multicast Neighbor Solicitations as in [RFC4861] 1475 to resolve each others link-layer addresses. Thus Routers MAY 1476 multicast Neighbor Solicitations for other routers, for example as a 1477 result of receiving some routing protocol update. Routers MUST 1478 respond to multicast Neighbor Solicitations. This implies that 1479 Routers MUST join the Solicited-node multicast addresses as specified 1480 in [RFC4861]. 1482 7. Border Router Behavior 1484 A 6LBR handles sending of Router Advertisements and processing of 1485 Neighbor Solicitations from hosts as specified above in section 1486 Section 6. A 6LBR SHOULD always include an Authoritative Border 1487 Router option in the Router Advertisements it sends, listing itself 1488 as the 6LBR Address. That requires that the 6LBR maintain the 1489 version number in stable storage, and increases the version number 1490 when some information in its Router Advertisements change. The 1491 information whose change affects the version are in the Prefix 1492 Information options (the prefixes or their lifetimes) and in the 6CO 1493 option (the prefixes, Context IDs, or lifetimes.) 1495 In addition, a 6LBR is somehow configured with the prefix or prefixes 1496 that are assigned to the LoWPAN, and advertises those in Router 1497 Advertisements as in [RFC4861]. In the case of route-over, those 1498 prefixes can be disseminated to all the 6LRs using the technique in 1499 Section 8.1. However, there might be mechanisms outside of the scope 1500 of this document that can be used as a substitute for prefix 1501 dissemination in the route-over topology (see Section 1.4). 1503 If the 6LoWPAN uses Header Compression [RFC6282] with context then 1504 the 6LBR needs to manage the context IDs, and advertise those in 1505 Router Advertisements by including 6CO options in its Router 1506 Advertisements so that directly attached hosts are informed about the 1507 context IDs. Below we specify things to consider when the 6LBR needs 1508 to add, remove, or change the context information. In the case of 1509 route-over, the context information is disseminated to all the 6LRs 1510 using the technique in Section 8 unless a different specification 1511 provides a substitute for this multihop distribution. 1513 7.1. Prefix Determination 1515 The prefix or prefixes used in a LoWPAN can be manually configured, 1516 or can be acquired using DHCPv6 Prefix Delegation [RFC3633]. For a 1517 LoWPAN that is isolated from the network, either permanently or 1518 occasionally, the 6LBR can assign a ULA prefix using [RFC4193]. The 1519 ULA prefix should be stored in stable storage so that the same prefix 1520 is used after a failure of the 6LBR. If the LoWPAN has multiple 1521 6LBRs, then they should be configured with the same set of prefixes. 1522 The set of prefixes are included in the Router Advertisement messages 1523 as specified in [RFC4861]. 1525 7.2. Context Configuration and Management 1527 If the LoWPAN uses Header Compression [RFC6282] with context then the 1528 6LBR must be configured with context information and related context 1529 IDs. If the LoWPAN has multiple 6LBRs, then they MUST be configured 1530 with the same context information and context IDs. For [RFC6282], 1531 maintaining consistency of context information is crucial for 1532 ensuring packets will be decompressed correctly. 1534 The context information carried in Router Advertisement (RA) messages 1535 originate at 6LBRs and must be disseminated to all the routers and 1536 hosts within the LoWPAN. RAs include one 6CO for each context. 1538 For the dissemination of context information using the 6CO, a strict 1539 lifecycle SHOULD be used in order to ensure the context information 1540 stays synchronized throughout the LoWPAN. New context information 1541 SHOULD be introduced into the LoWPAN with C=0, to ensure it is known 1542 by all nodes that may have to decompress based on this context 1543 information. Only when it is reasonable to assume that this 1544 information was successfully disseminated SHOULD an option with C=1 1545 be sent, enabling the actual use of the context information for 1546 compression. 1548 Conversely, to avoid that nodes send packets making use of previous 1549 values of contexts, resulting in ambiguity when receiving a packet 1550 that uses a recently changed context, old values of a context SHOULD 1551 be taken out of use for a while before new values are assigned to 1552 this specific context. That is, in preparation for a change of 1553 context information, its dissemination SHOULD continue for at least 1554 MIN_CONTEXT_CHANGE_DELAY with C=0. Only when it is reasonable to 1555 assume that the fact that the context is now invalid was successfully 1556 disseminated, should the context ID be taken out of dissemination or 1557 reused with a different Context Prefix field. In the latter case, 1558 dissemination of the new value again SHOULD start with C=0, as above. 1560 8. Substitutable Feature Behavior 1562 Normally in a 6LoWPAN multihop network, the Router Advertisement 1563 messages are used to disseminate prefixes and context information to 1564 all the 6LRs in a route-over topology. If all routers are configured 1565 to use a substitute mechanism for such information distribution, any 1566 remaining use of the 6LoWPAN-ND mechanisms is governed by the 1567 substitute specification. 1569 There is also the option for a 6LR to perform multihop DAD (for non- 1570 EUI-64 derived IPv6 addresses) against a 6LBR in a route-over 1571 topology by using the DAR and DAC messages. This is substitutable 1572 because there might be other ways to either allocate unique address, 1573 such as DHCPv6 [RFC3315], or other future mechanisms for multihop 1574 DAD. Again in this case, any remaining use of the 6LoWPAN-ND 1575 mechanisms is governed by the substitute specification. 1577 To be clear: Implementations MUST support the features describes in 1578 Section 8.1 and Section 8.2, unless the implementation supports some 1579 alternative ("substitute") from some some other specification. 1581 8.1. Multihop Prefix and Context Distribution 1583 The multihop distribution relies on Router Solicitation messages and 1584 Router Advertisement (RA) messages sent between routers, and using 1585 the ABRO version number to control the propagation of the information 1586 (prefixes and context information) that is being sent in the RAs. 1588 This multihop distribution mechanism can handle arbitrary information 1589 from an arbitrary number of 6LBRs. However, the semantics of the 1590 context information requires that all the 6LNs use the same 1591 information, whether they send, forward, or receive compressed 1592 packets. Thus the manager of the 6LBRs need to somehow ensure that 1593 the context information is in synchrony across the 6LBRs. This can 1594 be handled in different ways. One possible way to ensure it is to 1595 treat the context and prefix information as originating from some 1596 logical or virtual source, which in essence means that it looks like 1597 the information is distributed from a single source. 1599 If a set of 6LBRs behave as a single one (using mechanisms out of 1600 scope of this document) so that the prefixes and contexts and ABRO 1601 version number will be the same from all the 6LBRs, then those 6LBRs 1602 can pick a single IP address to use in the ABRO option. 1604 8.1.1. 6LBRs Sending Router Advertisements 1606 6LBRs supporting multihop prefix and context distribution MUST 1607 include an ABRO in each of its RAs. The ABRO Version Number field is 1608 used to keep prefix and context information consistent throughout the 1609 LoWPAN along with the guidelines in Section 7.2. Each time any 1610 information in the set of PIO or 6CO options change, the ABRO Version 1611 is increased by one. 1613 This requires that the 6LBR maintain the PIO, 6CO, and ABRO Version 1614 Number in stable storage, since an old version number will be 1615 silently ignored by the 6LRs. 1617 8.1.2. Routers Sending Router Solicitations 1619 In a 6LoWPAN, unless substituted, multihop distribution is done using 1620 Router Advertisement (RA) messages. Thus on interface initialization 1621 a router (6LR) MUST send Router Solicitation messages following the 1622 rules specified for hosts in [RFC4861]. That will cause the routers 1623 to respond with RA messages which then can be used to initially seed 1624 the prefix and context information. 1626 8.1.3. Routers Processing Router Advertisements 1628 If multihop distribution is not done using RA messages, then the 1629 routers follow [RFC4861] which states that they merely do some 1630 consistency checks and nothing in Section 8.1 applies. Otherwise the 1631 routers will check and record the prefix and context information from 1632 the receive RAs, and use that information as follows. 1634 If a received RA does not contain a Authoritative Border Router 1635 option, then the RA MUST be silently ignored. 1637 The router uses the 6LBR Address field in the ABRO to check if it has 1638 previously received information from the 6LBR. If it finds no such 1639 information, then it just records the 6LBR Address, Version, Valid 1640 Lifetime and the associated prefixes and context information. If the 1641 6LBR is previously known, then the Version number field MUST be 1642 compared against the recorded version number for that 6LBR. If the 1643 version number received in the packet is less than the stored version 1644 number then the information in the RA is silently ignored. Otherwise 1645 the recorded information and version number are updated. 1647 8.1.4. Storing the Information 1649 The router keeps state for each 6LBR that it sees with an ABRO. This 1650 includes the Version number, the Valid Lifetime, and the complete set 1651 of Prefix Information options and 6LoWPAN Context options. The 1652 prefixes are timed out based on the Valid lifetime in the Prefix 1653 Information Option. The Context Prefix is timed out based on the 1654 Valid lifetime in the 6LoWPAN Context option. 1656 While the prefixes and context information are stored in the router 1657 their valid and preferred lifetimes are decremented as time passes. 1658 This ensures that when the router is in turn later advertising that 1659 information in the Router Advertisements it sends, the 'expiry time' 1660 doesn't accidentally move further into the future. For example, if a 1661 6CO with a Valid lifetime of 10 minutes is received at time T, and 1662 the router includes this in a RA it sends at time T+5 minutes, the 1663 Valid lifetime in the 6CO it sends will be only 5 minutes. 1665 8.1.5. Sending Router Advertisements 1667 When multihop distribution is performed using RA messages, the 1668 routers MUST ensure that the ABRO always stay together with the 1669 prefixes and context information received with that ABRO. Thus if 1670 the router has received prefix P1 with ABRO saying it is from one 1671 6LBR, and prefix P2 from another 6LBR, then the router MUST NOT 1672 include the two prefixes in the same RA message. Prefix P1 MUST be 1673 in a RA that include a ABRO from the first 6LBR etc. Note that 1674 multiple 6LBRs might advertise the same prefix and context 1675 information, but they still need to be associated with the 6LBRs that 1676 advertised them. 1678 The routers periodically send Router Advertisements as in [RFC4861]. 1679 This is for the benefit of the other routers receiving the prefixes 1680 and context information. And the routers also respond to Router 1681 Solicitations by unicasting RA messages. In both cases the above 1682 constraint of keeping the ABRO together with 'its' prefixes and 1683 context information apply. 1685 When a router receives new information from a 6LBR, that is, either 1686 it hears from a new 6LBR (a new 6LBR Address in the ABRO) or the ABRO 1687 version number of an existing 6LBR has increased, then it is useful 1688 to send out a few triggered updates. The recommendation is to behave 1689 the same as when an interface has become an advertising interface in 1690 [RFC4861], that is, send up to three RA messages. This ensures rapid 1691 propagation of new information to all the 6LRs. 1693 8.2. Multihop Duplicate Address Detection 1695 The ARO can be used, in addition to registering an address in a 6LR, 1696 to have the 6LR verify that the address isn't used by some other host 1697 known to the 6LR. However, that isn't sufficient in a route-over 1698 topology (or in a LoWPAN with multiple 6LBRs) since some host 1699 attached to another 6LR could be using the same address. There might 1700 be different ways for the 6LRs to coordinate such Duplicate Address 1701 Detection in the future, or addresses could be assigned using a 1702 DHCPv6 server that verifies uniqueness as part of the assignment. 1704 This specification offers a substitutable simple technique for 6LRs 1705 and 6LBRs to perform Duplicate Address Detection that reuses the 1706 information from Address Registration option in the DAR and DAC 1707 messages. This technique is not needed when the Interface ID in the 1708 address is based on an EUI-64, since those are assumed to be globally 1709 unique. The technique assumes that the 6LRs either register with all 1710 the 6LBRs, or that the network uses some out-of-scope mechanism to 1711 keep the DAD tables in the 6LBRs synchronized. 1713 The multihop DAD mechanism is used synchronously the first time an 1714 address is registered with a particular 6LR. That is, the ARO option 1715 is not returned to the host until multihop DAD has been completed 1716 against the 6LBRs. For existing registrations in the 6LR the 1717 multihop DAD needs to be repeated against the 6LBRs to ensure that 1718 the entry for the address in the 6LBRs does not time out, but that 1719 can be done asynchronously with the response to the hosts. For 1720 instance, by tracking how much is left of the lifetime the 6LR 1721 registered with the 6LBRs and re-registering with the 6LBR when this 1722 lifetime is about to run out. 1724 For the synchronous multihop DAD the 6LR performs some additional 1725 checks to ensure that it has a Neighbor Cache entry it can use to 1726 respond to the host when it receives a response from a 6LBR. This 1727 consists of checking for an already existing (Tentative or 1728 Registered) Neighbor Cache entry for the registered address with a 1729 different EUI-64. If such a Registered NCE exists, then the 6LR 1730 SHOULD respond that the address is a duplicate. If such a Tentative 1731 NCE exists, then the 6LR SHOULD silently ignore the ARO thereby 1732 relying on the host retransmitting the ARO. This is needed to handle 1733 the case when multiple hosts try to register the same IPv6 address at 1734 the same time. If no Neighbor Cache entry exists, then the 6LR MUST 1735 create a Tentative Neighbor Cache entry with the EUI-64 and the SLLA 1736 option. This entry will be used to send the response to the host 1737 when the 6LBR responds positively. 1739 When a 6LR receives a Neighbor Solicitation containing an Address 1740 Registration option with a non-zero Registration Lifetime and it has 1741 no existing Registered Neighbor Cache entry, then with this mechanism 1742 the 6LR will invoke synchronous multihop DAD. 1744 The 6LR will unicast a Duplicate Address Request message to one or 1745 more 6LBRs, where the DAR contains the host's address in the 1746 Registered Address field. The DAR will be forwarded by 6LRs until it 1747 reaches the 6LBR, hence its IPv6 hop limit field will not be 255 when 1748 received by the 6LBR. The 6LBR will respond with a Duplicate Address 1749 Confirmation message, which will have a hop limit less than 255 when 1750 it reaches the 6LR. 1752 When the 6LR receives the DAC from the 6LBR, it will look for a 1753 matching (same IP address and EUI-64) (Tentative or Registered) 1754 Neighbor Cache entry. If no such entry is found then the DAC is 1755 silently ignored. If an entry is found and the DAC had Status=0 then 1756 the 6LR will mark the Tentative Neighbor Cache entry as Registered. 1757 In all cases when an entry is found then the 6LR will respond to the 1758 host with an NA, copying the Status and EUI-64 fields from the DAC to 1759 an ARO option in the NA. In case the status is an error, then the 1760 destination IP address of the NA is derived from the EUI-64 field of 1761 the DAC. 1763 A Tentative Neighbor Cache entry SHOULD be timed out 1764 TENTATIVE_NCE_LIFETIME seconds after it was created in order to allow 1765 for another host to attempt to register the IPv6 address. 1767 8.2.1. Message Validation for DAR and DAC 1769 A node MUST silently discard any received Duplicate Address Request 1770 and Confirmation messages for which at least one of the following 1771 validity checks is not satisfied: 1773 o If the message includes an IP Authentication Header, the message 1774 authenticates correctly. 1776 o ICMP Checksum is valid. 1778 o ICMP Code is 0. 1780 o ICMP length (derived from the IP length) is 32 or more bytes. 1782 o The Registered Address is not a multicast address. 1784 o All included options have a length that is greater than zero. 1786 o The IP source address is not the unspecified address, nor a 1787 multicast address. 1789 The contents of the Reserved field, and of any unrecognized options, 1790 MUST be ignored. Future, backward-compatible changes to the protocol 1791 may specify the contents of the Reserved field or add new options; 1792 backward-incompatible changes may use different Code values. 1794 Note that due to the forwarding of the DAR and DAC messages between 1795 the 6LR and 6LBR there is no hop limit check on receipt for these 1796 ICMPv6 message types. 1798 8.2.2. Conceptual Data Structures 1800 A 6LBR implementing multihop DAD needs to maintain some state 1801 separate from the Neighbor Cache. We call this conceptual data 1802 structure the DAD table. It is indexed by the IPv6 address - the 1803 Registered Address in the DAR - and contains the EUI-64 and the 1804 registration lifetime of the host that is using that address. 1806 8.2.3. 6LR Sending a Duplicate Address Request 1808 When a 6LR that implements multihop DAD receives an NS from a host 1809 and subject to the above checks, the 6LR forms and sends a DAR to at 1810 least one 6LBR. The DAR contains the following information: 1812 o In the IPv6 source address, a global address of the 6LR. 1814 o In the IPv6 destination address, the address of the 6LBR. 1816 o In the IPv6 hop limit, MULTIHOP_HOPLIMIT. 1818 o The Status field MUST be set to zero 1820 o The EUI-64 and Registration lifetime are copied from the ARO 1821 received from the host. 1823 o The Registered Address set to the IPv6 address of the host, that 1824 is, the sender of the triggering NS. 1826 When a 6LR receives an NS from a host with a zero Registration 1827 Lifetime then, in addition to removing the Neighbor Cache entry for 1828 the host as specified in Section 6, an DAR is sent to the 6LBRs as 1829 above. 1831 A router MUST NOT modify the Neighbor Cache as a result of receiving 1832 a Duplicate Address Request. 1834 8.2.4. 6LBR Receiving a Duplicate Address Request 1836 When a 6LBR that implements the substitutable multihop DAD receives 1837 an DAR from a 6LR, it performs the message validation specified in 1838 Section 8.2.1. If the DAR is valid the 6LBR proceeds to look for the 1839 Registration Address in the DAD Table. If an entry is found and the 1840 recorded EUI-64 is different than the EUI-64 in the DAR, then it 1841 returns a DAC NA with the Status set to 1 ('Duplicate Address'). 1842 Otherwise it returns a DAC with Status set to zero and updates the 1843 lifetime. 1845 If no entry is found in the DAD Table and the Registration Lifetime 1846 is non-zero, then an entry is created and the EUI-64 and Registered 1847 Address from the DAR are stored in that entry. 1849 If an entry is found in the DAD Table, the EUI-64 matches, and the 1850 Registration Lifetime is zero then the entry is deleted from the 1851 table. 1853 In both of the above cases the 6LBR forms an DAC with the information 1854 copied from the DAR and the Status field is set to zero. The DAC is 1855 sent back to the 6LR i.e., back to the source of the DAR. The IPv6 1856 hop limit is set to MULTIHOP_HOPLIMIT 1858 8.2.5. Processing a Duplicate Address Confirmation 1860 When a 6LR implementing multihop DAD receives a DAC message, then it 1861 first validates the message per Section 8.2.1. For a valid DAC, if 1862 there is no Tentative Neighbor Cache entry matching the Registered 1863 address and EUI-64, then the DAC is silently ignored. Otherwise, the 1864 information in the DAC and in the Tentative Neighbor Cache entry is 1865 used to form an NA to send to the host. The Status code is copied 1866 from the DAC to the ARO that is sent to the host. In case of the DAC 1867 indicates an error (the Status is non-zero), the NA is returned to 1868 the host as described in Section 6.5.2 and the Tentative Neighbor 1869 Cache entry for the Registered Address is removed. Otherwise it is 1870 made into a Registered Neighbor Cache entry. 1872 A router MUST NOT modify the Neighbor Cache as a result of receiving 1873 a Duplicate Address Confirmation, unless there is a Tentative 1874 Neighbor Cache entry matching the IPv6 address and EUI-64. 1876 8.2.6. Recovering from Failures 1878 If there is no response from a 6LBR after RETRANS_TIMER [RFC4861] 1879 then the 6LR would retransmit the DAR to the 6LBR up to 1880 MAX_UNICAST_SOLICIT [RFC4861] times. After this the 6LR SHOULD 1881 respond to the host with an ARO Status of zero. 1883 9. Protocol Constants 1885 This section defines the relevant protocol constants used in this 1886 document based on a subset of [RFC4861] constants. (*) indicates 1887 constants modified from [RFC4861] and (+) indicates new constants. 1889 Additional protocol constants are defined in Section 4. 1891 6LBR Constants: 1893 MIN_CONTEXT_CHANGE_DELAY+ 300 seconds 1895 6LR Constants: 1897 MAX_RTR_ADVERTISEMENTS 3 transmissions 1899 MIN_DELAY_BETWEEN_RAS* 10 seconds 1901 MAX_RA_DELAY_TIME* 2 seconds 1903 TENTATIVE_NCE_LIFETIME+ 20 seconds 1905 Router Constants: 1907 MULTIHOP_HOPLIMIT+ 64 1909 Host Constants: 1911 RTR_SOLICITATION_INTERVAL* 10 seconds 1913 MAX_RTR_SOLICITATIONS 3 transmissions 1915 MAX_RTR_SOLICITATION_INTERVAL+ 60 seconds 1917 10. Examples 1919 10.1. Message Examples 1921 STEP 1923 6LN 6LR 1925 | | 1927 1. | ---------- Router Solicitation --------> | 1929 | [SLLAO] | 1931 | | 1933 2. | <-------- Router Advertisement --------- | 1935 | [PIO + 6CO + ABRO + SLLAO] | 1937 Figure 2: Basic Router Solicitation/Router Advertisement exchange 1938 between a node and 6LR or 6LBR 1940 6LN 6LR 1942 | | 1944 1. | ------- NS with Address Registration ------> | 1946 | [ARO + SLLAO] | 1948 | | 1950 2. | <----- NA with Address Registration -------- | 1952 | [ARO with Status] | 1954 Figure 3: Neighbor Discovery Address Registration 1956 6LN 6LR 6LBR 1958 | | | 1960 1. | --- NS with Address Reg --> | | 1962 | [ARO + SLLAO] | | 1964 | | | 1966 2. | | ----------- DAR ----------> | 1968 | | | 1970 3. | | <---------- DAC ----------- | 1972 | | | 1974 4. | <-- NA with Address Reg --- | | 1976 | [ARO with Status] | 1978 Figure 4: Neighbor Discovery Address Registration with Multihop DAD 1980 10.2. Host Bootstrapping Example 1982 The following example describes the address bootstrapping scenarios 1983 using the improved ND mechanisms specified in this document. It is 1984 assumed that the 6LN first performs a sequence of operations in order 1985 to get secure access at the link-layer of the LoWPAN and obtain a key 1986 for link-layer security. The methods of how to establish the link- 1987 layer security is out of scope of this document. In this example an 1988 IEEE 802.15.4 6LN forms a 16-bit short-address based IPv6 addresses 1989 without using DHCPv6 (i.e., the M flag is not set in the Router 1990 Advertisements). 1992 1. After obtaining link-level security, a 6LN assigns a link-local 1993 IPv6 address to itself. A link-local IPv6 address is configured 1994 based on the 6LN's EUI-64 link-layer address formed as per [RFC4944]. 1996 2. Next the 6LN determines one or more default routers in the 1997 network by sending an RS to the all-routers multicast address with 1998 the SLLA Option set to its EUI-64 link-local address. If the 6LN was 1999 able to obtain the link-layer address of a router through its link- 2000 layer operations then the 6LN may form a link-local destination IPv6 2001 address for the router and send it a unicast RS. The 6LR responds 2002 with a unicast RA to the IP source using the SLLA option from the RS 2003 (it may have created a tentative NCE). See Figure 2. 2005 3. In order to communicate more than one IP hop away the 6LN 2006 configures a global IPv6 address. In order to save overhead, this 2007 6LN wishes to configure its IPv6 address based on a 16-bit short 2008 address as per [RFC4944]. As the network is unmanaged (M flag not 2009 set in RA), the 6LN randomly chooses a 16-bit link-layer address and 2010 forms a tentative IPv6 address from it. 2012 4. Next the 6LN registers that address with one or more of its 2013 default routers by sending a unicast NS message with an ARO 2014 containing its tentative global IPv6 address to register, the 2015 registration lifetime and its EUI-64. An SLLA option is also 2016 included with the link-layer address corresponding to the address 2017 being registered. If a successful (status 0) NA message is received 2018 the address can then be used and the 6LN assumes it has been 2019 successfully checked for duplicates. If a duplicate address (status 2020 1) NA message is received, the 6LN then removes the temporary IPv6 2021 address and 16-bit link-layer address and goes back to step 3. If a 2022 neighbor cache full (status 2) message is received, the 6LN attempts 2023 to register with another default router, or if none, goes back to 2024 step 2. See Figure 3. Note that an NA message returning an error 2025 would be sent back to the link-local EUI-64 based IPv6 address of the 2026 6LN instead of the 16-bit (duplicate) address. 2028 5. The 6LN now performs maintenance by sending a new NS address 2029 registration before the lifetime expires. 2031 If multihop DAD and multihop prefix and context distribution is used, 2032 the effect of the 6LRs and hosts following the above bootstrapping is 2033 a "wavefront" of 6LRs and host being configured spreading from the 2034 6LBRs. First the hosts and 6LRs that can directly reach a 6LBR would 2035 receive one or more RAs and configure and register their IPv6 2036 addresses. Once that is done they would enable the routing protocol 2037 and start sending out Router Advertisements. That would result in a 2038 new set of 6LRs and hosts to receive responses to their Router 2039 Solicitations, form and register their addresses, etc. That repeats 2040 until all of the 6LRs and hosts have been configured. 2042 10.2.1. Host Bootstrapping Messages 2044 This section brings specific message examples to the previous 2045 bootstrapping process. When discussing messages, the following 2046 notation is used: 2048 LL64: Link-Local Address based on the EUI-64, which is also the 2049 802.15.4 Long Address. 2051 GP16: Global Address based on the 802.15.4 Short Address. This 2052 address may not be unique. 2054 GP64: Global addresses derived from the EUI-64 address as specified 2055 in [RFC4944]. 2057 MAC64: EUI-64 address used as the link-layer address. 2059 MAC16: IEEE 802.15.4 16-bit short address. 2061 Note that some implementations may use LL64 and GP16 style addresses 2062 instead of LL64 and GP64. In the following, we will show an example 2063 message flow as to how a node uses LL64 to register a GP16 address 2064 for multihop DAD verification. 2066 6LN-----RS-------->6LR 2067 Src= LL64 (6LN) 2068 Dst= All-router-link-scope-multicast 2069 SLLAO= MAC64 (6LN) 2071 6LR------RA--------->6LN 2072 Src= LL64 (6LR) 2073 Dst= LL64 (6LN) 2075 Note: Source address of RA must be a link-local 2076 address (Section 4.2, RFC 4861). 2078 6LN-------NS Reg------>6LR 2079 Src= GP16 (6LN) 2080 Dst= LL64 (6LR) 2081 ARO 2082 SLLAO= MAC16 (6LN) 2084 6LR---------DAR----->6LBR 2085 Src= GP64 or GP16 (6LR) 2086 Dst= GP64 or GP16 (6LBR) 2087 Registered Address= GP16 (6LN) and EUI-64 (6LN) 2089 6LBR-------DAC--------->6LR 2090 Src= GP64 or GP16 (6LBR) 2091 Dst= GP64 or GP16 (6LR) 2092 Copy of information from DAR 2094 If Status is a Success: 2096 6LR ---------NA-Reg------->6LN 2097 Src= LL64 (6LR) 2098 Dst= GP16 (6LN) 2099 ARO with Status = 0 2101 If Status is not a success: 2103 6LR ---------NA-Reg-------->6LN 2104 Src= LL64 (6LR) 2105 Dst= LL64 (6LN) --> Derived from the EUI-64 of ARO 2106 ARO with Status > 0 2108 Figure 5: Detailed Message Address Examples 2110 10.3. Router Interaction Example 2112 In the Route-over topology, when a routing protocol is run across 2113 6LRs the bootstrapping and neighbor cache management are handled a 2114 little differently. The description in this paragraph provides only 2115 a guideline for an implementation. 2117 At the initialization of a 6LR, it may choose to bootstrap as a host 2118 with the help of a parent 6LR if the substitutable multihop DAD is 2119 performed with the 6LBR. The neighbor cache management of a router 2120 and address resolution among the neighboring routers are described in 2121 Section 6.5.3 and Section 6.5.5, respectively. In this example, we 2122 assume that the neighboring 6LoWPAN link is secure. 2124 10.3.1. Bootstrapping a Router 2126 In this scenario, the bootstrapping 6LR, 'R1', is multiple hops away 2127 from the 6LBR and surrounded by other 6LR neighbors. Initially R1 2128 behaves as a host. It sends multicast RS and receives an RA from one 2129 or more neighboring 6LRs. R1 picks one 6LR as its temporary default 2130 router and performs address resolution via this default router. 2131 Note, if multihop DAD is not required (e.g. in a managed network or 2132 using EUI-64 based addresses) then it does not need to pick a 2133 temporary default router, however it may still want to send the 2134 initial RS message if it wants to autoconfigure its address with the 2135 global prefix disseminated by the 6LBR. 2137 Based on the information received in the RAs, R1 updates its cache 2138 with entries for all the neighboring 6LRs. Upon completion of the 2139 address registration, the bootstrapping router deletes the temporary 2140 entry of the default router and the routing protocol is started. 2142 Also note that R1 may refresh its multihop DAD registration directly 2143 with the 6LBR (using the next hop neighboring 6LR determined by the 2144 routing protocol for reaching the 6LBR). 2146 10.3.2. Updating the Neighbor Cache 2148 In this example, there are three 6LRs, R1, R2, R3. Initially when R2 2149 boots it sees only R1, and accordingly R2 creates a neighbor cache 2150 entry for R1. Now assume R2 receives a valid routing update from 2151 router R3. R2 does not have any neighbor cache entry for R3. If the 2152 implementation of R2 supports detecting link-layer address from the 2153 routing information packets then it directly updates the its neighbor 2154 cache using that link-layer information. If this is not possible, 2155 then R2 should perform multicast NS with source set with its link- 2156 local or global address depending on the scope of the source IP- 2157 address received in the routing update packet. The target address of 2158 the NS message is the source IPv6 address of the received routing 2159 update packet. The format of the NS message is as described in 2160 Section 4.3 of [RFC4861]. 2162 More generally any 6LR that receives a valid route-update from a 2163 neighboring router for which it does not have any neighbor cache 2164 entry is required to update its neighbor cache as described above. 2166 The router (6LR and 6LBR) IP-addresses learned via Neighbor Discovery 2167 are not redistributed to the routing protocol. 2169 11. Security Considerations 2171 The security considerations of IPv6 Neighbor Discovery [RFC4861] and 2172 Address Autoconfiguration [RFC4862] apply. Additional considerations 2173 can be found in [RFC3756]. 2175 There is a slight modification to those considerations due to the 2176 fact that in this specification the M-flag in the Router 2177 Advertisements disable the use of stateless address autoconfiguration 2178 for addresses not derived from EUI-64. Thus a rogue router on the 2179 link can force the use of only DHCP for short addresses, whereas in 2180 [RFC4861] and [RFC4862] the rogue router could only cause the 2181 addition of DHCP and not disable SLAAC for short addresses. 2183 This specification assumes that the link layer is sufficiently 2184 protected, for instance using MAC sublayer cryptography. Thus, its 2185 threat model is no different from that of IPv6 Neighbor Discovery 2186 [RFC4861]. The threat model number 1 in section 3 of [RFC3756] 2187 applies here. However, any future 6LoWPAN security protocol that 2188 applies to Neighbor Discovery for 6LoWPAN protocol, is out of scope 2189 of this document. 2191 The multihop DAD mechanisms rely on DAR and DAC messages that are 2192 forwarded by 6LRs, and as a result the hop_limit=255 check on the 2193 receiver does not apply to those messages. This implies that any 2194 node on the Internet could successfully send such messages. We avoid 2195 any additional security issues due to this by requiring that the 2196 routers never modify the Neighbor Cache entry due to such messages, 2197 and that they discard them unless they are received on an interface 2198 that has been explicitly configured to use these optimizations. 2200 In some future deployments one might want to use SEcure Neighbor 2201 Discovery [RFC3971] [RFC3972]. This is possible with the Address 2202 Registration option as sent between hosts and routers, since the 2203 address that is being registered is the IPv6 source address of the 2204 Neighbor Solicitation and SeND verifies the IPv6 source address of 2205 the packet. Applying SeND to the router-to-router communication in 2206 this document is out of scope. 2208 12. IANA Considerations 2210 The document requires three new Neighbor Discovery option types under 2211 the subregistry "IPv6 Neighbor Discovery Option Formats": 2213 o Address Registration Option (TBD1) 2215 o 6LoWPAN Context Option (TBD2) 2217 o Authoritative Border Router Option (TBD3) 2219 The document requires two new ICMPv6 types under the subregistry 2220 "ICMPv6 type Numbers": 2222 o Duplicate Address Request (TBD4) 2224 o Duplicate Address Confirmation (TBD5) 2226 This document also requests IANA to create a new sub-registry for the 2227 Status values of the Address Registration Option, under the ICMPv6 2228 parameters registry. 2230 Address Registration Option Status Values registry: 2232 Possible values are 8-bit unsigned integers (0..255). 2234 Registration procedure is "Standards Action" [RFC5226]. 2236 Initial allocation is as indicated in Table 2: 2238 +--------+--------------------------------------------+ 2239 | Status | Description | 2240 +--------+--------------------------------------------+ 2241 | 0 | Success | 2242 | 1 | Duplicate Address | 2243 | 2 | Neighbor Cache Full | 2244 | 3-255 | Allocated using Standards Action [RFC5226] | 2245 +--------+--------------------------------------------+ 2247 Table 2 2249 13. Interaction with other Neighbor Discovery Extensions 2251 There are two classes of Neighbor Discovery Extensions that have 2252 different interaction with this specification. 2254 One class are extensions to to the Duplicate Address Detection 2255 mechanisms in [RFC4861] and [RFC4862]. An example of this is 2256 Optimistic DAD [RFC4429]. Such extensions does not apply when this 2257 specification is being used, since it uses ARO for DAD (which is 2258 neither optimistic nor pessimistic - always one roundtrip to the 2259 router to check DAD). 2261 All other (non-DAD) Neighbor Discovery extensions, be it path 2262 selection ones like Default Router Preferences [RFC4191], 2263 configuration ones like DNS config [RFC5006], or others like DNA 2264 [RFC6059], are completely orthogonal to this specification, and will 2265 work as is. 2267 14. Guideline for New Features 2269 This section discusses a guideline of new protocol features defined 2270 in this document. It also sets some expectations for implementation 2271 and deployment of these features. This section is informative in 2272 nature: It does not override the detailed specifications of the 2273 previous sections, but summarizes them and presents them in a compact 2274 form that can be used as a checklist. The checklist acts as a 2275 guideline to indicate the possible importance of a feature in terms 2276 of a deployment as per information available as of the writing of the 2277 document. Note that in some cases the deployment is 'SHOULD' where 2278 the implementation is a 'MUST'. This is due to the presence of 2279 substitutable features; the deployment may use alternative methods 2280 for those. Therefore, implementing a configuration knob is 2281 recommended for the substitutable features. The lists emphasize 2282 conciseness over completeness. 2284 +----------+---------------------------------+----------+-----------+ 2285 | Section | Description | Deploy | Implement | 2286 +----------+---------------------------------+----------+-----------+ 2287 | 3.1 | Host initiated RA | MUST | MUST | 2288 | 3.2 | EUI-64 based IPv6-address | MUST | MUST | 2289 | | 16bit-MAC based address | MAY | SHOULD | 2290 | | Other non-unique addresses | MAY | MAY | 2291 | 3.3 | Host Initiated RS | MUST | MUST | 2292 | | ABRO Processing | SHOULD | MUST | 2293 | 4.1 | Registration with ARO | MUST | MUST | 2294 | 4.2, 5.4 | 6LoWPAN Context Option | SHOULD | SHOULD | 2295 | 5.1 | Re-direct Message Acceptance | MUST NOT | MUST NOT | 2296 | | Joining Solicited Node | N/A | N/A | 2297 | | Multicast | | | 2298 | | Joining all-node Multicast | MUST | MUST | 2299 | | Using link-layer indication for | MAY | MAY | 2300 | | NUD | | | 2301 | 5.5 | 6LoWPAN-ND NUD | MUST | MUST | 2302 | 5.8.2 | Behavior on wake-up | SHOULD | SHOULD | 2303 +----------+---------------------------------+----------+-----------+ 2305 Table 3: Guideline for 6LoWPAN-ND features for hosts 2307 +---------------+-------------------------+------------+------------+ 2308 | Section | Description | deploy | implement | 2309 +---------------+-------------------------+------------+------------+ 2310 | 3.1 | Periodic RA | SHOULD NOT | SHOULD NOT | 2311 | 3.2 | Address assignment | SHOULD | MUST | 2312 | | during Startup | | | 2313 | 3.3 | Supporting EUI-64 based | MUST | MUST | 2314 | | MAC Hosts | | | 2315 | | Supporting 16-bit MAC | MAY | SHOULD | 2316 | | hosts | | | 2317 | 3.4, 4.3, | ABRO Processing/sending | SHOULD | MUST | 2318 | 8.1.3, 8.1.4 | | | | 2319 | 8.1 | Multihop Prefix storing | SHOULD | MUST | 2320 | | and re-distribution | | | 2321 | 3.5 | Tentative NCE | MUST | MUST | 2322 | 8.2 | Multihop DAD | SHOULD | MUST | 2323 | 4.1, 6.5, | ARO Support | MUST | MUST | 2324 | 6.5.1 - 6.5.5 | | | | 2325 | 4.2 | 6LoWPAN Context Option | SHOULD | SHOULD | 2326 | 6.3 | Process RS/ARO | MUST | MUST | 2327 +---------------+-------------------------+------------+------------+ 2329 Table 4: Guideline for 6LR features in 6LoWPAN-ND 2331 +--------------+--------------------------+------------+------------+ 2332 | Section | Description | deploy | implement | 2333 +--------------+--------------------------+------------+------------+ 2334 | 3.1 | Periodic RA | SHOULD NOT | SHOULD NOT | 2335 | 3.2 | Address autoconf on | MUST NOT | MUST NOT | 2336 | | Router interface | | | 2337 | 3.3 | EUI-64 MAC support on | MUST | MUST | 2338 | | 6LoWPAN interface | | | 2339 | 8.1 - 8.1.1, | Multihop Prefix | SHOULD | MUST | 2340 | 8.1.5 | distribution | | | 2341 | 8.2 | Multihop DAD | SHOULD | MUST | 2342 +--------------+--------------------------+------------+------------+ 2344 Table 5: Guideline for 6LBR features in 6LoWPAN-ND 2346 15. Acknowledgments 2348 The authors thank Pascal Thubert, Jonathan Hui, Carsten Bormann, 2349 Richard Kelsey, Geoff Mulligan, Julien Abeille, Alexandru Petrescu, 2350 Peter Siklosi, Pieter De Mil, Fred Baker, Anthony Schoofs, Phil 2351 Roberts, Daniel Gavelle, Joseph Reddy, Robert Cragie, Mathilde Durvy, 2352 Colin O'Flynn, Dario Tedeschi, Esko Dijk and Joakim Eriksson for 2353 useful discussions and comments that have helped shaped and improve 2354 this document. 2356 Additionally, the authors would like to recognize Carsten Bormann for 2357 the suggestions on the Context Prefix Option and contribution to 2358 earlier version of the draft, Pascal Thubert for contribution of the 2359 original registration idea and extensive contributions to earlier 2360 versions of the draft, Jonathan Hui for original ideas on prefix/ 2361 context distribution and extensive contributions to earlier versions 2362 of the draft, Colin O'Flynn for useful Error-to suggestions and 2363 contributions to the Examples section, Geoff Mulligan for suggesting 2364 the use of Address Registration as part of existing IPv6 Neighbor 2365 Discovery messages, and Mathilde Durvy for helping to clarify router 2366 interaction. 2368 16. Changelog 2370 Changes from -20 to -21: 2372 o Clarified the address an address registration error is sent to. 2374 o Added a new section explaining the interaction with other 2375 Neighbor Discovery extensions. 2377 Changes from -19 to -20: 2379 o Further clarification on substitutable features. 2381 o Changed RFC 6282 to a normative reference. 2383 Changes from -18 to -19: 2385 o Editorial improvements as a result of IESG comments (#135, 2386 #142). 2388 o Extended ABRO with longer version number and valid lifetime, 2389 while maintaining backward compatibility (#141). 2391 o Renamed optional features and described them as substitutable 2392 (#138). 2394 Changes from -17 to -18: 2396 o Fixed nits related to IESG submission. 2398 Changes from -16 to -17: 2400 o Removed unnecessary normative text from Assumptions. 2402 o Clarified the next-hop determination of multicast addresses. 2404 o Editorial improvements from WGLC review. 2406 Changes from -15 to -16: 2408 o Added an applicability section (#133) 2410 o Updated document title to align with HC 2412 o Minor editing as result of WGLC review (#134) 2414 Changes from -14 to -15: 2416 o Changed use of redirect to SHOULD NOT for route-over and MAY for 2417 mesh-under. (#130) 2419 o Changed the 16-bit lifetimes to a unit of 60 seconds (#131) 2421 o Added text to Section 5.4.2 adding a receive-only state to 2422 context entries that timeout. (#132) 2424 Changes from -13 to -14: 2426 o Introduced the new DAR and DAC ICMPv6 message types for multihop 2427 DAD to avoid relying on the Length=4 checks for the ARO. This 2428 simplifies implementing the hop limit check. 2430 o Clarified the hop limit values for the multihop DAD messages by 2431 introducing the MULTIHOP_HOPLIMIT constant set to 64. 2433 o Clarified when a host should de-register from a router. 2435 o Added a section on next-hop determination for routers. 2437 o Removed the infinite lifetime from 6CO. 2439 o Increased MIN_CONTEXT_CHANGE_DELAY to 300 seconds. 2441 Changes from -12 to -13: 2443 o Error-to solution added for returning NA messages carrying an 2444 error ARO option to the link-local EUI-64 based IPv6 address of 2445 the host (#126). 2447 o New examples added. 2449 Changes from -11 to -12: 2451 o Version field of ABRO moved after Length for 32-bit alignment of 2452 the reserved space (#90). 2454 o Several clarifications were made on router interaction, 2455 including a new section with router interaction examples (#91). 2457 o Temporary Neighbor Cache Entry created upon host sending NS+ARO, 2458 and SLLAO removed from multihop DAD NS/NA messages (#87). 2460 Changes from -10 to -11: 2462 o Reference to RFC1982 for version number comparison (#80) 2464 o RA Router Lifetime field use clarified (#81) 2466 o Make fields 16-bit rather than 32-bit where possible (#83) 2468 o Unicast RA clarification (#84) 2470 o Temporary ND option types (#85) 2472 o SLLA/TLLA clarification (#86) 2473 o GP16 as source address in initial NS clarification (#87) 2475 Changes from -09 to -10: 2477 o Clarifications made to Section 8.2 (#66) 2479 o Explained behavior of Neighbor Cache (#67) 2481 o Clarified use of SLLAO in RS and NS messages (#68) 2483 o Added new term 6LN (#69) 2485 o Small clarification on 6CO flag (#70) 2487 o Defined host behavior on ARO failure better (#72) 2489 o Added bootstrapping example for a host (#73) 2491 o Added new Neighbor Cache Full ARO error (#74) 2493 o Added rule on the use of the M flag (#75) 2495 Changes from -08 to -09: 2497 o Clean re-write of the draft (re-use of some introductory 2498 material) 2500 o Merged in draft-chakrabarti-6lowpan-ipv6-nd-simple-00 2502 o Changed address registration to an option piggybacked on NS/NA 2504 o New Authoritative Border Router option 2506 o New Address Registration Option 2508 o Separated Prefix Information and Content Information 2510 o Optional DAD to the edge 2512 Changes from -07 to -08: 2514 o Removed Extended LoWPAN and Whiteboard related sections. 2516 o Included reference to the autoconf addressing model. 2518 o Added Optimistic Flag to 6AO. 2520 o Added guidelines on routers performing DAD. 2522 o Removed the NR/NC Advertising Interval. 2524 o Added assumption of uniform IID formation and DAD throughout a 2525 LoWPAN. 2527 Changes from -06 to -07: 2529 o Updated addressing and address resolution (#60). 2531 o Changed the Address Option to 6LoWPAN Address Option, fixed S 2532 values (#61). 2534 o Added support for classic RFC4861 RA Prefix Information messages 2535 to be processed (#62). 2537 o Added a section on using 6LoWPAN-ND under a hard-wired RFC4861 2538 stack (#63). 2540 o Updated the NR/NC message with a new Router flag, combined the 2541 Code and Status fields into one byte, and added the capability to 2542 carry 6IOs (#64). 2544 o Made co-existence with other ND mechanisms clear (#59). 2546 o Added a new Protocol Specification section with all mechanisms 2547 specified there (#59). 2549 o Removed dependencies and conflicts with RFC4861 wherever 2550 possible (#59). 2552 o Some editorial cleanup. 2554 Changes from -05 to -06: 2556 o Fixed the Prf codes (#52). 2558 o Corrected the OIIO TID field to 8-bits. Changed the Nonce/OII 2559 order in both the OIIO and the NR/NC. (#53) 2561 o Corrected an error in Table 1 (#54). 2563 o Fixed asymmetric and a misplaced transient in the 6LoWPAN 2564 terminology section. 2566 o Added Updates RFC4861 to header 2568 Changes from -04 to -05: 2570 o Meaning of the RA's M-bit changed to original [RFC4861] meaning 2571 (#46). 2573 o Terms "on-link" and "off-link" used in place of "on-link" and 2574 "off-link". 2576 o Next-hop determination text simplified (#49). 2578 o Neighbor cache and destination cache removed. 2580 o IID to link-layer address requirement relaxed. 2582 o NR/NC changes to enable on-link refresh with routers (#48). 2584 o Modified 6LoWPAN Information Option (#47). 2586 o Added a Protocol Constants section (#24) 2588 o Added the NR processing table (#51) 2590 o Considered the use of SeND on backbone NS/NA messages (#50) 2592 Changes from -03 to -04: 2594 o Moved Ad-hoc LoWPAN operation to Section 7 and made ULA prefix 2595 generation a features useful also in Simple and Extended LoWPANs. 2596 (#41) 2598 o Added a 32-bit Owner Nonce to the NR/NC messages and the 2599 Whiteboard, removed the TID history. (#39) 2601 o Improved the duplicate OII detection algorithm using the Owner 2602 Nonce. (#39) 2604 o Clarified the use of Source and Target link-layer options in 2605 NR/NC. (#43) 2607 o Included text on the use of alternative methods to acquire 2608 addresses. (#38) 2610 o Removed S=2 from Address Option (not needed). (#36) 2612 o Added a section on router dissemination consistency. (#44) 2614 o Small improvements and extensive editing. (#42, #37, #35) 2616 Changes from -02 to -03: 2618 o Updated terminology, with RFC4861 non-transitive link model. 2620 o 6LoWPAN and ND terminology separated. 2622 o Protocol overview explains RFC4861 diff in detail. 2624 o RR/RC is now Node Registration/Confirmation (NR/NC). 2626 o Added NR failure codes. 2628 o ER Metric now included in 6LoWPAN Summary Option for use in 2629 default router determination by hosts. 2631 o Examples of host data structures, and the Whiteboard given. 2633 o Whiteboard is supported by all Edge Routers for option 2634 simplicity. 2636 o Edge Router Specification chapter re-structured, clarifying 2637 optional Extended LoWPAN operation. 2639 o NS/NA now completely optional for nodes. No address resolution 2640 or NS/NA NUD required. 2642 o link-local operation now compatible with oDAD (was broken). 2644 o Exception to hop limit = 255 for NR/NC messages. 2646 o Security considerations improved. 2648 o ICMPv6 destination unreachable supported. 2650 Changes from -01 to -02: 2652 o Fixed 16 != 0xff bug (ticket closed). 2654 o Specified use of ULAs in ad-hoc LoWPAN section 9 (ticket 2655 closed). 2657 o Terminology cleanup based on Alex's comments. 2659 o General editing improvements. 2661 Changes from -00 to -01: 2663 o Specified the duplicate owner interface identifier procedures. 2664 A TID lollipop algorithm was sufficient (nonce unnecessary). 2666 o Defined fault tolerance using secondary bindings. 2668 o Defined ad-hoc network operation. 2670 o Removed the E flag from RA and the X flag from RR/RC. 2672 o Completed message examples. 2674 o Lots of improvements in text quality and consistency were made. 2676 17. References 2678 17.1. Normative References 2680 [ETHERNET] 2681 "Information technology - Telecommunications and 2682 information exchange between systems - Local and 2683 metropolitan area networks - Specific requirements - Part 2684 3: Carrier sense multiple access with Collision Detection 2685 (CSMA/CD) Access Method and Physical Layer 2686 Specifications", IEEE Std 802.3-2008, December 2008, . 2690 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2691 Requirement Levels", BCP 14, RFC 2119, March 1997. 2693 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2694 (IPv6) Specification", RFC 2460, December 1998. 2696 [RFC2491] Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6 2697 over Non-Broadcast Multiple Access (NBMA) networks", 2698 RFC 2491, January 1999. 2700 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 2701 More-Specific Routes", RFC 4191, November 2005. 2703 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 2704 Addresses", RFC 4193, October 2005. 2706 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2707 Architecture", RFC 4291, February 2006. 2709 [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control 2710 Message Protocol (ICMPv6) for the Internet Protocol 2711 Version 6 (IPv6) Specification", RFC 4443, March 2006. 2713 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2714 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2715 September 2007. 2717 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2718 Address Autoconfiguration", RFC 4862, September 2007. 2720 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 2721 "Transmission of IPv6 Packets over IEEE 802.15.4 2722 Networks", RFC 4944, September 2007. 2724 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 2725 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 2726 May 2008. 2728 [RFC6282] Hui, J. and P. Thubert, "Compression Format for IPv6 2729 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 2730 September 2011. 2732 17.2. Informative References 2734 [EUI64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64) 2735 Registration Authority", . 2738 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 2739 and M. Carney, "Dynamic Host Configuration Protocol for 2740 IPv6 (DHCPv6)", RFC 3315, July 2003. 2742 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 2743 Host Configuration Protocol (DHCP) version 6", RFC 3633, 2744 December 2003. 2746 [RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor 2747 Discovery (ND) Trust Models and Threats", RFC 3756, 2748 May 2004. 2750 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 2751 Neighbor Discovery (SEND)", RFC 3971, March 2005. 2753 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 2754 RFC 3972, March 2005. 2756 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 2757 for IPv6", RFC 4429, April 2006. 2759 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 2760 over Low-Power Wireless Personal Area Networks (6LoWPANs): 2761 Overview, Assumptions, Problem Statement, and Goals", 2762 RFC 4919, August 2007. 2764 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 2765 Extensions for Stateless Address Autoconfiguration in 2766 IPv6", RFC 4941, September 2007. 2768 [RFC5006] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 2769 "IPv6 Router Advertisement Option for DNS Configuration", 2770 RFC 5006, September 2007. 2772 [RFC5889] Baccelli, E. and M. Townsley, "IP Addressing Model in Ad 2773 Hoc Networks", RFC 5889, September 2010. 2775 [RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for 2776 Detecting Network Attachment in IPv6", RFC 6059, 2777 November 2010. 2779 Authors' Addresses 2781 Zach Shelby (editor) 2782 Sensinode 2783 Konekuja 2 2784 Oulu 90620 2785 FINLAND 2787 Phone: +358407796297 2788 Email: zach@sensinode.com 2790 Samita Chakrabarti 2791 Ericsson 2793 Email: samita.chakrabarti@ericsson.com 2795 Erik Nordmark 2796 Cisco Systems 2798 Email: nordmark@cisco.com