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Thubert, Ed. 3 Internet-Draft Cisco Systems 4 Updates: 6550, 6775, 8505 (if approved) M. Richardson 5 Intended status: Standards Track Sandelman 6 Expires: 20 June 2021 17 December 2020 8 Routing for RPL Leaves 9 draft-ietf-roll-unaware-leaves-27 11 Abstract 13 This specification updates RFC6550, RFC6775, and RFC8505. It 14 provides a mechanism for a host that implements a routing-agnostic 15 interface based on 6LoWPAN Neighbor Discovery to obtain reachability 16 services across a network that leverages RFC6550 for its routing 17 operations. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at https://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on 20 June 2021. 36 Copyright Notice 38 Copyright (c) 2020 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 43 license-info) in effect on the date of publication of this document. 44 Please review these documents carefully, as they describe your rights 45 and restrictions with respect to this document. Code Components 46 extracted from this document must include Simplified BSD License text 47 as described in Section 4.e of the Trust Legal Provisions and are 48 provided without warranty as described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 53 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 54 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 6 55 2.2. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 6 56 2.3. References . . . . . . . . . . . . . . . . . . . . . . . 7 57 3. RPL External Routes and Dataplane Artifacts . . . . . . . . . 8 58 4. 6LoWPAN Neighbor Discovery . . . . . . . . . . . . . . . . . 9 59 4.1. RFC 6775 Address Registration . . . . . . . . . . . . . . 9 60 4.2. RFC 8505 Extended Address Registration . . . . . . . . . 9 61 4.2.1. R Flag . . . . . . . . . . . . . . . . . . . . . . . 10 62 4.2.2. TID, "I" Field and Opaque Fields . . . . . . . . . . 10 63 4.2.3. Route Ownership Verifier . . . . . . . . . . . . . . 11 64 4.3. RFC 8505 Extended DAR/DAC . . . . . . . . . . . . . . . . 11 65 4.3.1. RFC 7400 Capability Indication Option . . . . . . . . 12 66 5. Requirements on the RPL-Unware leaf . . . . . . . . . . . . . 12 67 5.1. Support of 6LoWPAN ND . . . . . . . . . . . . . . . . . . 12 68 5.2. Support of IPv6 Encapsulation . . . . . . . . . . . . . . 13 69 5.3. Support of the Hop-by-Hop Header . . . . . . . . . . . . 13 70 5.4. Support of the Routing Header . . . . . . . . . . . . . . 13 71 6. Enhancements to RFC 6550 . . . . . . . . . . . . . . . . . . 14 72 6.1. Updated RPL Target Option . . . . . . . . . . . . . . . . 14 73 6.2. Additional Flag in the RPL DODAG Configuration Option . . 16 74 6.3. Updated RPL Status . . . . . . . . . . . . . . . . . . . 17 75 7. Enhancements to draft-ietf-roll-efficient-npdao . . . . . . . 19 76 8. Enhancements to RFC 6775 and RFC8505 . . . . . . . . . . . . 19 77 9. Protocol Operations for Unicast Addresses . . . . . . . . . . 20 78 9.1. General Flow . . . . . . . . . . . . . . . . . . . . . . 20 79 9.2. Detailed Operation . . . . . . . . . . . . . . . . . . . 23 80 9.2.1. Perspective of the 6LN Acting as RUL . . . . . . . . 23 81 9.2.2. Perspective of the 6LR Acting as Border router . . . 25 82 9.2.3. Perspective of the RPL Root . . . . . . . . . . . . . 29 83 9.2.4. Perspective of the 6LBR . . . . . . . . . . . . . . . 30 84 10. Protocol Operations for Multicast Addresses . . . . . . . . . 30 85 11. Security Considerations . . . . . . . . . . . . . . . . . . . 33 86 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 87 12.1. Fixing the Address Registration Option Flags . . . . . . 34 88 12.2. Resizing the ARO Status values . . . . . . . . . . . . . 35 89 12.3. New RPL DODAG Configuration Option Flag . . . . . . . . 35 90 12.4. RPL Target Option Registry . . . . . . . . . . . . . . . 35 91 12.5. New Subregistry for RPL Non-Rejection Status values . . 36 92 12.6. New Subregistry for RPL Rejection Status values . . . . 36 93 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 37 94 14. Normative References . . . . . . . . . . . . . . . . . . . . 37 95 15. Informative References . . . . . . . . . . . . . . . . . . . 38 96 Appendix A. Example Compression . . . . . . . . . . . . . . . . 40 97 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41 99 1. Introduction 101 The design of Low Power and Lossy Networks (LLNs) is generally 102 focused on saving energy, which is the most constrained resource of 103 all. Other design constraints, such as a limited memory capacity, 104 duty cycling of the LLN devices and low-power lossy transmissions, 105 derive from that primary concern. 107 The IETF produced the "Routing Protocol for Low Power and Lossy 108 Networks" [RFC6550] (RPL) to provide IPv6 [RFC8200] routing services 109 within such constraints. RPL belongs to the class of Distance-Vector 110 protocols, which, compared to link-state protocols, limit the amount 111 of topological knowledge that needs to be installed and maintained in 112 each node, and does not require convergence to avoid micro-loops. 114 To save signaling and routing state in constrained networks, RPL 115 allows a path stretch (see [RFC6687]), whereby routing is only 116 performed along a Destination-Oriented Directed Acyclic Graph (DODAG) 117 that is optimized to reach a Root node, as opposed to along the 118 shortest path between 2 peers, whatever that would mean in a given 119 LLN. This trades the quality of peer-to-peer (P2P) paths for a 120 vastly reduced amount of control traffic and routing state that would 121 be required to operate an any-to-any shortest path protocol. 122 Additionally, broken routes may be fixed lazily and on-demand, based 123 on dataplane inconsistency discovery, which avoids wasting energy in 124 the proactive repair of unused paths. 126 For many of the nodes, though not all, the DODAG provides multiple 127 forwarding solutions towards the Root of the topology via so-called 128 parents. RPL is designed to adapt to fuzzy connectivity, whereby the 129 physical topology cannot be expected to reach a stable state, with a 130 lazy control that creates the routes proactively, but may only fix 131 them reactively, upon actual traffic. The result is that RPL 132 provides reachability for most of the LLN nodes, most of the time, 133 but may not converge in the classical sense. 135 RPL can be deployed in conjunction with IPv6 Neighbor Discovery (ND) 136 [RFC4861] [RFC4862] and 6LoWPAN ND [RFC6775] [RFC8505] to maintain 137 reachability within a Non-Broadcast Multiple-Access (NBMA) Multi-Link 138 subnet. 140 In that mode, IPv6 addresses are advertised individually as host 141 routes. Some nodes may act as routers and participate in the 142 forwarding operations whereas others will only receive/originate 143 packets, acting as hosts in the data-plane. In [RFC6550] terms, an 144 IPv6 host [RFC8504] that is reachable over the RPL network is called 145 a leaf. 147 Section 2 of [USEofRPLinfo] defines the terms RPL leaf, RPL-Aware- 148 leaf (RAL) and RPL-Unaware Leaf (RUL). A RPL leaf is a host attached 149 to one or more RPL router(s); as such, it relies on the RPL router(s) 150 to forward its traffic across the RPL domain but does not forward 151 traffic from another node. As opposed to the RAL, the RUL does not 152 participate to RPL, and relies on its RPL router(s) also to inject 153 the routes to its IPv6 addresses in the RPL domain. 155 A RUL may be unable to participate because it is very energy- 156 constrained, code-space constrained, or because it would be unsafe to 157 let it inject routes in RPL. Using 6LoWPAN ND as opposed to RPL as 158 the host-to-router interface limits the surface of the possible 159 attacks by the RUL against the RPL domain. If all RULs and RANs use 160 6LoWPAN ND for Neighbor Discovery, it is also possible to protect the 161 address ownership of all nodes, including the RULs. 163 This document specifies how the router injects the host routes in the 164 RPL domain on behalf of the RUL. Section 5 details how the RUL can 165 leverage 6LoWPAN ND to obtain the routing services from the router. 166 In that model, the RUL is also a 6LoWPAN Node (6LN) and the RPL-Aware 167 router is also a 6LoWPAN router (6LR). Using the 6LoWPAN ND Address 168 Registration mechanism, the RUL signals that the router must inject a 169 host route for the Registered Address. 171 ------+--------- 172 | Internet 173 | 174 +-----+ 175 | | <------------- 6LBR / RPL Root 176 +-----+ ^ 177 | | 178 o o o o | RPL 179 o o o o o o o o | 180 o o o o o o o o o o | + 181 o o o o o o o | 182 o o o o o o o o o | 6LoWPAN ND 183 o o o o o o | 184 o o o o v 185 o o o <------------- 6LR / RPL Border router 186 ^ 187 | 6LoWPAN ND only 188 v 189 u <------------- 6LN / RPL-Unaware Leaf 191 Figure 1: Injecting Routes on behalf of RULs 193 The RPL Non-Storing Mode mechanism is used to extend the routing 194 state with connectivity to the RULs even when the DODAG is operated 195 in Storing Mode. The unicast packet forwarding operation by the 6LR 196 serving a RUL is described in section 4.1 of [USEofRPLinfo]. 198 Examples of possible RULs include severely energy constrained sensors 199 such as window smash sensor (alarm system), and kinetically powered 200 light switches. Other applications of this specification may include 201 a smart grid network that controls appliances - such as washing 202 machines or the heating system - in the home. Appliances may not 203 participate to the RPL protocol operated in the Smartgrid network but 204 can still interact with the Smartgrid for control and/or metering. 206 This specification can be deployed incrementally in a network that 207 implements [USEofRPLinfo]. Only the Root and the 6LRs that connect 208 the RULs need to be upgraded. The RPL routers on path will only see 209 unicast IPv6 traffic between the Root and the 6LR. 211 This document is organized as follows: 213 * Section 3 and Section 4 present in a non-normative fashion the 214 salient aspects of RPL and 6LoWPAN ND, respectively, that are 215 leveraged in this specification to provide connectivity to a 6LN 216 acting as a RUL across a RPL network. 218 * Section 5 lists the expectations that a RUL needs to match in 219 order to be served by a RPL router that complies with this 220 specification. 222 * Section 6 presents the changes made to [RFC6550]; a new behavior 223 is introduced whereby the 6LR advertises the 6LN's addresses in a 224 RPL DAO message based on the ND registration by the 6LN, and the 225 RPL root performs the EDAR/EDAC exchange with the 6LBR on behalf 226 of the 6LR; modifications are introduced to some RPL options and 227 to the RPL Status to facilitate the integration of the protocols. 229 * Section 7 presents the changes made to [EFFICIENT-NPDAO]; the use 230 of the DCO message is extended to the Non-Storing MOP to report 231 asynchronous issues from the Root to the 6LR. 233 * Section 8 presents the changes made to [RFC6775] and [RFC8505]; 234 The range of the ND status codes is reduced down to 64 values, and 235 the remaining bits in the original status field are now reserved. 237 * Section 9 and Section 10 present the operation of this 238 specification for unicast and multicast flows, respectively, and 239 Section 11 presents associated security considerations. 241 2. Terminology 243 2.1. Requirements Language 245 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 246 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 247 "OPTIONAL" in this document are to be interpreted as described in BCP 248 14 [RFC2119] [RFC8174] when, and only when, they appear in all 249 capitals, as shown here. 251 2.2. Glossary 253 This document uses the following acronyms: 255 6CIO: 6LoWPAN Capability Indication Option 256 6LN: 6LoWPAN Node (a Low Power host or router) 257 6LR: 6LoWPAN router 258 6LBR: 6LoWPAN Border router 259 (E)ARO: (Extended) Address Registration Option 260 (E)DAR: (Extended) Duplicate Address Request 261 (E)DAC: (Extended) Duplicate Address Confirmation 262 DAD: Duplicate Address Detection 263 DAO: Destination Advertisement Object (a RPL message) 264 DCO: Destination Cleanup Object (a RPL message) 265 DIO: DODAG Information Object (a RPL message) 266 DODAG: Destination-Oriented Directed Acyclic Graph 267 LLN: Low-Power and Lossy Network 268 MOP: RPL Mode of Operation 269 NA: Neighbor Advertisement 270 NCE: Neighbor Cache Entry 271 ND: Neighbor Discovery 272 NS: Neighbor solicitation 273 RA: router Advertisement 274 ROVR: Registration Ownership Verifier 275 RPI: RPL Packet Information 276 RAL: RPL-aware Leaf 277 RAN: RPL-Aware Node (either a RPL router or a RPL-aware Leaf) 278 RUL: RPL-Unaware Leaf 279 SRH: Source-Routing Header 280 TID: Transaction ID (a sequence counter in the EARO) 282 2.3. References 284 The Terminology used in this document is consistent with and 285 incorporates that described in "Terms Used in Routing for Low-Power 286 and Lossy Networks (LLNs)" [RFC7102]. A glossary of classical 287 6LoWPAN acronyms is given in Section 2.2. Other terms in use in LLNs 288 are found in "Terminology for Constrained-Node Networks" [RFC7228]. 289 This specification uses the terms 6LN and 6LR to refer specifically 290 to nodes that implement the 6LN and 6LR roles in 6LoWPAN ND and does 291 not expect other functionality such as 6LoWPAN Header Compression 292 [RFC6282] from those nodes. 294 "RPL", the "RPL Packet Information" (RPI), "RPL Instance" (indexed by 295 a RPLInstanceID), "up", "down" are defined in "RPL: IPv6 Routing 296 Protocol for Low-Power and Lossy Networks" [RFC6550]. The RPI is the 297 abstract information that RPL defines to be placed in data packets, 298 e.g., as the RPL Option [RFC6553] within the IPv6 Hop-By-Hop Header. 299 By extension, the term "RPI" is often used to refer to the RPL Option 300 itself. The Destination Advertisement Object (DAO) and DODAG 301 Information Object (DIO) messages are also specified in [RFC6550]. 302 The Destination Cleanup Object (DCO) message is defined in 303 [EFFICIENT-NPDAO]. 305 This document uses the terms RPL-Unaware Leaf (RUL), RPL-Aware Node 306 (RAN) and RPL aware Leaf (RAL) consistently with [USEofRPLinfo]. A 307 RAN is either an RAL or a RPL router. As opposed to a RUL, a RAN 308 manages the reachability of its addresses and prefixes by injecting 309 them in RPL by itself. 311 In this document, readers will encounter terms and concepts that are 312 discussed in the following documents: 314 Classical IPv6 ND: "Neighbor Discovery for IP version 6" [RFC4861] 315 and "IPv6 Stateless Address Autoconfiguration" [RFC4862], 317 6LoWPAN: "Problem Statement and Requirements for IPv6 over Low-Power 318 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606] and 319 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 320 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 321 and 323 6LoWPAN ND: Neighbor Discovery Optimization for Low-Power and Lossy 324 Networks [RFC6775], "Registration Extensions for 6LoWPAN Neighbor 325 Discovery" [RFC8505], "Address Protected Neighbor Discovery for 326 Low-power and Lossy Networks" [RFC8928], and "IPv6 Backbone 327 Router" [RFC8929]. 329 3. RPL External Routes and Dataplane Artifacts 331 Section 4.1 of [USEofRPLinfo] provides a set of rules summarized 332 below that must be followed for routing packets from and to a RUL. 334 A 6LR that acts as a border router for external routes advertises 335 them using Non-Storing Mode DAO messages that are unicast directly to 336 the Root, even if the DODAG is operated in Storing Mode. Non-Storing 337 Mode routes are not visible inside the RPL domain and all packets are 338 routed via the Root. The RPL Root tunnels the packets directly to 339 the 6LR that advertised the external route, which decapsulates and 340 forwards the original (inner) packet. 342 The RPL Non-Storing MOP signaling and the associated IPv6-in-IPv6 343 encapsulated packets appear as normal traffic to the intermediate 344 routers. The support of external routes only impacts the Root and 345 the 6LR. It can be operated with legacy intermediate routers and 346 does not add to the amount of state that must be maintained in those 347 routers. A RUL is an example of a destination that is reachable via 348 an external route that happens to be also a host route. 350 The RPL data packets typically carry a Hop-by-Hop Header with a RPL 351 Option [RFC6553] that contains the Packet Information (RPI) defined 352 in section 11.2 of [RFC6550]. Unless the RUL already placed a RPL 353 Option in outer header chain, the packets from and to the RUL are 354 encapsulated using an IPv6-in-IPv6 tunnel between the Root and the 355 6LR that serves the RUL (see sections 7 and 8 of [USEofRPLinfo] for 356 details). If the packet from the RUL has an RPI, the 6LR as a RPL 357 border router rewrites the RPI to indicate the selected Instance and 358 set the flags, but it does not need to encapsulate the packet (see 359 Section 9.2.2) . 361 In Non-Storing Mode, packets going down carry a Source Routing Header 362 (SRH). The IPv6-in-IPv6 encapsulation, the RPI and the SRH are 363 collectively called the "RPL artifacts" and can be compressed using 364 [RFC8138]. Appendix A presents an example compressed format for a 365 packet forwarded by the Root to a RUL in a Storing Mode DODAG. 367 The inner packet that is forwarded to the RUL may carry some RPL 368 artifacts, e.g., an RPI if the original packet was generated with it, 369 and an SRH in a Non-Storing Mode DODAG. [USEofRPLinfo] expects the 370 RUL to support the basic "IPv6 Node Requirements" [RFC8504] and in 371 particular the mandates in Sections 4.2 and 4.4 of [RFC8200]. As 372 such, the RUL is expected to ignore the RPL artifacts that may be 373 left over, either an SRH with zero Segments Left or a RPL Option in 374 the Hop-by-Hop Header, which can be skipped when not recognized, see 375 Section 5 for more. 377 A RUL is not expected to support the compression method defined in 378 [RFC8138]. For that reason, the border router (the 6LR here) 379 uncompresses the packet before forwarding it over an external route 380 to a RUL [USEofRPLinfo]. 382 4. 6LoWPAN Neighbor Discovery 384 This section goes through the 6LoWPAN ND mechanisms that this 385 specification leverages, as a non-normative reference to the reader. 386 The full normative text is to be found in [RFC6775], [RFC8505], and 387 [RFC8928]. 389 4.1. RFC 6775 Address Registration 391 The classical "IPv6 Neighbor Discovery (IPv6 ND) Protocol" [RFC4861] 392 [RFC4862] was defined for serial links and transit media such as 393 Ethernet. It is a reactive protocol that relies heavily on multicast 394 operations for Address Discovery (aka Lookup) and Duplicate Address 395 Detection (DAD). 397 "Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775] 398 adapts IPv6 ND for operations over energy-constrained LLNs. The main 399 functions of [RFC6775] are to proactively establish the Neighbor 400 Cache Entry (NCE) in the 6LR and to prevent address duplication. To 401 that effect, [RFC6775] introduces a new unicast Address Registration 402 mechanism that contributes to reducing the use of multicast messages 403 compared to the classical IPv6 ND protocol. 405 [RFC6775] defines a new Address Registration Option (ARO) that is 406 carried in the unicast Neighbor solicitation (NS) and Neighbor 407 Advertisement (NA) messages between the 6LoWPAN Node (6LN) and the 408 6LoWPAN router (6LR). It also defines the Duplicate Address Request 409 (DAR) and Duplicate Address Confirmation (DAC) messages between the 410 6LR and the 6LoWPAN Border router (6LBR). In an LLN, the 6LBR is the 411 central repository of all the Registered Addresses in its domain and 412 the source of truth for uniqueness and ownership. 414 4.2. RFC 8505 Extended Address Registration 416 "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505] 417 updates RFC 6775 into a generic Address Registration mechanism that 418 can be used to access services such as routing and ND proxy. To that 419 effect, [RFC8505] defines the Extended Address Registration Option 420 (EARO), shown in Figure 2: 422 0 1 2 3 423 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 1 424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 425 | Type | Length | Status | Opaque | 426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 427 | Rsvd | I |R|T| TID | Registration Lifetime | 428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 429 | | 430 ... Registration Ownership Verifier ... 431 | | 432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 434 Figure 2: EARO Option Format 436 4.2.1. R Flag 438 [RFC8505] introduces the R Flag in the EARO. The Registering Node 439 sets the R Flag to indicate whether the 6LR should ensure 440 reachability for the Registered Address. If the R Flag is set to 0, 441 then the Registering Node handles the reachability of the Registered 442 Address by other means. In a RPL network, this means that either it 443 is a RAN that injects the route by itself or that it uses another RPL 444 router for reachability services. 446 This document specifies how the R Flag is used in the context of RPL. 447 A RPL leaf that implements the 6LN functionality in [RFC8505] 448 requires reachability services for an IPv6 address if and only if it 449 sets the R Flag in the NS(EARO) used to register the address to a 6LR 450 acting as a RPL border router. Upon receiving the NS(EARO), the RPL 451 router generates a DAO message for the Registered Address if and only 452 if the R flag is set to 1. 454 Section 9.2 specifies additional operations when R flag is set to 1 455 in an EARO that is placed either in an NS or an NA message. 457 4.2.2. TID, "I" Field and Opaque Fields 459 When the T Flag is set to 1, the EARO includes a sequence counter 460 called Transaction ID (TID), that is needed to fill the Path Sequence 461 Field in the RPL Transit Option. This is the reason why the support 462 of [RFC8505] by the RUL, as opposed to only [RFC6775] is a 463 prerequisite for this specification)/; this requirement is fully 464 explained in Section 5.1. The EARO also transports an Opaque field 465 and an associated "I" field that describes what the Opaque field 466 transports and how to use it. 468 Section 9.2.1 specifies the use of the "I" field and the Opaque field 469 by a RUL. 471 4.2.3. Route Ownership Verifier 473 Section 5.3 of [RFC8505] introduces the Registration Ownership 474 Verifier (ROVR) field of variable length from 64 to 256 bits. The 475 ROVR is a replacement of the EUI-64 in the ARO [RFC6775] that was 476 used to identify uniquely an Address Registration with the Link-Layer 477 address of the owner but provided no protection against spoofing. 479 "Address Protected Neighbor Discovery for Low-power and Lossy 480 Networks" [RFC8928] leverages the ROVR field as a cryptographic proof 481 of ownership to prevent a rogue third party from registering an 482 address that is already owned. The use of ROVR field enables the 6LR 483 to block traffic that is not sourced at an owned address. 485 This specification does not address how the protection by [RFC8928] 486 could be extended for use in RPL. On the other hand, it adds the 487 ROVR to the DAO to build the proxied EDAR at the Root (see 488 Section 6.1), which means that nodes that are aware of the host route 489 are also aware of the ROVR associated to the Target Address. 491 4.3. RFC 8505 Extended DAR/DAC 493 [RFC8505] updates the DAR/DAC messages into the Extended DAR/DAC to 494 carry the ROVR field. The EDAR/EDAC exchange takes place between the 495 6LR and the 6LBR. It is triggered by an NS(EARO) message from a 6LN 496 to create, refresh, and delete the corresponding state in the 6LBR. 497 The exchange is protected by the retry mechanism specified in 498 Section 8.2.6 of [RFC6775], though in an LLN, a duration longer than 499 the default value of the RetransTimer (RETRANS_TIMER) [RFC4861] of 1 500 second may be necessary to cover the round trip delay between the 6LR 501 and the 6LBR. 503 RPL [RFC6550] specifies a periodic DAO from the 6LN all the way to 504 the Root that maintains the routing state in the RPL network for the 505 lifetime indicated by the source of the DAO. This means that for 506 each address, there are two keep-alive messages that traverse the 507 whole network, one to the Root and one to the 6LBR. 509 This specification avoids the periodic EDAR/EDAC exchange across the 510 LLN. The 6LR turns the periodic NS(EARO) from the RUL into a DAO 511 message to the Root on every refresh, but it only generates the EDAR 512 upon the first registration, for the purpose of DAD, which must be 513 verified before the address is injected in RPL. Upon the DAO 514 message, the Root proxies the EDAR exchange to refresh the state at 515 the 6LBR on behalf of the 6LR, as illustrated in Figure 8 in 516 Section 9.1. 518 4.3.1. RFC 7400 Capability Indication Option 520 "6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power 521 Wireless Personal Area Networks (6LoWPANs)" [RFC7400] defines the 522 6LoWPAN Capability Indication Option (6CIO) that enables a node to 523 expose its capabilities in router Advertisement (RA) messages. 525 [RFC8505] defines a number of bits in the 6CIO, in particular: 527 L: Node is a 6LR. 528 E: Node is an IPv6 ND Registrar -- i.e., it supports registrations 529 based on EARO. 530 P: Node is a Routing Registrar, -- i.e., an IPv6 ND Registrar that 531 also provides reachability services for the Registered Address. 533 0 1 2 3 534 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 1 535 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 536 | Type | Length = 1 | Reserved |D|L|B|P|E|G| 537 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 538 | Reserved | 539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 541 Figure 3: 6CIO flags 543 A 6LR that provides reachability services for a RUL in a RPL network 544 as specified in this document includes a 6CIO in its RA messages and 545 set the L, P and E flags to 1 as prescribed by [RFC8505]; this is 546 fully explained in Section 9.2. 548 5. Requirements on the RPL-Unware leaf 550 This document describes how RPL routing can be extended to reach a 551 RUL. This section specifies the minimal RPL-independent 552 functionality that the RUL needs to implement to obtain routing 553 services for its addresses. 555 5.1. Support of 6LoWPAN ND 557 To obtain routing services from a router that implements this 558 specification, a RUL needs to implement [RFC8505] and sets the "R" 559 and "T" flags in the EARO to 1 as discussed in Section 4.2.1 and 560 Section 4.2.2, respectively. Section 9.2.1 specifies new behaviors 561 for the RUL, e.g., when the R Flag set to 1 in a NS(EARO) is not 562 echoed in the NA(EARO), which indicates that the route injection 563 failed. 565 The RUL is expected to request routing services from a router only if 566 that router originates RA messages with a CIO that has the L, P, and 567 E flags all set to 1 as discussed in Section 4.3.1, unless configured 568 to do so. It is suggested that the RUL also implements [RFC8928] to 569 protect the ownership of its addresses. 571 A RUL that may attach to multiple 6LRs is expected to prefer those 572 that provide routing services. The RUL needs to register to all the 573 6LRs from which it desires routing services. 575 Parallel Address Registrations to several 6LRs should be performed in 576 a rapid sequence, using the same EARO for the same Address. Gaps 577 between the Address Registrations will invalidate some of the routes 578 till the Address Registration finally shows on those routes. 580 [RFC8505] introduces error Status values in the NA(EARO) which can be 581 received synchronously upon an NS(EARO) or asynchronously. The RUL 582 needs to support both cases and refrain from using the address when 583 the Status value indicates a rejection (see Section 6.3). 585 5.2. Support of IPv6 Encapsulation 587 Section 2.1 of [USEofRPLinfo] defines the rules for tunneling either 588 to the final destination (e.g., a RUL) or to its attachment router 589 (designated as 6LR). In order to terminate the IPv6-in-IPv6 tunnel, 590 the RUL, as an IPv6 host, would have to be capable of decapsulating 591 the tunneled packet and either drop the encapsulated packet if it is 592 not the final destination, or pass it to the upper layer for further 593 processing. As indicated in section 4.1 of [USEofRPLinfo], this is 594 not mandated by [RFC8504], so the Root typically terminates the IPv6- 595 in-IPv6 tunnel at the parent 6LR. It is thus not necessary for a RUL 596 to support IPv6-in-IPv6 decapsulation. 598 5.3. Support of the Hop-by-Hop Header 600 A RUL is expected to process an Option Type in a Hop-by-Hop Header as 601 prescribed by section 4.2 of [RFC8200]. An RPI with an Option Type 602 of 0x23 [USEofRPLinfo] is thus skipped when not recognized. 604 5.4. Support of the Routing Header 606 A RUL is expected to process an unknown Routing Header Type as 607 prescribed by section 4.4 of [RFC8200]. This implies that the Source 608 Routing Header, which has a Routing Type of 3 [RFC6554], is ignored 609 when the Segments Left is zero. When the Segments Left is non-zero, 610 the RUL discards the packet and send an ICMP Parameter Problem, Code 611 0, message to the packet's Source Address, pointing to the 612 unrecognized Routing Type. 614 6. Enhancements to RFC 6550 616 This document specifies a new behavior whereby a 6LR injects DAO 617 messages for unicast addresses (see Section 9) and multicast 618 addresses (see Section 10) on behalf of leaves that are not aware of 619 RPL. The RUL addresses are exposed as external targets [RFC6550]. 620 Conforming to [USEofRPLinfo], an IPv6-in-IPv6 encapsulation between 621 the 6LR and the RPL Root is used to carry the RPL artifacts and 622 remove them when forwarding outside the RPL domain, e.g., to a RUL. 624 This document also synchronizes the liveness monitoring at the Root 625 and the 6LBR. The same value of lifetime is used for both, and a 626 single keep-alive message, the RPL DAO, traverses the RPL network. A 627 new behavior is introduced whereby the RPL Root proxies the EDAR 628 message to the 6LBR on behalf of the 6LR (see Section 8), for any 629 leaf node that implements the 6LN functionality in [RFC8505]. 631 Section 6.7.7 of [RFC6550] introduces the RPL Target Option, which 632 can be used in RPL Control messages such as the DAO message to signal 633 a destination prefix. This document adds the capabilities to 634 transport the ROVR field (see Section 4.2.3) and the IPv6 Address of 635 the prefix advertiser when the Target is a shorter prefix. Their use 636 is signaled respectively by a new ROVR Size field being non-zero and 637 a new "Advertiser address in Full" 'F' flag set to 1, see 638 Section 6.1. 640 This specification defines a new flag, "Root Proxies EDAR/EDAC" (P), 641 in the RPL DODAG Configuration option, see Section 6.2. 643 The RPL Status defined in section 6.5.1 of [RFC6550] for use in the 644 DAO-ACK message is extended to be placed in DCO messages 645 [EFFICIENT-NPDAO] as well. Furthermore, this specification enables 646 to carry the EARO Status defined for 6LoWPAN ND in RPL DAO and DCO 647 messages, embedded in a RPL Status, see Section 6.3. 649 Section 12 of [RFC6550] details the RPL support for multicast flows 650 when the RPLInstance is operated in the MOP of 3 ("Storing Mode of 651 Operation with multicast support"). This specification extends the 652 RPL Root operation to proxy-relay the MLDv2 [RFC3810] operation 653 between the RUL and the 6LR, see Section 10. 655 6.1. Updated RPL Target Option 657 This specification updates the RPL Target Option to transport the 658 ROVR that was also defined for 6LoWPAN ND messages. This enables the 659 RPL Root to generate the proxied EDAR message to the 6LBR. 661 The Target Prefix of the RPL Target Option is left (high bit) 662 justified and contains the advertised prefix; its size may be smaller 663 than 128 when it indicates a Prefix route. The Prefix Length field 664 signals the number of bits that correspond to the advertised Prefix; 665 it is 128 for a host route or less in the case of a Prefix route. 666 This remains unchanged. 668 This specification defines the new 'F' flag. When it is set to 1, 669 the size of the Target Prefix field MUST be 128 bits and it MUST 670 contain an IPv6 address of the advertising node taken from the 671 advertised Prefix. In that case, the Target Prefix field carries two 672 distinct pieces of information: a route that can be a host route or a 673 Prefix route depending on the Prefix Length, and an IPv6 address that 674 can be used to reach the advertising node and validate the route. 676 If the 'F' flag is set to 0, the Target Prefix field can be shorter 677 than 128 bits and it MUST be aligned to the next byte boundary after 678 the end of the prefix. Any additional bits in the rightmost octet 679 are filled with padding bits. Padding bits are reserved and set to 0 680 as specified in section 6.7.7 of [RFC6550]. 682 With this specification the ROVR is the remainder of the RPL Target 683 Option. The size of the ROVR is indicated in a new ROVR Size field 684 that is encoded to map one-to-one with the Code Suffix in the EDAR 685 message (see table 4 of [RFC8505]). The ROVR Size field is taken 686 from the flags field, which is an update to the RPL Target Option 687 Flags IANA registry. 689 The updated format is illustrated in Figure 4. It is backward 690 compatible with the Target Option in [RFC6550]. It is recommended 691 that the updated format be used as a replacement in new 692 implementations in all MOPs in preparation for upcoming Route 693 Ownership Validation mechanisms based on the ROVR, unless the device 694 or the network is so constrained that this is not feasible. 696 0 1 2 3 697 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 1 698 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 699 | Type = 0x05 | Option Length |F|X|Flg|ROVRsz | Prefix Length | 700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 701 | | 702 | Target Prefix (Variable Length) | 703 . . 704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 705 | | 706 ... Registration Ownership Verifier (ROVR) ... 707 | | 708 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 709 Figure 4: Updated Target Option 711 New fields: 713 F: 1-bit flag. Set to 1 to indicate that Target Prefix field 714 contains the complete (128 bit) IPv6 address of the advertising 715 node. 717 X: 1-bit flag. Set to 1 to request that the Root performs a proxy 718 EDAR/EDAC exchange. 720 The 'X' flag can only be set to 1 if the DODAG is operating in 721 Non-Storing Mode and if the Root sets the "Root Proxies EDAR/EDAC 722 (P)" flag to 1 in the DODAG Configuration Option, see Section 6.2. 724 The 'X' flag can be set for host routes to RULs and RANs; it can 725 also be set for internal prefix routes if the 'F' flag is set, 726 using the node's address in the Target Prefix field to form the 727 EDAR, but it cannot be used otherwise. 729 Flg (Flags): The 2 bits remaining unused in the Flags field are 730 reserved for flags. The field MUST be initialized to zero by the 731 sender and MUST be ignored by the receiver. 733 ROVRsz (ROVR Size): Indicates the Size of the ROVR. It MUST be set 734 to 1, 2, 3, or 4, indicating a ROVR size of 64, 128, 192, or 256 735 bits, respectively. 737 If a legacy Target Option is used, then the value must remain 0, 738 as specified in [RFC6550]. 740 In case of a value above 4, the size of the ROVR is undetermined 741 and this node cannot validate the ROVR; an implementation SHOULD 742 propagate the whole Target Option upwards as received to enable 743 the verification by an ancestor that would support the upgraded 744 ROVR. 746 Registration Ownership Verifier (ROVR): This is the same field as in 747 the EARO, see [RFC8505] 749 6.2. Additional Flag in the RPL DODAG Configuration Option 751 The DODAG Configuration Option is defined in Section 6.7.6 of 752 [RFC6550]. Its purpose is extended to distribute configuration 753 information affecting the construction and maintenance of the DODAG, 754 as well as operational parameters for RPL on the DODAG, through the 755 DODAG. This Option was originally designed with 4 bit positions 756 reserved for future use as Flags. 758 0 1 2 3 759 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 1 760 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 761 | Type = 0x04 |Opt Length = 14| |P| | |A| ... | 762 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 763 |4 bits | 765 Figure 5: DODAG Configuration Option (Partial View) 767 This specification defines a new flag "Root Proxies EDAR/EDAC" (P). 768 The 'P' flag is encoded in bit position 1 of the reserved Flags in 769 the DODAG Configuration Option (counting from bit 0 as the most 770 significant bit) and it is set to 0 in legacy implementations as 771 specified respectively in Sections 20.14 and 6.7.6 of [RFC6550]. 773 The 'P' flag is set to 1 to indicate that the Root performs the proxy 774 operation, which implies that it supports this specification and the 775 updated RPL Target Option (see Section 6.1). 777 Section 4.3 of [USEofRPLinfo] updates [RFC6550] to indicate that the 778 definition of the Flags applies to Mode of Operation (MOP) values 779 zero (0) to six (6) only. For a MOP value of 7, the implementation 780 MUST consider that the Root performs the proxy operation. 782 The RPL DODAG Configuration Option is typically placed in a DODAG 783 Information Object (DIO) message. The DIO message propagates down 784 the DODAG to form and then maintain its structure. The DODAG 785 Configuration Option is copied unmodified from parents to children. 786 [RFC6550] states that "Nodes other than the DODAG Root MUST NOT 787 modify this information when propagating the DODAG Configuration 788 option". Therefore, a legacy parent propagates the 'P' Flag as set 789 by the Root, and when the 'P' Flag is set to 1, it is transparently 790 flooded to all the nodes in the DODAG. 792 6.3. Updated RPL Status 794 The RPL Status is defined in section 6.5.1 of [RFC6550] for use in 795 the DAO-ACK message and values are assigned as follows: 797 +---------+--------------------------------+ 798 | Range | Meaning | 799 +---------+--------------------------------+ 800 | 0 | Success/Unqualified acceptance | 801 +---------+--------------------------------+ 802 | 1-127 | Not an outright rejection | 803 +---------+--------------------------------+ 804 | 128-255 | Rejection | 805 +---------+--------------------------------+ 807 Table 1: RPL Status per RFC 6550 809 The 6LoWPAN ND Status was defined for use in the EARO, see section 810 4.1 of [RFC8505]. This specification adds a capability to allow the 811 carriage of 6LoWPAN ND Status values in RPL DAO and DCO messages, 812 embedded in the RPL Status field. 814 To achieve this, the range of the ARO/EARO Status values is reduced 815 to 0-63, which updates the IANA registry created for [RFC6775]. This 816 reduction ensures that the values fit within a RPL Status as shown in 817 Figure 6. See Section 12.2, Section 12.5, and Section 12.6 for the 818 respective IANA declarations. 820 0 1 2 3 4 5 6 7 821 +-+-+-+-+-+-+-+-+ 822 |E|A|StatusValue| 823 +-+-+-+-+-+-+-+-+ 825 Figure 6: RPL Status Format 827 This specification updates the RPL Status with subfields as indicated 828 below: 830 E: 1-bit flag. set to 1 to indicate a rejection. When set to 0, a 831 Status value of 0 indicates Success/Unqualified acceptance and 832 other values indicate "not an outright rejection" as per RFC 6550. 834 A: 1-bit flag. Indicates the type of the RPL Status value. 836 Status Value: 6-bit unsigned integer. 838 If the 'A' flag is set to 1 this field transports a value defined 839 for the 6LoWPAN ND EARO Status. 841 When the 'A' flag is set to 0, this field transports a Status 842 Value defined for RPL. 844 When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a EDAC 845 message, the RPL Root MUST copy the 6LoWPAN ND status code unchanged 846 in the RPL Status Value and set the 'A' flag to 1. The RPL Root MUST 847 set the 'E' flag to 1 for all rejection and unknown status codes. 848 The status codes in the 1-10 range [RFC8505] are all considered 849 rejections. 851 Reciprocally, upon a DCO or a DAO-ACK message from the RPL Root with 852 a RPL Status that has the 'A' flag set, the 6LR MUST copy the RPL 853 Status value unchanged in the Status field of the EARO when 854 generating an NA to the RUL. 856 7. Enhancements to draft-ietf-roll-efficient-npdao 858 [EFFICIENT-NPDAO] defines the DCO message for RPL Storing Mode only, 859 with a link-local scope. All nodes in the RPL network are expected 860 to support the specification since the message is processed hop by 861 hop along the path that is being cleaned up. 863 This specification extends the use of the DCO message to the Non- 864 Storing MOP, whereby the DCO is sent end-to-end by the Root directly 865 to the RAN that injected the DAO message for the considered target. 866 In that case, intermediate nodes do not need to support 867 [EFFICIENT-NPDAO]; they forward the DCO message as a plain IPv6 868 packet between the Root and the RAN. 870 In the case of a RUL, the 6LR that serves the RUL acts as the RAN 871 that receives the Non-Storing DCO. This specification leverages the 872 Non-Storing DCO between the Root and the 6LR that serves as 873 attachment router for a RUL. A 6LR and a Root that support this 874 specification MUST implement the Non-Storing DCO. 876 8. Enhancements to RFC 6775 and RFC8505 878 This document updates [RFC6775] and [RFC8505] to reduce the range of 879 the ND status codes down to 64 values. The two most significant 880 (leftmost) bits if the original ND status field are now reserved, 881 they MUST be set to zero by the sender and ignored by the receiver. 883 This document also changes the behavior of a 6LR acting as RPL router 884 and of a 6LN acting as RUL in the 6LoWPAN ND Address Registration as 885 follows: 887 * If the RPL Root advertises the capability to proxy the EDAR/EDAC 888 exchange to the 6LBR, the 6LR refrains from sending the keep-alive 889 EDAR message. If it is separated from the 6LBR, the Root 890 regenerates the EDAR message to the 6LBR periodically, upon a DAO 891 message that signals the liveliness of the address. 893 * The use of the R Flag is extended to the NA(EARO) to confirm 894 whether the route was installed. 896 9. Protocol Operations for Unicast Addresses 898 The description below assumes that the Root sets the 'P' flag in the 899 DODAG Configuration Option and performs the EDAR proxy operation 900 presented in Section 4.3 . 902 If the 'P' flag is set to 0, the 6LR MUST generate the periodic EDAR 903 messages and process the returned status as specified in [RFC8505]. 904 If the EDAC indicates success, the rest of the flow takes place as 905 presented but without the proxied EDAR/EDAC exchange. 907 Section 9.1 provides an overview of the route injection in RPL, 908 whereas Section 9.2 offers more details from the perspective of the 909 different nodes involved in the flow. 911 9.1. General Flow 913 This specification eliminates the need to exchange keep-alive 914 Extended Duplicate Address messages, EDAR and EDAC, all the way from 915 a 6LN to the 6LBR across a RPL mesh. Instead, the EDAR/EDAC exchange 916 with the 6LBR is proxied by the RPL Root upon the DAO message that 917 refreshes the RPL routing state. The first EDAR upon a new 918 Registration cannot be proxied, though, as it serves for the purpose 919 of DAD, which must be verified before the address is injected in RPL. 921 In a RPL network where the function is enabled, refreshing the state 922 in the 6LBR is the responsibility of the Root. Consequently, only 923 addresses that are injected in RPL will be kept alive at the 6LBR by 924 the RPL Root. Since RULs are advertised using Non-Storing Mode, the 925 DAO message flow and the keep alive EDAR/EDAC can be nested within 926 the Address (re)Registration flow. Figure 7 illustrates that, for 927 the first Registration, both the DAD and the keep-alive EDAR/EDAC 928 exchanges happen in the same sequence. 930 6LN/RUL 6LR <6LR*> Root 6LBR 931 |<---Using ND--->|<--Using RPL->|<-----Using ND---->| 932 | |<-----------Using ND------------->| 933 | | | | 934 | NS(EARO) | | | 935 |--------------->| | 936 | | EDAR | 937 | |--------------------------------->| 938 | | | 939 | | EDAC | 940 | |<---------------------------------| 941 | | | 942 | | DAO(X=0) | | 943 | |------------->| | 944 | | | 945 | | DAO-ACK | | 946 | |<-------------| | 947 | NA(EARO) | | | 948 |<---------------| | | 949 | | | | 951 Figure 7: First RUL Registration Flow 953 This flow requires that the lifetimes and sequence counters in 954 6LoWPAN ND and RPL are aligned. 956 To achieve this, the Path Sequence and the Path Lifetime in the DAO 957 message are taken from the Transaction ID and the Address 958 Registration lifetime in the NS(EARO) message from the 6LN. 960 On the first Address Registration, illustrated in Figure 7 for RPL 961 Non-Storing Mode, the Extended Duplicate Address exchange takes place 962 as prescribed by [RFC8505]. If the exchange fails, the 6LR returns 963 an NA message with a non-zero status to the 6LN, the NCE is not 964 created, and the address is not injected in RPL. Otherwise, the 6LR 965 creates an NCE and injects the Registered Address in the RPL routing 966 using a DAO/DAO-ACK exchange with the RPL DODAG Root. 968 An Address Registration refresh is performed by the 6LN to keep the 969 NCE in the 6LR alive before the lifetime expires. Upon the refresh 970 of a registration, the 6LR reinjects the corresponding route in RPL 971 before it expires, as illustrated in Figure 8. 973 6LN/RUL <-ND-> 6LR <-RPL-> Root <-ND-> 6LBR 974 | | | | 975 | NS(EARO) | | | 976 |--------------->| | | 977 | | DAO(X=1) | | 978 | |------------->| | 979 | | | EDAR | 980 | | |------------------>| 981 | | | EDAC | 982 | | |<------------------| 983 | | DAO-ACK | | 984 | |<-------------| | 985 | NA(EARO) | | | 986 |<---------------| | | 988 Figure 8: Next RUL Registration Flow 990 This is what causes the RPL Root to refresh the state in the 6LBR, 991 using an EDAC message. In case of an error in the proxied EDAR flow, 992 the error is returned in the DAO-ACK using a RPL Status with the 'A' 993 flag set to 1 that imbeds a 6LoWPAN Status value as discussed in 994 Section 6.3. 996 The 6LR may receive a requested DAO-ACK after it received an 997 asynchronous Non-Storing DCO, but the non-zero status in the DCO 998 supersedes a positive Status in the DAO-ACK regardless of the order 999 in which they are received. Upon the DAO-ACK - or the DCO if one 1000 arrives first - the 6LR responds to the RUL with an NA(EARO). 1002 An issue may be detected later, e.g., the address moves to a 1003 different DODAG with the 6LBR attached to a different 6LoWPAN 1004 Backbone router (6BBR), see Figure 5 in section 3.3 of [RFC8929]. 1005 The 6BBR may send a negative ND status, e.g., in an asynchronous 1006 NA(EARO) to the 6LBR. 1008 [RFC8929] expects that the 6LBR is collocated with the RPL Root, but 1009 if not, the 6LBR MUST forward the status code to the originator of 1010 the EDAR, either the 6LR or the RPL Root that proxies for it. The ND 1011 status code is mapped in a RPL Status value by the RPL Root, and then 1012 back by the 6LR. Note that a legacy RAN that receives a Non-Storing 1013 DCO that it does not support will ignore it silently, as specified in 1014 section 6 of [RFC6550]. The result is that it may ignore for a while 1015 that it is no more reachable. The situation will be cleared upon the 1016 next Non-Storing DAO exchange if the error is returned in a DAO-ACK. 1018 Figure 9 illustrates this in the case where the 6LBR and the Root are 1019 not collocated, and the Root proxies the EDAR/EDAC flow. 1021 6LN/RUL <-ND-> 6LR <-RPL-> Root <-ND-> 6LBR <-ND-> 6BBR 1022 | | | | | 1023 | | | | NA(EARO) | 1024 | | | |<------------| 1025 | | | EDAC | | 1026 | | |<-------------| | 1027 | | DCO | | | 1028 | |<------------| | | 1029 | NA(EARO) | | | | 1030 |<-------------| | | | 1031 | | | | | 1033 Figure 9: Asynchronous Issue 1035 If the Root does not proxy, then the EDAC with a non-zero status 1036 reaches the 6LR directly. In that case, the 6LR MUST clean up the 1037 route using a DAO with a Lifetime of zero, and it MUST propagate the 1038 status back to the RUL in a NA(EARO) with the R Flag set to 0. 1040 The RUL may terminate the registration at any time by using a 1041 Registration Lifetime of 0. This specification requires that the RPL 1042 Target Option transports the ROVR. This way, the same flow as the 1043 heartbeat flow is sufficient to inform the 6LBR using the Root as 1044 proxy, as illustrated in Figure 8. 1046 Any combination of the logical functions of 6LR, Root, and 6LBR might 1047 be collapsed in a single node. 1049 9.2. Detailed Operation 1051 The following section specify respectively the behaviour of the 6LN 1052 Acting as RUL, the 6LR Acting as Border router and serving the 6LN, 1053 the RPL Root and the 6LBR in the control flows that enable RPL 1054 routing back to the RUL. 1056 9.2.1. Perspective of the 6LN Acting as RUL 1058 This specification builds on the operation of a 6LoWPAN ND-compliant 1059 6LN/RUL, which is expected to operate as follows: 1061 1. The 6LN selects a 6LR that provides reachability services for a 1062 RUL. This is signaled by a 6CIO in the RA messages with the L, P 1063 and E flags set to 1 as prescribed by [RFC8505]. 1065 2. The 6LN obtains an IPv6 global address, either using Stateless 1066 Address Autoconfiguration (SLAAC) [RFC4862] based on a Prefix 1067 Information Option (PIO) [RFC4861] found in an RA message, or 1068 some other means, such as DHCPv6 [RFC8415]. 1070 3. Once it has formed an address, the 6LN registers its address and 1071 refreshes its registration periodically, early enough within the 1072 Lifetime of the previous Address Registration, as prescribed by 1073 [RFC6775], to refresh the NCE before the lifetime indicated in 1074 the EARO expires. It sets the T Flag to 1 as prescribed in 1075 [RFC8505]. The TID is incremented each time and wraps in a 1076 lollipop fashion (see section 5.2.1 of [RFC8505], which is fully 1077 compatible with section 7.2 of [RFC6550]). 1079 4. As stated in section 5.2 of [RFC8505], the 6LN can register to 1080 more than one 6LR at the same time. In that case, it uses the 1081 same EARO for all of the parallel Address Registrations, with the 1082 exception of the Registration Lifetime field and the setting of 1083 the R flag that may differ. The 6LN may cancel a subset of its 1084 registrations, or transfer a registration from one or more old 1085 6LR(s) to one or more new 6LR(s). To do so, the 6LN sends a 1086 series of NS(EARO) messages, all with the same TID, with a zero 1087 Registration Lifetime to the old 6LR(s) and with a non-zero 1088 Registration Lifetime to the new 6LR(s). In that process, the 1089 6LN SHOULD send the NS(EARO) with a non-zero Registration 1090 Lifetime and ensure that at least one succeeds before it sends an 1091 NS(EARO) that terminates another registration. This avoids the 1092 churn related to transient route invalidation in the RPL network 1093 above the common parent of the involved 6LRs. 1095 5. Following section 5.1 of [RFC8505], a 6LN acting as a RUL sets 1096 the R Flag in the EARO of its registration(s) for which it 1097 requires routing services. If the R Flag is not echoed in the 1098 NA, the RUL MUST consider that establishing the routing services 1099 via this 6LR failed and it SHOULD attempt to use another 6LR. 1100 The RUL SHOULD ensure that one registration succeeds before 1101 setting the R Flag to 0. In case of a conflict with the 1102 preceding rule on lifetime, the rule on lifetime has precedence. 1104 6. The 6LN may use any of the 6LRs to which it registered as the 1105 default gateway. Using a 6LR to which the 6LN is not registered 1106 may result in packets dropped at the 6LR by a Source Address 1107 Validation function (SAVI) [RFC7039] so it is not recommended. 1109 Even without support for RPL, the RUL may be configured with an 1110 opaque value to be provided to the routing protocol. If the RUL has 1111 knowledge of the RPL Instance the packet should be injected into, 1112 then it SHOULD set the Opaque field in the EARO to the RPLInstanceID, 1113 otherwise it MUST leave the Opaque field as zero. 1115 Regardless of the setting of the Opaque field, the 6LN MUST set the 1116 "I" field to zero to signal "topological information to be passed to 1117 a routing process", as specified in section 5.1 of [RFC8505]. 1119 A RUL is not expected to produce RPL artifacts in the data packets, 1120 but it may do so. For instance, if the RUL has minimal awareness of 1121 the RPL Instance then it can build an RPI. A RUL that places an RPI 1122 in a data packet SHOULD indicate the RPLInstanceID of the RPL 1123 Instance where the packet should be forwarded. It is up to the 6LR 1124 (e.g., by policy) to use the RPLInstanceID information provided by 1125 the RUL or rewrite it to the selected RPLInstanceID for forwarding 1126 inside the RPL domain. All the flags and the Rank field are set to 0 1127 as specified by section 11.2 of [RFC6550]. 1129 9.2.2. Perspective of the 6LR Acting as Border router 1131 A 6LR that provides reachability services for a RUL in a RPL network 1132 as specified in this document MUST include a 6CIO in its RA messages 1133 and set the L, P and E flags to 1 as prescribed by [RFC8505]. 1135 As prescribed by [RFC8505], the 6LR generates an EDAR message upon 1136 reception of a valid NS(EARO) message for the registration of a new 1137 IPv6 address by a 6LN. If the initial EDAR/EDAC exchange succeeds, 1138 then the 6LR installs an NCE for the Registration Lifetime. 1140 If the R Flag is set to 1 in the NS(EARO), the 6LR SHOULD inject the 1141 host route in RPL, unless this is barred for other reasons, such as 1142 the saturation of the RPL parents. The 6LR MUST use a RPL Non- 1143 Storing Mode signaling and the updated Target Option (see 1144 Section 6.1). The 6LR SHOULD refrain from setting the 'X' flag to 1145 avoid a redundant EDAR/EDAC flow to the 6LBR. The 6LR MUST request a 1146 DAO-ACK by setting the 'K' flag in the DAO message. Success 1147 injecting the route to the RUL's address is indicated by the 'E' flag 1148 set to 0 in the RPL status of the DAO-ACK message. 1150 For the registration refreshes, if the RPL Root sets the 'P' flag in 1151 the DODAG Configuration Option to 1, then the 6LR MUST refrain from 1152 sending the keep-alive EDAR; instead, it MUST set the 'X' flag to 1 1153 in the Target Option of the DAO messages, to request that the Root 1154 proxies the keep-alive EDAR/EDAC exchange with the 6LBR (see 1155 Section 6); if the 'P' flag is set to 0 then the 6LR MUST set the 'X' 1156 flag to 0 and handle the EDAR/EDAC flow itself. 1158 The Opaque field in the EARO provides a means to signal which RPL 1159 Instance is to be used for the DAO advertisements and the forwarding 1160 of packets sourced at the Registered Address when there is no RPI in 1161 the packet. 1163 As described in [RFC8505], if the "I" field is zero, then the Opaque 1164 field is expected to carry the RPLInstanceID suggested by the 6LN; 1165 otherwise, there is no suggested Instance. If the 6LR participates 1166 in the suggested RPL Instance, then the 6LR MUST use that RPL 1167 Instance for the Registered Address. 1169 If there is no suggested RPL Instance or else if the 6LR does not 1170 participate to the suggested Instance, it is expected that the 1171 packets coming from the 6LN "can unambiguously be associated to at 1172 least one RPL Instance" [RFC6550] by the 6LR, e.g., using a policy 1173 that maps the 6-tuple into an Instance. 1175 The DAO message advertising the Registered Address MUST be 1176 constructed as follows: 1178 1. The Registered Address is signaled as the Target Prefix in the 1179 updated Target Option in the DAO message; the Prefix Length is 1180 set to 128 but the 'F' flag is set to 0 since the advertiser is 1181 not the RUL. The ROVR field is copied unchanged from the EARO 1182 (see Section 6.1). 1184 2. The 6LR indicates one of its global or unique-local IPv6 unicast 1185 addresses as the Parent Address in the RPL Transit Information 1186 Option (TIO) associated with the Target Option 1188 3. The 6LR sets the External 'E' flag in the TIO to indicate that it 1189 is redistributing an external target into the RPL network 1191 4. the Path Lifetime in the TIO is computed from the Registration 1192 Lifetime in the EARO. This operation converts seconds to the 1193 Lifetime Units used in the RPL operation. This creates the 1194 deployment constraint that the Lifetime Unit is reasonably 1195 compatible with the expression of the Registration Lifetime. 1196 e.g., a Lifetime Unit of 0x4000 maps the most significant byte of 1197 the Registration Lifetime to the Path Lifetime. 1199 In that operation, the Path Lifetime must be rounded, if needed, 1200 to the upper value to ensure that the path has a longer lifetime 1201 than the registration. 1203 Note that if the Registration Lifetime is 0, then the Path 1204 Lifetime is also 0 and the DAO message becomes a No-Path DAO, 1205 which cleans up the routes down to the RUL's address; this also 1206 causes the Root as a proxy to send an EDAR message to the 6LBR 1207 with a Lifetime of 0. 1209 5. the Path Sequence in the TIO is set to the TID value found in the 1210 EARO option. 1212 Upon receiving or timing out the DAO-ACK after an implementation- 1213 specific number of retries, the 6LR MUST send the corresponding 1214 NA(EARO) to the RUL. Upon receiving an asynchronous DCO message, it 1215 MUST send an asynchronous NA(EARO) to the RUL immediately, but still 1216 be capable of processing the DAO-ACK if one is pending. 1218 The 6LR MUST set the R Flag to 1 in the NA(EARO) back if and only if 1219 the 'E' flag in the RPL Status is set to 0, indicating that the 6LR 1220 injected the Registered Address in the RPL routing successfully and 1221 that the EDAR proxy operation succeeded. 1223 If the 'A' flag in the RPL Status is set to 1, the embedded Status 1224 value is passed back to the RUL in the EARO Status. If the 'E' flag 1225 is also set to 1, the registration failed for 6LoWPAN ND related 1226 reasons, and the NCE is removed. 1228 An error injecting the route causes the 'E' flag to be set to 1. If 1229 the error is not related to ND, the 'A' flag is set to 0. In that 1230 case, the registration succeeds, but the RPL route is not installed. 1231 So the NA(EARO) is returned with a status indicating success but the 1232 R Flag set to 0, which means that the 6LN obtained a binding but no 1233 route. 1235 If the 'A' flag is set to 0 in the RPL Status of the DAO-ACK, then 1236 the 6LoWPAN ND operation succeeded, and an EARO Status of 0 (Success) 1237 MUST be returned to the 6LN. The EARO Status of 0 MUST also be used 1238 if the 6LR did not attempt to inject the route but could create the 1239 binding after a successful EDAR/EDAC exchange or refresh it. 1241 If the 'E' flag is set to 1 in the RPL Status of the DAO-ACK, then 1242 the route was not installed and the R flag MUST be set to 0 in the 1243 NA(EARO). The R flag MUST be set to 0 if the 6LR did not attempt to 1244 inject the route. 1246 In a network where Address Protected Neighbor Discovery (AP-ND) is 1247 enabled, in case of a DAO-ACK or a DCO transporting an EARO Status 1248 value of 5 (Validation Requested), the 6LR MUST challenge the 6LN for 1249 ownership of the address, as described in section 6.1 of [RFC8928], 1250 before the Registration is complete. This flow, illustrated in 1251 Figure 10, ensures that the address is validated before it is 1252 injected in the RPL routing. 1254 If the challenge succeeds, then the operations continue as normal. 1255 In particular, a DAO message is generated upon the NS(EARO) that 1256 proves the ownership of the address. If the challenge failed, the 1257 6LR rejects the registration as prescribed by AP-ND and may take 1258 actions to protect itself against DoS attacks by a rogue 6LN, see 1259 Section 11. 1261 6LN 6LR Root 6LBR 1262 | | | | 1263 |<--------------- RA ---------------------| | | 1264 | | | | 1265 |------ NS EARO (ROVR=Crypto-ID) -------->| | | 1266 | | | | 1267 |<- NA EARO(status=Validation Requested) -| | | 1268 | | | | 1269 |----- NS EARO and Proof-of-ownership -->| | 1270 | | | | 1271 | | | 1272 | | | 1273 |<----------- NA EARO (status=10)--- | | 1274 | | | 1275 | | | 1276 | | | | 1277 | |--------- EDAR ------->| 1278 | | | 1279 | |<-------- EDAC --------| 1280 | | | 1281 | | | | 1282 | |-DAO(X=0)->| | 1283 | | | | 1284 | |<- DAO-ACK-| | 1285 | | | | 1286 |<----------- NA EARO (status=0)----------| | | 1287 | | | | 1288 ... 1289 | | | | 1290 |------ NS EARO (ROVR=Crypto-ID) -------->| | | 1291 | |-DAO(X=1)->| | 1292 | | |-- EDAR -->| 1293 | | | | 1294 | | |<-- EDAC --| 1295 | |<- DAO-ACK-| | 1296 |<----------- NA EARO (status=0)----------| | | 1297 | | | | 1298 ... 1300 Figure 10: Address Protection 1302 The 6LR may at any time send a unicast asynchronous NA(EARO) with the 1303 R Flag set to 0 to signal that it stops providing routing services, 1304 and/or with the EARO Status 2 "Neighbor Cache full" to signal that it 1305 removes the NCE. It may also send a final RA, unicast or multicast, 1306 with a router Lifetime field of zero, to signal that it is ceasing to 1307 serve as router, as specified in section 6.2.5 of [RFC4861]. This 1308 may happen upon a DCO or a DAO-ACK message indicating the path is 1309 already removed; else the 6LR MUST remove the host route to the 6LN 1310 using a DAO message with a Path Lifetime of zero. 1312 A valid NS(EARO) message with the R Flag set to 0 and a Registration 1313 Lifetime that is not zero signals that the 6LN wishes to maintain the 1314 binding but does not require the routing services from the 6LR (any 1315 more). Upon this message, if, due to previous NS(EARO) with the R 1316 Flag set to 1, the 6LR was injecting the host route to the Registered 1317 Address in RPL using DAO messages, then the 6LR MUST invalidate the 1318 host route in RPL using a DAO with a Path Lifetime of zero. It is up 1319 to the Registering 6LN to maintain the corresponding route from then 1320 on, either keeping it active via a different 6LR or by acting as a 1321 RAN and managing its own reachability. 1323 When forwarding a packet from the RUL into the RPL domain, if the 1324 packet does not have an RPI then the 6LR MUST encapsulate the packet 1325 to the Root, and add an RPI. If there is an RPI in the packet, the 1326 6LR MUST rewrite the RPI but it does not need to encapsulate. 1328 9.2.3. Perspective of the RPL Root 1330 A RPL Root MUST set the 'P' flag to 1 in the RPL DODAG Configuration 1331 Option of the DIO messages that it generates (see Section 6) to 1332 signal that it proxies the EDAR/EDAC exchange and supports the 1333 Updated RPL Target option. 1335 Upon reception of a DAO message, for each updated RPL Target Option 1336 (see Section 6.1) with the 'X' flag set to 1, the Root MUST notify 1337 the 6LBR by using a proxied EDAR/EDAC exchange; if the RPL Root and 1338 the 6LBR are integrated, an internal API can be used instead. 1340 The EDAR message MUST be constructed as follows: 1342 1. The Target IPv6 address from the RPL Target Option is placed in 1343 the Registered Address field of the EDAR message; 1345 2. the Registration Lifetime is adapted from the Path Lifetime in 1346 the TIO by converting the Lifetime Units used in RPL into units 1347 of 60 seconds used in the 6LoWPAN ND messages; 1349 3. the TID value is set to the Path Sequence in the TIO and 1350 indicated with an ICMP code of 1 in the EDAR message; 1352 4. The ROVR in the RPL Target Option is copied as is in the EDAR and 1353 the ICMP Code Suffix is set to the appropriate value as shown in 1354 Table 4 of [RFC8505] depending on the size of the ROVR field. 1356 Upon receiving an EDAC message from the 6LBR, if a DAO is pending, 1357 then the Root MUST send a DAO-ACK back to the 6LR. Otherwise, if the 1358 Status in the EDAC message is not "Success", then it MUST send an 1359 asynchronous DCO to the 6LR. 1361 In either case, the EDAC Status is embedded in the RPL Status with 1362 the 'A' flag set to 1. 1364 The proxied EDAR/EDAC exchange MUST be protected with a timer of an 1365 appropriate duration and a number of retries, that are 1366 implementation-dependent, and SHOULD be configurable since the Root 1367 and the 6LBR are typically nodes with a higher capacity and 1368 manageability than 6LRs. Upon timing out, the Root MUST send an 1369 error back to the 6LR as above, either using a DAO-ACK or a DCO, as 1370 appropriate, with the 'A' and 'E' flags set to 1 in the RPL status, 1371 and a RPL Status value of of "6LBR Registry Saturated" [RFC8505]. 1373 9.2.4. Perspective of the 6LBR 1375 The 6LBR is unaware that the RPL Root is not the new attachment 6LR 1376 of the RUL, so it is not impacted by this specification. 1378 Upon reception of an EDAR message, the 6LBR acts as prescribed by 1379 [RFC8505] and returns an EDAC message to the sender. 1381 10. Protocol Operations for Multicast Addresses 1383 Section 12 of [RFC6550] details the RPL support for multicast flows. 1384 This support is activated by the MOP of 3 ("Storing Mode of Operation 1385 with multicast support") in the DIO messages that form the DODAG. 1386 This section also applies if and only if the MOP of the RPLInstance 1387 is 3. 1389 The RPL support of multicast is not source-specific and only operates 1390 as an extension to the Storing Mode of Operation for unicast packets. 1391 Note that it is the RPL model that the multicast packet is passed as 1392 a Layer-2 unicast to each of the interested children. This remains 1393 true when forwarding between the 6LR and the listener 6LN. 1395 "Multicast Listener Discovery Version 2 (MLDv2) for IPv6" [RFC3810] 1396 provides an interface for a listener to register to multicast flows. 1397 In the MLD model, the router is a "querier", and the host is a 1398 multicast listener that registers to the querier to obtain copies of 1399 the particular flows it is interested in. 1401 The equivalent of the first Address Registration happens as 1402 illustrated in Figure 11. The 6LN, as an MLD listener, sends an 1403 unsolicited Report to the 6LR. This enables it to start receiving 1404 the flow immediately, and causes the 6LR to inject the multicast 1405 route in RPL. 1407 This specification does not change MLD but will operate more 1408 efficiently if the asynchronous messages for unsolicited Report and 1409 Done are sent by the 6LN as Layer-2 unicast to the 6LR, in particular 1410 on wireless. 1412 The 6LR acts as a generic MLD querier and generates a DAO with the 1413 Multicast Address as the Target Prefix as described in section 12 of 1414 [RFC6550]. As for the Unicast host routes, the Path Lifetime 1415 associated to the Target is mapped from the Query Interval, and set 1416 to be larger to account for variable propagation delays to the Root. 1417 The Root proxies the MLD exchange as a listener with the 6LBR acting 1418 as the querier, so as to get packets from a source external to the 1419 RPL domain. 1421 Upon a DAO with a Target option for a multicast address, the RPL Root 1422 checks if it is already registered as a listener for that address, 1423 and if not, it performs its own unsolicited Report for the multicast 1424 address as described in section 5.1 of [RFC3810]. The report is 1425 source independent, so there is no Source Address listed. 1427 6LN/RUL 6LR Root 6LBR 1428 | | | | 1429 | unsolicited Report | | | 1430 |------------------->| | | 1431 | | DAO | | 1432 | |-------------->| | 1433 | | DAO-ACK | | 1434 | |<--------------| | 1435 | | | | 1436 | | | unsolicited Report | 1437 | | |---------------------->| 1438 | | | | 1440 Figure 11: First Multicast Registration Flow 1442 The equivalent of the registration refresh is pulled periodically by 1443 the 6LR acting as querier. Upon the timing out of the Query 1444 Interval, the 6LR sends a Multicast Address Specific Query to each of 1445 its listeners, for each Multicast Address, and gets a Report back 1446 that is mapped into a DAO one by one. Optionally, the 6LR MAY send a 1447 General Query, where the Multicast Address field is set to zero. In 1448 that case, the multicast packet is passed as a Layer-2 unicast to 1449 each of the interested children. . 1451 Upon a Report, the 6LR generates a DAO with as many Target Options as 1452 there are Multicast Address Records in the Report message, copying 1453 the Multicast Address field in the Target Prefix of the RPL Target 1454 Option. The DAO message is a Storing Mode DAO, passed to a selection 1455 of the 6LR's parents. 1457 Asynchronously to this, a similar procedure happens between the Root 1458 and a router such as the 6LBR that serves multicast flows on the Link 1459 where the Root is located. Again the Query and Report messages are 1460 source independent. The Root lists exactly once each Multicast 1461 Address for which it has at least one active multicast DAO state, 1462 copying the multicast address in the DAO state in the Multicast 1463 Address field of the Multicast Address Records in the Report message. 1465 This is illustrated in Figure 12: 1467 6LN/RUL 6LR Root 6LBR 1468 | | | | 1469 | Query | | | 1470 |<-------------------| | | 1471 | Report | | | 1472 |------------------->| | | 1473 | | DAO | | 1474 | |-------------->| | 1475 | | DAO-ACK | | 1476 | |<--------------| | 1477 | | | Query | 1478 | | |<-------------------| 1479 | | | Report | 1480 | | |------------------->| 1481 | | | | 1483 Figure 12: Next Registration Flow 1485 Note that any of the functions 6LR, Root and 6LBR might be collapsed 1486 in a single node, in which case the flow above happens internally, 1487 and possibly through internal API calls as opposed to messaging. 1489 11. Security Considerations 1491 It is worth noting that with [RFC6550], every node in the LLN is RPL- 1492 aware and can inject any RPL-based attack in the network. This 1493 specification improves the situation by isolating edge nodes that can 1494 only interact with the RPL routers using 6LoWPAN ND, meaning that 1495 they cannot perform RPL insider attacks. 1497 The LLN nodes depend on the 6LBR and the RPL participants for their 1498 operation. A trust model must be put in place to ensure that the 1499 right devices are acting in these roles, so as to avoid threats such 1500 as black-holing, (see [RFC7416] section 7), Denial-Of-Service attacks 1501 whereby a rogue 6LR creates a high churn in the RPL network by 1502 advertising and removing many forged addresses, or bombing attack 1503 whereby an impersonated 6LBR would destroy state in the network by 1504 using the status code of 4 ("Removed"). 1506 This trust model could be at a minimum based on a Layer-2 Secure 1507 joining and the Link-Layer security. This is a generic 6LoWPAN 1508 requirement, see Req5.1 in Appendix B.5 of [RFC8505]. 1510 In a general manner, the Security Considerations in [RFC6550], 1511 [RFC7416] [RFC6775], and [RFC8505] apply to this specification as 1512 well. 1514 The Link-Layer security is needed in particular to prevent Denial-Of- 1515 Service attacks whereby a rogue 6LN creates a high churn in the RPL 1516 network by constantly registering and deregistering addresses with 1517 the R Flag set to 1 in the EARO. 1519 [RFC8928] updated 6LoWPAN ND with the called Address-Protected 1520 Neighbor Discovery (AP-ND). AP-ND protects the owner of an address 1521 against address theft and impersonation attacks in a Low-Power and 1522 Lossy Network (LLN). Nodes supporting th extension compute a 1523 cryptographic identifier (Crypto-ID), and use it with one or more of 1524 their Registered Addresses. The Crypto-ID identifies the owner of 1525 the Registered Address and can be used to provide proof of ownership 1526 of the Registered Addresses. Once an address is registered with the 1527 Crypto-ID and a proof of ownership is provided, only the owner of 1528 that address can modify the registration information, thereby 1529 enforcing Source Address Validation. [RFC8928] reduces even more the 1530 attack perimeter that is available to the edge nodes and its use is 1531 suggested in this specification. 1533 Additionally, the trust model could include a role validation (e.g., 1534 using a role-based authorization) to ensure that the node that claims 1535 to be a 6LBR or a RPL Root is entitled to do so. 1537 The Opaque field in the EARO enables the RUL to suggest a 1538 RPLInstanceID where its traffic is placed. It is also possible for 1539 an attacker RUL to include an RPI in the packet. This opens to 1540 attacks where a RPL instance would be reserved for critical traffic, 1541 e.g., with a specific bandwidth reservation, that the additional 1542 traffic generated by a rogue may disrupt. The attack may be 1543 alleviated by traditional access control and traffic shaping 1544 mechanisms where the 6LR controls the incoming traffic from the 6LN. 1545 More importantly, the 6LR is the node that injects the traffic in the 1546 RPL domain, so it has the final word on which RPLInstance is to be 1547 used for the traffic coming from the RUL, per its own policy. In 1548 particular, a policy can override the formal language that forces to 1549 use the Opaque field or to rewrite the RPI provided by the RUL, in a 1550 situation where the network administrator finds it relevant. 1552 At the time of this writing, RPL does not have a Route Ownership 1553 Validation model whereby it is possible to validate the origin of an 1554 address that is injected in a DAO. This specification makes a first 1555 step in that direction by allowing the Root to challenge the RUL via 1556 the 6LR that serves it. 1558 Section 6.1 indicates that when the length of the ROVR field is 1559 unknown, the RPL Target Option must be passed on as received in RPL 1560 storing Mode. This creates a possible opening for using DAO messages 1561 as a covert channel. Note that DAO messages are rare and the 1562 overusing that channel could be detected. An implementation SHOULD 1563 notify the network management when a RPL Target Option is receives 1564 with an unknown ROVR field size, to ensure that the situation is 1565 known to the network administrator. 1567 [EFFICIENT-NPDAO] introduces the ability for a rogue common ancestor 1568 node to invalidate a route on behalf of the target node. In this 1569 case, the RPL Status in the DCO has the 'A' flag set to 0, and a 1570 NA(EARO) is returned to the 6LN with the R flag set to 0. This 1571 encourages the 6LN to try another 6LR. If a 6LR exists that does not 1572 use the rogue common ancestor, then the 6LN will eventually succeed 1573 gaining reachability over the RPL network in spite of the rogue node. 1575 12. IANA Considerations 1577 12.1. Fixing the Address Registration Option Flags 1579 Section 9.1 of [RFC8505] creates a Registry for the 8-bit Address 1580 Registration Option Flags field. IANA is requested to rename the 1581 first column of the table from "ARO Status" to "Bit number". 1583 12.2. Resizing the ARO Status values 1585 Section 12 of [RFC6775] creates the Address Registration Option 1586 Status values Registry with a range 0-255. 1588 This specification reduces that range to 0-63, see Section 6.3. 1590 IANA is requested to modify the Address Registration Option Status 1591 values Registry so that the upper bound of the unassigned values is 1592 63. This document should be added as a reference. The registration 1593 procedure does not change. 1595 12.3. New RPL DODAG Configuration Option Flag 1597 IANA is requested to assign a flag from the "DODAG Configuration 1598 Option Flags for MOP 0..6" [USEofRPLinfo] registry as follows: 1600 +---------------+----------------------------+-----------+ 1601 | Bit Number | Capability Description | Reference | 1602 +---------------+----------------------------+-----------+ 1603 | 1 (suggested) | Root Proxies EDAR/EDAC (P) | THIS RFC | 1604 +---------------+----------------------------+-----------+ 1606 Table 2: New DODAG Configuration Option Flag 1608 12.4. RPL Target Option Registry 1610 This document modifies the "RPL Target Option Flags" registry 1611 initially created in Section 20.15 of [RFC6550] . The registry now 1612 includes only 4 bits (Section 6.1) and should point to this document 1613 as an additional reference. The registration procedure doesn't 1614 change. 1616 Section 6.1 also defines 2 new entries in the Registry as follows: 1618 +---------------+--------------------------------+-----------+ 1619 | Bit Number | Capability Description | Reference | 1620 +---------------+--------------------------------+-----------+ 1621 | 0 (suggested) | Advertiser address in Full (F) | THIS RFC | 1622 +---------------+--------------------------------+-----------+ 1623 | 1 (suggested) | Proxy EDAR Requested (X) | THIS RFC | 1624 +---------------+--------------------------------+-----------+ 1626 Table 3: RPL Target Option Registry 1628 12.5. New Subregistry for RPL Non-Rejection Status values 1630 This specification creates a new Subregistry for the RPL Non- 1631 Rejection Status values for use in the RPL DAO-ACK, DCO, and DCO-ACK 1632 messages with the 'A' flag set to 0, under the RPL registry. 1634 * Possible values are 6-bit unsigned integers (0..63). 1636 * Registration procedure is "IETF Review" [RFC8126]. 1638 * Initial allocation is as indicated in Table 4: 1640 +-------+------------------------+---------------------+ 1641 | Value | Meaning | Reference | 1642 +-------+------------------------+---------------------+ 1643 | 0 | Unqualified acceptance | THIS RFC / RFC 6550 | 1644 +-------+------------------------+---------------------+ 1645 | 1..63 | Unassigned | | 1646 +-------+------------------------+---------------------+ 1648 Table 4: Acceptance values of the RPL Status 1650 12.6. New Subregistry for RPL Rejection Status values 1652 This specification creates a new Subregistry for the RPL Rejection 1653 Status values for use in the RPL DAO-ACK and DCO messages with the 1654 'A' flag set to 0, under the RPL registry. 1656 * Possible values are 6-bit unsigned integers (0..63). 1658 * Registration procedure is "IETF Review" [RFC8126]. 1660 * Initial allocation is as indicated in Table 5: 1662 +-------+-----------------------+-----------+ 1663 | Value | Meaning | Reference | 1664 +-------+-----------------------+-----------+ 1665 | 0 | Unqualified rejection | THIS RFC | 1666 +-------+-----------------------+-----------+ 1667 | 1..63 | Unassigned | | 1668 +-------+-----------------------+-----------+ 1670 Table 5: Rejection values of the RPL Status 1672 13. Acknowledgments 1674 The authors wish to thank Ines Robles, Georgios Papadopoulos and 1675 especially Rahul Jadhav and Alvaro Retana for their reviews and 1676 contributions to this document. Also many thanks to Eric Vyncke, 1677 Erik Kline, Murray Kucherawy, Peter Van der Stok, Carl Wallace, and 1678 especially Benjamin Kaduk and Elwyn Davies, for their reviews and 1679 useful comments during the IETF Last Call and the IESG review 1680 sessions. 1682 14. Normative References 1684 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1685 Requirement Levels", BCP 14, RFC 2119, 1686 DOI 10.17487/RFC2119, March 1997, 1687 . 1689 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1690 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1691 DOI 10.17487/RFC3810, June 2004, 1692 . 1694 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1695 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1696 DOI 10.17487/RFC4861, September 2007, 1697 . 1699 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1700 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1701 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1702 Low-Power and Lossy Networks", RFC 6550, 1703 DOI 10.17487/RFC6550, March 2012, 1704 . 1706 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1707 Bormann, "Neighbor Discovery Optimization for IPv6 over 1708 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1709 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1710 . 1712 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1713 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1714 2014, . 1716 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 1717 IPv6 over Low-Power Wireless Personal Area Networks 1718 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 1719 2014, . 1721 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1722 Writing an IANA Considerations Section in RFCs", BCP 26, 1723 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1724 . 1726 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1727 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1728 May 2017, . 1730 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1731 (IPv6) Specification", STD 86, RFC 8200, 1732 DOI 10.17487/RFC8200, July 2017, 1733 . 1735 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node 1736 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504, 1737 January 2019, . 1739 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1740 Perkins, "Registration Extensions for IPv6 over Low-Power 1741 Wireless Personal Area Network (6LoWPAN) Neighbor 1742 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1743 . 1745 [RFC8928] Thubert, P., Ed., Sarikaya, B., Sethi, M., and R. Struik, 1746 "Address-Protected Neighbor Discovery for Low-Power and 1747 Lossy Networks", RFC 8928, DOI 10.17487/RFC8928, November 1748 2020, . 1750 [USEofRPLinfo] 1751 Robles, I., Richardson, M., and P. Thubert, "Using RPI 1752 Option Type, Routing Header for Source Routes and IPv6-in- 1753 IPv6 encapsulation in the RPL Data Plane", Work in 1754 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-42, 1755 12 November 2020, . 1758 [EFFICIENT-NPDAO] 1759 Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient 1760 Route Invalidation", Work in Progress, Internet-Draft, 1761 draft-ietf-roll-efficient-npdao-18, 15 April 2020, 1762 . 1765 15. Informative References 1767 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1768 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1769 Overview, Assumptions, Problem Statement, and Goals", 1770 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1771 . 1773 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1774 Address Autoconfiguration", RFC 4862, 1775 DOI 10.17487/RFC4862, September 2007, 1776 . 1778 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1779 Power and Lossy Networks (RPL) Option for Carrying RPL 1780 Information in Data-Plane Datagrams", RFC 6553, 1781 DOI 10.17487/RFC6553, March 2012, 1782 . 1784 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1785 Routing Header for Source Routes with the Routing Protocol 1786 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1787 DOI 10.17487/RFC6554, March 2012, 1788 . 1790 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1791 Statement and Requirements for IPv6 over Low-Power 1792 Wireless Personal Area Network (6LoWPAN) Routing", 1793 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1794 . 1796 [RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed., 1797 "Source Address Validation Improvement (SAVI) Framework", 1798 RFC 7039, DOI 10.17487/RFC7039, October 2013, 1799 . 1801 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1802 Constrained-Node Networks", RFC 7228, 1803 DOI 10.17487/RFC7228, May 2014, 1804 . 1806 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1807 "IPv6 over Low-Power Wireless Personal Area Network 1808 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1809 April 2017, . 1811 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 1812 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 1813 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 1814 RFC 8415, DOI 10.17487/RFC8415, November 2018, 1815 . 1817 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1818 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1819 DOI 10.17487/RFC6282, September 2011, 1820 . 1822 [RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur, 1823 Ed., "Performance Evaluation of the Routing Protocol for 1824 Low-Power and Lossy Networks (RPL)", RFC 6687, 1825 DOI 10.17487/RFC6687, October 2012, 1826 . 1828 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1829 and M. Richardson, Ed., "A Security Threat Analysis for 1830 the Routing Protocol for Low-Power and Lossy Networks 1831 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1832 . 1834 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1835 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1836 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1837 . 1839 [RFC8929] Thubert, P., Ed., Perkins, C.E., and E. Levy-Abegnoli, 1840 "IPv6 Backbone Router", RFC 8929, DOI 10.17487/RFC8929, 1841 November 2020, . 1843 Appendix A. Example Compression 1845 Figure 13 illustrates the case in Storing Mode where the packet is 1846 received from the Internet, then the Root encapsulates the packet to 1847 insert the RPI and deliver to the 6LR that is the parent and last hop 1848 to the final destination, which is not known to support [RFC8138]. 1850 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1851 |11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP 1852 |Page 1 |Type1 S=0| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 1853 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1854 <-4 bytes-> <- RFC 6282 -> 1855 <- No RPL artifact ... 1857 Figure 13: Encapsulation to Parent 6LR in Storing Mode 1859 The difference with the example presented in Figure 19 of [RFC8138] 1860 is the addition of a SRH-6LoRH before the RPI-6LoRH to transport the 1861 compressed address of the 6LR as the destination address of the outer 1862 IPv6 header. In the [RFC8138] example the destination IP of the 1863 outer header was elided and was implicitly the same address as the 1864 destination of the inner header. Type 1 was arbitrarily chosen, and 1865 the size of 0 denotes a single address in the SRH. 1867 In Figure 13, the source of the IPv6-in-IPv6 encapsulation is the 1868 Root, so it is elided in the IPv6-in-IPv6 6LoRH. The destination is 1869 the parent 6LR of the destination of the encapsulated packet so it 1870 cannot be elided. If the DODAG is operated in Storing Mode, it is 1871 the single entry in the SRH-6LoRH and the SRH-6LoRH Size is encoded 1872 as 0. The SRH-6LoRH is the first 6LoRH in the chain. In this 1873 particular example, the 6LR address can be compressed to 2 bytes so a 1874 Type of 1 is used. It results that the total length of the SRH-6LoRH 1875 is 4 bytes. 1877 In Non-Storing Mode, the encapsulation from the Root would be similar 1878 to that represented in Figure 13 with possibly more hops in the SRH- 1879 6LoRH and possibly multiple SRH-6LoRHs if the various addresses in 1880 the routing header are not compressed to the same format. Note that 1881 on the last hop to the parent 6LR, the RH3 is consumed and removed 1882 from the compressed form, so the use of Non-Storing Mode vs. Storing 1883 Mode is indistinguishable from the packet format. 1885 The SRH-6LoRHs are followed by RPI-6LoRH and then the IPv6-in-IPv6 1886 6LoRH. When the IPv6-in-IPv6 6LoRH is removed, all the 6LoRH Headers 1887 that precede it are also removed. The Paging Dispatch [RFC8025] may 1888 also be removed if there was no previous Page change to a Page other 1889 than 0 or 1, since the LOWPAN_IPHC is encoded in the same fashion in 1890 the default Page 0 and in Page 1. The resulting packet to the 1891 destination is the encapsulated packet compressed with [RFC6282]. 1893 Authors' Addresses 1895 Pascal Thubert (editor) 1896 Cisco Systems, Inc 1897 Building D 1898 45 Allee des Ormes - BP1200 1899 06254 Mougins - Sophia Antipolis 1900 France 1902 Phone: +33 497 23 26 34 1903 Email: pthubert@cisco.com 1904 Michael C. Richardson 1905 Sandelman Software Works 1907 Email: mcr+ietf@sandelman.ca 1908 URI: http://www.sandelman.ca/