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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: 26 July 2021 22 January 2021 8 Routing for RPL Leaves 9 draft-ietf-roll-unaware-leaves-30 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 26 July 2021. 36 Copyright Notice 38 Copyright (c) 2021 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 . . . . . . . . . 10 61 4.2.1. R Flag . . . . . . . . . . . . . . . . . . . . . . . 10 62 4.2.2. TID, "I" Field and Opaque Fields . . . . . . . . . . 11 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 . . . . . . . . . . . . . 13 67 5.1. Support of 6LoWPAN ND . . . . . . . . . . . . . . . . . . 13 68 5.2. Support of IPv6 Encapsulation . . . . . . . . . . . . . . 14 69 5.3. Support of the Hop-by-Hop Header . . . . . . . . . . . . 14 70 5.4. Support of the Routing Header . . . . . . . . . . . . . . 14 71 6. Enhancements to RFC 6550 . . . . . . . . . . . . . . . . . . 14 72 6.1. Updated RPL Target Option . . . . . . . . . . . . . . . . 15 73 6.2. Additional Flag in the RPL DODAG Configuration Option . . 17 74 6.3. Updated RPL Status . . . . . . . . . . . . . . . . . . . 18 75 7. Enhancements to draft-ietf-roll-efficient-npdao . . . . . . . 20 76 8. Enhancements to RFC6775 and RFC8505 . . . . . . . . . . . . . 20 77 9. Protocol Operations for Unicast Addresses . . . . . . . . . . 20 78 9.1. General Flow . . . . . . . . . . . . . . . . . . . . . . 21 79 9.2. Detailed Operation . . . . . . . . . . . . . . . . . . . 24 80 9.2.1. Perspective of the 6LN Acting as RUL . . . . . . . . 24 81 9.2.2. Perspective of the 6LR Acting as Border router . . . 25 82 9.2.3. Perspective of the RPL Root . . . . . . . . . . . . . 30 83 9.2.4. Perspective of the 6LBR . . . . . . . . . . . . . . . 31 84 10. Protocol Operations for Multicast Addresses . . . . . . . . . 31 85 11. Security Considerations . . . . . . . . . . . . . . . . . . . 34 86 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 87 12.1. Fixing the Address Registration Option Flags . . . . . . 35 88 12.2. Resizing the ARO Status values . . . . . . . . . . . . . 36 89 12.3. New RPL DODAG Configuration Option Flag . . . . . . . . 36 90 12.4. RPL Target Option Registry . . . . . . . . . . . . . . . 36 91 12.5. New Subregistry for RPL Non-Rejection Status values . . 37 92 12.6. New Subregistry for RPL Rejection Status values . . . . 37 93 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 38 94 14. Normative References . . . . . . . . . . . . . . . . . . . . 38 95 15. Informative References . . . . . . . . . . . . . . . . . . . 39 96 Appendix A. Example Compression . . . . . . . . . . . . . . . . 41 97 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42 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 requirements 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 6LoWPAN Border 226 Router (6LBR) on behalf of the 6LR; modifications are introduced 227 to some RPL options and to the RPL Status to facilitate the 228 integration of the protocols. 230 * Section 7 presents the changes made to [EFFICIENT-NPDAO]; the use 231 of the DCO message is extended to the Non-Storing MOP to report 232 asynchronous issues from the Root to the 6LR. 234 * Section 8 presents the changes made to [RFC6775] and [RFC8505]; 235 The range of the ND status codes is reduced down to 64 values, and 236 the remaining bits in the original status field are now reserved. 238 * Section 9 and Section 10 present the operation of this 239 specification for unicast and multicast flows, respectively, and 240 Section 11 presents associated security considerations. 242 2. Terminology 244 2.1. Requirements Language 246 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 247 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 248 "OPTIONAL" in this document are to be interpreted as described in BCP 249 14 [RFC2119] [RFC8174] when, and only when, they appear in all 250 capitals, as shown here. 252 2.2. Glossary 254 This document uses the following acronyms: 256 6CIO: 6LoWPAN Capability Indication Option 257 6LN: 6LoWPAN Node (a Low Power host or router) 258 6LR: 6LoWPAN router 259 6LBR: 6LoWPAN Border router 260 (E)ARO: (Extended) Address Registration Option 261 (E)DAR: (Extended) Duplicate Address Request 262 (E)DAC: (Extended) Duplicate Address Confirmation 263 DAD: Duplicate Address Detection 264 DAO: Destination Advertisement Object (a RPL message) 265 DCO: Destination Cleanup Object (a RPL message) 266 DIO: DODAG Information Object (a RPL message) 267 DODAG: Destination-Oriented Directed Acyclic Graph 268 LLN: Low-Power and Lossy Network 269 MOP: RPL Mode of Operation 270 NA: Neighbor Advertisement 271 NCE: Neighbor Cache Entry 272 ND: Neighbor Discovery 273 NS: Neighbor Solicitation 274 RA: router Advertisement 275 ROVR: Registration Ownership Verifier 276 RPI: RPL Packet Information 277 RAL: RPL-aware Leaf 278 RAN: RPL-Aware Node (either a RPL router or a RPL-aware Leaf) 279 RUL: RPL-Unaware Leaf 280 SRH: Source-Routing Header 281 TID: Transaction ID (a sequence counter in the EARO) 282 TIO: Transit Information Option 284 2.3. References 286 The Terminology used in this document is consistent with and 287 incorporates that described in "Terms Used in Routing for Low-Power 288 and Lossy Networks (LLNs)" [RFC7102]. A glossary of classical 289 6LoWPAN acronyms is given in Section 2.2. Other terms in use in LLNs 290 are found in "Terminology for Constrained-Node Networks" [RFC7228]. 291 This specification uses the terms 6LN and 6LR to refer specifically 292 to nodes that implement the 6LN and 6LR roles in 6LoWPAN ND and does 293 not expect other functionality such as 6LoWPAN Header Compression 294 [RFC6282] from those nodes. 296 "RPL", the "RPL Packet Information" (RPI), "RPL Instance" (indexed by 297 a RPLInstanceID), "up", "down" are defined in "RPL: IPv6 Routing 298 Protocol for Low-Power and Lossy Networks" [RFC6550]. The RPI is the 299 abstract information that RPL defines to be placed in data packets, 300 e.g., as the RPL Option [RFC6553] within the IPv6 Hop-By-Hop Header. 301 By extension, the term "RPI" is often used to refer to the RPL Option 302 itself. The Destination Advertisement Object (DAO) and DODAG 303 Information Object (DIO) messages are also specified in [RFC6550]. 304 The Destination Cleanup Object (DCO) message is defined in 305 [EFFICIENT-NPDAO]. 307 This document uses the terms RPL-Unaware Leaf (RUL), RPL-Aware Node 308 (RAN) and RPL aware Leaf (RAL) consistently with [USEofRPLinfo]. A 309 RAN is either a RAL or a RPL router. As opposed to a RUL, a RAN 310 manages the reachability of its addresses and prefixes by injecting 311 them in RPL by itself. 313 In this document, readers will encounter terms and concepts that are 314 discussed in the following documents: 316 Classical IPv6 ND: "Neighbor Discovery for IP version 6" [RFC4861] 317 and "IPv6 Stateless Address Autoconfiguration" [RFC4862], 319 6LoWPAN: "Problem Statement and Requirements for IPv6 over Low-Power 320 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606] and 321 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 322 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 323 and 325 6LoWPAN ND: Neighbor Discovery Optimization for Low-Power and Lossy 326 Networks [RFC6775], "Registration Extensions for 6LoWPAN Neighbor 327 Discovery" [RFC8505], "Address Protected Neighbor Discovery for 328 Low-power and Lossy Networks" [RFC8928], and "IPv6 Backbone 329 Router" [RFC8929]. 331 3. RPL External Routes and Dataplane Artifacts 333 RPL was initially designed to build stub networks whereby the only 334 border router would be the RPL Root (typically collocated with the 335 6LBR) and all the nodes in the stub would be RPL-Aware. But 336 [RFC6550] was also prepared to be extended for external routes 337 (targets in RPL parlance) with the External 'E' flag in the Transit 338 Information Option (TIO). External targets enable to reach 339 destinations that are outside the RPL domain and connected to the RPL 340 domain via RPL border routers that are not the Root. Section 4.1 of 341 [USEofRPLinfo] provides a set of rules summarized below that must be 342 followed for routing packets to and from an external destination. A 343 RUL is a special case of an external target that is also a host 344 directly connected to the RPL domain. 346 A 6LR that acts as a border router for external routes advertises 347 them using Non-Storing Mode DAO messages that are unicast directly to 348 the Root, even if the DODAG is operated in Storing Mode. Non-Storing 349 Mode routes are not visible inside the RPL domain and all packets are 350 routed via the Root. The RPL Root tunnels the data packets directly 351 to the 6LR that advertised the external route, which decapsulates and 352 forwards the original (inner) packets. 354 The RPL Non-Storing MOP signaling and the associated IPv6-in-IPv6 355 encapsulated packets appear as normal traffic to the intermediate 356 routers. The support of external routes only impacts the Root and 357 the 6LR. It can be operated with legacy intermediate routers and 358 does not add to the amount of state that must be maintained in those 359 routers. A RUL is an example of a destination that is reachable via 360 an external route that happens to be also a host route. 362 The RPL data packets typically carry a Hop-by-Hop Header with a RPL 363 Option [RFC6553] that contains the Packet Information (RPI) defined 364 in section 11.2 of [RFC6550]. Unless the RUL already placed a RPL 365 Option in outer header chain, the packets from and to the RUL are 366 encapsulated using an IPv6-in-IPv6 tunnel between the Root and the 367 6LR that serves the RUL (see sections 7 and 8 of [USEofRPLinfo] for 368 details). If the packet from the RUL has an RPI, the 6LR as a RPL 369 border router rewrites the RPI to indicate the selected Instance and 370 set the flags, but it does not need to encapsulate the packet (see 371 Section 9.2.2) . 373 In Non-Storing Mode, packets going down carry a Source Routing Header 374 (SRH). The IPv6-in-IPv6 encapsulation, the RPI and the SRH are 375 collectively called the "RPL artifacts" and can be compressed using 376 [RFC8138]. Appendix A presents an example compressed format for a 377 packet forwarded by the Root to a RUL in a Storing Mode DODAG. 379 The inner packet that is forwarded to the RUL may carry some RPL 380 artifacts, e.g., an RPI if the original packet was generated with it, 381 and an SRH in a Non-Storing Mode DODAG. [USEofRPLinfo] expects the 382 RUL to support the basic "IPv6 Node Requirements" [RFC8504] and in 383 particular the mandates in Sections 4.2 and 4.4 of [RFC8200]. As 384 such, the RUL is expected to ignore the RPL artifacts that may be 385 left over, either an SRH with zero Segments Left or a RPL Option in 386 the Hop-by-Hop Header, which can be skipped when not recognized, see 387 Section 5 for more. 389 A RUL is not expected to support the compression method defined in 390 [RFC8138]. For that reason, the border router (the 6LR here) 391 uncompresses the packet before forwarding it over an external route 392 to a RUL [USEofRPLinfo]. 394 4. 6LoWPAN Neighbor Discovery 396 This section goes through the 6LoWPAN ND mechanisms that this 397 specification leverages, as a non-normative reference to the reader. 398 The full normative text is to be found in [RFC6775], [RFC8505], and 399 [RFC8928]. 401 4.1. RFC 6775 Address Registration 403 The classical "IPv6 Neighbor Discovery (IPv6 ND) Protocol" [RFC4861] 404 [RFC4862] was defined for serial links and transit media such as 405 Ethernet. It is a reactive protocol that relies heavily on multicast 406 operations for Address Discovery (aka Lookup) and Duplicate Address 407 Detection (DAD). 409 "Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775] 410 adapts IPv6 ND for operations over energy-constrained LLNs. The main 411 functions of [RFC6775] are to proactively establish the Neighbor 412 Cache Entry (NCE) in the 6LR and to prevent address duplication. To 413 that effect, [RFC6775] introduces a new unicast Address Registration 414 mechanism that contributes to reducing the use of multicast messages 415 compared to the classical IPv6 ND protocol. 417 [RFC6775] defines a new Address Registration Option (ARO) that is 418 carried in the unicast Neighbor Solicitation (NS) and Neighbor 419 Advertisement (NA) messages between the 6LoWPAN Node (6LN) and the 420 6LoWPAN router (6LR). It also defines the Duplicate Address Request 421 (DAR) and Duplicate Address Confirmation (DAC) messages between the 422 6LR and the 6LBR). In an LLN, the 6LBR is the central repository of 423 all the Registered Addresses in its domain and the source of truth 424 for uniqueness and ownership. 426 4.2. RFC 8505 Extended Address Registration 428 "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505] 429 updates RFC 6775 into a generic Address Registration mechanism that 430 can be used to access services such as routing and ND proxy. To that 431 effect, [RFC8505] defines the Extended Address Registration Option 432 (EARO), shown in Figure 2: 434 0 1 2 3 435 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 1 436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 437 | Type | Length | Status | Opaque | 438 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 439 | Rsvd | I |R|T| TID | Registration Lifetime | 440 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 441 | | 442 ... Registration Ownership Verifier ... 443 | | 444 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 446 Figure 2: EARO Option Format 448 4.2.1. R Flag 450 [RFC8505] introduces the R Flag in the EARO. The Registering Node 451 sets the R Flag to indicate whether the 6LR should ensure 452 reachability for the Registered Address. If the R Flag is set to 0, 453 then the Registering Node handles the reachability of the Registered 454 Address by other means. In a RPL network, this means that either it 455 is a RAN that injects the route by itself or that it uses another RPL 456 router for reachability services. 458 This document specifies how the R Flag is used in the context of RPL. 459 A RPL leaf that implements the 6LN functionality from [RFC8505] 460 requires reachability services for an IPv6 address if and only if it 461 sets the R Flag in the NS(EARO) used to register the address to a 6LR 462 acting as a RPL border router. Upon receiving the NS(EARO), the RPL 463 router generates a DAO message for the Registered Address if and only 464 if the R flag is set to 1. 466 Section 9.2 specifies additional operations when R flag is set to 1 467 in an EARO that is placed either in an NS or an NA message. 469 4.2.2. TID, "I" Field and Opaque Fields 471 When the T Flag is set to 1, the EARO includes a sequence counter 472 called Transaction ID (TID), that is needed to fill the Path Sequence 473 Field in the RPL Transit Option. This is the reason why the support 474 of [RFC8505] by the RUL, as opposed to only [RFC6775], is a 475 prerequisite for this specification); this requirement is fully 476 explained in Section 5.1. The EARO also transports an Opaque field 477 and an associated "I" field that describes what the Opaque field 478 transports and how to use it. 480 Section 9.2.1 specifies the use of the "I" field and the Opaque field 481 by a RUL. 483 4.2.3. Route Ownership Verifier 485 Section 5.3 of [RFC8505] introduces the Registration Ownership 486 Verifier (ROVR) field of variable length from 64 to 256 bits. The 487 ROVR is a replacement of the EUI-64 in the ARO [RFC6775] that was 488 used to identify uniquely an Address Registration with the Link-Layer 489 address of the owner but provided no protection against spoofing. 491 "Address Protected Neighbor Discovery for Low-power and Lossy 492 Networks" [RFC8928] leverages the ROVR field as a cryptographic proof 493 of ownership to prevent a rogue third party from registering an 494 address that is already owned. The use of ROVR field enables the 6LR 495 to block traffic that is not sourced at an owned address. 497 This specification does not address how the protection by [RFC8928] 498 could be extended for use in RPL. On the other hand, it adds the 499 ROVR to the DAO to build the proxied EDAR at the Root (see 500 Section 6.1), which means that nodes that are aware of the host route 501 are also aware of the ROVR associated to the Target Address. 503 4.3. RFC 8505 Extended DAR/DAC 505 [RFC8505] updates the DAR/DAC messages into the Extended DAR/DAC to 506 carry the ROVR field. The EDAR/EDAC exchange takes place between the 507 6LR and the 6LBR. It is triggered by an NS(EARO) message from a 6LN 508 to create, refresh, and delete the corresponding state in the 6LBR. 509 The exchange is protected by the retry mechanism specified in 510 Section 8.2.6 of [RFC6775], though in an LLN, a duration longer than 511 the default value of the RetransTimer (RETRANS_TIMER) [RFC4861] of 1 512 second may be necessary to cover the round trip delay between the 6LR 513 and the 6LBR. 515 RPL [RFC6550] specifies a periodic DAO from the 6LN all the way to 516 the Root that maintains the routing state in the RPL network for the 517 lifetime indicated by the source of the DAO. This means that for 518 each address, there are two keep-alive messages that traverse the 519 whole network, one to the Root and one to the 6LBR. 521 This specification avoids the periodic EDAR/EDAC exchange across the 522 LLN. The 6LR turns the periodic NS(EARO) from the RUL into a DAO 523 message to the Root on every refresh, but it only generates the EDAR 524 upon the first registration, for the purpose of DAD, which must be 525 verified before the address is injected in RPL. Upon the DAO 526 message, the Root proxies the EDAR exchange to refresh the state at 527 the 6LBR on behalf of the 6LR, as illustrated in Figure 8 in 528 Section 9.1. 530 4.3.1. RFC 7400 Capability Indication Option 532 "6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power 533 Wireless Personal Area Networks (6LoWPANs)" [RFC7400] defines the 534 6LoWPAN Capability Indication Option (6CIO) that enables a node to 535 expose its capabilities in router Advertisement (RA) messages. 537 [RFC8505] defines a number of bits in the 6CIO, in particular: 539 L: Node is a 6LR. 540 E: Node is an IPv6 ND Registrar -- i.e., it supports registrations 541 based on EARO. 542 P: Node is a Routing Registrar, -- i.e., an IPv6 ND Registrar that 543 also provides reachability services for the Registered Address. 545 0 1 2 3 546 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 1 547 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 548 | Type | Length = 1 | Reserved |D|L|B|P|E|G| 549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 550 | Reserved | 551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 553 Figure 3: 6CIO flags 555 A 6LR that provides reachability services for a RUL in a RPL network 556 as specified in this document includes a 6CIO in its RA messages and 557 set the L, P and E flags to 1 as prescribed by [RFC8505]; this is 558 fully explained in Section 9.2. 560 5. Requirements on the RPL-Unware leaf 562 This document describes how RPL routing can be extended to reach a 563 RUL. This section specifies the minimal RPL-independent 564 functionality that the RUL needs to implement to obtain routing 565 services for its addresses. 567 5.1. Support of 6LoWPAN ND 569 To obtain routing services from a router that implements this 570 specification, a RUL needs to implement [RFC8505] and sets the "R" 571 and "T" flags in the EARO to 1 as discussed in Section 4.2.1 and 572 Section 4.2.2, respectively. Section 9.2.1 specifies new behaviors 573 for the RUL, e.g., when the R Flag set to 1 in a NS(EARO) is not 574 echoed in the NA(EARO), which indicates that the route injection 575 failed. 577 The RUL is expected to request routing services from a router only if 578 that router originates RA messages with a 6CIO that has the L, P, and 579 E flags all set to 1 as discussed in Section 4.3.1, unless configured 580 to do so. It is suggested that the RUL also implements [RFC8928] to 581 protect the ownership of its addresses. 583 A RUL that may attach to multiple 6LRs is expected to prefer those 584 that provide routing services. The RUL needs to register to all the 585 6LRs from which it desires routing services. 587 Parallel Address Registrations to several 6LRs should be performed in 588 a rapid sequence, using the same EARO for the same Address. Gaps 589 between the Address Registrations will invalidate some of the routes 590 till the Address Registration finally shows on those routes. 592 [RFC8505] introduces error Status values in the NA(EARO) which can be 593 received synchronously upon an NS(EARO) or asynchronously. The RUL 594 needs to support both cases and refrain from using the address when 595 the Status value indicates a rejection (see Section 6.3). 597 5.2. Support of IPv6 Encapsulation 599 Section 2.1 of [USEofRPLinfo] defines the rules for tunneling either 600 to the final destination (e.g., a RUL) or to its attachment router 601 (designated as 6LR). In order to terminate the IPv6-in-IPv6 tunnel, 602 the RUL, as an IPv6 host, would have to be capable of decapsulating 603 the tunneled packet and either drop the encapsulated packet if it is 604 not the final destination, or pass it to the upper layer for further 605 processing. As indicated in section 4.1 of [USEofRPLinfo], this is 606 not mandated by [RFC8504], and the IPv6-in-IPv6 tunnel from the Root 607 is terminated at the parent 6LR. It is thus not necessary for a RUL 608 to support IPv6-in-IPv6 decapsulation. 610 5.3. Support of the Hop-by-Hop Header 612 A RUL is expected to process an Option Type in a Hop-by-Hop Header as 613 prescribed by section 4.2 of [RFC8200]. An RPI with an Option Type 614 of 0x23 [USEofRPLinfo] is thus skipped when not recognized. 616 5.4. Support of the Routing Header 618 A RUL is expected to process an unknown Routing Header Type as 619 prescribed by section 4.4 of [RFC8200]. This implies that the Source 620 Routing Header, which has a Routing Type of 3 [RFC6554], is ignored 621 when the Segments Left is zero. When the Segments Left is non-zero, 622 the RUL discards the packet and send an ICMP Parameter Problem, Code 623 0, message to the packet's Source Address, pointing to the 624 unrecognized Routing Type. 626 6. Enhancements to RFC 6550 628 This document specifies a new behavior whereby a 6LR injects DAO 629 messages for unicast addresses (see Section 9) and multicast 630 addresses (see Section 10) on behalf of leaves that are not aware of 631 RPL. The RUL addresses are exposed as external targets [RFC6550]. 632 Conforming to [USEofRPLinfo], an IPv6-in-IPv6 encapsulation between 633 the 6LR and the RPL Root is used to carry the RPL artifacts and 634 remove them when forwarding outside the RPL domain, e.g., to a RUL. 636 This document also synchronizes the liveness monitoring at the Root 637 and the 6LBR. The same value of lifetime is used for both, and a 638 single keep-alive message, the RPL DAO, traverses the RPL network. A 639 new behavior is introduced whereby the RPL Root proxies the EDAR 640 message to the 6LBR on behalf of the 6LR (see Section 8), for any 641 leaf node that implements the 6LN functionality in [RFC8505]. 643 Section 6.7.7 of [RFC6550] introduces the RPL Target Option, which 644 can be used in RPL Control messages such as the DAO message to signal 645 a destination prefix. This document adds the capabilities to 646 transport the ROVR field (see Section 4.2.3) and the IPv6 Address of 647 the prefix advertiser when the Target is a shorter prefix. Their use 648 is signaled respectively by a new ROVR Size field being non-zero and 649 a new "Advertiser address in Full" 'F' flag set to 1, see 650 Section 6.1. 652 This specification defines a new flag, "Root Proxies EDAR/EDAC" (P), 653 in the RPL DODAG Configuration option, see Section 6.2. 655 The RPL Status defined in section 6.5.1 of [RFC6550] for use in the 656 DAO-ACK message is extended to be placed in DCO messages 657 [EFFICIENT-NPDAO] as well. Furthermore, this specification enables 658 to carry the EARO Status defined for 6LoWPAN ND in RPL DAO and DCO 659 messages, embedded in a RPL Status, see Section 6.3. 661 Section 12 of [RFC6550] details the RPL support for multicast flows 662 when the RPLInstance is operated in the MOP of 3 ("Storing Mode of 663 Operation with multicast support"). This specification extends the 664 RPL Root operation to proxy-relay the MLDv2 [RFC3810] operation 665 between the RUL and the 6LR, see Section 10. 667 6.1. Updated RPL Target Option 669 This specification updates the RPL Target Option to transport the 670 ROVR that was also defined for 6LoWPAN ND messages. This enables the 671 RPL Root to generate the proxied EDAR message to the 6LBR. 673 The Target Prefix of the RPL Target Option is left (high bit) 674 justified and contains the advertised prefix; its size may be smaller 675 than 128 when it indicates a Prefix route. The Prefix Length field 676 signals the number of bits that correspond to the advertised Prefix; 677 it is 128 for a host route or less in the case of a Prefix route. 678 This remains unchanged. 680 This specification defines the new 'F' flag. When it is set to 1, 681 the size of the Target Prefix field MUST be 128 bits and it MUST 682 contain an IPv6 address of the advertising node taken from the 683 advertised Prefix. In that case, the Target Prefix field carries two 684 distinct pieces of information: a route that can be a host route or a 685 Prefix route depending on the Prefix Length, and an IPv6 address that 686 can be used to reach the advertising node and validate the route. 688 If the 'F' flag is set to 0, the Target Prefix field can be shorter 689 than 128 bits and it MUST be aligned to the next byte boundary after 690 the end of the prefix. Any additional bits in the rightmost octet 691 are filled with padding bits. Padding bits are reserved and set to 0 692 as specified in section 6.7.7 of [RFC6550]. 694 With this specification the ROVR is the remainder of the RPL Target 695 Option. The size of the ROVR is indicated in a new ROVR Size field 696 that is encoded to map one-to-one with the Code Suffix in the EDAR 697 message (see table 4 of [RFC8505]). The ROVR Size field is taken 698 from the flags field, which is an update to the RPL Target Option 699 Flags IANA registry. 701 The updated format is illustrated in Figure 4. It is backward 702 compatible with the Target Option in [RFC6550]. It is recommended 703 that the updated format be used as a replacement in new 704 implementations in all MOPs in preparation for upcoming Route 705 Ownership Validation mechanisms based on the ROVR, unless the device 706 or the network is so constrained that this is not feasible. 708 0 1 2 3 709 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 1 710 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 711 | Type = 0x05 | Option Length |F|X|Flg|ROVRsz | Prefix Length | 712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 713 | | 714 | Target Prefix (Variable Length) | 715 . . 716 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 717 | | 718 ... Registration Ownership Verifier (ROVR) ... 719 | | 720 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 722 Figure 4: Updated Target Option 724 New fields: 726 F: 1-bit flag. Set to 1 to indicate that Target Prefix field 727 contains the complete (128 bit) IPv6 address of the advertising 728 node. 730 X: 1-bit flag. Set to 1 to request that the Root performs a proxy 731 EDAR/EDAC exchange. 733 The 'X' flag can only be set to 1 if the DODAG is operating in 734 Non-Storing Mode and if the Root sets the "Root Proxies EDAR/EDAC 735 (P)" flag to 1 in the DODAG Configuration Option, see Section 6.2. 737 The 'X' flag can be set for host routes to RULs and RANs; it can 738 also be set for internal prefix routes if the 'F' flag is set, 739 using the node's address in the Target Prefix field to form the 740 EDAR, but it cannot be used otherwise. 742 Flg (Flags): The 2 bits remaining unused in the Flags field are 743 reserved for flags. The field MUST be initialized to zero by the 744 sender and MUST be ignored by the receiver. 746 ROVRsz (ROVR Size): Indicates the Size of the ROVR. It MUST be set 747 to 1, 2, 3, or 4, indicating a ROVR size of 64, 128, 192, or 256 748 bits, respectively. 750 If a legacy Target Option is used, then the value must remain 0, 751 as specified in [RFC6550]. 753 In case of a value above 4, the size of the ROVR is undetermined 754 and this node cannot validate the ROVR; an implementation SHOULD 755 propagate the whole Target Option upwards as received to enable 756 the verification by an ancestor that would support the upgraded 757 ROVR. 759 Registration Ownership Verifier (ROVR): This is the same field as in 760 the EARO, see [RFC8505] 762 6.2. Additional Flag in the RPL DODAG Configuration Option 764 The DODAG Configuration Option is defined in Section 6.7.6 of 765 [RFC6550]. Its purpose is extended to distribute configuration 766 information affecting the construction and maintenance of the DODAG, 767 as well as operational parameters for RPL on the DODAG, through the 768 DODAG. This Option was originally designed with 4 bit positions 769 reserved for future use as Flags. 771 0 1 2 3 772 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 1 773 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 774 | Type = 0x04 |Opt Length = 14| |P| | |A| ... | 775 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 776 |4 bits | 778 Figure 5: DODAG Configuration Option (Partial View) 780 This specification defines a new flag "Root Proxies EDAR/EDAC" (P). 781 The 'P' flag is encoded in bit position 1 of the reserved Flags in 782 the DODAG Configuration Option (counting from bit 0 as the most 783 significant bit) and it is set to 0 in legacy implementations as 784 specified respectively in Sections 20.14 and 6.7.6 of [RFC6550]. 786 The 'P' flag is set to 1 to indicate that the Root performs the proxy 787 operation, which implies that it supports this specification and the 788 updated RPL Target Option (see Section 6.1). 790 Section 4.3 of [USEofRPLinfo] updates [RFC6550] to indicate that the 791 definition of the Flags applies to Mode of Operation (MOP) values 792 from zero (0) to six (6) only. For a MOP value of 7, the 793 implementation MUST consider that the Root performs the proxy 794 operation. 796 The RPL DODAG Configuration Option is typically placed in a DODAG 797 Information Object (DIO) message. The DIO message propagates down 798 the DODAG to form and then maintain its structure. The DODAG 799 Configuration Option is copied unmodified from parents to children. 800 [RFC6550] states that "Nodes other than the DODAG Root MUST NOT 801 modify this information when propagating the DODAG Configuration 802 option". Therefore, a legacy parent propagates the 'P' Flag as set 803 by the Root, and when the 'P' Flag is set to 1, it is transparently 804 flooded to all the nodes in the DODAG. 806 6.3. Updated RPL Status 808 The RPL Status is defined in section 6.5.1 of [RFC6550] for use in 809 the DAO-ACK message and values are assigned as follows: 811 +---------+--------------------------------+ 812 | Range | Meaning | 813 +---------+--------------------------------+ 814 | 0 | Success/Unqualified acceptance | 815 +---------+--------------------------------+ 816 | 1-127 | Not an outright rejection | 817 +---------+--------------------------------+ 818 | 128-255 | Rejection | 819 +---------+--------------------------------+ 821 Table 1: RPL Status per RFC 6550 823 The 6LoWPAN ND Status was defined for use in the EARO, see section 824 4.1 of [RFC8505]. This specification adds a capability to allow the 825 carriage of 6LoWPAN ND Status values in RPL DAO and DCO messages, 826 embedded in the RPL Status field. 828 To achieve this, the range of the ARO/EARO Status values is reduced 829 to 0-63, which updates the IANA registry created for [RFC6775]. This 830 reduction ensures that the values fit within a RPL Status as shown in 831 Figure 6. See Section 12.2, Section 12.5, and Section 12.6 for the 832 respective IANA declarations. This ask is reasonable because the 833 associated registry relies on standards action for registration and 834 only values up to 10 are currently allocated. 836 0 1 2 3 4 5 6 7 837 +-+-+-+-+-+-+-+-+ 838 |E|A|StatusValue| 839 +-+-+-+-+-+-+-+-+ 841 Figure 6: RPL Status Format 843 This specification updates the RPL Status with subfields as indicated 844 below: 846 E: 1-bit flag. set to 1 to indicate a rejection. When set to 0, a 847 Status value of 0 indicates Success/Unqualified acceptance and 848 other values indicate "not an outright rejection" as per RFC 6550. 850 A: 1-bit flag. Indicates the type of the RPL Status value. 852 Status Value: 6-bit unsigned integer. 854 If the 'A' flag is set to 1 this field transports a value defined 855 for the 6LoWPAN ND EARO Status. 857 When the 'A' flag is set to 0, this field transports a Status 858 Value defined for RPL. 860 When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a EDAC 861 message, the RPL Root MUST copy the 6LoWPAN ND status code unchanged 862 in the RPL Status Value and set the 'A' flag to 1. The RPL Root MUST 863 set the 'E' flag to 1 for all rejection and unknown status codes. 864 The status codes in the 1-10 range [RFC8505] are all considered 865 rejections. 867 Reciprocally, upon a DCO or a DAO-ACK message from the RPL Root with 868 a RPL Status that has the 'A' flag set, the 6LR MUST copy the RPL 869 Status value unchanged in the Status field of the EARO when 870 generating an NA to the RUL. 872 7. Enhancements to draft-ietf-roll-efficient-npdao 874 [EFFICIENT-NPDAO] defines the DCO message for RPL Storing Mode only, 875 with a link-local scope. All nodes in the RPL network are expected 876 to support the specification since the message is processed hop-by- 877 hop along the path that is being cleaned up. 879 This specification extends the use of the DCO message to the Non- 880 Storing MOP, whereby the DCO is sent end-to-end by the Root directly 881 to the RAN that injected the DAO message for the considered target. 882 In that case, intermediate nodes do not need to support 883 [EFFICIENT-NPDAO]; they forward the DCO message as a plain IPv6 884 packet between the Root and the RAN. 886 In the case of a RUL, the 6LR that serves the RUL acts as the RAN 887 that receives the Non-Storing DCO. This specification leverages the 888 Non-Storing DCO between the Root and the 6LR that serves as 889 attachment router for a RUL. A 6LR and a Root that support this 890 specification MUST implement the Non-Storing DCO. 892 8. Enhancements to RFC6775 and RFC8505 894 This document updates [RFC6775] and [RFC8505] to reduce the range of 895 the ND status codes down to 64 values. The two most significant 896 (leftmost) bits if the original ND status field are now reserved, 897 they MUST be set to zero by the sender and ignored by the receiver. 899 This document also updates the behavior of a 6LR acting as RPL router 900 and of a 6LN acting as RUL in the 6LoWPAN ND Address Registration as 901 follows: 903 * If the RPL Root advertises the capability to proxy the EDAR/EDAC 904 exchange to the 6LBR, the 6LR refrains from sending the keep-alive 905 EDAR message. If it is separated from the 6LBR, the Root 906 regenerates the EDAR message to the 6LBR periodically, upon a DAO 907 message that signals the liveliness of the address. 909 * The use of the R Flag is extended to the NA(EARO) to confirm 910 whether the route was installed. 912 9. Protocol Operations for Unicast Addresses 914 The description below assumes that the Root sets the 'P' flag in the 915 DODAG Configuration Option and performs the EDAR proxy operation 916 presented in Section 4.3 . 918 If the 'P' flag is set to 0, the 6LR MUST generate the periodic EDAR 919 messages and process the returned status as specified in [RFC8505]. 920 If the EDAC indicates success, the rest of the flow takes place as 921 presented but without the proxied EDAR/EDAC exchange. 923 Section 9.1 provides an overview of the route injection in RPL, 924 whereas Section 9.2 offers more details from the perspective of the 925 different nodes involved in the flow. 927 9.1. General Flow 929 This specification eliminates the need to exchange keep-alive 930 Extended Duplicate Address messages, EDAR and EDAC, all the way from 931 a 6LN to the 6LBR across a RPL mesh. Instead, the EDAR/EDAC exchange 932 with the 6LBR is proxied by the RPL Root upon the DAO message that 933 refreshes the RPL routing state. The first EDAR upon a new 934 Registration cannot be proxied, though, as it serves for the purpose 935 of DAD, which must be verified before the address is injected in RPL. 937 In a RPL network where the function is enabled, refreshing the state 938 in the 6LBR is the responsibility of the Root. Consequently, only 939 addresses that are injected in RPL will be kept alive at the 6LBR by 940 the RPL Root. Since RULs are advertised using Non-Storing Mode, the 941 DAO message flow and the keep alive EDAR/EDAC can be nested within 942 the Address (re)Registration flow. Figure 7 illustrates that, for 943 the first Registration, both the DAD and the keep-alive EDAR/EDAC 944 exchanges happen in the same sequence. 946 6LN/RUL 6LR <6LR*> Root 6LBR 947 |<---Using ND--->|<--Using RPL->|<-----Using ND---->| 948 | |<-----------Using ND------------->| 949 | | | | 950 | NS(EARO) | | | 951 |--------------->| | 952 | | EDAR | 953 | |--------------------------------->| 954 | | | 955 | | EDAC | 956 | |<---------------------------------| 957 | | | 958 | | DAO(X=0) | | 959 | |------------->| | 960 | | | 961 | | DAO-ACK | | 962 | |<-------------| | 963 | NA(EARO) | | | 964 |<---------------| | | 965 | | | | 966 Figure 7: First RUL Registration Flow 968 This flow requires that the lifetimes and sequence counters in 969 6LoWPAN ND and RPL are aligned. 971 To achieve this, the Path Sequence and the Path Lifetime in the DAO 972 message are taken from the Transaction ID and the Address 973 Registration lifetime in the NS(EARO) message from the 6LN. 975 On the first Address Registration, illustrated in Figure 7 for RPL 976 Non-Storing Mode, the Extended Duplicate Address exchange takes place 977 as prescribed by [RFC8505]. If the exchange fails, the 6LR returns 978 an NA message with a non-zero status to the 6LN, the NCE is not 979 created, and the address is not injected in RPL. Otherwise, the 6LR 980 creates an NCE and injects the Registered Address in the RPL routing 981 using a DAO/DAO-ACK exchange with the RPL DODAG Root. 983 An Address Registration refresh is performed by the 6LN to keep the 984 NCE in the 6LR alive before the lifetime expires. Upon the refresh 985 of a registration, the 6LR reinjects the corresponding route in RPL 986 before it expires, as illustrated in Figure 8. 988 6LN/RUL <-ND-> 6LR <-RPL-> Root <-ND-> 6LBR 989 | | | | 990 | NS(EARO) | | | 991 |--------------->| | | 992 | | DAO(X=1) | | 993 | |------------->| | 994 | | | EDAR | 995 | | |------------------>| 996 | | | EDAC | 997 | | |<------------------| 998 | | DAO-ACK | | 999 | |<-------------| | 1000 | NA(EARO) | | | 1001 |<---------------| | | 1003 Figure 8: Next RUL Registration Flow 1005 This is what causes the RPL Root to refresh the state in the 6LBR, 1006 using an EDAC message. In case of an error in the proxied EDAR flow, 1007 the error is returned in the DAO-ACK using a RPL Status with the 'A' 1008 flag set to 1 that imbeds a 6LoWPAN Status value as discussed in 1009 Section 6.3. 1011 The 6LR may receive a requested DAO-ACK after it received an 1012 asynchronous Non-Storing DCO, but the non-zero status in the DCO 1013 supersedes a positive Status in the DAO-ACK regardless of the order 1014 in which they are received. Upon the DAO-ACK - or the DCO if one 1015 arrives first - the 6LR responds to the RUL with an NA(EARO). 1017 An issue may be detected later, e.g., the address moves to a 1018 different DODAG with the 6LBR attached to a different 6LoWPAN 1019 Backbone router (6BBR), see Figure 5 in section 3.3 of [RFC8929]. 1020 The 6BBR may send a negative ND status, e.g., in an asynchronous 1021 NA(EARO) to the 6LBR. 1023 [RFC8929] expects that the 6LBR is collocated with the RPL Root, but 1024 if not, the 6LBR MUST forward the status code to the originator of 1025 the EDAR, either the 6LR or the RPL Root that proxies for it. The ND 1026 status code is mapped in a RPL Status value by the RPL Root, and then 1027 back by the 6LR. Note that a legacy RAN that receives a Non-Storing 1028 DCO that it does not support will ignore it silently, as specified in 1029 section 6 of [RFC6550]. The result is that it may ignore for a while 1030 that it is no more reachable. The situation will be cleared upon the 1031 next Non-Storing DAO exchange if the error is returned in a DAO-ACK. 1033 Figure 9 illustrates this in the case where the 6LBR and the Root are 1034 not collocated, and the Root proxies the EDAR/EDAC flow. 1036 6LN/RUL <-ND-> 6LR <-RPL-> Root <-ND-> 6LBR <-ND-> 6BBR 1037 | | | | | 1038 | | | | NA(EARO) | 1039 | | | |<------------| 1040 | | | EDAC | | 1041 | | |<-------------| | 1042 | | DCO | | | 1043 | |<------------| | | 1044 | NA(EARO) | | | | 1045 |<-------------| | | | 1046 | | | | | 1048 Figure 9: Asynchronous Issue 1050 If the Root does not proxy, then the EDAC with a non-zero status 1051 reaches the 6LR directly. In that case, the 6LR MUST clean up the 1052 route using a DAO with a Lifetime of zero, and it MUST propagate the 1053 status back to the RUL in a NA(EARO) with the R Flag set to 0. 1055 The RUL may terminate the registration at any time by using a 1056 Registration Lifetime of 0. This specification requires that the RPL 1057 Target Option transports the ROVR. This way, the same flow as the 1058 heartbeat flow is sufficient to inform the 6LBR using the Root as 1059 proxy, as illustrated in Figure 8. 1061 Any combination of the logical functions of 6LR, Root, and 6LBR might 1062 be collapsed in a single node. 1064 9.2. Detailed Operation 1066 The following section specify respectively the behaviour of the 6LN 1067 Acting as RUL, the 6LR Acting as Border router and serving the 6LN, 1068 the RPL Root and the 6LBR in the control flows that enable RPL 1069 routing back to the RUL. 1071 9.2.1. Perspective of the 6LN Acting as RUL 1073 This specification builds on the operation of a 6LoWPAN ND-compliant 1074 6LN/RUL, which is expected to operate as follows: 1076 1. The 6LN selects a 6LR that provides reachability services for a 1077 RUL. This is signaled by a 6CIO in the RA messages with the L, P 1078 and E flags set to 1 as prescribed by [RFC8505]. 1080 2. The 6LN obtains an IPv6 global address, either using Stateless 1081 Address Autoconfiguration (SLAAC) [RFC4862] based on a Prefix 1082 Information Option (PIO) [RFC4861] found in an RA message, or 1083 some other means, such as DHCPv6 [RFC8415]. 1085 3. Once it has formed an address, the 6LN registers its address and 1086 refreshes its registration periodically, early enough within the 1087 Lifetime of the previous Address Registration, as prescribed by 1088 [RFC6775], to refresh the NCE before the lifetime indicated in 1089 the EARO expires. It sets the T Flag to 1 as prescribed in 1090 [RFC8505]. The TID is incremented each time and wraps in a 1091 lollipop fashion (see section 5.2.1 of [RFC8505], which is fully 1092 compatible with section 7.2 of [RFC6550]). 1094 4. As stated in section 5.2 of [RFC8505], the 6LN can register to 1095 more than one 6LR at the same time. In that case, it uses the 1096 same EARO for all of the parallel Address Registrations, with the 1097 exception of the Registration Lifetime field and the setting of 1098 the R flag that may differ. The 6LN may cancel a subset of its 1099 registrations, or transfer a registration from one or more old 1100 6LR(s) to one or more new 6LR(s). To do so, the 6LN sends a 1101 series of NS(EARO) messages, all with the same TID, with a zero 1102 Registration Lifetime to the old 6LR(s) and with a non-zero 1103 Registration Lifetime to the new 6LR(s). In that process, the 1104 6LN SHOULD send the NS(EARO) with a non-zero Registration 1105 Lifetime and ensure that at least one succeeds before it sends an 1106 NS(EARO) that terminates another registration. This avoids the 1107 churn related to transient route invalidation in the RPL network 1108 above the common parent of the involved 6LRs. 1110 5. Following section 5.1 of [RFC8505], a 6LN acting as a RUL sets 1111 the R Flag in the EARO of its registration(s) for which it 1112 requires routing services. If the R Flag is not echoed in the 1113 NA, the RUL MUST consider that establishing the routing services 1114 via this 6LR failed and it SHOULD attempt to use another 6LR. 1115 The RUL SHOULD ensure that one registration succeeds before 1116 setting the R Flag to 0. In case of a conflict with the 1117 preceding rule on lifetime, the rule on lifetime has precedence. 1119 6. The 6LN may use any of the 6LRs to which it registered as the 1120 default gateway. Using a 6LR to which the 6LN is not registered 1121 may result in packets dropped at the 6LR by a Source Address 1122 Validation function (SAVI) [RFC7039] so it is not recommended. 1124 Even without support for RPL, the RUL may be configured with an 1125 opaque value to be provided to the routing protocol. If the RUL has 1126 knowledge of the RPL Instance the packet should be injected into, 1127 then it SHOULD set the Opaque field in the EARO to the RPLInstanceID, 1128 otherwise it MUST leave the Opaque field as zero. 1130 Regardless of the setting of the Opaque field, the 6LN MUST set the 1131 "I" field to zero to signal "topological information to be passed to 1132 a routing process", as specified in section 5.1 of [RFC8505]. 1134 A RUL is not expected to produce RPL artifacts in the data packets, 1135 but it may do so. For instance, if the RUL has minimal awareness of 1136 the RPL Instance then it can build an RPI. A RUL that places an RPI 1137 in a data packet SHOULD indicate the RPLInstanceID of the RPL 1138 Instance where the packet should be forwarded. It is up to the 6LR 1139 (e.g., by policy) to use the RPLInstanceID information provided by 1140 the RUL or rewrite it to the selected RPLInstanceID for forwarding 1141 inside the RPL domain. All the flags and the Rank field are set to 0 1142 as specified by section 11.2 of [RFC6550]. 1144 9.2.2. Perspective of the 6LR Acting as Border router 1146 A 6LR that provides reachability services for a RUL in a RPL network 1147 as specified in this document MUST include a 6CIO in its RA messages 1148 and set the L, P and E flags to 1 as prescribed by [RFC8505]. 1150 As prescribed by [RFC8505], the 6LR generates an EDAR message upon 1151 reception of a valid NS(EARO) message for the registration of a new 1152 IPv6 address by a 6LN. If the initial EDAR/EDAC exchange succeeds, 1153 then the 6LR installs an NCE for the Registration Lifetime. 1155 If the R Flag is set to 1 in the NS(EARO), the 6LR SHOULD inject the 1156 host route in RPL, unless this is barred for other reasons, such as 1157 the saturation of the RPL parents. The 6LR MUST use a RPL Non- 1158 Storing Mode signaling and the updated Target Option (see 1159 Section 6.1). The 6LR SHOULD refrain from setting the 'X' flag to 1160 avoid a redundant EDAR/EDAC flow to the 6LBR. The 6LR MUST request a 1161 DAO-ACK by setting the 'K' flag in the DAO message. Success 1162 injecting the route to the RUL's address is indicated by the 'E' flag 1163 set to 0 in the RPL status of the DAO-ACK message. 1165 For the registration refreshes, if the RPL Root sets the 'P' flag in 1166 the DODAG Configuration Option to 1, then the 6LR MUST refrain from 1167 sending the keep-alive EDAR; instead, it MUST set the 'X' flag to 1 1168 in the Target Option of the DAO messages, to request that the Root 1169 proxies the keep-alive EDAR/EDAC exchange with the 6LBR (see 1170 Section 6); if the 'P' flag is set to 0 then the 6LR MUST set the 'X' 1171 flag to 0 and handle the EDAR/EDAC flow itself. 1173 The Opaque field in the EARO provides a means to signal which RPL 1174 Instance is to be used for the DAO advertisements and the forwarding 1175 of packets sourced at the Registered Address when there is no RPI in 1176 the packet. 1178 As described in [RFC8505], if the "I" field is zero, then the Opaque 1179 field is expected to carry the RPLInstanceID suggested by the 6LN; 1180 otherwise, there is no suggested Instance. If the 6LR participates 1181 in the suggested RPL Instance, then the 6LR MUST use that RPL 1182 Instance for the Registered Address. 1184 If there is no suggested RPL Instance or else if the 6LR does not 1185 participate to the suggested Instance, it is expected that the 1186 packets coming from the 6LN "can unambiguously be associated to at 1187 least one RPL Instance" [RFC6550] by the 6LR, e.g., using a policy 1188 that maps the 6-tuple into an Instance. 1190 The DAO message advertising the Registered Address MUST be 1191 constructed as follows: 1193 1. The Registered Address is signaled as the Target Prefix in the 1194 updated Target Option in the DAO message; the Prefix Length is 1195 set to 128 but the 'F' flag is set to 0 since the advertiser is 1196 not the RUL. The ROVR field is copied unchanged from the EARO 1197 (see Section 6.1). 1199 2. The 6LR indicates one of its global or unique-local IPv6 unicast 1200 addresses as the Parent Address in the TIO associated with the 1201 Target Option 1203 3. The 6LR sets the External 'E' flag in the TIO to indicate that it 1204 is redistributing an external target into the RPL network 1206 4. The Path Lifetime in the TIO is computed from the Registration 1207 Lifetime in the EARO. This operation converts seconds to the 1208 Lifetime Units used in the RPL operation. This creates the 1209 deployment constraint that the Lifetime Unit is reasonably 1210 compatible with the expression of the Registration Lifetime; 1211 e.g., a Lifetime Unit of 0x4000 maps the most significant byte of 1212 the Registration Lifetime to the Path Lifetime. 1214 In that operation, the Path Lifetime must be set to ensure that 1215 the path has a longer lifetime than the registration and covers 1216 in addition the round trip time to the Root. 1218 Note that if the Registration Lifetime is 0, then the Path 1219 Lifetime is also 0 and the DAO message becomes a No-Path DAO, 1220 which cleans up the routes down to the RUL's address; this also 1221 causes the Root as a proxy to send an EDAR message to the 6LBR 1222 with a Lifetime of 0. 1224 5. the Path Sequence in the TIO is set to the TID value found in the 1225 EARO option. 1227 Upon receiving or timing out the DAO-ACK after an implementation- 1228 specific number of retries, the 6LR MUST send the corresponding 1229 NA(EARO) to the RUL. Upon receiving an asynchronous DCO message, it 1230 MUST send an asynchronous NA(EARO) to the RUL immediately, but still 1231 be capable of processing the DAO-ACK if one is pending. 1233 The 6LR MUST set the R Flag to 1 in the NA(EARO) back if and only if 1234 the 'E' flag in the RPL Status is set to 0, indicating that the 6LR 1235 injected the Registered Address in the RPL routing successfully and 1236 that the EDAR proxy operation succeeded. 1238 If the 'A' flag in the RPL Status is set to 1, the embedded Status 1239 value is passed back to the RUL in the EARO Status. If the 'E' flag 1240 is also set to 1, the registration failed for 6LoWPAN-ND-related 1241 reasons, and the NCE is removed. 1243 An error injecting the route causes the 'E' flag to be set to 1. If 1244 the error is not related to ND, the 'A' flag is set to 0. In that 1245 case, the registration succeeds, but the RPL route is not installed. 1246 So the NA(EARO) is returned with a status indicating success but the 1247 R Flag set to 0, which means that the 6LN obtained a binding but no 1248 route. 1250 If the 'A' flag is set to 0 in the RPL Status of the DAO-ACK, then 1251 the 6LoWPAN ND operation succeeded, and an EARO Status of 0 (Success) 1252 MUST be returned to the 6LN. The EARO Status of 0 MUST also be used 1253 if the 6LR did not attempt to inject the route but could create the 1254 binding after a successful EDAR/EDAC exchange or refresh it. 1256 If the 'E' flag is set to 1 in the RPL Status of the DAO-ACK, then 1257 the route was not installed and the R flag MUST be set to 0 in the 1258 NA(EARO). The R flag MUST be set to 0 if the 6LR did not attempt to 1259 inject the route. 1261 In a network where Address Protected Neighbor Discovery (AP-ND) is 1262 enabled, in case of a DAO-ACK or a DCO transporting an EARO Status 1263 value of 5 (Validation Requested), the 6LR MUST challenge the 6LN for 1264 ownership of the address, as described in section 6.1 of [RFC8928], 1265 before the Registration is complete. This flow, illustrated in 1266 Figure 10, ensures that the address is validated before it is 1267 injected in the RPL routing. 1269 If the challenge succeeds, then the operations continue as normal. 1270 In particular, a DAO message is generated upon the NS(EARO) that 1271 proves the ownership of the address. If the challenge failed, the 1272 6LR rejects the registration as prescribed by AP-ND and may take 1273 actions to protect itself against DoS attacks by a rogue 6LN, see 1274 Section 11. 1276 6LN 6LR Root 6LBR 1277 | | | | 1278 |<--------------- RA ---------------------| | | 1279 | | | | 1280 |------ NS EARO (ROVR=Crypto-ID) -------->| | | 1281 | | | | 1282 |<- NA EARO(status=Validation Requested) -| | | 1283 | | | | 1284 |----- NS EARO and Proof-of-ownership -->| | 1285 | | | | 1286 | | | 1287 | | | 1288 |<----------- NA EARO (status=10)--- | | 1289 | | | 1290 | | | 1291 | | | | 1292 | |--------- EDAR ------->| 1293 | | | 1294 | |<-------- EDAC --------| 1295 | | | 1296 | | | | 1297 | |-DAO(X=0)->| | 1298 | | | | 1299 | |<- DAO-ACK-| | 1300 | | | | 1301 |<----------- NA EARO (status=0)----------| | | 1302 | | | | 1303 ... 1304 | | | | 1305 |------ NS EARO (ROVR=Crypto-ID) -------->| | | 1306 | |-DAO(X=1)->| | 1307 | | |-- EDAR -->| 1308 | | | | 1309 | | |<-- EDAC --| 1310 | |<- DAO-ACK-| | 1311 |<----------- NA EARO (status=0)----------| | | 1312 | | | | 1313 ... 1315 Figure 10: Address Protection 1317 The 6LR may at any time send a unicast asynchronous NA(EARO) with the 1318 R Flag set to 0 to signal that it stops providing routing services, 1319 and/or with the EARO Status 2 "Neighbor Cache full" to signal that it 1320 removes the NCE. It may also send a final RA, unicast or multicast, 1321 with a router Lifetime field of zero, to signal that it is ceasing to 1322 serve as router, as specified in section 6.2.5 of [RFC4861]. This 1323 may happen upon a DCO or a DAO-ACK message indicating the path is 1324 already removed; else the 6LR MUST remove the host route to the 6LN 1325 using a DAO message with a Path Lifetime of zero. 1327 A valid NS(EARO) message with the R Flag set to 0 and a Registration 1328 Lifetime that is not zero signals that the 6LN wishes to maintain the 1329 binding but does not require the routing services from the 6LR (any 1330 more). Upon this message, if, due to previous NS(EARO) with the R 1331 Flag set to 1, the 6LR was injecting the host route to the Registered 1332 Address in RPL using DAO messages, then the 6LR MUST invalidate the 1333 host route in RPL using a DAO with a Path Lifetime of zero. It is up 1334 to the Registering 6LN to maintain the corresponding route from then 1335 on, either keeping it active via a different 6LR or by acting as a 1336 RAN and managing its own reachability. 1338 When forwarding a packet from the RUL into the RPL domain, if the 1339 packet does not have an RPI then the 6LR MUST encapsulate the packet 1340 to the Root, and add an RPI. If there is an RPI in the packet, the 1341 6LR MUST rewrite the RPI but it does not need to encapsulate. 1343 9.2.3. Perspective of the RPL Root 1345 A RPL Root MUST set the 'P' flag to 1 in the RPL DODAG Configuration 1346 Option of the DIO messages that it generates (see Section 6) to 1347 signal that it proxies the EDAR/EDAC exchange and supports the 1348 Updated RPL Target option. 1350 Upon reception of a DAO message, for each updated RPL Target Option 1351 (see Section 6.1) with the 'X' flag set to 1, the Root MUST notify 1352 the 6LBR by using a proxied EDAR/EDAC exchange; if the RPL Root and 1353 the 6LBR are integrated, an internal API can be used instead. 1355 The EDAR message MUST be constructed as follows: 1357 1. The Target IPv6 address from the RPL Target Option is placed in 1358 the Registered Address field of the EDAR message; 1360 2. the Registration Lifetime is adapted from the Path Lifetime in 1361 the TIO by converting the Lifetime Units used in RPL into units 1362 of 60 seconds used in the 6LoWPAN ND messages; 1364 3. The TID value is set to the Path Sequence in the TIO and 1365 indicated with an ICMP code of 1 in the EDAR message; 1367 4. The ROVR in the RPL Target Option is copied as is in the EDAR and 1368 the ICMP Code Suffix is set to the appropriate value as shown in 1369 Table 4 of [RFC8505] depending on the size of the ROVR field. 1371 Upon receiving an EDAC message from the 6LBR, if a DAO is pending, 1372 then the Root MUST send a DAO-ACK back to the 6LR. Otherwise, if the 1373 Status in the EDAC message is not "Success", then it MUST send an 1374 asynchronous DCO to the 6LR. 1376 In either case, the EDAC Status is embedded in the RPL Status with 1377 the 'A' flag set to 1. 1379 The proxied EDAR/EDAC exchange MUST be protected with a timer of an 1380 appropriate duration and a number of retries, that are 1381 implementation-dependent, and SHOULD be configurable since the Root 1382 and the 6LBR are typically nodes with a higher capacity and 1383 manageability than 6LRs. Upon timing out, the Root MUST send an 1384 error back to the 6LR as above, either using a DAO-ACK or a DCO, as 1385 appropriate, with the 'A' and 'E' flags set to 1 in the RPL status, 1386 and a RPL Status value of of "6LBR Registry Saturated" [RFC8505]. 1388 9.2.4. Perspective of the 6LBR 1390 The 6LBR is unaware that the RPL Root is not the new attachment 6LR 1391 of the RUL, so it is not impacted by this specification. 1393 Upon reception of an EDAR message, the 6LBR acts as prescribed by 1394 [RFC8505] and returns an EDAC message to the sender. 1396 10. Protocol Operations for Multicast Addresses 1398 Section 12 of [RFC6550] details the RPL support for multicast flows. 1399 This support is activated by the MOP of 3 ("Storing Mode of Operation 1400 with multicast support") in the DIO messages that form the DODAG. 1401 This section also applies if and only if the MOP of the RPLInstance 1402 is 3. 1404 The RPL support of multicast is not source-specific and only operates 1405 as an extension to the Storing Mode of Operation for unicast packets. 1406 Note that it is the RPL model that the multicast packet is passed as 1407 a Layer-2 unicast to each of the interested children. This remains 1408 true when forwarding between the 6LR and the listener 6LN. 1410 "Multicast Listener Discovery Version 2 (MLDv2) for IPv6" [RFC3810] 1411 provides an interface for a listener to register to multicast flows. 1412 In the MLD model, the router is a "querier", and the host is a 1413 multicast listener that registers to the querier to obtain copies of 1414 the particular flows it is interested in. 1416 The equivalent of the first Address Registration happens as 1417 illustrated in Figure 11. The 6LN, as an MLD listener, sends an 1418 unsolicited Report to the 6LR. This enables it to start receiving 1419 the flow immediately, and causes the 6LR to inject the multicast 1420 route in RPL. 1422 This specification does not change MLD but will operate more 1423 efficiently if the asynchronous messages for unsolicited Report and 1424 Done are sent by the 6LN as Layer-2 unicast to the 6LR, in particular 1425 on wireless. 1427 The 6LR acts as a generic MLD querier and generates a DAO with the 1428 Multicast Address as the Target Prefix as described in section 12 of 1429 [RFC6550]. As for the Unicast host routes, the Path Lifetime 1430 associated to the Target is mapped from the Query Interval, and set 1431 to be larger to account for variable propagation delays to the Root. 1432 The Root proxies the MLD exchange as a listener with the 6LBR acting 1433 as the querier, so as to get packets from a source external to the 1434 RPL domain. 1436 Upon a DAO with a Target option for a multicast address, the RPL Root 1437 checks if it is already registered as a listener for that address, 1438 and if not, it performs its own unsolicited Report for the multicast 1439 address as described in section 5.1 of [RFC3810]. The report is 1440 source independent, so there is no Source Address listed. 1442 6LN/RUL 6LR Root 6LBR 1443 | | | | 1444 | unsolicited Report | | | 1445 |------------------->| | | 1446 | | DAO | | 1447 | |-------------->| | 1448 | | DAO-ACK | | 1449 | |<--------------| | 1450 | | | | 1451 | | | unsolicited Report | 1452 | | |---------------------->| 1453 | | | | 1455 Figure 11: First Multicast Registration Flow 1457 The equivalent of the registration refresh is pulled periodically by 1458 the 6LR acting as querier. Upon the timing out of the Query 1459 Interval, the 6LR sends a Multicast Address Specific Query to each of 1460 its listeners, for each Multicast Address, and gets a Report back 1461 that is mapped into a DAO one by one. Optionally, the 6LR MAY send a 1462 General Query, where the Multicast Address field is set to zero. In 1463 that case, the multicast packet is passed as a Layer-2 unicast to 1464 each of the interested children. . 1466 Upon a Report, the 6LR generates a DAO with as many Target Options as 1467 there are Multicast Address Records in the Report message, copying 1468 the Multicast Address field in the Target Prefix of the RPL Target 1469 Option. The DAO message is a Storing Mode DAO, passed to a selection 1470 of the 6LR's parents. 1472 Asynchronously to this, a similar procedure happens between the Root 1473 and a router such as the 6LBR that serves multicast flows on the Link 1474 where the Root is located. Again the Query and Report messages are 1475 source independent. The Root lists exactly once each Multicast 1476 Address for which it has at least one active multicast DAO state, 1477 copying the multicast address in the DAO state in the Multicast 1478 Address field of the Multicast Address Records in the Report message. 1480 This is illustrated in Figure 12: 1482 6LN/RUL 6LR Root 6LBR 1483 | | | | 1484 | Query | | | 1485 |<-------------------| | | 1486 | Report | | | 1487 |------------------->| | | 1488 | | DAO | | 1489 | |-------------->| | 1490 | | DAO-ACK | | 1491 | |<--------------| | 1492 | | | Query | 1493 | | |<-------------------| 1494 | | | Report | 1495 | | |------------------->| 1496 | | | | 1498 Figure 12: Next Registration Flow 1500 Note that any of the functions 6LR, Root and 6LBR might be collapsed 1501 in a single node, in which case the flow above happens internally, 1502 and possibly through internal API calls as opposed to messaging. 1504 11. Security Considerations 1506 It is worth noting that with [RFC6550], every node in the LLN is RPL- 1507 aware and can inject any RPL-based attack in the network. This 1508 specification improves the situation by isolating edge nodes that can 1509 only interact with the RPL routers using 6LoWPAN ND, meaning that 1510 they cannot perform RPL insider attacks. 1512 The LLN nodes depend on the 6LBR and the RPL participants for their 1513 operation. A trust model must be put in place to ensure that the 1514 right devices are acting in these roles, so as to avoid threats such 1515 as black-holing, (see [RFC7416] section 7), Denial-Of-Service attacks 1516 whereby a rogue 6LR creates a high churn in the RPL network by 1517 advertising and removing many forged addresses, or bombing attack 1518 whereby an impersonated 6LBR would destroy state in the network by 1519 using the status code of 4 ("Removed"). 1521 This trust model could be at a minimum based on a Layer-2 Secure 1522 joining and the Link-Layer security. This is a generic 6LoWPAN 1523 requirement, see Req5.1 in Appendix B.5 of [RFC8505]. 1525 In a general manner, the Security Considerations in [RFC6550], 1526 [RFC7416] [RFC6775], and [RFC8505] apply to this specification as 1527 well. 1529 The Link-Layer security is needed in particular to prevent Denial-Of- 1530 Service attacks whereby a rogue 6LN creates a high churn in the RPL 1531 network by constantly registering and deregistering addresses with 1532 the R Flag set to 1 in the EARO. 1534 [RFC8928] updated 6LoWPAN ND with the called Address-Protected 1535 Neighbor Discovery (AP-ND). AP-ND protects the owner of an address 1536 against address theft and impersonation attacks in a Low-Power and 1537 Lossy Network (LLN). Nodes supporting the extension compute a 1538 cryptographic identifier (Crypto-ID), and use it with one or more of 1539 their Registered Addresses. The Crypto-ID identifies the owner of 1540 the Registered Address and can be used to provide proof of ownership 1541 of the Registered Addresses. Once an address is registered with the 1542 Crypto-ID and a proof of ownership is provided, only the owner of 1543 that address can modify the registration information, thereby 1544 enforcing Source Address Validation. [RFC8928] reduces even more the 1545 attack perimeter that is available to the edge nodes and its use is 1546 suggested in this specification. 1548 Additionally, the trust model could include a role validation (e.g., 1549 using a role-based authorization) to ensure that the node that claims 1550 to be a 6LBR or a RPL Root is entitled to do so. 1552 The Opaque field in the EARO enables the RUL to suggest a 1553 RPLInstanceID where its traffic is placed. It is also possible for 1554 an attacker RUL to include an RPI in the packet. This opens to 1555 attacks where a RPL instance would be reserved for critical traffic, 1556 e.g., with a specific bandwidth reservation, that the additional 1557 traffic generated by a rogue may disrupt. The attack may be 1558 alleviated by traditional access control and traffic shaping 1559 mechanisms where the 6LR controls the incoming traffic from the 6LN. 1560 More importantly, the 6LR is the node that injects the traffic in the 1561 RPL domain, so it has the final word on which RPLInstance is to be 1562 used for the traffic coming from the RUL, per its own policy. In 1563 particular, a policy can override the formal language that forces to 1564 use the Opaque field or to rewrite the RPI provided by the RUL, in a 1565 situation where the network administrator finds it relevant. 1567 At the time of this writing, RPL does not have a Route Ownership 1568 Validation model whereby it is possible to validate the origin of an 1569 address that is injected in a DAO. This specification makes a first 1570 step in that direction by allowing the Root to challenge the RUL via 1571 the 6LR that serves it. 1573 Section 6.1 indicates that when the length of the ROVR field is 1574 unknown, the RPL Target Option must be passed on as received in RPL 1575 storing Mode. This creates a possible opening for using DAO messages 1576 as a covert channel. Note that DAO messages are rare and overusing 1577 that channel could be detected. An implementation SHOULD notify the 1578 network management when a RPL Target Option is receives with an 1579 unknown ROVR field size, to ensure that the situation is known to the 1580 network administrator. 1582 [EFFICIENT-NPDAO] introduces the ability for a rogue common ancestor 1583 node to invalidate a route on behalf of the target node. In this 1584 case, the RPL Status in the DCO has the 'A' flag set to 0, and a 1585 NA(EARO) is returned to the 6LN with the R flag set to 0. This 1586 encourages the 6LN to try another 6LR. If a 6LR exists that does not 1587 use the rogue common ancestor, then the 6LN will eventually succeed 1588 gaining reachability over the RPL network in spite of the rogue node. 1590 12. IANA Considerations 1592 12.1. Fixing the Address Registration Option Flags 1594 Section 9.1 of [RFC8505] creates a Registry for the 8-bit Address 1595 Registration Option Flags field. IANA is requested to rename the 1596 first column of the table from "ARO Status" to "Bit number". 1598 12.2. Resizing the ARO Status values 1600 Section 12 of [RFC6775] creates the Address Registration Option 1601 Status values Registry with a range 0-255. 1603 This specification reduces that range to 0-63, see Section 6.3. 1605 IANA is requested to modify the Address Registration Option Status 1606 values Registry so that the upper bound of the unassigned values is 1607 63. This document should be added as a reference. The registration 1608 procedure does not change. 1610 12.3. New RPL DODAG Configuration Option Flag 1612 IANA is requested to assign a flag from the "DODAG Configuration 1613 Option Flags for MOP 0..6" [USEofRPLinfo] registry as follows: 1615 +---------------+----------------------------+-----------+ 1616 | Bit Number | Capability Description | Reference | 1617 +---------------+----------------------------+-----------+ 1618 | 1 (suggested) | Root Proxies EDAR/EDAC (P) | THIS RFC | 1619 +---------------+----------------------------+-----------+ 1621 Table 2: New DODAG Configuration Option Flag 1623 IANA is requested to add [this document] as a reference for MOP 7 in 1624 the RPL Mode of Operation registry. 1626 12.4. RPL Target Option Registry 1628 This document modifies the "RPL Target Option Flags" registry 1629 initially created in Section 20.15 of [RFC6550] . The registry now 1630 includes only 4 bits (Section 6.1) and should point to this document 1631 as an additional reference. The registration procedure does not 1632 change. 1634 Section 6.1 also defines 2 new entries in the Registry as follows: 1636 +---------------+--------------------------------+-----------+ 1637 | Bit Number | Capability Description | Reference | 1638 +---------------+--------------------------------+-----------+ 1639 | 0 (suggested) | Advertiser address in Full (F) | THIS RFC | 1640 +---------------+--------------------------------+-----------+ 1641 | 1 (suggested) | Proxy EDAR Requested (X) | THIS RFC | 1642 +---------------+--------------------------------+-----------+ 1644 Table 3: RPL Target Option Registry 1646 12.5. New Subregistry for RPL Non-Rejection Status values 1648 This specification creates a new Subregistry for the RPL Non- 1649 Rejection Status values for use in the RPL DAO-ACK, DCO, and DCO-ACK 1650 messages with the 'A' flag set to 0, under the RPL registry. 1652 * Possible values are 6-bit unsigned integers (0..63). 1654 * Registration procedure is "IETF Review" [RFC8126]. 1656 * Initial allocation is as indicated in Table 4: 1658 +-------+------------------------+---------------------+ 1659 | Value | Meaning | Reference | 1660 +-------+------------------------+---------------------+ 1661 | 0 | Unqualified acceptance | THIS RFC / RFC 6550 | 1662 +-------+------------------------+---------------------+ 1663 | 1..63 | Unassigned | | 1664 +-------+------------------------+---------------------+ 1666 Table 4: Acceptance values of the RPL Status 1668 12.6. New Subregistry for RPL Rejection Status values 1670 This specification creates a new Subregistry for the RPL Rejection 1671 Status values for use in the RPL DAO-ACK and DCO messages with the 1672 'A' flag set to 0, under the RPL registry. 1674 * Possible values are 6-bit unsigned integers (0..63). 1676 * Registration procedure is "IETF Review" [RFC8126]. 1678 * Initial allocation is as indicated in Table 5: 1680 +--------------------+-----------------------+-------------------+ 1681 | Value | Meaning | Reference | 1682 +--------------------+-----------------------+-------------------+ 1683 | 0 | Unqualified rejection | THIS RFC | 1684 +--------------------+-----------------------+-------------------+ 1685 | 1 (suggested in | No routing entry | [EFFICIENT-NPDAO] | 1686 | [EFFICIENT-NPDAO]) | | | 1687 +--------------------+-----------------------+-------------------+ 1688 | 2..63 | Unassigned | | 1689 +--------------------+-----------------------+-------------------+ 1691 Table 5: Rejection values of the RPL Status 1693 13. Acknowledgments 1695 The authors wish to thank Ines Robles, Georgios Papadopoulos and 1696 especially Rahul Jadhav and Alvaro Retana for their reviews and 1697 contributions to this document. Also many thanks to Eric Vyncke, 1698 Erik Kline, Murray Kucherawy, Peter Van der Stok, Carl Wallace, Barry 1699 Leiba, Julien Meuric, and especially Benjamin Kaduk and Elwyn Davies, 1700 for their reviews and useful comments during the IETF Last Call and 1701 the IESG review sessions. 1703 14. Normative References 1705 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1706 Requirement Levels", BCP 14, RFC 2119, 1707 DOI 10.17487/RFC2119, March 1997, 1708 . 1710 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1711 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1712 DOI 10.17487/RFC3810, June 2004, 1713 . 1715 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1716 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1717 DOI 10.17487/RFC4861, September 2007, 1718 . 1720 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1721 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1722 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1723 Low-Power and Lossy Networks", RFC 6550, 1724 DOI 10.17487/RFC6550, March 2012, 1725 . 1727 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1728 Bormann, "Neighbor Discovery Optimization for IPv6 over 1729 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1730 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1731 . 1733 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1734 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1735 2014, . 1737 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 1738 IPv6 over Low-Power Wireless Personal Area Networks 1739 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 1740 2014, . 1742 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1743 Writing an IANA Considerations Section in RFCs", BCP 26, 1744 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1745 . 1747 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1748 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1749 May 2017, . 1751 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1752 (IPv6) Specification", STD 86, RFC 8200, 1753 DOI 10.17487/RFC8200, July 2017, 1754 . 1756 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node 1757 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504, 1758 January 2019, . 1760 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1761 Perkins, "Registration Extensions for IPv6 over Low-Power 1762 Wireless Personal Area Network (6LoWPAN) Neighbor 1763 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1764 . 1766 [RFC8928] Thubert, P., Ed., Sarikaya, B., Sethi, M., and R. Struik, 1767 "Address-Protected Neighbor Discovery for Low-Power and 1768 Lossy Networks", RFC 8928, DOI 10.17487/RFC8928, November 1769 2020, . 1771 [USEofRPLinfo] 1772 Robles, I., Richardson, M., and P. Thubert, "Using RPI 1773 Option Type, Routing Header for Source Routes and IPv6-in- 1774 IPv6 encapsulation in the RPL Data Plane", Work in 1775 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-43, 1776 10 January 2021, . 1779 [EFFICIENT-NPDAO] 1780 Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient 1781 Route Invalidation", Work in Progress, Internet-Draft, 1782 draft-ietf-roll-efficient-npdao-18, 15 April 2020, 1783 . 1786 15. Informative References 1788 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1789 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1790 Overview, Assumptions, Problem Statement, and Goals", 1791 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1792 . 1794 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1795 Address Autoconfiguration", RFC 4862, 1796 DOI 10.17487/RFC4862, September 2007, 1797 . 1799 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1800 Power and Lossy Networks (RPL) Option for Carrying RPL 1801 Information in Data-Plane Datagrams", RFC 6553, 1802 DOI 10.17487/RFC6553, March 2012, 1803 . 1805 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1806 Routing Header for Source Routes with the Routing Protocol 1807 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1808 DOI 10.17487/RFC6554, March 2012, 1809 . 1811 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1812 Statement and Requirements for IPv6 over Low-Power 1813 Wireless Personal Area Network (6LoWPAN) Routing", 1814 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1815 . 1817 [RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed., 1818 "Source Address Validation Improvement (SAVI) Framework", 1819 RFC 7039, DOI 10.17487/RFC7039, October 2013, 1820 . 1822 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1823 Constrained-Node Networks", RFC 7228, 1824 DOI 10.17487/RFC7228, May 2014, 1825 . 1827 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1828 "IPv6 over Low-Power Wireless Personal Area Network 1829 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1830 April 2017, . 1832 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 1833 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 1834 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 1835 RFC 8415, DOI 10.17487/RFC8415, November 2018, 1836 . 1838 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1839 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1840 DOI 10.17487/RFC6282, September 2011, 1841 . 1843 [RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur, 1844 Ed., "Performance Evaluation of the Routing Protocol for 1845 Low-Power and Lossy Networks (RPL)", RFC 6687, 1846 DOI 10.17487/RFC6687, October 2012, 1847 . 1849 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1850 and M. Richardson, Ed., "A Security Threat Analysis for 1851 the Routing Protocol for Low-Power and Lossy Networks 1852 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1853 . 1855 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1856 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1857 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1858 . 1860 [RFC8929] Thubert, P., Ed., Perkins, C.E., and E. Levy-Abegnoli, 1861 "IPv6 Backbone Router", RFC 8929, DOI 10.17487/RFC8929, 1862 November 2020, . 1864 Appendix A. Example Compression 1866 Figure 13 illustrates the case in Storing Mode where the packet is 1867 received from the Internet, then the Root encapsulates the packet to 1868 insert the RPI and deliver to the 6LR that is the parent and last hop 1869 to the final destination, which is not known to support [RFC8138]. 1871 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1872 |11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP 1873 |Page 1 |Type1 S=0| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 1874 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1875 <-4 bytes-> <- RFC 6282 -> 1876 <- No RPL artifact ... 1878 Figure 13: Encapsulation to Parent 6LR in Storing Mode 1880 The difference with the example presented in Figure 19 of [RFC8138] 1881 is the addition of a SRH-6LoRH before the RPI-6LoRH to transport the 1882 compressed address of the 6LR as the destination address of the outer 1883 IPv6 header. In the [RFC8138] example the destination IP of the 1884 outer header was elided and was implicitly the same address as the 1885 destination of the inner header. Type 1 was arbitrarily chosen, and 1886 the size of 0 denotes a single address in the SRH. 1888 In Figure 13, the source of the IPv6-in-IPv6 encapsulation is the 1889 Root, so it is elided in the IPv6-in-IPv6 6LoRH. The destination is 1890 the parent 6LR of the destination of the encapsulated packet so it 1891 cannot be elided. If the DODAG is operated in Storing Mode, it is 1892 the single entry in the SRH-6LoRH and the SRH-6LoRH Size is encoded 1893 as 0. The SRH-6LoRH is the first 6LoRH in the chain. In this 1894 particular example, the 6LR address can be compressed to 2 bytes so a 1895 Type of 1 is used. It results that the total length of the SRH-6LoRH 1896 is 4 bytes. 1898 In Non-Storing Mode, the encapsulation from the Root would be similar 1899 to that represented in Figure 13 with possibly more hops in the SRH- 1900 6LoRH and possibly multiple SRH-6LoRHs if the various addresses in 1901 the routing header are not compressed to the same format. Note that 1902 on the last hop to the parent 6LR, the RH3 is consumed and removed 1903 from the compressed form, so the use of Non-Storing Mode vs. Storing 1904 Mode is indistinguishable from the packet format. 1906 The SRH-6LoRHs are followed by RPI-6LoRH and then the IPv6-in-IPv6 1907 6LoRH. When the IPv6-in-IPv6 6LoRH is removed, all the 6LoRH Headers 1908 that precede it are also removed. The Paging Dispatch [RFC8025] may 1909 also be removed if there was no previous Page change to a Page other 1910 than 0 or 1, since the LOWPAN_IPHC is encoded in the same fashion in 1911 the default Page 0 and in Page 1. The resulting packet to the 1912 destination is the encapsulated packet compressed with [RFC6282]. 1914 Authors' Addresses 1916 Pascal Thubert (editor) 1917 Cisco Systems, Inc 1918 Building D 1919 45 Allee des Ormes - BP1200 1920 06254 Mougins - Sophia Antipolis 1921 France 1923 Phone: +33 497 23 26 34 1924 Email: pthubert@cisco.com 1925 Michael C. Richardson 1926 Sandelman Software Works 1928 Email: mcr+ietf@sandelman.ca 1929 URI: http://www.sandelman.ca/