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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: 19 June 2021 16 December 2020 8 Routing for RPL Leaves 9 draft-ietf-roll-unaware-leaves-26 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 19 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 . . . . . . . . . . . . . . . . . . . . . . . . . 5 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 . . . . . . . 18 76 8. Enhancements to RFC 6775 and RFC8505 . . . . . . . . . . . . 19 77 9. Protocol Operations for Unicast Addresses . . . . . . . . . . 19 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 . . . 24 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 . . . . . . . . . . . . . . . . . . . 32 86 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 87 12.1. Fixing the Address Registration Option Flags . . . . . . 34 88 12.2. Resizing the ARO Status values . . . . . . . . . . . . . 34 89 12.3. New RPL DODAG Configuration Option Flag . . . . . . . . 34 90 12.4. RPL Target Option Registry . . . . . . . . . . . . . . . 35 91 12.5. New Subregistry for RPL Non-Rejection Status values . . 35 92 12.6. New Subregistry for RPL Rejection Status values . . . . 36 93 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 36 94 14. Normative References . . . . . . . . . . . . . . . . . . . . 36 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, and can protect RUL for 160 its address ownership. 162 This document specifies how the router injects the host routes in the 163 RPL domain on behalf of the RUL. Section 5 details how the RUL can 164 leverage 6LoWPAN ND to obtain the routing services from the router. 165 In that model, the RUL is also a 6LoWPAN Node (6LN) and the RPL-Aware 166 router is also a 6LoWPAN router (6LR). Using the 6LoWPAN ND Address 167 Registration mechanism, the RUL signals that the router must inject a 168 host route for the Registered Address. 170 ------+--------- 171 | Internet 172 | 173 +-----+ 174 | | <------------- 6LBR / RPL Root 175 +-----+ ^ 176 | | 177 o o o o | RPL 178 o o o o o o o o | 179 o o o o o o o o o o | + 180 o o o o o o o | 181 o o o o o o o o o | 6LoWPAN ND 182 o o o o o o | 183 o o o o v 184 o o o <------------- 6LR / RPL Border router 185 ^ 186 | 6LoWPAN ND only 187 v 188 u <------------- 6LN / RPL-Unaware Leaf 190 Figure 1: Injecting Routes on behalf of RULs 192 The RPL Non-Storing Mode mechanism is used to extend the routing 193 state with connectivity to the RULs even when the DODAG is operated 194 in Storing Mode. The unicast packet forwarding operation by the 6LR 195 serving a RUL is described in section 4.1 of [USEofRPLinfo]. 197 Examples of possible RULs include severely energy constrained sensors 198 such as window smash sensor (alarm system), and kinetically powered 199 light switches. Other applications of this specification may include 200 a smart grid network that controls appliances - such as washing 201 machines or the heating system - in the home. Appliances may not 202 participate to the RPL protocol operated in the Smartgrid network but 203 can still interact with the Smartgrid for control and/or metering. 205 This document is organized as follows: 207 * Section 3 and Section 4 present in a non-normative fashion the 208 salient aspects of RPL and 6LoWPAN ND, respectively, that are 209 leveraged in this specification to provide connectivity to a 6LN 210 acting as a RUL across a RPL network. 212 * Section 5 lists the expectations that a RUL needs to match in 213 order to be served by a RPL router that complies with this 214 specification. 216 * Section 6 presents the changes made to [RFC6550]; a new behavior 217 is introduced whereby the 6LR advertises the 6LN's addresses in a 218 RPL DAO message based on the ND registration by the 6LN, and the 219 RPL root performs the EDAR/EDAC exchange with the 6LBR on behalf 220 of the 6LR; modifications are introduced to some RPL options and 221 to the RPL Status to facilitate the integration of the protocols. 223 * Section 7 presents the changes made to [EFFICIENT-NPDAO]; the use 224 of the DCO message is extended to the Non-Storing MOP to report 225 asynchronous issues from the Root to the 6LR. 227 * Section 8 presents the changes made to [RFC6775] and [RFC8505]; 228 The range of the ND status codes is reduced down to 64 values, and 229 the remaining bits in the original status field are now reserved. 231 * Section 9 and Section 10 present the operation of this 232 specification for unicast and multicast flows, respectively, and 233 Section 11 presents associated security considerations. 235 2. Terminology 236 2.1. Requirements Language 238 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 239 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 240 "OPTIONAL" in this document are to be interpreted as described in BCP 241 14 [RFC2119] [RFC8174] when, and only when, they appear in all 242 capitals, as shown here. 244 2.2. Glossary 246 This document uses the following acronyms: 248 AR: Address Resolution (aka Address Lookup) 249 ARQ: Automatic Repeat reQuest 250 6CIO: 6LoWPAN Capability Indication Option 251 6LN: 6LoWPAN Node (a Low Power host or router) 252 6LR: 6LoWPAN router 253 6LBR: 6LoWPAN Border router 254 (E)ARO: (Extended) Address Registration Option 255 (E)DAR: (Extended) Duplicate Address Request 256 (E)DAC: (Extended) Duplicate Address Confirmation 257 DAD: Duplicate Address Detection 258 DAO: Destination Advertisement Object (a RPL message) 259 DCO: Destination Cleanup Object (a RPL message) 260 DIS: DODAG Information solicitation (a RPL message) 261 DIO: DODAG Information Object (a RPL message) 262 DODAG: Destination-Oriented Directed Acyclic Graph 263 LLN: Low-Power and Lossy Network 264 MOP: RPL Mode of Operation 265 NA: Neighbor Advertisement 266 NCE: Neighbor Cache Entry 267 ND: Neighbor Discovery 268 NS: Neighbor solicitation 269 RA: router Advertisement 270 ROVR: Registration Ownership Verifier 271 RPI: RPL Packet Information 272 RAL: RPL-aware Leaf 273 RAN: RPL-Aware Node (either a RPL router or a RPL-aware Leaf) 274 RUL: RPL-Unaware Leaf 275 SRH: Source-Routing Header 276 TID: Transaction ID (a sequence counter in the EARO) 278 2.3. References 280 The Terminology used in this document is consistent with and 281 incorporates that described in "Terms Used in Routing for Low-Power 282 and Lossy Networks (LLNs)" [RFC7102]. A glossary of classical 283 6LoWPAN acronyms is given in Section 2.2. Other terms in use in LLNs 284 are found in "Terminology for Constrained-Node Networks" [RFC7228]. 285 This specification uses the terms 6LN and 6LR to refer specifically 286 to nodes that implement the 6LN and 6LR roles in 6LoWPAN ND and does 287 not expect other functionality such as 6LoWPAN Header Compression 288 [RFC6282] from those nodes. 290 "RPL", the "RPL Packet Information" (RPI), "RPL Instance" (indexed by 291 a RPLInstanceID), "up", "down" are defined in "RPL: IPv6 Routing 292 Protocol for Low-Power and Lossy Networks" [RFC6550]. The RPI is the 293 abstract information that RPL defines to be placed in data packets, 294 e.g., as the RPL Option [RFC6553] within the IPv6 Hop-By-Hop Header. 295 By extension, the term "RPI" is often used to refer to the RPL Option 296 itself. The DODAG Information solicitation (DIS), Destination 297 Advertisement Object (DAO) and DODAG Information Object (DIO) 298 messages are also specified in [RFC6550]. The Destination Cleanup 299 Object (DCO) message is defined in [EFFICIENT-NPDAO]. 301 This document uses the terms RPL-Unaware Leaf (RUL), RPL-Aware Node 302 (RAN) and RPL aware Leaf (RAL) consistently with [USEofRPLinfo]. A 303 RAN is either an RAL or a RPL router. As opposed to a RUL, a RAN 304 manages the reachability of its addresses and prefixes by injecting 305 them in RPL by itself. 307 In this document, readers will encounter terms and concepts that are 308 discussed in the following documents: 310 Classical IPv6 ND: "Neighbor Discovery for IP version 6" [RFC4861] 311 and "IPv6 Stateless Address Autoconfiguration" [RFC4862], 313 6LoWPAN: "Problem Statement and Requirements for IPv6 over Low-Power 314 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606] and 315 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 316 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 317 and 319 6LoWPAN ND: Neighbor Discovery Optimization for Low-Power and Lossy 320 Networks [RFC6775], "Registration Extensions for 6LoWPAN Neighbor 321 Discovery" [RFC8505], and "Address Protected Neighbor Discovery 322 for Low-power and Lossy Networks" [RFC8928]. 324 3. RPL External Routes and Dataplane Artifacts 326 Section 4.1 of [USEofRPLinfo] provides a set of rules summarized 327 below that must be followed for routing packets from and to a RUL. 329 A 6LR that acts as a border router for external routes advertises 330 them using Non-Storing Mode DAO messages that are unicast directly to 331 the Root, even if the DODAG is operated in Storing Mode. Non-Storing 332 Mode routes are not visible inside the RPL domain and all packets are 333 routed via the Root. The RPL Root tunnels the packets directly to 334 the 6LR that advertised the external route, which decapsulates and 335 forwards the original (inner) packet. 337 The RPL Non-Storing MOP signaling and the associated IPv6-in-IPv6 338 encapsulated packets appear as normal traffic to the intermediate 339 routers. The support of external routes only impacts the Root and 340 the 6LR. It can be operated with legacy intermediate routers and 341 does not add to the amount of state that must be maintained in those 342 routers. A RUL is an example of a destination that is reachable via 343 an external route that happens to be also a host route. 345 The RPL data packets typically carry a Hop-by-Hop Header with a RPL 346 Option [RFC6553] that contains the Packet Information (RPI) defined 347 in section 11.2 of [RFC6550]. Unless the RUL already placed a RPL 348 Option in outer header chain, the packets from and to the RUL are 349 encapsulated using an IPv6-in-IPv6 tunnel between the Root and the 350 6LR that serves the RUL (see sections 7 and 8 of [USEofRPLinfo] for 351 details). If the packet from the RUL has an RPI, the 6LR as a RPL 352 border router SHOULD rewrite the RPI to indicate the selected 353 Instance and set the flags, but it does not need to encapsulate the 354 packet. 356 In Non-Storing Mode, packets going down carry a Source Routing Header 357 (SRH). The IPv6-in-IPv6 encapsulation, the RPI and the SRH are 358 collectively called the "RPL artifacts" and can be compressed using 359 [RFC8138]. Appendix A presents an example compressed format for a 360 packet forwarded by the Root to a RUL in a Storing Mode DODAG. 362 The inner packet that is forwarded to the RUL may carry some RPL 363 artifacts, e.g., an RPI if the original packet was generated with it, 364 and an SRH in a Non-Storing Mode DODAG. [USEofRPLinfo] expects the 365 RUL to support the basic "IPv6 Node Requirements" [RFC8504] and in 366 particular the mandates in Sections 4.2 and 4.4 of [RFC8200]. As 367 such, the RUL is expected to ignore the RPL artifacts that may be 368 left over, either an SRH with zero Segments Left or a RPL Option in 369 the Hop-by-Hop Header, which can be skipped when not recognized, see 370 Section 5 for more. 372 A RUL is not expected to support the compression method defined in 373 [RFC8138]. For that reason, the border router uncompresses the 374 packet before forwarding it over an external route to a RUL 375 [USEofRPLinfo]. 377 4. 6LoWPAN Neighbor Discovery 379 This section goes through the 6LoWPAN ND mechanisms that this 380 specification leverages, as a non-normative reference to the reader. 381 The full normative text is to be found in [RFC6775], [RFC8505], and 382 [RFC8928]. 384 4.1. RFC 6775 Address Registration 386 The classical "IPv6 Neighbor Discovery (IPv6 ND) Protocol" [RFC4861] 387 [RFC4862] was defined for serial links and transit media such as 388 Ethernet. It is a reactive protocol that relies heavily on multicast 389 operations for Address Discovery (aka Lookup) and Duplicate Address 390 Detection (DAD). 392 "Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775] 393 adapts IPv6 ND for operations over energy-constrained LLNs. The main 394 functions of [RFC6775] are to proactively establish the Neighbor 395 Cache Entry (NCE) in the 6LR and to prevent address duplication. To 396 that effect, [RFC6775] introduces a new unicast Address Registration 397 mechanism that contributes to reducing the use of multicast messages 398 compared to the classical IPv6 ND protocol. 400 [RFC6775] defines a new Address Registration Option (ARO) that is 401 carried in the unicast Neighbor solicitation (NS) and Neighbor 402 Advertisement (NA) messages between the 6LoWPAN Node (6LN) and the 403 6LoWPAN router (6LR). It also defines the Duplicate Address Request 404 (DAR) and Duplicate Address Confirmation (DAC) messages between the 405 6LR and the 6LoWPAN Border router (6LBR). In an LLN, the 6LBR is the 406 central repository of all the Registered Addresses in its domain and 407 the source of truth for uniqueness and ownership. 409 4.2. RFC 8505 Extended Address Registration 411 "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505] 412 updates the behavior of RFC 6775 to enable a generic Address 413 Registration to services such as routing and ND proxy, and defines 414 the Extended Address Registration Option (EARO) as shown in Figure 2: 416 0 1 2 3 417 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 1 418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 419 | Type | Length | Status | Opaque | 420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 421 | Rsvd | I |R|T| TID | Registration Lifetime | 422 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 423 | | 424 ... Registration Ownership Verifier ... 425 | | 426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 428 Figure 2: EARO Option Format 430 4.2.1. R Flag 432 [RFC8505] introduces the R Flag in the EARO. The Registering Node 433 sets the R Flag to indicate whether the 6LR should ensure 434 reachability for the Registered Address. If the R Flag is set to 0, 435 then the Registering Node handles the reachability of the Registered 436 Address by other means. In a RPL network, this means that either it 437 is a RAN that injects the route by itself or that it uses another RPL 438 router for reachability services. 440 This document specifies how the R Flag is used in the context of RPL. 441 A RPL leaf that implements the 6LN functionality in [RFC8505] 442 requires reachability services for an IPv6 address if and only if it 443 sets the R Flag in the NS(EARO) used to register the address to a 6LR 444 acting as a RPL border router. Upon receiving the NS(EARO), the RPL 445 router generates a DAO message for the Registered Address if and only 446 if the R flag is set to 1. 448 Section 9.2 specifies additional operations when R flag is set to 1 449 in an EARO that is placed either in an NS or an NA message. 451 4.2.2. TID, "I" Field and Opaque Fields 453 When the T Flag is set to 1, the EARO includes a sequence counter 454 called Transaction ID (TID), that is needed to fill the Path Sequence 455 Field in the RPL Transit Option. This is the reason why the support 456 of [RFC8505] by the RUL, as opposed to only [RFC6775] is a 457 prerequisite for this specification)/; this requirement is fully 458 explained in Section 5.1. The EARO also transports an Opaque field 459 and an associated "I" field that describes what the Opaque field 460 transports and how to use it. 462 Section 9.2.1 specifies the use of the "I" field and the Opaque field 463 by a RUL. 465 4.2.3. Route Ownership Verifier 467 Section 5.3 of [RFC8505] introduces the Registration Ownership 468 Verifier (ROVR) field of variable length from 64 to 256 bits. The 469 ROVR is a replacement of the EUI-64 in the ARO [RFC6775] that was 470 used to identify uniquely an Address Registration with the Link-Layer 471 address of the owner but provided no protection against spoofing. 473 "Address Protected Neighbor Discovery for Low-power and Lossy 474 Networks" [RFC8928] leverages the ROVR field as a cryptographic proof 475 of ownership to prevent a rogue third party from registering an 476 address that is already owned. The use of ROVR field enables the 6LR 477 to block traffic that is not sourced at an owned address. 479 This specification does not address how the protection by [RFC8928] 480 could be extended for use in RPL. On the other hand, it adds the 481 ROVR to the DAO to build the proxied EDAR at the Root (see 482 Section 6.1), which means that nodes that are aware of the host route 483 are also aware of the ROVR associated to the Target Address. 485 4.3. RFC 8505 Extended DAR/DAC 487 [RFC8505] updates the DAR/DAC messages into the Extended DAR/DAC to 488 carry the ROVR field. The EDAR/EDAC exchange takes place between the 489 6LR and the 6LBR. It is triggered by an NS(EARO) message from a 6LN 490 to create, refresh, and delete the corresponding state in the 6LBR. 491 The exchange is protected by the retry mechanism (ARQ) specified in 492 Section 8.2.6 of [RFC6775], though in an LLN, a duration longer than 493 the default value of the RetransTimer (RETRANS_TIMER) [RFC4861] of 1 494 second may be necessary to cover the round trip delay between the 6LR 495 and the 6LBR. 497 RPL [RFC6550] specifies a periodic DAO from the 6LN all the way to 498 the Root that maintains the routing state in the RPL network for the 499 lifetime indicated by the source of the DAO. This means that for 500 each address, there are two keep-alive messages that traverse the 501 whole network, one to the Root and one to the 6LBR. 503 This specification avoids the periodic EDAR/EDAC exchange across the 504 LLN. The 6LR turns the periodic NS(EARO) from the RUL into a DAO 505 message to the Root on every refresh, but it only generates the EDAR 506 upon the first registration, for the purpose of DAD, which must be 507 verified before the address is injected in RPL. Upon the DAO 508 message, the Root proxies the EDAR exchange to refresh the state at 509 the 6LBR on behalf of the 6LR, as illustrated in Figure 8 in 510 Section 9.1. 512 4.3.1. RFC 7400 Capability Indication Option 514 "6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power 515 Wireless Personal Area Networks (6LoWPANs)" [RFC7400] defines the 516 6LoWPAN Capability Indication Option (6CIO) that enables a node to 517 expose its capabilities in router Advertisement (RA) messages. 519 [RFC8505] defines a number of bits in the 6CIO, in particular: 521 L: Node is a 6LR. 522 E: Node is an IPv6 ND Registrar -- i.e., it supports registrations 523 based on EARO. 524 P: Node is a Routing Registrar, -- i.e., an IPv6 ND Registrar that 525 also provides reachability services for the Registered Address. 527 0 1 2 3 528 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 1 529 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 530 | Type | Length = 1 | Reserved |D|L|B|P|E|G| 531 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 532 | Reserved | 533 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 535 Figure 3: 6CIO flags 537 A 6LR that provides reachability services for a RUL in a RPL network 538 as specified in this document includes a 6CIO in its RA messages and 539 set the L, P and E flags to 1 as prescribed by [RFC8505]; this is 540 fully explained in Section 9.2. 542 5. Requirements on the RPL-Unware leaf 544 This document describes how RPL routing can be extended to reach a 545 RUL. This section specifies the minimal RPL-independent 546 functionality that the RUL needs to implement to obtain routing 547 services for its addresses. 549 5.1. Support of 6LoWPAN ND 551 To obtain routing services from a router that implements this 552 specification, a RUL needs to implement [RFC8505] and sets the "R" 553 and "T" flags in the EARO to 1 as discussed in Section 4.2.1 and 554 Section 4.2.3, respectively. Section 9.2.1 specifies new behaviors 555 for the RUL, e.g., when the R Flag set to 1 in a NS(EARO) is not 556 echoed in the NA(EARO), which indicates that the route injection 557 failed. 559 The RUL is expected to request routing services from a router only if 560 that router originates RA messages with a CIO that has the L, P, and 561 E flags all set to 1 as discussed in Section 4.3.1, unless configured 562 to do so. It is suggested that the RUL also implements [RFC8928] to 563 protect the ownership of its addresses. 565 A RUL that may attach to multiple 6LRs is expected to prefer those 566 that provide routing services. The RUL needs to register to all the 567 6LRs from which it desires routing services. 569 Parallel Address Registrations to several 6LRs should be performed in 570 a rapid sequence, using the same EARO for the same Address. Gaps 571 between the Address Registrations will invalidate some of the routes 572 till the Address Registration finally shows on those routes. 574 [RFC8505] introduces error Status values in the NA(EARO) which can be 575 received synchronously upon an NS(EARO) or asynchronously. The RUL 576 needs to support both cases and refrain from using the address when 577 the Status value indicates a rejection (see Section 6.3). 579 5.2. Support of IPv6 Encapsulation 581 Section 2.1 of [USEofRPLinfo] defines the rules for tunneling either 582 to the final destination (e.g., a RUL) or to its attachment router 583 (designated as 6LR). In order to terminate the IPv6-in-IPv6 tunnel, 584 the RUL, as an IPv6 host, would have to be capable of decapsulating 585 the tunneled packet and either drop the encapsulated packet if it is 586 not the final destination, or pass it to the upper layer for further 587 processing. As indicated in section 4.1 of [USEofRPLinfo], this is 588 not mandated by [RFC8504], so the Root typically terminates the IPv6- 589 in-IPv6 tunnel at the parent 6LR. It is thus not necessary for a RUL 590 to support IPv6-in-IPv6 decapsulation. 592 5.3. Support of the Hop-by-Hop Header 594 A RUL is expected to process an Option Type in a Hop-by-Hop Header as 595 prescribed by section 4.2 of [RFC8200]. An RPI with an Option Type 596 of 0x23 [USEofRPLinfo] is thus skipped when not recognized. 598 5.4. Support of the Routing Header 600 A RUL is expected to process an unknown Routing Header Type as 601 prescribed by section 4.4 of [RFC8200]. This implies that the Source 602 Routing Header with a Routing Type of 3 [RFC6554] is ignored when the 603 Segments Left is zero. 605 6. Enhancements to RFC 6550 607 This document specifies a new behavior whereby a 6LR injects DAO 608 messages for unicast addresses (see Section 9) and multicast 609 addresses (see Section 10) on behalf of leaves that are not aware of 610 RPL. The RUL addresses are exposed as external targets [RFC6550]. 611 Conforming to [USEofRPLinfo], an IPv6-in-IPv6 encapsulation between 612 the 6LR and the RPL Root is used to carry the RPL artifacts and 613 remove them when forwarding outside the RPL domain, e.g., to a RUL. 615 This document also synchronizes the liveness monitoring at the Root 616 and the 6LBR. The same value of lifetime is used for both, and a 617 single keep-alive message, the RPL DAO, traverses the RPL network. A 618 new behavior is introduced whereby the RPL Root proxies the EDAR 619 message to the 6LBR on behalf of the 6LR (see Section 8), for any 620 leaf node that implements the 6LN functionality in [RFC8505]. 622 Section 6.7.7 of [RFC6550] introduces the RPL Target Option, which 623 can be used in RPL Control messages such as the DAO message to signal 624 a destination prefix. This document adds the capabilities to 625 transport the ROVR field (see Section 4.2.3) and the IPv6 Address of 626 the prefix advertiser when the Target is a shorter prefix. Their use 627 is signaled respectively by a new ROVR Size field being non-zero and 628 a new "Advertiser address in Full" 'F' flag set to 1, see 629 Section 6.1. 631 This specification defines a new flag, "Root Proxies EDAR/EDAC" (P), 632 in the RPL DODAG Configuration option, see Section 6.2. 634 The RPL Status defined in section 6.5.1 of [RFC6550] for use in the 635 DAO-ACK message is extended to be placed in DCO messages 636 [EFFICIENT-NPDAO] as well. Furthermore, this specification enables 637 to carry the EARO Status defined for 6LoWPAN ND in RPL DAO and DCO 638 messages, embedded in a RPL Status, see Section 6.3. 640 Section 12 of [RFC6550] details the RPL support for multicast flows 641 when the RPLInstance is operated in the MOP of 3 ("Storing Mode of 642 Operation with multicast support"). This specification extends the 643 RPL Root operation to proxy-relay the MLDv2 [RFC3810] operation 644 between the RUL and the 6LR, see Section 10. 646 6.1. Updated RPL Target Option 648 This specification updates the RPL Target Option to transport the 649 ROVR that was also defined for 6LoWPAN ND messages. This enables the 650 RPL Root to generate the proxied EDAR message to the 6LBR. 652 The Target Prefix of the RPL Target Option is left (high bit) 653 justified and contains the advertised prefix; its size may be smaller 654 than 128 when it indicates a Prefix route. The Prefix Length field 655 signals the number of bits that correspond to the advertised Prefix; 656 it is 128 for a host route or less in the case of a Prefix route. 657 This remains unchanged. 659 This specification defines the new 'F' flag. When it is set to 1, 660 the size of the Target Prefix field MUST be 128 bits and it MUST 661 contain an IPv6 address of the advertising node taken from the 662 advertised Prefix. In that case, the Target Prefix field carries two 663 distinct pieces of information: a route that can be a host route or a 664 Prefix route depending on the Prefix Length, and an IPv6 address that 665 can be used to reach the advertising node and validate the route. 667 If the 'F' flag is set to 0, the Target Prefix field can be shorter 668 than 128 bits and it MUST be aligned to the next byte boundary after 669 the end of the prefix. Any additional bits in the rightmost octet 670 are filled with padding bits. Padding bits are reserved and set to 0 671 as specified in section 6.7.7 of [RFC6550]. 673 With this specification the ROVR is the remainder of the RPL Target 674 Option. The size of the ROVR is indicated in a new ROVR Size field 675 that is encoded to map one-to-one with the Code Suffix in the EDAR 676 message (see table 4 of [RFC8505]). The ROVR Size field is taken 677 from the flags field, which is an update to the RPL Target Option 678 Flags IANA registry. 680 The updated format is illustrated in Figure 4. It is backward 681 compatible with the Target Option in [RFC6550]. It is recommended 682 that the updated format be used as a replacement in new 683 implementations in all MOPs in preparation for upcoming Route 684 Ownership Validation mechanisms based on the ROVR, unless the device 685 or the network is so constrained that this is not feasible. 687 0 1 2 3 688 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 1 689 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 690 | Type = 0x05 | Option Length |ROVRsz |F|Flags| Prefix Length | 691 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 692 | | 693 | Target Prefix (Variable Length) | 694 . . 695 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 696 | | 697 ... Registration Ownership Verifier (ROVR) ... 698 | | 699 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 700 Figure 4: Updated Target Option 702 New fields: 704 ROVRsz (ROVR Size): Indicates the Size of the ROVR. It MUST be set 705 to 1, 2, 3, or 4, indicating a ROVR size of 64, 128, 192, or 256 706 bits, respectively. If a legacy Target Option is used, then the 707 value must remain 0, as specified in [RFC6550]. In case of a 708 value above 4, the size of the ROVR is undetermined and this node 709 cannot validate the ROVR; an implementation SHOULD propagate the 710 whole Target Option upwards as received to enable the verification 711 by an ancestor that would support the upgraded ROVR. 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 Flags: The 3 bits remaining unused in the Flags field are reserved 718 for flags. The field MUST be initialized to zero by the sender 719 and MUST be ignored by the receiver. 721 Registration Ownership Verifier (ROVR): This is the same field as in 722 the EARO, see [RFC8505] 724 6.2. Additional Flag in the RPL DODAG Configuration Option 726 The DODAG Configuration Option is defined in Section 6.7.6 of 727 [RFC6550]. Its purpose is extended to distribute configuration 728 information affecting the construction and maintenance of the DODAG, 729 as well as operational parameters for RPL on the DODAG, through the 730 DODAG. This Option was originally designed with 4 bit positions 731 reserved for future use as Flags. 733 0 1 2 3 734 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 1 735 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 736 | Type = 0x04 |Opt Length = 14| |P| | |A| ... | 737 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 738 |4 bits | 740 Figure 5: DODAG Configuration Option (Partial View) 742 This specification defines a new flag "Root Proxies EDAR/EDAC" (P). 743 The 'P' flag is encoded in bit position 1 of the reserved Flags in 744 the DODAG Configuration Option (counting from bit 0 as the most 745 significant bit) and it is set to 0 in legacy implementations as 746 specified respectively in Sections 20.14 and 6.7.6 of [RFC6550]. 748 The 'P' flag is set to 1 to indicate that the Root performs the proxy 749 operation, which implies that it supports this specification and the 750 updated RPL Target Option (see Section 6.1). 752 Section 4.3 of [USEofRPLinfo] updates [RFC6550] to indicate that the 753 definition of the Flags applies to Mode of Operation (MOP) values 754 zero (0) to six (6) only. For a MOP value of 7, the implementation 755 MUST consider that the Root performs the proxy operation. 757 The RPL DODAG Configuration Option is typically placed in a DODAG 758 Information Object (DIO) message. The DIO message propagates down 759 the DODAG to form and then maintain its structure. The DODAG 760 Configuration Option is copied unmodified from parents to children. 761 [RFC6550] states that "Nodes other than the DODAG Root MUST NOT 762 modify this information when propagating the DODAG Configuration 763 option". Therefore, a legacy parent propagates the 'P' Flag as set 764 by the Root, and when the 'P' Flag is set to 1, it is transparently 765 flooded to all the nodes in the DODAG. 767 6.3. Updated RPL Status 769 The RPL Status is defined in section 6.5.1 of [RFC6550] for use in 770 the DAO-ACK message and values are assigned as follows: 772 +---------+--------------------------------+ 773 | Range | Meaning | 774 +---------+--------------------------------+ 775 | 0 | Success/Unqualified acceptance | 776 +---------+--------------------------------+ 777 | 1-127 | Not an outright rejection | 778 +---------+--------------------------------+ 779 | 128-255 | Rejection | 780 +---------+--------------------------------+ 782 Table 1: RPL Status per RFC 6550 784 The 6LoWPAN ND Status was defined for use in the EARO, see section 785 4.1 of [RFC8505]. This specification adds a capability to allow the 786 carriage of 6LoWPAN ND Status values in RPL DAO and DCO messages, 787 embedded in the RPL Status field. 789 To achieve this, the range of the ARO/EARO Status values is reduced 790 to 0-63, which updates the IANA registry created for [RFC6775]. This 791 reduction ensures that the values fit within a RPL Status as shown in 792 Figure 6. See Section 12.2, Section 12.5, and Section 12.6 for the 793 respective IANA declarations. 795 0 1 2 3 4 5 6 7 796 +-+-+-+-+-+-+-+-+ 797 |E|A|StatusValue| 798 +-+-+-+-+-+-+-+-+ 800 Figure 6: RPL Status Format 802 This specification updates the RPL Status with subfields as indicated 803 below: 805 E: 1-bit flag. set to 1 to indicate a rejection. When set to 0, a 806 Status value of 0 indicates Success/Unqualified acceptance and 807 other values indicate "not an outright rejection" as per RFC 6550. 809 A: 1-bit flag. Indicates the type of the RPL Status value. 811 Status Value: 6-bit unsigned integer. If the 'A' flag is set to 1 812 this field transports a Status value defined for IPv6 ND EARO. 813 When the 'A' flag is set to 0, the Status value is defined for 814 RPL. 816 When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a EDAC 817 message, the RPL Root MUST copy the 6LoWPAN ND status code unchanged 818 in the RPL Status value and set the 'A' flag to 1. The RPL Root MUST 819 set the 'E' flag to 1 for all rejection and unknown status codes. 820 The status codes in the 1-10 range [RFC8505] are all considered 821 rejections. 823 Reciprocally, upon a DCO or a DAO-ACK message from the RPL Root with 824 a RPL Status that has the 'A' flag set, the 6LR MUST copy the RPL 825 Status value unchanged in the Status field of the EARO when 826 generating an NA to the RUL. 828 7. Enhancements to draft-ietf-roll-efficient-npdao 830 [EFFICIENT-NPDAO] defines the DCO message for RPL Storing Mode only, 831 with a link-local scope. All nodes in the RPL network are expected 832 to support the specification since the message is processed hop by 833 hop along the path that is being cleaned up. 835 This specification extends the use of the DCO message to the Non- 836 Storing MOP, whereby the DCO is sent end-to-end by the Root directly 837 to the RAN that injected the DAO message for the considered target. 838 In that case, intermediate nodes do not need to support 839 [EFFICIENT-NPDAO]; they forward the DCO message as a plain IPv6 840 packet between the Root and the RAN. 842 In the case of a RUL, the 6LR that serves the RUL acts as the RAN 843 that receives the Non-Storing DCO. This specification leverages the 844 Non-Storing DCO between the Root and the 6LR that serves as 845 attachment router for a RUL. A 6LR and a Root that support this 846 specification MUST implement the Non-Storing DCO. 848 8. Enhancements to RFC 6775 and RFC8505 850 This document updates [RFC6775] and [RFC8505] to reduce the range of 851 the ND status codes down to 64 values. The two most significant 852 (leftmost) bits if the original ND status field are now reserved, 853 they MUST be set to zero by the sender and ignored by the receiver. 855 This document also changes the behavior of a 6LR acting as RPL router 856 and of a 6LN acting as RUL in the 6LoWPAN ND Address Registration as 857 follows: 859 * If the RPL Root advertises the capability to proxy the EDAR/EDAC 860 exchange to the 6LBR, the 6LR refrains from sending the keep-alive 861 EDAR message. If it is separated from the 6LBR, the Root 862 regenerates the EDAR message to the 6LBR periodically, upon a DAO 863 message that signals the liveliness of the address. 865 * The use of the R Flag is extended to the NA(EARO) to confirm 866 whether the route was installed. 868 9. Protocol Operations for Unicast Addresses 870 The description below assumes that the Root sets the 'P' flag in the 871 DODAG Configuration Option and performs the EDAR proxy operation 872 presented in Section 4.3 . 874 If the 'P' flag is set to 0, the 6LR MUST generate the periodic EDAR 875 messages and process the returned status as specified in [RFC8505]. 876 If the EDAC indicates success, the rest of the flow takes place as 877 presented but without the proxied EDAR/EDAC exchange. 879 Section 9.1 provides an overview of the route injection in RPL, 880 whereas Section 9.2 offers more details from the perspective of the 881 different nodes involved in the flow. 883 9.1. General Flow 885 This specification eliminates the need to exchange keep-alive 886 Extended Duplicate Address messages, EDAR and EDAC, all the way from 887 a 6LN to the 6LBR across a RPL mesh. Instead, the EDAR/EDAC exchange 888 with the 6LBR is proxied by the RPL Root upon the DAO message that 889 refreshes the RPL routing state. The first EDAR upon a new 890 Registration cannot be proxied, though, as it serves for the purpose 891 of DAD, which must be verified before the address is injected in RPL. 893 In a RPL network where the function is enabled, refreshing the state 894 in the 6LBR is the responsibility of the Root. Consequently, only 895 addresses that are injected in RPL will be kept alive at the 6LBR by 896 the RPL Root. Since RULs are advertised using Non-Storing Mode, the 897 DAO message flow and the keep alive EDAR/EDAC can be nested within 898 the Address (re)Registration flow. Figure 7 illustrates that, for 899 the first Registration, both the DAD and the keep-alive EDAR/EDAC 900 exchanges happen in the same sequence. 902 6LN/RUL 6LR <6LR*> Root 6LBR 903 | | | | 904 |<------ND------>|<----RPL----->|<-------ND-------->| 905 | |<----------------ND-------------->| 906 | | | | 907 | NS(EARO) | | | 908 |--------------->| | 909 | | EDAR | 910 | |--------------------------------->| 911 | | | 912 | | EDAC | 913 | |<---------------------------------| 914 | | DAO | | 915 | |------------->| | 916 | | | EDAR | 917 | | |------------------>| 918 | | | EDAC | 919 | | |<------------------| 920 | | DAO-ACK | | 921 | |<-------------| | 922 | NA(EARO) | | | 923 |<---------------| | | 924 | | | | 926 Figure 7: First RUL Registration Flow 928 This flow requires that the lifetimes and sequence counters in 929 6LoWPAN ND and RPL are aligned. 931 To achieve this, the Path Sequence and the Path Lifetime in the DAO 932 message are taken from the Transaction ID and the Address 933 Registration lifetime in the NS(EARO) message from the 6LN. 935 On the first Address Registration, illustrated in Figure 7 for RPL 936 Non-Storing Mode, the Extended Duplicate Address exchange takes place 937 as prescribed by [RFC8505]. If the exchange fails, the 6LR returns 938 an NA message with a non-zero status to the 6LN, the NCE is not 939 created, and the address is not injected in RPL. Otherwise, the 6LR 940 creates an NCE and injects the Registered Address in the RPL routing 941 using a DAO/DAO-ACK exchange with the RPL DODAG Root. 943 An Address Registration refresh is performed by the 6LN to maintain 944 the NCE in the 6LR alive before the lifetime expires. Upon the 945 refresh of a registration, the 6LR reinjects the corresponding route 946 in RPL before it expires, as illustrated in Figure 8. 948 6LN/RUL <-ND-> 6LR <-RPL-> Root <-ND-> 6LBR 949 | | | | 950 | NS(EARO) | | | 951 |--------------->| | | 952 | | DAO | | 953 | |------------->| | 954 | | | EDAR | 955 | | |------------------>| 956 | | | EDAC | 957 | | |<------------------| 958 | | DAO-ACK | | 959 | |<-------------| | 960 | NA(EARO) | | | 961 |<---------------| | | 963 Figure 8: Next RUL Registration Flow 965 This is what causes the RPL Root to refresh the state in the 6LBR, 966 using an EDAC message. In case of an error in the proxied EDAR flow, 967 the error is returned in the DAO-ACK using a RPL Status with the 'A' 968 flag set to 1 that imbeds a 6LoWPAN Status value as discussed in 969 Section 6.3. 971 The 6LR may receive a requested DAO-ACK after it received an 972 asynchronous Non-Storing DCO, but the non-zero status in the DCO 973 supersedes a positive Status in the DAO-ACK regardless of the order 974 in which they are received. Upon the DAO-ACK - or the DCO if one 975 arrives first - the 6LR responds to the RUL with an NA(EARO). 977 An issue may be detected later, e.g., the address moves to a 978 different DODAG with the 6LBR attached to a different 6LoWPAN 979 Backbone router (6BBR), see Figure 5 in section 3.3 of [RFC8929]. 980 The 6BBR may send a negative ND status, e.g., in an asynchronous 981 NA(EARO) to the 6LBR. 983 [RFC8929] expects that the 6LBR is collocated with the RPL Root, but 984 if not, the 6LBR MUST forward the status code to the originator of 985 the EDAR, either the 6LR or the RPL Root that proxies for it. The ND 986 status code is mapped in a RPL Status value by the RPL Root, and then 987 back by the 6LR. 989 Figure 9 illustrates this in the case where the 6LBR and the Root are 990 not collocated, and the Root proxies the EDAR messages. 992 6LN/RUL <-ND-> 6LR <-RPL-> Root <-ND-> 6LBR <-ND-> 6BBR 993 | | | | | 994 | | | | NA(EARO) | 995 | | | |<------------| 996 | | | EDAC | | 997 | | |<-------------| | 998 | | DCO | | | 999 | |<------------| | | 1000 | NA(EARO) | | | | 1001 |<-------------| | | | 1002 | | | | | 1004 Figure 9: Asynchronous Issue 1006 If the Root does not proxy, then the EDAC with a non-zero status 1007 reaches the 6LR directly. In that case, the 6LR MUST clean up the 1008 route using a DAO with a Lifetime of zero, and it MUST propagate the 1009 status back to the RUL in a NA(EARO) with the R Flag set to 0. 1011 The RUL may terminate the registration at any time by using a 1012 Registration Lifetime of 0. This specification requires that the RPL 1013 Target Option transports the ROVR. This way, the same flow as the 1014 heartbeat flow is sufficient to inform the 6LBR using the Root as 1015 proxy, as illustrated in Figure 8. 1017 Any combination of the logical functions of 6LR, Root, and 6LBR might 1018 be collapsed in a single node. 1020 9.2. Detailed Operation 1022 The following section specify respectively the behaviour of the 6LN 1023 Acting as RUL, the 6LR Acting as Border router ad serving the 6LN, 1024 the RPL Root and the 6LBR in the control flows that enable RPL 1025 routing back to the RUL. 1027 9.2.1. Perspective of the 6LN Acting as RUL 1029 This specification does not alter the operation of a 6LoWPAN ND- 1030 compliant 6LN/RUL, which is expected to operate as follows: 1032 1. The 6LN selects a 6LR that provides reachability services for a 1033 RUL. This is signaled a 6CIO in the RA messages with the L, P 1034 and E flags set to 1 as prescribed by [RFC8505]. 1036 2. The 6LN obtains an IPv6 global address, either using Stateless 1037 Address Autoconfiguration (SLAAC) [RFC4862] based on a Prefix 1038 Information Option (PIO) [RFC4861] found in an RA message, or 1039 some other means, such as DHCPv6 [RFC8415]. 1041 3. Once it has formed an address, the 6LN registers its address and 1042 refreshes its registration periodically, early enough within the 1043 Lifetime of the previous Address Registration, as prescribed by 1044 [RFC6775], to refresh the NCE before the lifetime indicated in 1045 the EARO expires. It sets the T Flag to 1 as prescribed in 1046 [RFC8505]. The TID is incremented each time and wraps in a 1047 lollipop fashion (see section 5.2.1 of [RFC8505], which is fully 1048 compatible with section 7.2 of [RFC6550]). 1050 4. As stated in section 5.2 of [RFC8505], the 6LN can register to 1051 more than one 6LR at the same time. In that case, it uses the 1052 same EARO for all of the parallel Address Registrations, with the 1053 exception of the Registration Lifetime field and the setting of 1054 the R flag that may differ. The 6LN may cancel a subset of its 1055 registrations, or transfer a registration from one or more old 1056 6LR(s) to one or more new 6LR(s). To do so, the 6LN sends a 1057 series of NS(EARO) messages, all with the same TID, with a zero 1058 Registration Lifetime to the old 6LR(s) and with a non-zero 1059 Registration Lifetime to the new 6LR(s). In that process, the 1060 6LN SHOULD send the NS(EARO) with a non-zero Registration 1061 Lifetime and ensure that at least one succeeds before it sends an 1062 NS(EARO) that terminates another registration. This avoids the 1063 churn related to transient route invalidation in the RPL network 1064 above the common parent of the involved 6LRs. 1066 5. Following section 5.1 of [RFC8505], a 6LN acting as a RUL sets 1067 the R Flag in the EARO of its registration(s) for which it 1068 requires routing services. If the R Flag is not echoed in the 1069 NA, the RUL SHOULD attempt to use another 6LR. The RUL SHOULD 1070 ensure that one registration succeeds before setting the R Flag 1071 to 0. In case of a conflict with the preceding rule on lifetime, 1072 the rule on lifetime has precedence. 1074 6. The 6LN may use any of the 6LRs to which it registered as the 1075 default gateway. Using a 6LR to which the 6LN is not registered 1076 may result in packets dropped at the 6LR by a Source Address 1077 Validation function (SAVI) [RFC7039] so it is not recommended. 1079 Even without support for RPL, the RUL may be configured with an 1080 opaque value to be provided to the routing protocol. If the RUL has 1081 knowledge of the RPL Instance the packet should be injected into, 1082 then it SHOULD set the Opaque field in the EARO to the RPLInstanceID, 1083 otherwise it MUST leave the Opaque field as zero. 1085 Regardless of the setting of the Opaque field, the 6LN MUST set the 1086 "I" field to zero to signal "topological information to be passed to 1087 a routing process", as specified in section 5.1 of [RFC8505]. 1089 A RUL is not expected to produce RPL artifacts in the data packets, 1090 but it may do so. For instance, if the RUL has minimal awareness of 1091 the RPL Instance then it can build an RPI. A RUL that places an RPI 1092 in a data packet SHOULD indicate the RPLInstanceID of the RPL 1093 Instance where the packet should be forwarded. It is up to the 6LR 1094 (e.g., by policy) to use the RPLInstanceID information provided by 1095 the RUL or rewrite it to the selected RPLInstanceID for forwarding 1096 inside the RPL domain. All the flags and the Rank field are set to 0 1097 as specified by section 11.2 of [RFC6550]. 1099 9.2.2. Perspective of the 6LR Acting as Border router 1101 A 6LR that provides reachability services for a RUL in a RPL network 1102 as specified in this document MUST include a 6CIO in its RA messages 1103 and set the L, P and E flags to 1 as prescribed by [RFC8505]. 1105 As prescribed by [RFC8505], the 6LR generates an EDAR message upon 1106 reception of a valid NS(EARO) message for the registration of a new 1107 IPv6 address by a 6LN. If the initial EDAR/EDAC exchange succeeds, 1108 then the 6LR installs an NCE for the Registration Lifetime. For the 1109 registration refreshes, if the RPL Root has indicated that it proxies 1110 the keep-alive EDAR/EDAC exchange with the 6LBR (see Section 6), the 1111 6LR MUST refrain from sending the keep-alive EDAR. 1113 If the R Flag is set to 1 in the NS(EARO), the 6LR SHOULD inject the 1114 host route in RPL, unless this is barred for other reasons, such as 1115 the saturation of the RPL parents. The 6LR MUST use a RPL Non- 1116 Storing Mode signaling and the updated Target Option (see 1117 Section 6.1). The 6LR MUST request a DAO-ACK by setting the 'K' flag 1118 in the DAO message. Success injecting the route to the RUL's address 1119 is indicated by the 'E' flag set to 0 in the RPL status of the DAO- 1120 ACK message. 1122 The Opaque field in the EARO provides a means to signal which RPL 1123 Instance is to be used for the DAO advertisements and the forwarding 1124 of packets sourced at the Registered Address when there is no RPI in 1125 the packet. 1127 As described in [RFC8505], if the "I" field is zero, then the Opaque 1128 field is expected to carry the RPLInstanceID suggested by the 6LN; 1129 otherwise, there is no suggested Instance. If the 6LR participates 1130 in the suggested RPL Instance, then the 6LR MUST use that RPL 1131 Instance for the Registered Address. 1133 If there is no suggested RPL Instance or else if the 6LR does not 1134 participate to the suggested Instance, it is expected that the 1135 packets coming from the 6LN "can unambiguously be associated to at 1136 least one RPL Instance" [RFC6550] by the 6LR, e.g., using a policy 1137 that maps the 6-tuple into an Instance. 1139 The DAO message advertising the Registered Address MUST be 1140 constructed as follows: 1142 1. The Registered Address is signaled as the Target Prefix in the 1143 updated Target Option in the DAO message; the Prefix Length is 1144 set to 128 but the 'F' flag is set to 0 since the advertiser is 1145 not the RUL. The ROVR field is copied unchanged from the EARO 1146 (see Section 6.1). 1148 2. The 6LR indicates one of its global or unique-local IPv6 unicast 1149 addresses as the Parent Address in the RPL Transit Information 1150 Option (TIO) associated with the Target Option 1152 3. The 6LR sets the External 'E' flag in the TIO to indicate that it 1153 is redistributing an external target into the RPL network 1155 4. the Path Lifetime in the TIO is computed from the Registration 1156 Lifetime in the EARO. This operation converts seconds to the 1157 Lifetime Units used in the RPL operation. This creates the 1158 deployment constraint that the Lifetime Unit is reasonably 1159 compatible with the expression of the Registration Lifetime. 1160 e.g., a Lifetime Unit of 0x4000 maps the most significant byte of 1161 the Registration Lifetime to the Path Lifetime. 1163 In that operation, the Path Lifetime must be rounded, if needed, 1164 to the upper value to ensure that the path has a longer lifetime 1165 than the registration. 1167 Note that if the Registration Lifetime is 0, then the Path 1168 Lifetime is also 0 and the DAO message becomes a No-Path DAO, 1169 which cleans up the routes down to the RUL's address; this also 1170 causes the Root as a proxy to send an EDAR message to the 6LBR 1171 with a Lifetime of 0. 1173 5. the Path Sequence in the TIO is set to the TID value found in the 1174 EARO option. 1176 Upon receiving or timing out the DAO-ACK after an implementation- 1177 specific number of retries, the 6LR MUST send the corresponding 1178 NA(EARO) to the RUL. Upon receiving an asynchronous DCO message, if 1179 a DAO-ACK is pending then the 6LR MUST wait for the DAO-ACK to send 1180 the NA(EARO) and deliver the status found in the DCO, else it MUST 1181 send an asynchronous NA(EARO) to the RUL immediately. 1183 The 6LR MUST set the R Flag to 1 in the NA(EARO) back if and only if 1184 the 'E' flag is set to 0, indicating that the 6LR injected the 1185 Registered Address in the RPL routing successfully and that the EDAR 1186 proxy operation succeeded. 1188 If the 'A' flag in the RPL Status is set to 1, the embedded Status 1189 value is passed back to the RUL in the EARO Status. If the 'E' flag 1190 is also set to 1, the registration failed for 6LoWPAN ND related 1191 reasons, and the NCE is removed. 1193 An error injecting the route causes the 'E' flag to be set to 1. If 1194 the error is not related to ND, the 'A' flag is set to 0. In that 1195 case, the registration succeeds, but the RPL route is not installed. 1196 So the NA(EARO) is returned with a status indicating success but the 1197 R Flag set to 0, which means that the 6LN obtained a binding but no 1198 route. 1200 If the 'A' flag is set to 0 in the RPL Status of the DAO-ACK, then 1201 the 6LoWPAN ND operation succeeded, and an EARO Status of 0 (Success) 1202 MUST be returned to the 6LN. The EARO Status of 0 MUST also be used 1203 if the 6LR did not attempt to inject the route but could create the 1204 binding after a successful EDAR/EDAC exchange or refresh it. 1206 If the 'E' flag is set to 1 in the RPL Status of the DAO-ACK, then 1207 the route was not installed and the R flag MUST be set to 0 in the 1208 NA(EARO). The R flag MUST be set to 0 if the 6LR did not attempt to 1209 inject the route. 1211 In a network where Address Protected Neighbor Discovery (AP-ND) is 1212 enabled, in case of a DAO-ACK or a DCO indicating transporting an 1213 EARO Status value of 5 (Validation Requested), the 6LR MUST challenge 1214 the 6LN for ownership of the address, as described in section 6.1 of 1215 [RFC8928], before the Registration is complete. This flow, 1216 illustrated in Figure 10, ensures that the address is validated 1217 before it is injected in the RPL routing. 1219 If the challenge succeeds, then the operations continue as normal. 1220 In particular, a DAO message is generated upon the NS(EARO) that 1221 proves the ownership of the address. If the challenge failed, the 1222 6LR rejects the registration as prescribed by AP-ND and may take 1223 actions to protect itself against DoS attacks by a rogue 6LN, see 1224 Section 11. 1226 6LN 6LR Root 6LBR 1227 | | | | 1228 |<--------------- RA ---------------------| | | 1229 | | | | 1230 |------ NS EARO (ROVR=Crypto-ID) -------->| | | 1231 | | | | 1232 |<- NA EARO(status=Validation Requested) -| | | 1233 | | | | 1234 |----- NS EARO and Proof-of-ownership -->| | 1235 | |--------- EDAR ------->| 1236 | | | 1237 | |<-------- EDAC --------| 1238 | | | 1239 | | | | 1240 | |-- DAO --->| | 1241 | | |-- EDAR -->| 1242 | | | | 1243 | | |<-- EDAC --| 1244 | |<- DAO-ACK-| | 1245 | | | | 1246 |<----------- NA EARO (status=0)----------| | | 1247 | | | | 1248 ... 1249 | | | | 1250 |------ NS EARO (ROVR=Crypto-ID) -------->| | | 1251 | |-- DAO --->| | 1252 | | |-- EDAR -->| 1253 | | | | 1254 | | |<-- EDAC --| 1255 | |<- DAO-ACK-| | 1256 |<----------- NA EARO (status=0)----------| | | 1257 | | | | 1258 ... 1260 Figure 10: Address Protection 1262 The 6LR may at any time send a unicast asynchronous NA(EARO) with the 1263 R Flag set to 0 to signal that it stops providing routing services, 1264 and/or with the EARO Status 2 "Neighbor Cache full" to signal that it 1265 removes the NCE. It may also send a final RA, unicast or multicast, 1266 with a router Lifetime field of zero, to signal that it is ceasing to 1267 serve as router, as specified in section 6.2.5 of [RFC4861]. This 1268 may happen upon a DCO or a DAO-ACK message indicating the path is 1269 already removed; else the 6LR MUST remove the host route to the 6LN 1270 using a DAO message with a Path Lifetime of zero. 1272 A valid NS(EARO) message with the R Flag set to 0 and a Registration 1273 Lifetime that is not zero signals that the 6LN wishes to maintain the 1274 binding but does not require the routing services from the 6LR (any 1275 more). Upon this message, if, due to previous NS(EARO) with the R 1276 Flag set to 1, the 6LR was injecting the host route to the Registered 1277 Address in RPL using DAO messages, then the 6LR MUST invalidate the 1278 host route in RPL using a DAO with a Path Lifetime of zero. It is up 1279 to the Registering 6LN to maintain the corresponding route from then 1280 on, either keeping it active via a different 6LR or by acting as a 1281 RAN and managing its own reachability. 1283 9.2.3. Perspective of the RPL Root 1285 A RPL Root MUST set the 'P' flag to 1 in the RPL DODAG Configuration 1286 Option of the DIO messages that it generates (see Section 6) to 1287 signal that it proxies the EDAR/EDAC exchange and supports the 1288 Updated RPL Target option. 1290 Upon reception of a DAO message, for each updated RPL Target Option 1291 (see Section 6.1) that creates or updates an existing RPL state, the 1292 Root MUST notify the 6LBR by using a proxied EDAR/EDAC exchange. If 1293 if the RPL Root and the 6LBR are integrated, an internal API can be 1294 used. 1296 The EDAR message MUST be constructed as follows: 1298 1. The Target IPv6 address from the RPL Target Option is placed in 1299 the Registered Address field of the EDAR message; 1301 2. the Registration Lifetime is adapted from the Path Lifetime in 1302 the TIO by converting the Lifetime Units used in RPL into units 1303 of 60 seconds used in the 6LoWPAN ND messages; 1305 3. the TID value is set to the Path Sequence in the TIO and 1306 indicated with an ICMP code of 1 in the EDAR message; 1308 4. The ROVR in the RPL Target Option is copied as is in the EDAR and 1309 the ICMP Code Suffix is set to the appropriate value as shown in 1310 Table 4 of [RFC8505] depending on the size of the ROVR field. 1312 Upon receiving an EDAC message from the 6LBR, if a DAO is pending, 1313 then the Root MUST send a DAO-ACK back to the 6LR. Otherwise, if the 1314 Status in the EDAC message is not "Success", then it MUST send an 1315 asynchronous DCO to the 6LR. 1317 In either case, the EDAC Status is embedded in the RPL Status with 1318 the 'A' flag set to 1. 1320 The proxied EDAR/EDAC exchange MUST be protected with a timer of an 1321 appropriate duration and a number of retries, that are 1322 implementation-dependent, and SHOULD be configurable since the Root 1323 and the 6LBR are typically nodes with a higher capacity and 1324 manageability than 6LRs. Upon timing out, the Root MUST send an 1325 error back to the 6LR as above, either using a DAO-ACK or a DCO, as 1326 appropriate, with the 'A' and 'E' flags set to 1 in the RPL status, 1327 and a RPL Status value of of "6LBR Registry Saturated" [RFC8505]. 1329 9.2.4. Perspective of the 6LBR 1331 The 6LBR is unaware that the RPL Root is not the new attachment 6LR 1332 of the RUL, so it is not impacted by this specification. 1334 Upon reception of an EDAR message, the 6LBR acts as prescribed by 1335 [RFC8505] and returns an EDAC message to the sender. 1337 10. Protocol Operations for Multicast Addresses 1339 Section 12 of [RFC6550] details the RPL support for multicast flows. 1340 This support is activated by the MOP of 3 ("Storing Mode of Operation 1341 with multicast support") in the DIO messages that form the DODAG. 1342 This section also applies if and only if the MOP of the RPLInstance 1343 is 3. 1345 The RPL support of multicast is not source-specific and only operates 1346 as an extension to the Storing Mode of Operation for unicast packets. 1347 Note that it is the RPL model that the multicast packet is passed as 1348 a Layer-2 unicast to each of the interested children. This remains 1349 true when forwarding between the 6LR and the listener 6LN. 1351 "Multicast Listener Discovery Version 2 (MLDv2) for IPv6" [RFC3810] 1352 provides an interface for a listener to register to multicast flows. 1353 In the MLD model, the router is a "querier", and the host is a 1354 multicast listener that registers to the querier to obtain copies of 1355 the particular flows it is interested in. 1357 The equivalent of the first Address Registration happens as 1358 illustrated in Figure 11. The 6LN, as an MLD listener, sends an 1359 unsolicited Report to the 6LR. This enables it to start receiving 1360 the flow immediately, and causes the 6LR to inject the multicast 1361 route in RPL. 1363 This specification does not change MLD but will operate more 1364 efficiently if the asynchronous messages for unsolicited Report and 1365 Done are sent by the 6LN as Layer-2 unicast to the 6LR, in particular 1366 on wireless. 1368 The 6LR acts as a generic MLD querier and generates a DAO with the 1369 Multicast Address as the Target Prefix as described in section 12 of 1370 [RFC6550]. As for the Unicast host routes, the Path Lifetime 1371 associated to the Target is mapped from the Query Interval, and set 1372 to be larger to account for variable propagation delays to the Root. 1373 The Root proxies the MLD exchange as a listener with the 6LBR acting 1374 as the querier, so as to get packets from a source external to the 1375 RPL domain. 1377 Upon a DAO with a Target option for a multicast address, the RPL Root 1378 checks if it is already registered as a listener for that address, 1379 and if not, it performs its own unsolicited Report for the multicast 1380 address as described in section 5.1 of [RFC3810]. The report is 1381 source independent, so there is no Source Address listed. 1383 6LN/RUL 6LR Root 6LBR 1384 | | | | 1385 | unsolicited Report | | | 1386 |------------------->| | | 1387 | | DAO | | 1388 | |-------------->| | 1389 | | DAO-ACK | | 1390 | |<--------------| | 1391 | | | | 1392 | | | unsolicited Report | 1393 | | |---------------------->| 1394 | | | | 1396 Figure 11: First Multicast Registration Flow 1398 The equivalent of the registration refresh is pulled periodically by 1399 the 6LR acting as querier. Upon the timing out of the Query 1400 Interval, the 6LR sends a Multicast Address Specific Query to each of 1401 its listeners, for each Multicast Address, and gets a Report back 1402 that is mapped into a DAO one by one. Optionally, the 6LR MAY send a 1403 General Query, where the Multicast Address field is set to zero. In 1404 that case, the multicast packet is passed as a Layer-2 unicast to 1405 each of the interested children. . 1407 Upon a Report, the 6LR generates a DAO with as many Target Options as 1408 there are Multicast Address Records in the Report message, copying 1409 the Multicast Address field in the Target Prefix of the RPL Target 1410 Option. The DAO message is a Storing Mode DAO, passed to a selection 1411 of the 6LR's parents. 1413 Asynchronously to this, a similar procedure happens between the Root 1414 and a router such as the 6LBR that serves multicast flows on the Link 1415 where the Root is located. Again the Query and Report messages are 1416 source independent. The Root lists exactly once each Multicast 1417 Address for which it has at least one active multicast DAO state, 1418 copying the multicast address in the DAO state in the Multicast 1419 Address field of the Multicast Address Records in the Report message. 1421 This is illustrated in Figure 12: 1423 6LN/RUL 6LR Root 6LBR 1424 | | | | 1425 | Query | | | 1426 |<-------------------| | | 1427 | Report | | | 1428 |------------------->| | | 1429 | | DAO | | 1430 | |-------------->| | 1431 | | DAO-ACK | | 1432 | |<--------------| | 1433 | | | Query | 1434 | | |<-------------------| 1435 | | | Report | 1436 | | |------------------->| 1437 | | | | 1439 Figure 12: Next Registration Flow 1441 Note that any of the functions 6LR, Root and 6LBR might be collapsed 1442 in a single node, in which case the flow above happens internally, 1443 and possibly through internal API calls as opposed to messaging. 1445 11. Security Considerations 1447 It is worth noting that with [RFC6550], every node in the LLN is RPL- 1448 aware and can inject any RPL-based attack in the network. This 1449 specification isolates edge nodes that can only interact with the RPL 1450 routers using 6LoWPAN ND, meaning that they cannot perform RPL 1451 insider attacks. 1453 The LLN nodes depend on the 6LBR and the RPL participants for their 1454 operation. A trust model must be put in place to ensure that the 1455 right devices are acting in these roles, so as to avoid threats such 1456 as black-holing, (see [RFC7416] section 7), Denial-Of-Service attacks 1457 whereby a rogue 6LR creates a high churn in the RPL network by 1458 advertising and removing many forged addresses, or bombing attack 1459 whereby an impersonated 6LBR would destroy state in the network by 1460 using the status code of 4 ("Removed"). 1462 This trust model could be at a minimum based on a Layer-2 Secure 1463 joining and the Link-Layer security. This is a generic 6LoWPAN 1464 requirement, see Req5.1 in Appendix B.5 of [RFC8505]. 1466 In a general manner, the Security Considerations in [RFC7416] 1467 [RFC6775], and [RFC8505] apply to this specification as well. 1469 The Link-Layer security is needed in particular to prevent Denial-Of- 1470 Service attacks whereby a rogue 6LN creates a high churn in the RPL 1471 network by constantly registering and deregistering addresses with 1472 the R Flag set to 1 in the EARO. 1474 [RFC8928] updated 6LoWPAN ND with the called Address-Protected 1475 Neighbor Discovery (AP-ND). AP-ND protects the owner of an address 1476 against address theft and impersonation attacks in a Low-Power and 1477 Lossy Network (LLN). Nodes supporting th extension compute a 1478 cryptographic identifier (Crypto-ID), and use it with one or more of 1479 their Registered Addresses. The Crypto-ID identifies the owner of 1480 the Registered Address and can be used to provide proof of ownership 1481 of the Registered Addresses. Once an address is registered with the 1482 Crypto-ID and a proof of ownership is provided, only the owner of 1483 that address can modify the registration information, thereby 1484 enforcing Source Address Validation. [RFC8928] reduces even more the 1485 attack perimeter that is available to the edge nodes and its use is 1486 suggested in this specification. 1488 Additionally, the trust model could include a role validation (e.g., 1489 using a role-based authorization) to ensure that the node that claims 1490 to be a 6LBR or a RPL Root is entitled to do so. 1492 The Opaque field in the EARO enables the RUL to suggest a 1493 RPLInstanceID where its traffic is placed. It is also possible for 1494 an attacker RUL to include an RPI in the packet. This opens to 1495 attacks where a RPL instance would be reserved for critical traffic, 1496 e.g., with a specific bandwidth reservation, that the additional 1497 traffic generated by a rogue may disrupt. The attack may be 1498 alleviated by traditional access control and traffic shaping 1499 mechanisms where the 6LR controls the incoming traffic from the 6LN. 1500 More importantly, the 6LR is the node that injects the traffic in the 1501 RPL domain, so it has the final word on which RPLInstance is to be 1502 used for the traffic coming from the RUL, per its own policy. 1504 At the time of this writing, RPL does not have a Route Ownership 1505 Validation model whereby it is possible to validate the origin of an 1506 address that is injected in a DAO. This specification makes a first 1507 step in that direction by allowing the Root to challenge the RUL via 1508 the 6LR that serves it. 1510 Section 6.1 indicates that when the length of the ROVR field is 1511 unknown, the RPL Target Option must be passed on as received in RPL 1512 storing Mode. This creates a possible opening for using DAO messages 1513 as a covert channel. Note that DAO messages are rare and the 1514 overusing that channel could be detected. An implementation SHOULD 1515 notify the network management when a RPL Target Option is receives 1516 with an unknown ROVR field size, to ensure that the situation is 1517 known to the network administrator. 1519 [EFFICIENT-NPDAO] introduces the ability for a rogue common ancestor 1520 node to invalidate a route on behalf of the target node. In this 1521 case, the RPL Status in the DCO has the 'A' flag set to 0, and a 1522 NA(EARO) is returned to the 6LN with the R flag set to 0. This 1523 encourages the 6LN to try another 6LR. If a 6LR exists that does not 1524 use the rogue common ancestor, then the 6LN will eventually succeed 1525 gaining reachability over the RPL network in spite of the rogue node. 1527 12. IANA Considerations 1529 12.1. Fixing the Address Registration Option Flags 1531 Section 9.1 of [RFC8505] creates a Registry for the 8-bit Address 1532 Registration Option Flags field. IANA is requested to rename the 1533 first column of the table from "ARO Status" to "Bit number". 1535 12.2. Resizing the ARO Status values 1537 Section 12 of [RFC6775] creates the Address Registration Option 1538 Status values Registry with a range 0-255. 1540 This specification reduces that range to 0-63, see Section 6.3. 1542 IANA is requested to modify the Address Registration Option Status 1543 values Registry so that the upper bound of the unassigned values is 1544 63. This document should be added as a reference. The registration 1545 procedure does not change. 1547 12.3. New RPL DODAG Configuration Option Flag 1549 IANA is requested to assign a flag from the "DODAG Configuration 1550 Option Flags for MOP 0..6" [USEofRPLinfo] registry as follows: 1552 +---------------+----------------------------+-----------+ 1553 | Bit Number | Capability Description | Reference | 1554 +---------------+----------------------------+-----------+ 1555 | 1 (suggested) | Root Proxies EDAR/EDAC (P) | THIS RFC | 1556 +---------------+----------------------------+-----------+ 1558 Table 2: New DODAG Configuration Option Flag 1560 12.4. RPL Target Option Registry 1562 This document modifies the "RPL Target Option Flags" registry 1563 initially created in Section 20.15 of [RFC6550] . The registry now 1564 includes only 4 bits (Section 6.1) and should point to this document 1565 as an additional reference. The registration procedure doesn't 1566 change. 1568 Section 6.1 also defines a new entry in the Registry as follows: 1570 +---------------+--------------------------------+-----------+ 1571 | Bit Number | Capability Description | Reference | 1572 +---------------+--------------------------------+-----------+ 1573 | 0 (suggested) | Advertiser address in Full (F) | THIS RFC | 1574 +---------------+--------------------------------+-----------+ 1576 Table 3: RPL Target Option Registry 1578 12.5. New Subregistry for RPL Non-Rejection Status values 1580 This specification creates a new Subregistry for the RPL Non- 1581 Rejection Status values for use in the RPL DAO-ACK, DCO, and DCO-ACK 1582 messages with the 'A' flag set to 0, under the RPL registry. 1584 * Possible values are 6-bit unsigned integers (0..63). 1586 * Registration procedure is "IETF Review" [RFC8126]. 1588 * Initial allocation is as indicated in Table 4: 1590 +-------+------------------------+---------------------+ 1591 | Value | Meaning | Reference | 1592 +-------+------------------------+---------------------+ 1593 | 0 | Unqualified acceptance | THIS RFC / RFC 6550 | 1594 +-------+------------------------+---------------------+ 1595 | 1..63 | Unassigned | | 1596 +-------+------------------------+---------------------+ 1598 Table 4: Acceptance values of the RPL Status 1600 12.6. New Subregistry for RPL Rejection Status values 1602 This specification creates a new Subregistry for the RPL Rejection 1603 Status values for use in the RPL DAO-ACK and DCO messages with the 1604 'A' flag set to 0, under the RPL registry. 1606 * Possible values are 6-bit unsigned integers (0..63). 1608 * Registration procedure is "IETF Review" [RFC8126]. 1610 * Initial allocation is as indicated in Table 5: 1612 +-------+-----------------------+-----------+ 1613 | Value | Meaning | Reference | 1614 +-------+-----------------------+-----------+ 1615 | 0 | Unqualified rejection | THIS RFC | 1616 +-------+-----------------------+-----------+ 1617 | 1..63 | Unassigned | | 1618 +-------+-----------------------+-----------+ 1620 Table 5: Rejection values of the RPL Status 1622 13. Acknowledgments 1624 The authors wish to thank Ines Robles, Georgios Papadopoulos and 1625 especially Rahul Jadhav and Alvaro Retana for their reviews and 1626 contributions to this document. Also many thanks to Elwyn Davies, 1627 Eric Vyncke, Peter Van der Stok and Carl Wallace for their reviews 1628 and useful comments during the IETF Last Call and the IESG review 1629 sessions. 1631 14. Normative References 1633 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1634 Requirement Levels", BCP 14, RFC 2119, 1635 DOI 10.17487/RFC2119, March 1997, 1636 . 1638 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1639 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1640 DOI 10.17487/RFC3810, June 2004, 1641 . 1643 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1644 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1645 DOI 10.17487/RFC4861, September 2007, 1646 . 1648 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1649 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1650 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1651 Low-Power and Lossy Networks", RFC 6550, 1652 DOI 10.17487/RFC6550, March 2012, 1653 . 1655 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1656 Bormann, "Neighbor Discovery Optimization for IPv6 over 1657 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1658 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1659 . 1661 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1662 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1663 2014, . 1665 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 1666 IPv6 over Low-Power Wireless Personal Area Networks 1667 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 1668 2014, . 1670 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1671 Writing an IANA Considerations Section in RFCs", BCP 26, 1672 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1673 . 1675 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1676 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1677 May 2017, . 1679 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1680 (IPv6) Specification", STD 86, RFC 8200, 1681 DOI 10.17487/RFC8200, July 2017, 1682 . 1684 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node 1685 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504, 1686 January 2019, . 1688 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1689 Perkins, "Registration Extensions for IPv6 over Low-Power 1690 Wireless Personal Area Network (6LoWPAN) Neighbor 1691 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1692 . 1694 [RFC8928] Thubert, P., Ed., Sarikaya, B., Sethi, M., and R. Struik, 1695 "Address-Protected Neighbor Discovery for Low-Power and 1696 Lossy Networks", RFC 8928, DOI 10.17487/RFC8928, November 1697 2020, . 1699 [USEofRPLinfo] 1700 Robles, I., Richardson, M., and P. Thubert, "Using RPI 1701 Option Type, Routing Header for Source Routes and IPv6-in- 1702 IPv6 encapsulation in the RPL Data Plane", Work in 1703 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-42, 1704 12 November 2020, . 1707 [EFFICIENT-NPDAO] 1708 Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient 1709 Route Invalidation", Work in Progress, Internet-Draft, 1710 draft-ietf-roll-efficient-npdao-18, 15 April 2020, 1711 . 1714 15. Informative References 1716 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1717 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1718 Overview, Assumptions, Problem Statement, and Goals", 1719 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1720 . 1722 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1723 Address Autoconfiguration", RFC 4862, 1724 DOI 10.17487/RFC4862, September 2007, 1725 . 1727 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1728 Power and Lossy Networks (RPL) Option for Carrying RPL 1729 Information in Data-Plane Datagrams", RFC 6553, 1730 DOI 10.17487/RFC6553, March 2012, 1731 . 1733 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1734 Routing Header for Source Routes with the Routing Protocol 1735 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1736 DOI 10.17487/RFC6554, March 2012, 1737 . 1739 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1740 Statement and Requirements for IPv6 over Low-Power 1741 Wireless Personal Area Network (6LoWPAN) Routing", 1742 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1743 . 1745 [RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed., 1746 "Source Address Validation Improvement (SAVI) Framework", 1747 RFC 7039, DOI 10.17487/RFC7039, October 2013, 1748 . 1750 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1751 Constrained-Node Networks", RFC 7228, 1752 DOI 10.17487/RFC7228, May 2014, 1753 . 1755 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1756 "IPv6 over Low-Power Wireless Personal Area Network 1757 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1758 April 2017, . 1760 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 1761 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 1762 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 1763 RFC 8415, DOI 10.17487/RFC8415, November 2018, 1764 . 1766 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1767 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1768 DOI 10.17487/RFC6282, September 2011, 1769 . 1771 [RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur, 1772 Ed., "Performance Evaluation of the Routing Protocol for 1773 Low-Power and Lossy Networks (RPL)", RFC 6687, 1774 DOI 10.17487/RFC6687, October 2012, 1775 . 1777 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1778 and M. Richardson, Ed., "A Security Threat Analysis for 1779 the Routing Protocol for Low-Power and Lossy Networks 1780 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1781 . 1783 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1784 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1785 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1786 . 1788 [RFC8929] Thubert, P., Ed., Perkins, C.E., and E. Levy-Abegnoli, 1789 "IPv6 Backbone Router", RFC 8929, DOI 10.17487/RFC8929, 1790 November 2020, . 1792 Appendix A. Example Compression 1794 Figure 13 illustrates the case in Storing Mode where the packet is 1795 received from the Internet, then the Root encapsulates the packet to 1796 insert the RPI and deliver to the 6LR that is the parent and last hop 1797 to the final destination, which is not known to support [RFC8138]. 1799 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1800 |11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP 1801 |Page 1 |Type1 S=0| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 1802 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1803 <-4 bytes-> <- RFC 6282 -> 1804 <- No RPL artifact ... 1806 Figure 13: Encapsulation to Parent 6LR in Storing Mode 1808 The difference with the example presented in Figure 19 of [RFC8138] 1809 is the addition of a SRH-6LoRH before the RPI-6LoRH to transport the 1810 compressed address of the 6LR as the destination address of the outer 1811 IPv6 header. In the [RFC8138] example the destination IP of the 1812 outer header was elided and was implicitly the same address as the 1813 destination of the inner header. Type 1 was arbitrarily chosen, and 1814 the size of 0 denotes a single address in the SRH. 1816 In Figure 13, the source of the IPv6-in-IPv6 encapsulation is the 1817 Root, so it is elided in the IPv6-in-IPv6 6LoRH. The destination is 1818 the parent 6LR of the destination of the encapsulated packet so it 1819 cannot be elided. If the DODAG is operated in Storing Mode, it is 1820 the single entry in the SRH-6LoRH and the SRH-6LoRH Size is encoded 1821 as 0. The SRH-6LoRH is the first 6LoRH in the chain. In this 1822 particular example, the 6LR address can be compressed to 2 bytes so a 1823 Type of 1 is used. It results that the total length of the SRH-6LoRH 1824 is 4 bytes. 1826 In Non-Storing Mode, the encapsulation from the Root would be similar 1827 to that represented in Figure 13 with possibly more hops in the SRH- 1828 6LoRH and possibly multiple SRH-6LoRHs if the various addresses in 1829 the routing header are not compressed to the same format. Note that 1830 on the last hop to the parent 6LR, the RH3 is consumed and removed 1831 from the compressed form, so the use of Non-Storing Mode vs. Storing 1832 Mode is indistinguishable from the packet format. 1834 The SRH-6LoRHs are followed by RPI-6LoRH and then the IPv6-in-IPv6 1835 6LoRH. When the IPv6-in-IPv6 6LoRH is removed, all the 6LoRH Headers 1836 that precede it are also removed. The Paging Dispatch [RFC8025] may 1837 also be removed if there was no previous Page change to a Page other 1838 than 0 or 1, since the LOWPAN_IPHC is encoded in the same fashion in 1839 the default Page 0 and in Page 1. The resulting packet to the 1840 destination is the encapsulated packet compressed with [RFC6282]. 1842 Authors' Addresses 1844 Pascal Thubert (editor) 1845 Cisco Systems, Inc 1846 Building D 1847 45 Allee des Ormes - BP1200 1848 06254 Mougins - Sophia Antipolis 1849 France 1851 Phone: +33 497 23 26 34 1852 Email: pthubert@cisco.com 1854 Michael C. Richardson 1855 Sandelman Software Works 1857 Email: mcr+ietf@sandelman.ca 1858 URI: http://www.sandelman.ca/