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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: 18 June 2021 15 December 2020 8 Routing for RPL Leaves 9 draft-ietf-roll-unaware-leaves-25 11 Abstract 13 This specification updates RFC6550, RFC6775, and RFC8505, to provide 14 routing services to IPv6 Nodes that implement RFC6775, RFC8505, and 15 their extensions therein, but do not support RFC6550. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at https://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on 18 June 2021. 34 Copyright Notice 36 Copyright (c) 2020 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 41 license-info) in effect on the date of publication of this document. 42 Please review these documents carefully, as they describe your rights 43 and restrictions with respect to this document. Code Components 44 extracted from this document must include Simplified BSD License text 45 as described in Section 4.e of the Trust Legal Provisions and are 46 provided without warranty as described in the Simplified BSD License. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 51 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 52 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 6 53 2.2. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 6 54 2.3. References . . . . . . . . . . . . . . . . . . . . . . . 7 55 3. RPL External Routes and Dataplane Artifacts . . . . . . . . . 8 56 4. 6LoWPAN Neighbor Discovery . . . . . . . . . . . . . . . . . 9 57 4.1. RFC 6775 Address Registration . . . . . . . . . . . . . . 9 58 4.2. RFC 8505 Extended Address Registration . . . . . . . . . 9 59 4.2.1. R Flag . . . . . . . . . . . . . . . . . . . . . . . 10 60 4.2.2. TID, "I" Field and Opaque Fields . . . . . . . . . . 10 61 4.2.3. Route Ownership Verifier . . . . . . . . . . . . . . 11 62 4.3. RFC 8505 Extended DAR/DAC . . . . . . . . . . . . . . . . 11 63 4.3.1. RFC 7400 Capability Indication Option . . . . . . . . 12 64 5. Requirements on the RPL-Unware leaf . . . . . . . . . . . . . 12 65 5.1. Support of 6LoWPAN ND . . . . . . . . . . . . . . . . . . 12 66 5.2. Support of IPv6 Encapsulation . . . . . . . . . . . . . . 13 67 5.3. Support of the Hop-by-Hop Header . . . . . . . . . . . . 13 68 5.4. Support of the Routing Header . . . . . . . . . . . . . . 13 69 6. Enhancements to RFC 6550 . . . . . . . . . . . . . . . . . . 14 70 6.1. Updated RPL Target Option . . . . . . . . . . . . . . . . 14 71 6.2. Additional Flag in the RPL DODAG Configuration Option . . 16 72 6.3. Updated RPL Status . . . . . . . . . . . . . . . . . . . 17 73 7. Enhancements to draft-ietf-roll-efficient-npdao . . . . . . . 18 74 8. Enhancements to RFC 6775 and RFC8505 . . . . . . . . . . . . 19 75 9. Protocol Operations for Unicast Addresses . . . . . . . . . . 19 76 9.1. General Flow . . . . . . . . . . . . . . . . . . . . . . 20 77 9.2. Detailed Operation . . . . . . . . . . . . . . . . . . . 23 78 9.2.1. Perspective of the 6LN Acting as RUL . . . . . . . . 23 79 9.2.2. Perspective of the 6LR Acting as Border router . . . 24 80 9.2.3. Perspective of the RPL Root . . . . . . . . . . . . . 29 81 9.2.4. Perspective of the 6LBR . . . . . . . . . . . . . . . 30 82 10. Protocol Operations for Multicast Addresses . . . . . . . . . 30 83 11. Security Considerations . . . . . . . . . . . . . . . . . . . 32 84 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 85 12.1. Fixing the Address Registration Option Flags . . . . . . 34 86 12.2. Resizing the ARO Status values . . . . . . . . . . . . . 34 87 12.3. New RPL DODAG Configuration Option Flag . . . . . . . . 34 88 12.4. RPL Target Option Registry . . . . . . . . . . . . . . . 35 89 12.5. New Subregistry for RPL Non-Rejection Status values . . 35 90 12.6. New Subregistry for RPL Rejection Status values . . . . 36 91 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 36 92 14. Normative References . . . . . . . . . . . . . . . . . . . . 36 93 15. Informative References . . . . . . . . . . . . . . . . . . . 38 94 Appendix A. Example Compression . . . . . . . . . . . . . . . . 40 95 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41 97 1. Introduction 99 The design of Low Power and Lossy Networks (LLNs) is generally 100 focused on saving energy, which is the most constrained resource of 101 all. Other design constraints, such as a limited memory capacity, 102 duty cycling of the LLN devices and low-power lossy transmissions, 103 derive from that primary concern. 105 The IETF produced the "Routing Protocol for Low Power and Lossy 106 Networks" [RFC6550] (RPL) to provide IPv6 [RFC8200] routing services 107 within such constraints. RPL belongs to the class of Distance-Vector 108 protocols, which, compared to link-state protocols, limit the amount 109 of topological knowledge that needs to be installed and maintained in 110 each node, and does not require convergence to avoid micro-loops. 112 To save signaling and routing state in constrained networks, RPL 113 allows a path stretch (see [RFC6687]), whereby routing is only 114 performed along a Destination-Oriented Directed Acyclic Graph (DODAG) 115 that is optimized to reach a Root node, as opposed to along the 116 shortest path between 2 peers, whatever that would mean in a given 117 LLN. This trades the quality of peer-to-peer (P2P) paths for a 118 vastly reduced amount of control traffic and routing state that would 119 be required to operate an any-to-any shortest path protocol. 120 Additionally, broken routes may be fixed lazily and on-demand, based 121 on dataplane inconsistency discovery, which avoids wasting energy in 122 the proactive repair of unused paths. 124 For many of the nodes, though not all, the DODAG provides multiple 125 forwarding solutions towards the Root of the topology via so-called 126 parents. RPL is designed to adapt to fuzzy connectivity, whereby the 127 physical topology cannot be expected to reach a stable state, with a 128 lazy control that creates the routes proactively, but may only fix 129 them reactively, upon actual traffic. The result is that RPL 130 provides reachability for most of the LLN nodes, most of the time, 131 but may not converge in the classical sense. 133 RPL can be deployed in conjunction with IPv6 Neighbor Discovery (ND) 134 [RFC4861] [RFC4862] and 6LoWPAN ND [RFC6775] [RFC8505] to maintain 135 reachability within a Non-Broadcast Multiple-Access (NBMA) Multi-Link 136 subnet. 138 In that mode, IPv6 addresses are advertised individually as host 139 routes. Some nodes may act as routers and participate in the 140 forwarding operations whereas others will only receive/originate 141 packets, acting as hosts in the data-plane. In [RFC6550] terms, an 142 IPv6 host [RFC8504] that is reachable over the RPL network is called 143 a leaf. 145 Section 2 of [USEofRPLinfo] defines the terms RPL leaf, RPL-Aware- 146 leaf (RAL) and RPL-Unaware Leaf (RUL). A RPL leaf is a host attached 147 to one or more RPL router(s); as such, it relies on the RPL router(s) 148 to forward its traffic across the RPL domain but does not forward 149 traffic from another node. As opposed to the RAL, the RUL does not 150 participate to RPL, and relies on its RPL router(s) also to inject 151 the routes to its IPv6 addresses in the RPL domain. 153 A RUL may be unable to participate because it is very energy- 154 constrained, code-space constrained, or because it would be unsafe to 155 let it inject routes in RPL. Using 6LoWPAN ND as opposed to RPL as 156 the host-to-router interface limits the surface of the possible 157 attacks by the RUL against the RPL domain, and can protect RUL for 158 its address ownership. 160 This document specifies how the router injects the host routes in the 161 RPL domain on behalf of the RUL. Section 5 details how the RUL can 162 leverage 6LoWPAN ND to obtain the routing services from the router. 163 In that model, the RUL is also a 6LoWPAN Node (6LN) and the RPL-Aware 164 router is also a 6LoWPAN router (6LR). Using the 6LoWPAN ND Address 165 Registration mechanism, the RUL signals that the router must inject a 166 host route for the Registered Address. 168 ------+--------- 169 | Internet 170 | 171 +-----+ 172 | | <------------- 6LBR / RPL Root 173 +-----+ ^ 174 | | 175 o o o o | RPL 176 o o o o o o o o | 177 o o o o o o o o o o | + 178 o o o o o o o | 179 o o o o o o o o o | 6LoWPAN ND 180 o o o o o o | 181 o o o o v 182 o o o <------------- 6LR / RPL Border router 183 ^ 184 | 6LoWPAN ND only 185 v 186 u <------------- 6LN / RPL-Unaware Leaf 188 Figure 1: Injecting Routes on behalf of RULs 190 The RPL Non-Storing Mode mechanism is used to extend the routing 191 state with connectivity to the RULs even when the DODAG is operated 192 in Storing Mode. The unicast packet forwarding operation by the 6LR 193 serving a RUL is described in section 4.1 of [USEofRPLinfo]. 195 Examples of possible RULs include severely energy constrained sensors 196 such as window smash sensor (alarm system), and kinetically powered 197 light switches. Other applications of this specification may include 198 a smart grid network that controls appliances - such as washing 199 machines or the heating system - in the home. Appliances may not 200 participate to the RPL protocol operated in the Smartgrid network but 201 can still interact with the Smartgrid for control and/or metering. 203 This document is organized as follows: 205 * Section 3 and Section 4 present in a non-normative fashion the 206 salient aspects of RPL and 6LoWPAN ND, respectively, that are 207 leveraged in this specification to provide connectivity to a 6LN 208 acting as a RUL across a RPL network. 210 * Section 5 lists the expectations that a RUL needs to match in 211 order to be served by a RPL router that complies with this 212 specification. 214 * Section 6 presents the changes made to [RFC6550]; a new behavior 215 is introduced whereby the 6LR advertises the 6LN's addresses in a 216 RPL DAO message based on the ND registration by the 6LN, and the 217 RPL root performs the EDAR/EDAC exchange with the 6LBR on behalf 218 of the 6LR; modifications are introduced to some RPL options and 219 to the RPL Status to facilitate the integration of the protocols. 221 * Section 7 presents the changes made to [EFFICIENT-NPDAO]; the use 222 of the DCO message is extended to the Non-Storing MOP to report 223 asynchronous issues from the Root to the 6LR. 225 * Section 8 presents the changes made to [RFC6775] and [RFC8505]; 226 The range of the ND status codes is reduced down to 64 values, and 227 the remaining bits in the original status field are now reserved. 229 * Section 9 and Section 10 present the operation of this 230 specification for unicast and multicast flows, respectively, and 231 Section 11 presents associated security considerations. 233 2. Terminology 234 2.1. Requirements Language 236 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 237 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 238 "OPTIONAL" in this document are to be interpreted as described in BCP 239 14 [RFC2119] [RFC8174] when, and only when, they appear in all 240 capitals, as shown here. 242 2.2. Glossary 244 This document uses the following acronyms: 246 AR: Address Resolution (aka Address Lookup) 247 ARQ: Automatic Repeat reQuest 248 6CIO: 6LoWPAN Capability Indication Option 249 6LN: 6LoWPAN Node (a Low Power host or router) 250 6LR: 6LoWPAN router 251 6LBR: 6LoWPAN Border router 252 (E)ARO: (Extended) Address Registration Option 253 (E)DAR: (Extended) Duplicate Address Request 254 (E)DAC: (Extended) Duplicate Address Confirmation 255 DAD: Duplicate Address Detection 256 DAO: Destination Advertisement Object (a RPL message) 257 DCO: Destination Cleanup Object (a RPL message) 258 DIS: DODAG Information solicitation (a RPL message) 259 DIO: DODAG Information Object (a RPL message) 260 DODAG: Destination-Oriented Directed Acyclic Graph 261 LLN: Low-Power and Lossy Network 262 MOP: RPL Mode of Operation 263 NA: Neighbor Advertisement 264 NCE: Neighbor Cache Entry 265 ND: Neighbor Discovery 266 NS: Neighbor solicitation 267 RA: router Advertisement 268 ROVR: Registration Ownership Verifier 269 RPI: RPL Packet Information 270 RAL: RPL-aware Leaf 271 RAN: RPL-Aware Node (either a RPL router or a RPL-aware Leaf) 272 RUL: RPL-Unaware Leaf 273 SRH: Source-Routing Header 274 TID: Transaction ID (a sequence counter in the EARO) 276 2.3. References 278 The Terminology used in this document is consistent with and 279 incorporates that described in "Terms Used in Routing for Low-Power 280 and Lossy Networks (LLNs)" [RFC7102]. A glossary of classical 281 6LoWPAN acronyms is given in Section 2.2. Other terms in use in LLNs 282 are found in "Terminology for Constrained-Node Networks" [RFC7228]. 283 This specification uses the terms 6LN and 6LR to refer specifically 284 to nodes that implement the 6LN and 6LR roles in 6LoWPAN ND and does 285 not expect other functionality such as 6LoWPAN Header Compression 286 [RFC6282] from those nodes. 288 "RPL", the "RPL Packet Information" (RPI), "RPL Instance" (indexed by 289 a RPLInstanceID), "up", "down" are defined in "RPL: IPv6 Routing 290 Protocol for Low-Power and Lossy Networks" [RFC6550]. The RPI is the 291 abstract information that RPL defines to be placed in data packets, 292 e.g., as the RPL Option [RFC6553] within the IPv6 Hop-By-Hop Header. 293 By extension, the term "RPI" is often used to refer to the RPL Option 294 itself. The DODAG Information solicitation (DIS), Destination 295 Advertisement Object (DAO) and DODAG Information Object (DIO) 296 messages are also specified in [RFC6550]. The Destination Cleanup 297 Object (DCO) message is defined in [EFFICIENT-NPDAO]. 299 This document uses the terms RPL-Unaware Leaf (RUL), RPL-Aware Node 300 (RAN) and RPL aware Leaf (RAL) consistently with [USEofRPLinfo]. A 301 RAN is either an RAL or a RPL router. As opposed to a RUL, a RAN 302 manages the reachability of its addresses and prefixes by injecting 303 them in RPL by itself. 305 In this document, readers will encounter terms and concepts that are 306 discussed in the following documents: 308 Classical IPv6 ND: "Neighbor Discovery for IP version 6" [RFC4861] 309 and "IPv6 Stateless Address Autoconfiguration" [RFC4862], 311 6LoWPAN: "Problem Statement and Requirements for IPv6 over Low-Power 312 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606] and 313 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 314 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 315 and 317 6LoWPAN ND: Neighbor Discovery Optimization for Low-Power and Lossy 318 Networks [RFC6775], "Registration Extensions for 6LoWPAN Neighbor 319 Discovery" [RFC8505], and "Address Protected Neighbor Discovery 320 for Low-power and Lossy Networks" [RFC8928]. 322 3. RPL External Routes and Dataplane Artifacts 324 Section 4.1 of [USEofRPLinfo] provides a set of rules summarized 325 below that must be followed for routing packets from and to a RUL. 327 A 6LR that acts as a border router for external routes advertises 328 them using Non-Storing Mode DAO messages that are unicast directly to 329 the Root, even if the DODAG is operated in Storing Mode. Non-Storing 330 Mode routes are not visible inside the RPL domain and all packets are 331 routed via the Root. The RPL Root tunnels the packets directly to 332 the 6LR that advertised the external route, which decapsulates and 333 forwards the original (inner) packet. 335 The RPL Non-Storing MOP signaling and the associated IPv6-in-IPv6 336 encapsulated packets appear as normal traffic to the intermediate 337 routers. The support of external routes only impacts the Root and 338 the 6LR. It can be operated with legacy intermediate routers and 339 does not add to the amount of state that must be maintained in those 340 routers. A RUL is an example of a destination that is reachable via 341 an external route that happens to be also a host route. 343 The RPL data packets typically carry a Hop-by-Hop Header with a RPL 344 Option [RFC6553] that contains the Packet Information (RPI) defined 345 in section 11.2 of [RFC6550]. Unless the RUL already placed a RPL 346 Option in outer header chain, the packets from and to the RUL are 347 encapsulated using an IPv6-in-IPv6 tunnel between the Root and the 348 6LR that serves the RUL (see sections 7 and 8 of [USEofRPLinfo] for 349 details). If the packet from the RUL has an RPI, the 6LR as a RPL 350 border router SHOULD rewrite the RPI to indicate the selected 351 Instance and set the flags, but it does not need to encapsulate the 352 packet. 354 In Non-Storing Mode, packets going down carry a Source Routing Header 355 (SRH). The IPv6-in-IPv6 encapsulation, the RPI and the SRH are 356 collectively called the "RPL artifacts" and can be compressed using 357 [RFC8138]. Appendix A presents an example compressed format for a 358 packet forwarded by the Root to a RUL in a Storing Mode DODAG. 360 The inner packet that is forwarded to the RUL may carry some RPL 361 artifacts, e.g., an RPI if the original packet was generated with it, 362 and an SRH in a Non-Storing Mode DODAG. [USEofRPLinfo] expects the 363 RUL to support the basic "IPv6 Node Requirements" [RFC8504]. In 364 particular the RUL is expected to ignore the RPL artifacts that are 365 either consumed or not applicable to a host. 367 A RUL is not expected to support the compression method defined in 368 [RFC8138]. For that reason, the border router uncompresses the 369 packet before forwarding it over an external route to a RUL 370 [USEofRPLinfo]. 372 4. 6LoWPAN Neighbor Discovery 374 This section goes through the 6LoWPAN ND mechanisms that this 375 specification leverages, as a non-normative reference to the reader. 376 The full normative text is to be found in [RFC6775], [RFC8505], and 377 [RFC8928]. 379 4.1. RFC 6775 Address Registration 381 The classical "IPv6 Neighbor Discovery (IPv6 ND) Protocol" [RFC4861] 382 [RFC4862] was defined for serial links and transit media such as 383 Ethernet. It is a reactive protocol that relies heavily on multicast 384 operations for Address Discovery (aka Lookup) and Duplicate Address 385 Detection (DAD). 387 "Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775] 388 adapts IPv6 ND for operations over energy-constrained LLNs. The main 389 functions of [RFC6775] are to proactively establish the Neighbor 390 Cache Entry (NCE) in the 6LR and to prevent address duplication. To 391 that effect, [RFC6775] introduces a new unicast Address Registration 392 mechanism that contributes to reducing the use of multicast messages 393 compared to the classical IPv6 ND protocol. 395 [RFC6775] defines a new Address Registration Option (ARO) that is 396 carried in the unicast Neighbor solicitation (NS) and Neighbor 397 Advertisement (NA) messages between the 6LoWPAN Node (6LN) and the 398 6LoWPAN router (6LR). It also defines the Duplicate Address Request 399 (DAR) and Duplicate Address Confirmation (DAC) messages between the 400 6LR and the 6LoWPAN Border router (6LBR). In an LLN, the 6LBR is the 401 central repository of all the Registered Addresses in its domain and 402 the source of truth for uniqueness and ownership. 404 4.2. RFC 8505 Extended Address Registration 406 "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505] 407 updates the behavior of RFC 6775 to enable a generic Address 408 Registration to services such as routing and ND proxy, and defines 409 the Extended Address Registration Option (EARO) as shown in Figure 2: 411 0 1 2 3 412 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 1 413 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 414 | Type | Length | Status | Opaque | 415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 416 | Rsvd | I |R|T| TID | Registration Lifetime | 417 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 418 | | 419 ... Registration Ownership Verifier ... 420 | | 421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 423 Figure 2: EARO Option Format 425 4.2.1. R Flag 427 [RFC8505] introduces the R Flag in the EARO. The Registering Node 428 sets the R Flag to indicate whether the 6LR should ensure 429 reachability for the Registered Address. If the R Flag is set to 0, 430 then the Registering Node handles the reachability of the Registered 431 Address by other means. In a RPL network, this means that either it 432 is a RAN that injects the route by itself or that it uses another RPL 433 router for reachability services. 435 This document specifies how the R Flag is used in the context of RPL. 436 A RPL leaf that implements the 6LN functionality in [RFC8505] 437 requires reachability services for an IPv6 address if and only if it 438 sets the R Flag in the NS(EARO) used to register the address to a 6LR 439 acting as a RPL border router. Upon receiving the NS(EARO), the RPL 440 router generates a DAO message for the Registered Address if and only 441 if the R flag is set to 1. 443 Section 9.2 specifies additional operations when R flag is set to 1 444 in an EARO that is placed either in an NS or an NA message. 446 4.2.2. TID, "I" Field and Opaque Fields 448 When the T Flag is set to 1, the EARO includes a sequence counter 449 called Transaction ID (TID), that is needed to fill the Path Sequence 450 Field in the RPL Transit Option. This is the reason why the support 451 of [RFC8505] by the RUL, as opposed to only [RFC6775] is a 452 prerequisite for this specification)/; this requirement is fully 453 explained in Section 5.1. The EARO also transports an Opaque field 454 and an associated "I" field that describes what the Opaque field 455 transports and how to use it. 457 Section 9.2.1 specifies the use of the "I" field and the Opaque field 458 by a RUL. 460 4.2.3. Route Ownership Verifier 462 Section 5.3 of [RFC8505] introduces the Registration Ownership 463 Verifier (ROVR) field of variable length from 64 to 256 bits. The 464 ROVR is a replacement of the EUI-64 in the ARO [RFC6775] that was 465 used to identify uniquely an Address Registration with the Link-Layer 466 address of the owner but provided no protection against spoofing. 468 "Address Protected Neighbor Discovery for Low-power and Lossy 469 Networks" [RFC8928] leverages the ROVR field as a cryptographic proof 470 of ownership to prevent a rogue third party from registering an 471 address that is already owned. The use of ROVR field enables the 6LR 472 to block traffic that is not sourced at an owned address. 474 This specification does not address how the protection by [RFC8928] 475 could be extended for use in RPL. On the other hand, it adds the 476 ROVR to the DAO to build the proxied EDAR at the Root (see 477 Section 6.1), which means that nodes that are aware of the host route 478 are also aware of the ROVR associated to the Target Address. 480 4.3. RFC 8505 Extended DAR/DAC 482 [RFC8505] updates the DAR/DAC messages into the Extended DAR/DAC to 483 carry the ROVR field. The EDAR/EDAC exchange takes place between the 484 6LR and the 6LBR. It is triggered by an NS(EARO) message from a 6LN 485 to create, refresh, and delete the corresponding state in the 6LBR. 486 The exchange is protected by the retry mechanism (ARQ) specified in 487 Section 8.2.6 of [RFC6775], though in an LLN, a duration longer than 488 the default value of the RetransTimer (RETRANS_TIMER) [RFC4861] of 1 489 second may be necessary to cover the round trip delay between the 6LR 490 and the 6LBR. 492 RPL [RFC6550] specifies a periodic DAO from the 6LN all the way to 493 the Root that maintains the routing state in the RPL network for the 494 lifetime indicated by the source of the DAO. This means that for 495 each address, there are two keep-alive messages that traverse the 496 whole network, one to the Root and one to the 6LBR. 498 This specification avoids the periodic EDAR/EDAC exchange across the 499 LLN. The 6LR turns the periodic NS(EARO) from the RUL into a DAO 500 message to the Root on every refresh, but it only generates the EDAR 501 upon the first registration, for the purpose of DAD, which must be 502 verified before the address is injected in RPL. Upon the DAO 503 message, the Root proxies the EDAR exchange to refresh the state at 504 the 6LBR on behalf of the 6LR, as illustrated in Figure 8 in 505 Section 9.1. 507 4.3.1. RFC 7400 Capability Indication Option 509 "6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power 510 Wireless Personal Area Networks (6LoWPANs)" [RFC7400] defines the 511 6LoWPAN Capability Indication Option (6CIO) that enables a node to 512 expose its capabilities in router Advertisement (RA) messages. 514 [RFC8505] defines a number of bits in the 6CIO, in particular: 516 L: Node is a 6LR. 517 E: Node is an IPv6 ND Registrar -- i.e., it supports registrations 518 based on EARO. 519 P: Node is a Routing Registrar, -- i.e., an IPv6 ND Registrar that 520 also provides reachability services for the Registered Address. 522 0 1 2 3 523 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 1 524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 525 | Type | Length = 1 | Reserved |D|L|B|P|E|G| 526 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 527 | Reserved | 528 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 530 Figure 3: 6CIO flags 532 A 6LR that provides reachability services for a RUL in a RPL network 533 as specified in this document includes a 6CIO in its RA messages and 534 set the L, P and E flags to 1 as prescribed by [RFC8505]; this is 535 fully explained in Section 9.2. 537 5. Requirements on the RPL-Unware leaf 539 This document describes how RPL routing can be extended to reach a 540 RUL. This section specifies the minimal RPL-independent 541 functionality that the RUL needs to implement to obtain routing 542 services for its addresses. 544 5.1. Support of 6LoWPAN ND 546 To obtain routing services from a router that implements this 547 specification, a RUL needs to implement [RFC8505] and sets the "R" 548 and "T" flags in the EARO to 1 as discussed in Section 4.2.1 and 549 Section 4.2.3, respectively. Section 9.2.1 specifies new behaviors 550 for the RUL, e.g., when the R Flag set to 1 in a NS(EARO) is not 551 echoed in the NA(EARO), which indicates that the route injection 552 failed. 554 The RUL is expected to request routing services from a router only if 555 that router originates RA messages with a CIO that has the L, P, and 556 E flags all set to 1 as discussed in Section 4.3.1, unless configured 557 to do so. It is suggested that the RUL also implements [RFC8928] to 558 protect the ownership of its addresses. 560 A RUL that may attach to multiple 6LRs is expected to prefer those 561 that provide routing services. The RUL needs to register to all the 562 6LRs from which it desires routing services. 564 Parallel Address Registrations to several 6LRs should be performed in 565 a rapid sequence, using the same EARO for the same Address. Gaps 566 between the Address Registrations will invalidate some of the routes 567 till the Address Registration finally shows on those routes. 569 [RFC8505] introduces error Status values in the NA(EARO) which can be 570 received synchronously upon an NS(EARO) or asynchronously. The RUL 571 needs to support both cases and refrain from using the address when 572 the Status value indicates a rejection (see Section 6.3). 574 5.2. Support of IPv6 Encapsulation 576 Section 2.1 of [USEofRPLinfo] defines the rules for tunneling either 577 to the final destination (e.g., a RUL) or to its attachment router 578 (designated as 6LR). In order to terminate the IPv6-in-IPv6 tunnel, 579 the RUL, as an IPv6 host, would have to be capable of decapsulating 580 the tunneled packet and either drop the encapsulated packet if it is 581 not the final destination, or pass it to the upper layer for further 582 processing. As indicated in section 4.1 of [USEofRPLinfo], this is 583 not mandated by [RFC8504], so the Root typically terminates the IPv6- 584 in-IPv6 tunnel at the parent 6LR. It is thus not necessary for a RUL 585 to support IPv6-in-IPv6 decapsulation. 587 5.3. Support of the Hop-by-Hop Header 589 A RUL is expected to process an Option Type in a Hop-by-Hop Header as 590 prescribed by section 4.2 of [RFC8200]. An RPI with an Option Type 591 of 0x23 [USEofRPLinfo] is thus skipped when not recognized. 593 5.4. Support of the Routing Header 595 A RUL is expected to process an unknown Routing Header Type as 596 prescribed by section 4.4 of [RFC8200]. This implies that the Source 597 Routing Header with a Routing Type of 3 [RFC6554] is ignored when the 598 Segments Left is zero. 600 6. Enhancements to RFC 6550 602 This document specifies a new behavior whereby a 6LR injects DAO 603 messages for unicast addresses (see Section 9) and multicast 604 addresses (see Section 10) on behalf of leaves that are not aware of 605 RPL. The RUL addresses are exposed as external targets [RFC6550]. 606 Conforming to [USEofRPLinfo], an IPv6-in-IPv6 encapsulation between 607 the 6LR and the RPL Root is used to carry the RPL artifacts and 608 remove them when forwarding outside the RPL domain, e.g., to a RUL. 610 This document also synchronizes the liveness monitoring at the Root 611 and the 6LBR. The same value of lifetime is used for both, and a 612 single keep-alive message, the RPL DAO, traverses the RPL network. A 613 new behavior is introduced whereby the RPL Root proxies the EDAR 614 message to the 6LBR on behalf of the 6LR (see Section 8), for any 615 leaf node that implements the 6LN functionality in [RFC8505]. 617 Section 6.7.7 of [RFC6550] introduces the RPL Target Option, which 618 can be used in RPL Control messages such as the DAO message to signal 619 a destination prefix. This document adds the capabilities to 620 transport the ROVR field (see Section 4.2.3) and the IPv6 Address of 621 the prefix advertiser when the Target is a shorter prefix. Their use 622 is signaled respectively by a new ROVR Size field being non-zero and 623 a new "Advertiser address in Full" 'F' flag set to 1, see 624 Section 6.1. 626 This specification defines a new flag, "Root Proxies EDAR/EDAC" (P), 627 in the RPL DODAG Configuration option, see Section 6.2. 629 The RPL Status defined in section 6.5.1 of [RFC6550] for use in the 630 DAO-ACK message is extended to be placed in DCO messages 631 [EFFICIENT-NPDAO] as well. Furthermore, this specification enables 632 to carry the EARO Status defined for 6LoWPAN ND in RPL DAO and DCO 633 messages, embedded in a RPL Status, see Section 6.3. 635 Section 12 of [RFC6550] details the RPL support for multicast flows 636 when the RPLInstance is operated in the MOP of 3 ("Storing Mode of 637 Operation with multicast support"). This specification extends the 638 RPL Root operation to proxy-relay the MLDv2 [RFC3810] operation 639 between the RUL and the 6LR, see Section 10. 641 6.1. Updated RPL Target Option 643 This specification updates the RPL Target Option to transport the 644 ROVR that was also defined for 6LoWPAN ND messages. This enables the 645 RPL Root to generate the proxied EDAR message to the 6LBR. 647 The Target Prefix of the RPL Target Option is left (high bit) 648 justified and contains the advertised prefix; its size may be smaller 649 than 128 when it indicates a Prefix route. The Prefix Length field 650 signals the number of bits that correspond to the advertised Prefix; 651 it is 128 for a host route or less in the case of a Prefix route. 652 This remains unchanged. 654 This specification defines the new 'F' flag. When it is set to 1, 655 the size of the Target Prefix field MUST be 128 bits and it MUST 656 contain an IPv6 address of the advertising node taken from the 657 advertised Prefix. In that case, the Target Prefix field carries two 658 distinct pieces of information: a route that can be a host route or a 659 Prefix route depending on the Prefix Length, and an IPv6 address that 660 can be used to reach the advertising node and validate the route. 662 If the 'F' flag is set to 0, the Target Prefix field can be shorter 663 than 128 bits and it MUST be aligned to the next byte boundary after 664 the end of the prefix. Any additional bits in the rightmost octet 665 are filled with padding bits. Padding bits are reserved and set to 0 666 as specified in section 6.7.7 of [RFC6550]. 668 With this specification the ROVR is the remainder of the RPL Target 669 Option. The size of the ROVR is indicated in a new ROVR Size field 670 that is encoded to map one-to-one with the Code Suffix in the EDAR 671 message (see table 4 of [RFC8505]). The ROVR Size field is taken 672 from the flags field, which is an update to the RPL Target Option 673 Flags IANA registry. 675 The updated format is illustrated in Figure 4. It is backward 676 compatible with the Target Option in [RFC6550]. It is recommended 677 that the updated format be used as a replacement in new 678 implementations in all MOPs in preparation for upcoming Route 679 Ownership Validation mechanisms based on the ROVR, unless the device 680 or the network is so constrained that this is not feasible. 682 0 1 2 3 683 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 1 684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 685 | Type = 0x05 | Option Length |ROVRsz |F|Flags| Prefix Length | 686 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 687 | | 688 | Target Prefix (Variable Length) | 689 . . 690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 691 | | 692 ... Registration Ownership Verifier (ROVR) ... 693 | | 694 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 695 Figure 4: Updated Target Option 697 New fields: 699 ROVRsz (ROVR Size): Indicates the Size of the ROVR. It SHOULD be 1, 700 2, 3, or 4, indicating a ROVR size of 64, 128, 192, or 256 bits, 701 respectively. If a legacy Target Option is used, then the value 702 must remain 0, as specified in [RFC6550]. In case of a value 703 above 4, the size of the ROVR is undetermined and this node cannot 704 validate the ROVR; an implementation SHOULD propagate the whole 705 Target Option upwards as received to enable the verification by an 706 ancestor that would support the upgraded ROVR. 708 F: 1-bit flag. Set to 1 to indicate that Target Prefix field 709 contains the complete (128 bit) IPv6 address of the advertising 710 node. 712 Flags: The 3 bits remaining unused in the Flags field are reserved 713 for flags. The field MUST be initialized to zero by the sender 714 and MUST be ignored by the receiver. 716 Registration Ownership Verifier (ROVR): This is the same field as in 717 the EARO, see [RFC8505] 719 6.2. Additional Flag in the RPL DODAG Configuration Option 721 The DODAG Configuration Option is defined in Section 6.7.6 of 722 [RFC6550]. Its purpose is extended to distribute configuration 723 information affecting the construction and maintenance of the DODAG, 724 as well as operational parameters for RPL on the DODAG, through the 725 DODAG. This Option was originally designed with 4 bit positions 726 reserved for future use as Flags. 728 0 1 2 3 729 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 1 730 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 731 | Type = 0x04 |Opt Length = 14| |P| | |A| ... | 732 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 733 |4 bits | 735 Figure 5: DODAG Configuration Option (Partial View) 737 This specification defines a new flag "Root Proxies EDAR/EDAC" (P). 738 The 'P' flag is encoded in bit position 1 of the reserved Flags in 739 the DODAG Configuration Option (counting from bit 0 as the most 740 significant bit) and it is set to 0 in legacy implementations as 741 specified respectively in Sections 20.14 and 6.7.6 of [RFC6550]. 743 The 'P' flag is set to 1 to indicate that the Root performs the proxy 744 operation, which implies that it supports this specification and the 745 updated RPL Target Option (see Section 6.1). 747 Section 4.3 of [USEofRPLinfo] updates [RFC6550] to indicate that the 748 definition of the Flags applies to Mode of Operation (MOP) values 749 zero (0) to six (6) only. For a MOP value of 7, the implementation 750 MUST consider that the Root performs the proxy operation. 752 The RPL DODAG Configuration Option is typically placed in a DODAG 753 Information Object (DIO) message. The DIO message propagates down 754 the DODAG to form and then maintain its structure. The DODAG 755 Configuration Option is copied unmodified from parents to children. 756 [RFC6550] states that "Nodes other than the DODAG Root MUST NOT 757 modify this information when propagating the DODAG Configuration 758 option". Therefore, a legacy parent propagates the 'P' Flag as set 759 by the Root, and when the 'P' Flag is set to 1, it is transparently 760 flooded to all the nodes in the DODAG. 762 6.3. Updated RPL Status 764 The RPL Status is defined in section 6.5.1 of [RFC6550] for use in 765 the DAO-ACK message and values are assigned as follows: 767 +---------+--------------------------------+ 768 | Range | Meaning | 769 +---------+--------------------------------+ 770 | 0 | Success/Unqualified acceptance | 771 +---------+--------------------------------+ 772 | 1-127 | Not an outright rejection | 773 +---------+--------------------------------+ 774 | 128-255 | Rejection | 775 +---------+--------------------------------+ 777 Table 1: RPL Status per RFC 6550 779 The 6LoWPAN ND Status was defined for use in the EARO, see section 780 4.1 of [RFC8505]. This specification adds a capability to allow the 781 carriage of 6LoWPAN ND Status values in RPL DAO and DCO messages, 782 embedded in the RPL Status field. 784 To achieve this, the range of the ARO/EARO Status values is reduced 785 to 0-63, which updates the IANA registry created for [RFC6775]. This 786 reduction ensures that the values fit within a RPL Status as shown in 787 Figure 6. See Section 12.2, Section 12.5, and Section 12.6 for the 788 respective IANA declarations. 790 0 1 2 3 4 5 6 7 791 +-+-+-+-+-+-+-+-+ 792 |E|A|StatusValue| 793 +-+-+-+-+-+-+-+-+ 795 Figure 6: RPL Status Format 797 This specification updates the RPL Status with subfields as indicated 798 below: 800 E: 1-bit flag. set to 1 to indicate a rejection. When set to 0, a 801 Status value of 0 indicates Success/Unqualified acceptance and 802 other values indicate "not an outright rejection" as per RFC 6550. 804 A: 1-bit flag. Indicates the type of the RPL Status value. 806 Status Value: 6-bit unsigned integer. If the 'A' flag is set to 1 807 this field transports a Status value defined for IPv6 ND EARO. 808 When the 'A' flag is set to 0, the Status value is defined for 809 RPL. 811 When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a EDAC 812 message, the RPL Root MUST copy the 6LoWPAN ND status code unchanged 813 in the RPL Status value and set the 'A' flag to 1. The RPL Root MUST 814 set the 'E' flag to 1 for all rejection and unknown status codes. 815 The status codes in the 1-10 range [RFC8505] are all considered 816 rejections. 818 Reciprocally, upon a DCO or a DAO-ACK message from the RPL Root with 819 a RPL Status that has the 'A' flag set, the 6LR MUST copy the RPL 820 Status value unchanged in the Status field of the EARO when 821 generating an NA to the RUL. 823 7. Enhancements to draft-ietf-roll-efficient-npdao 825 [EFFICIENT-NPDAO] defines the DCO message for RPL Storing Mode only, 826 with a link-local scope. All nodes in the RPL network are expected 827 to support the specification since the message is processed hop by 828 hop along the path that is being cleaned up. 830 This specification extends the use of the DCO message to the Non- 831 Storing MOP, whereby the DCO is sent end-to-end by the Root directly 832 to the RAN that injected the DAO message for the considered target. 833 In that case, intermediate nodes do not need to support 834 [EFFICIENT-NPDAO]; they forward the DCO message as a plain IPv6 835 packet between the Root and the RAN. 837 In the case of a RUL, the 6LR that serves the RUL acts as the RAN 838 that receives the Non-Storing DCO. This specification leverages the 839 Non-Storing DCO between the Root and the 6LR that serves as 840 attachment router for a RUL. A 6LR and a Root that support this 841 specification MUST implement the Non-Storing DCO. 843 8. Enhancements to RFC 6775 and RFC8505 845 This document updates [RFC6775] and [RFC8505] to reduce the range of 846 the ND status codes down to 64 values. The two most significant 847 (leftmost) bits if the original ND status field are now reserved, 848 they MUST be set to zero by the sender and ignored by the receiver. 850 This document also changes the behavior of a 6LR acting as RPL router 851 and of a 6LN acting as RUL in the 6LoWPAN ND Address Registration as 852 follows: 854 * If the RPL Root advertises the capability to proxy the EDAR/EDAC 855 exchange to the 6LBR, the 6LR refrains from sending the keep-alive 856 EDAR message. If it is separated from the 6LBR, the Root 857 regenerates the EDAR message to the 6LBR periodically, upon a DAO 858 message that signals the liveliness of the address. 860 * The use of the R Flag is extended to the NA(EARO) to confirm 861 whether the route was installed. 863 9. Protocol Operations for Unicast Addresses 865 The description below assumes that the Root sets the 'P' flag in the 866 DODAG Configuration Option and performs the EDAR proxy operation 867 presented in Section 4.3 . 869 If the 'P' flag is set to 0, the 6LR MUST generate the periodic EDAR 870 messages and process the returned status as specified in [RFC8505]. 871 If the EDAC indicates success, the rest of the flow takes place as 872 presented but without the proxied EDAR/EDAC exchange. 874 Section 9.1 provides an overview of the route injection in RPL, 875 whereas Section 9.2 offers more details from the perspective of the 876 different nodes involved in the flow. 878 9.1. General Flow 880 This specification eliminates the need to exchange keep-alive 881 Extended Duplicate Address messages, EDAR and EDAC, all the way from 882 a 6LN to the 6LBR across a RPL mesh. Instead, the EDAR/EDAC exchange 883 with the 6LBR is proxied by the RPL Root upon the DAO message that 884 refreshes the RPL routing state. The first EDAR upon a new 885 Registration cannot be proxied, though, as it serves for the purpose 886 of DAD, which must be verified before the address is injected in RPL. 888 In a RPL network where the function is enabled, refreshing the state 889 in the 6LBR is the responsibility of the Root. Consequently, only 890 addresses that are injected in RPL will be kept alive at the 6LBR by 891 the RPL Root. Since RULs are advertised using Non-Storing Mode, the 892 DAO message flow and the keep alive EDAR/EDAC can be nested within 893 the Address (re)Registration flow. Figure 7 illustrates that, for 894 the first Registration, both the DAD and the keep-alive EDAR/EDAC 895 exchanges happen in the same sequence. 897 6LN/RUL 6LR <6LR*> Root 6LBR 898 | | | | 899 |<------ND------>|<----RPL----->|<-------ND-------->| 900 | |<----------------ND-------------->| 901 | | | | 902 | NS(EARO) | | | 903 |--------------->| | 904 | | EDAR | 905 | |--------------------------------->| 906 | | | 907 | | EDAC | 908 | |<---------------------------------| 909 | | DAO | | 910 | |------------->| | 911 | | | EDAR | 912 | | |------------------>| 913 | | | EDAC | 914 | | |<------------------| 915 | | DAO-ACK | | 916 | |<-------------| | 917 | NA(EARO) | | | 918 |<---------------| | | 919 | | | | 921 Figure 7: First RUL Registration Flow 923 This flow requires that the lifetimes and sequence counters in 924 6LoWPAN ND and RPL are aligned. 926 To achieve this, the Path Sequence and the Path Lifetime in the DAO 927 message are taken from the Transaction ID and the Address 928 Registration lifetime in the NS(EARO) message from the 6LN. 930 On the first Address Registration, illustrated in Figure 7 for RPL 931 Non-Storing Mode, the Extended Duplicate Address exchange takes place 932 as prescribed by [RFC8505]. If the exchange fails, the 6LR returns 933 an NA message with a non-zero status to the 6LN, the NCE is not 934 created, and the address is not injected in RPL. Otherwise, the 6LR 935 creates an NCE and injects the Registered Address in the RPL routing 936 using a DAO/DAO-ACK exchange with the RPL DODAG Root. 938 An Address Registration refresh is performed by the 6LN to maintain 939 the NCE in the 6LR alive before the lifetime expires. Upon the 940 refresh of a registration, the 6LR reinjects the corresponding route 941 in RPL before it expires, as illustrated in Figure 8. 943 6LN/RUL <-ND-> 6LR <-RPL-> Root <-ND-> 6LBR 944 | | | | 945 | NS(EARO) | | | 946 |--------------->| | | 947 | | DAO | | 948 | |------------->| | 949 | | | EDAR | 950 | | |------------------>| 951 | | | EDAC | 952 | | |<------------------| 953 | | DAO-ACK | | 954 | |<-------------| | 955 | NA(EARO) | | | 956 |<---------------| | | 958 Figure 8: Next RUL Registration Flow 960 This is what causes the RPL Root to refresh the state in the 6LBR, 961 using an EDAC message. In case of an error in the proxied EDAR flow, 962 the error is returned in the DAO-ACK using a RPL Status with the 'A' 963 flag set to 1 that imbeds a 6LoWPAN Status value as discussed in 964 Section 6.3. 966 The 6LR may receive a requested DAO-ACK after it received an 967 asynchronous Non-Storing DCO, but the non-zero status in the DCO 968 supersedes a positive Status in the DAO-ACK regardless of the order 969 in which they are received. Upon the DAO-ACK - or the DCO if one 970 arrives first - the 6LR responds to the RUL with an NA(EARO). 972 An issue may be detected later, e.g., the address moves to a 973 different DODAG with the 6LBR attached to a different 6LoWPAN 974 Backbone router (6BBR), see Figure 5 in section 3.3 of [RFC8929]. 975 The 6BBR may send a negative ND status, e.g., in an asynchronous 976 NA(EARO) to the 6LBR. 978 [RFC8929] expects that the 6LBR is collocated with the RPL Root, but 979 if not, the 6LBR MUST forward the status code to the originator of 980 the EDAR, either the 6LR or the RPL Root that proxies for it. The ND 981 status code is mapped in a RPL Status value by the RPL Root, and then 982 back by the 6LR. 984 Figure 9 illustrates this in the case where the 6LBR and the Root are 985 not collocated, and the Root proxies the EDAR messages. 987 6LN/RUL <-ND-> 6LR <-RPL-> Root <-ND-> 6LBR <-ND-> 6BBR 988 | | | | | 989 | | | | NA(EARO) | 990 | | | |<------------| 991 | | | EDAC | | 992 | | |<-------------| | 993 | | DCO | | | 994 | |<------------| | | 995 | NA(EARO) | | | | 996 |<-------------| | | | 997 | | | | | 999 Figure 9: Asynchronous Issue 1001 If the Root does not proxy, then the EDAC with a non-zero status 1002 reaches the 6LR directly. In that case, the 6LR MUST clean up the 1003 route using a DAO with a Lifetime of zero, and it MUST propagate the 1004 status back to the RUL in a NA(EARO) with the R Flag set to 0. 1006 The RUL may terminate the registration at any time by using a 1007 Registration Lifetime of 0. This specification requires that the RPL 1008 Target Option transports the ROVR. This way, the same flow as the 1009 heartbeat flow is sufficient to inform the 6LBR using the Root as 1010 proxy, as illustrated in Figure 8. 1012 Any combination of the logical functions of 6LR, Root, and 6LBR might 1013 be collapsed in a single node. 1015 9.2. Detailed Operation 1017 The following section specify respectively the behaviour of the 6LN 1018 Acting as RUL, the 6LR Acting as Border router ad serving the 6LN, 1019 the RPL Root and the 6LBR in the control flows that enable RPL 1020 routing back to the RUL. 1022 9.2.1. Perspective of the 6LN Acting as RUL 1024 This specification does not alter the operation of a 6LoWPAN ND- 1025 compliant 6LN/RUL, which is expected to operate as follows: 1027 1. The 6LN selects a 6LR that provides reachability services for a 1028 RUL. This is signaled a 6CIO in the RA messages with the L, P 1029 and E flags set to 1 as prescribed by [RFC8505]. 1031 2. The 6LN obtains an IPv6 global address, either using Stateless 1032 Address Autoconfiguration (SLAAC) [RFC4862] based on a Prefix 1033 Information Option (PIO) [RFC4861] found in an RA message, or 1034 some other means, such as DHCPv6 [RFC8415]. 1036 3. Once it has formed an address, the 6LN registers its address and 1037 refreshes its registration periodically, early enough within the 1038 Lifetime of the previous Address Registration, as prescribed by 1039 [RFC6775], to refresh the NCE before the lifetime indicated in 1040 the EARO expires. It sets the T Flag to 1 as prescribed in 1041 [RFC8505]. The TID is incremented each time and wraps in a 1042 lollipop fashion (see section 5.2.1 of [RFC8505], which is fully 1043 compatible with section 7.2 of [RFC6550]). 1045 4. As stated in section 5.2 of [RFC8505], the 6LN can register to 1046 more than one 6LR at the same time. In that case, it uses the 1047 same EARO for all of the parallel Address Registrations, with the 1048 exception of the Registration Lifetime field and the setting of 1049 the R flag that may differ. The 6LN may cancel a subset of its 1050 registrations, or transfer a registration from one or more old 1051 6LR(s) to one or more new 6LR(s). To do so, the 6LN sends a 1052 series of NS(EARO) messages, all with the same TID, with a zero 1053 Registration Lifetime to the old 6LR(s) and with a non-zero 1054 Registration Lifetime to the new 6LR(s). In that process, the 1055 6LN SHOULD send the NS(EARO) with a non-zero Registration 1056 Lifetime and ensure that at least one succeeds before it sends an 1057 NS(EARO) that terminates another registration. This avoids the 1058 churn related to transient route invalidation in the RPL network 1059 above the common parent of the involved 6LRs. 1061 5. Following section 5.1 of [RFC8505], a 6LN acting as a RUL sets 1062 the R Flag in the EARO of its registration(s) for which it 1063 requires routing services. If the R Flag is not echoed in the 1064 NA, the RUL SHOULD attempt to use another 6LR. The RUL SHOULD 1065 ensure that one registration succeeds before setting the R Flag 1066 to 0. In case of a conflict with the preceding rule on lifetime, 1067 the rule on lifetime has precedence. 1069 6. The 6LN may use any of the 6LRs to which it registered as the 1070 default gateway. Using a 6LR to which the 6LN is not registered 1071 may result in packets dropped at the 6LR by a Source Address 1072 Validation function (SAVI) [RFC7039] so it is not recommended. 1074 Even without support for RPL, the RUL may be configured with an 1075 opaque value to be provided to the routing protocol. If the RUL has 1076 knowledge of the RPL Instance the packet should be injected into, 1077 then it SHOULD set the Opaque field in the EARO to the RPLInstanceID, 1078 otherwise it MUST leave the Opaque field as zero. 1080 Regardless of the setting of the Opaque field, the 6LN MUST set the 1081 "I" field to zero to signal "topological information to be passed to 1082 a routing process", as specified in section 5.1 of [RFC8505]. 1084 A RUL is not expected to produce RPL artifacts in the data packets, 1085 but it may do so. For instance, if the RUL has minimal awareness of 1086 the RPL Instance then it can build an RPI. A RUL that places an RPI 1087 in a data packet SHOULD indicate the RPLInstanceID of the RPL 1088 Instance where the packet should be forwarded. It is up to the 6LR 1089 (e.g., by policy) to use the RPLInstanceID information provided by 1090 the RUL or rewrite it to the selected RPLInstanceID for forwarding 1091 inside the RPL domain. All the flags and the Rank field are set to 0 1092 as specified by section 11.2 of [RFC6550]. 1094 9.2.2. Perspective of the 6LR Acting as Border router 1096 A 6LR that provides reachability services for a RUL in a RPL network 1097 as specified in this document MUST include a 6CIO in its RA messages 1098 and set the L, P and E flags to 1 as prescribed by [RFC8505]. 1100 As prescribed by [RFC8505], the 6LR generates an EDAR message upon 1101 reception of a valid NS(EARO) message for the registration of a new 1102 IPv6 address by a 6LN. If the initial EDAR/EDAC exchange succeeds, 1103 then the 6LR installs an NCE for the Registration Lifetime. For the 1104 registration refreshes, if the RPL Root has indicated that it proxies 1105 the keep-alive EDAR/EDAC exchange with the 6LBR (see Section 6), the 1106 6LR MUST refrain from sending the keep-alive EDAR. 1108 If the R Flag is set to 1 in the NS(EARO), the 6LR SHOULD inject the 1109 host route in RPL, unless this is barred for other reasons, such as 1110 the saturation of the RPL parents. The 6LR MUST use a RPL Non- 1111 Storing Mode signaling and the updated Target Option (see 1112 Section 6.1). The 6LR MUST request a DAO-ACK by setting the 'K' flag 1113 in the DAO message. Success injecting the route to the RUL's address 1114 is indicated by the 'E' flag set to 0 in the RPL status of the DAO- 1115 ACK message. 1117 The Opaque field in the EARO provides a means to signal which RPL 1118 Instance is to be used for the DAO advertisements and the forwarding 1119 of packets sourced at the Registered Address when there is no RPI in 1120 the packet. 1122 As described in [RFC8505], if the "I" field is zero, then the Opaque 1123 field is expected to carry the RPLInstanceID suggested by the 6LN; 1124 otherwise, there is no suggested Instance. If the 6LR participates 1125 in the suggested RPL Instance, then the 6LR MUST use that RPL 1126 Instance for the Registered Address. 1128 If there is no suggested RPL Instance or else if the 6LR does not 1129 participate to the suggested Instance, it is expected that the 1130 packets coming from the 6LN "can unambiguously be associated to at 1131 least one RPL Instance" [RFC6550] by the 6LR, e.g., using a policy 1132 that maps the 6-tuple into an Instance. 1134 The DAO message advertising the Registered Address MUST be 1135 constructed as follows: 1137 1. The Registered Address is signaled as the Target Prefix in the 1138 updated Target Option in the DAO message; the Prefix Length is 1139 set to 128 but the 'F' flag is set to 0 since the advertiser is 1140 not the RUL. The ROVR field is copied unchanged from the EARO 1141 (see Section 6.1). 1143 2. The 6LR indicates one of its global or unique-local IPv6 unicast 1144 addresses as the Parent Address in the RPL Transit Information 1145 Option (TIO) associated with the Target Option 1147 3. The 6LR sets the External 'E' flag in the TIO to indicate that it 1148 is redistributing an external target into the RPL network 1150 4. the Path Lifetime in the TIO is computed from the Registration 1151 Lifetime in the EARO. This operation converts seconds to the 1152 Lifetime Units used in the RPL operation. This creates the 1153 deployment constraint that the Lifetime Unit is reasonably 1154 compatible with the expression of the Registration Lifetime. 1155 e.g., a Lifetime Unit of 0x4000 maps the most significant byte of 1156 the Registration Lifetime to the Path Lifetime. 1158 In that operation, the Path Lifetime must be rounded, if needed, 1159 to the upper value to ensure that the path has a longer lifetime 1160 than the registration. 1162 Note that if the Registration Lifetime is 0, then the Path 1163 Lifetime is also 0 and the DAO message becomes a No-Path DAO, 1164 which cleans up the routes down to the RUL's address; this also 1165 causes the Root as a proxy to send an EDAR message to the 6LBR 1166 with a Lifetime of 0. 1168 5. the Path Sequence in the TIO is set to the TID value found in the 1169 EARO option. 1171 Upon receiving or timing out the DAO-ACK after an implementation- 1172 specific number of retries, the 6LR MUST send the corresponding 1173 NA(EARO) to the RUL. Upon receiving an asynchronous DCO message, if 1174 a DAO-ACK is pending then the 6LR MUST wait for the DAO-ACK to send 1175 the NA(EARO) and deliver the status found in the DCO, else it MUST 1176 send an asynchronous NA(EARO) to the RUL immediately. 1178 The 6LR MUST set the R Flag to 1 in the NA(EARO) back if and only if 1179 the 'E' flag is set to 0, indicating that the 6LR injected the 1180 Registered Address in the RPL routing successfully and that the EDAR 1181 proxy operation succeeded. 1183 If the 'A' flag in the RPL Status is set to 1, the embedded Status 1184 value is passed back to the RUL in the EARO Status. If the 'E' flag 1185 is also set to 1, the registration failed for 6LoWPAN ND related 1186 reasons, and the NCE is removed. 1188 An error injecting the route causes the 'E' flag to be set to 1. If 1189 the error is not related to ND, the 'A' flag is set to 0. In that 1190 case, the registration succeeds, but the RPL route is not installed. 1191 So the NA(EARO) is returned with a status indicating success but the 1192 R Flag set to 0, which means that the 6LN obtained a binding but no 1193 route. 1195 If the 'A' flag is set to 0 in the RPL Status of the DAO-ACK, then 1196 the 6LoWPAN ND operation succeeded, and an EARO Status of 0 (Success) 1197 MUST be returned to the 6LN. The EARO Status of 0 MUST also be used 1198 if the 6LR did not attempt to inject the route but could create the 1199 binding after a successful EDAR/EDAC exchange or refresh it. 1201 If the 'E' flag is set to 1 in the RPL Status of the DAO-ACK, then 1202 the route was not installed and the R flag MUST be set to 0 in the 1203 NA(EARO). The R flag MUST be set to 0 if the 6LR did not attempt to 1204 inject the route. 1206 In a network where Address Protected Neighbor Discovery (AP-ND) is 1207 enabled, in case of a DAO-ACK or a DCO indicating transporting an 1208 EARO Status value of 5 (Validation Requested), the 6LR MUST challenge 1209 the 6LN for ownership of the address, as described in section 6.1 of 1210 [RFC8928], before the Registration is complete. This flow, 1211 illustrated in Figure 10, ensures that the address is validated 1212 before it is injected in the RPL routing. 1214 If the challenge succeeds, then the operations continue as normal. 1215 In particular, a DAO message is generated upon the NS(EARO) that 1216 proves the ownership of the address. If the challenge failed, the 1217 6LR rejects the registration as prescribed by AP-ND and may take 1218 actions to protect itself against DoS attacks by a rogue 6LN, see 1219 Section 11. 1221 6LN 6LR Root 6LBR 1222 | | | | 1223 |<--------------- RA ---------------------| | | 1224 | | | | 1225 |------ NS EARO (ROVR=Crypto-ID) -------->| | | 1226 | | | | 1227 |<- NA EARO(status=Validation Requested) -| | | 1228 | | | | 1229 |----- NS EARO and Proof-of-ownership -->| | 1230 | |--------- EDAR ------->| 1231 | | | 1232 | |<-------- EDAC --------| 1233 | | | 1234 | | | | 1235 | |-- DAO --->| | 1236 | | |-- EDAR -->| 1237 | | | | 1238 | | |<-- EDAC --| 1239 | |<- DAO-ACK-| | 1240 | | | | 1241 |<----------- NA EARO (status=0)----------| | | 1242 | | | | 1243 ... 1244 | | | | 1245 |------ NS EARO (ROVR=Crypto-ID) -------->| | | 1246 | |-- DAO --->| | 1247 | | |-- EDAR -->| 1248 | | | | 1249 | | |<-- EDAC --| 1250 | |<- DAO-ACK-| | 1251 |<----------- NA EARO (status=0)----------| | | 1252 | | | | 1253 ... 1255 Figure 10: Address Protection 1257 The 6LR may at any time send a unicast asynchronous NA(EARO) with the 1258 R Flag set to 0 to signal that it stops providing routing services, 1259 and/or with the EARO Status 2 "Neighbor Cache full" to signal that it 1260 removes the NCE. It may also send a final RA, unicast or multicast, 1261 with a router Lifetime field of zero, to signal that it is ceasing to 1262 serve as router, as specified in section 6.2.5 of [RFC4861]. This 1263 may happen upon a DCO or a DAO-ACK message indicating the path is 1264 already removed; else the 6LR MUST remove the host route to the 6LN 1265 using a DAO message with a Path Lifetime of zero. 1267 A valid NS(EARO) message with the R Flag set to 0 and a Registration 1268 Lifetime that is not zero signals that the 6LN wishes to maintain the 1269 binding but does not require the routing services from the 6LR (any 1270 more). Upon this message, if, due to previous NS(EARO) with the R 1271 Flag set to 1, the 6LR was injecting the host route to the Registered 1272 Address in RPL using DAO messages, then the 6LR MUST invalidate the 1273 host route in RPL using a DAO with a Path Lifetime of zero. It is up 1274 to the Registering 6LN to maintain the corresponding route from then 1275 on, either keeping it active via a different 6LR or by acting as a 1276 RAN and managing its own reachability. 1278 9.2.3. Perspective of the RPL Root 1280 A RPL Root MUST set the 'P' flag to 1 in the RPL DODAG Configuration 1281 Option of the DIO messages that it generates (see Section 6) to 1282 signal that it proxies the EDAR/EDAC exchange and supports the 1283 Updated RPL Target option. 1285 Upon reception of a DAO message, for each updated RPL Target Option 1286 (see Section 6.1) that creates or updates an existing RPL state, the 1287 Root MUST notify the 6LBR by using a proxied EDAR/EDAC exchange. If 1288 if the RPL Root and the 6LBR are integrated, an internal API can be 1289 used. 1291 The EDAR message MUST be constructed as follows: 1293 1. The Target IPv6 address from the RPL Target Option is placed in 1294 the Registered Address field of the EDAR message; 1296 2. the Registration Lifetime is adapted from the Path Lifetime in 1297 the TIO by converting the Lifetime Units used in RPL into units 1298 of 60 seconds used in the 6LoWPAN ND messages; 1300 3. the TID value is set to the Path Sequence in the TIO and 1301 indicated with an ICMP code of 1 in the EDAR message; 1303 4. The ROVR in the RPL Target Option is copied as is in the EDAR and 1304 the ICMP Code Suffix is set to the appropriate value as shown in 1305 Table 4 of [RFC8505] depending on the size of the ROVR field. 1307 Upon receiving an EDAC message from the 6LBR, if a DAO is pending, 1308 then the Root MUST send a DAO-ACK back to the 6LR. Otherwise, if the 1309 Status in the EDAC message is not "Success", then it MUST send an 1310 asynchronous DCO to the 6LR. 1312 In either case, the EDAC Status is embedded in the RPL Status with 1313 the 'A' flag set to 1. 1315 The proxied EDAR/EDAC exchange MUST be protected with a timer of an 1316 appropriate duration and a number of retries, that are 1317 implementation-dependent, and SHOULD be configurable since the Root 1318 and the 6LBR are typically nodes with a higher capacity and 1319 manageability than 6LRs. Upon timing out, the Root MUST send an 1320 error back to the 6LR as above, either using a DAO-ACK or a DCO, as 1321 appropriate, with the 'A' and 'E' flags set to 1 in the RPL status, 1322 and a RPL Status value of of "6LBR Registry Saturated" [RFC8505]. 1324 9.2.4. Perspective of the 6LBR 1326 The 6LBR is unaware that the RPL Root is not the new attachment 6LR 1327 of the RUL, so it is not impacted by this specification. 1329 Upon reception of an EDAR message, the 6LBR acts as prescribed by 1330 [RFC8505] and returns an EDAC message to the sender. 1332 10. Protocol Operations for Multicast Addresses 1334 Section 12 of [RFC6550] details the RPL support for multicast flows. 1335 This support is activated by the MOP of 3 ("Storing Mode of Operation 1336 with multicast support") in the DIO messages that form the DODAG. 1337 This section also applies if and only if the MOP of the RPLInstance 1338 is 3. 1340 The RPL support of multicast is not source-specific and only operates 1341 as an extension to the Storing Mode of Operation for unicast packets. 1342 Note that it is the RPL model that the multicast packet is passed as 1343 a Layer-2 unicast to each of the interested children. This remains 1344 true when forwarding between the 6LR and the listener 6LN. 1346 "Multicast Listener Discovery Version 2 (MLDv2) for IPv6" [RFC3810] 1347 provides an interface for a listener to register to multicast flows. 1348 In the MLD model, the router is a "querier", and the host is a 1349 multicast listener that registers to the querier to obtain copies of 1350 the particular flows it is interested in. 1352 The equivalent of the first Address Registration happens as 1353 illustrated in Figure 11. The 6LN, as an MLD listener, sends an 1354 unsolicited Report to the 6LR. This enables it to start receiving 1355 the flow immediately, and causes the 6LR to inject the multicast 1356 route in RPL. 1358 This specification does not change MLD but will operate more 1359 efficiently if the asynchronous messages for unsolicited Report and 1360 Done are sent by the 6LN as Layer-2 unicast to the 6LR, in particular 1361 on wireless. 1363 The 6LR acts as a generic MLD querier and generates a DAO with the 1364 Multicast Address as the Target Prefix as described in section 12 of 1365 [RFC6550]. As for the Unicast host routes, the Path Lifetime 1366 associated to the Target is mapped from the Query Interval, and set 1367 to be larger to account for variable propagation delays to the Root. 1368 The Root proxies the MLD exchange as a listener with the 6LBR acting 1369 as the querier, so as to get packets from a source external to the 1370 RPL domain. 1372 Upon a DAO with a Target option for a multicast address, the RPL Root 1373 checks if it is already registered as a listener for that address, 1374 and if not, it performs its own unsolicited Report for the multicast 1375 address as described in section 5.1 of [RFC3810]. The report is 1376 source independent, so there is no Source Address listed. 1378 6LN/RUL 6LR Root 6LBR 1379 | | | | 1380 | unsolicited Report | | | 1381 |------------------->| | | 1382 | | DAO | | 1383 | |-------------->| | 1384 | | DAO-ACK | | 1385 | |<--------------| | 1386 | | | | 1387 | | | unsolicited Report | 1388 | | |---------------------->| 1389 | | | | 1391 Figure 11: First Multicast Registration Flow 1393 The equivalent of the registration refresh is pulled periodically by 1394 the 6LR acting as querier. Upon the timing out of the Query 1395 Interval, the 6LR sends a Multicast Address Specific Query to each of 1396 its listeners, for each Multicast Address, and gets a Report back 1397 that is mapped into a DAO one by one. Optionally, the 6LR MAY send a 1398 General Query, where the Multicast Address field is set to zero. In 1399 that case, the multicast packet is passed as a Layer-2 unicast to 1400 each of the interested children. . 1402 Upon a Report, the 6LR generates a DAO with as many Target Options as 1403 there are Multicast Address Records in the Report message, copying 1404 the Multicast Address field in the Target Prefix of the RPL Target 1405 Option. The DAO message is a Storing Mode DAO, passed to a selection 1406 of the 6LR's parents. 1408 Asynchronously to this, a similar procedure happens between the Root 1409 and a router such as the 6LBR that serves multicast flows on the Link 1410 where the Root is located. Again the Query and Report messages are 1411 source independent. The Root lists exactly once each Multicast 1412 Address for which it has at least one active multicast DAO state, 1413 copying the multicast address in the DAO state in the Multicast 1414 Address field of the Multicast Address Records in the Report message. 1416 This is illustrated in Figure 12: 1418 6LN/RUL 6LR Root 6LBR 1419 | | | | 1420 | Query | | | 1421 |<-------------------| | | 1422 | Report | | | 1423 |------------------->| | | 1424 | | DAO | | 1425 | |-------------->| | 1426 | | DAO-ACK | | 1427 | |<--------------| | 1428 | | | Query | 1429 | | |<-------------------| 1430 | | | Report | 1431 | | |------------------->| 1432 | | | | 1434 Figure 12: Next Registration Flow 1436 Note that any of the functions 6LR, Root and 6LBR might be collapsed 1437 in a single node, in which case the flow above happens internally, 1438 and possibly through internal API calls as opposed to messaging. 1440 11. Security Considerations 1442 It is worth noting that with [RFC6550], every node in the LLN is RPL- 1443 aware and can inject any RPL-based attack in the network. This 1444 specification isolates edge nodes that can only interact with the RPL 1445 routers using 6LoWPAN ND, meaning that they cannot perform RPL 1446 insider attacks. 1448 The LLN nodes depend on the 6LBR and the RPL participants for their 1449 operation. A trust model must be put in place to ensure that the 1450 right devices are acting in these roles, so as to avoid threats such 1451 as black-holing, (see [RFC7416] section 7), Denial-Of-Service attacks 1452 whereby a rogue 6LR creates a high churn in the RPL network by 1453 advertising and removing many forged addresses, or bombing attack 1454 whereby an impersonated 6LBR would destroy state in the network by 1455 using the status code of 4 ("Removed"). 1457 This trust model could be at a minimum based on a Layer-2 Secure 1458 joining and the Link-Layer security. This is a generic 6LoWPAN 1459 requirement, see Req5.1 in Appendix B.5 of [RFC8505]. 1461 In a general manner, the Security Considerations in [RFC7416] 1462 [RFC6775], and [RFC8505] apply to this specification as well. 1464 The Link-Layer security is needed in particular to prevent Denial-Of- 1465 Service attacks whereby a rogue 6LN creates a high churn in the RPL 1466 network by constantly registering and deregistering addresses with 1467 the R Flag set to 1 in the EARO. 1469 [RFC8928] updated 6LoWPAN ND with the called Address-Protected 1470 Neighbor Discovery (AP-ND). AP-ND protects the owner of an address 1471 against address theft and impersonation attacks in a Low-Power and 1472 Lossy Network (LLN). Nodes supporting th extension compute a 1473 cryptographic identifier (Crypto-ID), and use it with one or more of 1474 their Registered Addresses. The Crypto-ID identifies the owner of 1475 the Registered Address and can be used to provide proof of ownership 1476 of the Registered Addresses. Once an address is registered with the 1477 Crypto-ID and a proof of ownership is provided, only the owner of 1478 that address can modify the registration information, thereby 1479 enforcing Source Address Validation. [RFC8928] reduces even more the 1480 attack perimeter that is available to the edge nodes and its use is 1481 suggested in this specification. 1483 Additionally, the trust model could include a role validation to 1484 ensure that the node that claims to be a 6LBR or a RPL Root is 1485 entitled to do so. 1487 The Opaque field in the EARO enables the RUL to suggest a 1488 RPLInstanceID where its traffic is placed. It is also possible for 1489 an attacker RUL to include an RPI in the packet. This opens to 1490 attacks where a RPL instance would be reserved for critical traffic, 1491 e.g., with a specific bandwidth reservation, that the additional 1492 traffic generated by a rogue may disrupt. The attack may be 1493 alleviated by traditional access control and traffic shaping 1494 mechanisms where the 6LR controls the incoming traffic from the 6LN. 1495 More importantly, the 6LR is the node that injects the traffic in the 1496 RPL domain, so it has the final word on which RPLInstance is to be 1497 used for the traffic coming from the RUL, per its own policy. 1499 At the time of this writing, RPL does not have a Route Ownership 1500 Validation model whereby it is possible to validate the origin of an 1501 address that is injected in a DAO. This specification makes a first 1502 step in that direction by allowing the Root to challenge the RUL via 1503 the 6LR that serves it. 1505 Section 6.1 indicates that when the length of the ROVR field is 1506 unknown, the RPL Target Option must be passed on as received in RPL 1507 storing Mode. This creates a possible opening for using DAO messages 1508 as a covert channel. Note that DAO messages are rare and the 1509 overusing that channel could be detected. An implementation SHOULD 1510 notify the network management when a RPL Target Option is receives 1511 with an unknown ROVR field size, to ensure that the situation is 1512 known to the network administrator. 1514 [EFFICIENT-NPDAO] introduces the ability for a rogue common ancestor 1515 node to invalidate a route on behalf of the target node. In this 1516 case, the RPL Status in the DCO has the 'A' flag set to 0, and a 1517 NA(EARO) is returned to the 6LN with the R flag set to 0. This 1518 encourages the 6LN to try another 6LR. If a 6LR exists that does not 1519 use the rogue common ancestor, then the 6LN will eventually succeed 1520 gaining reachability over the RPL network in spite of the rogue node. 1522 12. IANA Considerations 1524 12.1. Fixing the Address Registration Option Flags 1526 Section 9.1 of [RFC8505] creates a Registry for the 8-bit Address 1527 Registration Option Flags field. IANA is requested to rename the 1528 first column of the table from "ARO Status" to "Bit number". 1530 12.2. Resizing the ARO Status values 1532 Section 12 of [RFC6775] creates the Address Registration Option 1533 Status values Registry with a range 0-255. 1535 This specification reduces that range to 0-63, see Section 6.3. 1537 IANA is requested to modify the Address Registration Option Status 1538 values Registry so that the upper bound of the unassigned values is 1539 63. This document should be added as a reference. The registration 1540 procedure does not change. 1542 12.3. New RPL DODAG Configuration Option Flag 1544 IANA is requested to assign a flag from the "DODAG Configuration 1545 Option Flags for MOP 0..6" [USEofRPLinfo] registry as follows: 1547 +---------------+----------------------------+-----------+ 1548 | Bit Number | Capability Description | Reference | 1549 +---------------+----------------------------+-----------+ 1550 | 1 (suggested) | Root Proxies EDAR/EDAC (P) | THIS RFC | 1551 +---------------+----------------------------+-----------+ 1553 Table 2: New DODAG Configuration Option Flag 1555 12.4. RPL Target Option Registry 1557 This document modifies the "RPL Target Option Flags" registry 1558 initially created in Section 20.15 of [RFC6550] . The registry now 1559 includes only 4 bits (Section 6.1) and should point to this document 1560 as an additional reference. The registration procedure doesn't 1561 change. 1563 Section 6.1 also defines a new entry in the Registry as follows: 1565 +---------------+--------------------------------+-----------+ 1566 | Bit Number | Capability Description | Reference | 1567 +---------------+--------------------------------+-----------+ 1568 | 0 (suggested) | Advertiser address in Full (F) | THIS RFC | 1569 +---------------+--------------------------------+-----------+ 1571 Table 3: RPL Target Option Registry 1573 12.5. New Subregistry for RPL Non-Rejection Status values 1575 This specification creates a new Subregistry for the RPL Non- 1576 Rejection Status values for use in the RPL DAO-ACK, DCO, and DCO-ACK 1577 messages with the 'A' flag set to 0, under the RPL registry. 1579 * Possible values are 6-bit unsigned integers (0..63). 1581 * Registration procedure is "IETF Review" [RFC8126]. 1583 * Initial allocation is as indicated in Table 4: 1585 +-------+------------------------+---------------------+ 1586 | Value | Meaning | Reference | 1587 +-------+------------------------+---------------------+ 1588 | 0 | Unqualified acceptance | THIS RFC / RFC 6550 | 1589 +-------+------------------------+---------------------+ 1590 | 1..63 | Unassigned | | 1591 +-------+------------------------+---------------------+ 1593 Table 4: Acceptance values of the RPL Status 1595 12.6. New Subregistry for RPL Rejection Status values 1597 This specification creates a new Subregistry for the RPL Rejection 1598 Status values for use in the RPL DAO-ACK and DCO messages with the 1599 'A' flag set to 0, under the RPL registry. 1601 * Possible values are 6-bit unsigned integers (0..63). 1603 * Registration procedure is "IETF Review" [RFC8126]. 1605 * Initial allocation is as indicated in Table 5: 1607 +-------+-----------------------+-----------+ 1608 | Value | Meaning | Reference | 1609 +-------+-----------------------+-----------+ 1610 | 0 | Unqualified rejection | THIS RFC | 1611 +-------+-----------------------+-----------+ 1612 | 1..63 | Unassigned | | 1613 +-------+-----------------------+-----------+ 1615 Table 5: Rejection values of the RPL Status 1617 13. Acknowledgments 1619 The authors wish to thank Ines Robles, Georgios Papadopoulos and 1620 especially Rahul Jadhav and Alvaro Retana for their reviews and 1621 contributions to this document. Also many thanks to Elwyn Davies, 1622 Eric Vyncke, Peter Van der Stok and Carl Wallace for their reviews 1623 and useful comments during the IETF Last Call and the IESG review 1624 sessions. 1626 14. Normative References 1628 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1629 Requirement Levels", BCP 14, RFC 2119, 1630 DOI 10.17487/RFC2119, March 1997, 1631 . 1633 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1634 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1635 DOI 10.17487/RFC3810, June 2004, 1636 . 1638 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1639 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1640 DOI 10.17487/RFC4861, September 2007, 1641 . 1643 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1644 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1645 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1646 Low-Power and Lossy Networks", RFC 6550, 1647 DOI 10.17487/RFC6550, March 2012, 1648 . 1650 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1651 Bormann, "Neighbor Discovery Optimization for IPv6 over 1652 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1653 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1654 . 1656 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1657 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1658 2014, . 1660 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 1661 IPv6 over Low-Power Wireless Personal Area Networks 1662 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 1663 2014, . 1665 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1666 Writing an IANA Considerations Section in RFCs", BCP 26, 1667 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1668 . 1670 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1671 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1672 May 2017, . 1674 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1675 (IPv6) Specification", STD 86, RFC 8200, 1676 DOI 10.17487/RFC8200, July 2017, 1677 . 1679 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node 1680 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504, 1681 January 2019, . 1683 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1684 Perkins, "Registration Extensions for IPv6 over Low-Power 1685 Wireless Personal Area Network (6LoWPAN) Neighbor 1686 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1687 . 1689 [RFC8928] Thubert, P., Ed., Sarikaya, B., Sethi, M., and R. Struik, 1690 "Address-Protected Neighbor Discovery for Low-Power and 1691 Lossy Networks", RFC 8928, DOI 10.17487/RFC8928, November 1692 2020, . 1694 [USEofRPLinfo] 1695 Robles, I., Richardson, M., and P. Thubert, "Using RPI 1696 Option Type, Routing Header for Source Routes and IPv6-in- 1697 IPv6 encapsulation in the RPL Data Plane", Work in 1698 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-42, 1699 12 November 2020, . 1702 [EFFICIENT-NPDAO] 1703 Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient 1704 Route Invalidation", Work in Progress, Internet-Draft, 1705 draft-ietf-roll-efficient-npdao-18, 15 April 2020, 1706 . 1709 15. Informative References 1711 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1712 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1713 Overview, Assumptions, Problem Statement, and Goals", 1714 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1715 . 1717 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1718 Address Autoconfiguration", RFC 4862, 1719 DOI 10.17487/RFC4862, September 2007, 1720 . 1722 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1723 Power and Lossy Networks (RPL) Option for Carrying RPL 1724 Information in Data-Plane Datagrams", RFC 6553, 1725 DOI 10.17487/RFC6553, March 2012, 1726 . 1728 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1729 Routing Header for Source Routes with the Routing Protocol 1730 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1731 DOI 10.17487/RFC6554, March 2012, 1732 . 1734 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1735 Statement and Requirements for IPv6 over Low-Power 1736 Wireless Personal Area Network (6LoWPAN) Routing", 1737 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1738 . 1740 [RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed., 1741 "Source Address Validation Improvement (SAVI) Framework", 1742 RFC 7039, DOI 10.17487/RFC7039, October 2013, 1743 . 1745 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1746 Constrained-Node Networks", RFC 7228, 1747 DOI 10.17487/RFC7228, May 2014, 1748 . 1750 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1751 "IPv6 over Low-Power Wireless Personal Area Network 1752 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1753 April 2017, . 1755 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 1756 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 1757 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 1758 RFC 8415, DOI 10.17487/RFC8415, November 2018, 1759 . 1761 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1762 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1763 DOI 10.17487/RFC6282, September 2011, 1764 . 1766 [RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur, 1767 Ed., "Performance Evaluation of the Routing Protocol for 1768 Low-Power and Lossy Networks (RPL)", RFC 6687, 1769 DOI 10.17487/RFC6687, October 2012, 1770 . 1772 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1773 and M. Richardson, Ed., "A Security Threat Analysis for 1774 the Routing Protocol for Low-Power and Lossy Networks 1775 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1776 . 1778 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1779 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1780 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1781 . 1783 [RFC8929] Thubert, P., Ed., Perkins, C.E., and E. Levy-Abegnoli, 1784 "IPv6 Backbone Router", RFC 8929, DOI 10.17487/RFC8929, 1785 November 2020, . 1787 Appendix A. Example Compression 1789 Figure 13 illustrates the case in Storing Mode where the packet is 1790 received from the Internet, then the Root encapsulates the packet to 1791 insert the RPI and deliver to the 6LR that is the parent and last hop 1792 to the final destination, which is not known to support [RFC8138]. 1794 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1795 |11110001|SRH-6LoRH| RPI- |IPv6-in-IPv6| NH=1 |11110CPP| UDP | UDP 1796 |Page 1 |Type1 S=0| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 1797 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1798 <-4 bytes-> <- RFC 6282 -> 1799 <- No RPL artifact ... 1801 Figure 13: Encapsulation to Parent 6LR in Storing Mode 1803 The difference with the example presented in Figure 19 of [RFC8138] 1804 is the addition of a SRH-6LoRH before the RPI-6LoRH to transport the 1805 compressed address of the 6LR as the destination address of the outer 1806 IPv6 header. In the [RFC8138] example the destination IP of the 1807 outer header was elided and was implicitly the same address as the 1808 destination of the inner header. Type 1 was arbitrarily chosen, and 1809 the size of 0 denotes a single address in the SRH. 1811 In Figure 13, the source of the IPv6-in-IPv6 encapsulation is the 1812 Root, so it is elided in the IPv6-in-IPv6 6LoRH. The destination is 1813 the parent 6LR of the destination of the encapsulated packet so it 1814 cannot be elided. If the DODAG is operated in Storing Mode, it is 1815 the single entry in the SRH-6LoRH and the SRH-6LoRH Size is encoded 1816 as 0. The SRH-6LoRH is the first 6LoRH in the chain. In this 1817 particular example, the 6LR address can be compressed to 2 bytes so a 1818 Type of 1 is used. It results that the total length of the SRH-6LoRH 1819 is 4 bytes. 1821 In Non-Storing Mode, the encapsulation from the Root would be similar 1822 to that represented in Figure 13 with possibly more hops in the SRH- 1823 6LoRH and possibly multiple SRH-6LoRHs if the various addresses in 1824 the routing header are not compressed to the same format. Note that 1825 on the last hop to the parent 6LR, the RH3 is consumed and removed 1826 from the compressed form, so the use of Non-Storing Mode vs. Storing 1827 Mode is indistinguishable from the packet format. 1829 The SRH-6LoRHs are followed by RPI-6LoRH and then the IPv6-in-IPv6 1830 6LoRH. When the IPv6-in-IPv6 6LoRH is removed, all the 6LoRH Headers 1831 that precede it are also removed. The Paging Dispatch [RFC8025] may 1832 also be removed if there was no previous Page change to a Page other 1833 than 0 or 1, since the LOWPAN_IPHC is encoded in the same fashion in 1834 the default Page 0 and in Page 1. The resulting packet to the 1835 destination is the encapsulated packet compressed with [RFC6282]. 1837 Authors' Addresses 1839 Pascal Thubert (editor) 1840 Cisco Systems, Inc 1841 Building D 1842 45 Allee des Ormes - BP1200 1843 06254 Mougins - Sophia Antipolis 1844 France 1846 Phone: +33 497 23 26 34 1847 Email: pthubert@cisco.com 1849 Michael C. Richardson 1850 Sandelman Software Works 1852 Email: mcr+ietf@sandelman.ca 1853 URI: http://www.sandelman.ca/