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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ROLL P. Thubert, Ed. 3 Internet-Draft Cisco Systems 4 Updates: 6550, 8505 (if approved) M. Richardson 5 Intended status: Standards Track Sandelman 6 Expires: 13 September 2020 12 March 2020 8 Routing for RPL Leaves 9 draft-ietf-roll-unaware-leaves-10 11 Abstract 13 This specification extends RFC6550 and RFC8505 to provide unicast and 14 multicast routing services in a RPL domain to 6LNs that are plain 15 Hosts and do not participate to RPL, and enables the RPL Root to 16 proxy the EDAR/EDAC flow on behalf of the RULs and RANs in its DODAG. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at https://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on 13 September 2020. 35 Copyright Notice 37 Copyright (c) 2020 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 42 license-info) in effect on the date of publication of this document. 43 Please review these documents carefully, as they describe your rights 44 and restrictions with respect to this document. Code Components 45 extracted from this document must include Simplified BSD License text 46 as described in Section 4.e of the Trust Legal Provisions and are 47 provided without warranty as described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 52 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 53 2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 4 54 2.2. References . . . . . . . . . . . . . . . . . . . . . . . 4 55 2.3. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 5 56 3. 6LoWPAN Neighbor Discovery . . . . . . . . . . . . . . . . . 7 57 3.1. RFC 6775 Address Registration . . . . . . . . . . . . . . 7 58 3.2. RFC 8505 Extended Address Registration . . . . . . . . . 7 59 3.2.1. R Flag . . . . . . . . . . . . . . . . . . . . . . . 8 60 3.2.2. TID, I Field and Opaque Fields . . . . . . . . . . . 8 61 3.2.3. ROVR . . . . . . . . . . . . . . . . . . . . . . . . 8 62 3.3. RFC 8505 Extended DAR/DAC . . . . . . . . . . . . . . . . 9 63 3.3.1. RFC 7400 Capability Indication Option . . . . . . . . 9 64 4. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 10 65 5. Updating RFC 8505 . . . . . . . . . . . . . . . . . . . . . . 11 66 6. Requirements on the RPL-Unware Leaf . . . . . . . . . . . . . 11 67 6.1. Support of 6LoWPAN ND . . . . . . . . . . . . . . . . . . 11 68 6.2. External Routes and RPL Artifacts . . . . . . . . . . . . 12 69 6.2.1. Support of IPv6 Encapsulation . . . . . . . . . . . . 13 70 6.2.2. Support of the HbH Header . . . . . . . . . . . . . . 13 71 6.2.3. Support of the Routing Header . . . . . . . . . . . . 13 72 7. Updated RPL Status . . . . . . . . . . . . . . . . . . . . . 13 73 8. Updated RPL Target option . . . . . . . . . . . . . . . . . . 14 74 9. Protocol Operations for Unicast Addresses . . . . . . . . . . 15 75 9.1. General Flow . . . . . . . . . . . . . . . . . . . . . . 15 76 9.1.1. In RPL Non-Storing-Mode . . . . . . . . . . . . . . . 16 77 9.1.2. In RPL Storing-Mode . . . . . . . . . . . . . . . . . 18 78 9.2. Detailed Operation . . . . . . . . . . . . . . . . . . . 19 79 9.2.1. By the 6LN . . . . . . . . . . . . . . . . . . . . . 19 80 9.2.2. By the 6LR . . . . . . . . . . . . . . . . . . . . . 20 81 9.2.3. By the RPL Root . . . . . . . . . . . . . . . . . . . 22 82 9.2.4. By the 6LBR . . . . . . . . . . . . . . . . . . . . . 23 83 10. Protocol Operations for Multicast Addresses . . . . . . . . . 24 84 11. Security Considerations . . . . . . . . . . . . . . . . . . . 25 85 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 86 12.1. Resizing the ARO Status values . . . . . . . . . . . . . 26 87 12.2. New DODAG Configuration Option Flag . . . . . . . . . . 26 88 12.3. RPL Target Option Flags . . . . . . . . . . . . . . . . 27 89 12.4. New Subregistry for the RPL Non-Rejection Status 90 values . . . . . . . . . . . . . . . . . . . . . . . . . 27 91 12.5. New Subregistry for the RPL Rejection Status values . . 27 92 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28 93 14. Normative References . . . . . . . . . . . . . . . . . . . . 28 94 15. Informative References . . . . . . . . . . . . . . . . . . . 30 95 Appendix A. Example Compression . . . . . . . . . . . . . . . . 31 96 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 98 1. Introduction 100 The design of Low Power and Lossy Networks (LLNs) is generally 101 focused on saving energy, which is the most constrained resource of 102 all. Other design constraints, such as a limited memory capacity, 103 duty cycling of the LLN devices and low-power lossy transmissions, 104 derive from that primary concern. 106 The IETF produced the "Routing Protocol for Low Power and Lossy 107 Networks" [RFC6550] (RPL) to provide IPv6 [RFC8200] routing services 108 within such constraints. RPL belongs to the class of Distance-Vector 109 protocol, which, compared to link-state protocols, limits the amount 110 of topological knowledge that needs to be installed and maintained in 111 each node. 113 In order to operate in constrained networks, RPL allows a routing 114 stretch (see [RFC6687]), whereby routing is only performed along an 115 acyclic graph optimized to reach a Root node, as opposed to straight 116 along a shortest path between 2 peers, whatever that would mean in a 117 given 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 a any-to-any shortest path protocol. Finally, 120 broken routes may be fixed lazily and on-demand, based on dataplane 121 inconsistency discovery, which avoids wasting energy in the proactive 122 repair of unused paths. 124 In order to cope with lossy transmissions, RPL forms Direction- 125 Oriented Directed Acyclic Graphs (DODAGs) using DODAG Information 126 Solicitation (DIS) and DODAG Information Object (DIO) messages. For 127 many of the nodes, though not all, a DODAG provides multiple 128 forwarding solutions towards the Root of the topology via so-called 129 parents. RPL is designed to adapt to fuzzy connectivity, whereby the 130 physical topology cannot be expected to reach a stable state, with a 131 lazy control that creates the routes proactively, but may only fix 132 them reactively, upon actual traffic. The result is that RPL 133 provides reachability for most of the LLN nodes, most of the time, 134 but may not converge in the classical sense. 136 [RFC6550] provides unicast and multicast routing services back to 137 RPL-Aware nodes (RANs), either as a collection tree or with routing 138 back. In tha latter case, a RAN injects routes to itself using 139 Destination Advertisement Object (DAO) messages sent to either 140 parent-nodes in the RPL Storing Mode or to the Root indicating their 141 parent in the Non-Storing Mode. This process effectively forms a 142 DODAG back to the device that is a subset of the DODAG to the Root 143 with all links reversed. 145 RPL can be deployed as an extension to IPv6 Neighbor Discovery (ND) 146 [RFC4861][RFC4862] and 6LoWPAN ND [RFC6775][RFC8505] to maintain 147 reachability within a Non-Broadcast Multi-Access (NBMA) subnet. In 148 that mode, some nodes may act as Routers and participate to the 149 forwarding operations whereas others will only terminate packets, 150 acting as Hosts in the data-plane. In [RFC6550] terms, a Host that 151 is reachable over the RPL network is called a Leaf. 153 "When to use RFC 6553, 6554 and IPv6-in-IPv6" [USEofRPLinfo] 154 introduces the term RPL-Aware-Leaf (RAL) for a Leaf that injects 155 routes in RPL to manage the reachability of its own IPv6 addresses. 156 In contrast, the term RPL-Unaware Leaf (RUL) designates a Leaf does 157 not participate to RPL at all. A RUL is a plain Host that needs a 158 RPL-Aware Router to obtain routing services over the RPL network. 160 This specification leverages the Address Registration mechanism 161 defined in 6LoWPAN ND to enable a RUL as a 6LoWPAN Node (6LN) to 162 interface with a RPL-Aware Router as a 6LoWPAN Router (6LR) to 163 request that the 6LR injects the relevant routing information for the 164 Registered Address in the RPL domain on its behalf. The unicast 165 packet forwarding operation by the 6LR serving a 6LN that is a RPL 166 Leaf is described in [USEofRPLinfo]. 168 Examples of routing-agnostic 6LNs include lightly-powered sensors 169 such as window smash sensor (alarm system), and kinetically powered 170 light switches. Other application of this specification may include 171 a smart grid network that controls appliances - such as washing 172 machines or the heating system - in the home. Appliances may not 173 participate to the RPL protocol operated in the Smartgrid network but 174 can still interact with the Smartgrid for control and/or metering. 176 2. Terminology 178 2.1. BCP 14 180 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 181 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 182 "OPTIONAL" in this document are to be interpreted as described in BCP 183 14 [RFC2119][RFC8174] when, and only when, they appear in all 184 capitals, as shown here. 186 2.2. References 188 The Terminology used in this document is consistent with and 189 incorporates that described in Terms Used in Routing for Low-Power 190 and Lossy Networks (LLNs). [RFC7102]. 192 A glossary of classical 6LoWPAN acronyms is given in Section 2.3. 194 The term "byte" is used in its now customary sense as a synonym for 195 "octet". 197 "RPL", the "RPL Packet Information" (RPI), "RPL Instance" (indexed by 198 a RPLInstanceID)are defined in "RPL: IPv6 Routing Protocol for 199 Low-Power and Lossy Networks" [RFC6550] . The DODAG Information 200 Solicitation (DIS), Destination Advertisement Object (DAO) and DODAG 201 Information Object (DIO) messages are also specified in [RFC6550]. 202 The Destination Cleanup Object (DCO) message is defined in 203 [EFFICIENT-NPDAO]. 205 This document uses the terms RPL-Unaware Leaf (RUL) and RPL Aware 206 Leaf (RAL) consistently with [USEofRPLinfo]. The term RPL-Aware Node 207 (RAN) is introduced to refer to a node that is either a RAL or a RPL 208 Router. As opposed to a RUL, a RAN manages the reachability of its 209 addresses and prefixes by injecting them in RPL by itself. 211 Other terms in use in LLNs are found in Terminology for 212 Constrained-Node Networks [RFC7228]. 214 Readers are expected to be familiar with all the terms and concepts 215 that are discussed in 217 * "Neighbor Discovery for IP version 6" [RFC4861], 219 * "IPv6 Stateless Address Autoconfiguration" [RFC4862], 221 * "Problem Statement and Requirements for IPv6 over Low-Power 222 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606], 224 * "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 225 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 227 * "Neighbor Discovery Optimization for Low-power and Lossy Networks" 228 [RFC6775], and 230 * "Registration Extensions for IPv6 over Low-Power Wireless Personal 231 Area Network (6LoWPAN) Neighbor Discovery" [RFC8505]. 233 2.3. Glossary 235 This document often uses the following acronyms: 237 AR: Address Resolution (aka Address Lookup) 239 6CIO: 6LoWPAN Capability Indication Option 240 6LN: 6LoWPAN Node (a Low Power Host or Router) 242 6LR: 6LoWPAN Router 244 (E)ARO: (Extended) Address Registration Option 246 (E)DAR: (Extended) Duplicate Address Request 248 (E)DAC: (Extended) Duplicate Address Confirmation 250 DAD: Duplicate Address Detection 252 DAO: Destination Advertisement Object (a RPL message) 254 DCO: Destination Cleanup Object (a RPL message) 256 DIS: DODAG Information Solicitation (a RPL message) 258 DIO: DODAG Information Object (a RPL message) 260 DODAG: Destination-Oriented Directed Acyclic Graph 262 LLN: Low-Power and Lossy Network 264 NA: Neighbor Advertisement 266 NCE: Neighbor Cache Entry 268 ND: Neighbor Discovery 270 NS: Neighbor Solicitation 272 RA: Router Advertisement 274 ROVR: Registration Ownership Verifier 276 RPI: RPL Packet Information (the abstract information RPL places in 277 data packets as the RPL Option within the IPv6 Hop-By-Hop Header, 278 and by extension the RPL Option itself) 280 RAL: RPL-Aware Leaf 282 RAN: RPL-Aware Node (either a RPL Router or a RPL-Aware Leaf) 284 RUL: RPL-Unaware Leaf 286 TID: Transaction ID (a sequence counter in the EARO) 288 3. 6LoWPAN Neighbor Discovery 290 3.1. RFC 6775 Address Registration 292 The classical "IPv6 Neighbor Discovery (IPv6 ND) Protocol" [RFC4861] 293 [RFC4862] was defined for transit media such a Ethernet. It is a 294 reactive protocol that relies heavily on multicast operations for 295 address discovery (aka lookup) and duplicate address detection (DAD). 297 "Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775] 298 adapts IPv6 ND for operations over energy-constrained LLNs. The main 299 functions of [RFC6775] are to proactively establish the Neighbor 300 Cache Entry (NCE) in the 6LR and to prevent address duplication. To 301 that effect, [RFC6775] introduces a new unicast Address Registration 302 mechanism that contributes to reducing the use of multicast messages 303 compared to the classical IPv6 ND protocol. 305 [RFC6775] defines a new Address Registration Option (ARO) that is 306 carried in the unicast Neighbor Solicitation (NS) and Neighbor 307 Advertisement (NA) messages between the 6LoWPAN Node (6LN) and the 308 6LoWPAN Router (6LR). It also defines the Duplicate Address Request 309 (DAR) and Duplicate Address Confirmation (DAC) messages between the 310 6LR and the 6LoWPAN Border Router (6LBR). In an LLN, the 6LBR is the 311 central repository of all the Registered Addresses in its domain and 312 the source of truth for uniqueness and ownership. 314 3.2. RFC 8505 Extended Address Registration 316 "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505] 317 updates the behavior of RFC 6775 to enable a generic Address 318 Registration to services such as routing and ND proxy, and defines 319 the Extended Address Registration Option (EARO) as shown in Figure 1: 321 0 1 2 3 322 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 1 323 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 324 | Type | Length | Status | Opaque | 325 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 326 | Rsvd | I |R|T| TID | Registration Lifetime | 327 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 328 | | 329 ... Registration Ownership Verifier ... 330 | | 331 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 333 Figure 1: EARO Option Format 335 3.2.1. R Flag 337 [RFC8505] introduces the "R" flag in the EARO. The Registering Node 338 sets the "R" flag to indicate whether the 6LR should ensure 339 reachability for the Registered Address. If the "R" flag is not set, 340 then the Registering Node handles the reachability of the Registered 341 Address by other means, which means in a RPL network that it is a RAN 342 or that it uses another RPL Router for reachability services. 344 This document specifies how the "R" flag is used in the context of 345 RPL. A 6LN is a RUL that requires reachability services for an IPv6 346 address iff it sets the "R" flag in the EARO used to register the 347 address to a RPL router. Conversely, this document specifies the 348 behavior of a RPL Router acting as 6LR depending on the setting of 349 the "R" flag in the EARO. The RPL Router generates a DAO message for 350 the Registered Address upon an NS(EARO) iff the "R" flag is set. 352 3.2.2. TID, I Field and Opaque Fields 354 The EARO also includes a sequence counter called Transaction ID 355 (TID), which maps to the Path Sequence Field found in Transit Options 356 in RPL DAO messages. This is the reason why the support of [RFC8505] 357 by the RUL as opposed to only [RFC6775] is a prerequisite for this 358 specification (more in Section 6.1). The EARO also transports an 359 Opaque field and an "I" field that describes what the Opaque field 360 transports and how to use it. Section 9.2.1 specifies the use of the 361 "I" field and of the Opaque field by a RUL. 363 3.2.3. ROVR 365 Section 5.3. of [RFC8505] introduces the Registration Ownership 366 Verifier (ROVR) field of variable length from 64 to 256 bits. The 367 ROVR is a replacement of the EUI-64 in the ARO [RFC6775] that was 368 used to identify uniquely an Address Registration with the Link-Layer 369 address of the owner, but provided no protection against spoofing. 371 "Address Protected Neighbor Discovery for Low-power and Lossy 372 Networks" [AP-ND] leverages the ROVR field as a cryptographic proof 373 of ownership to prevent a rogue third party from misusing the 374 address. [AP-ND] adds a challenge/response exchange to the [RFC8505] 375 Address Registration and enables Source Address Validation by a 6LR 376 that will drop packets with a spoofed address. 378 This specification does not address how the protection by [AP-ND] 379 could be extended to RPL. On the other hand, it adds the ROVR to the 380 DAO to build the proxied EDAR at the Root (see Section 8), which 381 means that nodes that are aware of the Host route to the 6LN are made 382 aware of the associated ROVR as well. 384 3.3. RFC 8505 Extended DAR/DAC 386 [RFC8505] updates the periodic DAR/DAC exchange that takes place 387 between the 6LR and the 6LBR using Extended DAR/DAC messages which 388 can carry a ROVR field of variable size. The periodic EDAR/EDAC 389 exchange is triggered by a NS(EARO) message and is intended to create 390 and then refresh the corresponding state in the 6LBR for a lifetime 391 that is indicated by the 6LN. 393 Conversely, RPL [RFC6550] specifies a periodic DAO from the 6LN all 394 the way to the Root that maintains the routing state in the RPL 395 network for the lifetime indicated by the source of the DAO. This 396 means that for each address, there are two keep-alive messages that 397 traverse the whole network, one to the Root and one to the 6LBR. 399 This specification saves the extraneous keep-alive across the LLN. 400 The 6LR turns the periodic Address Registration from the RUL into a 401 DAO message to the Root every time, but only generates the EDAR upon 402 the first registration, for the purpose of DAD. Upon a refresher 403 DAO, the Root proxies the EDAR exchange to refresh the state at the 404 6LBR on behalf of the 6LR, as illustrated in Figure 7. 406 3.3.1. RFC 7400 Capability Indication Option 408 "6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power 409 Wireless Personal Area Networks (6LoWPANs)" [RFC7400] defines the 410 6LoWPAN Capability Indication Option (6CIO) that enables a node to 411 expose its capabilities in Router Advertisement (RA) messages. 412 [RFC8505] defines a number of bits in the 6CIO, in particular: 414 L: Node is a 6LR. 416 E: Node is an IPv6 ND Registrar -- i.e., it supports registrations 417 based on EARO. 419 P: Node is a Routing Registrar, -- i.e., an IPv6 ND Registrar that 420 also provides reachability services for the Registered Addres 422 0 1 2 3 423 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 425 | Type | Length = 1 | Reserved |D|L|B|P|E|G| 426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 427 | Reserved | 428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 430 Figure 2: 6CIO flags 432 A 6LR that can provide reachability services for a RUL in a RPL 433 network as specified in this document SHOULD include a 6CIO in its RA 434 messages and set the L, P and E flags as prescribed by [RFC8505], see 435 Section 6.1 for the behavior of the RUL. 437 4. Updating RFC 6550 439 This document specifies a new behavior whereby a 6LR injects DAO 440 messages for unicast addresses (see Section 9) and multicast 441 addresses (see Section 10) on behalf of leaves that are not aware of 442 RPL. The addresses are exposed as external targets [RFC6550]. Per 443 [USEofRPLinfo], an IP-in-IP encapsulation that terminates at the RPL 444 Root is used to remove RPL artifacts and compression techniques that 445 may not be processed correctly outside of the RPL domain. 447 This document also synchronizes the liveness monitoring at the Root 448 and the 6LBR. A same value of lifetime is used for both, and a 449 single keep-alive message, the RPL DAO, traverses the RPL network. A 450 new behavior is introduced whereby the RPL Root proxies the EDAR 451 message to the 6LBR on behalf of the 6LR (more in Section 5), for any 452 6LN, RUL or RAN. 454 RPL defines a configuration option that is registered to IANA in 455 section 20.14. of [RFC6550]. This specification defines a new flag 456 "Root Proxies EDAR/EDAC" (P) that is encoded in one of the reserved 457 control bits in the option. The new flag is set to indicate that the 458 Root performs the proxy operation and that all nodes in the network 459 must refrain from renewing the 6LBR state directly. The bit position 460 of the "P" flag is indicated in Section 12.2. 462 Section 6.3.1. of [RFC6550] defines a 3-bit Mode of Operation (MOP) 463 in the DIO Base Object. The new "P" flag is defined only for MOP 464 value between 0 to 6. For a MOP value of 7 or above, the flag MAY 465 indicate something different and MUST NOT be interpreted as "Root 466 Proxies EDAR/EDAC" unless the specification of the MOP indicates to 467 do so. 469 The RPL Status defined in section 6.5.1. of [RFC6550] for use in the 470 DAO-Ack message is extended to be used in the DCO messages 471 [EFFICIENT-NPDAO] as well. Furthermore, this specification enables 472 to use a RPL Status to transport the IPv6 ND Status defined for use 473 in the EARO, more in Section 7. 475 Section 6.7. of [RFC6550] introduces the RPL Control message Options 476 such as the RPL Target Option that can be included in a RPL Control 477 message such as the DAO. Section 8 updates the RPL Target Option to 478 optionally transport the ROVR used in the IPv6 Registration (see 479 Section 3.2.3) so the RPL Root can generate a full EDAR message. 481 5. Updating RFC 8505 483 This document updates [RFC8505] to introduce the anonymous EDAR and 484 NS(EARO) messages. The anonymous messages are used for backward 485 compatibility. The anonymous messages are recognizable by a zero 486 ROVR field and can only be used as a refresher for a pre-existing 487 state associated to the Registered Address. More specifically, an 488 anonymous message can only increase the lifetime and/or increment the 489 TID of an existing state at the 6LBR. 491 Upon the renewal of a 6LoWPAN ND Address Registration, this 492 specification changes the behavior of a RPL Router acting as 6LR for 493 the registration. If the Root indicates the capability to proxy the 494 EDAR/EDAC exchange to the 6LBR then the 6LR refrains from sending an 495 EDAR message; if the Root is separated from the 6LBR, the Root 496 regenerates the EDAR message to the 6LBR upon a DAO message that 497 signals the liveliness of the Address. The regenerated message is 498 anonymous iff the DAO is a legacy message that does not carry a ROVR 499 as specified in Section 8. 501 6. Requirements on the RPL-Unware Leaf 503 This document provides RPL routing for a RUL, that is a 6LN acting as 504 an IPv6 Host and not aware of RPL. Still, a minimal RPL-independent 505 functionality is required from the RUL in order to obtain routing 506 services from the 6LR. 508 6.1. Support of 6LoWPAN ND 510 In order to obtain routing services from a 6LR, a RUL MUST implement 511 [RFC8505] and set the "R" flag in the EARO option. The RUL MUST NOT 512 request routing services from a 6LR unless the 6LR originates RA 513 messages with a CIO that has the L, P and E flags are all set as 514 discussed in Section 3.3.1. 516 The RUL MUST register to all the 6LRs from which it requests routing 517 services. The Address Registrations SHOULD be performed in a rapid 518 sequence, using the exact same EARO for a same Address. Gaps between 519 the Address Registrations will invalidate some of the routes till the 520 Address Registration finally shows on those routes as well. 522 [RFC8505] introduces error Status values in the NA(EARO) which can be 523 received synchronously upon an NS(EARO) or asynchronously. The RUL 524 MUST support both cases and MUST refrain from using the address when 525 the Status value indicates a rejection. 527 A RUL SHOULD support [AP-ND] to protect the ownership of its 528 addresses. 530 6.2. External Routes and RPL Artifacts 532 Section 4.1. of [USEofRPLinfo] provides a set of rules that MUST be 533 followed for the routing operations to a RUL. 535 Non-Storing Mode DAO messages are used to signal external routes to 536 the Root, even if the DODAG is operated in Storing Mode. A RUL is an 537 example of a destination that is reachable via an external route 538 which happens to be a Host route. 540 The Non-Storing Mode DAO messaging enables to advertise the 6LR that 541 serves the RUL and injects the route to the Root. It also forces all 542 packets to the RUL to be routed via the Root since the path to the 543 RUL is not known inside the RPL domain, even in Storing Mode. 545 The use of Non-Storing Mode signaling in Storing Mode and the 546 associated IP-in-IP encapsulation are transparent to intermediate 547 Routers that only see packets back and forth between the Root and the 548 6LR and do not need a special support for external routes, so the 549 mmechanism is backward compatible. 551 The RPL data packets from/to a RUL are encapsulated using an IP-in-IP 552 tunnel between the Root and the 6LR that serves the RUL, except for 553 packets from the RUL to a RAN in the RPL domain. The RPL data 554 packets also carry a Hop-by-Hop Header to transport a RPL Packet 555 Information (RPI) [RFC6550]. In Non-Storing Mode, packets going down 556 carry a Source Routing Header (SRH). These headers are called the 557 "RPL artifacts" and can be compressed with [RFC8138]. 559 RPL data packets going down to the RUL (see Figure 12 for the 560 compressed format in Storing Mode) are decapsulated by the 6LR that 561 serves the RUL. The inner packet that is forwarded to the RUL is 562 free of RPL artifacts, except for an RPI if the packet was generated 563 by a RAN in the same RPL domain as the RUL and reencapsulated with 564 the original RPI still present in the inner header by the Root. 566 [USEofRPLinfo] expects the RUL to support the basic "IPv6 Node 567 Requirements" [RFC8504], in particular to ignore the RPL artifacts 568 that are either consumed or not applicable to a Host, which is the 569 case of the RPI. 571 Additionally, the RUL is not expected to support the compression 572 method defined in [RFC8138]. The 6LR that injected the route MUST 573 uncompress the packet before forwarding over an external route, even 574 when delivering to a RUL, even when it is not the destination in the 575 outer header of the incoming packet, unless configured to do 576 otherwise. 578 6.2.1. Support of IPv6 Encapsulation 580 Section 2.1 of [USEofRPLinfo] sets the rules for forwarding IP-in-IP 581 either to the final 6LN or to a parent 6LR. In order to enable IP- 582 in-IP to the 6LN in Non-Storing Mode, the 6LN must be able to 583 decapsulate the tunneled packet and either drop the inner packet if 584 it is not the final destination, or pass it to the upper layer for 585 further processing. Unless it is aware that the RUL can handle IP- 586 in-IP properly, the Root that encapsulates a packet to a RUL 587 terminates the IP-in-IP tunnel at the parent 6LR . For that reason, 588 it is beneficial but not necessary for a RUL to support IP-in-IP. 590 6.2.2. Support of the HbH Header 592 A RUL is expected to process an unknown Option Type in a Hop-by-Hop 593 Header as prescribed by section 4.2 of [RFC8200]. This means in 594 particular that an RPI with an Option Type of 0x23 [USEofRPLinfo] is 595 ignored when not understood. 597 6.2.3. Support of the Routing Header 599 A RUL is expected to process an unknown Routing Header Type as 600 prescribed by section 4.4 of [RFC8200]. This means in particular 601 that Routing Header with a Routing Type of 3 [RFC6553] is ignored 602 when the Segments Left is zero, and dropped otherwise. 604 7. Updated RPL Status 606 The RPL Status is defined in section 6.5.1. of [RFC6550] for use in 607 the DAO-Ack message and values are assigned as follows: 609 +---------+--------------------------------+ 610 | Range | Meaning | 611 +=========+================================+ 612 | 0 | Success/Unqualified acceptance | 613 +---------+--------------------------------+ 614 | 1-127 | Not an outright rejection | 615 +---------+--------------------------------+ 616 | 128-255 | Rejection | 617 +---------+--------------------------------+ 619 Table 1: RPL Status per RFC 6550 621 This specification extends the scope of the RPL Status to be used in 622 RPL DCO messages. Furthermore, this specification enables to carry 623 the IPv6 ND Status values defined for use in the EARO and initially 624 listed in table 1 of [RFC8505] in a RPL Status. 626 Section 12.1 reduces the range of EARO Status values to 0-63 ensure 627 that they fit within a RPL Status as shown in Figure 3. 629 0 630 0 1 2 3 4 5 6 7 631 +-+-+-+-+-+-+-+-+ 632 |E|A| Value | 633 +-+-+-+-+-+-+-+-+ 635 Figure 3: RPL Status Format 637 RPL Status subfields: 639 E: 1-bit flag. Set to indicate a rejection. When not set, a value 640 of 0 indicates Success/Unqualified acceptance and other values 641 indicate "not an outright rejection" as per RFC 6550. 643 A: 1-bit flag. Indicates the type of the Status value. 645 Status Value: 6-bit unsigned integer. If the 'A' flag is set this 646 field transports a Status value defined for IPv6 ND EARO. When 647 the 'A' flag is not set, the Status value is defined in a RPL 648 extension. 650 When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a DAC 651 message, the RPL Root MUST copy the ARO Status unchanged in a RPL 652 Status with the 'A' bit set. The RPL Root MUST set the 'E' flag for 653 all values in range 1-10 which are all considered rejections. 655 Conversely, the 6LR MUST copy the value of the RPL Status unchanged 656 in the EARO of an NA message that is built upon a RPL Status with the 657 'A' bit set in a DCO or a DAO-ACK message. 659 8. Updated RPL Target option 661 This specification updates the RPL Target option to transport the 662 ROVR. This enables the RPL Root to generate a full EDAR message as 663 opposed to an anonymous EDAR that has restricted properties. 665 The Target Prefix field MUST be aligned to the next 4-byte boundary 666 after the size indicated by the Prefix Length. If necessary the 667 transported prefix MUST be padded with zeros. 669 With this specification the ROVR is the remainder of the RPL Target 670 Option. The size of the ROVR is indicated in a new ROVR Size field 671 that is encoded to map one-to-one with the Code Suffix in the EDAR 672 message (see table 4 of [RFC8505]). 674 The modified format is illustrated in Figure 4. It is backward 675 compatible with the Target Option in [RFC6550] and SHOULD be used as 676 a replacement. 678 0 1 2 3 679 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 1 680 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 681 | Type = 0x05 | Option Length |ROVRsz | Flags | Prefix Length | 682 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 683 | | 684 + + 685 | Target Prefix (Variable Length) | 686 . Aligned to 4-byte boundary . 687 . . 688 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 689 | | 690 ... Registration Ownership Verifier (ROVR) ... 691 | | 692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 694 Figure 4: Updated Target Option 696 New fields: 698 ROVRsz: Indicates the Size of the ROVR. It MAY be 1, 2, 3, or 4, 699 denoting a ROVR size of 64, 128, 192, or 256 bits, respectively. 701 Registration Ownership Verifier (ROVR): This is the same field as in 702 the EARO, see [RFC8505] 704 9. Protocol Operations for Unicast Addresses 706 The description below assumes that the Root sets the "P" flag in the 707 DODAG Configuration Option and performs the EDAR proxy operation. 709 9.1. General Flow 711 This specification enables to save the exchange of keep-alive 712 Extended Duplicate Address messages, EDAR and EDAC, from a 6LN all 713 the way to the 6LBR across a RPL mesh. Instead, the EDAR/EDAC 714 exchange with the 6LBR is proxied by the RPL Root upon a DAO message 715 that refreshes the RPL routing state. 717 To achieve this, the lifetimes and sequence counters in 6LoWPAN ND 718 and RPL are aligned. In other words, the Path Sequence and the Path 719 Lifetime in the DAO message are taken from the Transaction ID and the 720 Address Registration lifetime in the NS(EARO) message from the 6LN. 722 The proxy operation applies to both RULs and RANs. In a RPL network 723 where the function is enabled, refreshing the state in the 6LBR is 724 the responsibility of the Root. Consequently, only addresses that 725 are injected in RPL will be kept alive by the RPL Root. 727 In a same fashion, if an additional routing protocol is deployed on a 728 same network, that additional routing protocol may need to handle the 729 keep alive procedure for the addresses that it serves. 731 On the first Address Registration, illustrated in Figure 5 and 732 Figure 8 for RPL Non-Storing and Storing Mode respectively, the 733 Extended Duplicate Address exchange takes place as prescribed by 734 [RFC8505]. Any of the functions 6LR, Root and 6LBR might be 735 collapsed in a single node. 737 When successful, the flow creates a Neighbor Cache Entry (NCE) in the 738 6LR, and the 6LR injects the Registered Address in RPL using DAO/DAO- 739 ACK exchanges all the way to the RPL DODAG Root. The protocol does 740 not carry a specific information that the Extended Duplicate Address 741 messages were already exchanged, so the Root proxies them anyway. 743 9.1.1. In RPL Non-Storing-Mode 745 In Non-Storing Mode, the DAO message flow can be nested within the 746 Address Registration flow as illustrated in Figure 5. 748 6LN 6LR Root 6LBR 749 | | | | 750 | NS(EARO) | | | 751 |--------------->| | 752 | | Extended DAR | 753 | |--------------------------------->| 754 | | | 755 | | Extended DAC | 756 | |<---------------------------------| 757 | | DAO | | 758 | |------------->| | 759 | | | (anonymous) EDAR | 760 | | |------------------>| 761 | | | EDAC | 762 | | |<------------------| 763 | | DAO-ACK | | 764 | |<-------------| | 765 | NA(EARO) | | | 766 |<---------------| | | 767 | | | | 769 Figure 5: First Registration Flow in Non-Storing Mode 771 An issue may be detected later, e.g., the address moves within the 772 LLN or to a different Root on a backbone [6BBR]. In that case the 773 value of the status that indicates the issue can be passed from 774 6LoWPAN ND to RPL and back as illustrated in Figure 6. 776 6LN 6LR Root 6LBR 777 | | | | 778 | | | NA(EARO, Status) | 779 | | |<-----------------| 780 | | DCO(Status) | | 781 | |<------------| | 782 | NA(EARO, Status) | | | 783 |<-----------------| | | 784 | | | | 786 Figure 6: Asynchronous Issue 788 An Address re-Registration is performed by the 6LN to maintain the 789 NCE in the 6LR alive before lifetime expires. Upon an Address re- 790 Registration, as illustrated in Figure 7, the 6LR redistributes the 791 Registered Address NS(EARO) in RPL. 793 6LN 6LR Root 6LBR 794 | | | | 795 | NS(EARO) | | | 796 |--------------->| | 797 | | DAO | | 798 | |------------->| | 799 | | | (anonymous) EDAR | 800 | | |------------------>| 801 | | | EDAC | 802 | | |<------------------| 803 | | DAO-ACK | | 804 | |<-------------| | 805 | NA(EARO) | | | 806 |<---------------| | | 808 Figure 7: Next Registration Flow in Non-Storing Mode 810 This causes the RPL DODAG Root to refresh the state in the 6LBR with 811 an EDAC message or an anonymous EDAC if the ROVR is not indicated in 812 the Target Option. In both cases, the EDAC message sent in response 813 by the 6LBR contains the actual value of the ROVR field for that 814 Address Registration. In case of an error on the proxied EDAR flow, 815 the error MUST be returned in the DAO-ACK - if one was requested - 816 using a RPL Status with the 'A' flag set that imbeds a 6LoWPAN Status 817 value as discussed in Section 7. 819 If the Root could not return the negative Status in the DAO-ACK then 820 it sends an asynchronous Destination Cleanup Object (DCO) message 821 [EFFICIENT-NPDAO] to the 6LR placing the negative Status in the RPL 822 Status with the 'A' flag set. Note that if both are used in a short 823 interval of time, the DAO-ACK and DCO messages are not guaranteed to 824 arrive in the same order at the 6LR. 826 The 6LR may still receive a requested DAO-ACK even after it received 827 a DCO, but the negative Status in the DCO supercedes a positive 828 Status in the DAO-ACK regardless of the order in which they are 829 received. Upon the DAO-ACK - or the DCO if it arrives first - the 830 6LR responds to the RUL with a NA(EARO). If the RPL Status has the 831 'A' flag set, then the ND Status is extracted and passed in the EARO; 832 else, if the 'E' flag is set, indicating a rejection, then the status 833 4 "Removed" is used; else, the ND Status of 0 indicating "Success" is 834 used. 836 9.1.2. In RPL Storing-Mode 838 In RPL Storing Mode, the DAO-ACK is optional. When it is used, it is 839 generated by the RPL parent, which does not need to wait for the 840 grand-parent to send the acknowledgement. A successful DAO-ACK is 841 not a guarantee that the DAO has yet reached the Root or that the 842 EDAR has succeeded. 844 6LN 6LR 6LR Root 6LBR 845 | | | | | 846 | NS(EARO) | | | | 847 |-------------->| | | | 848 | NA(EARO) | | | | 849 |<--------------| | | | 850 | | | | | 851 | | DAO | | | 852 | |-------------->| | | 853 | | DAO-ACK | | | 854 | |<--------------| | | 855 | | | | | 856 | | | DAO | | 857 | | |-------------->| | 858 | | | DAO-ACK | | 859 | | |<--------------| | 860 | | | | | 861 | | | | (anonymous) EDAR | 862 | | | |----------------->| 863 | | | | EDAC(ROVR) | 864 | | | |<-----------------| 865 | | | | | 866 Figure 8: Next Registration Flow in Storing Mode 868 If the keep-alive fails, or an asynchronous issue is reported, the 869 path can be cleaned up asynchronously using a DCO message 870 [EFFICIENT-NPDAO] as illustrated in Figure 9 and described in further 871 details in Section 9.2.3. 873 6LN 6LR 6LR Root 6LBR 874 | | | | | 875 | | | | NA(EARO, Status) | 876 | | | |<-----------------| 877 | | | | | 878 | | | DCO(Status) | | 879 | | |<------------| | 880 | | | | | 881 | | DCO(Status) | | | 882 | |<------------| | | 883 | | | | | 884 | NA(EARO, Status) | | | | 885 |<-----------------| | | | 886 | | | | | 888 Figure 9: Issue in Storing Mode 890 9.2. Detailed Operation 892 9.2.1. By the 6LN 894 This specification does not alter the operation of a 6LoWPAN ND- 895 compliant 6LN, and a RUL is expected to operate as follows: 897 * The 6LN obtains an IPv6 global address, either using Stateless 898 Address Autoconfiguration (SLAAC) [RFC4862] based on a Prefix 899 Information Option (PIO) [RFC4861] found in a Router Advertisement 900 message, or some other means such as DHCPv6 [RFC3315]. 902 * Once it has formed an address, the 6LN (re)registers its address 903 periodically, within the Lifetime of the previous Address 904 Registration, as prescribed by [RFC6775] and [RFC8505]. 906 * The 6LN can register to more than one 6LR at the same time. In 907 that case, it MUST use the same value of TID for all of the 908 parallel Address Registrations. 910 * Following section 5.1 of [RFC8505], a 6LN acting as a RUL sets the 911 "R" flag in the EARO of at least one registration, whereas acting 912 as a RAN it never does. If the "R" flag is set in the NS but not 913 echoed in the NA, the RUL SHOULD attempt to use another 6LR. 915 * Upon each consecutive Address Registration, the 6LN increases the 916 TID field in the EARO, as prescribed by [RFC8505] section 5.2. 918 * The 6LN may use any of the 6LRs to which it register to forward 919 its packets. Using a 6LR to which the 6LN is not registered may 920 result in packets dropped at the 6LR by a Source Address 921 Validation function (SAVI) so it is NOT RECOMMENDED. 923 Even without support for RPL, a RUL may be aware of opaque values to 924 be provided to the routing protocol. If the RUL has a knowledge of 925 the RPL Instance the packet should be injected into, then it SHOULD 926 set the Opaque field in the EARO to the RPLInstanceID, else it MUST 927 leave the Opaque field to zero. 929 Regardless of the setting of the Opaque field, the 6LN MUST set the 930 "I" field to zero to signal "topological information to be passed to 931 a routing process" as specified in section 5.1 of [RFC8505]. 933 A RUL is not expected to produce RPL artifacts in the data packets, 934 but it MAY do so. For instance, if the RUL has a minimal awareness 935 of the RPL Instance then it can build an RPI. A RUL that places an 936 RPI in a data packet MUST indicate the RPLInstanceID that corresponds 937 to the RPL Instance the packet should be injected into. All the 938 flags and the Rank field are set to zero as specified by section 11.2 939 of [RFC6550]. 941 9.2.2. By the 6LR 943 Also as prescribed by [RFC8505], the 6LR generates an EDAR message 944 upon reception of a valid NS(EARO) message for the Address 945 Registration of a new IPv6 Address by a 6LN. If the Duplicate 946 Address exchange succeeds, then the 6LR installs an NCE. If the "R" 947 flag was set in the EARO of the NS message, and this 6LR can manage 948 the reachability of Registered Address, then the 6LR sets the "R" 949 flag in the EARO of the NA message that is sends in response. 951 From then on, the 6LN periodically sends a new NS(EARO) to refresh 952 the NCE state before the lifetime indicated in the EARO expires, with 953 TID that is incremented each time till it wraps in a lollipop fashion 954 (see section 5.2.1 of [RFC8505] which is fully compatible with 955 section 7.2 of [RFC6550]). As long as the "R" flag is set and this 956 Router can still manage the reachability of Registered Address, the 957 6LR keeps setting the "R" flag in the EARO of the response NA 958 message, but the exchange of keep-alive Extended Duplicate Address 959 messages with the 6LBR is avoided if the RPL Root has indicated that 960 it proxies for it. 962 The Opaque field in the EARO hints the 6LR on the RPL Instance that 963 should be used for the DAO advertisements, and for the forwarding of 964 packets sourced at the registered address when there is no RPI in the 965 packet, in which case the 6LR MUST encapsulate the packet to the Root 966 adding an RPI in the outer header. If the Opaque field is zero, the 967 6LR is free to use the default RPL Instance (zero) for the registered 968 address or to select an Instance of its choice. 970 if the "I" field is not zero, then the 6LR MUST consider that the 971 Opaque field is zero. If the Opaque field is not zero, then it is 972 expected to carry a RPLInstanceID for the RPL Instance suggested by 973 the 6LN. If the 6LR does not participate to the associated Instance, 974 then the 6LR MUST consider that the Opaque field is zero; else, that 975 is if the 6LR participates to the suggested Instance, then the 6LR 976 SHOULD use that Instance for the registered address. 978 The DAO message advertising the Registered Address MUST be 979 constructed as follows: 981 * The Registered Address is placed in a RPL Target Option in the DAO 982 message as the Target Prefix, and the Prefix Length is set to 128; 984 * RPL Non-Storing Mode is used, and the 6LR indicates one of its 985 global or unique-local IPv6 unicast addresses as the Parent 986 Address in the associated RPL Transit Information Option (TIO). 988 * the External 'E' flag in the TIO is set to indicate that the 6LR 989 redistributes an external target into the RPL network. 991 * the Path Lifetime in the TIO is computed from the Lifetime in the 992 EARO Option to adapt it to the Lifetime Units used in the RPL 993 operation. Note that if the lifetime is 0, then the 6LR generates 994 a No-Path DAO message that cleans up the routes down to the 995 Address of the 6LN; 997 * the Path Sequence in the TIO is set to the TID value found in the 998 EARO option; 1000 Upon an NS(EARO), iff the "R" flag was set, the 6LR SHOULD inject the 1001 Registered Address in RPL by sending a DAO message on behalf of the 1002 6LN. If the Registration Lifetime was 0, the effect is to remove the 1003 route and then the NCE. 1005 If for whatever reason the 6LR does not inject the Registered Address 1006 in RPL, it MUST send an NA(EARO) back with the appropriate status and 1007 the "R" flag not set. 1009 If the 6LR injects the Registered Address in RPL and either a DAO-ACK 1010 was not requested or is received with a RPL Status that is not a 1011 rejection ("E" flag not set), the 6LR MUST install or refresh the NCE 1012 for the address and reply to the RUL with an NA(EARO) with a Status 1013 of 0 (Success) and the "R" flag set. 1015 In case of a DAO-ACK or a DCO indicating transporting an EARO Status 1016 Value of 5 (Validation Requested), a 6LR that supports Address 1017 Protected Neighbor Discovery (AP-ND) MUST challenge the 6LN for 1018 ownership of the address, as described in section 6.1 of [AP-ND]. If 1019 the challenge succeeds then the operations continue as normal. In 1020 particular a DAO message is generated upon the NS(EARO) that proves 1021 the ownership of the address. If the challenge failed, the 6LR 1022 rejects the registration as prescribed by AP-ND and may take actions 1023 to protect itself against DoS attacks by a rogue 6LN, see Section 11. 1024 If the 6LR does not support AP-ND, it MUST send an NA to the 6LN with 1025 a Status of 0 (Success) and the "R" flag not set. 1027 The other rejection codes indicate that the 6LR failed to inject the 1028 address into the RPL network. If an EARO Status is transported, the 1029 6LR MUST send a NA(EARO) to the RUL with that Status value, and the 1030 "R" flag not set. Similarly, upon receiving a DCO message indicating 1031 that the address of a RUL should be removed from the routing table, 1032 the 6LR issues an asynchronous NA(EARO) to the RUL with the embedded 1033 ND Status value if there was one, and the "R" flag not set. 1035 If a 6LR receives a valid NS(EARO) message with the "R" flag reset 1036 and a Registration Lifetime that is not 0, and the 6LR was 1037 redistributing the Registered Address due to previous NS(EARO) 1038 messages with the flag set, then it MUST stop injecting the address. 1039 It is up to the Registering 6LN to maintain the corresponding route 1040 from then on, either keeping it active via a different 6LR or by 1041 acting as a RAN and managing its own reachability. 1043 9.2.3. By the RPL Root 1045 In RPL Storing Mode of Operation (MOP), the DAO message is propagated 1046 from child to parent all the way to the Root along the DODAG, 1047 populating routing state as it goes. In Non-Storing Mode, The DAO 1048 message is sent directly to the RPL Root. Upon reception of a DAO 1049 message, for each RPL Target option that creates or updates an 1050 existing RPL state: 1052 * the Root notifies the 6LBR using an internal API if they are co- 1053 located, or using a proxied EDAR/EDAC exchange if they are 1054 separated. If the RPL Target option transports a ROVR, then the 1055 Root MUST use it to build a full EDAR message; else, an anonymous 1056 EDAR is used with the ROVR field set to zero. 1058 The EDAR message MUST be constructed as follows: 1060 * The Target IPv6 address from the RPL Target Option is placed in 1061 the Registered Address field of the EDAR message; 1063 * the Registration Lifetime is adapted from the Path Lifetime in the 1064 TIO by converting the Lifetime Units used in RPL into units of 60 1065 seconds used in the 6LoWPAN ND messages; 1067 * the TID value is set to the Path Sequence in the TIO and indicated 1068 with an ICMP code of 1 in the EDAR message; 1070 * If the ROVR is present in the RPL Target option, it is copied as 1071 is in the EDAR and the ICMP Code Suffix is set to the appropriate 1072 value as shown in Table 4 of [RFC8505] depending on the size of 1073 the ROVR field; else, the ROVR field in the EDAR is set to zero 1074 indicating an anonymous EDAR. 1076 Upon a Status value in an EDAC message that is not "Success", the 1077 Root SHOULD destroy the formed paths using either a DAO-ACK (in Non- 1078 Storing Mode) or a DCO downwards as specified in [EFFICIENT-NPDAO]. 1079 Failure to destroy the former path would result in Stale routing 1080 state and local black holes if the address belongs to another party 1081 elsewhere in the network. The RPL Status value that maps the 6LoWPAN 1082 ND Status value MUST be embedded in the RPL Status in the DCO. 1084 9.2.4. By the 6LBR 1086 Upon reception of an EDAR message with the ROVR field is set to zero 1087 indicating an anonymous EDAR, the 6LBR checks whether an entry exists 1088 for the and computes whether the TID in the DAR message is fresher 1089 than that in the entry as prescribed in section 4.2.1. of [RFC8505]. 1091 If the entry does not exist, the 6LBR does not create the entry, and 1092 answers with a Status "Removed" in the EDAC message. If the entry 1093 exists but is not fresher, the 6LBR does not update the entry, and 1094 answers with a Status "Success" in the EDAC message. 1096 If the entry exists and the TID in the DAR message is fresher, the 1097 6LBR updates the TID in the entry, and if the lifetime of the entry 1098 is extended by the Registration Lifetime in the DAR message, it also 1099 updates the lifetime of the entry. In that case, the 6LBR replies 1100 with a Status "Success" in the DAC message. 1102 The EDAC that is constructed is the same as if the anonymous EDAR was 1103 a full EDAR, and includes the ROVR that is associated to the Address 1104 Registration. 1106 10. Protocol Operations for Multicast Addresses 1108 Section 12 of [RFC6550] details the RPL support for multicast flows. 1109 This support is not source-specific and only operates as an extension 1110 to the Storing Mode of Operation for unicast packets. Note that it 1111 is the RPL model that the multicast packet is passed as a Layer-2 1112 unicast to each if the interested children. This remains true when 1113 forwarding between the 6LR and the listener 6LN. 1115 "Multicast Listener Discovery (MLD) for IPv6" [RFC2710] and its 1116 updated version "Multicast Listener Discovery Version 2 (MLDv2) for 1117 IPv6" [RFC3810] provide an interface for a listener to register to 1118 multicast flows. MLDv2 is backwards compatible with MLD, and adds in 1119 particular the capability to filter the sources via black lists and 1120 white lists. In the MLD model, the Router is a "querier" and the 1121 Host is a multicast listener that registers to the querier to obtain 1122 copies of the particular flows it is interested in. 1124 On the first Address Registration, as illustrated in Figure 10, the 1125 6LN, as an MLD listener, sends an unsolicited Report to the 6LR in 1126 order to start receiving the flow immediately. Since multicast 1127 Layer-2 messages are avoided, it is important that the asynchronous 1128 messages for unsolicited Report and Done are sent reliably, for 1129 instance using an Layer-2 acknoledgement, or attempted multiple 1130 times. 1132 6LN 6LR Root 6LBR 1133 | | | | 1134 | unsolicited Report | | | 1135 |------------------->| | | 1136 | | | | 1137 | | DAO | | 1138 | |-------------->| | 1139 | | DAO-ACK | | 1140 | |<--------------| | 1141 | | | | 1142 | | | unsolicited Report | 1143 | | |------------------->| 1144 | | | | 1145 | | | | 1147 Figure 10: First Multicast Registration Flow 1149 The 6LR acts as a generic MLD querier and generates a DAO for the 1150 multicast target. The lifetime of the DAO is set to be in the order 1151 of the Query Interval, yet larger to account for variable propagation 1152 delays. 1154 The Root proxies the MLD echange as listener with the 6LBR acting as 1155 the querier, so as to get packets from a source external to the RPL 1156 domain. Upon a DAO with a multicast target, the RPL Root checks if 1157 it is already registered as a listener for that address, and if not, 1158 it performs its own unsolicited Report for the multicast target. 1160 An Address re-Registration is pulled periodically by 6LR acting as 1161 querier. Note that th message may be sent unicast to all the known 1162 individual listeners. Upon a time out of the Query Interval, the 6LR 1163 sends a Query to each of its listeners, and gets a Report back that 1164 is mapped into a DAO, as illustrated in Figure 11: 1166 6LN 6LR Root 6LBR 1167 | | | | 1168 | Query | | | 1169 |<-------------------| | | 1170 | Report | | | 1171 |------------------->| | | 1172 | | DAO | | 1173 | |-------------->| | 1174 | | DAO-ACK | | 1175 | |<--------------| | 1176 | | | | 1177 | | | Query | 1178 | | |<-------------------| 1179 | | | Report | 1180 | | |------------------->| 1181 | | | | 1182 | | | | 1184 Figure 11: Next Registration Flow 1186 Note that any of the functions 6LR, Root and 6LBR might be collapsed 1187 in a single node, in which case the flow above happens internally, 1188 and possibly through internal API calls as opposed to messaging. 1190 11. Security Considerations 1192 The LLN nodes depend on the 6LBR and the RPL participants for their 1193 operation. A trust model must be put in place to ensure that the 1194 right devices are acting in these roles, so as to avoid threats such 1195 as black-holing, (see [RFC7416] section 7) or bombing attack whereby 1196 an impersonated 6LBR would destroy state in the network by using the 1197 "Removed" Status code. 1199 This trust model could be at a minimum based on a Layer-2 Secure 1200 joining and the Link-Layer security. This is a generic 6LoWPAN 1201 requirement, see Req5.1 in Appendix of [RFC8505]. 1203 Additionally, the trust model could include a role validation to 1204 ensure that the node that claims to be a 6LBR or a RPL Root is 1205 entitled to do so. 1207 The anonymous EDAR message does not carry a valid Registration Unique 1208 ID [RFC8505] in the form of a ROVR and may be played by any node on 1209 the network without the need to know the ROVR. The 6LBR MUST NOT 1210 create an entry based on a anonymous EDAR that does not match an 1211 existing entry. All it can do is refresh the lifetime and the TID of 1212 an existing entry. So the message cannot be used to create a binding 1213 state in the 6LBR but it can be use to maitain one active longer than 1214 expected. 1216 Note that a full EDAR message with a lifetime of 0 will destroy that 1217 state and the anonymous message will not recreate it. Note also that 1218 a rogue that has access to the network can attack the 6LBR with other 1219 (forged) addresses and ROVR, and that this is a much easier DoS 1220 attack than trying to keep existing state alive longer. 1222 At the time of this writing RPL does not have a zerotrust model 1223 whereby the it is possible to validate the origin of an address that 1224 is injected in a DAO. This specification makes a first step in that 1225 direction by allowing the Root to challenge the RUL by the 6LR that 1226 serves it. 1228 12. IANA Considerations 1230 12.1. Resizing the ARO Status values 1232 IANA is requested to modify the Address Registration Option Status 1233 Values Registry as follows: The unassigned values range is reduced 1234 from 11-255 to 11-63. 1236 12.2. New DODAG Configuration Option Flag 1238 This specification updates the Registry for the "DODAG Configuration 1239 Option Flags" that was created for [RFC6550] as follows: 1241 +------------+----------------------------+-----------+ 1242 | Bit Number | Capability Description | Reference | 1243 +============+============================+===========+ 1244 | 1 | Root Proxies EDAR/EDAC (P) | THIS RFC | 1245 +------------+----------------------------+-----------+ 1247 Table 2: New DODAG Configuration Option Flag 1249 12.3. RPL Target Option Flags 1251 Section 20.15 of [RFC6550] creates a registry for the 8-bit RPL 1252 Target Option Flags field. This specification reduces the field to 4 1253 bits. The IANA is requested to reduce the size of the registry 1254 accordingly. 1256 12.4. New Subregistry for the RPL Non-Rejection Status values 1258 This specification creates a new Subregistry for the RPL Non- 1259 Rejection Status values for use in RPL DAO-ACK and RCO messages, 1260 under the ICMPv6 parameters registry. 1262 * Possible values are 6-bit unsigned integers (0..63). 1264 * Registration procedure is "Standards Action" [RFC8126]. 1266 * Initial allocation is as indicated in Table 3: 1268 +-------+------------------------+-----------+ 1269 | Value | Meaning | Reference | 1270 +=======+========================+===========+ 1271 | 0 | Unqualified acceptance | RFC 6550 | 1272 +-------+------------------------+-----------+ 1274 Table 3: Acceptance values of the RPL Status 1276 12.5. New Subregistry for the RPL Rejection Status values 1278 This specification creates a new Subregistry for the RPL Rejection 1279 Status values for use in RPL DAO-ACK and RCO messages, under the 1280 ICMPv6 parameters registry. 1282 * Possible values are 6-bit unsigned integers (0..63). 1284 * Registration procedure is "Standards Action" [RFC8126]. 1286 * Initial allocation is as indicated in Table 4: 1288 +-------+-----------------------+---------------+ 1289 | Value | Meaning | Reference | 1290 +=======+=======================+===============+ 1291 | 0 | Unqualified rejection | This document | 1292 +-------+-----------------------+---------------+ 1294 Table 4: Rejection values of the RPL Status 1296 13. Acknowledgments 1298 The authors wish to thank Georgios Papadopoulos for their early 1299 reviews of and contributions to this document 1301 14. Normative References 1303 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1304 Requirement Levels", BCP 14, RFC 2119, 1305 DOI 10.17487/RFC2119, March 1997, 1306 . 1308 [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast 1309 Listener Discovery (MLD) for IPv6", RFC 2710, 1310 DOI 10.17487/RFC2710, October 1999, 1311 . 1313 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1314 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1315 DOI 10.17487/RFC3810, June 2004, 1316 . 1318 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1319 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1320 Overview, Assumptions, Problem Statement, and Goals", 1321 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1322 . 1324 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1325 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1326 DOI 10.17487/RFC4861, September 2007, 1327 . 1329 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1330 Address Autoconfiguration", RFC 4862, 1331 DOI 10.17487/RFC4862, September 2007, 1332 . 1334 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1335 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1336 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1337 Low-Power and Lossy Networks", RFC 6550, 1338 DOI 10.17487/RFC6550, March 2012, 1339 . 1341 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1342 Power and Lossy Networks (RPL) Option for Carrying RPL 1343 Information in Data-Plane Datagrams", RFC 6553, 1344 DOI 10.17487/RFC6553, March 2012, 1345 . 1347 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1348 Bormann, "Neighbor Discovery Optimization for IPv6 over 1349 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1350 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1351 . 1353 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 1354 IPv6 over Low-Power Wireless Personal Area Networks 1355 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 1356 2014, . 1358 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1359 Writing an IANA Considerations Section in RFCs", BCP 26, 1360 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1361 . 1363 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1364 "IPv6 over Low-Power Wireless Personal Area Network 1365 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1366 April 2017, . 1368 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1369 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1370 May 2017, . 1372 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1373 (IPv6) Specification", STD 86, RFC 8200, 1374 DOI 10.17487/RFC8200, July 2017, 1375 . 1377 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1378 Perkins, "Registration Extensions for IPv6 over Low-Power 1379 Wireless Personal Area Network (6LoWPAN) Neighbor 1380 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1381 . 1383 [AP-ND] Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 1384 "Address Protected Neighbor Discovery for Low-power and 1385 Lossy Networks", Work in Progress, Internet-Draft, draft- 1386 ietf-6lo-ap-nd-19, 6 February 2020, 1387 . 1389 [USEofRPLinfo] 1390 Robles, I., Richardson, M., and P. Thubert, "Using RPI 1391 option Type, Routing Header for Source Routes and IPv6-in- 1392 IPv6 encapsulation in the RPL Data Plane", Work in 1393 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-36, 1394 26 February 2020, . 1397 [EFFICIENT-NPDAO] 1398 Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient 1399 Route Invalidation", Work in Progress, Internet-Draft, 1400 draft-ietf-roll-efficient-npdao-17, 30 October 2019, 1401 . 1404 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1405 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1406 2014, . 1408 15. Informative References 1410 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1411 Statement and Requirements for IPv6 over Low-Power 1412 Wireless Personal Area Network (6LoWPAN) Routing", 1413 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1414 . 1416 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 1417 C., and M. Carney, "Dynamic Host Configuration Protocol 1418 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 1419 2003, . 1421 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1422 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1423 DOI 10.17487/RFC6282, September 2011, 1424 . 1426 [RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur, 1427 Ed., "Performance Evaluation of the Routing Protocol for 1428 Low-Power and Lossy Networks (RPL)", RFC 6687, 1429 DOI 10.17487/RFC6687, October 2012, 1430 . 1432 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1433 Constrained-Node Networks", RFC 7228, 1434 DOI 10.17487/RFC7228, May 2014, 1435 . 1437 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1438 and M. Richardson, Ed., "A Security Threat Analysis for 1439 the Routing Protocol for Low-Power and Lossy Networks 1440 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1441 . 1443 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1444 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1445 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1446 . 1448 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node 1449 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504, 1450 January 2019, . 1452 [6BBR] Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6 1453 Backbone Router", Work in Progress, Internet-Draft, draft- 1454 ietf-6lo-backbone-router-19, 3 March 2020, 1455 . 1458 Appendix A. Example Compression 1460 Figure 12 illustrates the case in Storing Mode where the packet is 1461 received from the Internet, then the Root encapsulates the packet to 1462 insert the RPI and deliver to the 6LR that is the parent and last hop 1463 to the final destination, which is not known to support [RFC8138]. 1465 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1466 |11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP 1467 |Page 1 |Type1 S=0| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 1468 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1469 <-4 bytes-> <- RFC 6282 -> 1470 <- No RPL artifact ... 1472 Figure 12: Encapsulation to Parent 6LR in Storing Mode 1474 The difference with the example format presented in Figure 19 of 1475 [RFC8138] is the addition of a SRH-6LoRH before the RPI-6LoRH to 1476 transport the compressed address of the 6LR as the destination 1477 address of the outer IPv6 header. In the original example the 1478 destination IP of the outer header was elided and was implicitly the 1479 same address as the destination of the inner header. Type 1 was 1480 arbitrarily chosen for this example, and the size of 0 denotes a 1481 single address in the SRH. 1483 In Figure 12, the source of the IP-in-IP encapsulation is the Root, 1484 so it is elided in the IP-in-IP 6LoRH. The destination is the parent 1485 6LR of the destination of the inner packet so it cannot be elided. 1486 In Storing Mode, it is placed as the single entry in an SRH-6LoRH as 1487 the first 6LoRH. Since there is a single entry so the SRH-6LoRH Size 1488 is 0. In this particular example, the 6LR address can be compressed 1489 to 2 bytes so a Type of 1 is used. It results that the total length 1490 of the SRH-6LoRH is 4 bytes. 1492 In Non-Storing Mode, the encapsulation from the Root would be similar 1493 to that represented in Figure 12 with possibly more hops in the SRH- 1494 6LoRH and possibly multiple SRH-6LoRHs if the various addresses in 1495 the routing header are not compressed to the same format. Note that 1496 on the last hop to the parent 6LR, the RH3 is consumed and removed 1497 from the compressed form, so the use of Non-Storing Mode vs. Storing 1498 Mode is indistinguishable from the packet format. 1500 Follows the RPI-6LoRH and then the IP-in-IP 6LoRH. When the IP-in-IP 1501 6LoRH is removed, all the Router headers that precede it are also 1502 removed. 1504 The Paging Dispatch [RFC8025] may also be removed if there was no 1505 previous Page change to a Page other than 0 or 1, since the 1506 LOWPAN_IPHC is encoded in the same fashion in the default Page 0 and 1507 in Page 1. The resulting packet to the destination is the inner 1508 packet compressed with [RFC6282]. 1510 Authors' Addresses 1512 Pascal Thubert (editor) 1513 Cisco Systems, Inc 1514 Building D 1515 45 Allee des Ormes - BP1200 1516 06254 Mougins - Sophia Antipolis 1517 France 1519 Phone: +33 497 23 26 34 1520 Email: pthubert@cisco.com 1522 Michael C. Richardson 1523 Sandelman Software Works 1525 Email: mcr+ietf@sandelman.ca 1526 URI: http://www.sandelman.ca/