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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: 14 September 2020 13 March 2020 8 Routing for RPL Leaves 9 draft-ietf-roll-unaware-leaves-11 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 14 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 A 6LR that is upgraded to act as a border router for external routes 536 advertises them using Non-Storing Mode DAO messages that are unicast 537 directly to the Root, even if the DODAG is operated in Storing Mode. 538 Non-Storing Mode routes are not visible inside the RPL domain and all 539 packets are routed via the Root. An upgraded Root tunnels the 540 packets directly to the 6LR that advertised the external route which 541 decapsulates and forwards the original (inner) packet. 543 The RPL Non-Storing Mode signaling and the associated IP-in-IP 544 encapsulated packets are normal traffic for the intermediate Routers. 545 The support of external routes only impacts the Root and the 6LR. It 546 can be operated with legacy intermediate routers and does not add to 547 the amount of state that must be maintained in those routers. A RUL 548 is an example of a destination that is reachable via an external 549 route which happens to be a Host route. 551 The RPL data packets always carry a Hop-by-Hop Header to transport a 552 RPL Packet Information (RPI) [RFC6550]. So unless the RUL originates 553 its packets with an RPI, the 6LR needs to tunnel them to the Root to 554 add the RPI. As a rule of a thumb and except the very special case 555 above, the packets from and to a RUL are always encapsulated using an 556 IP-in-IP tunnel between the Root and the 6LR that serves the RUL. 558 In Non-Storing Mode, packets going down carry a Source Routing Header 559 (SRH). The IP-in-IP encapsulation, the RPI and the SRH are 560 collectively called the "RPL artifacts" and can be compressed using 561 [RFC8138]. Figure 12 presents an example compressed format for a 562 packet forwarded by the Root to a RUL in a Storing Mode DODAG. 564 The inner packet that is forwarded to the RUL may carry some RPL 565 artifacts, e.g., an RPI if the original packet was generated with it 566 and encapsulated by the Root with that RPI still present in the inner 567 header, and possibly an SRH in a Non-Storing Mode DODAG. 568 [USEofRPLinfo] expects the RUL to support the basic "IPv6 Node 569 Requirements" [RFC8504], in particular to ignore the RPL artifacts 570 that are either consumed or not applicable to a Host, but not 571 necessarily IP-in-IP encapsulation, more in the next sections. 573 A RUL is not expected to support the compression method defined in 574 [RFC8138]. Unless configured otherwise, the border router MUST 575 uncompress the outgoing packet before forwarding over an external 576 route, and if it is not the destination of the incoming packet, and 577 even when delivering to a RUL. 579 6.2.1. Support of IPv6 Encapsulation 581 Section 2.1 of [USEofRPLinfo] sets the rules for forwarding IP-in-IP 582 either to the final 6LN or to a parent 6LR. In order to enable IP- 583 in-IP to the 6LN in Non-Storing Mode, the 6LN must be able to 584 decapsulate the tunneled packet and either drop the inner packet if 585 it is not the final destination, or pass it to the upper layer for 586 further processing. Unless it is aware that the RUL can handle IP- 587 in-IP properly, the Root that encapsulates a packet to a RUL 588 terminates the IP-in-IP tunnel at the parent 6LR . For that reason, 589 it is beneficial but not necessary for a RUL to support IP-in-IP. 591 6.2.2. Support of the HbH Header 593 A RUL is expected to process an unknown Option Type in a Hop-by-Hop 594 Header as prescribed by section 4.2 of [RFC8200]. This means in 595 particular that an RPI with an Option Type of 0x23 [USEofRPLinfo] is 596 ignored when not understood. 598 6.2.3. Support of the Routing Header 600 A RUL is expected to process an unknown Routing Header Type as 601 prescribed by section 4.4 of [RFC8200]. This means in particular 602 that Routing Header with a Routing Type of 3 [RFC6553] is ignored 603 when the Segments Left is zero, and the packet is dropped otherwise. 605 7. Updated RPL Status 607 The RPL Status is defined in section 6.5.1. of [RFC6550] for use in 608 the DAO-Ack message and values are assigned as follows: 610 +---------+--------------------------------+ 611 | Range | Meaning | 612 +=========+================================+ 613 | 0 | Success/Unqualified acceptance | 614 +---------+--------------------------------+ 615 | 1-127 | Not an outright rejection | 616 +---------+--------------------------------+ 617 | 128-255 | Rejection | 618 +---------+--------------------------------+ 620 Table 1: RPL Status per RFC 6550 622 This specification extends the scope of the RPL Status to be used in 623 RPL DCO messages. Furthermore, this specification enables to carry 624 the IPv6 ND Status values defined for use in the EARO and initially 625 listed in table 1 of [RFC8505] in a RPL Status. 627 Section 12.1 reduces the range of EARO Status values to 0-63 ensure 628 that they fit within a RPL Status as shown in Figure 3. 630 0 631 0 1 2 3 4 5 6 7 632 +-+-+-+-+-+-+-+-+ 633 |E|A| Value | 634 +-+-+-+-+-+-+-+-+ 636 Figure 3: RPL Status Format 638 RPL Status subfields: 640 E: 1-bit flag. Set to indicate a rejection. When not set, a value 641 of 0 indicates Success/Unqualified acceptance and other values 642 indicate "not an outright rejection" as per RFC 6550. 644 A: 1-bit flag. Indicates the type of the Status value. 646 Status Value: 6-bit unsigned integer. If the 'A' flag is set this 647 field transports a Status value defined for IPv6 ND EARO. When 648 the 'A' flag is not set, the Status value is defined in a RPL 649 extension. 651 When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a DAC 652 message, the RPL Root MUST copy the ARO Status unchanged in a RPL 653 Status with the 'A' bit set. The RPL Root MUST set the 'E' flag for 654 all values in range 1-10 which are all considered rejections. 656 Conversely, the 6LR MUST copy the value of the RPL Status unchanged 657 in the EARO of an NA message that is built upon a RPL Status with the 658 'A' bit set in a DCO or a DAO-ACK message. 660 8. Updated RPL Target option 662 This specification updates the RPL Target option to transport the 663 ROVR. This enables the RPL Root to generate a full EDAR message as 664 opposed to an anonymous EDAR that has restricted properties. 666 The Target Prefix field MUST be aligned to the next 4-byte boundary 667 after the size indicated by the Prefix Length. If necessary the 668 transported prefix MUST be padded with zeros. 670 With this specification the ROVR is the remainder of the RPL Target 671 Option. The size of the ROVR is indicated in a new ROVR Size field 672 that is encoded to map one-to-one with the Code Suffix in the EDAR 673 message (see table 4 of [RFC8505]). 675 The modified format is illustrated in Figure 4. It is backward 676 compatible with the Target Option in [RFC6550] and SHOULD be used as 677 a replacement. 679 0 1 2 3 680 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 1 681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 682 | Type = 0x05 | Option Length |ROVRsz | Flags | Prefix Length | 683 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 684 | | 685 + + 686 | Target Prefix (Variable Length) | 687 . Aligned to 4-byte boundary . 688 . . 689 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 690 | | 691 ... Registration Ownership Verifier (ROVR) ... 692 | | 693 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 695 Figure 4: Updated Target Option 697 New fields: 699 ROVRsz: Indicates the Size of the ROVR. It MAY be 1, 2, 3, or 4, 700 denoting a ROVR size of 64, 128, 192, or 256 bits, respectively. 702 Registration Ownership Verifier (ROVR): This is the same field as in 703 the EARO, see [RFC8505] 705 9. Protocol Operations for Unicast Addresses 707 The description below assumes that the Root sets the "P" flag in the 708 DODAG Configuration Option and performs the EDAR proxy operation. 710 9.1. General Flow 712 This specification enables to save the exchange of keep-alive 713 Extended Duplicate Address messages, EDAR and EDAC, from a 6LN all 714 the way to the 6LBR across a RPL mesh. Instead, the EDAR/EDAC 715 exchange with the 6LBR is proxied by the RPL Root upon a DAO message 716 that refreshes the RPL routing state. 718 To achieve this, the lifetimes and sequence counters in 6LoWPAN ND 719 and RPL are aligned. In other words, the Path Sequence and the Path 720 Lifetime in the DAO message are taken from the Transaction ID and the 721 Address Registration lifetime in the NS(EARO) message from the 6LN. 723 The proxy operation applies to both RULs and RANs. In a RPL network 724 where the function is enabled, refreshing the state in the 6LBR is 725 the responsibility of the Root. Consequently, only addresses that 726 are injected in RPL will be kept alive by the RPL Root. 728 In a same fashion, if an additional routing protocol is deployed on a 729 same network, that additional routing protocol may need to handle the 730 keep alive procedure for the addresses that it serves. 732 On the first Address Registration, illustrated in Figure 5 and 733 Figure 8 for RPL Non-Storing and Storing Mode respectively, the 734 Extended Duplicate Address exchange takes place as prescribed by 735 [RFC8505]. Any of the functions 6LR, Root and 6LBR might be 736 collapsed in a single node. 738 When successful, the flow creates a Neighbor Cache Entry (NCE) in the 739 6LR, and the 6LR injects the Registered Address in RPL using DAO/DAO- 740 ACK exchanges all the way to the RPL DODAG Root. The protocol does 741 not carry a specific information that the Extended Duplicate Address 742 messages were already exchanged, so the Root proxies them anyway. 744 9.1.1. In RPL Non-Storing-Mode 746 In Non-Storing Mode, the DAO message flow can be nested within the 747 Address Registration flow as illustrated in Figure 5. 749 6LN 6LR Root 6LBR 750 | | | | 751 | NS(EARO) | | | 752 |--------------->| | 753 | | Extended DAR | 754 | |--------------------------------->| 755 | | | 756 | | Extended DAC | 757 | |<---------------------------------| 758 | | DAO | | 759 | |------------->| | 760 | | | (anonymous) EDAR | 761 | | |------------------>| 762 | | | EDAC | 763 | | |<------------------| 764 | | DAO-ACK | | 765 | |<-------------| | 766 | NA(EARO) | | | 767 |<---------------| | | 768 | | | | 770 Figure 5: First Registration Flow in Non-Storing Mode 772 An issue may be detected later, e.g., the address moves within the 773 LLN or to a different Root on a backbone [6BBR]. In that case the 774 value of the status that indicates the issue can be passed from 775 6LoWPAN ND to RPL and back as illustrated in Figure 6. 777 6LN 6LR Root 6LBR 778 | | | | 779 | | | NA(EARO, Status) | 780 | | |<-----------------| 781 | | DCO(Status) | | 782 | |<------------| | 783 | NA(EARO, Status) | | | 784 |<-----------------| | | 785 | | | | 787 Figure 6: Asynchronous Issue 789 An Address re-Registration is performed by the 6LN to maintain the 790 NCE in the 6LR alive before lifetime expires. Upon an Address re- 791 Registration, as illustrated in Figure 7, the 6LR redistributes the 792 Registered Address NS(EARO) in RPL. 794 6LN 6LR Root 6LBR 795 | | | | 796 | NS(EARO) | | | 797 |--------------->| | 798 | | DAO | | 799 | |------------->| | 800 | | | (anonymous) EDAR | 801 | | |------------------>| 802 | | | EDAC | 803 | | |<------------------| 804 | | DAO-ACK | | 805 | |<-------------| | 806 | NA(EARO) | | | 807 |<---------------| | | 809 Figure 7: Next Registration Flow in Non-Storing Mode 811 This causes the RPL DODAG Root to refresh the state in the 6LBR with 812 an EDAC message or an anonymous EDAC if the ROVR is not indicated in 813 the Target Option. In both cases, the EDAC message sent in response 814 by the 6LBR contains the actual value of the ROVR field for that 815 Address Registration. In case of an error on the proxied EDAR flow, 816 the error MUST be returned in the DAO-ACK - if one was requested - 817 using a RPL Status with the 'A' flag set that imbeds a 6LoWPAN Status 818 value as discussed in Section 7. 820 If the Root could not return the negative Status in the DAO-ACK then 821 it sends an asynchronous Destination Cleanup Object (DCO) message 822 [EFFICIENT-NPDAO] to the 6LR placing the negative Status in the RPL 823 Status with the 'A' flag set. Note that if both are used in a short 824 interval of time, the DAO-ACK and DCO messages are not guaranteed to 825 arrive in the same order at the 6LR. 827 The 6LR may still receive a requested DAO-ACK even after it received 828 a DCO, but the negative Status in the DCO supercedes a positive 829 Status in the DAO-ACK regardless of the order in which they are 830 received. Upon the DAO-ACK - or the DCO if it arrives first - the 831 6LR responds to the RUL with a NA(EARO). If the RPL Status has the 832 'A' flag set, then the ND Status is extracted and passed in the EARO; 833 else, if the 'E' flag is set, indicating a rejection, then the status 834 4 "Removed" is used; else, the ND Status of 0 indicating "Success" is 835 used. 837 9.1.2. In RPL Storing-Mode 839 In RPL Storing Mode, the DAO-ACK is optional. When it is used, it is 840 generated by the RPL parent, which does not need to wait for the 841 grand-parent to send the acknowledgement. A successful DAO-ACK is 842 not a guarantee that the DAO has yet reached the Root or that the 843 EDAR has succeeded. 845 6LN 6LR 6LR Root 6LBR 846 | | | | | 847 | NS(EARO) | | | | 848 |-------------->| | | | 849 | NA(EARO) | | | | 850 |<--------------| | | | 851 | | | | | 852 | | DAO | | | 853 | |-------------->| | | 854 | | DAO-ACK | | | 855 | |<--------------| | | 856 | | | | | 857 | | | DAO | | 858 | | |-------------->| | 859 | | | DAO-ACK | | 860 | | |<--------------| | 861 | | | | | 862 | | | | (anonymous) EDAR | 863 | | | |----------------->| 864 | | | | EDAC(ROVR) | 865 | | | |<-----------------| 866 | | | | | 867 Figure 8: Next Registration Flow in Storing Mode 869 If the keep-alive fails, or an asynchronous issue is reported, the 870 path can be cleaned up asynchronously using a DCO message 871 [EFFICIENT-NPDAO] as illustrated in Figure 9 and described in further 872 details in Section 9.2.3. 874 6LN 6LR 6LR Root 6LBR 875 | | | | | 876 | | | | NA(EARO, Status) | 877 | | | |<-----------------| 878 | | | | | 879 | | | DCO(Status) | | 880 | | |<------------| | 881 | | | | | 882 | | DCO(Status) | | | 883 | |<------------| | | 884 | | | | | 885 | NA(EARO, Status) | | | | 886 |<-----------------| | | | 887 | | | | | 889 Figure 9: Issue in Storing Mode 891 9.2. Detailed Operation 893 9.2.1. By the 6LN 895 This specification does not alter the operation of a 6LoWPAN ND- 896 compliant 6LN, and a RUL is expected to operate as follows: 898 * The 6LN obtains an IPv6 global address, either using Stateless 899 Address Autoconfiguration (SLAAC) [RFC4862] based on a Prefix 900 Information Option (PIO) [RFC4861] found in a Router Advertisement 901 message, or some other means such as DHCPv6 [RFC3315]. 903 * Once it has formed an address, the 6LN (re)registers its address 904 periodically, within the Lifetime of the previous Address 905 Registration, as prescribed by [RFC6775] and [RFC8505]. 907 * The 6LN can register to more than one 6LR at the same time. In 908 that case, it MUST use the same value of TID for all of the 909 parallel Address Registrations. 911 * Following section 5.1 of [RFC8505], a 6LN acting as a RUL sets the 912 "R" flag in the EARO of at least one registration, whereas acting 913 as a RAN it never does. If the "R" flag is set in the NS but not 914 echoed in the NA, the RUL SHOULD attempt to use another 6LR. 916 * Upon each consecutive Address Registration, the 6LN increases the 917 TID field in the EARO, as prescribed by [RFC8505] section 5.2. 919 * The 6LN may use any of the 6LRs to which it register to forward 920 its packets. Using a 6LR to which the 6LN is not registered may 921 result in packets dropped at the 6LR by a Source Address 922 Validation function (SAVI) so it is NOT RECOMMENDED. 924 Even without support for RPL, a RUL may be aware of opaque values to 925 be provided to the routing protocol. If the RUL has a knowledge of 926 the RPL Instance the packet should be injected into, then it SHOULD 927 set the Opaque field in the EARO to the RPLInstanceID, else it MUST 928 leave the Opaque field to zero. 930 Regardless of the setting of the Opaque field, the 6LN MUST set the 931 "I" field to zero to signal "topological information to be passed to 932 a routing process" as specified in section 5.1 of [RFC8505]. 934 A RUL is not expected to produce RPL artifacts in the data packets, 935 but it MAY do so. For instance, if the RUL has a minimal awareness 936 of the RPL Instance then it can build an RPI. A RUL that places an 937 RPI in a data packet MUST indicate the RPLInstanceID that corresponds 938 to the RPL Instance the packet should be injected into. All the 939 flags and the Rank field are set to zero as specified by section 11.2 940 of [RFC6550]. 942 9.2.2. By the 6LR 944 Also as prescribed by [RFC8505], the 6LR generates an EDAR message 945 upon reception of a valid NS(EARO) message for the Address 946 Registration of a new IPv6 Address by a 6LN. If the Duplicate 947 Address exchange succeeds, then the 6LR installs an NCE. If the "R" 948 flag was set in the EARO of the NS message, and this 6LR can manage 949 the reachability of Registered Address, then the 6LR sets the "R" 950 flag in the EARO of the NA message that is sends in response. 952 From then on, the 6LN periodically sends a new NS(EARO) to refresh 953 the NCE state before the lifetime indicated in the EARO expires, with 954 TID that is incremented each time till it wraps in a lollipop fashion 955 (see section 5.2.1 of [RFC8505] which is fully compatible with 956 section 7.2 of [RFC6550]). As long as the "R" flag is set and this 957 Router can still manage the reachability of Registered Address, the 958 6LR keeps setting the "R" flag in the EARO of the response NA 959 message, but the exchange of keep-alive Extended Duplicate Address 960 messages with the 6LBR is avoided if the RPL Root has indicated that 961 it proxies for it. 963 The Opaque field in the EARO hints the 6LR on the RPL Instance that 964 should be used for the DAO advertisements, and for the forwarding of 965 packets sourced at the registered address when there is no RPI in the 966 packet, in which case the 6LR MUST encapsulate the packet to the Root 967 adding an RPI in the outer header. If the Opaque field is zero, the 968 6LR is free to use the default RPL Instance (zero) for the registered 969 address or to select an Instance of its choice. 971 if the "I" field is not zero, then the 6LR MUST consider that the 972 Opaque field is zero. If the Opaque field is not zero, then it is 973 expected to carry a RPLInstanceID for the RPL Instance suggested by 974 the 6LN. If the 6LR does not participate to the associated Instance, 975 then the 6LR MUST consider that the Opaque field is zero; else, that 976 is if the 6LR participates to the suggested Instance, then the 6LR 977 SHOULD use that Instance for the registered address. 979 The DAO message advertising the Registered Address MUST be 980 constructed as follows: 982 * The Registered Address is placed in a RPL Target Option in the DAO 983 message as the Target Prefix, and the Prefix Length is set to 128; 985 * RPL Non-Storing Mode is used, and the 6LR indicates one of its 986 global or unique-local IPv6 unicast addresses as the Parent 987 Address in the associated RPL Transit Information Option (TIO). 989 * the External 'E' flag in the TIO is set to indicate that the 6LR 990 redistributes an external target into the RPL network. 992 * the Path Lifetime in the TIO is computed from the Lifetime in the 993 EARO Option to adapt it to the Lifetime Units used in the RPL 994 operation. Note that if the lifetime is 0, then the 6LR generates 995 a No-Path DAO message that cleans up the routes down to the 996 Address of the 6LN; 998 * the Path Sequence in the TIO is set to the TID value found in the 999 EARO option; 1001 Upon an NS(EARO), iff the "R" flag was set, the 6LR SHOULD inject the 1002 Registered Address in RPL by sending a DAO message on behalf of the 1003 6LN. If the Registration Lifetime was 0, the effect is to remove the 1004 route and then the NCE. 1006 If for whatever reason the 6LR does not inject the Registered Address 1007 in RPL, it MUST send an NA(EARO) back with the appropriate status and 1008 the "R" flag not set. 1010 If the 6LR injects the Registered Address in RPL and either a DAO-ACK 1011 was not requested or is received with a RPL Status that is not a 1012 rejection ("E" flag not set), the 6LR MUST install or refresh the NCE 1013 for the address and reply to the RUL with an NA(EARO) with a Status 1014 of 0 (Success) and the "R" flag set. 1016 In case of a DAO-ACK or a DCO indicating transporting an EARO Status 1017 Value of 5 (Validation Requested), a 6LR that supports Address 1018 Protected Neighbor Discovery (AP-ND) MUST challenge the 6LN for 1019 ownership of the address, as described in section 6.1 of [AP-ND]. If 1020 the challenge succeeds then the operations continue as normal. In 1021 particular a DAO message is generated upon the NS(EARO) that proves 1022 the ownership of the address. If the challenge failed, the 6LR 1023 rejects the registration as prescribed by AP-ND and may take actions 1024 to protect itself against DoS attacks by a rogue 6LN, see Section 11. 1025 If the 6LR does not support AP-ND, it MUST send an NA to the 6LN with 1026 a Status of 0 (Success) and the "R" flag not set. 1028 The other rejection codes indicate that the 6LR failed to inject the 1029 address into the RPL network. If an EARO Status is transported, the 1030 6LR MUST send a NA(EARO) to the RUL with that Status value, and the 1031 "R" flag not set. Similarly, upon receiving a DCO message indicating 1032 that the address of a RUL should be removed from the routing table, 1033 the 6LR issues an asynchronous NA(EARO) to the RUL with the embedded 1034 ND Status value if there was one, and the "R" flag not set. 1036 If a 6LR receives a valid NS(EARO) message with the "R" flag reset 1037 and a Registration Lifetime that is not 0, and the 6LR was 1038 redistributing the Registered Address due to previous NS(EARO) 1039 messages with the flag set, then it MUST stop injecting the address. 1040 It is up to the Registering 6LN to maintain the corresponding route 1041 from then on, either keeping it active via a different 6LR or by 1042 acting as a RAN and managing its own reachability. 1044 9.2.3. By the RPL Root 1046 In RPL Storing Mode of Operation (MOP), the DAO message is propagated 1047 from child to parent all the way to the Root along the DODAG, 1048 populating routing state as it goes. In Non-Storing Mode, The DAO 1049 message is sent directly to the RPL Root. Upon reception of a DAO 1050 message, for each RPL Target option that creates or updates an 1051 existing RPL state: 1053 * the Root notifies the 6LBR using an internal API if they are co- 1054 located, or using a proxied EDAR/EDAC exchange if they are 1055 separated. If the RPL Target option transports a ROVR, then the 1056 Root MUST use it to build a full EDAR message; else, an anonymous 1057 EDAR is used with the ROVR field set to zero. 1059 The EDAR message MUST be constructed as follows: 1061 * The Target IPv6 address from the RPL Target Option is placed in 1062 the Registered Address field of the EDAR message; 1064 * the Registration Lifetime is adapted from the Path Lifetime in the 1065 TIO by converting the Lifetime Units used in RPL into units of 60 1066 seconds used in the 6LoWPAN ND messages; 1068 * the TID value is set to the Path Sequence in the TIO and indicated 1069 with an ICMP code of 1 in the EDAR message; 1071 * If the ROVR is present in the RPL Target option, it is copied as 1072 is in the EDAR and the ICMP Code Suffix is set to the appropriate 1073 value as shown in Table 4 of [RFC8505] depending on the size of 1074 the ROVR field; else, the ROVR field in the EDAR is set to zero 1075 indicating an anonymous EDAR. 1077 Upon a Status value in an EDAC message that is not "Success", the 1078 Root SHOULD destroy the formed paths using either a DAO-ACK (in Non- 1079 Storing Mode) or a DCO downwards as specified in [EFFICIENT-NPDAO]. 1080 Failure to destroy the former path would result in Stale routing 1081 state and local black holes if the address belongs to another party 1082 elsewhere in the network. The RPL Status value that maps the 6LoWPAN 1083 ND Status value MUST be embedded in the RPL Status in the DCO. 1085 9.2.4. By the 6LBR 1087 Upon reception of an EDAR message with the ROVR field is set to zero 1088 indicating an anonymous EDAR, the 6LBR checks whether an entry exists 1089 for the and computes whether the TID in the DAR message is fresher 1090 than that in the entry as prescribed in section 4.2.1. of [RFC8505]. 1092 If the entry does not exist, the 6LBR does not create the entry, and 1093 answers with a Status "Removed" in the EDAC message. If the entry 1094 exists but is not fresher, the 6LBR does not update the entry, and 1095 answers with a Status "Success" in the EDAC message. 1097 If the entry exists and the TID in the DAR message is fresher, the 1098 6LBR updates the TID in the entry, and if the lifetime of the entry 1099 is extended by the Registration Lifetime in the DAR message, it also 1100 updates the lifetime of the entry. In that case, the 6LBR replies 1101 with a Status "Success" in the DAC message. 1103 The EDAC that is constructed is the same as if the anonymous EDAR was 1104 a full EDAR, and includes the ROVR that is associated to the Address 1105 Registration. 1107 10. Protocol Operations for Multicast Addresses 1109 Section 12 of [RFC6550] details the RPL support for multicast flows. 1110 This support is not source-specific and only operates as an extension 1111 to the Storing Mode of Operation for unicast packets. Note that it 1112 is the RPL model that the multicast packet is passed as a Layer-2 1113 unicast to each if the interested children. This remains true when 1114 forwarding between the 6LR and the listener 6LN. 1116 "Multicast Listener Discovery (MLD) for IPv6" [RFC2710] and its 1117 updated version "Multicast Listener Discovery Version 2 (MLDv2) for 1118 IPv6" [RFC3810] provide an interface for a listener to register to 1119 multicast flows. MLDv2 is backwards compatible with MLD, and adds in 1120 particular the capability to filter the sources via black lists and 1121 white lists. In the MLD model, the Router is a "querier" and the 1122 Host is a multicast listener that registers to the querier to obtain 1123 copies of the particular flows it is interested in. 1125 On the first Address Registration, as illustrated in Figure 10, the 1126 6LN, as an MLD listener, sends an unsolicited Report to the 6LR in 1127 order to start receiving the flow immediately. Since multicast 1128 Layer-2 messages are avoided, it is important that the asynchronous 1129 messages for unsolicited Report and Done are sent reliably, for 1130 instance using an Layer-2 acknoledgement, or attempted multiple 1131 times. 1133 6LN 6LR Root 6LBR 1134 | | | | 1135 | unsolicited Report | | | 1136 |------------------->| | | 1137 | | | | 1138 | | DAO | | 1139 | |-------------->| | 1140 | | DAO-ACK | | 1141 | |<--------------| | 1142 | | | | 1143 | | | unsolicited Report | 1144 | | |------------------->| 1145 | | | | 1146 | | | | 1148 Figure 10: First Multicast Registration Flow 1150 The 6LR acts as a generic MLD querier and generates a DAO for the 1151 multicast target. The lifetime of the DAO is set to be in the order 1152 of the Query Interval, yet larger to account for variable propagation 1153 delays. 1155 The Root proxies the MLD echange as listener with the 6LBR acting as 1156 the querier, so as to get packets from a source external to the RPL 1157 domain. Upon a DAO with a multicast target, the RPL Root checks if 1158 it is already registered as a listener for that address, and if not, 1159 it performs its own unsolicited Report for the multicast target. 1161 An Address re-Registration is pulled periodically by 6LR acting as 1162 querier. Note that th message may be sent unicast to all the known 1163 individual listeners. Upon a time out of the Query Interval, the 6LR 1164 sends a Query to each of its listeners, and gets a Report back that 1165 is mapped into a DAO, as illustrated in Figure 11: 1167 6LN 6LR Root 6LBR 1168 | | | | 1169 | Query | | | 1170 |<-------------------| | | 1171 | Report | | | 1172 |------------------->| | | 1173 | | DAO | | 1174 | |-------------->| | 1175 | | DAO-ACK | | 1176 | |<--------------| | 1177 | | | | 1178 | | | Query | 1179 | | |<-------------------| 1180 | | | Report | 1181 | | |------------------->| 1182 | | | | 1183 | | | | 1185 Figure 11: Next Registration Flow 1187 Note that any of the functions 6LR, Root and 6LBR might be collapsed 1188 in a single node, in which case the flow above happens internally, 1189 and possibly through internal API calls as opposed to messaging. 1191 11. Security Considerations 1193 The LLN nodes depend on the 6LBR and the RPL participants for their 1194 operation. A trust model must be put in place to ensure that the 1195 right devices are acting in these roles, so as to avoid threats such 1196 as black-holing, (see [RFC7416] section 7) or bombing attack whereby 1197 an impersonated 6LBR would destroy state in the network by using the 1198 "Removed" Status code. 1200 This trust model could be at a minimum based on a Layer-2 Secure 1201 joining and the Link-Layer security. This is a generic 6LoWPAN 1202 requirement, see Req5.1 in Appendix of [RFC8505]. 1204 Additionally, the trust model could include a role validation to 1205 ensure that the node that claims to be a 6LBR or a RPL Root is 1206 entitled to do so. 1208 The anonymous EDAR message does not carry a valid Registration Unique 1209 ID [RFC8505] in the form of a ROVR and may be played by any node on 1210 the network without the need to know the ROVR. The 6LBR MUST NOT 1211 create an entry based on a anonymous EDAR that does not match an 1212 existing entry. All it can do is refresh the lifetime and the TID of 1213 an existing entry. So the message cannot be used to create a binding 1214 state in the 6LBR but it can be use to maitain one active longer than 1215 expected. 1217 Note that a full EDAR message with a lifetime of 0 will destroy that 1218 state and the anonymous message will not recreate it. Note also that 1219 a rogue that has access to the network can attack the 6LBR with other 1220 (forged) addresses and ROVR, and that this is a much easier DoS 1221 attack than trying to keep existing state alive longer. 1223 At the time of this writing RPL does not have a zerotrust model 1224 whereby the it is possible to validate the origin of an address that 1225 is injected in a DAO. This specification makes a first step in that 1226 direction by allowing the Root to challenge the RUL by the 6LR that 1227 serves it. 1229 12. IANA Considerations 1231 12.1. Resizing the ARO Status values 1233 IANA is requested to modify the Address Registration Option Status 1234 Values Registry as follows: The unassigned values range is reduced 1235 from 11-255 to 11-63. 1237 12.2. New DODAG Configuration Option Flag 1239 This specification updates the Registry for the "DODAG Configuration 1240 Option Flags" that was created for [RFC6550] as follows: 1242 +------------+----------------------------+-----------+ 1243 | Bit Number | Capability Description | Reference | 1244 +============+============================+===========+ 1245 | 1 | Root Proxies EDAR/EDAC (P) | THIS RFC | 1246 +------------+----------------------------+-----------+ 1248 Table 2: New DODAG Configuration Option Flag 1250 12.3. RPL Target Option Flags 1252 Section 20.15 of [RFC6550] creates a registry for the 8-bit RPL 1253 Target Option Flags field. This specification reduces the field to 4 1254 bits. The IANA is requested to reduce the size of the registry 1255 accordingly. 1257 12.4. New Subregistry for the RPL Non-Rejection Status values 1259 This specification creates a new Subregistry for the RPL Non- 1260 Rejection Status values for use in RPL DAO-ACK and RCO messages, 1261 under the ICMPv6 parameters registry. 1263 * Possible values are 6-bit unsigned integers (0..63). 1265 * Registration procedure is "Standards Action" [RFC8126]. 1267 * Initial allocation is as indicated in Table 3: 1269 +-------+------------------------+-----------+ 1270 | Value | Meaning | Reference | 1271 +=======+========================+===========+ 1272 | 0 | Unqualified acceptance | RFC 6550 | 1273 +-------+------------------------+-----------+ 1275 Table 3: Acceptance values of the RPL Status 1277 12.5. New Subregistry for the RPL Rejection Status values 1279 This specification creates a new Subregistry for the RPL Rejection 1280 Status values for use in RPL DAO-ACK and RCO messages, under the 1281 ICMPv6 parameters registry. 1283 * Possible values are 6-bit unsigned integers (0..63). 1285 * Registration procedure is "Standards Action" [RFC8126]. 1287 * Initial allocation is as indicated in Table 4: 1289 +-------+-----------------------+---------------+ 1290 | Value | Meaning | Reference | 1291 +=======+=======================+===============+ 1292 | 0 | Unqualified rejection | This document | 1293 +-------+-----------------------+---------------+ 1295 Table 4: Rejection values of the RPL Status 1297 13. Acknowledgments 1299 The authors wish to thank Georgios Papadopoulos for their early 1300 reviews of and contributions to this document 1302 14. Normative References 1304 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1305 Requirement Levels", BCP 14, RFC 2119, 1306 DOI 10.17487/RFC2119, March 1997, 1307 . 1309 [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast 1310 Listener Discovery (MLD) for IPv6", RFC 2710, 1311 DOI 10.17487/RFC2710, October 1999, 1312 . 1314 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1315 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1316 DOI 10.17487/RFC3810, June 2004, 1317 . 1319 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1320 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1321 Overview, Assumptions, Problem Statement, and Goals", 1322 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1323 . 1325 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1326 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1327 DOI 10.17487/RFC4861, September 2007, 1328 . 1330 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1331 Address Autoconfiguration", RFC 4862, 1332 DOI 10.17487/RFC4862, September 2007, 1333 . 1335 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1336 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1337 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1338 Low-Power and Lossy Networks", RFC 6550, 1339 DOI 10.17487/RFC6550, March 2012, 1340 . 1342 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1343 Power and Lossy Networks (RPL) Option for Carrying RPL 1344 Information in Data-Plane Datagrams", RFC 6553, 1345 DOI 10.17487/RFC6553, March 2012, 1346 . 1348 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1349 Bormann, "Neighbor Discovery Optimization for IPv6 over 1350 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1351 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1352 . 1354 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 1355 IPv6 over Low-Power Wireless Personal Area Networks 1356 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 1357 2014, . 1359 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1360 Writing an IANA Considerations Section in RFCs", BCP 26, 1361 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1362 . 1364 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1365 "IPv6 over Low-Power Wireless Personal Area Network 1366 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1367 April 2017, . 1369 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1370 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1371 May 2017, . 1373 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1374 (IPv6) Specification", STD 86, RFC 8200, 1375 DOI 10.17487/RFC8200, July 2017, 1376 . 1378 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1379 Perkins, "Registration Extensions for IPv6 over Low-Power 1380 Wireless Personal Area Network (6LoWPAN) Neighbor 1381 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1382 . 1384 [AP-ND] Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 1385 "Address Protected Neighbor Discovery for Low-power and 1386 Lossy Networks", Work in Progress, Internet-Draft, draft- 1387 ietf-6lo-ap-nd-19, 6 February 2020, 1388 . 1390 [USEofRPLinfo] 1391 Robles, I., Richardson, M., and P. Thubert, "Using RPI 1392 option Type, Routing Header for Source Routes and IPv6-in- 1393 IPv6 encapsulation in the RPL Data Plane", Work in 1394 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-36, 1395 26 February 2020, . 1398 [EFFICIENT-NPDAO] 1399 Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient 1400 Route Invalidation", Work in Progress, Internet-Draft, 1401 draft-ietf-roll-efficient-npdao-17, 30 October 2019, 1402 . 1405 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1406 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1407 2014, . 1409 15. Informative References 1411 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1412 Statement and Requirements for IPv6 over Low-Power 1413 Wireless Personal Area Network (6LoWPAN) Routing", 1414 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1415 . 1417 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 1418 C., and M. Carney, "Dynamic Host Configuration Protocol 1419 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 1420 2003, . 1422 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1423 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1424 DOI 10.17487/RFC6282, September 2011, 1425 . 1427 [RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur, 1428 Ed., "Performance Evaluation of the Routing Protocol for 1429 Low-Power and Lossy Networks (RPL)", RFC 6687, 1430 DOI 10.17487/RFC6687, October 2012, 1431 . 1433 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1434 Constrained-Node Networks", RFC 7228, 1435 DOI 10.17487/RFC7228, May 2014, 1436 . 1438 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1439 and M. Richardson, Ed., "A Security Threat Analysis for 1440 the Routing Protocol for Low-Power and Lossy Networks 1441 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1442 . 1444 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1445 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1446 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1447 . 1449 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node 1450 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504, 1451 January 2019, . 1453 [6BBR] Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6 1454 Backbone Router", Work in Progress, Internet-Draft, draft- 1455 ietf-6lo-backbone-router-19, 3 March 2020, 1456 . 1459 Appendix A. Example Compression 1461 Figure 12 illustrates the case in Storing Mode where the packet is 1462 received from the Internet, then the Root encapsulates the packet to 1463 insert the RPI and deliver to the 6LR that is the parent and last hop 1464 to the final destination, which is not known to support [RFC8138]. 1466 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1467 |11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP 1468 |Page 1 |Type1 S=0| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 1469 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1470 <-4 bytes-> <- RFC 6282 -> 1471 <- No RPL artifact ... 1473 Figure 12: Encapsulation to Parent 6LR in Storing Mode 1475 The difference with the example format presented in Figure 19 of 1476 [RFC8138] is the addition of a SRH-6LoRH before the RPI-6LoRH to 1477 transport the compressed address of the 6LR as the destination 1478 address of the outer IPv6 header. In the original example the 1479 destination IP of the outer header was elided and was implicitly the 1480 same address as the destination of the inner header. Type 1 was 1481 arbitrarily chosen for this example, and the size of 0 denotes a 1482 single address in the SRH. 1484 In Figure 12, the source of the IP-in-IP encapsulation is the Root, 1485 so it is elided in the IP-in-IP 6LoRH. The destination is the parent 1486 6LR of the destination of the inner packet so it cannot be elided. 1487 In Storing Mode, it is placed as the single entry in an SRH-6LoRH as 1488 the first 6LoRH. Since there is a single entry so the SRH-6LoRH Size 1489 is 0. In this particular example, the 6LR address can be compressed 1490 to 2 bytes so a Type of 1 is used. It results that the total length 1491 of the SRH-6LoRH is 4 bytes. 1493 In Non-Storing Mode, the encapsulation from the Root would be similar 1494 to that represented in Figure 12 with possibly more hops in the SRH- 1495 6LoRH and possibly multiple SRH-6LoRHs if the various addresses in 1496 the routing header are not compressed to the same format. Note that 1497 on the last hop to the parent 6LR, the RH3 is consumed and removed 1498 from the compressed form, so the use of Non-Storing Mode vs. Storing 1499 Mode is indistinguishable from the packet format. 1501 Follows the RPI-6LoRH and then the IP-in-IP 6LoRH. When the IP-in-IP 1502 6LoRH is removed, all the Router headers that precede it are also 1503 removed. 1505 The Paging Dispatch [RFC8025] may also be removed if there was no 1506 previous Page change to a Page other than 0 or 1, since the 1507 LOWPAN_IPHC is encoded in the same fashion in the default Page 0 and 1508 in Page 1. The resulting packet to the destination is the inner 1509 packet compressed with [RFC6282]. 1511 Authors' Addresses 1513 Pascal Thubert (editor) 1514 Cisco Systems, Inc 1515 Building D 1516 45 Allee des Ormes - BP1200 1517 06254 Mougins - Sophia Antipolis 1518 France 1520 Phone: +33 497 23 26 34 1521 Email: pthubert@cisco.com 1523 Michael C. Richardson 1524 Sandelman Software Works 1526 Email: mcr+ietf@sandelman.ca 1527 URI: http://www.sandelman.ca/