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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: 18 September 2020 17 March 2020 8 Routing for RPL Leaves 9 draft-ietf-roll-unaware-leaves-13 11 Abstract 13 This specification extends RFC6550 and RFC8505 to provide routing 14 services to Hosts called RPL Unaware Leaves that implement 6LoWPAN ND 15 but do not participate to RPL. This specification also enables the 16 RPL Root to proxy the 6LoWPAN keep-alive flows 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 18 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 . . . . . . . . . . . . . . . . . . . . . . . 5 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 RUL Acting as 6LN . . . . . . . . . . . . . . 19 80 9.2.2. By the RPL Border Router Acting as 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 . . . . . . . . . . . . . . . . . . . 26 85 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 86 12.1. Resizing the ARO Status values . . . . . . . . . . . . . 26 87 12.2. New DODAG Configuration Option Flag . . . . . . . . . . 27 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 protocols, which, compared to link-state protocols, limit the amount 110 of topological knowledge that needs to be installed and maintained in 111 each node. 113 To save signaling and routing state in constrained networks, RPL 114 allows a routing stretch (see [RFC6687]), whereby routing is only 115 performed along an acyclic graph optimized to reach a Root node, as 116 opposed to straight along a shortest path between 2 peers, whatever 117 that would mean in a given LLN. This trades the quality of peer-to- 118 peer (P2P) paths for a vastly reduced amount of control traffic and 119 routing state that would be required to operate a any-to-any shortest 120 path protocol. Finally, broken routes may be fixed lazily and on- 121 demand, based on dataplane inconsistency discovery, which avoids 122 wasting energy in the proactive repair of unused paths. 124 To provide alternate paths in lossy networks, 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 to RPL- 137 Aware nodes (RANs), either as a collection tree or with routing back. 138 In the latter case, a RAN injects routes to itself using Destination 139 Advertisement Object (DAO) messages sent either to parent-nodes, in 140 the RPL Storing Mode, or to the Root indicating their parent, in the 141 Non-Storing Mode. This process effectively forms a DODAG back to the 142 device that is a subset of the DODAG to the Root with all links 143 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 that 157 does not participate to RPL at all. RULs may be unable to 158 participate because they are very energy constrained. 160 A RUL is an IPv6 Host [RFC8504] that needs a RPL-Aware Router to 161 obtain routing services over the RPL network. The Non-Storing Mode 162 mechanisms are used to extend the routing state with connectivity to 163 RULs even when the DODAG is operated in Storing-Mode DODAGs. 165 This specification leverages the Address Registration mechanism 166 defined in 6LoWPAN ND to enable a RUL as a 6LoWPAN Node (6LN) to 167 interface with a RPL-Aware Router as a 6LoWPAN Router (6LR) to 168 request that the 6LR injects the relevant routing information for the 169 Registered Address in the RPL domain on its behalf. The unicast 170 packet forwarding operation by the 6LR serving a 6LN that is a RPL 171 Leaf is described in [USEofRPLinfo]. 173 Examples of routing-agnostic 6LNs include lightly-powered sensors 174 such as window smash sensor (alarm system), and kinetically powered 175 light switches. Other applications of this specification may include 176 a smart grid network that controls appliances - such as washing 177 machines or the heating system - in the home. Appliances may not 178 participate to the RPL protocol operated in the Smartgrid network but 179 can still interact with the Smartgrid for control and/or metering. 181 2. Terminology 183 2.1. BCP 14 185 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 186 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 187 "OPTIONAL" in this document are to be interpreted as described in BCP 188 14 [RFC2119][RFC8174] when, and only when, they appear in all 189 capitals, as shown here. 191 2.2. References 193 The Terminology used in this document is consistent with and 194 incorporates that described in "Terms Used in Routing for Low-Power 195 and Lossy Networks (LLNs)" [RFC7102]. A glossary of classical 196 6LoWPAN acronyms is given in Section 2.3. Other terms in use in LLNs 197 are found in "Terminology for Constrained-Node Networks" [RFC7228]. 199 "RPL", the "RPL Packet Information" (RPI), "RPL Instance" (indexed by 200 a RPLInstanceID) are defined in "RPL: IPv6 Routing Protocol for 201 Low-Power and Lossy Networks" [RFC6550]. The RPI is the abstract 202 information that RPL defines to be placed in data packets, e.g., as 203 the RPL Option [RFC6553] within the IPv6 Hop-By-Hop Header. By 204 extension the term "RPI" is often used to refer to the RPL Option 205 itself. The DODAG Information Solicitation (DIS), Destination 206 Advertisement Object (DAO) and DODAG Information Object (DIO) 207 messages are also specified in [RFC6550]. The Destination Cleanup 208 Object (DCO) message is defined in [EFFICIENT-NPDAO]. 210 This document uses the terms RPL-Unaware Leaf (RUL) and RPL Aware 211 Leaf (RAL) consistently with [USEofRPLinfo]. The term RPL-Aware Node 212 (RAN) is introduced to refer to a node that is either a RAL or a RPL 213 Router. As opposed to a RUL, a RAN manages the reachability of its 214 addresses and prefixes by injecting them in RPL by itself. 216 In this document, readers will encounter terms and concepts that are 217 discussed in the following documents: 219 Classical IPv6 ND: "Neighbor Discovery for IP version 6" [RFC4861] 220 and "IPv6 Stateless Address Autoconfiguration" [RFC4862], 222 6LoWPAN: "Problem Statement and Requirements for IPv6 over Low-Power 223 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606] and 224 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 225 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 226 and 228 6LoWPAN ND: Neighbor Discovery Optimization for Low-Power and Lossy 229 Networks [RFC6775], "Registration Extensions for 6LoWPAN Neighbor 230 Discovery" [RFC8505], and "Address Protected Neighbor Discovery 231 for Low-power and Lossy Networks" [AP-ND] . 233 2.3. Glossary 235 This document often uses the following acronyms: 237 AR: Address Resolution (aka Address Lookup) 238 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 278 RAL: RPL-Aware Leaf 280 RAN: RPL-Aware Node (either a RPL Router or a RPL-Aware Leaf) 282 RUL: RPL-Unaware Leaf 284 TID: Transaction ID (a sequence counter in the EARO) 286 3. 6LoWPAN Neighbor Discovery 288 3.1. RFC 6775 Address Registration 290 The classical "IPv6 Neighbor Discovery (IPv6 ND) Protocol" [RFC4861] 291 [RFC4862] was defined for transit media such a Ethernet. It is a 292 reactive protocol that relies heavily on multicast operations for 293 address discovery (aka lookup) and duplicate address detection (DAD). 295 "Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775] 296 adapts IPv6 ND for operations over energy-constrained LLNs. The main 297 functions of [RFC6775] are to proactively establish the Neighbor 298 Cache Entry (NCE) in the 6LR and to prevent address duplication. To 299 that effect, [RFC6775] introduces a new unicast Address Registration 300 mechanism that contributes to reducing the use of multicast messages 301 compared to the classical IPv6 ND protocol. 303 [RFC6775] defines a new Address Registration Option (ARO) that is 304 carried in the unicast Neighbor Solicitation (NS) and Neighbor 305 Advertisement (NA) messages between the 6LoWPAN Node (6LN) and the 306 6LoWPAN Router (6LR). It also defines the Duplicate Address Request 307 (DAR) and Duplicate Address Confirmation (DAC) messages between the 308 6LR and the 6LoWPAN Border Router (6LBR). In an LLN, the 6LBR is the 309 central repository of all the Registered Addresses in its domain and 310 the source of truth for uniqueness and ownership. 312 3.2. RFC 8505 Extended Address Registration 314 "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505] 315 updates the behavior of RFC 6775 to enable a generic Address 316 Registration to services such as routing and ND proxy, and defines 317 the Extended Address Registration Option (EARO) as shown in Figure 1: 319 0 1 2 3 320 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 1 321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 322 | Type | Length | Status | Opaque | 323 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 324 | Rsvd | I |R|T| TID | Registration Lifetime | 325 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 326 | | 327 ... Registration Ownership Verifier ... 328 | | 329 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 331 Figure 1: EARO Option Format 333 3.2.1. R Flag 335 [RFC8505] introduces the "R" flag in the EARO. The Registering Node 336 sets the "R" flag to indicate whether the 6LR should ensure 337 reachability for the Registered Address. If the "R" flag is not set, 338 then the Registering Node handles the reachability of the Registered 339 Address by other means, which means in a RPL network that it is a RAN 340 or that it uses another RPL Router for reachability services. 342 This document specifies how the "R" flag is used in the context of 343 RPL. A 6LN is a RUL that requires reachability services for an IPv6 344 address iff it sets the "R" flag in the EARO used to register the 345 address to a RPL router. Conversely, this document specifies the 346 behavior of a RPL Router acting as 6LR depending on the setting of 347 the "R" flag in the EARO. The RPL Router generates a DAO message for 348 the Registered Address upon an NS(EARO) iff the "R" flag is set. 350 3.2.2. TID, I Field and Opaque Fields 352 The EARO also includes a sequence counter called Transaction ID 353 (TID), which maps to the Path Sequence Field found in Transit Options 354 in RPL DAO messages. This is the reason why the support of [RFC8505] 355 by the RUL as opposed to only [RFC6775] is a prerequisite for this 356 specification (more in Section 6.1). The EARO also transports an 357 Opaque field and an "I" field that describes what the Opaque field 358 transports and how to use it. Section 9.2.1 specifies the use of the 359 "I" field and of the Opaque field by a RUL. 361 3.2.3. ROVR 363 Section 5.3. of [RFC8505] introduces the Registration Ownership 364 Verifier (ROVR) field of variable length from 64 to 256 bits. The 365 ROVR is a replacement of the EUI-64 in the ARO [RFC6775] that was 366 used to identify uniquely an Address Registration with the Link-Layer 367 address of the owner, but provided no protection against spoofing. 369 "Address Protected Neighbor Discovery for Low-power and Lossy 370 Networks" [AP-ND] leverages the ROVR field as a cryptographic proof 371 of ownership to prevent a rogue third party from misusing the 372 address. [AP-ND] adds a challenge/response exchange to the [RFC8505] 373 Address Registration and enables Source Address Validation by a 6LR 374 that will drop packets with a spoofed address. 376 This specification does not address how the protection by [AP-ND] 377 could be extended to RPL. On the other hand, it adds the ROVR to the 378 DAO to build the proxied EDAR at the Root (see Section 8), which 379 means that nodes that are aware of the Host route to the 6LN are made 380 aware of the associated ROVR as well. 382 3.3. RFC 8505 Extended DAR/DAC 384 [RFC8505] updates the periodic DAR/DAC exchange that takes place 385 between the 6LR and the 6LBR using Extended DAR/DAC messages which 386 can carry a ROVR field of variable size. The periodic EDAR/EDAC 387 exchange is triggered by a NS(EARO) message and is intended to 388 create, refresh and delete the corresponding state in the 6LBR for a 389 lifetime that is indicated by the 6LN. 391 Conversely, RPL [RFC6550] specifies a periodic DAO from the 6LN all 392 the way to the Root that maintains the routing state in the RPL 393 network for the lifetime indicated by the source of the DAO. This 394 means that for each address, there are two keep-alive messages that 395 traverse the whole network, one to the Root and one to the 6LBR. 397 This specification removes the extraneous keep-alive across the LLN. 398 The 6LR turns the periodic Address Registration from the RUL into a 399 DAO message to the Root on every refresh, but it only generates the 400 EDAR upon the first registration, for the purpose of DAD. Upon a 401 refresher DAO, the Root proxies the EDAR exchange to refresh the 402 state at the 6LBR on behalf of the 6LR, as illustrated in Figure 7. 404 3.3.1. RFC 7400 Capability Indication Option 406 "6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power 407 Wireless Personal Area Networks (6LoWPANs)" [RFC7400] defines the 408 6LoWPAN Capability Indication Option (6CIO) that enables a node to 409 expose its capabilities in Router Advertisement (RA) messages. 410 [RFC8505] defines a number of bits in the 6CIO, in particular: 412 L: Node is a 6LR. 414 E: Node is an IPv6 ND Registrar -- i.e., it supports registrations 415 based on EARO. 417 P: Node is a Routing Registrar, -- i.e., an IPv6 ND Registrar that 418 also provides reachability services for the Registered Addres 420 0 1 2 3 421 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 1 422 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 423 | Type | Length = 1 | Reserved |D|L|B|P|E|G| 424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 425 | Reserved | 426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 428 Figure 2: 6CIO flags 430 A 6LR that can provide reachability services for a RUL in a RPL 431 network as specified in this document SHOULD include a 6CIO in its RA 432 messages and set the L, P and E flags as prescribed by [RFC8505], see 433 Section 6.1 for the behavior of the RUL. 435 4. Updating RFC 6550 437 This document specifies a new behavior whereby a 6LR injects DAO 438 messages for unicast addresses (see Section 9) and multicast 439 addresses (see Section 10) on behalf of leaves that are not aware of 440 RPL. The addresses are exposed as external targets [RFC6550]. Per 441 [USEofRPLinfo], an IP-in-IP encapsulation that terminates at the RPL 442 Root is used to remove RPL artifacts and compression techniques that 443 may not be processed correctly outside of the RPL domain. 445 This document also synchronizes the liveness monitoring at the Root 446 and the 6LBR. A same value of lifetime is used for both, and a 447 single keep-alive message, the RPL DAO, traverses the RPL network. A 448 new behavior is introduced whereby the RPL Root proxies the EDAR 449 message to the 6LBR on behalf of the 6LR (more in Section 5), for any 450 6LN, RUL or RAN. 452 RPL defines a configuration option that is registered to IANA in 453 section 20.14. of [RFC6550]. This specification defines a new flag 454 "Root Proxies EDAR/EDAC" (P) that is encoded in one of the reserved 455 control bits in the option. The new flag is set to indicate that the 456 Root performs the proxy operation and that all nodes in the network 457 must refrain from renewing the 6LBR state directly. The bit position 458 of the "P" flag is indicated in Section 12.2. 460 Section 6.3.1. of [RFC6550] defines a 3-bit Mode of Operation (MOP) 461 in the DIO Base Object. The new "P" flag is defined only for MOP 462 value between 0 to 6. For a MOP value of 7 or above, the flag MAY 463 indicate something different and MUST NOT be interpreted as "Root 464 Proxies EDAR/EDAC" unless the specification of the MOP indicates to 465 do so. 467 The RPL Status defined in section 6.5.1. of [RFC6550] for use in the 468 DAO-Ack message is extended to be used in the DCO messages 469 [EFFICIENT-NPDAO] as well. Furthermore, this specification enables 470 to use a RPL Status to transport the IPv6 ND Status defined for use 471 in the EARO, more in Section 7. 473 Section 6.7. of [RFC6550] introduces the RPL Control message Options 474 such as the RPL Target Option that can be included in a RPL Control 475 message such as the DAO. Section 8 updates the RPL Target Option to 476 optionally transport the ROVR used in the IPv6 Registration (see 477 Section 3.2.3) so the RPL Root can generate a full EDAR message. 479 5. Updating RFC 8505 481 This document updates [RFC8505] to introduce the anonymous EDAR and 482 NS(EARO) messages. The anonymous messages are used for backward 483 compatibility. The anonymous messages are recognizable by a zero 484 ROVR field and can only be used as a refresher for a pre-existing 485 state associated to the Registered Address. More specifically, an 486 anonymous message can only increase the lifetime and/or increment the 487 TID of an existing state at the 6LBR. 489 Upon the renewal of a 6LoWPAN ND Address Registration, this 490 specification changes the behavior of a RPL Router acting as 6LR for 491 the registration. If the Root indicates the capability to proxy the 492 EDAR/EDAC exchange to the 6LBR then the 6LR refrains from sending an 493 EDAR message; if the Root is separated from the 6LBR, the Root 494 regenerates the EDAR message to the 6LBR upon a DAO message that 495 signals the liveliness of the Address. The regenerated message is 496 anonymous iff the DAO is a legacy message that does not carry a ROVR 497 as specified in Section 8. 499 6. Requirements on the RPL-Unware Leaf 501 This document provides RPL routing for a RUL, that is a 6LN acting as 502 an IPv6 Host and not aware of RPL. Still, a minimal RPL-independent 503 functionality is required from the RUL to obtain routing services. 505 6.1. Support of 6LoWPAN ND 507 In order to obtain routing services from a 6LR, a RUL MUST implement 508 [RFC8505] and set the "R" flag in the EARO. The RUL SHOULD support 509 [AP-ND] and use it to protect the ownership of its addresses. The 510 RUL MUST NOT request routing services from a 6LR that does not 511 originate RA messages with a CIO that has the L, P, and E flags all 512 set as discussed in Section 3.3.1. 514 A RUL that has multiple potential routers MUST prefer those that 515 provide routing services. The RUL MUST register to all the 6LRs from 516 which it desires routing services. If there are no available 517 routers, the connection of the RUL fails. The Address Registrations 518 SHOULD be performed in a rapid sequence, using the exact same EARO 519 for a same Address. Gaps between the Address Registrations will 520 invalidate some of the routes till the Address Registration finally 521 shows on those routes as well. 523 [RFC8505] introduces error Status values in the NA(EARO) which can be 524 received synchronously upon an NS(EARO) or asynchronously. The RUL 525 MUST support both cases and MUST refrain from using the address when 526 the Status value indicates a rejection. 528 6.2. External Routes and RPL Artifacts 530 Section 4.1. of [USEofRPLinfo] provides a set of rules that MUST be 531 followed for the routing operations to a RUL. 533 A 6LR that is upgraded to act as a border router for external routes 534 advertises them using Non-Storing Mode DAO messages that are unicast 535 directly to the Root, even if the DODAG is operated in Storing Mode. 536 Non-Storing Mode routes are not visible inside the RPL domain and all 537 packets are routed via the Root. An upgraded Root tunnels the 538 packets directly to the 6LR that advertised the external route which 539 decapsulates and forwards the original (inner) packet. 541 The RPL Non-Storing Mode signaling and the associated IP-in-IP 542 encapsulated packets are normal traffic for the intermediate Routers. 543 The support of external routes only impacts the Root and the 6LR. It 544 can be operated with legacy intermediate routers and does not add to 545 the amount of state that must be maintained in those routers. A RUL 546 is an example of a destination that is reachable via an external 547 route which happens to be a Host route. 549 The RPL data packets always carry a Hop-by-Hop Header to transport a 550 RPL Packet Information (RPI) [RFC6550]. So unless the RUL originates 551 its packets with an RPI, the 6LR needs to tunnel them to the Root to 552 add the RPI. As a rule of a thumb and except for the very special 553 case above, the packets from and to a RUL are always encapsulated 554 using an IP-in-IP tunnel between the Root and the 6LR that serves the 555 RUL (see sections 7.1.4, 7.2.3, 7.2.4, 7.3.3, 7.3.4, 8.1.3, 8.1.4, 556 8.2.3, 8.2.4, 8.3.3 and 8.3.4 of [USEofRPLinfo] for details). 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 possibly an SRH in a Non-Storing Mode DODAG. [USEofRPLinfo] 567 expects the RUL to support the basic "IPv6 Node Requirements" 568 [RFC8504]. In particular the RUL is expected to ignore the RPL 569 artifacts that are either consumed or not applicable to a Host. 571 A RUL is not expected to support the compression method defined in 572 [RFC8138]. Unless configured otherwise, the border router MUST 573 uncompress the outgoing packet before forwarding over an external 574 route, even if it is not the destination of the incoming packet, and 575 even when delivering to a RUL. 577 6.2.1. Support of IPv6 Encapsulation 579 Section 2.1 of [USEofRPLinfo] sets the rules for forwarding IP-in-IP 580 either to the final 6LN or to a parent 6LR. In order to enable IP- 581 in-IP to the 6LN in Non-Storing Mode, the 6LN must be able to 582 decapsulate the tunneled packet and either drop the inner packet if 583 it is not the final destination, or pass it to the upper layer for 584 further processing. Unless it is aware that the RUL can handle IP- 585 in-IP properly, the Root that encapsulates a packet to a RUL 586 terminates the IP-in-IP tunnel at the parent 6LR . For that reason, 587 it is beneficial but not necessary for a RUL to support IP-in-IP. 589 6.2.2. Support of the HbH Header 591 A RUL is expected to process an unknown Option Type in a Hop-by-Hop 592 Header as prescribed by section 4.2 of [RFC8200]. This means in 593 particular that an RPI with an Option Type of 0x23 [USEofRPLinfo] is 594 ignored when not understood. 596 6.2.3. Support of the Routing Header 598 A RUL is expected to process an unknown Routing Header Type as 599 prescribed by section 4.4 of [RFC8200]. This means in particular 600 that Routing Header with a Routing Type of 3 [RFC6554] is ignored 601 when the Segments Left is zero, and the packet is dropped otherwise. 603 7. Updated RPL Status 605 The RPL Status is defined in section 6.5.1. of [RFC6550] for use in 606 the DAO-Ack message and values are assigned as follows: 608 +---------+--------------------------------+ 609 | Range | Meaning | 610 +=========+================================+ 611 | 0 | Success/Unqualified acceptance | 612 +---------+--------------------------------+ 613 | 1-127 | Not an outright rejection | 614 +---------+--------------------------------+ 615 | 128-255 | Rejection | 616 +---------+--------------------------------+ 618 Table 1: RPL Status per RFC 6550 620 This specification extends the scope of the RPL Status to be used in 621 RPL DCO messages. Furthermore, this specification enables to carry 622 the IPv6 ND Status values defined for use in the EARO and initially 623 listed in table 1 of [RFC8505] in a RPL Status. 625 Section 12.1 reduces the range of EARO Status values to 0-63 ensure 626 that they fit within a RPL Status as shown in Figure 3. 628 0 629 0 1 2 3 4 5 6 7 630 +-+-+-+-+-+-+-+-+ 631 |E|A| Value | 632 +-+-+-+-+-+-+-+-+ 634 Figure 3: RPL Status Format 636 RPL Status subfields: 638 E: 1-bit flag. Set to indicate a rejection. When not set, a value 639 of 0 indicates Success/Unqualified acceptance and other values 640 indicate "not an outright rejection" as per RFC 6550. 642 A: 1-bit flag. Indicates the type of the Status value. 644 Status Value: 6-bit unsigned integer. If the 'A' flag is set this 645 field transports a Status value defined for IPv6 ND EARO. When 646 the 'A' flag is not set, the Status value is defined in a RPL 647 extension. 649 When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a DAC 650 message, the RPL Root MUST copy the ARO Status unchanged in a RPL 651 Status with the 'A' bit set. The RPL Root MUST set the 'E' flag for 652 all values in range 1-10 which are all considered rejections. 654 Conversely, the 6LR MUST copy the value of the RPL Status unchanged 655 in the EARO of an NA message that is built upon a RPL Status with the 656 'A' bit set in a DCO or a DAO-ACK message. 658 8. Updated RPL Target option 660 This specification updates the RPL Target option to transport the 661 ROVR. This enables the RPL Root to generate a full EDAR message as 662 opposed to an anonymous EDAR that has restricted properties. 664 The Target Prefix field MUST be aligned to the next 4-byte boundary 665 after the size indicated by the Prefix Length. If necessary the 666 transported prefix MUST be padded with zeros. 668 With this specification the ROVR is the remainder of the RPL Target 669 Option. The size of the ROVR is indicated in a new ROVR Size field 670 that is encoded to map one-to-one with the Code Suffix in the EDAR 671 message (see table 4 of [RFC8505]). 673 The modified format is illustrated in Figure 4. It is backward 674 compatible with the Target Option in [RFC6550] and SHOULD be used as 675 a replacement. 677 0 1 2 3 678 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 1 679 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 680 | Type = 0x05 | Option Length |ROVRsz | Flags | Prefix Length | 681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 682 | | 683 + + 684 | Target Prefix (Variable Length) | 685 . Aligned to 4-byte boundary . 686 . . 687 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 688 | | 689 ... Registration Ownership Verifier (ROVR) ... 690 | | 691 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 693 Figure 4: Updated Target Option 695 New fields: 697 ROVRsz: Indicates the Size of the ROVR. It MAY be 1, 2, 3, or 4, 698 denoting a ROVR size of 64, 128, 192, or 256 bits, respectively. 700 Registration Ownership Verifier (ROVR): This is the same field as in 701 the EARO, see [RFC8505] 703 9. Protocol Operations for Unicast Addresses 705 The description below assumes that the Root sets the "P" flag in the 706 DODAG Configuration Option and performs the EDAR proxy operation. 708 9.1. General Flow 710 This specification eliminates the need to exchange keep-alive 711 Extended Duplicate Address messages, EDAR and EDAC, all the way from 712 a 6LN to the 6LBR across a RPL mesh. Instead, the EDAR/EDAC exchange 713 with the 6LBR is proxied by the RPL Root upon a DAO message that 714 refreshes the RPL routing state. 716 To achieve this, the lifetimes and sequence counters in 6LoWPAN ND 717 and RPL are aligned. In other words, the Path Sequence and the Path 718 Lifetime in the DAO message are taken from the Transaction ID and the 719 Address Registration lifetime in the NS(EARO) message from the 6LN. 721 The proxy operation applies to both RULs and RANs. In a RPL network 722 where the function is enabled, refreshing the state in the 6LBR is 723 the responsibility of the Root. Consequently, only addresses that 724 are injected in RPL will be kept alive by the RPL Root. 726 In a same fashion, if an additional routing protocol is deployed on a 727 same network, that additional routing protocol may need to handle the 728 keep alive procedure for the addresses that it serves. 730 On the first Address Registration, illustrated in Figure 5 and 731 Figure 8 for RPL Non-Storing and Storing Mode respectively, the 732 Extended Duplicate Address exchange takes place as prescribed by 733 [RFC8505]. Any of the functions 6LR, Root and 6LBR might be 734 collapsed in a single node. 736 When successful, the flow creates a Neighbor Cache Entry (NCE) in the 737 6LR, and the 6LR injects the Registered Address in RPL using DAO/DAO- 738 ACK exchanges all the way to the RPL DODAG Root. The protocol does 739 not carry a specific information that the Extended Duplicate Address 740 messages were already exchanged, so the Root proxies them anyway. 742 9.1.1. In RPL Non-Storing-Mode 744 In Non-Storing Mode, the DAO message flow can be nested within the 745 Address Registration flow as illustrated in Figure 5. 747 6LN/RUL 6LR Root 6LBR 748 | | | | 749 | NS(EARO) | | | 750 |--------------->| | 751 | | Extended DAR | 752 | |--------------------------------->| 753 | | | 754 | | Extended DAC | 755 | |<---------------------------------| 756 | | DAO | | 757 | |------------->| | 758 | | | (anonymous) EDAR | 759 | | |------------------>| 760 | | | EDAC | 761 | | |<------------------| 762 | | DAO-ACK | | 763 | |<-------------| | 764 | NA(EARO) | | | 765 |<---------------| | | 766 | | | | 768 Figure 5: First Registration Flow in Non-Storing Mode 770 An issue may be detected later, e.g., the address moves within the 771 LLN or to a different Root on a backbone [6BBR]. In that case the 772 value of the status that indicates the issue can be passed from 773 6LoWPAN ND to RPL and back as illustrated in Figure 6. 775 6LN/RUL 6LR Root 6LBR 776 | | | | 777 | | | NA(EARO, Status) | 778 | | |<-----------------| 779 | | DCO(Status) | | 780 | |<------------| | 781 | NA(EARO, Status) | | | 782 |<-----------------| | | 783 | | | | 785 Figure 6: Asynchronous Issue 787 An Address re-Registration is performed by the 6LN to maintain the 788 NCE in the 6LR alive before lifetime expires. Upon an Address re- 789 Registration, as illustrated in Figure 7, the 6LR redistributes the 790 Registered Address NS(EARO) in RPL. 792 6LN/RUL 6LR Root 6LBR 793 | | | | 794 | NS(EARO) | | | 795 |--------------->| | 796 | | DAO | | 797 | |------------->| | 798 | | | (anonymous) EDAR | 799 | | |------------------>| 800 | | | EDAC | 801 | | |<------------------| 802 | | DAO-ACK | | 803 | |<-------------| | 804 | NA(EARO) | | | 805 |<---------------| | | 807 Figure 7: Next Registration Flow in Non-Storing Mode 809 This causes the RPL DODAG Root to refresh the state in the 6LBR with 810 an EDAC message or an anonymous EDAC if the ROVR is not indicated in 811 the Target Option. In both cases, the EDAC message sent in response 812 by the 6LBR contains the actual value of the ROVR field for that 813 Address Registration. In case of an error on the proxied EDAR flow, 814 the error MUST be returned in the DAO-ACK - if one was requested - 815 using a RPL Status with the 'A' flag set that imbeds a 6LoWPAN Status 816 value as discussed in Section 7. 818 If the Root could not return the negative Status in the DAO-ACK then 819 it sends an asynchronous Destination Cleanup Object (DCO) message 820 [EFFICIENT-NPDAO] to the 6LR by placing the negative Status in the 821 RPL Status with the 'A' flag set. Note that if both are used in a 822 short interval of time, the DAO-ACK and DCO messages are not 823 guaranteed to arrive in the same order at the 6LR. 825 The 6LR may still receive a requested DAO-ACK even after it received 826 a DCO, but the negative Status in the DCO supercedes a positive 827 Status in the DAO-ACK regardless of the order in which they are 828 received. Upon the DAO-ACK - or the DCO if it arrives first - the 829 6LR responds to the RUL with a NA(EARO). If the RPL Status has the 830 'A' flag set, then the ND Status is extracted and passed in the EARO; 831 else, if the 'E' flag is set, indicating a rejection, then the status 832 4 "Removed" is used; else, the ND Status of 0 indicating "Success" is 833 used. 835 9.1.2. In RPL Storing-Mode 837 In RPL Storing Mode, the DAO-ACK is optional. When it is used, it is 838 generated by the RPL parent, which does not need to wait for the 839 grand-parent to send the acknowledgement. A successful DAO-ACK is 840 not a guarantee that the DAO has yet reached the Root or that the 841 EDAR has succeeded. 843 6LN/RUL 6LR 6LR Root 6LBR 844 | | | | | 845 | NS(EARO) | | | | 846 |-------------->| | | | 847 | NA(EARO) | | | | 848 |<--------------| | | | 849 | | | | | 850 | | DAO | | | 851 | |-------------->| | | 852 | | DAO-ACK | | | 853 | |<--------------| | | 854 | | | | | 855 | | | DAO | | 856 | | |-------------->| | 857 | | | DAO-ACK | | 858 | | |<--------------| | 859 | | | | | 860 | | | | (anonymous) EDAR | 861 | | | |----------------->| 862 | | | | EDAC(ROVR) | 863 | | | |<-----------------| 864 | | | | | 865 Figure 8: Next Registration Flow in Storing Mode 867 If the keep-alive fails, or an asynchronous issue is reported, the 868 path can be cleaned up asynchronously using a DCO message 869 [EFFICIENT-NPDAO] as illustrated in Figure 9 and described in further 870 details in Section 9.2.3. 872 6LN/RUL 6LR 6LR Root 6LBR 873 | | | | | 874 | | | | NA(EARO, Status) | 875 | | | |<-----------------| 876 | | | | | 877 | | | DCO(Status) | | 878 | | |<------------| | 879 | | | | | 880 | | DCO(Status) | | | 881 | |<------------| | | 882 | | | | | 883 | NA(EARO, Status) | | | | 884 |<-----------------| | | | 885 | | | | | 887 Figure 9: Issue in Storing Mode 889 9.2. Detailed Operation 891 9.2.1. By the RUL Acting as 6LN 893 This specification does not alter the operation of a 6LoWPAN ND- 894 compliant 6LN, and a RUL is expected to operate as follows: 896 1. The 6LN obtains an IPv6 global address, either using Stateless 897 Address Autoconfiguration (SLAAC) [RFC4862] based on a Prefix 898 Information Option (PIO) [RFC4861] found in a RA message, or some 899 other means such as DHCPv6 [RFC3315]. 901 2. Once it has formed an address, the 6LN (re)registers its address 902 periodically, within the Lifetime of the previous Address 903 Registration, as prescribed by [RFC6775] and [RFC8505], to 904 refresh the NCE before the lifetime indicated in the EARO 905 expires. The TID is incremented each time and wraps in a 906 lollipop fashion (see section 5.2.1 of [RFC8505] which is fully 907 compatible with section 7.2 of [RFC6550]). 909 3. As stated in section 5.2 of [RFC8505], the 6LN can register to 910 more than one 6LR at the same time. In that case, it MUST use 911 the same value of TID for all of the parallel Address 912 Registrations. 914 4. Following section 5.1 of [RFC8505], a 6LN acting as a RUL sets 915 the "R" flag in the EARO of at least one registration, whereas 916 acting as a RAN it never does. If the "R" flag is not echoed in 917 the NA, the RUL SHOULD attempt to use another 6LR. 919 5. The 6LN may use any of the 6LRs to which it registered as default 920 gateway. 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 RPL Border Router Acting as 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 and for the termination 947 of a registration (lifetime of 0). 949 If the initial EDAR/EDAC exchange succeeds, then the 6LR installs an 950 NCE for the registration lifetime. If the "R" flag was set in the 951 EARO of the NS message, and this 6LR can manage the reachability of 952 Registered Address, then the 6LR sets the "R" flag in the EARO of the 953 NA message that is sends in response. 955 From then on, as long as the "R" flag is set in the periodic NS(EARO) 956 from the 6LN and this Router can still manage the reachability of 957 Registered Address, the 6LR keeps setting the "R" flag in the EARO of 958 the response NA message. But if the RPL Root has indicated that it 959 proxies the keep-alive EDAR/EDAC exchange with the 6LBR (see 960 Section 4), the 6LR MUST refrain from sending the keep-alive EDAR 961 itself. 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 1. The Registered Address is placed in an RPL Target Option in the 983 DAO message as the Target Prefix, and the Prefix Length is set to 984 128; 986 2. RPL Non-Storing Mode is to be used. The 6LR indicates one of its 987 global or unique-local IPv6 unicast addresses as the Parent 988 Address in the associated RPL Transit Information Option (TIO). 990 3. the External 'E' flag in the TIO is set to indicate that the 6LR 991 redistributes an external target into the RPL network. 993 4. the Path Lifetime in the TIO is computed from the Lifetime in the 994 EARO Option. This adapts it to the Lifetime Units used in the 995 RPL operation. Note that if the lifetime is 0, then the 6LR 996 generates a No-Path DAO message that cleans up the routes down to 997 the Address of the 6LN; 999 5. the Path Sequence in the TIO is set to the TID value found in the 1000 EARO option; 1002 6. Upon receiving an NS message with an EARO and the "R" flag set, 1003 the 6LR SHOULD inject the Registered Address in RPL by sending a 1004 DAO message on behalf of the 6LN. If the Registration Lifetime 1005 was 0, the effect is to remove the route and then the NCE; 1007 If for whatever reason the 6LR does not inject the Registered Address 1008 in RPL, it MUST send an NA(EARO) back with the appropriate status and 1009 the "R" flag not set. 1011 If the 6LR injects the Registered Address in RPL and either a DAO-ACK 1012 was not requested or is received with a RPL Status that is not a 1013 rejection ("E" flag not set), the 6LR MUST install or refresh the NCE 1014 for the address and reply to the RUL with an NA(EARO) with a Status 1015 of 0 (Success) and the "R" flag set. 1017 In case of a DAO-ACK or a DCO indicating transporting an EARO Status 1018 Value of 5 (Validation Requested), a 6LR that supports Address 1019 Protected Neighbor Discovery (AP-ND) MUST challenge the 6LN for 1020 ownership of the address, as described in section 6.1 of [AP-ND]. If 1021 the challenge succeeds then the operations continue as normal. In 1022 particular a DAO message is generated upon the NS(EARO) that proves 1023 the ownership of the address. If the challenge failed, the 6LR 1024 rejects the registration as prescribed by AP-ND and may take actions 1025 to protect itself against DoS attacks by a rogue 6LN, see Section 11. 1026 If the 6LR does not support AP-ND, it MUST send an NA to the 6LN with 1027 a Status of 0 (Success) and the "R" flag not set. 1029 The other rejection codes indicate that the 6LR failed to inject the 1030 address into the RPL network. If an EARO Status is transported, the 1031 6LR MUST send a NA(EARO) to the RUL with that Status value, and the 1032 "R" flag not set. Similarly, upon receiving a DCO message indicating 1033 that the address of a RUL should be removed from the routing table, 1034 the 6LR issues an asynchronous NA(EARO) to the RUL with the embedded 1035 ND Status value if there was one, and the "R" flag not set. 1037 If a 6LR receives a valid NS(EARO) message with the "R" flag reset 1038 and a Registration Lifetime that is not 0, and the 6LR was 1039 redistributing the Registered Address due to previous NS(EARO) 1040 messages with the flag set, then it MUST stop injecting the address. 1041 It is up to the Registering 6LN to maintain the corresponding route 1042 from then on, either keeping it active via a different 6LR or by 1043 acting as a RAN and managing its own reachability. 1045 9.2.3. By the RPL Root 1047 A RPL Root SHOULD set the "P" flag in the RPL configuration option of 1048 the DIO messages that it generates (see Section 4) to signal that it 1049 proxies the keep-alive EDAR/EDAC echange. The remainder of this 1050 section assumes that it does. 1052 Upon reception of a DAO message, for each RPL Target option that 1053 creates or updates an existing RPL state, the Root notifies the 6LBR. 1054 This can be done using an internal API if they are co-located, or 1055 using a proxied EDAR/EDAC exchange if they are separated. 1057 If the RPL Target option transports a ROVR, then the Root MUST use it 1058 to build a full EDAR message; else, an anonymous EDAR is used with 1059 the ROVR field set to zero. 1061 The EDAR message MUST be constructed as follows: 1063 1. The Target IPv6 address from the RPL Target Option is placed in 1064 the Registered Address field of the EDAR message; 1066 2. the Registration Lifetime is adapted from the Path Lifetime in 1067 the TIO by converting the Lifetime Units used in RPL into units 1068 of 60 seconds used in the 6LoWPAN ND messages; 1070 3. the TID value is set to the Path Sequence in the TIO and 1071 indicated with an ICMP code of 1 in the EDAR message; 1073 4. If the ROVR is present in the RPL Target option, it is copied as 1074 is in the EDAR and the ICMP Code Suffix is set to the appropriate 1075 value as shown in Table 4 of [RFC8505] depending on the size of 1076 the ROVR field; else, the ROVR field in the EDAR is set to zero 1077 indicating an anonymous EDAR. 1079 Upon a Status value in an EDAC message that is not "Success", the 1080 Root SHOULD destroy the formed paths using either a DAO-ACK (in Non- 1081 Storing Mode) or a DCO downwards as specified in [EFFICIENT-NPDAO]. 1082 Failure to destroy the former path would result in Stale routing 1083 state and local black holes if the address belongs to another party 1084 elsewhere in the network. The RPL Status value that maps the 6LoWPAN 1085 ND Status value MUST be embedded in the RPL Status in the DCO. 1087 9.2.4. By the 6LBR 1089 Upon reception of an EDAR message with the ROVR field is set to 0 1090 indicating an anonymous EDAR, the 6LBR checks whether an entry exists 1091 for the address. If the entry does not exist, the 6LBR does not 1092 create the entry, and answers with a Status "Removed" in the EDAC 1093 message. 1095 If the entry exists, the 6LBR computes whether the TID in the EDAR 1096 message is fresher than the one in the entry as prescribed in section 1097 4.2.1. of [RFC8505] and MUST operate as below: 1099 1. If the anonymous EDAR message is fresher, the 6LBR updates the 1100 TID in the entry, restarts the heartbeat timer for the entry, and 1101 answers with a Status "Success" in the EDAC message. If the 1102 duration of the lifetime of the entry is extended by the 1103 Registration Lifetime in the EDAR message, it also updates the 1104 lifetime of the entry. 1106 2. If the TIDs are the same, the 6LBR does not update the entry, and 1107 answers with a Status "Success" in the EDAC message. 1109 3. If the TID in the entry is fresher, the 6LBR does not update the 1110 entry, and answers with a Status "Moved" in the EDAC message. 1112 The EDAC that is constructed is the same as if the anonymous EDAR was 1113 a full EDAR, and includes the ROVR that is associated to the Address 1114 Registration. 1116 10. Protocol Operations for Multicast Addresses 1118 Section 12 of [RFC6550] details the RPL support for multicast flows. 1119 This support is not source-specific and only operates as an extension 1120 to the Storing Mode of Operation for unicast packets. Note that it 1121 is the RPL model that the multicast packet is passed as a Layer-2 1122 unicast to each if the interested children. This remains true when 1123 forwarding between the 6LR and the listener 6LN. 1125 "Multicast Listener Discovery (MLD) for IPv6" [RFC2710] and its 1126 updated version "Multicast Listener Discovery Version 2 (MLDv2) for 1127 IPv6" [RFC3810] provide an interface for a listener to register to 1128 multicast flows. MLDv2 is backwards compatible with MLD, and adds in 1129 particular the capability to filter the sources via black lists and 1130 white lists. In the MLD model, the Router is a "querier" and the 1131 Host is a multicast listener that registers to the querier to obtain 1132 copies of the particular flows it is interested in. 1134 On the first Address Registration, as illustrated in Figure 10, the 1135 6LN, as an MLD listener, sends an unsolicited Report to the 6LR in 1136 order to start receiving the flow immediately. 1138 6LN/RUL 6LR Root 6LBR 1139 | | | | 1140 | unsolicited Report | | | 1141 |------------------->| | | 1142 | | | | 1143 | | DAO | | 1144 | |-------------->| | 1145 | | DAO-ACK | | 1146 | |<--------------| | 1147 | | | | 1148 | | | unsolicited Report | 1149 | | |------------------->| 1150 | | | | 1151 | | | | 1153 Figure 10: First Multicast Registration Flow 1155 Since multicast Layer-2 messages are avoided, it is important that 1156 the asynchronous messages for unsolicited Report and Done are sent 1157 reliably, for instance using a Layer-2 acknoledgement, or attempted 1158 multiple times. 1160 The 6LR acts as a generic MLD querier and generates a DAO for the 1161 multicast target. The lifetime of the DAO is set to be in the order 1162 of the Query Interval, yet larger to account for variable propagation 1163 delays. 1165 The Root proxies the MLD exchange as a listener with the 6LBR acting 1166 as the querier, so as to get packets from a source external to the 1167 RPL domain. Upon a DAO with a multicast target, the RPL Root checks 1168 if it is already registered as a listener for that address, and if 1169 not, it performs its own unsolicited Report for the multicast target. 1171 An Address re-Registration is pulled periodically by 6LR acting as 1172 querier. Note that the message may be sent unicast to all the known 1173 individual listeners. Upon a time out of the Query Interval, the 6LR 1174 sends a Query to each of its listeners, and gets a Report back that 1175 is mapped into a DAO, as illustrated in Figure 11: 1177 6LN/RUL 6LR Root 6LBR 1178 | | | | 1179 | Query | | | 1180 |<-------------------| | | 1181 | Report | | | 1182 |------------------->| | | 1183 | | DAO | | 1184 | |-------------->| | 1185 | | DAO-ACK | | 1186 | |<--------------| | 1187 | | | | 1188 | | | Query | 1189 | | |<-------------------| 1190 | | | Report | 1191 | | |------------------->| 1192 | | | | 1193 | | | | 1195 Figure 11: Next Registration Flow 1197 Note that any of the functions 6LR, Root and 6LBR might be collapsed 1198 in a single node, in which case the flow above happens internally, 1199 and possibly through internal API calls as opposed to messaging. 1201 11. Security Considerations 1203 The LLN nodes depend on the 6LBR and the RPL participants for their 1204 operation. A trust model must be put in place to ensure that the 1205 right devices are acting in these roles, so as to avoid threats such 1206 as black-holing, (see [RFC7416] section 7) or bombing attack whereby 1207 an impersonated 6LBR would destroy state in the network by using the 1208 "Removed" Status code. 1210 This trust model could be at a minimum based on a Layer-2 Secure 1211 joining and the Link-Layer security. This is a generic 6LoWPAN 1212 requirement, see Req5.1 in Appendix of [RFC8505]. 1214 Additionally, the trust model could include a role validation to 1215 ensure that the node that claims to be a 6LBR or a RPL Root is 1216 entitled to do so. 1218 The anonymous EDAR message does not carry a valid Registration Unique 1219 ID [RFC8505] in the form of a ROVR and may be played by any node on 1220 the network without the need to know the ROVR. The 6LBR MUST NOT 1221 create an entry based on a anonymous EDAR and it MUST NOT decrease 1222 the value of the lifetime. All it can do is refresh the lifetime and 1223 the TID of an existing entry. So the message cannot be used to 1224 create a binding state in the 6LBR but it can be used to maintain one 1225 active longer than expected. 1227 Note that a full EDAR message with a lifetime of 0 will destroy that 1228 state and the anonymous message will not recreate it. Note also that 1229 a rogue that has access to the network can attack the 6LBR with other 1230 (forged) addresses and ROVR, and that this is a much easier DoS 1231 attack than trying to keep existing state alive longer. 1233 At the time of this writing RPL does not have a zerotrust model 1234 whereby the it is possible to validate the origin of an address that 1235 is injected in a DAO. This specification makes a first step in that 1236 direction by allowing the Root to challenge the RUL by the 6LR that 1237 serves it. 1239 12. IANA Considerations 1241 12.1. Resizing the ARO Status values 1243 IANA is requested to modify the Address Registration Option Status 1244 Values Registry as follows: The unassigned values range is reduced 1245 from 11-255 to 11-63. 1247 12.2. New DODAG Configuration Option Flag 1249 This specification updates the Registry for the "DODAG Configuration 1250 Option Flags" that was created for [RFC6550] as follows: 1252 +------------+----------------------------+-----------+ 1253 | Bit Number | Capability Description | Reference | 1254 +============+============================+===========+ 1255 | 1 | Root Proxies EDAR/EDAC (P) | THIS RFC | 1256 +------------+----------------------------+-----------+ 1258 Table 2: New DODAG Configuration Option Flag 1260 12.3. RPL Target Option Flags 1262 Section 20.15 of [RFC6550] creates a registry for the 8-bit RPL 1263 Target Option Flags field. This specification reduces the field to 4 1264 bits. The IANA is requested to reduce the size of the registry 1265 accordingly. 1267 12.4. New Subregistry for the RPL Non-Rejection Status values 1269 This specification creates a new Subregistry for the RPL Non- 1270 Rejection Status values for use in RPL DAO-ACK and RCO messages, 1271 under the ICMPv6 parameters registry. 1273 * Possible values are 6-bit unsigned integers (0..63). 1275 * Registration procedure is "Standards Action" [RFC8126]. 1277 * Initial allocation is as indicated in Table 3: 1279 +-------+------------------------+-----------+ 1280 | Value | Meaning | Reference | 1281 +=======+========================+===========+ 1282 | 0 | Unqualified acceptance | RFC 6550 | 1283 +-------+------------------------+-----------+ 1285 Table 3: Acceptance values of the RPL Status 1287 12.5. New Subregistry for the RPL Rejection Status values 1289 This specification creates a new Subregistry for the RPL Rejection 1290 Status values for use in RPL DAO-ACK and RCO messages, under the 1291 ICMPv6 parameters registry. 1293 * Possible values are 6-bit unsigned integers (0..63). 1295 * Registration procedure is "Standards Action" [RFC8126]. 1297 * Initial allocation is as indicated in Table 4: 1299 +-------+-----------------------+---------------+ 1300 | Value | Meaning | Reference | 1301 +=======+=======================+===============+ 1302 | 0 | Unqualified rejection | This document | 1303 +-------+-----------------------+---------------+ 1305 Table 4: Rejection values of the RPL Status 1307 13. Acknowledgments 1309 The authors wish to thank Georgios Papadopoulos for their early 1310 reviews of and contributions to this document 1312 14. Normative References 1314 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1315 Requirement Levels", BCP 14, RFC 2119, 1316 DOI 10.17487/RFC2119, March 1997, 1317 . 1319 [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast 1320 Listener Discovery (MLD) for IPv6", RFC 2710, 1321 DOI 10.17487/RFC2710, October 1999, 1322 . 1324 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1325 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1326 DOI 10.17487/RFC3810, June 2004, 1327 . 1329 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1330 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1331 Overview, Assumptions, Problem Statement, and Goals", 1332 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1333 . 1335 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1336 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1337 DOI 10.17487/RFC4861, September 2007, 1338 . 1340 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1341 Address Autoconfiguration", RFC 4862, 1342 DOI 10.17487/RFC4862, September 2007, 1343 . 1345 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1346 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1347 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1348 Low-Power and Lossy Networks", RFC 6550, 1349 DOI 10.17487/RFC6550, March 2012, 1350 . 1352 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1353 Power and Lossy Networks (RPL) Option for Carrying RPL 1354 Information in Data-Plane Datagrams", RFC 6553, 1355 DOI 10.17487/RFC6553, March 2012, 1356 . 1358 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1359 Routing Header for Source Routes with the Routing Protocol 1360 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1361 DOI 10.17487/RFC6554, March 2012, 1362 . 1364 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1365 Bormann, "Neighbor Discovery Optimization for IPv6 over 1366 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1367 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1368 . 1370 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1371 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1372 2014, . 1374 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1375 Constrained-Node Networks", RFC 7228, 1376 DOI 10.17487/RFC7228, May 2014, 1377 . 1379 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 1380 IPv6 over Low-Power Wireless Personal Area Networks 1381 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 1382 2014, . 1384 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1385 Writing an IANA Considerations Section in RFCs", BCP 26, 1386 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1387 . 1389 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1390 "IPv6 over Low-Power Wireless Personal Area Network 1391 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1392 April 2017, . 1394 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1395 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1396 May 2017, . 1398 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1399 (IPv6) Specification", STD 86, RFC 8200, 1400 DOI 10.17487/RFC8200, July 2017, 1401 . 1403 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1404 Perkins, "Registration Extensions for IPv6 over Low-Power 1405 Wireless Personal Area Network (6LoWPAN) Neighbor 1406 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1407 . 1409 [AP-ND] Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 1410 "Address Protected Neighbor Discovery for Low-power and 1411 Lossy Networks", Work in Progress, Internet-Draft, draft- 1412 ietf-6lo-ap-nd-20, 9 March 2020, 1413 . 1415 [USEofRPLinfo] 1416 Robles, I., Richardson, M., and P. Thubert, "Using RPI 1417 option Type, Routing Header for Source Routes and IPv6-in- 1418 IPv6 encapsulation in the RPL Data Plane", Work in 1419 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-36, 1420 26 February 2020, . 1423 [EFFICIENT-NPDAO] 1424 Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient 1425 Route Invalidation", Work in Progress, Internet-Draft, 1426 draft-ietf-roll-efficient-npdao-17, 30 October 2019, 1427 . 1430 15. Informative References 1432 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1433 Statement and Requirements for IPv6 over Low-Power 1434 Wireless Personal Area Network (6LoWPAN) Routing", 1435 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1436 . 1438 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 1439 C., and M. Carney, "Dynamic Host Configuration Protocol 1440 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 1441 2003, . 1443 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1444 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1445 DOI 10.17487/RFC6282, September 2011, 1446 . 1448 [RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur, 1449 Ed., "Performance Evaluation of the Routing Protocol for 1450 Low-Power and Lossy Networks (RPL)", RFC 6687, 1451 DOI 10.17487/RFC6687, October 2012, 1452 . 1454 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1455 and M. Richardson, Ed., "A Security Threat Analysis for 1456 the Routing Protocol for Low-Power and Lossy Networks 1457 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1458 . 1460 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1461 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1462 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1463 . 1465 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node 1466 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504, 1467 January 2019, . 1469 [6BBR] Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6 1470 Backbone Router", Work in Progress, Internet-Draft, draft- 1471 ietf-6lo-backbone-router-19, 3 March 2020, 1472 . 1475 Appendix A. Example Compression 1477 Figure 12 illustrates the case in Storing Mode where the packet is 1478 received from the Internet, then the Root encapsulates the packet to 1479 insert the RPI and deliver to the 6LR that is the parent and last hop 1480 to the final destination, which is not known to support [RFC8138]. 1482 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1483 |11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP 1484 |Page 1 |Type1 S=0| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 1485 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1486 <-4 bytes-> <- RFC 6282 -> 1487 <- No RPL artifact ... 1489 Figure 12: Encapsulation to Parent 6LR in Storing Mode 1491 The difference with the example format presented in Figure 19 of 1492 [RFC8138] is the addition of a SRH-6LoRH before the RPI-6LoRH to 1493 transport the compressed address of the 6LR as the destination 1494 address of the outer IPv6 header. In the original example the 1495 destination IP of the outer header was elided and was implicitly the 1496 same address as the destination of the inner header. Type 1 was 1497 arbitrarily chosen for this example, and the size of 0 denotes a 1498 single address in the SRH. 1500 In Figure 12, the source of the IP-in-IP encapsulation is the Root, 1501 so it is elided in the IP-in-IP 6LoRH. The destination is the parent 1502 6LR of the destination of the inner packet so it cannot be elided. 1503 In Storing Mode, it is placed as the single entry in an SRH-6LoRH as 1504 the first 6LoRH. Since there is a single entry so the SRH-6LoRH Size 1505 is 0. In this particular example, the 6LR address can be compressed 1506 to 2 bytes so a Type of 1 is used. It results that the total length 1507 of the SRH-6LoRH is 4 bytes. 1509 In Non-Storing Mode, the encapsulation from the Root would be similar 1510 to that represented in Figure 12 with possibly more hops in the SRH- 1511 6LoRH and possibly multiple SRH-6LoRHs if the various addresses in 1512 the routing header are not compressed to the same format. Note that 1513 on the last hop to the parent 6LR, the RH3 is consumed and removed 1514 from the compressed form, so the use of Non-Storing Mode vs. Storing 1515 Mode is indistinguishable from the packet format. 1517 Follows the RPI-6LoRH and then the IP-in-IP 6LoRH. When the IP-in-IP 1518 6LoRH is removed, all the Router headers that precede it are also 1519 removed. 1521 The Paging Dispatch [RFC8025] may also be removed if there was no 1522 previous Page change to a Page other than 0 or 1, since the 1523 LOWPAN_IPHC is encoded in the same fashion in the default Page 0 and 1524 in Page 1. The resulting packet to the destination is the inner 1525 packet compressed with [RFC6282]. 1527 Authors' Addresses 1528 Pascal Thubert (editor) 1529 Cisco Systems, Inc 1530 Building D 1531 45 Allee des Ormes - BP1200 1532 06254 Mougins - Sophia Antipolis 1533 France 1535 Phone: +33 497 23 26 34 1536 Email: pthubert@cisco.com 1538 Michael C. Richardson 1539 Sandelman Software Works 1541 Email: mcr+ietf@sandelman.ca 1542 URI: http://www.sandelman.ca/