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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Informational RFC: RFC 4919 == Outdated reference: A later version (-23) exists of draft-ietf-6lo-ap-nd-13 == Outdated reference: A later version (-44) exists of draft-ietf-roll-useofrplinfo-34 == Outdated reference: A later version (-18) exists of draft-ietf-roll-efficient-npdao-17 ** Downref: Normative reference to an Informational RFC: RFC 7102 -- Obsolete informational reference (is this intentional?): RFC 3315 (Obsoleted by RFC 8415) Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 4 comments (--). 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: 30 July 2020 27 January 2020 8 Routing for RPL Leaves 9 draft-ietf-roll-unaware-leaves-09 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 30 July 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 . . . . . . . . . . . . . . . . . . . . . . . . 7 58 3.2. RFC 8505 Extended ARO . . . . . . . . . . . . . . . . . . 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 the HbH Header . . . . . . . . . . . . . . 13 70 6.2.2. Support of the Routing Header . . . . . . . . . . . . 13 71 6.2.3. Support of IPv6 Encapsulation . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . 19 78 9.2. Detailed Operation . . . . . . . . . . . . . . . . . . . 19 79 9.2.1. By the 6LN . . . . . . . . . . . . . . . . . . . . . 20 80 9.2.2. By the 6LR . . . . . . . . . . . . . . . . . . . . . 21 81 9.2.3. By the RPL Root . . . . . . . . . . . . . . . . . . . 23 82 9.2.4. By the 6LBR . . . . . . . . . . . . . . . . . . . . . 24 83 10. Protocol Operations for Multicast Addresses . . . . . . . . . 24 84 11. Security Considerations . . . . . . . . . . . . . . . . . . . 26 85 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 86 12.1. New DODAG Configuration Option Flag . . . . . . . . . . 27 87 12.2. RPL Target Option Flags . . . . . . . . . . . . . . . . 27 88 12.3. New Subregistry for the RPL Non-Rejection Status 89 values . . . . . . . . . . . . . . . . . . . . . . . . . 27 90 12.4. New Subregistry for the RPL Rejection Status values . . 27 91 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28 92 14. Normative References . . . . . . . . . . . . . . . . . . . . 28 93 15. Informative References . . . . . . . . . . . . . . . . . . . 30 94 Appendix A. Example Compression . . . . . . . . . . . . . . . . 31 95 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 97 1. Introduction 99 The design of Low Power and Lossy Networks (LLNs) is generally 100 focused on saving energy, which is the most constrained resource of 101 all. Other design constraints, such as a limited memory capacity, 102 duty cycling of the LLN devices and low-power lossy transmissions, 103 derive from that primary concern. 105 The IETF produced the "Routing Protocol for Low Power and Lossy 106 Networks" [RFC6550] (RPL) to provide IPv6 [RFC8200] routing services 107 within such constraints. RPL belongs to the class of Distance-Vector 108 protocol, which, compared to link-state protocols, limits the amount 109 of topological knowledge that needs to be installed and maintained in 110 each node. 112 In order to operate in constrained networks, RPL allows a routing 113 stretch (see [RFC6687]), whereby routing is only performed along an 114 acyclic graph optimized to reach a Root node, as opposed to straight 115 along a shortest path between 2 peers, whatever that would mean in a 116 given LLN. This trades the quality of peer-to-peer (P2P) paths for a 117 vastly reduced amount of control traffic and routing state that would 118 be required to operate a any-to-any shortest path protocol. Finally, 119 broken routes may be fixed lazily and on-demand, based on dataplane 120 inconsistency discovery, which avoids wasting energy in the proactive 121 repair of unused paths. 123 In order to cope with lossy transmissions, RPL forms Direction- 124 Oriented Directed Acyclic Graphs (DODAGs) using DODAG Information 125 Solicitation (DIS) and DODAG Information Object (DIO) messages. For 126 most of the nodes, though not all, a DODAG provides multiple 127 forwarding solutions towards the Root of the topology via so-called 128 parents. RPL is designed to adapt to fuzzy connectivity, whereby the 129 physical topology cannot be expected to reach a stable state, with a 130 lazy control that creates routes proactively but only fixes them when 131 they are used by actual traffic. 133 The result is that RPL provides reachability for most of the LLN 134 nodes, most of the time, but may not really converge in the classical 135 sense. RPL provides unicast and multicast routing services back to 136 RPL-Aware nodes (RANs). 138 A RAN will inject routes to itself using Destination Advertisement 139 Object (DAO) messages sent to either parent-nodes in Storing Mode or 140 to the Root indicating their parent in Non-Storing Mode. This 141 process effectively forms a DODAG back to the device that is a subset 142 of the DODAG to the Root with all links reversed. 144 RPL can be deployed as an extension to IPv6 Neighbor Discovery (ND) 145 [RFC4861][RFC4862] and 6LoWPAN ND [RFC6775][RFC8505] to maintain 146 reachability within a Non-Broadcast Multi-Access (NBMA) subnet. In 147 that mode, some nodes may act as Routers and participate to the 148 forwarding operations whereas others will only terminate packets, 149 acting as Hosts in the data-plane. In [RFC6550] terms, a Host that 150 is reachable over the RPL network is called a Leaf. 152 "When to use RFC 6553, 6554 and IPv6-in-IPv6" [USEofRPLinfo] 153 introduces the term RPL-Aware-Leaf (RAL) for a Leaf that injects 154 routes in RPL to manage the reachability of its own IPv6 addresses. 155 In contrast, a RPL-Unaware Leaf (RUL) designates a Leaf does not 156 participate to RPL at all. A RUL is a plain Host that needs an 157 interface to its RPL Router to obtain routing services over the LLN. 159 This specification enables a RUL that is a 6LoWPAN Node (6LN) to 160 announce itself as a Host to its 6LoWPAN Router (6LR) in the 6LoWPAN 161 ND Address Address Registration, and to request that the 6LR injects 162 the relevant routing information for the Registered Address in the 163 RPL domain on its behalf. The unicast packet forwarding operation by 164 the 6LR serving a 6LN that is a RPL Leaf is described in 165 [USEofRPLinfo]. 167 Examples of routing-agnostic 6LN may include lightly-powered sensors 168 such as window smash sensor (alarm system), and kinetically powered 169 light switches. Other application of this specification may include 170 a smart grid network that controls appliances - such as washing 171 machines or the heating system - in the home. Appliances may not 172 participate to the RPL protocol operated in the Smartgrid network but 173 can still receive control packet from the Smartgrid. 175 2. Terminology 177 2.1. BCP 14 179 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 180 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 181 "OPTIONAL" in this document are to be interpreted as described in BCP 182 14 [RFC2119][RFC8174] when, and only when, they appear in all 183 capitals, as shown here. 185 2.2. References 187 The Terminology used in this document is consistent with and 188 incorporates that described in Terms Used in Routing for Low-Power 189 and Lossy Networks (LLNs). [RFC7102]. 191 A glossary of classical 6LoWPAN acronyms is given in Section 2.3. 193 The term "byte" is used in its now customary sense as a synonym for 194 "octet". 196 "RPL", the "RPL Packet Information" (RPI), "RPL Instance" (indexed by 197 a RPLInstanceID)are defined in "RPL: IPv6 Routing Protocol for 198 Low-Power and Lossy Networks" [RFC6550] . The DODAG Information 199 Solicitation (DIS), Destination Advertisement Object (DAO) and DODAG 200 Information Object (DIO) messages are also specified in [RFC6550]. 201 The Destination Cleanup Object (DCO) message is defined in 202 [EFFICIENT-NPDAO]. 204 This document uses the terms RPL-Unaware Leaf (RUL) and RPL Aware 205 Leaf (RAL) consistently with [USEofRPLinfo]. The term RPL-Aware Node 206 (RAN) is introduced to refer to a node that is either a RAL or a RPL 207 Router. As opposed to a RUL, a RAN manages the reachability of its 208 addresses and prefixes by injecting them in RPL by itself. 210 Other terms in use in LLNs are found in Terminology for 211 Constrained-Node Networks [RFC7228]. 213 Readers are expected to be familiar with all the terms and concepts 214 that are discussed in 216 * "Neighbor Discovery for IP version 6" [RFC4861], 218 * "IPv6 Stateless Address Autoconfiguration" [RFC4862], 220 * "Problem Statement and Requirements for IPv6 over Low-Power 221 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606], 223 * "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 224 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 226 * "Neighbor Discovery Optimization for Low-power and Lossy Networks" 227 [RFC6775], and 229 * "Registration Extensions for IPv6 over Low-Power Wireless Personal 230 Area Network (6LoWPAN) Neighbor Discovery" [RFC8505]. 232 2.3. Glossary 234 This document often uses the following acronyms: 236 AR: Address Resolution (aka Address Lookup) 238 6CIO: 6LoWPAN Capability Indication Option 239 6LN: 6LoWPAN Node (a Low Power Host or Router) 241 6LR: 6LoWPAN Router 243 (E)ARO: (Extended) Address Registration Option 245 (E)DAR: (Extended) Duplicate Address Request 247 (E)DAC: (Extended) Duplicate Address Confirmation 249 DAD: Duplicate Address Detection 251 DAO: Destination Advertisement Object (a RPL message) 253 DCO: Destination Cleanup Object (a RPL message) 255 DIS: DODAG Information Solicitation (a RPL message) 257 DIO: DODAG Information Object (a RPL message) 259 DODAG: Destination-Oriented Directed Acyclic Graph 261 LLN: Low-Power and Lossy Network 263 NA: Neighbor Advertisement 265 NCE: Neighbor Cache Entry 267 ND: Neighbor Discovery 269 NS: Neighbor Solicitation 271 RA: Router Advertisement 273 ROVR: Registration Ownership Verifier 275 RPI: RPL Packet Information (the abstract information RPL places in 276 data packets as the RPL Option within the IPv6 Hop-By-Hop Header, 277 and by extension the RPL Option itself) 279 RAL: RPL-Aware Leaf 281 RAN: RPL-Aware Node (either a RPL Router or a RPL-Aware Leaf) 283 RUL: RPL-Unaware Leaf 285 TID: Transaction ID (a sequence counter in the EARO) 287 3. 6LoWPAN Neighbor Discovery 289 3.1. RFC 6775 291 The "IPv6 Neighbor Discovery (IPv6 ND) Protocol" suite [RFC4861] 292 [RFC4862] was defined for transit media such a Ethernet, and relies 293 heavily on multicast operations for address discovery and duplicate 294 address detection (DAD). "Neighbor Discovery Optimizations for 295 6LoWPAN networks" [RFC6775] (6LoWPAN ND) adapts IPv6 ND for 296 operations over energy-constrained LLNs. In particular, 6LoWPAN ND 297 introduces a unicast Host Registration mechanism that contributes to 298 reducing the use of multicast messages that are present in the 299 classical IPv6 ND protocol. 301 6LoWPAN ND defines a new Address Registration Option (ARO) that is 302 carried in the unicast Neighbor Solicitation (NS) and Neighbor 303 Advertisement (NA) messages between the 6LoWPAN Node (6LN) and the 304 6LoWPAN Router (6LR). 6LoWPAN ND also defines the Duplicate Address 305 Request (DAR) and Duplicate Address Confirmation (DAC) messages 306 between the 6LR and the 6LoWPAN Border Router (6LBR). In an LLN, the 307 6LBR is the central repository of all the Registered Addresses in its 308 domain. 310 The main functions of [RFC6775] are to proactively establish the 311 Neighbor Cache Entry in the 6LR and to avoid address duplication. 313 3.2. RFC 8505 Extended ARO 315 "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505] 316 updates the behavior of RFC 6775 to enable a generic Address 317 Registration to services such as routing and ND proxy, and defines 318 the Extended Address Registration Option (EARO) as shown in Figure 1: 320 0 1 2 3 321 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 1 322 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 323 | Type | Length | Status | Opaque | 324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 325 | Rsvd | I |R|T| TID | Registration Lifetime | 326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 | | 328 ... Registration Ownership Verifier ... 329 | | 330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 332 Figure 1: EARO Option Format 334 3.2.1. R Flag 336 [RFC8505] introduces the "R" flag in the EARO. The Registering Node 337 sets the "R" flag to indicate whether the 6LR should ensure 338 reachability for the Registered Address, e.g., by means of routing or 339 proxying ND. If the "R" flag is not set, then the Registering Node 340 is expected to be a RAN that handles the reachability of the 341 Registered Address by itself. 343 This document specifies how the "R" flag is used in the context of 344 RPL. A 6LN operates as a RUL for an IPv6 address iff it sets the "R" 345 flag in the EARO used to register the address. The RPL Router 346 generates a DAO message for the Registered Address upon an NS(EARO) 347 iff the "R" flag in the EARO is set. Conversely, this document 348 specifies the behavior of a RPL Router acting as 6LR that depends on 349 the setting of the "R" flag in the EARO. 351 3.2.2. TID, I Field and Opaque Fields 353 The EARO also includes a sequence counter called Transaction ID 354 (TID), which maps to the Path Sequence Field found in Transit Options 355 in RPL DAO messages. This is the reason why the support of [RFC8505] 356 by the RUL as opposed to only [RFC6775] is a prerequisite for this 357 specification (more in Section 6.1). The EARO also transports an 358 Opaque field and an "I" field that describes what the Opaque field 359 transports and how to use it. Section 9.2.1 specifies the use of the 360 "I" field and of the Opaque field by a RUL. 362 3.2.3. ROVR 364 Section 5.3. of [RFC8505] introduces the Registration Ownership 365 Verifier (ROVR) field of variable length from 64 to 256 bits. The 366 ROVR is a replacement of the EUI-64 in the ARO [RFC6775] that was 367 used to identify uniquely an Address Registration with the Link-Layer 368 address of the owner, but provided no protection against spoofing. 370 "Address Protected Neighbor Discovery for Low-power and Lossy 371 Networks" [AP-ND] leverages the ROVR field as a cryptographic proof 372 of ownership to prevent a rogue third party from misusing the 373 address. [AP-ND] adds a challenge/response exchange to the [RFC8505] 374 Address Registration and enables Source Address Validation by a 6LR 375 that will drop packets with a spoofed address. 377 This specification does not address how the protection by [AP-ND] 378 could be extended to RPL. On the other hand, it adds the ROVR to the 379 DAO to build the proxied EDAR at the Root, which means that nodes 380 that are aware of the Host route to the 6LN are now aware of the 381 associated ROVR as well. 383 3.3. RFC 8505 Extended DAR/DAC 385 [RFC8505] updates the periodic DAR/DAC exchange that takes place 386 between the 6LR and the 6LBR using Extended DAR/DAC messages. The 387 Extended Duplicate Address messages can carry a ROVR field of 388 variable size. The periodic EDAR/EDAC exchange is triggered by a 389 NS(EARO) message and is intended to create and then refresh the 390 corresponding state in the 6LBR for a lifetime that is indicated by 391 the 6LN. Conversely, RPL [RFC6550] specifies a periodic DAO from the 392 6LN all the way to the Root that maintains the routing state in the 393 RPL network for a lifetime that is indicated by the source of the 394 DAO. This means that there are two periodic messages that traverse 395 the whole network to indicate that an address is still reachable, one 396 to the Root and one to the 6LBR. 398 This specification saves the support of RPL in a 6LN called a RUL and 399 avoids an extraneous periodic flow across the LLN. The RUL only 400 needs to perform a [RFC8505] Address Registration to the 6LR. The 401 6LR turns it into a DAO message to the Root on behalf of the RUL. 402 Upon the new DAO, the Root proxies the EDAR exchange to the 6LBR on 403 behalf of the 6LR. This is illustrated in Figure 6. 405 3.3.1. RFC 7400 Capability Indication Option 407 "6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power 408 Wireless Personal Area Networks (6LoWPANs)" [RFC7400] defines the 409 6LoWPAN Capability Indication Option (6CIO) that enables a node to 410 expose its capabilities in Router Advertisement (RA) Messages. 411 [RFC8505] defines a number of bits in the 6CIO, in particular: 413 L: Node is a 6LR. 415 E: Node is an IPv6 ND Registrar -- i.e., it supports registrations 416 based on EARO. 418 P: Node is a Routing Registrar, -- i.e., an IPv6 ND Registrar that 419 also provides reachability services for the Registered Addres 421 0 1 2 3 422 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 1 423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 424 | Type | Length = 1 | Reserved |D|L|B|P|E|G| 425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 426 | Reserved | 427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 429 Figure 2: 6CIO flags 431 A RUL can get reachability services from a 6LR if and only if the L, 432 P and E flags are set in a 6CIO originated by the 6LR. A 6LR that 433 can provide reachability services for a RUL node in a RPL network as 434 specified in this document sets the L, P and E flags. 436 4. Updating RFC 6550 438 This document specifies a new behavior whereby a 6LR injects DAO 439 messages for unicast addresses (see Section 9) and multicast 440 addresses (see Section 10) on behalf of leaves that are not aware of 441 RPL. The Targets are exposed as External addresses. An IP-in-IP 442 encapsulation that terminates at the border 6LR is used to remove RPL 443 artifacts and compression techniques that may not be processed 444 correctly outside of the RPL domain. 446 This document also synchronizes the liveness monitoring at the Root 447 and the 6LBR. A same value of lifetime is used for both, and a 448 single heartbeat message, the RPL DAO, traverses the RPL network. A 449 new behavior is introduced whereby the RPL Root proxies the EDAR 450 message to the 6LBR on behalf of the 6LR (more in Section 5), for any 451 6LN, RUL or RAN. 453 RPL defines a configuration option that is registered to IANA in 454 section 20.14. of [RFC6550]. This specification defines a new flag 455 "Root Proxies EDAR/EDAC" (P) that is encoded in one of the reserved 456 control bits in the option. The new flag is set to indicate that the 457 Root performs the proxy operation and that all nodes in the network 458 must refrain from renewing the 6LBR state directly. The bit position 459 of the "P" flag is indicated in Section 12.1. 461 Section 6.3.1. of [RFC6550] defines a 3-bit Mode of Operation (MOP) 462 in the DIO Base Object. The new "P" flag is defined only for MOP 463 value between 0 to 6. For a MOP value of 7 or above, the flag MAY 464 indicate something different and MUST NOT be interpreted as "Root 465 Proxies EDAR/EDAC" unless the specification of the MOP indicates to 466 do so. 468 The RPL Status defined in section 6.5.1. of [RFC6550] for use in the 469 DAO-Ack message is extended to be used in the DCO messages 470 [EFFICIENT-NPDAO] as well. Furthermore, this specification enables 471 to use a RPL Status to transport the IPv6 ND Status defined for use 472 in the EARO, more in Section 7. 474 Section 6.7. of [RFC6550] introduces the RPL Control Message Options 475 such as the RPL Target Option that can be included in a RPL Control 476 Message such as the DAO. Section 8 updates the RPL Target Option to 477 optionally transport the ROVR used in the IPv6 Registration (see 478 Section 3.2.3) so the RPL Root can generate a full EDAR Message. 480 5. Updating RFC 8505 482 This document updates [RFC8505] to introduce a keep-alive EDAR 483 message and a keep-alive NS(EARO) message. The keep-alive messages 484 are used for backward compatibility, when the DAO does not transport 485 a ROVR as specified in Section 8. The keep-alive messages have a 486 zero ROVR field and can only be used to refresh a pre-existing state 487 associated to the Registered Address. More specifically, a keep- 488 alive message can only increase the lifetime and/or increment the TID 489 of the existing state in a 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 Address Registration as follows. If the Root indicates the 494 capability to proxy the EDAR/EDAC exchange to the 6LBR then the 6LR 495 refrains from sending an EDAR message; if the Root is separated from 496 the 6LBR, the Root regenerates the EDAR message to the 6LBR upon a 497 DAO message that signals the liveliness of the Address. 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 in order to obtain routing 504 services from the 6LR. 506 6.1. Support of 6LoWPAN ND 508 In order to obtain routing services from a 6LR, a RUL MUST implement 509 [RFC8505] and set the "R" flag in the EARO option. The RUL MAY 510 request routing services from a 6LR if and only if the L, R and E 511 flags are all set in the 6CIO [RFC7400] originated by the 6LR. 513 The RUL MUST register to all the 6LRs from which it requests routing 514 services. The Address Registrations SHOULD be performed in a rapid 515 sequence, using the exact same EARO for a same Address. Gaps between 516 the Address Registrations will invalidate some of the routes till the 517 Address Registration finally shows on those routes as well. 519 [RFC8505] introduces error Status values in the NA(EARO) which can be 520 received synchronously upon an NS(EARO) or asynchronously. The RUL 521 MUST support both cases and refrain from using the Registered Address 522 as specified by [RFC8505] depending on the Status value. 524 A RUL SHOULD support [AP-ND] to protect the ownership of its 525 addresses. 527 6.2. External Routes and RPL Artifacts 529 Section 4.1. of [USEofRPLinfo] provides a set of rules that MUST be 530 followed when forwarding packets over an external route: 532 RPL data packets are often encapsulated using IP-in-IP and in Non- 533 Storing Mode, packets going down will carry an SRH as well. RPL data 534 packets also typically carry a Hop-by-Hop Header to transport a RPL 535 Packet Information (RPI) [RFC6550]. These additional headers are 536 called RPL artifacts. 538 When IP-in-IP is used and the outer headers terminate at a 6LR down 539 the path (see Figure 10 for the compressed format in Storing Mode), 540 then the 6LR decapsulates the IP-in-IP and the packet that is 541 forwarded to the external destination is free of RPL artifacts - but 542 possibly an RPI if packet was generated by a RAN in the same RPL 543 domain as the destination RUL. 545 Non-Storing Mode DAO messages are used to signal external routes to 546 the Root, even if the DODAG is operated in Storing Mode. This 547 enables to advertise the 6LR that injects the route for use as tunnel 548 endpoint in the data path. 550 For all external routes, the Root should use an IP-in-IP tunnel to 551 that 6LR, with the RPL artifacts in the outer header to be stripped 552 by the 6LR. The IP-in-IP encapsulation may be avoided in Storing 553 Mode if the path to the external destination beyond the 6LR is known 554 to handle or ignore the RPL artifacts properly [RFC8200]. 556 A RUL is an example of a destination that is reachable via an 557 external (Host) route for which IP-in-IP tunneling may be avoided as 558 it ignores the RPI and the consumed SRH artifacts. The use of non- 559 Storing Mode signaling in Storing Mode and the associated IP-in-IP 560 encapsulation are transparent to intermediate Routers that only see 561 packets back and forth between the Root and the 6LR and do not need a 562 special support for external routes. 564 The RUL may not support IP-in-IP tunneling [RFC8504], so if IP-in-IP 565 is used, and unless the Root as a better knowledge, the tunnel should 566 terminate at the 6LR that injected the external route to the RUL. 568 Additionally, the RUL is not expected to support the compression 569 method defined in [RFC8138]. The 6LR that injected the route MUST 570 uncompress the packet before forwarding over an external route, even 571 when delivering to a RUL, even when it is not the destination in the 572 outer header of the incoming packet, unless configured to do 573 otherwise. 575 6.2.1. Support of the HbH Header 577 A RUL is expected to process an unknown Option Type in a Hop-by-Hop 578 Header as prescribed by section 4.2 of [RFC8200]. This means in 579 particular that an RPI with an Option Type of 0x23 [USEofRPLinfo] is 580 ignored when not understood. 582 6.2.2. Support of the Routing Header 584 A RUL is expected to process an unknown Routing Header Type as 585 prescribed by section 4.4 of [RFC8200]. This means in particular 586 that Routing Header with a Routing Type of 3 [RFC6553] is ignored 587 when the Segments Left is zero, and dropped otherwise. 589 6.2.3. Support of IPv6 Encapsulation 591 Section 2.1 of [USEofRPLinfo] sets the rules for forwarding IP-in-IP 592 either to the final 6LN or to a parent 6LR. In order to enable IP- 593 in-IP to the 6LN in Non-Storing Mode, the 6LN must be able to 594 decapsulate the tunneled packet and either drop the inner packet if 595 it is not the final destination, or pass it to the upper layer for 596 further processing. Unless it is aware that the RUL can handle IP- 597 in-IP properly, the Root that encapsulates a packet to a RUL 598 terminates the IP-in-IP tunnel at the parent 6LR . For that reason, 599 it is beneficial but not necessary for a RUL to support IP-in-IP. 601 7. Updated RPL Status 603 The RPL Status is defined in section 6.5.1. of [RFC6550] for use in 604 the DAO-Ack message and values are assigned as follows: 606 +---------+--------------------------------+ 607 | Range | Meaning | 608 +=========+================================+ 609 | 0 | Success/Unqualified acceptance | 610 +---------+--------------------------------+ 611 | 1-127 | Not an outright rejection | 612 +---------+--------------------------------+ 613 | 128-255 | Rejection | 614 +---------+--------------------------------+ 616 Table 1: RPL Status per RFC 6550 618 This specification extends the scope of the RPL Status to be used in 619 RPL DCO messages. Furthermore, this specification enables to carry 620 the IPv6 ND Status values defined for use in the EARO and initially 621 listed in table 1 of [RFC8505] in a RPL Status. Only EARO Status 622 values in the range 0-63 can be transported. 624 The resulting RPL Status is as follows: 626 0 627 0 1 2 3 4 5 6 7 628 +-+-+-+-+-+-+-+-+ 629 |E|A| Value | 630 +-+-+-+-+-+-+-+-+ 632 Figure 3: RPL Status Format 634 RPL Status subfields: 636 E: 1-bit flag. Set to indicate a rejection. When not set, a value 637 of 0 indicates Success/Unqualified acceptance and other values 638 indicate "not an outright rejection" as per RFC 6550. 640 A: 1-bit flag. Indicates the type of the Status value. 642 Status Value: 6-bit unsigned integer. If the 'A' flag is set this 643 field transports a Status value defined for IPv6 ND EARO. When 644 the 'A' flag is not set, the Status value is defined in a RPL 645 extension. 647 When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a DAC 648 message, the RPL Root MUST copy the ARO Status unchanged in a RPL 649 Status with the 'A' bit set. Conversely the 6LR MUST copy the value 650 of the RPL Status unchanged in the EARO of an NA message that is 651 built upon a RPL Status with the 'A' bit set in a DCO or a DAO-ACK 652 message. 654 8. Updated RPL Target option 656 This specification updates the RPL Target option to transport the 657 ROVR as illustrated in Figure 4. This enables the RPL Root to 658 generate a full EDAR Message as opposed to a keep-alive EDAR that has 659 restricted properties. 661 The Target Prefix MUST be aligned to the next 4-byte boundary after 662 the size indicated by the Prefix Length. if necessary it is padded 663 with zeros. The size of the ROVR is indicated in a new ROVR Type 664 field that is encoded to map the CodePfx in the EDAR message (see 665 section 4.2 of [RFC8505]). 667 With this specification the ROVR is the remainder of the RPL Target 668 Option. The format is backward compatible with the Target Option in 669 [RFC6550] and SHOULD be used as a replacement. 671 0 1 2 3 672 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 1 673 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 674 | Type = 0x05 | Option Length |ROVRsz | Flags | Prefix Length | 675 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 676 | | 677 + + 678 | Target Prefix (Variable Length) | 679 . Aligned to 4-byte boundary . 680 . . 681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 682 | | 683 ... Registration Ownership Verifier (ROVR) ... 684 | | 685 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 687 Figure 4: Updated Target Option 689 New fields: 691 ROVRsz: Indicates the Size of the ROVR. It MAY be 1, 2, 3, or 4, 692 denoting a ROVR size of 64, 128, 192, or 256 bits, respectively. 694 Registration Ownership Verifier (ROVR): This is the same field as in 695 the EARO, see [RFC8505] 697 9. Protocol Operations for Unicast Addresses 699 The description below assumes that the Root sets the "P" flag in the 700 DODAG Configuration Option and performs the EDAR proxy operation. 702 9.1. General Flow 704 This specification enables to save the exchange of Extended Duplicate 705 Address messages, EDAR and EDAC, from a 6LN all the way to the 6LBR 706 across a RPL mesh, for the sole purpose of refreshing an existing 707 state in the 6LBR. Instead, the EDAR/EDAC exchange is proxied by the 708 RPL Root upon a DAO message that refreshes the RPL routing state. 710 To achieve this, the lifetimes and sequence counters in 6LoWPAN ND 711 and RPL are aligned. In other words, the Path Sequence and the Path 712 Lifetime in the DAO message are taken from the Transaction ID and the 713 Address Registration lifetime in the NS(EARO) message from the 6LN. 715 In that flow, the RPL Root acts as a proxy to refresh the state in 716 the 6LBR. The proxy operation applies to both RUL and RAN. This 717 means that in a RPL network where the function is enabled, refreshing 718 the state in the 6LBR is the responsibility of the Root. 720 Consequently, only addresses that are injected in RPL will be kept 721 alive by the RPL Root. 723 In a same fashion, if an additional routing protocol is deployed on a 724 same network, that additional routing protocol may need to handle the 725 keep alive procedure for the addresses that it serves. 727 On the first Address Registration, illustrated in Figure 5 and 728 Figure 7 for RPL Non-Storing and Storing Mode respectively, the 729 Extended Duplicate Address exchange takes place as prescribed by 730 [RFC8505]. Any of the functions 6LR, Root and 6LBR might be 731 collapsed in a single node. 733 When successful, the flow creates a Neighbor Cache Entry (NCE) in the 734 6LR, and the 6LR injects the Registered Address in RPL using DAO/DAO- 735 ACK exchanges all the way to the RPL DODAG Root. The protocol does 736 not carry a specific information that the Extended Duplicate Address 737 messages were already exchanged, so the Root proxies them anyway. 739 9.1.1. In RPL Non-Storing-Mode 741 In Non-Storing Mode, the DAO message flow can be nested within the 742 Address Registration flow as illustrated in Figure 5 and it is 743 possible to carry information such as an updated lifetime from the 744 6LBR all the way back to the 6LN. 746 6LN 6LR Root 6LBR 747 | | | | 748 | NS(EARO) | | | 749 |--------------->| | 750 | | Extended DAR | 751 | |--------------------------------->| 752 | | | 753 | | Extended DAC | 754 | |<---------------------------------| 755 | | DAO | | 756 | |------------->| | 757 | | | (keep-alive) EDAR | 758 | | |------------------>| 759 | | | EDAC | 760 | | |<------------------| 761 | | DAO-ACK | | 762 | |<-------------| | 763 | NA(EARO) | | | 764 |<---------------| | | 765 | | | | 766 (in case if an Error not reported in DAO-ACK) 767 | | | | 768 | | DCO | | 769 | |<-------------| | 770 | NA(EARO) | | | 771 |<---------------| | | 772 | | | | 774 Figure 5: First Registration Flow in Non-Storing Mode 776 An Address re-Registration is performed by the 6LN to maintain the 777 NCE in the 6LR alive before lifetime expires. Upon an Address re- 778 Registration, as illustrated in Figure 6, the 6LR redistributes the 779 Registered Address NS(EARO) in RPL. 781 6LN 6LR Root 6LBR 782 | | | | 783 | NS(EARO) | | | 784 |--------------->| | 785 | | DAO | | 786 | |------------->| | 787 | | | (keep-alive) EDAR | 788 | | |------------------>| 789 | | | EDAC | 790 | | |<------------------| 791 | | DAO-ACK | | 792 | |<-------------| | 793 | NA(EARO) | | | 794 |<---------------| | | 796 Figure 6: Next Registration Flow in Non-Storing Mode 798 This causes the RPL DODAG Root to refresh the state in the 6LBR with 799 an EDAC message or a keep-alive EDAC if the ROVR is not indicated in 800 the Target Option. In any case, the EDAC message sent in response by 801 the 6LBR contains the actual value of the ROVR field for that Address 802 Registration. In case of an error on the proxied EDAR flow, the 803 error SHOULD be returned in the DAO-ACK - if one was requested - 804 using a RPL Status with the 'A' flag set that imbeds a 6LoWPAN Status 805 value as discussed in Section 7. 807 If the Root could not return the negative Status in the DAO-ACK then 808 it sends an asynchronous Destination Cleanup Object (DCO) message 809 [EFFICIENT-NPDAO] to the 6LR placing the negative Status in the RPL 810 Status with the 'A' flag set. Note that if both are used in a short 811 interval of time, the DAO-ACK and DCO messages are not guaranteed to 812 arrive in the same order at the 6LR. 814 The 6LR may still receive a requested DAO-ACK even after it received 815 a DCO, but the negative Status in the DCO supercedes a positive 816 Status in the DAO-ACK regardless of the order in which they are 817 received. Upon the DAO-ACK - or the DCO if it arrives first - the 818 6LR responds to the RUL with a NA(EARO). If the RPL Status has the 819 'A' flag set, then the ND Status is extracted and passed in the EARO; 820 else, if the 'E' flag is set, indicating a rejection, then the status 821 4 "Removed" is used; else, the ND Status of 0 indicating "Success" is 822 used. 824 9.1.2. In RPL Storing-Mode 826 In RPL Storing Mode, the DAO-ACK is optional. When it is used, it is 827 generated by the RPL parent, which does not need to wait for the 828 grand-parent to send the acknowledgement. A successful DAO-ACK is 829 not a guarantee that the DAO has yet reached the Root or that the 830 keep-alive EDAR has succeeded. 832 6LN 6LR 6LR Root 6LBR 833 | | | | | 834 | NS(EARO) | | | | 835 |-------------->| | | | 836 | NA(EARO) | | | | 837 |<--------------| | | | 838 | | | | | 839 | | DAO | | | 840 | |-------------->| | | 841 | | DAO-ACK | | | 842 | |<--------------| | | 843 | | | | | 844 | | | DAO | | 845 | | |-------------->| | 846 | | | DAO-ACK | | 847 | | |<--------------| | 848 | | | | | 849 | | | | keep-alive EDAR | 850 | | | |---------------->| 851 | | | | EDAC(ROVR) | 852 | | | |<----------------| 853 | | | | | 854 (in case if an Error) 855 | | | | | 856 | | DCO | | 857 | |<------------------------------| | 858 | NA(EARO) | | | | 859 |<--------------| | | | 860 | | | | | 862 Figure 7: Next Registration Flow in Storing Mode 864 If the keep alive fails, the path is cleaned up asynchronously using 865 a DCO message [EFFICIENT-NPDAO] as illustrated in Figure 7 and 866 described in further details in Section 9.2.3. 868 9.2. Detailed Operation 869 9.2.1. By the 6LN 871 This specification does not alter the operation of a 6LoWPAN ND- 872 compliant 6LN, and a RUL is expected to operate as follows: 874 * The 6LN obtains an IPv6 global address, for instance using 875 autoconfiguration [RFC4862] based on a Prefix Information Option 876 (PIO) [RFC4861] found in a Router Advertisement message or by some 877 other means such as DHCPv6 [RFC3315]. 879 * Once it has formed an address, the 6LN (re)registers its address 880 periodically, within the Lifetime of the previous Address 881 Registration, as prescribed by [RFC6775] and [RFC8505]. 883 * A 6LN acting as a RUL sets the "R" flag in the EARO whereas a 6LN 884 acting as a RAN does not set the "R" flag as prescribed by 885 [RFC8505] section 5.1. 887 * Upon each consecutive Address Registration, the 6LN increases the 888 TID field in the EARO, as prescribed by [RFC8505] section 5.2. 890 * The 6LN can register to more than one 6LR at the same time. In 891 that case, it MUST use the same value of TID for all of the 892 parallel Address Registrations. 894 * The 6LN may use any of the 6LRs to which it register to forward 895 its packets. Using a 6LR to which the 6LN is not registered may 896 result in packets dropped at the 6LR by a Source Address 897 Validation function (SAVI). 899 Even without support for RPL, a RUL may be aware of opaque values to 900 be provided to the routing protocol. If the RUL has a knowledge of 901 the RPL Instance the packet should be injected into, then it SHOULD 902 set the Opaque field in the EARO to the RPLInstanceID, else it MUST 903 leave the Opaque field to zero. 905 Regardless of the setting of the Opaque field, the 6LN MUST set the 906 "I" field to zero to signal "topological information to be passed to 907 a routing process" as specified in section 5.1 of [RFC8505]. 909 A RUL is not expected to produce RPL artifacts in the data packets, 910 but it MAY do so. for instance, if the RUL has a minimal awareness of 911 the RPL Instance and can build an RPI. A RUL that places an RPI in a 912 data packet MUST indicate the RPLInstanceID that corresponds to the 913 RPL Instance the packet should be injected into. All the flags and 914 the Rank field are set to zero as specified by section 11.2 of 915 [RFC6550]. 917 9.2.2. By the 6LR 919 Also as prescribed by [RFC8505], the 6LR generates a DAR message upon 920 reception of a valid NS(EARO) message for the Address Registration of 921 a new IPv6 Address by a 6LN. If the Duplicate Address exchange 922 succeeds, then the 6LR installs an NCE. If the "R" flag was set in 923 the EARO of the NS message, and this 6LR can manage the reachability 924 of Registered Address, then the 6LR sets the "R" flag in the EARO of 925 the NA message that is sent in response. 927 From then on, the 6LN periodically sends a new NS(EARO) to refresh 928 the NCE state before the lifetime indicated in the EARO expires, with 929 TID that is incremented each time till it wraps in a lollipop fashion 930 (see section 5.2.1 of [RFC8505] which is fully compatible with 931 section 7.2 of [RFC6550]). As long as the R flag is set and this 932 Router can still manage the reachability of Registered Address, the 933 6LR keeps setting the "R" flag in the EARO of the response NA 934 message, but the exchange of Extended Duplicate Address messages is 935 skipped. 937 The Opaque field in the EARO hints the 6LR on the RPL Instance that 938 should be used for the DAO advertisements, and for the forwarding of 939 packets sourced at the registered address when there is no RPI in the 940 packet, in which case the 6LR MUST enacapsulate the packet to the 941 Root adding an RPI in the outer header. if the "I" field is not 942 zero, then the 6LR MUST consider that the Opaque field is zero. If 943 the Opaque field is not set to zero, then it should carry a 944 RPLInstanceID for the Instance suggested by the 6LN. If the 6LR does 945 not participate to the associated Instance, then the 6LR MUST 946 consider that the Opaque field is zero. If the Opaque field is zero, 947 the 6LR is free to use the default RPL Instance (zero) for the 948 registered address or to select an Instance of its choice; else, that 949 is if the 6LR participates to the suggested Instance, then the 6LR 950 SHOULD use that Instance for the registered address. 952 The DAO message advertising the Registered Address MUST be 953 constructed as follows: 955 * The Registered Address is placed in a RPL Target Option in the DAO 956 message as the Target Prefix, and the Prefix Length is set to 128; 958 * RPL Non-Storing Mode is used, and the 6LR indicates one of its 959 global IPv6 unicast addresses as the Parent Address in the RPL 960 Transit Information Option (TIO) associated to the Target Option. 962 * the External 'E' flag in the TIO is set to indicate that the 6LR 963 redistributes an external target into the RPL network. 965 * the Path Lifetime in the TIO is computed from the Lifetime in the 966 EARO Option to adapt it to the Lifetime Units used in the RPL 967 operation. Note that if the lifetime is 0, then the 6LR generates 968 a No-Path DAO message that cleans up the routes down to the 969 Address of the 6LN; 971 * the Path Sequence in the TIO is set to the TID value found in the 972 EARO option; 974 Upon a successful NS/NA(EARO) exchange: if the "R" flag was set in 975 the EARO of the NS message, then the 6LR SHOULD inject the Registered 976 Address in RPL by sending a DAO message on behalf of the 6LN; else 977 the 6LR MUST NOT inject the Registered Address into RPL. 979 If a DAO-ACK is not requested, or has a Status that is not a 980 rejection, indicating the DAO was accepted respectively by a parent 981 in Storing Mode or by the Root in non-Storing Mode, the 6LR replies 982 with a NA(EARO) to the RUL with a Status of 0 (Success). 984 In case of a DAO-ACK or a DCO indicating a rejection and transporting 985 an EARO Status Value of 5 (Validation Requested) the 6LR challenges 986 the 6LN for ownership of the address, as described in section 6.1 of 987 [RFC8505]. If the challenge succeeds then the operations continue as 988 normal. In particular a DAO message is generated upon the NS(EARO) 989 that proves the ownership of the address. If the challenge failed 990 the 6LR MUST refrain from injecting the address in RPL and may take 991 actions to protect itself against DoS attacks by a rogue 6LN, see 992 Section 11 994 The other rejection codes indicate that the 6LR failed to inject the 995 address into the RPL network. If an EARO Status is transported, the 996 6LR MUST send a NA(EARO) to the RUL with that Status value. If for 997 any other reason the 6LR fails to inject the address into the RPL 998 network, the 6LR SHOULD send a NA(EARO) to the RUL with a Status of 2 999 (Out of Storage) which indicates a possibility to retry later. 1000 Similarly, upon a DCO message indicating that the address of a RUL 1001 should be removed from the routing table, the 6LR issues an 1002 asynchronous NA(EARO) to the RUL with the embedded ND Status value. 1004 If a 6LR receives a valid NS(EARO) message with the "R" flag reset 1005 and the 6LR was redistributing the Registered Address due to previous 1006 NS(EARO) messages with the flag set, then it MUST stop injecting the 1007 address. It is up to the Registering Node to maintain the 1008 corresponding route from then on, either keeping it active by sending 1009 further DAO messages, or destroying it using a No-Path DAO. 1011 9.2.3. By the RPL Root 1013 In RPL Storing Mode of Operation (MOP), the DAO message is propagated 1014 from child to parent all the way to the Root along the DODAG, 1015 populating routing state as it goes. In Non-Storing Mode, The DAO 1016 message is sent directly to the RPL Root. Upon reception of a DAO 1017 message, for each RPL Target option that creates or updates an 1018 existing RPL state: 1020 * the Root notifies the 6LBR using an internal API if they are co- 1021 located, or performs an EDAR/EDAC exchange on behalf of the 6LR if 1022 they are separated. If the Target option transports a ROVR, then 1023 the Root MUST use it to build a full EDAR message as the 6LR 1024 would. Else, a keep-alive EDAR is used with the ROVR field set to 1025 zero. 1027 An EDAR message MUST be constructed as follows: 1029 * The Target IPv6 address from in the RPL Target Option is placed in 1030 the Registered Address field of the EDAR message and in the Target 1031 field of the NS message, respectively; 1033 * the Registration Lifetime is adapted from the Path Lifetime in the 1034 TIO by converting the Lifetime Units used in RPL into units of 60 1035 seconds used in the 6LoWPAN ND messages; 1037 * the RPL Root indicates its own MAC Address as Source Link Layer 1038 Address (SLLA) in the NS(EARO); 1040 * the TID value is set to the Path Sequence in the TIO and indicated 1041 with an ICMP code of 1 in the EDAR message; 1043 * when present in the RPL Target option, the ROVR field is used as 1044 is in the EDAR and the ICMP Code Suffix is set to the appropriate 1045 value as shown in Table 4 of [RFC8505] depending on the length of 1046 the ROVR field. If it is not present the ROVR field in the EDAR 1047 is set to zero indicating that this is a keep-alive EDAR. 1049 Upon a Status value in an EDAC message that is not "Success", the 1050 Root SHOULD destroy the formed paths using either a DAO-ACK (in Non- 1051 Storing Mode) or a DCO downwards as specified in [EFFICIENT-NPDAO]. 1052 Failure to destroy the former path would result in Stale routing 1053 state and local black holes if the address belongs to another party 1054 elsewhere in the network. The RPL Status value that maps the 6LowpAN 1055 ND Status value MUST be placed in the DCO. 1057 9.2.4. By the 6LBR 1059 Upon reception of an EDAR message with the ROVR field is set to zero 1060 indicating a keep-alive EDAR, the 6LBR checks whether an entry exists 1061 for the and computes whether the TID in the DAR message is fresher 1062 than that in the entry as prescribed in section 4.2.1. of [RFC8505]. 1064 If the entry does not exist, the 6LBR does not create the entry, and 1065 answers with a Status "Removed" in the EDAC message. 1067 If the entry exists but is not fresher, the 6LBR does not update the 1068 entry, and answers with a Status "Success" in the EDAC message. 1070 If the entry exists and the TID in the DAR message is fresher, the 1071 6LBR updates the TID in the entry, and if the lifetime of the entry 1072 is extended by the Registration Lifetime in the DAR message, it also 1073 updates the lifetime of the entry. In that case, the 6LBR replies 1074 with a Status "Success" in the DAC message. 1076 The EDAC that is constructed is the same as if the keep-alive EDAR 1077 was a full EDAR, and includes the ROVR that is associated to the 1078 Address Registration. 1080 10. Protocol Operations for Multicast Addresses 1082 Section 12 of [RFC6550] details the RPL support for multicast flows. 1083 This support is not source-specific and only operates as an extension 1084 to the Storing Mode of Operation for unicast packets. Note that it 1085 is the RPL model that the multicast packet is passed as a Layer-2 1086 unicast to each if the interested children. This remains true when 1087 forwarding between the 6LR and the listener 6LN. 1089 "Multicast Listener Discovery (MLD) for IPv6" [RFC2710] and its 1090 updated version "Multicast Listener Discovery Version 2 (MLDv2) for 1091 IPv6" [RFC3810] provide an interface for a listener to register to 1092 multicast flows. MLDv2 is backwards compatible with MLD, and adds in 1093 particular the capability to filter the sources via black lists and 1094 white lists. In the MLD model, the Router is a "querier" and the 1095 Host is a multicast listener that registers to the querier to obtain 1096 copies of the particular flows it is interested in. 1098 On the first Address Registration, as illustrated in Figure 8, the 1099 6LN, as an MLD listener, sends an unsolicited Report to the 6LR in 1100 order to start receiving the flow immediately. Since multicast 1101 Layer-2 messages are avoided, it is important that the asynchronous 1102 messages for unsolicited Report and Done are sent reliably, for 1103 instance using an Layer-2 acknoledgement, or attempted multiple 1104 times. 1106 The 6LR acts as a generic MLD querier and generates a DAO for the 1107 multicast target. The lifetime of the DAO is set to be in the order 1108 of the Query Interval, yet larger to account for variable propagation 1109 delays. 1111 The Root proxies the MLD echange as listener with the 6LBR acting as 1112 the querier, so as to get packets from a source external to the RPL 1113 domain. Upon a DAO with a multicast target, the RPL Root checks if 1114 it is already registered as a listener for that address, and if not, 1115 it performs its own unsolicited Report for the multicast target. 1117 6LN 6LR Root 6LBR 1118 | | | | 1119 | unsolicited Report | | | 1120 |------------------->| | | 1121 | | | | 1122 | | DAO | | 1123 | |-------------->| | 1124 | | DAO-ACK | | 1125 | |<--------------| | 1126 | | | | 1127 | | | unsolicited Report | 1128 | | |------------------->| 1129 | | | | 1130 | | | | 1132 Figure 8: First Multicast Registration Flow 1134 An Address re-Registration is pulled by 6LR acting as querier. Note 1135 that the message may be sent unicast to all the known individual 1136 listeners. Upon a time out of the Query Interval, the 6LR sends a 1137 Query to each of its listeners, and gets a Report back that is mapped 1138 into a DAO, as illustrated in Figure 9: 1140 6LN 6LR Root 6LBR 1141 | | | | 1142 | Query | | | 1143 |<-------------------| | | 1144 | Report | | | 1145 |------------------->| | | 1146 | | DAO | | 1147 | |-------------->| | 1148 | | DAO-ACK | | 1149 | |<--------------| | 1150 | | | | 1151 | | | Query | 1152 | | |<-------------------| 1153 | | | Report | 1154 | | |------------------->| 1155 | | | | 1156 | | | | 1158 Figure 9: Next Registration Flow 1160 Note that any of the functions 6LR, Root and 6LBR might be collapsed 1161 in a single node, in which case the flow above happens internally, 1162 and possibly through internal API calls as opposed to messaging. 1164 11. Security Considerations 1166 The LLN nodes depend on the 6LBR and the RPL participants for their 1167 operation. A trust model must be put in place to ensure that the 1168 right devices are acting in these roles, so as to avoid threats such 1169 as black-holing, (see [RFC7416] section 7) or bombing attack whereby 1170 an impersonated 6LBR would destroy state in the network by using the 1171 "Removed" Status code. This trust model could be at a minimum based 1172 on a Layer-2 access control, or could provide role validation as 1173 well. This is a generic 6LoWPAN requirement, see Req5.1 in 1174 Appendix of [RFC8505]. 1176 The keep-alive EDAR message does not carry a valid Registration 1177 Unique ID [RFC8505] and it cannot be used to create a binding state 1178 in the 6LBR. The 6LBR MUST NOT create an entry based on a keep-alive 1179 EDAR that does not match an existing entry. All it can do is refresh 1180 the lifetime and the TID of an existing entry. 1182 At the time of this writing RPL does not have a zerotrust model 1183 whereby the it is possible to validate the origin of an address that 1184 is injected in a DAO. This specification makes a first step in that 1185 direction by allowing the Root to challenge the RUL by the 6LR that 1186 serves it. 1188 12. IANA Considerations 1190 12.1. New DODAG Configuration Option Flag 1192 This specification updates the Registry for the "DODAG Configuration 1193 Option Flags" that was created for [RFC6550] as follows: 1195 +------------+----------------------------+-----------+ 1196 | Bit Number | Capability Description | Reference | 1197 +============+============================+===========+ 1198 | 1 | Root Proxies EDAR/EDAC (P) | THIS RFC | 1199 +------------+----------------------------+-----------+ 1201 Table 2: New DODAG Configuration Option Flag 1203 12.2. RPL Target Option Flags 1205 Section 20.15 of [RFC6550] creates a registry for the 8-bit RPL 1206 Target Option Flags field. This specification reduces the field to 4 1207 bits. The IANA is requested to reduce the size of the registry 1208 accordingly. 1210 12.3. New Subregistry for the RPL Non-Rejection Status values 1212 This specification creates a new Subregistry for the RPL Non- 1213 Rejection Status values for use in RPL DAO-ACK and RCO Messages, 1214 under the ICMPv6 parameters registry. 1216 * Possible values are 6-bit unsigned integers (0..63). 1218 * Registration procedure is "Standards Action" [RFC8126]. 1220 * Initial allocation is as indicated in Table 3: 1222 +-------+------------------------+-----------+ 1223 | Value | Meaning | Reference | 1224 +=======+========================+===========+ 1225 | 0 | Unqualified acceptance | RFC 6550 | 1226 +-------+------------------------+-----------+ 1228 Table 3: Acceptance values of the RPL Status 1230 12.4. New Subregistry for the RPL Rejection Status values 1232 This specification creates a new Subregistry for the RPL Rejection 1233 Status values for use in RPL DAO-ACK and RCO Messages, under the 1234 ICMPv6 parameters registry. 1236 * Possible values are 6-bit unsigned integers (0..63). 1238 * Registration procedure is "Standards Action" [RFC8126]. 1240 * Initial allocation is as indicated in Table 4: 1242 +-------+-----------------------+---------------+ 1243 | Value | Meaning | Reference | 1244 +=======+=======================+===============+ 1245 | 0 | Unqualified rejection | This document | 1246 +-------+-----------------------+---------------+ 1248 Table 4: Rejection values of the RPL Status 1250 13. Acknowledgments 1252 The authors wish to thank Georgios Papadopoulos for their early 1253 reviews of and contributions to this document 1255 14. Normative References 1257 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1258 Requirement Levels", BCP 14, RFC 2119, 1259 DOI 10.17487/RFC2119, March 1997, 1260 . 1262 [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast 1263 Listener Discovery (MLD) for IPv6", RFC 2710, 1264 DOI 10.17487/RFC2710, October 1999, 1265 . 1267 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1268 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1269 DOI 10.17487/RFC3810, June 2004, 1270 . 1272 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1273 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1274 Overview, Assumptions, Problem Statement, and Goals", 1275 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1276 . 1278 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1279 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1280 DOI 10.17487/RFC4861, September 2007, 1281 . 1283 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1284 Address Autoconfiguration", RFC 4862, 1285 DOI 10.17487/RFC4862, September 2007, 1286 . 1288 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1289 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1290 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1291 Low-Power and Lossy Networks", RFC 6550, 1292 DOI 10.17487/RFC6550, March 2012, 1293 . 1295 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1296 Power and Lossy Networks (RPL) Option for Carrying RPL 1297 Information in Data-Plane Datagrams", RFC 6553, 1298 DOI 10.17487/RFC6553, March 2012, 1299 . 1301 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1302 Bormann, "Neighbor Discovery Optimization for IPv6 over 1303 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1304 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1305 . 1307 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 1308 IPv6 over Low-Power Wireless Personal Area Networks 1309 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 1310 2014, . 1312 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1313 Writing an IANA Considerations Section in RFCs", BCP 26, 1314 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1315 . 1317 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1318 "IPv6 over Low-Power Wireless Personal Area Network 1319 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1320 April 2017, . 1322 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1323 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1324 May 2017, . 1326 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1327 (IPv6) Specification", STD 86, RFC 8200, 1328 DOI 10.17487/RFC8200, July 2017, 1329 . 1331 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1332 Perkins, "Registration Extensions for IPv6 over Low-Power 1333 Wireless Personal Area Network (6LoWPAN) Neighbor 1334 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1335 . 1337 [AP-ND] Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 1338 "Address Protected Neighbor Discovery for Low-power and 1339 Lossy Networks", Work in Progress, Internet-Draft, draft- 1340 ietf-6lo-ap-nd-13, 6 January 2020, 1341 . 1343 [USEofRPLinfo] 1344 Robles, I., Richardson, M., and P. Thubert, "Using RPI 1345 Option Type, Routing Header for Source Routes and IPv6-in- 1346 IPv6 encapsulation in the RPL Data Plane", Work in 1347 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-34, 1348 20 January 2020, . 1351 [EFFICIENT-NPDAO] 1352 Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient 1353 Route Invalidation", Work in Progress, Internet-Draft, 1354 draft-ietf-roll-efficient-npdao-17, 30 October 2019, 1355 . 1358 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1359 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1360 2014, . 1362 15. Informative References 1364 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1365 Statement and Requirements for IPv6 over Low-Power 1366 Wireless Personal Area Network (6LoWPAN) Routing", 1367 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1368 . 1370 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 1371 C., and M. Carney, "Dynamic Host Configuration Protocol 1372 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 1373 2003, . 1375 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1376 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1377 DOI 10.17487/RFC6282, September 2011, 1378 . 1380 [RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur, 1381 Ed., "Performance Evaluation of the Routing Protocol for 1382 Low-Power and Lossy Networks (RPL)", RFC 6687, 1383 DOI 10.17487/RFC6687, October 2012, 1384 . 1386 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1387 Constrained-Node Networks", RFC 7228, 1388 DOI 10.17487/RFC7228, May 2014, 1389 . 1391 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1392 and M. Richardson, Ed., "A Security Threat Analysis for 1393 the Routing Protocol for Low-Power and Lossy Networks 1394 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1395 . 1397 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1398 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1399 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1400 . 1402 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node 1403 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504, 1404 January 2019, . 1406 Appendix A. Example Compression 1408 Figure 10 illustrates the case in Storing Mode where the packet is 1409 received from the Internet, then the Root encapsulates the packet to 1410 insert the RPI and deliver to the 6LR that is the parent and last hop 1411 to the final destination, which is not known to support [RFC8138]. 1412 The difference with the format presented in Figure 19 of [RFC8138] is 1413 the addition of a SRH-6LoRH before the RPI-6LoRH to transport the 1414 destination address of the outer IPv6 header. 1416 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1417 |11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP 1418 |Page 1 |Type1 S=0| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 1419 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1420 <-4bytes-> <- RFC 6282 -> 1421 No RPL artifact 1423 Figure 10: Encapsulation to Parent 6LR in Storing Mode 1425 In Figure 10, the source of the IP-in-IP encapsulation is the Root, 1426 so it is elided in the IP-in-IP 6LoRH. The destination is the parent 1427 6LR of the destination of the inner packet so it cannot be elided. 1429 In Storing Mode, it is placed as the single entry in an SRH-6LoRH as 1430 the first 6LoRH. Since there is a single entry so the SRH-6LoRH Size 1431 is 0. In this particular example, the 6LR address can be compressed 1432 to 2 bytes so a Type of 1 is used. It results that the total length 1433 of the SRH-6LoRH is 4 bytes. 1435 In Non-Storing Mode, the encapsulation from the Root would be similar 1436 to that represented in Figure 10 with possibly more hops in the SRH- 1437 6LoRH and possibly multiple SRH-6LoRHs if the various addresses in 1438 the routing header are not compressed to the same format. Note that 1439 on the last hop to the parent 6LR, the RH3 is consumed and removed 1440 from the compressed form, so the use of Non-Storing Mode vs. Storing 1441 Mode is indistinguishable from the packet format. 1443 Follows the RPI-6LoRH and then the IP-in-IP 6LoRH. When the IP-in-IP 1444 6LoRH is removed, all the Router headers that precede it are also 1445 removed. 1447 The Paging Dispatch [RFC8025] may also be removed if there was no 1448 previous Page change to a Page other than 0 or 1, since the 1449 LOWPAN_IPHC is encoded in the same fashion in the default Page 0 and 1450 in Page 1. The resulting packet to the destination is the inner 1451 packet compressed with [RFC6282]. 1453 Authors' Addresses 1455 Pascal Thubert (editor) 1456 Cisco Systems, Inc 1457 Building D 1458 45 Allee des Ormes - BP1200 1459 06254 Mougins - Sophia Antipolis 1460 France 1462 Phone: +33 497 23 26 34 1463 Email: pthubert@cisco.com 1465 Michael C. Richardson 1466 Sandelman Software Works 1468 Email: mcr+ietf@sandelman.ca 1469 URI: http://www.sandelman.ca/