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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: 17 October 2020 15 April 2020 8 Routing for RPL Leaves 9 draft-ietf-roll-unaware-leaves-15 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 17 October 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 . . . . . . . . . . . . . . . . . 19 78 9.2. Detailed Operation . . . . . . . . . . . . . . . . . . . 21 79 9.2.1. By the RUL Acting as 6LN . . . . . . . . . . . . . . 21 80 9.2.2. By the RPL Border Router Acting as 6LR . . . . . . . 22 81 9.2.3. By the RPL Root . . . . . . . . . . . . . . . . . . . 24 82 9.2.4. By the 6LBR . . . . . . . . . . . . . . . . . . . . . 25 83 10. Protocol Operations for Multicast Addresses . . . . . . . . . 26 84 11. Security Considerations . . . . . . . . . . . . . . . . . . . 28 85 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 86 12.1. Resizing the ARO Status values . . . . . . . . . . . . . 29 87 12.2. New DODAG Configuration Option Flag . . . . . . . . . . 29 88 12.3. RPL Target Option Flags . . . . . . . . . . . . . . . . 29 89 12.4. New Subregistry for the RPL Non-Rejection Status 90 values . . . . . . . . . . . . . . . . . . . . . . . . . 29 91 12.5. New Subregistry for the RPL Rejection Status values . . 30 92 13. acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 30 93 14. Normative References . . . . . . . . . . . . . . . . . . . . 30 94 15. Informative References . . . . . . . . . . . . . . . . . . . 32 95 Appendix A. Example Compression . . . . . . . . . . . . . . . . 34 96 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35 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, an 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. A RUL is an IPv6 Host [RFC8504] 158 that needs a RPL-Aware Router to obtain routing services over the RPL 159 network. 161 This specification leverages the Address Registration mechanism 162 defined in 6LoWPAN ND to enable a RUL as a 6LoWPAN Node (6LN) to 163 interface with a RPL-Aware Router as a 6LoWPAN Router (6LR) to 164 request that the 6LR injects the relevant routing information for the 165 Registered Address in the RPL domain on its behalf. A RUL may be 166 unable to participate because it is very energy-constrained, or 167 because it is unsafe to let it inject routes in RPL, in which case 168 using 6LowPAN ND as the interface for the RUL limits the surface of 169 the possible attacks and optionally protects the address ownership. 171 The Non-Storing Mode mechanisms are used to extend the routing state 172 with connectivity to RULs even when the DODAG is operated in Storing- 173 Mode DODAGs. The unicast packet forwarding operation by the 6LR 174 serving a 6LN that is a RPL Leaf is described in [USEofRPLinfo]. 176 Examples of routing-agnostic 6LNs include lightly-powered sensors 177 such as window smash sensor (alarm system), and kinetically powered 178 light switches. Other applications of this specification may include 179 a smart grid network that controls appliances - such as washing 180 machines or the heating system - in the home. Appliances may not 181 participate to the RPL protocol operated in the Smartgrid network but 182 can still interact with the Smartgrid for control and/or metering. 184 2. Terminology 186 2.1. BCP 14 188 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 189 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 190 "OPTIONAL" in this document are to be interpreted as described in BCP 191 14 [RFC2119][RFC8174] when, and only when, they appear in all 192 capitals, as shown here. 194 2.2. References 196 The Terminology used in this document is consistent with and 197 incorporates that described in "Terms Used in Routing for Low-Power 198 and Lossy Networks (LLNs)" [RFC7102]. A glossary of classical 199 6LoWPAN acronyms is given in Section 2.3. Other terms in use in LLNs 200 are found in "Terminology for Constrained-Node Networks" [RFC7228]. 202 "RPL", the "RPL Packet Information" (RPI), "RPL Instance" (indexed by 203 a RPLInstanceID) are defined in "RPL: IPv6 Routing Protocol for 204 Low-Power and Lossy Networks" [RFC6550]. The RPI is the abstract 205 information that RPL defines to be placed in data packets, e.g., as 206 the RPL Option [RFC6553] within the IPv6 Hop-By-Hop Header. By 207 extension the term "RPI" is often used to refer to the RPL Option 208 itself. The DODAG Information Solicitation (DIS), Destination 209 Advertisement Object (DAO) and DODAG Information Object (DIO) 210 messages are also specified in [RFC6550]. The Destination Cleanup 211 Object (DCO) message is defined in [EFFICIENT-NPDAO]. 213 This document uses the terms RPL-Unaware Leaf (RUL) and RPL Aware 214 Leaf (RAL) consistently with [USEofRPLinfo]. The term RPL-Aware Node 215 (RAN) is introduced to refer to a node that is either an RAL or a RPL 216 Router. As opposed to a RUL, an RAN manages the reachability of its 217 addresses and prefixes by injecting them in RPL by itself. 219 In this document, readers will encounter terms and concepts that are 220 discussed in the following documents: 222 Classical IPv6 ND: "Neighbor Discovery for IP version 6" [RFC4861] 223 and "IPv6 Stateless Address Autoconfiguration" [RFC4862], 225 6LoWPAN: "Problem Statement and Requirements for IPv6 over Low-Power 226 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606] and 227 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 228 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 229 and 231 6LoWPAN ND: Neighbor Discovery Optimization for Low-Power and Lossy 232 Networks [RFC6775], "Registration Extensions for 6LoWPAN Neighbor 233 Discovery" [RFC8505], and "Address Protected Neighbor Discovery 234 for Low-power and Lossy Networks" [AP-ND] . 236 2.3. Glossary 238 This document often uses the following acronyms: 240 AR: Address Resolution (aka Address Lookup) 241 6CIO: 6LoWPAN Capability Indication Option 243 6LN: 6LoWPAN Node (a Low Power Host or Router) 245 6LR: 6LoWPAN Router 247 (E)ARO: (Extended) Address Registration Option 249 (E)DAR: (Extended) Duplicate Address Request 251 (E)DAC: (Extended) Duplicate Address Confirmation 253 DAD: Duplicate Address Detection 255 DAO: Destination Advertisement Object (a RPL message) 257 DCO: Destination Cleanup Object (a RPL message) 259 DIS: DODAG Information Solicitation (a RPL message) 261 DIO: DODAG Information Object (a RPL message) 263 DODAG: Destination-Oriented Directed Acyclic Graph 265 LLN: Low-Power and Lossy Network 267 NA: Neighbor Advertisement 269 NCE: Neighbor Cache Entry 271 ND: Neighbor Discovery 273 NS: Neighbor Solicitation 275 RA: Router Advertisement 277 ROVR: Registration Ownership Verifier 279 RPI: RPL Packet Information 281 RAL: RPL-Aware Leaf 283 RAN: RPL-Aware Node (either a RPL Router or a RPL-Aware Leaf) 285 RUL: RPL-Unaware Leaf 287 TID: Transaction ID (a sequence counter in the EARO) 289 3. 6LoWPAN Neighbor Discovery 291 3.1. RFC 6775 Address Registration 293 The classical "IPv6 Neighbor Discovery (IPv6 ND) Protocol" [RFC4861] 294 [RFC4862] was defined for transit media such a Ethernet. It is a 295 reactive protocol that relies heavily on multicast operations for 296 address discovery (aka lookup) and duplicate address detection (DAD). 298 "Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775] 299 adapts IPv6 ND for operations over energy-constrained LLNs. The main 300 functions of [RFC6775] are to proactively establish the Neighbor 301 Cache Entry (NCE) in the 6LR and to prevent address duplication. To 302 that effect, [RFC6775] introduces a new unicast Address Registration 303 mechanism that contributes to reducing the use of multicast messages 304 compared to the classical IPv6 ND protocol. 306 [RFC6775] defines a new Address Registration Option (ARO) that is 307 carried in the unicast Neighbor Solicitation (NS) and Neighbor 308 Advertisement (NA) messages between the 6LoWPAN Node (6LN) and the 309 6LoWPAN Router (6LR). It also defines the Duplicate Address Request 310 (DAR) and Duplicate Address Confirmation (DAC) messages between the 311 6LR and the 6LoWPAN Border Router (6LBR). In an LLN, the 6LBR is the 312 central repository of all the Registered Addresses in its domain and 313 the source of truth for uniqueness and ownership. 315 3.2. RFC 8505 Extended Address Registration 317 "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505] 318 updates the behavior of RFC 6775 to enable a generic Address 319 Registration to services such as routing and ND proxy, and defines 320 the Extended Address Registration Option (EARO) as shown in Figure 1: 322 0 1 2 3 323 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 1 324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 325 | Type | Length | Status | Opaque | 326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 | Rsvd | I |R|T| TID | Registration Lifetime | 328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 329 | | 330 ... Registration Ownership Verifier ... 331 | | 332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 334 Figure 1: EARO Option Format 336 3.2.1. R Flag 338 [RFC8505] introduces the "R" flag in the EARO. The Registering Node 339 sets the "R" flag to indicate whether the 6LR should ensure 340 reachability for the Registered Address. If the "R" flag is not set, 341 then the Registering Node handles the reachability of the Registered 342 Address by other means, which means in a RPL network that it is an 343 RAN or that it uses another RPL Router for reachability services. 345 This document specifies how the "R" flag is used in the context of 346 RPL. A 6LN is a RUL that requires reachability services for an IPv6 347 address if and only if it sets the "R" flag in the NS(EARO) used to 348 register the address to a RPL border router acting as 6LR. Upon 349 receiving the NS(EARO), the RPL router generates a DAO message for 350 the Registered Address if and only if the "R" flag is set. 352 3.2.2. TID, I Field and Opaque Fields 354 The EARO also includes a sequence counter called Transaction ID 355 (TID), which maps to the Path Sequence Field found in Transit Options 356 in RPL DAO messages. This is the reason why the support of [RFC8505] 357 by the RUL as opposed to only [RFC6775] is a prerequisite for this 358 specification (more in Section 6.1). The EARO also transports an 359 Opaque field and an "I" field that describes what the Opaque field 360 transports and how to use it. Section 9.2.1 specifies the use of the 361 "I" field and of the Opaque field by a RUL. 363 3.2.3. ROVR 365 Section 5.3. of [RFC8505] introduces the Registration Ownership 366 Verifier (ROVR) field of variable length from 64 to 256 bits. The 367 ROVR is a replacement of the EUI-64 in the ARO [RFC6775] that was 368 used to identify uniquely an Address Registration with the Link-Layer 369 address of the owner, but provided no protection against spoofing. 371 "Address Protected Neighbor Discovery for Low-power and Lossy 372 Networks" [AP-ND] leverages the ROVR field as a cryptographic proof 373 of ownership to prevent a rogue third party from misusing the 374 address. [AP-ND] adds a challenge/response exchange to the [RFC8505] 375 Address Registration and enables Source Address Validation by a 6LR 376 that will drop packets with a spoofed address. 378 This specification does not address how the protection by [AP-ND] 379 could be extended to RPL. On the other hand, it adds the ROVR to the 380 DAO to build the proxied EDAR at the Root (see Section 8), which 381 means that nodes that are aware of the Host route to the 6LN are made 382 aware of the associated ROVR as well. 384 3.3. RFC 8505 Extended DAR/DAC 386 [RFC8505] updates the periodic DAR/DAC exchange that takes place 387 between the 6LR and the 6LBR using Extended DAR/DAC messages which 388 can carry a ROVR field of variable size. The exchange is triggered 389 by an NS(EARO) message and is intended to create, refresh and delete 390 the corresponding state in the 6LBR for a lifetime that is indicated 391 by the 6LN. It is protected by the ARQ mechanism specified in 8.2.6 392 of [RFC6775], though in an LLN, a duration longer than the 393 RETRANS_TIMER [RFC4861] of 1 second may be necessary to cover the 394 Turn Around Trip delay from the 6LR to the 6LBR. 396 RPL [RFC6550] specifies a periodic DAO from the 6LN all the way to 397 the Root that maintains the routing state in the RPL network for the 398 lifetime indicated by the source of the DAO. This means that for 399 each address, there are two keep-alive messages that traverse the 400 whole network, one to the Root and one to the 6LBR. 402 This specification removes the extraneous keep-alive across the LLN. 403 The 6LR turns the periodic Address Registration from the RUL into a 404 DAO message to the Root on every refresh, but it only generates the 405 EDAR upon the first registration, for the purpose of DAD. Upon a 406 refresher DAO, the Root proxies the EDAR exchange to refresh the 407 state at the 6LBR on behalf of the 6LR, as illustrated in Figure 7. 409 3.3.1. RFC 7400 Capability Indication Option 411 "6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power 412 Wireless Personal Area Networks (6LoWPANs)" [RFC7400] defines the 413 6LoWPAN Capability Indication Option (6CIO) that enables a node to 414 expose its capabilities in Router Advertisement (RA) messages. 415 [RFC8505] defines a number of bits in the 6CIO, in particular: 417 L: Node is a 6LR. 418 E: Node is an IPv6 ND Registrar -- i.e., it supports registrations 419 based on EARO. 420 P: Node is a Routing Registrar, -- i.e., an IPv6 ND Registrar that 421 also provides reachability services for the Registered Address. 423 0 1 2 3 424 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 1 425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 426 | Type | Length = 1 | Reserved |D|L|B|P|E|G| 427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 428 | Reserved | 429 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 431 Figure 2: 6CIO flags 433 A 6LR that can provide reachability services for a RUL in a RPL 434 network as specified in this document SHOULD include a 6CIO in its RA 435 messages and set the L, P and E flags as prescribed by [RFC8505], see 436 Section 6.1 for the behavior of the RUL. 438 4. Updating RFC 6550 440 This document specifies a new behavior whereby a 6LR injects DAO 441 messages for unicast addresses (see Section 9) and multicast 442 addresses (see Section 10) on behalf of leaves that are not aware of 443 RPL. The addresses are exposed as external targets [RFC6550]. Per 444 [USEofRPLinfo], an IP-in-IP encapsulation that terminates at the RPL 445 Root is used to remove RPL artifacts and compression techniques that 446 may not be processed correctly outside of the RPL domain. 448 This document also synchronizes the liveness monitoring at the Root 449 and the 6LBR. A same value of lifetime is used for both, and a 450 single keep-alive message, the RPL DAO, traverses the RPL network. A 451 new behavior is introduced whereby the RPL Root proxies the EDAR 452 message to the 6LBR on behalf of the 6LR (more in Section 5), for any 453 6LN, RUL or RAN. 455 RPL defines a configuration option that is registered to IANA in 456 section 20.14. of [RFC6550]. This specification defines a new flag 457 "Root Proxies EDAR/EDAC" (P) that is encoded in one of the reserved 458 control bits in the option. The new flag is set to indicate that the 459 Root performs the proxy operation and that all nodes in the RPL 460 network must refrain from renewing the 6LBR state directly. The bit 461 position of the "P" flag is indicated in Section 12.2. 463 Section 6.3.1. of [RFC6550] defines a 3-bit Mode of Operation (MOP) 464 in the DIO Base Object. The new "P" flag is defined only for MOP 465 value between 0 to 6. For a MOP value of 7 or above, the flag MAY 466 indicate something different and MUST NOT be interpreted as "Root 467 Proxies EDAR/EDAC" unless the specification of the MOP indicates to 468 do so. 470 The RPL Status defined in section 6.5.1. of [RFC6550] for use in the 471 DAO-Ack message is extended to be used in the DCO messages 472 [EFFICIENT-NPDAO] as well. Furthermore, this specification enables 473 to use a RPL Status to transport the IPv6 ND Status defined for use 474 in the EARO, more in Section 7. 476 Section 6.7. of [RFC6550] introduces the RPL Control message Options 477 such as the RPL Target Option that can be included in a RPL Control 478 message such as the DAO. Section 8 updates the RPL Target Option to 479 optionally transport the ROVR used in the IPv6 Registration (see 480 Section 3.2.3) so the RPL Root can generate a full EDAR message. 482 5. Updating RFC 8505 484 This document updates [RFC8505] to introduce the anonymous EDAR and 485 NS(EARO) messages. The anonymous messages are used for backward 486 compatibility. The anonymous messages are recognizable by a zero 487 ROVR field and can only be used as a refresher for a pre-existing 488 state associated to the Registered Address. More specifically, an 489 anonymous message can only increase the lifetime and/or increment the 490 TID of an existing state at the 6LBR. 492 Upon the renewal of a 6LoWPAN ND Address Registration, this 493 specification changes the behavior of a RPL Router acting as 6LR for 494 the registration. If the Root indicates the capability to proxy the 495 EDAR/EDAC exchange to the 6LBR then the 6LR refrains from sending an 496 EDAR message; if the Root is separated from the 6LBR, the Root 497 regenerates the EDAR message to the 6LBR upon a DAO message that 498 signals the liveliness of the Address. The regenerated message is 499 anonymous iff the DAO is a legacy message that does not carry a ROVR 500 as specified in Section 8. 502 6. Requirements on the RPL-Unware Leaf 504 This document provides RPL routing for a RUL, that is a 6LN acting as 505 an IPv6 Host and not aware of RPL. Still, a minimal RPL-independent 506 functionality is required from the RUL to obtain routing services. 508 6.1. Support of 6LoWPAN ND 510 In order to obtain routing services from a 6LR, a RUL MUST implement 511 [RFC8505] and set the "R" flag in the EARO. The RUL SHOULD support 512 [AP-ND] and use it to protect the ownership of its addresses. The 513 RUL MUST NOT request routing services from a 6LR that does not 514 originate RA messages with a CIO that has the L, P, and E flags all 515 set as discussed in Section 3.3.1. 517 A RUL that has multiple potential routers MUST prefer those that 518 provide routing services. The RUL MUST register to all the 6LRs from 519 which it desires routing services. If there are no available 520 routers, the connection of the RUL fails. The Address Registrations 521 SHOULD be performed in an RApid sequence, using the exact same EARO 522 for a same Address. Gaps between the Address Registrations will 523 invalidate some of the routes till the Address Registration finally 524 shows on those routes as well. 526 [RFC8505] introduces error Status values in the NA(EARO) which can be 527 received synchronously upon an NS(EARO) or asynchronously. The RUL 528 MUST support both cases and MUST refrain from using the address when 529 the Status value indicates a rejection. 531 6.2. External Routes and RPL Artifacts 533 Section 4.1. of [USEofRPLinfo] provides a set of rules that MUST be 534 followed for the routing operations to a RUL. 536 A 6LR that is upgraded to act as a border router for external routes 537 advertises them using Non-Storing Mode DAO messages that are unicast 538 directly to the Root, even if the DODAG is operated in Storing Mode. 539 Non-Storing Mode routes are not visible inside the RPL domain and all 540 packets are routed via the Root. An upgraded Root tunnels the 541 packets directly to the 6LR that advertised the external route which 542 decapsulates and forwards the original (inner) packet. 544 The RPL Non-Storing Mode signaling and the associated IP-in-IP 545 encapsulated packets are normal traffic for the intermediate Routers. 546 The support of external routes only impacts the Root and the 6LR. It 547 can be operated with legacy intermediate routers and does not add to 548 the amount of state that must be maintained in those routers. A RUL 549 is an example of a destination that is reachable via an external 550 route which happens to be a Host route. 552 The RPL data packets always carry a Hop-by-Hop Header to transport a 553 RPL Packet Information (RPI) [RFC6550]. So unless the RUL originates 554 its packets with an RPI, the 6LR needs to tunnel them to the Root to 555 add the RPI. As a rule of a thumb and except for the very special 556 case above, the packets from and to a RUL are always encapsulated 557 using an IP-in-IP tunnel between the Root and the 6LR that serves the 558 RUL (see sections 7.1.4, 7.2.3, 7.2.4, 7.3.3, 7.3.4, 8.1.3, 8.1.4, 559 8.2.3, 8.2.4, 8.3.3 and 8.3.4 of [USEofRPLinfo] for details). 561 In Non-Storing Mode, packets going down carry a Source Routing Header 562 (SRH). The IP-in-IP encapsulation, the RPI and the SRH are 563 collectively called the "RPL artifacts" and can be compressed using 564 [RFC8138]. Figure 14 presents an example compressed format for a 565 packet forwarded by the Root to a RUL in a Storing Mode DODAG. 567 The inner packet that is forwarded to the RUL may carry some RPL 568 artifacts, e.g., an RPI if the original packet was generated with it 569 and possibly an SRH in a Non-Storing Mode DODAG. [USEofRPLinfo] 570 expects the RUL to support the basic "IPv6 Node Requirements" 571 [RFC8504]. In particular the RUL is expected to ignore the RPL 572 artifacts that are either consumed or not applicable to a Host. 574 A RUL is not expected to support the compression method defined in 575 [RFC8138]. Unless configured otherwise, the border router MUST 576 uncompress the outgoing packet before forwarding over an external 577 route, even if it is not the destination of the incoming packet, and 578 even when delivering to a RUL. 580 6.2.1. Support of IPv6 Encapsulation 582 Section 2.1 of [USEofRPLinfo] sets the rules for forwarding IP-in-IP 583 either to the final 6LN or to a parent 6LR. In order to enable IP- 584 in-IP to the 6LN in Non-Storing Mode, the 6LN must be able to 585 decapsulate the tunneled packet and either drop the inner packet if 586 it is not the final destination, or pass it to the upper layer for 587 further processing. Unless it is aware that the RUL can handle IP- 588 in-IP properly, the Root that encapsulates a packet to a RUL 589 terminates the IP-in-IP tunnel at the parent 6LR . For that reason, 590 it is beneficial but not necessary for a RUL to support IP-in-IP. 592 6.2.2. Support of the HbH Header 594 A RUL is expected to process an unknown Option Type in a Hop-by-Hop 595 Header as prescribed by section 4.2 of [RFC8200]. This means in 596 particular that an RPI with an Option Type of 0x23 [USEofRPLinfo] is 597 ignored when not understood. 599 6.2.3. Support of the Routing Header 601 A RUL is expected to process an unknown Routing Header Type as 602 prescribed by section 4.4 of [RFC8200]. This means in particular 603 that Routing Header with a Routing Type of 3 [RFC6554] is ignored 604 when the Segments Left is zero, and the packet is dropped otherwise. 606 7. Updated RPL Status 608 The RPL Status is defined in section 6.5.1. of [RFC6550] for use in 609 the DAO-Ack message and values are assigned as follows: 611 +---------+--------------------------------+ 612 | Range | Meaning | 613 +=========+================================+ 614 | 0 | Success/Unqualified acceptance | 615 +---------+--------------------------------+ 616 | 1-127 | Not an outright rejection | 617 +---------+--------------------------------+ 618 | 128-255 | Rejection | 619 +---------+--------------------------------+ 621 Table 1: RPL Status per RFC 6550 623 This specification extends the scope of the RPL Status to be used in 624 RPL DCO messages. Furthermore, this specification enables to carry 625 the IPv6 ND Status values defined for use in the EARO and initially 626 listed in table 1 of [RFC8505] in a RPL Status. 628 Section 12.1 reduces the range of EARO Status values to 0-63 ensure 629 that they fit within a RPL Status as shown in Figure 3. 631 0 632 0 1 2 3 4 5 6 7 633 +-+-+-+-+-+-+-+-+ 634 |E|A| Value | 635 +-+-+-+-+-+-+-+-+ 637 Figure 3: RPL Status Format 639 RPL Status subfields: 641 E: 1-bit flag. Set to indicate a rejection. When not set, a value 642 of 0 indicates Success/Unqualified acceptance and other values 643 indicate "not an outright rejection" as per RFC 6550. 645 A: 1-bit flag. Indicates the type of the Status value. 647 Status Value: 6-bit unsigned integer. If the 'A' flag is set this 648 field transports a Status value defined for IPv6 ND EARO. When 649 the 'A' flag is not set, the Status value is defined in a RPL 650 extension. 652 When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a DAC 653 message, the RPL Root MUST copy the ARO Status unchanged in a RPL 654 Status with the 'A' bit set. The RPL Root MUST set the 'E' flag for 655 all values in range 1-10 which are all considered rejections. 657 Conversely, the 6LR MUST copy the value of the RPL Status unchanged 658 in the EARO of an NA message that is built upon a RPL Status with the 659 'A' bit set in a DCO or a DAO-ACK message. 661 8. Updated RPL Target option 663 This specification updates the RPL Target option to transport the 664 ROVR. This enables the RPL Root to generate a full EDAR message as 665 opposed to an anonymous EDAR that has restricted properties. 667 The Target Prefix field MUST be aligned to the next 4-byte boundary 668 after the size indicated by the Prefix Length. If necessary the 669 transported prefix MUST be padded with zeros. 671 With this specification the ROVR is the remainder of the RPL Target 672 Option. The size of the ROVR is indicated in a new ROVR Size field 673 that is encoded to map one-to-one with the Code Suffix in the EDAR 674 message (see table 4 of [RFC8505]). 676 The modified format is illustrated in Figure 4. It is backward 677 compatible with the Target Option in [RFC6550] and SHOULD be used as 678 a replacement. 680 0 1 2 3 681 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 1 682 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 683 | Type = 0x05 | Option Length |ROVRsz | Flags | Prefix Length | 684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 685 | | 686 + + 687 | Target Prefix (Variable Length) | 688 . Aligned to 4-byte boundary . 689 . . 690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 691 | | 692 ... Registration Ownership Verifier (ROVR) ... 693 | | 694 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 696 Figure 4: Updated Target Option 698 New fields: 700 ROVRsz: Indicates the Size of the ROVR. It MAY be 1, 2, 3, or 4, 701 denoting a ROVR size of 64, 128, 192, or 256 bits, respectively. 703 Registration Ownership Verifier (ROVR): This is the same field as in 704 the EARO, see [RFC8505] 706 9. Protocol Operations for Unicast Addresses 708 The description below assumes that the Root sets the "P" flag in the 709 DODAG Configuration Option and performs the EDAR proxy operation. 711 9.1. General Flow 713 This specification eliminates the need to exchange keep-alive 714 Extended Duplicate Address messages, EDAR and EDAC, all the way from 715 a 6LN to the 6LBR across a RPL mesh. Instead, the EDAR/EDAC exchange 716 with the 6LBR is proxied by the RPL Root upon a DAO message that 717 refreshes the RPL routing state. Any combination of the logical 718 functions of 6LR, Root and 6LBR might be collapsed in a single node. 720 To achieve this, the lifetimes and sequence counters in 6LoWPAN ND 721 and RPL are aligned. In other words, the Path Sequence and the Path 722 Lifetime in the DAO message are taken from the Transaction ID and the 723 Address Registration lifetime in the NS(EARO) message from the 6LN. 725 In a RPL network where the function is enabled, refreshing the state 726 in the 6LBR is the responsibility of the Root. Consequently, only 727 addresses that are injected in RPL will be kept alive by the RPL 728 Root. In a same fashion, if an additional routing protocol is 729 deployed on a same network, that additional routing protocol may need 730 to handle the keep alive procedure for the addresses that it serves. 732 On the first Address Registration, illustrated in Figure 5 for RPL 733 Non-Storing Mode, the Extended Duplicate Address exchange takes place 734 as prescribed by [RFC8505]. If the exchange fails, the 6LR returns 735 an NA message with a negative status to the 6LN, the NCE is not 736 created and the address is not injected in RPL. If it is successful, 737 the 6LR creates an NCE and injects the Registered Address in RPL 738 using DAO/DAO-ACK exchanges all the way to the RPL DODAG Root. 740 The 6LN signals the termination of a registration with a 6LR using an 741 NS(EARO) with a Registration Lifetime set to 0. Upon this, the 6LR 742 MUST perform an EDAR/EDAC exchange to clean up the state at the 6LBR, 743 as illustrated in Figure 8, unless it uses the ROVR in the RPL Target 744 Option and, in Storing Mode, it is propagated to the Root. 746 9.1.1. In RPL Non-Storing-Mode 748 In Non-Storing Mode, the DAO message flow can be nested within the 749 Address Registration flow as illustrated in Figure 5. 751 6LN/RUL 6LR Root 6LBR 752 | | | | 753 | NS(EARO) | | | 754 |--------------->| | 755 | | Extended DAR | 756 | |--------------------------------->| 757 | | | 758 | | Extended DAC | 759 | |<---------------------------------| 760 | | DAO | | 761 | |------------->| | 762 | | | (anonymous) EDAR | 763 | | |------------------>| 764 | | | EDAC | 765 | | |<------------------| 766 | | DAO-ACK | | 767 | |<-------------| | 768 | NA(EARO) | | | 769 |<---------------| | | 770 | | | | 772 Figure 5: First Registration Flow in Non-Storing Mode 774 An issue may be detected later, e.g., the address moves within the 775 LLN or to a different Root on a backbone [6BBR]. In that case the 776 value of the status that indicates the issue can be passed from 777 6LoWPAN ND to RPL and back as illustrated in Figure 6. 779 6LN/RUL 6LR Root 6LBR 780 | | | | 781 | | | NA(EARO, Status) | 782 | | |<-----------------| 783 | | DCO(Status) | | 784 | |<------------| | 785 | NA(EARO, Status) | | | 786 |<-----------------| | | 787 | | | | 789 Figure 6: Asynchronous Issue 791 An Address re-Registration is performed by the 6LN to maintain the 792 NCE in the 6LR alive before lifetime expires. Upon an Address re- 793 Registration, as illustrated in Figure 7, the 6LR redistributes the 794 Registered Address NS(EARO) in RPL. 796 6LN/RUL 6LR Root 6LBR 797 | | | | 798 | NS(EARO) | | | 799 |--------------->| | 800 | | DAO | | 801 | |------------->| | 802 | | | (anonymous) EDAR | 803 | | |------------------>| 804 | | | EDAC | 805 | | |<------------------| 806 | | DAO-ACK | | 807 | |<-------------| | 808 | NA(EARO) | | | 809 |<---------------| | | 811 Figure 7: Next Registration Flow in Non-Storing Mode 813 This causes the RPL DODAG Root to refresh the state in the 6LBR with 814 an EDAC message or an anonymous EDAC if the ROVR is not indicated in 815 the Target Option. In both cases, the EDAC message sent in response 816 by the 6LBR contains the actual value of the ROVR field for that 817 Address Registration. In case of an error on the proxied EDAR flow, 818 the error MUST be returned in the DAO-ACK - if one was requested - 819 using a RPL Status with the 'A' flag set that imbeds a 6LoWPAN Status 820 value as discussed in Section 7. 822 If the Root could not return the negative Status in the DAO-ACK then 823 it sends an asynchronous Destination Cleanup Object (DCO) message 824 [EFFICIENT-NPDAO] to the 6LR by placing the negative Status in the 825 RPL Status with the 'A' flag set. Note that if both are used in a 826 short interval of time, the DAO-ACK and DCO messages are not 827 guaranteed to arrive in the same order at the 6LR. 829 The 6LR may receive a requested DAO-ACK even after it received a DCO, 830 but the negative Status in the DCO supercedes a positive Status in 831 the DAO-ACK regardless of the order in which they are received. Upon 832 the DAO-ACK - or the DCO if it arrives first - the 6LR responds to 833 the RUL with an NA(EARO). If the RPL Status has the 'A' flag set, 834 then the ND Status is extracted and passed in the EARO; else, if the 835 'E' flag is set, indicating a rejection, then the status 4 "Removed" 836 is used; else, the ND Status of 0 indicating "Success" is used. 838 The RUL may terminate the registration at anytime by using a 839 Registration Lifetime of 0. This specification expects that the RPL 840 Target option transports a ROVR. If that is the case, the normal 841 heartbeat flow is sufficient to inform the 6LBR using the Root as 842 proxy as illustrated in Figure 7. If the 6LR could not add the ROVR 843 to the DAO message, then it MUST inform the 6LBR separately using as 844 illustrated in Figure 8. 846 6LN/RUL 6LR Root 6LBR 847 | | | | 848 |NS(EARO,Lifet=0)| | | 849 |--------------->| | 850 | | Extended DAR | 851 | |--------------------------------->| 852 | | | 853 | | Extended DAC | 854 | |<---------------------------------| 855 | |DAO (Lifeti=0)| | 856 | |------------->| | 857 | | | anonymous EDAR | 858 | | |------------------>| 859 | | | EDAC | 860 | | |<------------------| 861 | | DAO-ACK | | 862 | |<-------------| | 863 | NA(EARO) | | | 864 |<---------------| | | 865 | | | | 866 | | | 867 | | | | 869 Figure 8: Last Registration Flow in Non-Storing Mode, No ROVR 871 9.1.2. In RPL Storing-Mode 873 In RPL Storing Mode, the DAO-ACK is optional. When it is used, it is 874 generated by the RPL parent, which does not need to wait for the 875 grand-parent to send the acknowledgment. A successful DAO-ACK is not 876 a guarantee that the DAO has yet reached the Root or that the EDAR 877 was successfully proxied by the Root. 879 The 6LR uses the EDAR/EDAC exchange as in Non-Storing Mode, for the 880 initial registration, and also possibly at the termination in the 881 case the 6LR could not add the ROVR to the RPL Target option of the 882 DAO message. 884 6LN/RUL 6LR 6LR Root 6LBR 885 | | | | | 886 | NS(EARO) | | | | 887 |-------------->| | | | 888 | | Extended DAR | 889 | |------------------------------------------------->| 890 | | | 891 | | Extended DAC | 892 | |<-------------------------------------------------| 893 | NA(EARO) | | | | 894 |<--------------| | | | 895 | | DAO | | | 896 | |-------------->| | | 897 | | DAO-ACK | | | 898 | |<--------------| | | 899 | | | DAO | | 900 | | |-------------->| | 901 | | | DAO-ACK | | 902 | | |<--------------| | 903 | | | | (anonymous) EDAR | 904 | | | |----------------->| 905 | | | | EDAC(ROVR) | 906 | | | |<-----------------| 907 | | | | | 909 Figure 9: First Registration Flow in Storing Mode 911 The Storing Mode of RPL does not provide and end-to-end confirmation 912 that a DAO reached the root. When the 6LR has just joined, and later 913 if DAO messages are lost before reaching the Root, the 6LR might not 914 be reachable back from the Root. Performing an EDAR/EDAC exchange on 915 behalf of a RUL provides that confirmation. On the other hand, if 916 the 6LR retries an EDAR and never gets and EDAC back, it SHOULD 917 resend a DAO to become reachable again, before it tries another 918 sequence of EDAR. 920 6LN/RUL 6LR 6LR Root 6LBR 921 | | | | | 922 | NS(EARO) | | | | 923 |-------------->| | | | 924 | NA(EARO) | | | | 925 |<--------------| | | | 926 | | DAO | | | 927 | |-------------->| | | 928 | | DAO-ACK | | | 929 | |<--------------| | | 930 | | | DAO | | 931 | | |-------------->| | 932 | | | DAO-ACK | | 933 | | |<--------------| | 934 | | | | (anonymous) EDAR | 935 | | | |----------------->| 936 | | | | EDAC(ROVR) | 937 | | | |<-----------------| 938 | | | | | 940 Figure 10: Next Registration Flow in Storing Mode 942 If the keep-alive fails, or an asynchronous issue is reported, the 943 path can be cleaned up asynchronously using a DCO message 944 [EFFICIENT-NPDAO] as illustrated in Figure 11 and described in 945 further details in Section 9.2.3. 947 6LN/RUL 6LR 6LR Root 6LBR 948 | | | | | 949 | | | | NA(EARO, Status) | 950 | | | |<-----------------| 951 | | | | | 952 | | | DCO(Status) | | 953 | | |<------------| | 954 | | | | | 955 | | DCO(Status) | | | 956 | |<------------| | | 957 | | | | | 958 | NA(EARO, Status) | | | | 959 |<-----------------| | | | 960 | | | | | 962 Figure 11: Issue in Storing Mode 964 In the case illustrated here, the issue is actually detected in the 965 ND protocol and reported in the State of a NA(EARO) message. That 966 statis is transported in the DCO message as a RPL Status with the 'A' 967 and typically the 'E' flags set. 969 9.2. Detailed Operation 971 9.2.1. By the RUL Acting as 6LN 973 This specification does not alter the operation of a 6LoWPAN ND- 974 compliant 6LN, and a RUL is expected to operate as follows: 976 1. The 6LN obtains an IPv6 global address, either using Stateless 977 Address Autoconfiguration (SLAAC) [RFC4862] based on a Prefix 978 Information Option (PIO) [RFC4861] found in an RA message, or 979 some other means such as DHCPv6 [RFC3315]. 981 2. Once it has formed an address, the 6LN (re)registers its address 982 periodically, within the Lifetime of the previous Address 983 Registration, as prescribed by [RFC6775] and [RFC8505], to 984 refresh the NCE before the lifetime indicated in the EARO 985 expires. The TID is incremented each time and wraps in a 986 lollipop fashion (see section 5.2.1 of [RFC8505] which is fully 987 compatible with section 7.2 of [RFC6550]). 989 3. As stated in section 5.2 of [RFC8505], the 6LN can register to 990 more than one 6LR at the same time. In that case, it MUST use 991 the same value of TID for all of the parallel Address 992 Registrations. The 6LN should send the registration(s) with a 993 non-zero Registration Lifetime and ensure that one succeeds 994 before it terminates other registrations to maintain the state in 995 the network and at the 6LBR and minimize the churn. 997 4. Following section 5.1 of [RFC8505], a 6LN acting as a RUL sets 998 the "R" flag in the EARO of at least one registration, whereas 999 acting as an RAN it never does. If the "R" flag is not echoed in 1000 the NA, the RUL SHOULD attempt to use another 6LR. The 6LN 1001 should send the registration(s) with the "R" flag set and ensure 1002 that one succeeds before it sends the registrations with the flag 1003 reset. In case of a conflict with the preceeding rule on 1004 lifetime, the rule on lifetime has precedence. 1006 5. The 6LN may use any of the 6LRs to which it registered as default 1007 gateway. Using a 6LR to which the 6LN is not registered may 1008 result in packets dropped at the 6LR by a Source Address 1009 Validation function (SAVI) so it is not recommended. 1011 Even without support for RPL, a RUL may be aware of opaque values to 1012 be provided to the routing protocol. If the RUL has a knowledge of 1013 the RPL Instance the packet should be injected into, then it SHOULD 1014 set the Opaque field in the EARO to the RPLInstanceID, else it MUST 1015 leave the Opaque field to zero. 1017 Regardless of the setting of the Opaque field, the 6LN MUST set the 1018 "I" field to zero to signal "topological information to be passed to 1019 a routing process" as specified in section 5.1 of [RFC8505]. 1021 A RUL is not expected to produce RPL artifacts in the data packets, 1022 but it MAY do so. For instance, if the RUL has a minimal awareness 1023 of the RPL Instance then it can build an RPI. A RUL that places an 1024 RPI in a data packet MUST indicate the RPLInstanceID of the RPL 1025 Instance where the packet should be forwarded. All the flags and the 1026 Rank field are set to zero as specified by section 11.2 of [RFC6550]. 1028 9.2.2. By the RPL Border Router Acting as 6LR 1030 Also as prescribed by [RFC8505], the 6LR generates an EDAR message 1031 upon reception of a valid NS(EARO) message for the registration of a 1032 new IPv6 Address by a 6LN. If the initial EDAR/EDAC exchange 1033 succeeds, then the 6LR installs an NCE for the Registration Lifetime. 1034 For the refreshes of the registration, if the RPL Root has indicated 1035 that it proxies the keep-alive EDAR/EDAC exchange with the 6LBR (see 1036 Section 4), the 6LR MUST refrain from sending the keep-alive EDAR 1037 itself. 1039 If the "R" flag is set in the NS(EARO), the 6LR SHOULD attempt to 1040 inject the host route in RPL, unless this is barred for other 1041 reasons, like a saturation of the network or if its RPL parent. The 1042 6LR MUST set "R" flag in the NA(EARO) back if and only if it 1043 successfully injected the Registered Address in RPL. 1045 The 6LR may at any time send a unicast asynchronous NA(EARO) with the 1046 "R" flag reset to signal that it stops providing routing services, 1047 and/or with the EARO Status 2 "Neighbor Cache full" to signal that it 1048 removes the NCE. It may also send a final RA, unicast or multicast, 1049 with a Router Lifetime field of zero, to signal that it stops serving 1050 as router, as specified in section 6.2.5 of [RFC4861]. 1052 The Opaque field in the EARO hints the 6LR on the RPL Instance that 1053 SHOULD be used for the DAO advertisements, and for the forwarding of 1054 packets sourced at the registered address when there is no RPI in the 1055 packet, in which case the 6LR MUST encapsulate the packet to the Root 1056 adding an RPI in the outer header. If the Opaque field is zero, the 1057 6LR is free to use the default RPL Instance (zero) for the registered 1058 address or to select an Instance of its choice. 1060 if the "I" field is not zero, then the 6LR MUST consider that the 1061 Opaque field is zero. If the Opaque field is not zero, then it is 1062 expected to carry a RPLInstanceID for the RPL Instance suggested by 1063 the 6LN. If the 6LR does not participate to the associated Instance, 1064 then the 6LR MUST consider that the Opaque field is zero; else, that 1065 is if the 6LR participates to the suggested Instance, then the 6LR 1066 SHOULD use that Instance for the registered address. 1068 The DAO message advertising the Registered Address MUST be 1069 constructed as follows: 1071 1. The Registered Address is signaled as Target Prefix in the RPL 1072 Target Option in the DAO message; the Prefix Length is set to 128 1074 2. RPL Non-Storing Mode is to be used. The 6LR indicates one of its 1075 global or unique-local IPv6 unicast addresses as the Parent 1076 Address in the associated RPL Transit Information Option (TIO) 1078 3. the External 'E' flag in the TIO is set to indicate that the 6LR 1079 redistributes an external target into the RPL network 1081 4. the Path Lifetime in the TIO is computed from the Lifetime in the 1082 EARO Option. This adapts it to the Lifetime Units used in the 1083 RPL operation; note that if the lifetime is 0, then the 6LR 1084 generates a No-Path DAO message that cleans up the routes down to 1085 the Address of the 6LN; this also causes the Root as a proxy to 1086 send an EDAR message to the 6LBR with a Lifetime of 0. 1088 5. the Path Sequence in the TIO is set to the TID value found in the 1089 EARO option. 1091 The NCE is removed if the 6LR tries to inject the route is RPL and 1092 fails for reasons related to ND, which is recognized by both the 'E' 1093 and the 'A' flags set in the RPL Status of the DAO-ACK or the DCO, as 1094 detailed below. 1096 Otherwise, success injecting the route is assumed if a DAO-ACK was 1097 not requested or if it is received with a RPL Status that is not a 1098 rejection (i.e., the 'E' flag not set). 1100 In case of success, if the 'A' flag is set in the RPL Status of the 1101 DAO-ACK, then the 6LR MUST use the Status Value in the RPL Status for 1102 the Status in the NA(EARO), else a Status of 0 (Success) is returned. 1104 The status of 0 MUST also be used if the 6LR could not even try to 1105 inject the route - note that the "R" flag is reset in that case. 1107 In a network where Address Protected Neighbor Discovery (AP-ND) is 1108 enabled, in case of a DAO-ACK or a DCO indicating transporting an 1109 EARO Status Value of 5 (Validation Requested), the 6LR MUST challenge 1110 the 6LN for ownership of the address, as described in section 6.1 of 1111 [AP-ND], before the Registration is complete. This ensures that the 1112 address validated before it is injected in RPL. 1114 If the challenge succeeds then the operations continue as normal. In 1115 particular a DAO message is generated upon the NS(EARO) that proves 1116 the ownership of the address. If the challenge failed, the 6LR 1117 rejects the registration as prescribed by AP-ND and may take actions 1118 to protect itself against DoS attacks by a rogue 6LN, see Section 11. 1120 The other rejection codes indicate that the 6LR failed to inject the 1121 address into the RPL network. If an EARO Status is transported, the 1122 6LR MUST send a NA(EARO) to the RUL with that Status value, and the 1123 "R" flag not set. Similarly, upon receiving a DCO message indicating 1124 that the address of a RUL should be removed from the routing table, 1125 the 6LR issues an asynchronous NA(EARO) to the RUL with the embedded 1126 ND Status value if there was one, and the "R" flag not set. 1128 If a 6LR receives a valid NS(EARO) message with the "R" flag reset 1129 and a Registration Lifetime that is not 0, and the 6LR was 1130 redistributing the Registered Address due to previous NS(EARO) 1131 messages with the flag set, then it MUST stop injecting the address. 1132 It is up to the Registering 6LN to maintain the corresponding route 1133 from then on, either keeping it active via a different 6LR or by 1134 acting as an RAN and managing its own reachability. 1136 9.2.3. By the RPL Root 1138 A RPL Root SHOULD set the "P" flag in the RPL configuration option of 1139 the DIO messages that it generates (see Section 4) to signal that it 1140 proxies the keep-alive EDAR/EDAC echange. The remainder of this 1141 section assumes that it does. 1143 Upon reception of a DAO message, for each RPL Target option that 1144 creates or updates an existing RPL state, the Root notifies the 6LBR. 1145 This can be done using an internal API if they are co-located, or 1146 using a proxied EDAR/EDAC exchange if they are separated. 1148 If the RPL Target option transports a ROVR, then the Root MUST use it 1149 to build a full EDAR message; else, an anonymous EDAR is used with 1150 the ROVR field set to zero. 1152 The EDAR message MUST be constructed as follows: 1154 1. The Target IPv6 address from the RPL Target Option is placed in 1155 the Registered Address field of the EDAR message; 1157 2. the Registration Lifetime is adapted from the Path Lifetime in 1158 the TIO by converting the Lifetime Units used in RPL into units 1159 of 60 seconds used in the 6LoWPAN ND messages; 1161 3. the TID value is set to the Path Sequence in the TIO and 1162 indicated with an ICMP code of 1 in the EDAR message; 1164 4. If the ROVR is present in the RPL Target option, it is copied as 1165 is in the EDAR and the ICMP Code Suffix is set to the appropriate 1166 value as shown in Table 4 of [RFC8505] depending on the size of 1167 the ROVR field; else, the ROVR field in the EDAR is set to zero 1168 indicating an anonymous EDAR. 1170 Upon a Status value in an EDAC message that is not "Success", the 1171 Root SHOULD destroy the formed paths using either a DAO-ACK (in Non- 1172 Storing Mode) or a DCO downwards as specified in [EFFICIENT-NPDAO]. 1173 Failure to destroy the former path would result in Stale routing 1174 state and local black holes if the address belongs to another party 1175 elsewhere in the network. The RPL Status value that maps the 6LoWPAN 1176 ND Status value MUST be embedded in the RPL Status in the DCO. 1178 9.2.4. By the 6LBR 1180 Upon reception of an EDAR message with the ROVR field set to a non- 1181 zero value, the 6LBR acts as prescribed by [RFC8505]. If the ROVR is 1182 set to 0, indicating an anonymous EDAR, the 6LBR MUST act as below: 1184 1. The 6LBR checks whether an entry exists for the address. If the 1185 entry does not exist, the 6LBR MUST NOT create the entry, and it 1186 MUST answer with a Status "Removed" in the EDAC message. If the 1187 entry exists, the 6LBR computes whether the TID in the EDAR 1188 message is fresher than the one in the entry as prescribed in 1189 section 4.2.1. of [RFC8505], and continues as follows: 1191 2. If the anonymous EDAR message is fresher, the 6LBR updates the 1192 TID in the entry, restarts the heartbeat timer for the entry, and 1193 answers with a Status "Success" in the EDAC message. If the 1194 value of the Registration Lifetime is smaller than the value in 1195 the entry, then the latter value MUST be used for the heartbeat; 1196 this means in particular that the Registration Lifetime of 0 is 1197 ignored. Conversely, if the duration of the Lifetime is extended 1198 by the Registration Lifetime in the EDAR message, it is used for 1199 the hearbeat and to the value in the entry is updated. 1201 3. If the TID in the entry is the same or fresher, the 6LBR does not 1202 update the entry, and answers with a Status "Success" and "Moved" 1203 in the EDAC message, respectively. 1205 The EDAC that is constructed is the same as if the anonymous EDAR was 1206 a full EDAR, but for the ROVR that is set to zero. 1208 10. Protocol Operations for Multicast Addresses 1210 Section 12 of [RFC6550] details the RPL support for multicast flows. 1211 This support is not source-specific and only operates as an extension 1212 to the Storing Mode of Operation for unicast packets. Note that it 1213 is the RPL model that the multicast packet is passed as a Layer-2 1214 unicast to each of the interested children. This remains true when 1215 forwarding between the 6LR and the listener 6LN. 1217 "Multicast Listener Discovery (MLD) for IPv6" [RFC2710] and its 1218 updated version "Multicast Listener Discovery Version 2 (MLDv2) for 1219 IPv6" [RFC3810] provide an interface for a listener to register to 1220 multicast flows. MLDv2 is backwards compatible with MLD, and adds in 1221 particular the capability to filter the sources via black lists and 1222 white lists. In the MLD model, the Router is a "querier" and the 1223 Host is a multicast listener that registers to the querier to obtain 1224 copies of the particular flows it is interested in. 1226 On the first Address Registration, as illustrated in Figure 12, the 1227 6LN, as an MLD listener, sends an unsolicited Report to the 6LR in 1228 order to start receiving the flow immediately. 1230 6LN/RUL 6LR Root 6LBR 1231 | | | | 1232 | unsolicited Report | | | 1233 |------------------->| | | 1234 | | DAO | | 1235 | |-------------->| | 1236 | | DAO-ACK | | 1237 | |<--------------| | 1238 | | | unsolicited Report | 1239 | | |------------------->| 1240 | | | | 1242 Figure 12: First Multicast Registration Flow 1244 Since multicast Layer-2 messages are avoided, it is important that 1245 the asynchronous messages for unsolicited Report and Done are sent 1246 reliably, for instance using a Layer-2 acknowledgment, or attempted 1247 multiple times. 1249 The 6LR acts as a generic MLD querier and generates a DAO for the 1250 multicast target. The lifetime of the DAO is set to be in the order 1251 of the Query Interval, yet larger to account for variable propagation 1252 delays. 1254 The Root proxies the MLD exchange as a listener with the 6LBR acting 1255 as the querier, so as to get packets from a source external to the 1256 RPL domain. Upon a DAO with a multicast target, the RPL Root checks 1257 if it is already registered as a listener for that address, and if 1258 not, it performs its own unsolicited Report for the multicast target. 1260 An Address re-Registration is pulled periodically by 6LR acting as 1261 querier. Note that the message may be sent unicast to all the known 1262 individual listeners. Upon a time out of the Query Interval, the 6LR 1263 sends a Query to each of its listeners, and gets a Report back that 1264 is mapped into a DAO, as illustrated in Figure 13: 1266 6LN/RUL 6LR Root 6LBR 1267 | | | | 1268 | Query | | | 1269 |<-------------------| | | 1270 | Report | | | 1271 |------------------->| | | 1272 | | DAO | | 1273 | |-------------->| | 1274 | | DAO-ACK | | 1275 | |<--------------| | 1276 | | | | 1277 | | | Query | 1278 | | |<-------------------| 1279 | | | Report | 1280 | | |------------------->| 1281 | | | | 1282 | | | | 1284 Figure 13: Next Registration Flow 1286 Note that any of the functions 6LR, Root and 6LBR might be collapsed 1287 in a single node, in which case the flow above happens internally, 1288 and possibly through internal API calls as opposed to messaging. 1290 11. Security Considerations 1292 First of all, it is worth noting that with [RFC6550], every node in 1293 the LLN is RPL-aware and can inject any RPL-based attack in the 1294 network. This specification isolates edge nodes that can only 1295 interact with the RPL routers using 6LoWPAN ND, meaning that they 1296 cannot perform RPL insider attacks. 6LoWPAN ND can optionally provide 1297 SAVI features, which reduces even more the attack perimeter that is 1298 available to the edge nodes. 1300 The LLN nodes depend on the 6LBR and the RPL participants for their 1301 operation. A trust model must be put in place to ensure that the 1302 right devices are acting in these roles, so as to avoid threats such 1303 as black-holing, (see [RFC7416] section 7) or bombing attack whereby 1304 an impersonated 6LBR would destroy state in the network by using the 1305 "Removed" Status code. 1307 This trust model could be at a minimum based on a Layer-2 Secure 1308 joining and the Link-Layer security. This is a generic 6LoWPAN 1309 requirement, see Req5.1 in Appendix of [RFC8505]. 1311 Additionally, the trust model could include a role validation to 1312 ensure that the node that claims to be a 6LBR or a RPL Root is 1313 entitled to do so. 1315 The anonymous EDAR message does not carry a valid Registration Unique 1316 ID [RFC8505] in the form of a ROVR and may be played by any node on 1317 the network without the need to know the ROVR. The 6LBR MUST NOT 1318 create an entry based on a anonymous EDAR and it MUST NOT decrease 1319 the value of the lifetime. All it can do is refresh the lifetime and 1320 the TID of an existing entry. So the message cannot be used to 1321 create a binding state in the 6LBR but it can be used to maintain one 1322 active longer than expected. 1324 Note that a full EDAR message with a lifetime of 0 will destroy that 1325 state and the anonymous message will not recreate it. Note also that 1326 a rogue that has access to the network can attack the 6LBR with other 1327 (forged) addresses and ROVR, and that this is a much easier DoS 1328 attack than trying to keep existing state alive longer. 1330 At the time of this writing RPL does not have a zerotrust model 1331 whereby it is possible to validate the origin of an address that is 1332 injected in a DAO. This specification makes a first step in that 1333 direction by allowing the Root to challenge the RUL by the 6LR that 1334 serves it. 1336 12. IANA Considerations 1337 12.1. Resizing the ARO Status values 1339 IANA is requested to modify the Address Registration Option Status 1340 Values Registry as follows: The unassigned values range is reduced 1341 from 11-255 to 11-63. 1343 12.2. New DODAG Configuration Option Flag 1345 This specification updates the Registry for the "DODAG Configuration 1346 Option Flags" that was created for [RFC6550] as follows: 1348 +------------+----------------------------+-----------+ 1349 | Bit Number | Capability Description | Reference | 1350 +============+============================+===========+ 1351 | 1 | Root Proxies EDAR/EDAC (P) | THIS RFC | 1352 +------------+----------------------------+-----------+ 1354 Table 2: New DODAG Configuration Option Flag 1356 12.3. RPL Target Option Flags 1358 Section 20.15 of [RFC6550] creates a registry for the 8-bit RPL 1359 Target Option Flags field. This specification reduces the field to 4 1360 bits. The IANA is requested to reduce the size of the registry 1361 accordingly. 1363 12.4. New Subregistry for the RPL Non-Rejection Status values 1365 This specification creates a new Subregistry for the RPL Non- 1366 Rejection Status values for use in RPL DAO-ACK and DCO messages with 1367 the 'A' flag reset, under the ICMPv6 parameters registry. 1369 * Possible values are 6-bit unsigned integers (0..63). 1371 * Registration procedure is "Standards Action" [RFC8126]. 1373 * Initial allocation is as indicated in Table 3: 1375 +-------+------------------------+-----------+ 1376 | Value | Meaning | Reference | 1377 +=======+========================+===========+ 1378 | 0 | Unqualified acceptance | RFC 6550 | 1379 +-------+------------------------+-----------+ 1381 Table 3: Acceptance values of the RPL Status 1383 12.5. New Subregistry for the RPL Rejection Status values 1385 This specification creates a new Subregistry for the RPL Rejection 1386 Status values for use in RPL DAO-ACK and RCO messages with the 'A' 1387 flag reset, under the ICMPv6 parameters registry. 1389 * Possible values are 6-bit unsigned integers (0..63). 1391 * Registration procedure is "Standards Action" [RFC8126]. 1393 * Initial allocation is as indicated in Table 4: 1395 +-------+-----------------------+---------------+ 1396 | Value | Meaning | Reference | 1397 +=======+=======================+===============+ 1398 | 0 | Unqualified rejection | This document | 1399 +-------+-----------------------+---------------+ 1401 Table 4: Rejection values of the RPL Status 1403 13. acknowledgments 1405 The authors wish to thank Georgios Papadopoulos and Rahul Jadhav for 1406 their early reviews of and contributions to this document 1408 14. Normative References 1410 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1411 Requirement Levels", BCP 14, RFC 2119, 1412 DOI 10.17487/RFC2119, March 1997, 1413 . 1415 [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast 1416 Listener Discovery (MLD) for IPv6", RFC 2710, 1417 DOI 10.17487/RFC2710, October 1999, 1418 . 1420 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1421 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1422 DOI 10.17487/RFC3810, June 2004, 1423 . 1425 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1426 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1427 Overview, Assumptions, Problem Statement, and Goals", 1428 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1429 . 1431 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1432 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1433 DOI 10.17487/RFC4861, September 2007, 1434 . 1436 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1437 Address Autoconfiguration", RFC 4862, 1438 DOI 10.17487/RFC4862, September 2007, 1439 . 1441 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1442 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1443 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1444 Low-Power and Lossy Networks", RFC 6550, 1445 DOI 10.17487/RFC6550, March 2012, 1446 . 1448 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1449 Power and Lossy Networks (RPL) Option for Carrying RPL 1450 Information in Data-Plane Datagrams", RFC 6553, 1451 DOI 10.17487/RFC6553, March 2012, 1452 . 1454 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1455 Routing Header for Source Routes with the Routing Protocol 1456 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1457 DOI 10.17487/RFC6554, March 2012, 1458 . 1460 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1461 Bormann, "Neighbor Discovery Optimization for IPv6 over 1462 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1463 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1464 . 1466 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1467 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1468 2014, . 1470 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1471 Constrained-Node Networks", RFC 7228, 1472 DOI 10.17487/RFC7228, May 2014, 1473 . 1475 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 1476 IPv6 over Low-Power Wireless Personal Area Networks 1477 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 1478 2014, . 1480 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1481 Writing an IANA Considerations Section in RFCs", BCP 26, 1482 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1483 . 1485 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1486 "IPv6 over Low-Power Wireless Personal Area Network 1487 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1488 April 2017, . 1490 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1491 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1492 May 2017, . 1494 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1495 (IPv6) Specification", STD 86, RFC 8200, 1496 DOI 10.17487/RFC8200, July 2017, 1497 . 1499 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1500 Perkins, "Registration Extensions for IPv6 over Low-Power 1501 Wireless Personal Area Network (6LoWPAN) Neighbor 1502 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1503 . 1505 [AP-ND] Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 1506 "Address Protected Neighbor Discovery for Low-power and 1507 Lossy Networks", Work in Progress, Internet-Draft, draft- 1508 ietf-6lo-ap-nd-20, 9 March 2020, 1509 . 1511 [USEofRPLinfo] 1512 Robles, I., Richardson, M., and P. Thubert, "Using RPI 1513 Option Type, Routing Header for Source Routes and IPv6-in- 1514 IPv6 encapsulation in the RPL Data Plane", Work in 1515 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-38, 1516 23 March 2020, . 1519 [EFFICIENT-NPDAO] 1520 Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient 1521 Route Invalidation", Work in Progress, Internet-Draft, 1522 draft-ietf-roll-efficient-npdao-17, 30 October 2019, 1523 . 1526 15. Informative References 1528 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1529 Statement and Requirements for IPv6 over Low-Power 1530 Wireless Personal Area Network (6LoWPAN) Routing", 1531 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1532 . 1534 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 1535 C., and M. Carney, "Dynamic Host Configuration Protocol 1536 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 1537 2003, . 1539 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1540 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1541 DOI 10.17487/RFC6282, September 2011, 1542 . 1544 [RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur, 1545 Ed., "Performance Evaluation of the Routing Protocol for 1546 Low-Power and Lossy Networks (RPL)", RFC 6687, 1547 DOI 10.17487/RFC6687, October 2012, 1548 . 1550 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1551 and M. Richardson, Ed., "A Security Threat Analysis for 1552 the Routing Protocol for Low-Power and Lossy Networks 1553 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1554 . 1556 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1557 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1558 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1559 . 1561 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node 1562 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504, 1563 January 2019, . 1565 [6BBR] Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6 1566 Backbone Router", Work in Progress, Internet-Draft, draft- 1567 ietf-6lo-backbone-router-20, 23 March 2020, 1568 . 1571 Appendix A. Example Compression 1573 Figure 14 illustrates the case in Storing Mode where the packet is 1574 received from the Internet, then the Root encapsulates the packet to 1575 insert the RPI and deliver to the 6LR that is the parent and last hop 1576 to the final destination, which is not known to support [RFC8138]. 1578 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1579 |11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP 1580 |Page 1 |Type1 S=0| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 1581 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1582 <-4 bytes-> <- RFC 6282 -> 1583 <- No RPL artifact ... 1585 Figure 14: Encapsulation to Parent 6LR in Storing Mode 1587 The difference with the example presented in Figure 19 of [RFC8138] 1588 is the addition of a SRH-6LoRH before the RPI-6LoRH to transport the 1589 compressed address of the 6LR as the destination address of the outer 1590 IPv6 header. In the original example the destination IP of the outer 1591 header was elided and was implicitly the same address as the 1592 destination of the inner header. Type 1 was arbitrarily chosen, and 1593 the size of 0 denotes a single address in the SRH. 1595 In Figure 14, the source of the IP-in-IP encapsulation is the Root, 1596 so it is elided in the IP-in-IP 6LoRH. The destination is the parent 1597 6LR of the destination of the inner packet so it cannot be elided. 1598 In Storing Mode, it is placed as the single entry in an SRH-6LoRH as 1599 the first 6LoRH. Since there is a single entry so the SRH-6LoRH Size 1600 is 0. In this particular example, the 6LR address can be compressed 1601 to 2 bytes so a Type of 1 is used. It results that the total length 1602 of the SRH-6LoRH is 4 bytes. 1604 In Non-Storing Mode, the encapsulation from the Root would be similar 1605 to that represented in Figure 14 with possibly more hops in the SRH- 1606 6LoRH and possibly multiple SRH-6LoRHs if the various addresses in 1607 the routing header are not compressed to the same format. Note that 1608 on the last hop to the parent 6LR, the RH3 is consumed and removed 1609 from the compressed form, so the use of Non-Storing Mode vs. Storing 1610 Mode is indistinguishable from the packet format. 1612 The SRH-6LoRHs are followed by RPI-6LoRH and then the IP-in-IP 6LoRH. 1613 When the IP-in-IP 6LoRH is removed, all the 6LoRH Headers that 1614 precede it are also removed. The Paging Dispatch [RFC8025] may also 1615 be removed if there was no previous Page change to a Page other than 1616 0 or 1, since the LOWPAN_IPHC is encoded in the same fashion in the 1617 default Page 0 and in Page 1. The resulting packet to the 1618 destination is the inner packet compressed with [RFC6282]. 1620 Authors' Addresses 1622 Pascal Thubert (editor) 1623 Cisco Systems, Inc 1624 Building D 1625 45 Allee des Ormes - BP1200 1626 06254 Mougins - Sophia Antipolis 1627 France 1629 Phone: +33 497 23 26 34 1630 Email: pthubert@cisco.com 1632 Michael C. Richardson 1633 Sandelman Software Works 1635 Email: mcr+ietf@sandelman.ca 1636 URI: http://www.sandelman.ca/