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Is this intentional? 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 ** Downref: Normative reference to an Informational RFC: RFC 7102 ** Downref: Normative reference to an Informational RFC: RFC 7228 == Outdated reference: A later version (-44) exists of draft-ietf-roll-useofrplinfo-38 -- Obsolete informational reference (is this intentional?): RFC 3315 (Obsoleted by RFC 8415) Summary: 3 errors (**), 0 flaws (~~), 2 warnings (==), 3 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: draft-ietf-roll-efficient-npdao, 6550, M. Richardson 5 8505 (if approved) Sandelman 6 Intended status: Standards Track 10 June 2020 7 Expires: 12 December 2020 9 Routing for RPL Leaves 10 draft-ietf-roll-unaware-leaves-17 12 Abstract 14 This specification extends RFC6550 and RFC8505 to provide routing 15 services to Hosts called RPL Unaware Leaves that implement 6LoWPAN ND 16 but do not participate to RPL. This specification also enables the 17 RPL Root to proxy the 6LoWPAN keep-alive flows in its DODAG. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at https://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on 12 December 2020. 36 Copyright Notice 38 Copyright (c) 2020 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 43 license-info) in effect on the date of publication of this document. 44 Please review these documents carefully, as they describe your rights 45 and restrictions with respect to this document. Code Components 46 extracted from this document must include Simplified BSD License text 47 as described in Section 4.e of the Trust Legal Provisions and are 48 provided without warranty as described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 53 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 54 2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 4 55 2.2. References . . . . . . . . . . . . . . . . . . . . . . . 5 56 2.3. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 5 57 3. 6LoWPAN Neighbor Discovery . . . . . . . . . . . . . . . . . 7 58 3.1. RFC 6775 Address Registration . . . . . . . . . . . . . . 7 59 3.2. RFC 8505 Extended Address Registration . . . . . . . . . 7 60 3.2.1. R Flag . . . . . . . . . . . . . . . . . . . . . . . 8 61 3.2.2. TID, I Field and Opaque Fields . . . . . . . . . . . 8 62 3.2.3. ROVR . . . . . . . . . . . . . . . . . . . . . . . . 8 63 3.3. RFC 8505 Extended DAR/DAC . . . . . . . . . . . . . . . . 9 64 3.3.1. RFC 7400 Capability Indication Option . . . . . . . . 9 65 4. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 10 66 5. Updating draft-ietf-roll-efficient-npdao . . . . . . . . . . 11 67 6. Updating RFC 8505 . . . . . . . . . . . . . . . . . . . . . . 11 68 7. Requirements on the RPL-Unware Leaf . . . . . . . . . . . . . 11 69 7.1. Support of 6LoWPAN ND . . . . . . . . . . . . . . . . . . 11 70 7.2. External Routes and RPL Artifacts . . . . . . . . . . . . 12 71 7.2.1. Support of IPv6 Encapsulation . . . . . . . . . . . . 13 72 7.2.2. Support of the HbH Header . . . . . . . . . . . . . . 13 73 7.2.3. Support of the Routing Header . . . . . . . . . . . . 13 74 8. Updated RPL Status . . . . . . . . . . . . . . . . . . . . . 13 75 9. Updated RPL Target Option . . . . . . . . . . . . . . . . . . 14 76 10. Protocol Operations for Unicast Addresses . . . . . . . . . . 15 77 10.1. General Flow . . . . . . . . . . . . . . . . . . . . . . 16 78 10.2. Detailed Operation . . . . . . . . . . . . . . . . . . . 18 79 10.2.1. Perspective of the RUL Acting as 6LN . . . . . . . . 18 80 10.2.2. Perspective of the Border Router Acting as 6LR . . . 19 81 10.2.3. Perspective of the RPL Root . . . . . . . . . . . . 22 82 10.2.4. Perspective of the 6LBR . . . . . . . . . . . . . . 22 83 11. Protocol Operations for Multicast Addresses . . . . . . . . . 23 84 12. Security Considerations . . . . . . . . . . . . . . . . . . . 24 85 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 86 13.1. Resizing the ARO Status values . . . . . . . . . . . . . 25 87 13.2. New DODAG Configuration Option Flag . . . . . . . . . . 25 88 13.3. New RPL Target Option Flag . . . . . . . . . . . . . . . 26 89 13.4. New Subregistry for the RPL Non-Rejection Status 90 values . . . . . . . . . . . . . . . . . . . . . . . . . 26 91 13.5. New Subregistry for the RPL Rejection Status values . . 26 92 13.6. Fixing the Address Registration Option Flags . . . . . . 27 93 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27 94 15. Normative References . . . . . . . . . . . . . . . . . . . . 27 95 16. Informative References . . . . . . . . . . . . . . . . . . . 29 96 Appendix A. Example Compression . . . . . . . . . . . . . . . . 30 97 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 99 1. Introduction 101 The design of Low Power and Lossy Networks (LLNs) is generally 102 focused on saving energy, which is the most constrained resource of 103 all. Other design constraints, such as a limited memory capacity, 104 duty cycling of the LLN devices and low-power lossy transmissions, 105 derive from that primary concern. 107 The IETF produced the "Routing Protocol for Low Power and Lossy 108 Networks" [RFC6550] (RPL) to provide IPv6 [RFC8200] routing services 109 within such constraints. RPL belongs to the class of Distance-Vector 110 protocols, which, compared to link-state protocols, limit the amount 111 of topological knowledge that needs to be installed and maintained in 112 each node, and does not require convergence to avoid micro-loops. 114 To save signaling and routing state in constrained networks, RPL 115 allows a routing stretch (see [RFC6687]), whereby routing is only 116 performed along an acyclic graph optimized to reach a Root node, as 117 opposed to straight along a shortest path between 2 peers, whatever 118 that would mean in a given LLN. This trades the quality of peer-to- 119 peer (P2P) paths for a vastly reduced amount of control traffic and 120 routing state that would be required to operate a any-to-any shortest 121 path protocol. Finally, broken routes may be fixed lazily and on- 122 demand, based on dataplane inconsistency discovery, which avoids 123 wasting energy in the proactive repair of unused paths. 125 To provide alternate paths in lossy networks, RPL forms Direction- 126 Oriented Directed Acyclic Graphs (DODAGs) using DODAG Information 127 Sollicitation (DIS) and DODAG Information Object (DIO) messages. For 128 many of the nodes, though not all, a DODAG provides multiple 129 forwarding solutions towards the Root of the topology via so-called 130 parents. RPL is designed to adapt to fuzzy connectivity, whereby the 131 physical topology cannot be expected to reach a stable state, with a 132 lazy control that creates the routes proactively, but may only fix 133 them reactively, upon actual traffic. The result is that RPL 134 provides reachability for most of the LLN nodes, most of the time, 135 but may not converge in the classical sense. 137 [RFC6550] provides unicast and multicast routing services to RPL- 138 Aware nodes (RANs), either as a collection tree or with routing back. 139 In the latter case, an RAN injects routes to itself using Destination 140 Advertisement Object (DAO) messages sent either to parent-nodes, in 141 the RPL Storing Mode, or to the Root indicating their parent, in the 142 Non-Storing Mode. This process effectively forms a DODAG back to the 143 device that is a subset of the DODAG to the Root with all links 144 reversed. 146 RPL can be deployed as an extension to IPv6 Neighbor Discovery (ND) 147 [RFC4861][RFC4862] and 6LoWPAN ND [RFC6775][RFC8505] to maintain 148 reachability within a Non-Broadcast Multi-Access (NBMA) subnet. In 149 that mode, some nodes may act as Routers and participate to the 150 forwarding operations whereas others will only terminate packets, 151 acting as Hosts in the data-plane. In [RFC6550] terms, a Host that 152 is reachable over the RPL network is called a Leaf. 154 "When to use RFC 6553, 6554 and IPv6-in-IPv6" [USEofRPLinfo] 155 introduces the term RPL-Aware-Leaf (RAL) for a Leaf that injects 156 routes in RPL to manage the reachability of its own IPv6 addresses. 157 In contrast, the term RPL-Unaware Leaf (RUL) designates a Leaf that 158 does not participate to RPL at all. A RUL is an IPv6 Host [RFC8504] 159 that needs a RPL-Aware Router to obtain routing services over the RPL 160 network. 162 This specification leverages the Address Registration mechanism 163 defined in 6LoWPAN ND to enable a RUL as a 6LoWPAN Node (6LN) to 164 interface with a RPL-Aware Router as a 6LoWPAN Router (6LR) and 165 request that the 6LR injects a Host route for the Registered Address 166 in the RPL routing on its behalf. A RUL may be unable to participate 167 because it is very energy-constrained, or because it is unsafe to let 168 it inject routes in RPL, in which case using 6LowPAN ND as the 169 interface for the RUL limits the surface of the possible attacks and 170 optionally protects the address ownership. 172 The RPL Non-Storing Mode mechanism is used to extend the routing 173 state with connectivity to the RULs even when the DODAG is operated 174 in Storing Mode. The unicast packet forwarding operation by the 6LR 175 serving a 6LN that is also a RUL is described in [USEofRPLinfo]. 177 Examples of routing-agnostic 6LNs include lightly powered sensors 178 such as window smash sensor (alarm system), and kinetically powered 179 light switches. Other applications of this specification may include 180 a smart grid network that controls appliances - such as washing 181 machines or the heating system - in the home. Appliances may not 182 participate to the RPL protocol operated in the Smartgrid network but 183 can still interact with the Smartgrid for control and/or metering. 185 2. Terminology 187 2.1. BCP 14 189 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 190 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 191 "OPTIONAL" in this document are to be interpreted as described in BCP 192 14 [RFC2119][RFC8174] when, and only when, they appear in all 193 capitals, as shown here. 195 2.2. References 197 The Terminology used in this document is consistent with and 198 incorporates that described in "Terms Used in Routing for Low-Power 199 and Lossy Networks (LLNs)" [RFC7102]. A glossary of classical 200 6LoWPAN acronyms is given in Section 2.3. Other terms in use in LLNs 201 are found in "Terminology for Constrained-Node Networks" [RFC7228]. 203 "RPL", the "RPL Packet Information" (RPI), "RPL Instance" (indexed by 204 a RPLInstanceID) are defined in "RPL: IPv6 Routing Protocol for 205 Low-Power and Lossy Networks" [RFC6550]. The RPI is the abstract 206 information that RPL defines to be placed in data packets, e.g., as 207 the RPL Option [RFC6553] within the IPv6 Hop-By-Hop Header. By 208 extension the term "RPI" is often used to refer to the RPL Option 209 itself. The DODAG Information Sollicitation (DIS), Destination 210 Advertisement Object (DAO) and DODAG Information Object (DIO) 211 messages are also specified in [RFC6550]. The Destination Cleanup 212 Object (DCO) message is defined in [EFFICIENT-NPDAO]. 214 This document uses the terms RPL-Unaware Leaf (RUL) and RPL Aware 215 Leaf (RAL) consistently with [USEofRPLinfo]. The term RPL-Aware Node 216 (RAN) is introduced to refer to a node that is either an RAL or a RPL 217 Router. As opposed to a RUL, an RAN manages the reachability of its 218 addresses and prefixes by injecting them in RPL by itself. 220 In this document, readers will encounter terms and concepts that are 221 discussed in the following documents: 223 Classical IPv6 ND: "Neighbor Discovery for IP version 6" [RFC4861] 224 and "IPv6 Stateless Address Autoconfiguration" [RFC4862], 226 6LoWPAN: "Problem Statement and Requirements for IPv6 over Low-Power 227 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606] and 228 "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 229 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 230 and 232 6LoWPAN ND: Neighbor Discovery Optimization for Low-Power and Lossy 233 Networks [RFC6775], "Registration Extensions for 6LoWPAN Neighbor 234 Discovery" [RFC8505], and "Address Protected Neighbor Discovery 235 for Low-power and Lossy Networks" [AP-ND] . 237 2.3. Glossary 239 This document often uses the following acronyms: 241 AR: Address Resolution (aka Address Lookup) 242 6CIO: 6LoWPAN Capability Indication Option 244 6LN: 6LoWPAN Node (a Low Power Host or Router) 246 6LR: 6LoWPAN Router 248 (E)ARO: (Extended) Address Registration Option 250 (E)DAR: (Extended) Duplicate Address Request 252 (E)DAC: (Extended) Duplicate Address Confirmation 254 DAD: Duplicate Address Detection 256 DAO: Destination Advertisement Object (a RPL message) 258 DCO: Destination Cleanup Object (a RPL message) 260 DIS: DODAG Information Sollicitation (a RPL message) 262 DIO: DODAG Information Object (a RPL message) 264 DODAG: Destination-Oriented Directed Acyclic Graph 266 LLN: Low-Power and Lossy Network 268 NA: Neighbor Advertisement 270 NCE: Neighbor Cache Entry 272 ND: Neighbor Discovery 274 NS: Neighbor Sollicitation 276 RA: Router Advertisement 278 ROVR: Registration Ownership Verifier 280 RPI: RPL Packet Information 282 RAL: RPL-Aware Leaf 284 RAN: RPL-Aware Node (either a RPL Router or a RPL-Aware Leaf) 286 RUL: RPL-Unaware Leaf 288 TID: Transaction ID (a sequence counter in the EARO) 290 3. 6LoWPAN Neighbor Discovery 292 3.1. RFC 6775 Address Registration 294 The classical "IPv6 Neighbor Discovery (IPv6 ND) Protocol" [RFC4861] 295 [RFC4862] was defined for serial links and transit media such a 296 Ethernet. It is a reactive protocol that relies heavily on multicast 297 operations for address discovery (aka lookup) and duplicate address 298 detection (DAD). 300 "Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775] 301 adapts IPv6 ND for operations over energy-constrained LLNs. The main 302 functions of [RFC6775] are to proactively establish the Neighbor 303 Cache Entry (NCE) in the 6LR and to prevent address duplication. To 304 that effect, [RFC6775] introduces a new unicast Address Registration 305 mechanism that contributes to reducing the use of multicast messages 306 compared to the classical IPv6 ND protocol. 308 [RFC6775] defines a new Address Registration Option (ARO) that is 309 carried in the unicast Neighbor Sollicitation (NS) and Neighbor 310 Advertisement (NA) messages between the 6LoWPAN Node (6LN) and the 311 6LoWPAN Router (6LR). It also defines the Duplicate Address Request 312 (DAR) and Duplicate Address Confirmation (DAC) messages between the 313 6LR and the 6LoWPAN Border Router (6LBR). In an LLN, the 6LBR is the 314 central repository of all the Registered Addresses in its domain and 315 the source of truth for uniqueness and ownership. 317 3.2. RFC 8505 Extended Address Registration 319 "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505] 320 updates the behavior of RFC 6775 to enable a generic Address 321 Registration to services such as routing and ND proxy, and defines 322 the Extended Address Registration Option (EARO) as shown in Figure 1: 324 0 1 2 3 325 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 1 326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 | Type | Length | Status | Opaque | 328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 329 | Rsvd | I |R|T| TID | Registration Lifetime | 330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 331 | | 332 ... Registration Ownership Verifier ... 333 | | 334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 336 Figure 1: EARO Option Format 338 3.2.1. R Flag 340 [RFC8505] introduces the "R" flag in the EARO. The Registering Node 341 sets the "R" flag to indicate whether the 6LR should ensure 342 reachability for the Registered Address. If the "R" flag is not set, 343 then the Registering Node handles the reachability of the Registered 344 Address by other means. In a RPL network, this means that either it 345 is a RAN that injects the route by itself or that it uses another RPL 346 Router for reachability services. 348 This document specifies how the "R" flag is used in the context of 349 RPL. A 6LN is a RUL that requires reachability services for an IPv6 350 address if and only if it sets the "R" flag in the NS(EARO) used to 351 register the address to a RPL border router acting as 6LR. Upon 352 receiving the NS(EARO), the RPL router generates a DAO message for 353 the Registered Address if and only if the "R" flag is set. 355 3.2.2. TID, I Field and Opaque Fields 357 The EARO also includes a sequence counter called Transaction ID 358 (TID), which maps to the Path Sequence Field found in Transit Options 359 in RPL DAO messages. This is the reason why the support of [RFC8505] 360 by the RUL as opposed to only [RFC6775] is a prerequisite for this 361 specification (more in Section 7.1). The EARO also transports an 362 Opaque field and an associated "I" field that describes what the 363 Opaque field transports and how to use it. Section 10.2.1 specifies 364 the use of the "I" field and of the Opaque field by a RUL. 366 3.2.3. ROVR 368 Section 5.3 of [RFC8505] introduces the Registration Ownership 369 Verifier (ROVR) field of variable length from 64 to 256 bits. The 370 ROVR is a replacement of the EUI-64 in the ARO [RFC6775] that was 371 used to identify uniquely an Address Registration with the Link-Layer 372 address of the owner but provided no protection against spoofing. 374 "Address Protected Neighbor Discovery for Low-power and Lossy 375 Networks" [AP-ND] leverages the ROVR field as a cryptographic proof 376 of ownership to prevent a rogue third party from misusing the 377 address. [AP-ND] adds a challenge/response exchange to the [RFC8505] 378 Address Registration and enables Source Address Validation by a 6LR 379 that will drop packets with a spoofed address. 381 This specification does not address how the protection by [AP-ND] 382 could be extended to RPL. On the other hand, it adds the ROVR to the 383 DAO to build the proxied EDAR at the Root (see Section 9), which 384 means that nodes that are aware of the Host route to the 6LN are made 385 aware of the associated ROVR as well. 387 3.3. RFC 8505 Extended DAR/DAC 389 [RFC8505] updates the DAR/DAC messages into the Extended DAR/DAC to 390 carry the ROVR field. The EDAR/EDAC exchange takes place between the 391 6LR and the 6LBR. It is triggered by an NS(EARO) message from a 6LN 392 to create, refresh and delete the corresponding state in the 6LBR. 393 The exchange is protected by the ARQ mechanism specified in 8.2.6 of 394 [RFC6775], though in an LLN, a duration longer than the RETRANS_TIMER 395 [RFC4861] of 1 second may be necessary to cover the Turn Around Trip 396 delay between the 6LR and the 6LBR. 398 RPL [RFC6550] specifies a periodic DAO from the 6LN all the way to 399 the Root that maintains the routing state in the RPL network for the 400 lifetime indicated by the source of the DAO. This means that for 401 each address, there are two keep-alive messages that traverse the 402 whole network, one to the Root and one to the 6LBR. 404 This specification avoids the periodic EDAR/EDAC exchange across the 405 LLN. The 6LR turns the periodic NS(EARO) from the RUL into a DAO 406 message to the Root on every refresh, but it only generates the EDAR 407 upon the first registration, for the purpose of DAD, which must be 408 verified before the address is injected in RPL. Upon the DAO 409 message, the Root proxies the EDAR exchange to refresh the state at 410 the 6LBR on behalf of the 6LR, as illustrated in Figure 7. 412 3.3.1. RFC 7400 Capability Indication Option 414 "6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power 415 Wireless Personal Area Networks (6LoWPANs)" [RFC7400] defines the 416 6LoWPAN Capability Indication Option (6CIO) that enables a node to 417 expose its capabilities in Router Advertisement (RA) messages. 418 [RFC8505] defines a number of bits in the 6CIO, in particular: 420 L: Node is a 6LR. 421 E: Node is an IPv6 ND Registrar -- i.e., it supports registrations 422 based on EARO. 423 P: Node is a Routing Registrar, -- i.e., an IPv6 ND Registrar that 424 also provides reachability services for the Registered Address. 426 0 1 2 3 427 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 1 428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 429 | Type | Length = 1 | Reserved |D|L|B|P|E|G| 430 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 431 | Reserved | 432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 434 Figure 2: 6CIO flags 436 A 6LR that can provide reachability services for a RUL in a RPL 437 network as specified in this document SHOULD include a 6CIO in its RA 438 messages and set the L, P and E flags as prescribed by [RFC8505], see 439 Section 7.1 for the corresponding behavior of the RUL. 441 4. Updating RFC 6550 443 This document specifies a new behavior whereby a 6LR injects DAO 444 messages for unicast addresses (see Section 10) and multicast 445 addresses (see Section 11) on behalf of leaves that are not aware of 446 RPL. The RUL addresses are exposed as external targets [RFC6550]. 447 Conforming [USEofRPLinfo], an IP-in-IP encapsulation between the 6LR 448 and the RPL Root is used to carry the RPL artifacts and remove them 449 when forwarding outside the RPL domain, e.g., to a RUL. 451 This document also synchronizes the liveness monitoring at the Root 452 and the 6LBR. The same value of lifetime is used for both, and a 453 single keep-alive message, the RPL DAO, traverses the RPL network. A 454 new behavior is introduced whereby the RPL Root proxies the EDAR 455 message to the 6LBR on behalf of the 6LR (more in Section 6), for any 456 6LN, RUL or RAN. 458 Section 6.7.7 of [RFC6550] introduces RPL Target Option, which can be 459 used in RPL Control messages such as the DAO message to signal a 460 destination prefix. Section 9 adds the capabilities to transport the 461 ROVR field (see Section 3.2.3) and the IPv6 Address of the prefix 462 advertiser when the Target is a shorter prefix, signaled by a new "F" 463 flag. The position of the "F" flag is indicated in Section 13.3. 465 Section 6.7.6 of [RFC6550] defines the DODAG Configuration option 466 with reserved flags. This specification defines the new "Root 467 Proxies EDAR/EDAC" (P) flag and encodes it in one of these reserved 468 flags. The "P" flag is set to indicate that the Root performs the 469 proxy operation, which implies that it supports the Updated RPL 470 Target Option (see Section 9). The position of the "P" flag is 471 indicated in Section 13.2. 473 Section 6.3.1 of [RFC6550] defines a 3-bit Mode of Operation (MOP) in 474 the DIO Base Object. The new "P" flag is defined only for MOP value 475 between 0 to 6. For a MOP value of 7 or above, the flag MAY be 476 redefined and MUST NOT be interpreted as "Root Proxies EDAR/EDAC" 477 unless the specification of the MOP indicates to do so. 479 The RPL Status defined in section 6.5.1 of [RFC6550] for use in the 480 DAO-ACK message is extended to be placed in DCO messages 481 [EFFICIENT-NPDAO] as well. Furthermore, this specification enables 482 to carry the EARO Status defined for 6LoWPAN ND in RPL DAO and DCO 483 messages, embedded in a RPL Status, more in Section 8. 485 5. Updating draft-ietf-roll-efficient-npdao 487 [EFFICIENT-NPDAO] defines the DCO for RPL Storing Mode only, with a 488 link-local scope. This specification extends its use to the Non- 489 Storing MOP, whereby the DCO is sent unicast by the Root directly to 490 the RAN that injected the DAO message for the considered target. 492 This specification leverages the DCO between the Root and the 6LR 493 that serves as attachment router for a RUL. 495 6. Updating RFC 8505 497 This document updates [RFC8505] to change the behavior of a RPL 498 Router acting as 6LR in the 6LoWPAN ND Address Registration of a RUL 499 acting as 6LN. If the RPL Root advertise the capability to proxy the 500 EDAR/EDAC exchange to the 6LBR, the 6LR refrains from sending the 501 keep-alive EDAR message. Instead, if it is separated from the 6LBR, 502 the Root regenerates the EDAR message to the 6LBR periodically, upon 503 a DAO message that signals the liveliness of the Address. 505 7. Requirements on the RPL-Unware Leaf 507 This document provides RPL routing for a RUL, that is a 6LN acting as 508 an IPv6 Host and not aware of RPL. Still, a minimal RPL-independent 509 functionality is required from the RUL to obtain routing services. 511 7.1. Support of 6LoWPAN ND 513 In order to obtain routing services from a 6LR, a RUL MUST implement 514 [RFC8505] and set the "R" flag in the EARO. The RUL SHOULD support 515 [AP-ND] to protect the ownership of its addresses. The RUL MUST NOT 516 request routing services from a 6LR that does not originate RA 517 messages with a CIO that has the L, P, and E flags all set as 518 discussed in Section 3.3.1, unless configured to do so. 520 A RUL that may attach to multiple 6LRs MUST prefer those that provide 521 routing services. The RUL MUST register to all the 6LRs from which 522 it desires routing services. 524 Parallel Address Registrations to several 6LRs SHOULD be performed in 525 an rapid sequence, using the exact same EARO for the same Address. 526 Gaps between the Address Registrations will invalidate some of the 527 routes till the Address Registration finally shows on those routes. 529 [RFC8505] introduces error Status values in the NA(EARO) which can be 530 received synchronously upon an NS(EARO) or asynchronously. The RUL 531 MUST support both cases and MUST refrain from using the address when 532 the Status Value indicates a rejection. 534 7.2. External Routes and RPL Artifacts 536 Section 4.1 of [USEofRPLinfo] provides a set of rules detailed below 537 that MUST be followed for routing packets from and to a RUL. 539 A 6LR that acts as a border router for external routes advertises 540 them using Non-Storing Mode DAO messages that are unicast directly to 541 the Root, even if the DODAG is operated in Storing Mode. Non-Storing 542 Mode routes are not visible inside the RPL domain and all packets are 543 routed via the Root. The RPL Root tunnels the packets directly to 544 the 6LR that advertised the external route, which decapsulates and 545 forwards the original (inner) packet. 547 The RPL Non-Storing MOP signaling and the associated IP-in-IP 548 encapsulated packets appear as normal traffic to the intermediate 549 Routers. The support of external routes only impacts the Root and 550 the 6LR. It can be operated with legacy intermediate routers and 551 does not add to the amount of state that must be maintained in those 552 routers. A RUL is an example of a destination that is reachable via 553 an external route that happens to be also a Host route. 555 The RPL data packets always carry a Hop-by-Hop Header to transport a 556 RPL Packet Information (RPI) [RFC6550]. So unless the RUL originates 557 its packets with an RPI, the 6LR needs to tunnel them to the Root to 558 add the RPI. As a rule of a thumb and except for the very special 559 case above, the packets from and to a RUL are always encapsulated 560 using an IP-in-IP tunnel between the Root and the 6LR that serves the 561 RUL (see sections 7.1.4, 7.2.3, 7.2.4, 7.3.3, 7.3.4, 8.1.3, 8.1.4, 562 8.2.3, 8.2.4, 8.3.3 and 8.3.4 of [USEofRPLinfo] for details). 564 In Non-Storing Mode, packets going down carry a Source Routing Header 565 (SRH). The IP-in-IP encapsulation, the RPI and the SRH are 566 collectively called the "RPL artifacts" and can be compressed using 567 [RFC8138]. Figure 10 presents an example compressed format for a 568 packet forwarded by the Root to a RUL in a Storing Mode DODAG. 570 The inner packet that is forwarded to the RUL may carry some RPL 571 artifacts, e.g., an RPI if the original packet was generated with it, 572 and an SRH in a Non-Storing Mode DODAG. [USEofRPLinfo] expects the 573 RUL to support the basic "IPv6 Node Requirements" [RFC8504]. In 574 particular the RUL is expected to ignore the RPL artifacts that are 575 either consumed or not applicable to a Host. 577 A RUL is not expected to support the compression method defined in 578 [RFC8138]. Unless configured otherwise, the border router MUST 579 restore the outgoing packet before forwarding over an external route, 580 even if it is not the destination of the incoming packet, and even 581 when delivering to a RUL. 583 7.2.1. Support of IPv6 Encapsulation 585 Section 2.1 of [USEofRPLinfo] defines the rules for tunneling either 586 to the final destination (6LN) or to its attachment router (6LR). To 587 terminate the IP-in-IP tunnel, the 6LN, as an IPv6 Host, must be able 588 to decapsulate the tunneled packet and either drop the inner packet 589 if it is not the final destination, or pass it to the upper layer for 590 further processing. Unless it is aware by other means that the RUL 591 can handle IP-in-IP properly, which is not mandated by [RFC8504], the 592 Root terminates the IP-in-IP tunnel at the parent 6LR. It is thus 593 not necessary for a RUL to support IP-in-IP decapsulation. 595 7.2.2. Support of the HbH Header 597 A RUL is expected to process an Option Type in a Hop-by-Hop Header as 598 prescribed by section 4.2 of [RFC8200]. This means that the RPI with 599 an Option Type of 0x23 [USEofRPLinfo] must be skipped when not 600 recognized. 602 7.2.3. Support of the Routing Header 604 A RUL is expected to process an unknown Routing Header Type as 605 prescribed by section 4.4 of [RFC8200]. This implies that the Source 606 Routing Header with a Routing Type of 3 [RFC6554] is ignored when the 607 Segments Left is zero, and the packet is dropped otherwise. 609 8. Updated RPL Status 611 The RPL Status is defined in section 6.5.1 of [RFC6550] for use in 612 the DAO-ACK message and values are assigned as follows: 614 +---------+--------------------------------+ 615 | Range | Meaning | 616 +=========+================================+ 617 | 0 | Success/Unqualified acceptance | 618 +---------+--------------------------------+ 619 | 1-127 | Not an outright rejection | 620 +---------+--------------------------------+ 621 | 128-255 | Rejection | 622 +---------+--------------------------------+ 624 Table 1: RPL Status per RFC 6550 626 The 6LoWPAN ND Status was defined for use in the EARO and the 627 currently defined values are listed in table 1 of [RFC8505]. This 628 specification enables to carry the 6LoWPAN ND Status values in RPL 629 DAO and DCO messages, embedded in the RPL Status field. 631 To achieve this, Section 13.1 reduces the range of the EARO Status 632 values to 0-63 to ensure that they fit within a RPL Status as shown 633 in Figure 3. 635 0 1 2 3 4 5 6 7 636 +-+-+-+-+-+-+-+-+ 637 |E|A| Value | 638 +-+-+-+-+-+-+-+-+ 640 Figure 3: RPL Status Format 642 The following RPL Status subfields are defined: 644 E: 1-bit flag. Set to indicate a rejection. When not set, a value 645 of 0 indicates Success/Unqualified acceptance and other values 646 indicate "not an outright rejection" as per RFC 6550. 648 A: 1-bit flag. Indicates the type of the Status Value. 650 Status Value: 6-bit unsigned integer. If the 'A' flag is set this 651 field transports a Status Value defined for IPv6 ND EARO. When 652 the 'A' flag is not set, the Status Value is defined for RPL. 654 When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a EDAC 655 message, the RPL Root MUST copy the 6LoWPAN ND Status unchanged in 656 the RPL Status and set the 'A' bit. The RPL Root MUST set the 'E' 657 flag for Values in range 1-10 which are all considered rejections. 659 Reciprocally, upon a DCO or a DAO-ACK message from the RPL Root with 660 a RPL Status that has the 'A' bit set, the 6LR MUST copy the RPL 661 Status Value unchanged in the Status field of the EARO when 662 generating an NA to the RUL. 664 9. Updated RPL Target Option 666 This specification updates the RPL Target Option to transport the 667 ROVR that was also defined for 6LoWPAN ND messages. This enables the 668 RPL Root to generate the proxied EDAR message to the 6LBR. 670 The new "F" flag is set to indicate that the Target Prefix field 671 contains the address of the advertising node in full, in which case 672 the length of the Target Prefix field is 16 bytes regardless of the 673 value of the Prefix Length field. 675 If the "F" flag is reset, the Target Prefix field MUST be aligned to 676 the next byte boundary after the size (expressed in bits) indicated 677 by the Prefix Length field. Padding bits are reserved and set to 0 a 678 prescribed by section 6.7.7 of [RFC6550]. 680 With this specification the ROVR is the remainder of the RPL Target 681 Option. The size of the ROVR is indicated in a new ROVR Size field 682 that is encoded to map one-to-one with the Code Suffix in the EDAR 683 message (see table 4 of [RFC8505]). 685 The modified format is illustrated in Figure 4. It is backward 686 compatible with the Target Option in [RFC6550] and SHOULD be used as 687 a replacement in new implementations even for Storing Mode operations 688 in preparation for upcoming security mechanisms based in the ROVR. 690 0 1 2 3 691 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 1 692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 693 | Type = 0x05 | Option Length |ROVRsz |F|Flags| Prefix Length | 694 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 695 | | 696 | Target Prefix (Variable Length) | 697 . . 698 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 699 | | 700 ... Registration Ownership Verifier (ROVR) ... 701 | | 702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 704 Figure 4: Updated Target Option 706 New fields: 708 ROVRsz: Indicates the Size of the ROVR. It MAY be 1, 2, 3, or 4, 709 denoting a ROVR size of 64, 128, 192, or 256 bits, respectively. 711 F: 1-bit flag. Set to indicate that Target Prefix field contains an 712 Address of prefix advertiser in full. 714 Registration Ownership Verifier (ROVR): This is the same field as in 715 the EARO, see [RFC8505] 717 10. Protocol Operations for Unicast Addresses 719 The description below assumes that the Root sets the "P" flag in the 720 DODAG Configuration Option and performs the EDAR proxy operation. 722 If the "P" flag is reset, the 6LR MUST generate the periodic EDAR 723 messages and process the returned status as specified in [RFC8505]. 724 If the EDAC indicates success, the rest of the flow takes place as 725 presented but without the proxied EDAR/EDAC exchange. 727 10.1. General Flow 729 This specification eliminates the need to exchange keep-alive 730 Extended Duplicate Address messages, EDAR and EDAC, all the way from 731 a 6LN to the 6LBR across a RPL mesh. Instead, the EDAR/EDAC exchange 732 with the 6LBR is proxied by the RPL Root upon the DAO message that 733 refreshes the RPL routing state. The first EDAR upon a new 734 Registration cannot be proxied, though, as it serves for the purpose 735 of DAD, which must be verified before the address is injected in RPL. 737 In a RPL network where the function is enabled, refreshing the state 738 in the 6LBR is the responsibility of the Root. Consequently, only 739 addresses that are injected in RPL will be kept alive at the 6LBR by 740 the RPL Root. 742 Since RULs are advertised using Non-Storing Mode, the DAO message 743 flow and the keep alive EDAR/EDAC can be nested within the Address 744 (re)Registration flow. Figure 5 illustrates that for the first 745 Registration, both the DAD and the keep-alive EDAR/EDAC exchanges 746 happen in the same sequence. 748 6LN/RUL 6LR Root 6LBR 749 | | | | 750 | NS(EARO) | | | 751 |--------------->| | 752 | | Extended DAR | 753 | |--------------------------------->| 754 | | | 755 | | Extended DAC | 756 | |<---------------------------------| 757 | | DAO | | 758 | |------------->| | 759 | | | EDAR | 760 | | |------------------>| 761 | | | EDAC | 762 | | |<------------------| 763 | | DAO-ACK | | 764 | |<-------------| | 765 | NA(EARO) | | | 766 |<---------------| | | 767 | | | | 769 Figure 5: First RUL Registration Flow 771 To achieve this, the lifetimes and sequence counters in 6LoWPAN ND 772 and RPL are aligned. In other words, the Path Sequence and the Path 773 Lifetime in the DAO message are taken from the Transaction ID and the 774 Address Registration lifetime in the NS(EARO) message from the 6LN. 776 On the first Address Registration, illustrated in Figure 5 for RPL 777 Non-Storing Mode, the Extended Duplicate Address exchange takes place 778 as prescribed by [RFC8505]. If the exchange fails, the 6LR returns 779 an NA message with a negative status to the 6LN, the NCE is not 780 created and the address is not injected in RPL. If it is successful, 781 the 6LR creates an NCE and injects the Registered Address in the RPL 782 routing using a DAO/DAO-ACK exchange with the RPL DODAG Root. 784 An issue may be detected later, e.g., the address moves within the 785 LLN or to a different Root on a backbone [6BBR]. In that case the 786 value of the status that indicates the issue can be passed from 787 6LoWPAN ND to RPL and back as illustrated in Figure 6. 789 6LN/RUL 6LR Root 6LBR 790 | | | | 791 | | | NA(EARO, Status) | 792 | | |<-----------------| 793 | | DCO(Status) | | 794 | |<------------| | 795 | NA(EARO, Status) | | | 796 |<-----------------| | | 797 | | | | 799 Figure 6: Asynchronous Issue 801 An Address re-Registration is performed by the 6LN to maintain the 802 NCE in the 6LR alive before lifetime expires. Upon the refresh of an 803 Address re-Registration, as illustrated in Figure 7, the 6LR injects 804 the Registered Address in RPL. 806 6LN/RUL 6LR Root 6LBR 807 | | | | 808 | NS(EARO) | | | 809 |--------------->| | 810 | | DAO | | 811 | |------------->| | 812 | | | EDAR | 813 | | |------------------>| 814 | | | EDAC | 815 | | |<------------------| 816 | | DAO-ACK | | 817 | |<-------------| | 818 | NA(EARO) | | | 819 |<---------------| | | 821 Figure 7: Next RUL Registration Flow 823 This is what causes the RPL Root to refresh the state in the 6LBR, 824 using an EDAC message. In case of an error in the proxied EDAR flow, 825 the error is returned in the DAO-ACK using a RPL Status with the 'A' 826 flag set that imbeds a 6LoWPAN Status Value as discussed in 827 Section 8. 829 The 6LR may receive a requested DAO-ACK after it received an 830 asynchronous DCO, but the negative Status in the DCO supersedes a 831 positive Status in the DAO-ACK regardless of the order in which they 832 are received. Upon the DAO-ACK - or the DCO if one arrives first - 833 the 6LR responds to the RUL with an NA(EARO). 835 The RUL MAY terminate the registration at any time by using a 836 Registration Lifetime of 0. This specification requires that the RPL 837 Target Option transports the ROVR. This way, the same flow as the 838 heartbeat flow is sufficient to inform the 6LBR using the Root as 839 proxy as illustrated in Figure 7. 841 Any combination of the logical functions of 6LR, Root and 6LBR might 842 be collapsed in a single node. 844 10.2. Detailed Operation 846 10.2.1. Perspective of the RUL Acting as 6LN 848 This specification does not alter the operation of a 6LoWPAN ND- 849 compliant 6LN, and a RUL is expected to operate as follows: 851 1. The 6LN obtains an IPv6 global address, either using Stateless 852 Address Autoconfiguration (SLAAC) [RFC4862] based on a Prefix 853 Information Option (PIO) [RFC4861] found in an RA message, or 854 some other means such as DHCPv6 [RFC3315]. 856 2. Once it has formed an address, the 6LN (re)registers its address 857 periodically, within the Lifetime of the previous Address 858 Registration, as prescribed by [RFC6775] and [RFC8505], to 859 refresh the NCE before the lifetime indicated in the EARO 860 expires. The TID is incremented each time and wraps in a 861 lollipop fashion (see section 5.2.1 of [RFC8505] which is fully 862 compatible with section 7.2 of [RFC6550]). 864 3. As stated in section 5.2 of [RFC8505], the 6LN can register to 865 more than one 6LR at the same time. In that case, it uses the 866 same EARO for all of the parallel Address Registrations. The 6LN 867 SHOULD send the registration(s) that have a non-zero Registration 868 Lifetime and ensure that one succeeds before it terminates other 869 registrations, to maintain the state in the network and at the 870 6LBR and minimize the churn. 872 4. Following section 5.1 of [RFC8505], a 6LN acting as a RUL sets 873 the "R" flag in the EARO of at least one registration, whereas 874 acting as an RAN it never does. If the "R" flag is not echoed in 875 the NA, the RUL SHOULD attempt to use another 6LR. The RUL 876 SHOULD send the registration(s) with the "R" flag set and ensure 877 that one succeeds before it sends the registrations with the flag 878 reset. In case of a conflict with the preceeding rule on 879 lifetime, the rule on lifetime has precedence. 881 5. The 6LN may use any of the 6LRs to which it registered as default 882 gateway. Using a 6LR to which the 6LN is not registered may 883 result in packets dropped at the 6LR by a Source Address 884 Validation function (SAVI) so it is NOT RECOMMENDED. 886 Even without support for RPL, a RUL may be aware of opaque values to 887 be provided to the routing protocol. If the RUL has a knowledge of 888 the RPL Instance the packet should be injected into, then it SHOULD 889 set the Opaque field in the EARO to the RPLInstanceID, else it MUST 890 leave the Opaque field to zero. 892 Regardless of the setting of the Opaque field, the 6LN MUST set the 893 "I" field to zero to signal "topological information to be passed to 894 a routing process" as specified in section 5.1 of [RFC8505]. 896 A RUL is not expected to produce RPL artifacts in the data packets, 897 but it MAY do so. For instance, if the RUL has a minimal awareness 898 of the RPL Instance then it can build an RPI. A RUL that places an 899 RPI in a data packet MUST indicate the RPLInstanceID of the RPL 900 Instance where the packet should be forwarded. All the flags and the 901 Rank field are set to zero as specified by section 11.2 of [RFC6550]. 903 10.2.2. Perspective of the Border Router Acting as 6LR 905 Also as prescribed by [RFC8505], the 6LR generates an EDAR message 906 upon reception of a valid NS(EARO) message for the registration of a 907 new IPv6 Address by a 6LN. If the initial EDAR/EDAC exchange 908 succeeds, then the 6LR installs an NCE for the Registration Lifetime. 909 For the refreshes of the registration, if the RPL Root has indicated 910 that it proxies the keep-alive EDAR/EDAC exchange with the 6LBR (see 911 Section 4), the 6LR MUST refrain from sending the keep-alive EDAR. 913 If the "R" flag is set in the NS(EARO), the 6LR SHOULD attempt to 914 inject the host route in RPL, unless this is barred for other 915 reasons, like a saturation of the network or if its RPL parent. The 916 6LR MUST use a RPL Non-Storing Mode signaling. The 6LR MUST request 917 a DAO-ACK by setting the 'K' flag in the DAO message. Success 918 injecting the route to the RUL is indicated by the 'E' flag set to 0 919 in the RPL status of the DAO-ACK message. 921 The Opaque field in the EARO hints the 6LR on the RPL Instance that 922 SHOULD be used for the DAO advertisements, and for the forwarding of 923 packets sourced at the registered address when there is no RPI in the 924 packet, in which case the 6LR MUST encapsulate the packet to the Root 925 adding an RPI in the outer header. If the Opaque field is zero, the 926 6LR is free to use the default RPL Instance (zero) for the registered 927 address or to select an Instance of its choice. 929 if the "I" field is not zero, then the 6LR MUST consider that the 930 Opaque field is zero. If the Opaque field is not zero, then it is 931 expected to carry a RPLInstanceID for the RPL Instance suggested by 932 the 6LN. If the 6LR does not participate to the associated Instance, 933 then the 6LR MUST consider that the Opaque field is zero; else, that 934 is if the 6LR participates to the suggested RPL Instance, then the 935 6LR SHOULD use that Instance for the Registered Address. 937 The DAO message advertising the Registered Address MUST be 938 constructed as follows: 940 1. The Registered Address is signaled as Target Prefix in the RPL 941 Target Option in the DAO message; the Prefix Length is set to 128 943 2. The 6LR indicates one of its global or unique-local IPv6 unicast 944 addresses as the Parent Address in the RPL Transit Information 945 Option (TIO) associated with the Target Option 947 3. The 6LR sets the External 'E' flag in the TIO to indicate that it 948 redistributes an external target into the RPL network 950 4. the Path Lifetime in the TIO is computed from the Lifetime in the 951 EARO Option. This adapts it to the Lifetime Units used in the 952 RPL operation; note that if the lifetime is 0, then the DAO 953 message is a No-Path DAO that cleans up the the routes down to 954 the RUL; this also causes the Root as a proxy to send an EDAR 955 message to the 6LBR with a Lifetime of 0. 957 5. the Path Sequence in the TIO is set to the TID value found in the 958 EARO option. 960 Upon receiving the DAO-ACK or an asynchronous DCO message, the 6LR 961 MUST send the NA(EARO) to the RUL. 963 The 6LR MUST set "R" flag in the NA(EARO) back if and only if the 'E' 964 flag is reset, indicating that the 6LR injected the Registered 965 Address in the RPL routing successfully and that the EDAR proxy 966 operation succeeded. 968 If the 'A' flag in the RPL Status is set, the embedded Status Value 969 is passed back to the RUL in the EARO Status. If the 'E' flags is 970 also set, the registration failed for 6LoWPAN ND related reasons, and 971 the NCE is removed. 973 If the 'A' flag is not set in the RPL Status of the DAO-ACK, then the 974 6LoWPAN ND operation succeeded and an EARO Status of 0 (Success) MUST 975 be returned to the RUL, even if the 'E' flag is set in the RPL 976 Status. The EARO Status of 0 MUST also be used if the 6LR could not 977 even try to inject the route. 979 This means that, in case of an error injecting the route that is not 980 related to ND, the registration succeeds but the RPL route is not 981 installed, which is signaled by the "R" flag reset. It is up to the 982 6LN to keep the binding with the 6LR or destroy it. 984 In a network where Address Protected Neighbor Discovery (AP-ND) is 985 enabled, in case of a DAO-ACK or a DCO indicating transporting an 986 EARO Status Value of 5 (Validation Requested), the 6LR MUST challenge 987 the 6LN for ownership of the address, as described in section 6.1 of 988 [AP-ND], before the Registration is complete. This ensures that the 989 address is validated before it is injected in the RPL routing. 991 If the challenge succeeds then the operations continue as normal. In 992 particular a DAO message is generated upon the NS(EARO) that proves 993 the ownership of the address. If the challenge failed, the 6LR 994 rejects the registration as prescribed by AP-ND and may take actions 995 to protect itself against DoS attacks by a rogue 6LN, see Section 12. 997 The 6LR may at any time send a unicast asynchronous NA(EARO) with the 998 "R" flag reset to signal that it stops providing routing services, 999 and/or with the EARO Status 2 "Neighbor Cache full" to signal that it 1000 removes the NCE. It may also send a final RA, unicast or multicast, 1001 with a Router Lifetime field of zero, to signal that it stops serving 1002 as router, as specified in section 6.2.5 of [RFC4861]. 1004 If a 6LR receives a valid NS(EARO) message with the "R" flag reset 1005 and a Registration Lifetime that is not 0, and the 6LR was injecting 1006 the Registered Address due to previous NS(EARO) messages with the "R" 1007 flag set, then the 6LR MUST stop injecting the address. It is up to 1008 the Registering 6LN to maintain the corresponding route from then on, 1009 either keeping it active via a different 6LR or by acting as an RAN 1010 and managing its own reachability. 1012 10.2.3. Perspective of the RPL Root 1014 A RPL Root SHOULD set the "P" flag in the RPL configuration option of 1015 the DIO messages that it generates (see Section 4) to signal that it 1016 proxies the EDAR/EDAC exchange and supports the Updated RPL Target 1017 option. The remainder of this section assumes that it does. 1019 Upon reception of a DAO message, for each RPL Target Option that 1020 creates or updates an existing RPL state, the Root MUST notify the 1021 6LBR. This can be done using an internal API if they are integrated, 1022 or using a proxied EDAR/EDAC exchange if they are separate entities. 1024 Upon receiving an EDAC message from the 6LBR, if a DAO is pending, 1025 then the Root MUST send a DAO-ACK back to the 6LR. Else, if the 1026 Status in the EDAC message is not "Success", then it MUST send an 1027 asynchronous DCO to the 6LR. 1029 In either case, the EDAC Status is embedded in the RPL Status with 1030 the 'A' flag set. 1032 The EDAR message MUST be constructed as follows: 1034 1. The Target IPv6 address from the RPL Target Option is placed in 1035 the Registered Address field of the EDAR message; 1037 2. the Registration Lifetime is adapted from the Path Lifetime in 1038 the TIO by converting the Lifetime Units used in RPL into units 1039 of 60 seconds used in the 6LoWPAN ND messages; 1041 3. the TID value is set to the Path Sequence in the TIO and 1042 indicated with an ICMP code of 1 in the EDAR message; 1044 4. The ROVR in the RPL Target Option is copied as is in the EDAR and 1045 the ICMP Code Suffix is set to the appropriate value as shown in 1046 Table 4 of [RFC8505] depending on the size of the ROVR field. 1048 10.2.4. Perspective of the 6LBR 1050 The 6LBR is unaware that the RPL Root is not the new attachment 6LR 1051 of the RUL, so it is not impacted by this specification. 1053 Upon reception of an EDAR message, the 6LBR acts as prescribed by 1054 [RFC8505] and returns an EDAC message to the sender. 1056 11. Protocol Operations for Multicast Addresses 1058 Section 12 of [RFC6550] details the RPL support for multicast flows. 1059 This support is not source-specific and only operates as an extension 1060 to the Storing Mode of Operation for unicast packets. Note that it 1061 is the RPL model that the multicast packet is passed as a Layer-2 1062 unicast to each of the interested children. This remains true when 1063 forwarding between the 6LR and the listener 6LN. 1065 "Multicast Listener Discovery (MLD) for IPv6" [RFC2710] and its 1066 updated version "Multicast Listener Discovery Version 2 (MLDv2) for 1067 IPv6" [RFC3810] provide an interface for a listener to register to 1068 multicast flows. MLDv2 is backwards compatible with MLD, and adds in 1069 particular the capability to filter the sources via black lists and 1070 white lists. In the MLD model, the Router is a "querier" and the 1071 Host is a multicast listener that registers to the querier to obtain 1072 copies of the particular flows it is interested in. 1074 On the first Address Registration, as illustrated in Figure 8, the 1075 6LN, as an MLD listener, sends an unsolicited Report to the 6LR in 1076 order to start receiving the flow immediately. 1078 6LN/RUL 6LR Root 6LBR 1079 | | | | 1080 | unsolicited Report | | | 1081 |------------------->| | | 1082 | | | | 1083 | | DAO | | 1084 | |-------------->| | 1085 | | DAO-ACK | | 1086 | |<--------------| | 1087 | | | | 1088 | | | unsolicited Report | 1089 | | |------------------->| 1090 | | | | 1092 Figure 8: First Multicast Registration Flow 1094 Since multicast Layer-2 messages are avoided, it is important that 1095 the asynchronous messages for unsolicited Report and Done are sent 1096 reliably, for instance using a Layer-2 acknowledgment, or attempted 1097 multiple times. 1099 The 6LR acts as a generic MLD querier and generates a DAO for the 1100 multicast target. The lifetime of the DAO is set to be in the order 1101 of the Query Interval, yet larger to account for variable propagation 1102 delays. 1104 The Root proxies the MLD exchange as a listener with the 6LBR acting 1105 as the querier, so as to get packets from a source external to the 1106 RPL domain. 1108 Upon a DAO with a multicast target, the RPL Root checks if it is 1109 already registered as a listener for that address, and if not, it 1110 performs its own unsolicited Report for the multicast target. 1112 An Address re-Registration is pulled periodically by 6LR acting as 1113 querier. Note that the message may be sent unicast to all the known 1114 individual listeners. 1116 Upon the timing out of the Query Interval, the 6LR sends a Query to 1117 each of its listeners, and gets a Report back that is mapped into a 1118 DAO, as illustrated in Figure 9: 1120 6LN/RUL 6LR Root 6LBR 1121 | | | | 1122 | Query | | | 1123 |<-------------------| | | 1124 | Report | | | 1125 |------------------->| | | 1126 | | | | 1127 | | DAO | | 1128 | |-------------->| | 1129 | | DAO-ACK | | 1130 | |<--------------| | 1131 | | | | 1132 | | | Query | 1133 | | |<-------------------| 1134 | | | Report | 1135 | | |------------------->| 1136 | | | | 1137 | | | | 1139 Figure 9: Next Registration Flow 1141 Note that any of the functions 6LR, Root and 6LBR might be collapsed 1142 in a single node, in which case the flow above happens internally, 1143 and possibly through internal API calls as opposed to messaging. 1145 12. Security Considerations 1147 First of all, it is worth noting that with [RFC6550], every node in 1148 the LLN is RPL-aware and can inject any RPL-based attack in the 1149 network. This specification isolates edge nodes that can only 1150 interact with the RPL routers using 6LoWPAN ND, meaning that they 1151 cannot perform RPL insider attacks. 1153 6LoWPAN ND can optionally provide SAVI features with [AP-ND], which 1154 reduces even more the attack perimeter that is available to the edge 1155 nodes. 1157 The LLN nodes depend on the 6LBR and the RPL participants for their 1158 operation. A trust model must be put in place to ensure that the 1159 right devices are acting in these roles, so as to avoid threats such 1160 as black-holing, (see [RFC7416] section 7) or bombing attack whereby 1161 an impersonated 6LBR would destroy state in the network by using the 1162 "Removed" Status code. 1164 This trust model could be at a minimum based on a Layer-2 Secure 1165 joining and the Link-Layer security. This is a generic 6LoWPAN 1166 requirement, see Req5.1 in Appendix of [RFC8505]. 1168 Additionally, the trust model could include a role validation to 1169 ensure that the node that claims to be a 6LBR or a RPL Root is 1170 entitled to do so. 1172 At the time of this writing RPL does not have a zerotrust model 1173 whereby it is possible to validate the origin of an address that is 1174 injected in a DAO. This specification makes a first step in that 1175 direction by allowing the Root to challenge the RUL via the 6LR that 1176 serves it. 1178 13. IANA Considerations 1180 13.1. Resizing the ARO Status values 1182 Section 12 of [RFC6775] creates the Address Registration Option 1183 Status Values Registry with a range 0-255. This specification 1184 reduces that range to 0-63. 1186 IANA is requested to reduce the unassigned values range from 11-255 1187 to 11-63. 1189 13.2. New DODAG Configuration Option Flag 1191 This specification updates the Registry for the "DODAG Configuration 1192 Option Flags" that was created for [RFC6550] as follows: 1194 +------------+----------------------------+-----------+ 1195 | Bit Number | Capability Description | Reference | 1196 +============+============================+===========+ 1197 | 1 | Root Proxies EDAR/EDAC (P) | THIS RFC | 1198 +------------+----------------------------+-----------+ 1200 Table 2: New DODAG Configuration Option Flag 1202 13.3. New RPL Target Option Flag 1204 Section 20.15 of [RFC6550] creates a Registry for the 8-bit "RPL 1205 Target Option Flags" field. IANA is requested to reduce the size of 1206 the field in the Registry to 4 bits. This specification also defines 1207 a new entry in the Registry as follows: 1209 +------------+--------------------------------+-----------+ 1210 | Bit Number | Capability Description | Reference | 1211 +============+================================+===========+ 1212 | 1 | Advertiser Address in Full (F) | THIS RFC | 1213 +------------+--------------------------------+-----------+ 1215 Table 3: New RPL Target Option Flag 1217 13.4. New Subregistry for the RPL Non-Rejection Status values 1219 This specification creates a new Subregistry for the RPL Non- 1220 Rejection Status values for use in RPL DAO-ACK and DCO messages with 1221 the 'A' flag reset, under the ICMPv6 parameters registry. 1223 * Possible values are 6-bit unsigned integers (0..63). 1225 * Registration procedure is "Standards Action" [RFC8126]. 1227 * Initial allocation is as indicated in Table 4: 1229 +-------+------------------------+-----------+ 1230 | Value | Meaning | Reference | 1231 +=======+========================+===========+ 1232 | 0 | Unqualified acceptance | RFC 6550 | 1233 +-------+------------------------+-----------+ 1235 Table 4: Acceptance values of the RPL Status 1237 13.5. New Subregistry for the RPL Rejection Status values 1239 This specification creates a new Subregistry for the RPL Rejection 1240 Status values for use in RPL DAO-ACK and RCO messages with the 'A' 1241 flag reset, under the ICMPv6 parameters registry. 1243 * Possible values are 6-bit unsigned integers (0..63). 1245 * Registration procedure is "Standards Action" [RFC8126]. 1247 * Initial allocation is as indicated in Table 5: 1249 +-------+-----------------------+---------------+ 1250 | Value | Meaning | Reference | 1251 +=======+=======================+===============+ 1252 | 0 | Unqualified rejection | This document | 1253 +-------+-----------------------+---------------+ 1255 Table 5: Rejection values of the RPL Status 1257 13.6. Fixing the Address Registration Option Flags 1259 Section 9.1 of [RFC8505] creates a Registry for the 8-bit Address 1260 Registration Option Flags field. 1262 IANA is requested to rename the first column of the table from "ARO 1263 Status" to "Bit number". 1265 14. Acknowledgments 1267 The authors wish to thank Ines Robles, Georgios Papadopoulos and 1268 Rahul Jadhav for their reviews and contributions to this document. 1270 15. Normative References 1272 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1273 Requirement Levels", BCP 14, RFC 2119, 1274 DOI 10.17487/RFC2119, March 1997, 1275 . 1277 [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast 1278 Listener Discovery (MLD) for IPv6", RFC 2710, 1279 DOI 10.17487/RFC2710, October 1999, 1280 . 1282 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1283 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1284 DOI 10.17487/RFC3810, June 2004, 1285 . 1287 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1288 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1289 Overview, Assumptions, Problem Statement, and Goals", 1290 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1291 . 1293 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1294 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1295 DOI 10.17487/RFC4861, September 2007, 1296 . 1298 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1299 Address Autoconfiguration", RFC 4862, 1300 DOI 10.17487/RFC4862, September 2007, 1301 . 1303 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1304 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1305 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1306 Low-Power and Lossy Networks", RFC 6550, 1307 DOI 10.17487/RFC6550, March 2012, 1308 . 1310 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1311 Power and Lossy Networks (RPL) Option for Carrying RPL 1312 Information in Data-Plane Datagrams", RFC 6553, 1313 DOI 10.17487/RFC6553, March 2012, 1314 . 1316 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1317 Routing Header for Source Routes with the Routing Protocol 1318 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1319 DOI 10.17487/RFC6554, March 2012, 1320 . 1322 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1323 Bormann, "Neighbor Discovery Optimization for IPv6 over 1324 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1325 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1326 . 1328 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1329 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1330 2014, . 1332 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1333 Constrained-Node Networks", RFC 7228, 1334 DOI 10.17487/RFC7228, May 2014, 1335 . 1337 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 1338 IPv6 over Low-Power Wireless Personal Area Networks 1339 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 1340 2014, . 1342 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1343 Writing an IANA Considerations Section in RFCs", BCP 26, 1344 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1345 . 1347 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1348 "IPv6 over Low-Power Wireless Personal Area Network 1349 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1350 April 2017, . 1352 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1353 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1354 May 2017, . 1356 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1357 (IPv6) Specification", STD 86, RFC 8200, 1358 DOI 10.17487/RFC8200, July 2017, 1359 . 1361 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1362 Perkins, "Registration Extensions for IPv6 over Low-Power 1363 Wireless Personal Area Network (6LoWPAN) Neighbor 1364 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1365 . 1367 [AP-ND] Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 1368 "Address Protected Neighbor Discovery for Low-power and 1369 Lossy Networks", Work in Progress, Internet-Draft, draft- 1370 ietf-6lo-ap-nd-23, 30 April 2020, 1371 . 1373 [USEofRPLinfo] 1374 Robles, I., Richardson, M., and P. Thubert, "Using RPI 1375 Option Type, Routing Header for Source Routes and IPv6-in- 1376 IPv6 encapsulation in the RPL Data Plane", Work in 1377 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-38, 1378 23 March 2020, . 1381 [EFFICIENT-NPDAO] 1382 Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient 1383 Route Invalidation", Work in Progress, Internet-Draft, 1384 draft-ietf-roll-efficient-npdao-18, 15 April 2020, 1385 . 1388 16. Informative References 1390 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1391 Statement and Requirements for IPv6 over Low-Power 1392 Wireless Personal Area Network (6LoWPAN) Routing", 1393 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1394 . 1396 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 1397 C., and M. Carney, "Dynamic Host Configuration Protocol 1398 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 1399 2003, . 1401 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1402 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1403 DOI 10.17487/RFC6282, September 2011, 1404 . 1406 [RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur, 1407 Ed., "Performance Evaluation of the Routing Protocol for 1408 Low-Power and Lossy Networks (RPL)", RFC 6687, 1409 DOI 10.17487/RFC6687, October 2012, 1410 . 1412 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1413 and M. Richardson, Ed., "A Security Threat Analysis for 1414 the Routing Protocol for Low-Power and Lossy Networks 1415 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1416 . 1418 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1419 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1420 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1421 . 1423 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node 1424 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504, 1425 January 2019, . 1427 [6BBR] Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6 1428 Backbone Router", Work in Progress, Internet-Draft, draft- 1429 ietf-6lo-backbone-router-20, 23 March 2020, 1430 . 1433 Appendix A. Example Compression 1435 Figure 10 illustrates the case in Storing Mode where the packet is 1436 received from the Internet, then the Root encapsulates the packet to 1437 insert the RPI and deliver to the 6LR that is the parent and last hop 1438 to the final destination, which is not known to support [RFC8138]. 1440 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1441 |11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP 1442 |Page 1 |Type1 S=0| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 1443 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1444 <-4 bytes-> <- RFC 6282 -> 1445 <- No RPL artifact ... 1447 Figure 10: Encapsulation to Parent 6LR in Storing Mode 1449 The difference with the example presented in Figure 19 of [RFC8138] 1450 is the addition of a SRH-6LoRH before the RPI-6LoRH to transport the 1451 compressed address of the 6LR as the destination address of the outer 1452 IPv6 header. In the original example the destination IP of the outer 1453 header was elided and was implicitly the same address as the 1454 destination of the inner header. Type 1 was arbitrarily chosen, and 1455 the size of 0 denotes a single address in the SRH. 1457 In Figure 10, the source of the IP-in-IP encapsulation is the Root, 1458 so it is elided in the IP-in-IP 6LoRH. The destination is the parent 1459 6LR of the destination of the inner packet so it cannot be elided. 1460 If the DODAG is operated in Storing Mode, it is the single entry in 1461 the SRH-6LoRH and the SRH-6LoRH Size is encoded as 0. The SRH-6LoRH 1462 is the first 6LoRH in the chain. In this particular example, the 6LR 1463 address can be compressed to 2 bytes so a Type of 1 is used. It 1464 results that the total length of the SRH-6LoRH is 4 bytes. 1466 In Non-Storing Mode, the encapsulation from the Root would be similar 1467 to that represented in Figure 10 with possibly more hops in the SRH- 1468 6LoRH and possibly multiple SRH-6LoRHs if the various addresses in 1469 the routing header are not compressed to the same format. Note that 1470 on the last hop to the parent 6LR, the RH3 is consumed and removed 1471 from the compressed form, so the use of Non-Storing Mode vs. Storing 1472 Mode is indistinguishable from the packet format. 1474 The SRH-6LoRHs are followed by RPI-6LoRH and then the IP-in-IP 6LoRH. 1475 When the IP-in-IP 6LoRH is removed, all the 6LoRH Headers that 1476 precede it are also removed. The Paging Dispatch [RFC8025] may also 1477 be removed if there was no previous Page change to a Page other than 1478 0 or 1, since the LOWPAN_IPHC is encoded in the same fashion in the 1479 default Page 0 and in Page 1. The resulting packet to the 1480 destination is the inner packet compressed with [RFC6282]. 1482 Authors' Addresses 1484 Pascal Thubert (editor) 1485 Cisco Systems, Inc 1486 Building D 1487 45 Allee des Ormes - BP1200 1488 06254 Mougins - Sophia Antipolis 1489 France 1491 Phone: +33 497 23 26 34 1492 Email: pthubert@cisco.com 1494 Michael C. Richardson 1495 Sandelman Software Works 1497 Email: mcr+ietf@sandelman.ca 1498 URI: http://www.sandelman.ca/