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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reference to an Informational RFC: RFC 7102 ** Downref: Normative reference to an Informational RFC: RFC 7228 == Outdated reference: A later version (-44) exists of draft-ietf-roll-useofrplinfo-38 -- Obsolete informational reference (is this intentional?): RFC 3315 (Obsoleted by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 12 June 2020 7 Expires: 14 December 2020 9 Routing for RPL Leaves 10 draft-ietf-roll-unaware-leaves-18 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 14 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. Fixing the Address Registration Option Flags . . . . . . 25 87 13.2. Resizing the ARO Status values . . . . . . . . . . . . . 25 88 14. New DODAG Configuration Option Flag . . . . . . . . . . . . . 26 89 15. New RPL Target Option Flag . . . . . . . . . . . . . . . . . 26 90 16. New Subregistry for the RPL Non-Rejection Status values . . . 26 91 17. New Subregistry for the RPL Rejection Status values . . . . . 27 92 18. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27 93 19. Normative References . . . . . . . . . . . . . . . . . . . . 27 94 20. Informative References . . . . . . . . . . . . . . . . . . . 29 95 Appendix A. Example Compression . . . . . . . . . . . . . . . . 31 96 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 98 1. Introduction 100 The design of Low Power and Lossy Networks (LLNs) is generally 101 focused on saving energy, which is the most constrained resource of 102 all. Other design constraints, such as a limited memory capacity, 103 duty cycling of the LLN devices and low-power lossy transmissions, 104 derive from that primary concern. 106 The IETF produced the "Routing Protocol for Low Power and Lossy 107 Networks" [RFC6550] (RPL) to provide IPv6 [RFC8200] routing services 108 within such constraints. RPL belongs to the class of Distance-Vector 109 protocols, which, compared to link-state protocols, limit the amount 110 of topological knowledge that needs to be installed and maintained in 111 each node, and does not require convergence to avoid micro-loops. 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 Destination- 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 for outwards traffic 138 only, or with routing back to the devices as well. In the latter 139 case, a RAN injects routes to itself using Destination Advertisement 140 Object (DAO) messages sent either to parent-nodes, in the RPL Storing 141 Mode, or to the Root indicating their parent, in the Non-Storing 142 Mode. This process effectively forms a DODAG back to the device that 143 is a subset of the DODAG to the Root with all links reversed. 145 RPL can be deployed as an extension to IPv6 Neighbor Discovery (ND) 146 [RFC4861][RFC4862] and 6LoWPAN ND [RFC6775][RFC8505] to maintain 147 reachability within a Non-Broadcast Multi-Access (NBMA) subnet. In 148 that mode, some nodes may act as Routers and participate to the 149 forwarding operations whereas others will only terminate packets, 150 acting as Hosts in the data-plane. In [RFC6550] terms, a Host that 151 is reachable over the RPL network is called a Leaf. 153 "When to use RFC 6553, 6554 and IPv6-in-IPv6" [USEofRPLinfo] 154 introduces the term RPL-Aware-Leaf (RAL) for a Leaf that injects 155 routes in RPL to manage the reachability of its own IPv6 addresses. 156 In contrast, the term RPL-Unaware Leaf (RUL) designates a Leaf 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) and 164 request that the 6LR injects a Host route for the Registered Address 165 in the RPL routing on its behalf. A RUL may be unable to participate 166 because it is very energy-constrained, or because it is unsafe to let 167 it inject routes in RPL, in which case using 6LowPAN ND as the 168 interface for the RUL limits the surface of the possible attacks and 169 optionally protects the address ownership. 171 The RPL Non-Storing Mode mechanism is used to extend the routing 172 state with connectivity to the RULs even when the DODAG is operated 173 in Storing Mode. The unicast packet forwarding operation by the 6LR 174 serving a 6LN that is also a RUL 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, a 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 serial links and transit media such as 295 Ethernet. It is a reactive protocol that relies heavily on multicast 296 operations for address discovery (aka lookup) and duplicate address 297 detection (DAD). 299 "Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775] 300 adapts IPv6 ND for operations over energy-constrained LLNs. The main 301 functions of [RFC6775] are to proactively establish the Neighbor 302 Cache Entry (NCE) in the 6LR and to prevent address duplication. To 303 that effect, [RFC6775] introduces a new unicast Address Registration 304 mechanism that contributes to reducing the use of multicast messages 305 compared to the classical IPv6 ND protocol. 307 [RFC6775] defines a new Address Registration Option (ARO) that is 308 carried in the unicast Neighbor solicitation (NS) and Neighbor 309 Advertisement (NA) messages between the 6LoWPAN Node (6LN) and the 310 6LoWPAN Router (6LR). It also defines the Duplicate Address Request 311 (DAR) and Duplicate Address Confirmation (DAC) messages between the 312 6LR and the 6LoWPAN Border Router (6LBR). In an LLN, the 6LBR is the 313 central repository of all the Registered Addresses in its domain and 314 the source of truth for uniqueness and ownership. 316 3.2. RFC 8505 Extended Address Registration 318 "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505] 319 updates the behavior of RFC 6775 to enable a generic Address 320 Registration to services such as routing and ND proxy, and defines 321 the Extended Address Registration Option (EARO) as shown in Figure 1: 323 0 1 2 3 324 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 1 325 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 326 | Type | Length | Status | Opaque | 327 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 328 | Rsvd | I |R|T| TID | Registration Lifetime | 329 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 330 | | 331 ... Registration Ownership Verifier ... 332 | | 333 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 335 Figure 1: EARO Option Format 337 3.2.1. R Flag 339 [RFC8505] introduces the "R" flag in the EARO. The Registering Node 340 sets the "R" flag to indicate whether the 6LR should ensure 341 reachability for the Registered Address. If the "R" flag is not set, 342 then the Registering Node handles the reachability of the Registered 343 Address by other means. In a RPL network, this means that either it 344 is a RAN that injects the route by itself or that it uses another RPL 345 Router for reachability services. 347 This document specifies how the "R" flag is used in the context of 348 RPL. A 6LN is a RUL that requires reachability services for an IPv6 349 address if and only if it sets the "R" flag in the NS(EARO) used to 350 register the address to a RPL border router acting as 6LR. Upon 351 receiving the NS(EARO), the RPL router generates a DAO message for 352 the Registered Address if and only if the "R" flag is set. 354 3.2.2. TID, I Field and Opaque Fields 356 When the "T" flag is set, the EARO includes a sequence counter called 357 Transaction ID (TID), which maps to the Path Sequence Field found in 358 the RPL Transit Option. This is the reason why the support of 359 [RFC8505] by the RUL as opposed to only [RFC6775] is a prerequisite 360 for this specification (more in Section 7.1). The EARO also 361 transports an Opaque field and an associated "I" field that describes 362 what the Opaque field transports and how to use it. Section 10.2.1 363 specifies the use of the "I" field and of the Opaque field by a RUL. 365 3.2.3. ROVR 367 Section 5.3 of [RFC8505] introduces the Registration Ownership 368 Verifier (ROVR) field of variable length from 64 to 256 bits. The 369 ROVR is a replacement of the EUI-64 in the ARO [RFC6775] that was 370 used to identify uniquely an Address Registration with the Link-Layer 371 address of the owner but provided no protection against spoofing. 373 "Address Protected Neighbor Discovery for Low-power and Lossy 374 Networks" [AP-ND] leverages the ROVR field as a cryptographic proof 375 of ownership to prevent a rogue third party from misusing the 376 address. [AP-ND] adds a challenge/response exchange to the [RFC8505] 377 Address Registration and enables Source Address Validation by a 6LR 378 that will drop packets with a spoofed address. 380 This specification does not address how the protection by [AP-ND] 381 could be extended to RPL. On the other hand, it adds the ROVR to the 382 DAO to build the proxied EDAR at the Root (see Section 9), which 383 means that nodes that are aware of the Host route to the 6LN are made 384 aware of the associated ROVR as well. 386 3.3. RFC 8505 Extended DAR/DAC 388 [RFC8505] updates the DAR/DAC messages into the Extended DAR/DAC to 389 carry the ROVR field. The EDAR/EDAC exchange takes place between the 390 6LR and the 6LBR. It is triggered by an NS(EARO) message from a 6LN 391 to create, refresh and delete the corresponding state in the 6LBR. 392 The exchange is protected by the ARQ mechanism specified in 8.2.6 of 393 [RFC6775], though in an LLN, a duration longer than the RETRANS_TIMER 394 [RFC4861] of 1 second may be necessary to cover the Turn Around Trip 395 delay between the 6LR and the 6LBR. 397 RPL [RFC6550] specifies a periodic DAO from the 6LN all the way to 398 the Root that maintains the routing state in the RPL network for the 399 lifetime indicated by the source of the DAO. This means that for 400 each address, there are two keep-alive messages that traverse the 401 whole network, one to the Root and one to the 6LBR. 403 This specification avoids the periodic EDAR/EDAC exchange across the 404 LLN. The 6LR turns the periodic NS(EARO) from the RUL into a DAO 405 message to the Root on every refresh, but it only generates the EDAR 406 upon the first registration, for the purpose of DAD, which must be 407 verified before the address is injected in RPL. Upon the DAO 408 message, the Root proxies the EDAR exchange to refresh the state at 409 the 6LBR on behalf of the 6LR, as illustrated in Figure 7. 411 3.3.1. RFC 7400 Capability Indication Option 413 "6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power 414 Wireless Personal Area Networks (6LoWPANs)" [RFC7400] defines the 415 6LoWPAN Capability Indication Option (6CIO) that enables a node to 416 expose its capabilities in Router Advertisement (RA) messages. 417 [RFC8505] defines a number of bits in the 6CIO, in particular: 419 L: Node is a 6LR. 420 E: Node is an IPv6 ND Registrar -- i.e., it supports registrations 421 based on EARO. 422 P: Node is a Routing Registrar, -- i.e., an IPv6 ND Registrar that 423 also provides reachability services for the Registered Address. 425 0 1 2 3 426 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 1 427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 428 | Type | Length = 1 | Reserved |D|L|B|P|E|G| 429 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 430 | Reserved | 431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 433 Figure 2: 6CIO flags 435 A 6LR that can provide reachability services for a RUL in a RPL 436 network as specified in this document SHOULD include a 6CIO in its RA 437 messages and set the L, P and E flags as prescribed by [RFC8505], see 438 Section 7.1 for the corresponding behavior of the RUL. 440 4. Updating RFC 6550 442 This document specifies a new behavior whereby a 6LR injects DAO 443 messages for unicast addresses (see Section 10) and multicast 444 addresses (see Section 11) on behalf of leaves that are not aware of 445 RPL. The RUL addresses are exposed as external targets [RFC6550]. 446 Conforming [USEofRPLinfo], an IP-in-IP encapsulation between the 6LR 447 and the RPL Root is used to carry the RPL artifacts and remove them 448 when forwarding outside the RPL domain, e.g., to a RUL. 450 This document also synchronizes the liveness monitoring at the Root 451 and the 6LBR. The same value of lifetime is used for both, and a 452 single keep-alive message, the RPL DAO, traverses the RPL network. A 453 new behavior is introduced whereby the RPL Root proxies the EDAR 454 message to the 6LBR on behalf of the 6LR (more in Section 6), for any 455 6LN, RUL or RAN. 457 Section 6.7.7 of [RFC6550] introduces RPL Target Option, which can be 458 used in RPL Control messages such as the DAO message to signal a 459 destination prefix. Section 9 adds the capabilities to transport the 460 ROVR field (see Section 3.2.3) and the IPv6 Address of the prefix 461 advertiser when the Target is a shorter prefix, signaled by a new "F" 462 flag. The position of the "F" flag is indicated in Section 15. 464 Section 6.7.6 of [RFC6550] defines the DODAG Configuration option 465 with reserved flags. This specification defines the new "Root 466 Proxies EDAR/EDAC" (P) flag and encodes it in one of these reserved 467 flags. The "P" flag is set to indicate that the Root performs the 468 proxy operation, which implies that it supports the Updated RPL 469 Target Option (see Section 9). The position of the "P" flag is 470 indicated in Section 14. 472 Section 6.3.1 of [RFC6550] defines a 3-bit Mode of Operation (MOP) in 473 the DIO Base Object. The new "P" flag is defined only for MOP value 474 between 0 to 6. For a MOP value of 7 or above, the flag MAY be 475 redefined and MUST NOT be interpreted as "Root Proxies EDAR/EDAC" 476 unless the specification of the MOP indicates to do so. 478 The RPL Status defined in section 6.5.1 of [RFC6550] for use in the 479 DAO-ACK message is extended to be placed in DCO messages 480 [EFFICIENT-NPDAO] as well. Furthermore, this specification enables 481 to carry the EARO Status defined for 6LoWPAN ND in RPL DAO and DCO 482 messages, embedded in a RPL Status, more in Section 8. 484 5. Updating draft-ietf-roll-efficient-npdao 486 [EFFICIENT-NPDAO] defines the DCO for RPL Storing Mode only, with a 487 link-local scope. This specification extends its use to the Non- 488 Storing MOP, whereby the DCO is sent unicast by the Root directly to 489 the RAN that injected the DAO message for the considered target. 491 This specification leverages the DCO between the Root and the 6LR 492 that serves as attachment router for a RUL. 494 6. Updating RFC 8505 496 This document updates [RFC8505] to change the behavior of a RPL 497 Router acting as 6LR in the 6LoWPAN ND Address Registration of a RUL 498 acting as 6LN. If the RPL Root advertise the capability to proxy the 499 EDAR/EDAC exchange to the 6LBR, the 6LR refrains from sending the 500 keep-alive EDAR message. Instead, if it is separated from the 6LBR, 501 the Root regenerates the EDAR message to the 6LBR periodically, upon 502 a DAO message that signals the liveliness of the Address. 504 7. Requirements on the RPL-Unware Leaf 506 This document provides RPL routing for a RUL, that is a 6LN acting as 507 an IPv6 Host and not aware of RPL. Still, a minimal RPL-independent 508 functionality is required from the RUL to obtain routing services. 510 7.1. Support of 6LoWPAN ND 512 In order to obtain routing services from a 6LR, a RUL MUST implement 513 [RFC8505] and set the "R" and "T" flags in the EARO. The RUL SHOULD 514 support [AP-ND] to protect the ownership of its addresses. The RUL 515 MUST NOT request routing services from a 6LR that does not originate 516 RA messages with a CIO that has the L, P, and E flags all set as 517 discussed in Section 3.3.1, unless configured to do so. 519 A RUL that may attach to multiple 6LRs MUST prefer those that provide 520 routing services. The RUL MUST register to all the 6LRs from which 521 it desires routing services. 523 Parallel Address Registrations to several 6LRs SHOULD be performed in 524 an rapid sequence, using the exact same EARO for the same Address. 525 Gaps between the Address Registrations will invalidate some of the 526 routes till the Address Registration finally shows on those routes. 528 [RFC8505] introduces error Status values in the NA(EARO) which can be 529 received synchronously upon an NS(EARO) or asynchronously. The RUL 530 MUST support both cases and MUST refrain from using the address when 531 the Status Value indicates a rejection. 533 7.2. External Routes and RPL Artifacts 535 Section 4.1 of [USEofRPLinfo] provides a set of rules detailed below 536 that MUST be followed for routing packets from and to a RUL. 538 A 6LR that acts as a border router for external routes advertises 539 them using Non-Storing Mode DAO messages that are unicast directly to 540 the Root, even if the DODAG is operated in Storing Mode. Non-Storing 541 Mode routes are not visible inside the RPL domain and all packets are 542 routed via the Root. The RPL Root tunnels the packets directly to 543 the 6LR that advertised the external route, which decapsulates and 544 forwards the original (inner) packet. 546 The RPL Non-Storing MOP signaling and the associated IP-in-IP 547 encapsulated packets appear as normal traffic to the intermediate 548 Routers. The support of external routes only impacts the Root and 549 the 6LR. It can be operated with legacy intermediate routers and 550 does not add to the amount of state that must be maintained in those 551 routers. A RUL is an example of a destination that is reachable via 552 an external route that happens to be also a Host route. 554 The RPL data packets always carry a Hop-by-Hop Header to transport a 555 RPL Packet Information (RPI) [RFC6550]. So unless the RUL originates 556 its packets with an RPI, the 6LR needs to tunnel them to the Root to 557 add the RPI. As a rule of a thumb and except for the very special 558 case above, the packets from and to a RUL are always encapsulated 559 using an IP-in-IP tunnel between the Root and the 6LR that serves the 560 RUL (see sections 7.1.4, 7.2.3, 7.2.4, 7.3.3, 7.3.4, 8.1.3, 8.1.4, 561 8.2.3, 8.2.4, 8.3.3 and 8.3.4 of [USEofRPLinfo] for details). 563 In Non-Storing Mode, packets going down carry a Source Routing Header 564 (SRH). The IP-in-IP encapsulation, the RPI and the SRH are 565 collectively called the "RPL artifacts" and can be compressed using 566 [RFC8138]. Figure 10 presents an example compressed format for a 567 packet forwarded by the Root to a RUL in a Storing Mode DODAG. 569 The inner packet that is forwarded to the RUL may carry some RPL 570 artifacts, e.g., an RPI if the original packet was generated with it, 571 and an SRH in a Non-Storing Mode DODAG. [USEofRPLinfo] expects the 572 RUL to support the basic "IPv6 Node Requirements" [RFC8504]. In 573 particular the RUL is expected to ignore the RPL artifacts that are 574 either consumed or not applicable to a Host. 576 A RUL is not expected to support the compression method defined in 577 [RFC8138]. Unless configured otherwise, the border router MUST 578 restore the outgoing packet before forwarding over an external route, 579 even if it is not the destination of the incoming packet, and even 580 when delivering to a RUL. 582 7.2.1. Support of IPv6 Encapsulation 584 Section 2.1 of [USEofRPLinfo] defines the rules for tunneling either 585 to the final destination (6LN) or to its attachment router (6LR). To 586 terminate the IP-in-IP tunnel, the 6LN, as an IPv6 Host, must be able 587 to decapsulate the tunneled packet and either drop the inner packet 588 if it is not the final destination, or pass it to the upper layer for 589 further processing. Unless it is aware by other means that the RUL 590 can handle IP-in-IP properly, which is not mandated by [RFC8504], the 591 Root terminates the IP-in-IP tunnel at the parent 6LR. It is thus 592 not necessary for a RUL to support IP-in-IP decapsulation. 594 7.2.2. Support of the HbH Header 596 A RUL is expected to process an Option Type in a Hop-by-Hop Header as 597 prescribed by section 4.2 of [RFC8200]. This means that the RPI with 598 an Option Type of 0x23 [USEofRPLinfo] must be skipped when not 599 recognized. 601 7.2.3. Support of the Routing Header 603 A RUL is expected to process an unknown Routing Header Type as 604 prescribed by section 4.4 of [RFC8200]. This implies that the Source 605 Routing Header with a Routing Type of 3 [RFC6554] is ignored when the 606 Segments Left is zero, and the packet is dropped otherwise. 608 8. Updated RPL Status 610 The RPL Status is defined in section 6.5.1 of [RFC6550] for use in 611 the DAO-ACK message and values are assigned as follows: 613 +---------+--------------------------------+ 614 | Range | Meaning | 615 +=========+================================+ 616 | 0 | Success/Unqualified acceptance | 617 +---------+--------------------------------+ 618 | 1-127 | Not an outright rejection | 619 +---------+--------------------------------+ 620 | 128-255 | Rejection | 621 +---------+--------------------------------+ 623 Table 1: RPL Status per RFC 6550 625 The 6LoWPAN ND Status was defined for use in the EARO and the 626 currently defined values are listed in table 1 of [RFC8505]. This 627 specification enables to carry the 6LoWPAN ND Status values in RPL 628 DAO and DCO messages, embedded in the RPL Status field. 630 To achieve this, Section 13.2 reduces the range of the EARO Status 631 values to 0-63 to ensure that they fit within a RPL Status as shown 632 in Figure 3. 634 0 1 2 3 4 5 6 7 635 +-+-+-+-+-+-+-+-+ 636 |E|A| Value | 637 +-+-+-+-+-+-+-+-+ 639 Figure 3: RPL Status Format 641 The following RPL Status subfields are defined: 643 E: 1-bit flag. Set to indicate a rejection. When not set, a value 644 of 0 indicates Success/Unqualified acceptance and other values 645 indicate "not an outright rejection" as per RFC 6550. 647 A: 1-bit flag. Indicates the type of the Status Value. 649 Status Value: 6-bit unsigned integer. If the 'A' flag is set this 650 field transports a Status Value defined for IPv6 ND EARO. When 651 the 'A' flag is not set, the Status Value is defined for RPL. 653 When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a EDAC 654 message, the RPL Root MUST copy the 6LoWPAN ND Status unchanged in 655 the RPL Status and set the 'A' bit. The RPL Root MUST set the 'E' 656 flag for Values in range 1-10 which are all considered rejections. 658 Reciprocally, upon a DCO or a DAO-ACK message from the RPL Root with 659 a RPL Status that has the 'A' bit set, the 6LR MUST copy the RPL 660 Status Value unchanged in the Status field of the EARO when 661 generating an NA to the RUL. 663 9. Updated RPL Target Option 665 This specification updates the RPL Target Option to transport the 666 ROVR that was also defined for 6LoWPAN ND messages. This enables the 667 RPL Root to generate the proxied EDAR message to the 6LBR. 669 The new "F" flag is set to indicate that the Target Prefix field 670 contains the address of the advertising node in full, in which case 671 the length of the Target Prefix field is 16 bytes regardless of the 672 value of the Prefix Length field. 674 If the "F" flag is reset, the Target Prefix field MUST be aligned to 675 the next byte boundary after the size (expressed in bits) indicated 676 by the Prefix Length field. Padding bits are reserved and set to 0 677 as prescribed by section 6.7.7 of [RFC6550]. 679 With this specification the ROVR is the remainder of the RPL Target 680 Option. The size of the ROVR is indicated in a new ROVR Size field 681 that is encoded to map one-to-one with the Code Suffix in the EDAR 682 message (see table 4 of [RFC8505]). 684 The modified format is illustrated in Figure 4. It is backward 685 compatible with the Target Option in [RFC6550] and SHOULD be used as 686 a replacement in new implementations even for Storing Mode operations 687 in preparation for upcoming security mechanisms based in the ROVR. 689 0 1 2 3 690 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 1 691 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 692 | Type = 0x05 | Option Length |ROVRsz |F|Flags| Prefix Length | 693 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 694 | | 695 | Target Prefix (Variable Length) | 696 . . 697 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 698 | | 699 ... Registration Ownership Verifier (ROVR) ... 700 | | 701 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 703 Figure 4: Updated Target Option 705 New fields: 707 ROVRsz: Indicates the Size of the ROVR. It MAY be 1, 2, 3, or 4, 708 denoting a ROVR size of 64, 128, 192, or 256 bits, respectively. 710 F: 1-bit flag. Set to indicate that Target Prefix field contains an 711 Address of prefix advertiser in full. 713 Registration Ownership Verifier (ROVR): This is the same field as in 714 the EARO, see [RFC8505] 716 10. Protocol Operations for Unicast Addresses 718 The description below assumes that the Root sets the "P" flag in the 719 DODAG Configuration Option and performs the EDAR proxy operation. 721 If the "P" flag is reset, the 6LR MUST generate the periodic EDAR 722 messages and process the returned status as specified in [RFC8505]. 723 If the EDAC indicates success, the rest of the flow takes place as 724 presented but without the proxied EDAR/EDAC exchange. 726 10.1. General Flow 728 This specification eliminates the need to exchange keep-alive 729 Extended Duplicate Address messages, EDAR and EDAC, all the way from 730 a 6LN to the 6LBR across a RPL mesh. Instead, the EDAR/EDAC exchange 731 with the 6LBR is proxied by the RPL Root upon the DAO message that 732 refreshes the RPL routing state. The first EDAR upon a new 733 Registration cannot be proxied, though, as it serves for the purpose 734 of DAD, which must be verified before the address is injected in RPL. 736 In a RPL network where the function is enabled, refreshing the state 737 in the 6LBR is the responsibility of the Root. Consequently, only 738 addresses that are injected in RPL will be kept alive at the 6LBR by 739 the RPL Root. 741 Since RULs are advertised using Non-Storing Mode, the DAO message 742 flow and the keep alive EDAR/EDAC can be nested within the Address 743 (re)Registration flow. Figure 5 illustrates that for the first 744 Registration, both the DAD and the keep-alive EDAR/EDAC exchanges 745 happen in the same sequence. 747 6LN/RUL 6LR Root 6LBR 748 | | | | 749 | NS(EARO) | | | 750 |--------------->| | 751 | | Extended DAR | 752 | |--------------------------------->| 753 | | | 754 | | Extended DAC | 755 | |<---------------------------------| 756 | | DAO | | 757 | |------------->| | 758 | | | EDAR | 759 | | |------------------>| 760 | | | EDAC | 761 | | |<------------------| 762 | | DAO-ACK | | 763 | |<-------------| | 764 | NA(EARO) | | | 765 |<---------------| | | 766 | | | | 768 Figure 5: First RUL Registration Flow 770 To achieve this, the lifetimes and sequence counters in 6LoWPAN ND 771 and RPL are aligned. In other words, the Path Sequence and the Path 772 Lifetime in the DAO message are taken from the Transaction ID and the 773 Address Registration lifetime in the NS(EARO) message from the 6LN. 775 On the first Address Registration, illustrated in Figure 5 for RPL 776 Non-Storing Mode, the Extended Duplicate Address exchange takes place 777 as prescribed by [RFC8505]. If the exchange fails, the 6LR returns 778 an NA message with a negative status to the 6LN, the NCE is not 779 created and the address is not injected in RPL. If it is successful, 780 the 6LR creates an NCE and injects the Registered Address in the RPL 781 routing using a DAO/DAO-ACK exchange with the RPL DODAG Root. 783 An issue may be detected later, e.g., the address moves within the 784 LLN or to a different Root on a backbone [6BBR]. In that case the 785 value of the status that indicates the issue can be passed from 786 6LoWPAN ND to RPL and back as illustrated in Figure 6. 788 6LN/RUL 6LR Root 6LBR 789 | | | | 790 | | | NA(EARO, Status) | 791 | | |<-----------------| 792 | | DCO(Status) | | 793 | |<------------| | 794 | NA(EARO, Status) | | | 795 |<-----------------| | | 796 | | | | 798 Figure 6: Asynchronous Issue 800 An Address re-Registration is performed by the 6LN to maintain the 801 NCE in the 6LR alive before lifetime expires. Upon the refresh of an 802 Address re-Registration, as illustrated in Figure 7, the 6LR injects 803 the Registered Address in RPL. 805 6LN/RUL 6LR Root 6LBR 806 | | | | 807 | NS(EARO) | | | 808 |--------------->| | 809 | | DAO | | 810 | |------------->| | 811 | | | EDAR | 812 | | |------------------>| 813 | | | EDAC | 814 | | |<------------------| 815 | | DAO-ACK | | 816 | |<-------------| | 817 | NA(EARO) | | | 818 |<---------------| | | 820 Figure 7: Next RUL Registration Flow 822 This is what causes the RPL Root to refresh the state in the 6LBR, 823 using an EDAC message. In case of an error in the proxied EDAR flow, 824 the error is returned in the DAO-ACK using a RPL Status with the 'A' 825 flag set that imbeds a 6LoWPAN Status Value as discussed in 826 Section 8. 828 The 6LR may receive a requested DAO-ACK after it received an 829 asynchronous DCO, but the negative Status in the DCO supersedes a 830 positive Status in the DAO-ACK regardless of the order in which they 831 are received. Upon the DAO-ACK - or the DCO if one arrives first - 832 the 6LR responds to the RUL with an NA(EARO). 834 The RUL MAY terminate the registration at any time by using a 835 Registration Lifetime of 0. This specification requires that the RPL 836 Target Option transports the ROVR. This way, the same flow as the 837 heartbeat flow is sufficient to inform the 6LBR using the Root as 838 proxy as illustrated in Figure 7. 840 Any combination of the logical functions of 6LR, Root and 6LBR might 841 be collapsed in a single node. 843 10.2. Detailed Operation 845 10.2.1. Perspective of the RUL Acting as 6LN 847 This specification does not alter the operation of a 6LoWPAN ND- 848 compliant 6LN, and a RUL is expected to operate as follows: 850 1. The 6LN obtains an IPv6 global address, either using Stateless 851 Address Autoconfiguration (SLAAC) [RFC4862] based on a Prefix 852 Information Option (PIO) [RFC4861] found in an RA message, or 853 some other means such as DHCPv6 [RFC3315]. 855 2. Once it has formed an address, the 6LN (re)registers its address 856 periodically, within the Lifetime of the previous Address 857 Registration, as prescribed by [RFC6775], to refresh the NCE 858 before the lifetime indicated in the EARO expires. It MUST set 859 the "T" flag and the TID is incremented each time and wraps in a 860 lollipop fashion (see section 5.2.1 of [RFC8505] which is fully 861 compatible with section 7.2 of [RFC6550]). 863 3. As stated in section 5.2 of [RFC8505], the 6LN can register to 864 more than one 6LR at the same time. In that case, it uses the 865 same EARO for all of the parallel Address Registrations. The 6LN 866 SHOULD send the registration(s) that have a non-zero Registration 867 Lifetime and ensure that one succeeds before it terminates other 868 registrations, to maintain the state in the network and at the 869 6LBR and minimize the churn. 871 4. Following section 5.1 of [RFC8505], a 6LN acting as a RUL sets 872 the "R" flag in the EARO of at least one registration, whereas 873 acting as a RAN it never does. If the "R" flag is not echoed in 874 the NA, the RUL SHOULD attempt to use another 6LR. The RUL 875 SHOULD send the registration(s) with the "R" flag set and ensure 876 that one succeeds before it sends the registrations with the flag 877 reset. In case of a conflict with the preceeding rule on 878 lifetime, the rule on lifetime has precedence. 880 5. The 6LN may use any of the 6LRs to which it registered as default 881 gateway. Using a 6LR to which the 6LN is not registered may 882 result in packets dropped at the 6LR by a Source Address 883 Validation function (SAVI) so it is NOT RECOMMENDED. 885 Even without support for RPL, a RUL may be aware of opaque values to 886 be provided to the routing protocol. If the RUL has a knowledge of 887 the RPL Instance the packet should be injected into, then it SHOULD 888 set the Opaque field in the EARO to the RPLInstanceID, else it MUST 889 leave the Opaque field to zero. 891 Regardless of the setting of the Opaque field, the 6LN MUST set the 892 "I" field to zero to signal "topological information to be passed to 893 a routing process" as specified in section 5.1 of [RFC8505]. 895 A RUL is not expected to produce RPL artifacts in the data packets, 896 but it MAY do so. For instance, if the RUL has a minimal awareness 897 of the RPL Instance then it can build an RPI. A RUL that places an 898 RPI in a data packet MUST indicate the RPLInstanceID of the RPL 899 Instance where the packet should be forwarded. All the flags and the 900 Rank field are set to zero as specified by section 11.2 of [RFC6550]. 902 10.2.2. Perspective of the Border Router Acting as 6LR 904 Also as prescribed by [RFC8505], the 6LR generates an EDAR message 905 upon reception of a valid NS(EARO) message for the registration of a 906 new IPv6 Address by a 6LN. If the initial EDAR/EDAC exchange 907 succeeds, then the 6LR installs an NCE for the Registration Lifetime. 908 For the registration refreshes, if the RPL Root has indicated that it 909 proxies the keep-alive EDAR/EDAC exchange with the 6LBR (see 910 Section 4), the 6LR MUST refrain from sending the keep-alive EDAR. 912 If the "R" flag is set in the NS(EARO), the 6LR MUST inject the Host 913 route in RPL, unless this is barred for other reasons, such as the 914 saturation of the RPL parents. The 6LR MUST use a RPL Non-Storing 915 Mode signaling and the updated Target Option (see Section 9). The 916 6LR MUST request a DAO-ACK by setting the 'K' flag in the DAO 917 message. Success injecting the route to the RUL is indicated by the 918 'E' flag set to 0 in the RPL status of the DAO-ACK message. 920 The Opaque field in the EARO hints the 6LR on the RPL Instance that 921 SHOULD be used for the DAO advertisements, and for the forwarding of 922 packets sourced at the registered address when there is no RPI in the 923 packet, in which case the 6LR MUST encapsulate the packet to the Root 924 adding an RPI in the outer header. If the Opaque field is zero, the 925 6LR is free to use the default RPL Instance (zero) for the registered 926 address or to select an Instance of its choice. 928 If the "I" field is not zero, then the 6LR MUST consider that the 929 Opaque field is zero. If the Opaque field is not zero, then it is 930 expected to carry a RPLInstanceID for the RPL Instance suggested by 931 the 6LN. If the 6LR does not participate to the associated Instance, 932 then the 6LR MUST consider that the Opaque field is zero; else, that 933 is if the 6LR participates to the suggested RPL Instance, then the 934 6LR SHOULD use that Instance for the Registered Address. 936 The DAO message advertising the Registered Address MUST be 937 constructed as follows: 939 1. The Registered Address is signaled as Target Prefix in the 940 updated Target Option in the DAO message; the Prefix Length is 941 set to 128. The ROVR field is copied unchanged from the EARO 942 (see Section 9). 944 2. The 6LR indicates one of its global or unique-local IPv6 unicast 945 addresses as the Parent Address in the RPL Transit Information 946 Option (TIO) associated with the Target Option 948 3. The 6LR sets the External 'E' flag in the TIO to indicate that it 949 redistributes an external target into the RPL network 951 4. the Path Lifetime in the TIO is computed from the Lifetime in the 952 EARO Option. This adapts it to the Lifetime Units used in the 953 RPL operation; note that if the lifetime is 0, then the DAO 954 message is a No-Path DAO that cleans up the the routes down to 955 the RUL; this also causes the Root as a proxy to send an EDAR 956 message to the 6LBR with a Lifetime of 0. 958 5. the Path Sequence in the TIO is set to the TID value found in the 959 EARO option. 961 Upon receiving the DAO-ACK or an asynchronous DCO message, the 6LR 962 MUST send the NA(EARO) to the RUL. 964 The 6LR MUST set "R" flag in the NA(EARO) back if and only if the 'E' 965 flag is reset, indicating that the 6LR injected the Registered 966 Address in the RPL routing successfully and that the EDAR proxy 967 operation succeeded. 969 If the 'A' flag in the RPL Status is set, the embedded Status Value 970 is passed back to the RUL in the EARO Status. If the 'E' flags is 971 also set, the registration failed for 6LoWPAN ND related reasons, and 972 the NCE is removed. 974 If the 'A' flag is not set in the RPL Status of the DAO-ACK, then the 975 6LoWPAN ND operation succeeded and an EARO Status of 0 (Success) MUST 976 be returned to the RUL, even if the 'E' flag is set in the RPL 977 Status. The EARO Status of 0 MUST also be used if the 6LR could not 978 even try to inject the route. 980 This means that, in case of an error injecting the route that is not 981 related to ND, the registration succeeds but the RPL route is not 982 installed, which is signaled by the "R" flag reset. It is up to the 983 6LN to keep the binding with the 6LR or destroy it. 985 In a network where Address Protected Neighbor Discovery (AP-ND) is 986 enabled, in case of a DAO-ACK or a DCO indicating transporting an 987 EARO Status Value of 5 (Validation Requested), the 6LR MUST challenge 988 the 6LN for ownership of the address, as described in section 6.1 of 989 [AP-ND], before the Registration is complete. This ensures that the 990 address is validated before it is injected in the RPL routing. 992 If the challenge succeeds then the operations continue as normal. In 993 particular a DAO message is generated upon the NS(EARO) that proves 994 the ownership of the address. If the challenge failed, the 6LR 995 rejects the registration as prescribed by AP-ND and may take actions 996 to protect itself against DoS attacks by a rogue 6LN, see Section 12. 998 The 6LR may at any time send a unicast asynchronous NA(EARO) with the 999 "R" flag reset to signal that it stops providing routing services, 1000 and/or with the EARO Status 2 "Neighbor Cache full" to signal that it 1001 removes the NCE. It may also send a final RA, unicast or multicast, 1002 with a Router Lifetime field of zero, to signal that it stops serving 1003 as router, as specified in section 6.2.5 of [RFC4861]. 1005 If a 6LR receives a valid NS(EARO) message with the "R" flag reset 1006 and a Registration Lifetime that is not 0, and the 6LR was injecting 1007 the Registered Address due to previous NS(EARO) messages with the "R" 1008 flag set, then the 6LR MUST stop injecting the address. It is up to 1009 the Registering 6LN to maintain the corresponding route from then on, 1010 either keeping it active via a different 6LR or by acting as a RAN 1011 and managing its own reachability. 1013 10.2.3. Perspective of the RPL Root 1015 A RPL Root SHOULD set the "P" flag in the RPL DODAG Configuration 1016 Option of the DIO messages that it generates (see Section 4) to 1017 signal that it proxies the EDAR/EDAC exchange and supports the 1018 Updated RPL Target option. The remainder of this section assumes 1019 that it does. 1021 Upon reception of a DAO message, for each updated RPL Target Option 1022 (see Section 9) that creates or updates an existing RPL state, the 1023 Root MUST notify the 6LBR. This can be done using an internal API if 1024 they are integrated, or using a proxied EDAR/EDAC exchange if they 1025 are separate entities. 1027 The EDAR message MUST be constructed as follows: 1029 1. The Target IPv6 address from the RPL Target Option is placed in 1030 the Registered Address field of the EDAR message; 1032 2. the Registration Lifetime is adapted from the Path Lifetime in 1033 the TIO by converting the Lifetime Units used in RPL into units 1034 of 60 seconds used in the 6LoWPAN ND messages; 1036 3. the TID value is set to the Path Sequence in the TIO and 1037 indicated with an ICMP code of 1 in the EDAR message; 1039 4. The ROVR in the RPL Target Option is copied as is in the EDAR and 1040 the ICMP Code Suffix is set to the appropriate value as shown in 1041 Table 4 of [RFC8505] depending on the size of the ROVR field. 1043 Upon receiving an EDAC message from the 6LBR, if a DAO is pending, 1044 then the Root MUST send a DAO-ACK back to the 6LR. Else, if the 1045 Status in the EDAC message is not "Success", then it MUST send an 1046 asynchronous DCO to the 6LR. 1048 In either case, the EDAC Status is embedded in the RPL Status with 1049 the 'A' flag set. 1051 10.2.4. Perspective of the 6LBR 1053 The 6LBR is unaware that the RPL Root is not the new attachment 6LR 1054 of the RUL, so it is not impacted by this specification. 1056 Upon reception of an EDAR message, the 6LBR acts as prescribed by 1057 [RFC8505] and returns an EDAC message to the sender. 1059 11. Protocol Operations for Multicast Addresses 1061 Section 12 of [RFC6550] details the RPL support for multicast flows. 1062 This support is not source-specific and only operates as an extension 1063 to the Storing Mode of Operation for unicast packets. Note that it 1064 is the RPL model that the multicast packet is passed as a Layer-2 1065 unicast to each of the interested children. This remains true when 1066 forwarding between the 6LR and the listener 6LN. 1068 "Multicast Listener Discovery (MLD) for IPv6" [RFC2710] and its 1069 updated version "Multicast Listener Discovery Version 2 (MLDv2) for 1070 IPv6" [RFC3810] provide an interface for a listener to register to 1071 multicast flows. MLDv2 is backwards compatible with MLD, and adds in 1072 particular the capability to filter the sources via black lists and 1073 white lists. In the MLD model, the Router is a "querier" and the 1074 Host is a multicast listener that registers to the querier to obtain 1075 copies of the particular flows it is interested in. 1077 On the first Address Registration, as illustrated in Figure 8, the 1078 6LN, as an MLD listener, sends an unsolicited Report to the 6LR in 1079 order to start receiving the flow immediately. 1081 6LN/RUL 6LR Root 6LBR 1082 | | | | 1083 | unsolicited Report | | | 1084 |------------------->| | | 1085 | | | | 1086 | | DAO | | 1087 | |-------------->| | 1088 | | DAO-ACK | | 1089 | |<--------------| | 1090 | | | | 1091 | | | unsolicited Report | 1092 | | |------------------->| 1093 | | | | 1095 Figure 8: First Multicast Registration Flow 1097 Since multicast Layer-2 messages are avoided, it is important that 1098 the asynchronous messages for unsolicited Report and Done are sent 1099 reliably, for instance using a Layer-2 acknowledgment, or attempted 1100 multiple times. 1102 The 6LR acts as a generic MLD querier and generates a DAO for the 1103 multicast target. The lifetime of the DAO is set to be in the order 1104 of the Query Interval, yet larger to account for variable propagation 1105 delays. 1107 The Root proxies the MLD exchange as a listener with the 6LBR acting 1108 as the querier, so as to get packets from a source external to the 1109 RPL domain. 1111 Upon a DAO with a multicast target, the RPL Root checks if it is 1112 already registered as a listener for that address, and if not, it 1113 performs its own unsolicited Report for the multicast target. 1115 An Address re-Registration is pulled periodically by 6LR acting as 1116 querier. Note that the message may be sent unicast to all the known 1117 individual listeners. 1119 Upon the timing out of the Query Interval, the 6LR sends a Query to 1120 each of its listeners, and gets a Report back that is mapped into a 1121 DAO, as illustrated in Figure 9: 1123 6LN/RUL 6LR Root 6LBR 1124 | | | | 1125 | Query | | | 1126 |<-------------------| | | 1127 | Report | | | 1128 |------------------->| | | 1129 | | | | 1130 | | DAO | | 1131 | |-------------->| | 1132 | | DAO-ACK | | 1133 | |<--------------| | 1134 | | | | 1135 | | | Query | 1136 | | |<-------------------| 1137 | | | Report | 1138 | | |------------------->| 1139 | | | | 1140 | | | | 1142 Figure 9: Next Registration Flow 1144 Note that any of the functions 6LR, Root and 6LBR might be collapsed 1145 in a single node, in which case the flow above happens internally, 1146 and possibly through internal API calls as opposed to messaging. 1148 12. Security Considerations 1150 First of all, it is worth noting that with [RFC6550], every node in 1151 the LLN is RPL-aware and can inject any RPL-based attack in the 1152 network. This specification isolates edge nodes that can only 1153 interact with the RPL routers using 6LoWPAN ND, meaning that they 1154 cannot perform RPL insider attacks. 1156 6LoWPAN ND can optionally provide SAVI features with [AP-ND], which 1157 reduces even more the attack perimeter that is available to the edge 1158 nodes. 1160 The LLN nodes depend on the 6LBR and the RPL participants for their 1161 operation. A trust model must be put in place to ensure that the 1162 right devices are acting in these roles, so as to avoid threats such 1163 as black-holing, (see [RFC7416] section 7) or bombing attack whereby 1164 an impersonated 6LBR would destroy state in the network by using the 1165 "Removed" Status code. 1167 This trust model could be at a minimum based on a Layer-2 Secure 1168 joining and the Link-Layer security. This is a generic 6LoWPAN 1169 requirement, see Req5.1 in Appendix of [RFC8505]. 1171 Additionally, the trust model could include a role validation to 1172 ensure that the node that claims to be a 6LBR or a RPL Root is 1173 entitled to do so. 1175 At the time of this writing RPL does not have a zerotrust model 1176 whereby it is possible to validate the origin of an address that is 1177 injected in a DAO. This specification makes a first step in that 1178 direction by allowing the Root to challenge the RUL via the 6LR that 1179 serves it. 1181 13. IANA Considerations 1183 13.1. Fixing the Address Registration Option Flags 1185 Section 9.1 of [RFC8505] creates a Registry for the 8-bit Address 1186 Registration Option Flags field. 1188 IANA is requested to rename the first column of the table from "ARO 1189 Status" to "Bit number". 1191 13.2. Resizing the ARO Status values 1193 Section 12 of [RFC6775] creates the Address Registration Option 1194 Status Values Registry with a range 0-255. 1196 This specification reduces that range to 0-63. 1198 IANA is requested to reduce the upper bound of the unassigned values 1199 in the Address Registration Option Status Values Registry from -255 1200 to -63. 1202 14. New DODAG Configuration Option Flag 1204 This specification updates the Registry for the "DODAG Configuration 1205 Option Flags" that was created for [RFC6550] as follows: 1207 +------------+----------------------------+-----------+ 1208 | Bit Number | Capability Description | Reference | 1209 +============+============================+===========+ 1210 | 1 | Root Proxies EDAR/EDAC (P) | THIS RFC | 1211 +------------+----------------------------+-----------+ 1213 Table 2: New DODAG Configuration Option Flag 1215 15. New RPL Target Option Flag 1217 Section 20.15 of [RFC6550] creates a Registry for the 8-bit "RPL 1218 Target Option Flags" field. IANA is requested to reduce the size of 1219 the field in the Registry to 4 bits. This specification also defines 1220 a new entry in the Registry as follows: 1222 +------------+--------------------------------+-----------+ 1223 | Bit Number | Capability Description | Reference | 1224 +============+================================+===========+ 1225 | 1 | Advertiser Address in Full (F) | THIS RFC | 1226 +------------+--------------------------------+-----------+ 1228 Table 3: New RPL Target Option Flag 1230 16. New Subregistry for the RPL Non-Rejection Status values 1232 This specification creates a new Subregistry for the RPL Non- 1233 Rejection Status values for use in RPL DAO-ACK and DCO messages with 1234 the 'A' flag reset, under the ICMPv6 parameters registry. 1236 * Possible values are 6-bit unsigned integers (0..63). 1238 * Registration procedure is "Standards Action" [RFC8126]. 1240 * Initial allocation is as indicated in Table 4: 1242 +-------+------------------------+-----------+ 1243 | Value | Meaning | Reference | 1244 +=======+========================+===========+ 1245 | 0 | Unqualified acceptance | RFC 6550 | 1246 +-------+------------------------+-----------+ 1248 Table 4: Acceptance values of the RPL Status 1250 17. New Subregistry for the RPL Rejection Status values 1252 This specification creates a new Subregistry for the RPL Rejection 1253 Status values for use in RPL DAO-ACK and RCO messages with the 'A' 1254 flag reset, under the ICMPv6 parameters registry. 1256 * Possible values are 6-bit unsigned integers (0..63). 1258 * Registration procedure is "Standards Action" [RFC8126]. 1260 * Initial allocation is as indicated in Table 5: 1262 +-------+-----------------------+---------------+ 1263 | Value | Meaning | Reference | 1264 +=======+=======================+===============+ 1265 | 0 | Unqualified rejection | This document | 1266 +-------+-----------------------+---------------+ 1268 Table 5: Rejection values of the RPL Status 1270 18. Acknowledgments 1272 The authors wish to thank Ines Robles, Georgios Papadopoulos and 1273 especially Rahul Jadhav for their reviews and contributions to this 1274 document. 1276 19. Normative References 1278 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1279 Requirement Levels", BCP 14, RFC 2119, 1280 DOI 10.17487/RFC2119, March 1997, 1281 . 1283 [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast 1284 Listener Discovery (MLD) for IPv6", RFC 2710, 1285 DOI 10.17487/RFC2710, October 1999, 1286 . 1288 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1289 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1290 DOI 10.17487/RFC3810, June 2004, 1291 . 1293 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1294 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1295 Overview, Assumptions, Problem Statement, and Goals", 1296 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1297 . 1299 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1300 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1301 DOI 10.17487/RFC4861, September 2007, 1302 . 1304 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1305 Address Autoconfiguration", RFC 4862, 1306 DOI 10.17487/RFC4862, September 2007, 1307 . 1309 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1310 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1311 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1312 Low-Power and Lossy Networks", RFC 6550, 1313 DOI 10.17487/RFC6550, March 2012, 1314 . 1316 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1317 Power and Lossy Networks (RPL) Option for Carrying RPL 1318 Information in Data-Plane Datagrams", RFC 6553, 1319 DOI 10.17487/RFC6553, March 2012, 1320 . 1322 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1323 Routing Header for Source Routes with the Routing Protocol 1324 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1325 DOI 10.17487/RFC6554, March 2012, 1326 . 1328 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1329 Bormann, "Neighbor Discovery Optimization for IPv6 over 1330 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1331 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1332 . 1334 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1335 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1336 2014, . 1338 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1339 Constrained-Node Networks", RFC 7228, 1340 DOI 10.17487/RFC7228, May 2014, 1341 . 1343 [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for 1344 IPv6 over Low-Power Wireless Personal Area Networks 1345 (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 1346 2014, . 1348 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1349 Writing an IANA Considerations Section in RFCs", BCP 26, 1350 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1351 . 1353 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1354 "IPv6 over Low-Power Wireless Personal Area Network 1355 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1356 April 2017, . 1358 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1359 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1360 May 2017, . 1362 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1363 (IPv6) Specification", STD 86, RFC 8200, 1364 DOI 10.17487/RFC8200, July 2017, 1365 . 1367 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1368 Perkins, "Registration Extensions for IPv6 over Low-Power 1369 Wireless Personal Area Network (6LoWPAN) Neighbor 1370 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1371 . 1373 [AP-ND] Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 1374 "Address Protected Neighbor Discovery for Low-power and 1375 Lossy Networks", Work in Progress, Internet-Draft, draft- 1376 ietf-6lo-ap-nd-23, 30 April 2020, 1377 . 1379 [USEofRPLinfo] 1380 Robles, I., Richardson, M., and P. Thubert, "Using RPI 1381 Option Type, Routing Header for Source Routes and IPv6-in- 1382 IPv6 encapsulation in the RPL Data Plane", Work in 1383 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-38, 1384 23 March 2020, . 1387 [EFFICIENT-NPDAO] 1388 Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient 1389 Route Invalidation", Work in Progress, Internet-Draft, 1390 draft-ietf-roll-efficient-npdao-18, 15 April 2020, 1391 . 1394 20. Informative References 1396 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1397 Statement and Requirements for IPv6 over Low-Power 1398 Wireless Personal Area Network (6LoWPAN) Routing", 1399 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1400 . 1402 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 1403 C., and M. Carney, "Dynamic Host Configuration Protocol 1404 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 1405 2003, . 1407 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1408 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1409 DOI 10.17487/RFC6282, September 2011, 1410 . 1412 [RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur, 1413 Ed., "Performance Evaluation of the Routing Protocol for 1414 Low-Power and Lossy Networks (RPL)", RFC 6687, 1415 DOI 10.17487/RFC6687, October 2012, 1416 . 1418 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1419 and M. Richardson, Ed., "A Security Threat Analysis for 1420 the Routing Protocol for Low-Power and Lossy Networks 1421 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1422 . 1424 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1425 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1426 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1427 . 1429 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node 1430 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504, 1431 January 2019, . 1433 [6BBR] Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6 1434 Backbone Router", Work in Progress, Internet-Draft, draft- 1435 ietf-6lo-backbone-router-20, 23 March 2020, 1436 . 1439 Appendix A. Example Compression 1441 Figure 10 illustrates the case in Storing Mode where the packet is 1442 received from the Internet, then the Root encapsulates the packet to 1443 insert the RPI and deliver to the 6LR that is the parent and last hop 1444 to the final destination, which is not known to support [RFC8138]. 1446 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1447 |11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP 1448 |Page 1 |Type1 S=0| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 1449 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1450 <-4 bytes-> <- RFC 6282 -> 1451 <- No RPL artifact ... 1453 Figure 10: Encapsulation to Parent 6LR in Storing Mode 1455 The difference with the example presented in Figure 19 of [RFC8138] 1456 is the addition of a SRH-6LoRH before the RPI-6LoRH to transport the 1457 compressed address of the 6LR as the destination address of the outer 1458 IPv6 header. In the original example the destination IP of the outer 1459 header was elided and was implicitly the same address as the 1460 destination of the inner header. Type 1 was arbitrarily chosen, and 1461 the size of 0 denotes a single address in the SRH. 1463 In Figure 10, the source of the IP-in-IP encapsulation is the Root, 1464 so it is elided in the IP-in-IP 6LoRH. The destination is the parent 1465 6LR of the destination of the inner packet so it cannot be elided. 1466 If the DODAG is operated in Storing Mode, it is the single entry in 1467 the SRH-6LoRH and the SRH-6LoRH Size is encoded as 0. The SRH-6LoRH 1468 is the first 6LoRH in the chain. In this particular example, the 6LR 1469 address can be compressed to 2 bytes so a Type of 1 is used. It 1470 results that the total length of the SRH-6LoRH is 4 bytes. 1472 In Non-Storing Mode, the encapsulation from the Root would be similar 1473 to that represented in Figure 10 with possibly more hops in the SRH- 1474 6LoRH and possibly multiple SRH-6LoRHs if the various addresses in 1475 the routing header are not compressed to the same format. Note that 1476 on the last hop to the parent 6LR, the RH3 is consumed and removed 1477 from the compressed form, so the use of Non-Storing Mode vs. Storing 1478 Mode is indistinguishable from the packet format. 1480 The SRH-6LoRHs are followed by RPI-6LoRH and then the IP-in-IP 6LoRH. 1481 When the IP-in-IP 6LoRH is removed, all the 6LoRH Headers that 1482 precede it are also removed. The Paging Dispatch [RFC8025] may also 1483 be removed if there was no previous Page change to a Page other than 1484 0 or 1, since the LOWPAN_IPHC is encoded in the same fashion in the 1485 default Page 0 and in Page 1. The resulting packet to the 1486 destination is the inner packet compressed with [RFC6282]. 1488 Authors' Addresses 1490 Pascal Thubert (editor) 1491 Cisco Systems, Inc 1492 Building D 1493 45 Allee des Ormes - BP1200 1494 06254 Mougins - Sophia Antipolis 1495 France 1497 Phone: +33 497 23 26 34 1498 Email: pthubert@cisco.com 1500 Michael C. Richardson 1501 Sandelman Software Works 1503 Email: mcr+ietf@sandelman.ca 1504 URI: http://www.sandelman.ca/