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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ROLL P. Thubert, Ed. 3 Internet-Draft Cisco 4 Updates: 6550, 8505 (if approved) May 28, 2019 5 Intended status: Standards Track 6 Expires: November 29, 2019 8 Routing for RPL Leaves 9 draft-ietf-roll-unaware-leaves-00 11 Abstract 13 This specification leverages 6LoWPAN ND to provide a unicast and 14 multicast routing service in a RPL domain to 6LNs that do not 15 participate to RPL. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at https://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on November 29, 2019. 34 Copyright Notice 36 Copyright (c) 2019 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (https://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 53 2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 4 54 2.2. References . . . . . . . . . . . . . . . . . . . . . . . 4 55 2.3. Subset of a 6LoWPAN Glossary . . . . . . . . . . . . . . 5 56 3. 6LoWPAN Neighbor Discovery . . . . . . . . . . . . . . . . . 6 57 4. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 7 58 5. Updating RFC 8505 . . . . . . . . . . . . . . . . . . . . . . 7 59 6. Dependencies on the 6LN . . . . . . . . . . . . . . . . . . . 8 60 7. Protocol Operations for Unicast Addresses . . . . . . . . . . 8 61 7.1. General Flow . . . . . . . . . . . . . . . . . . . . . . 8 62 7.2. 6LN Operation . . . . . . . . . . . . . . . . . . . . . . 11 63 7.3. 6LR Operation . . . . . . . . . . . . . . . . . . . . . . 12 64 7.4. RPL Root Operation . . . . . . . . . . . . . . . . . . . 13 65 7.5. 6LBR Operation . . . . . . . . . . . . . . . . . . . . . 14 66 8. Protocol Operations for Multicast Addresses . . . . . . . . . 15 67 9. Implementation Status . . . . . . . . . . . . . . . . . . . . 17 68 10. Security Considerations . . . . . . . . . . . . . . . . . . . 17 69 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 70 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 71 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 72 13.1. Normative References . . . . . . . . . . . . . . . . . . 17 73 13.2. Informative References . . . . . . . . . . . . . . . . . 19 74 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20 76 1. Introduction 78 The design of Low Power and Lossy Networks (LLNs) is generally 79 focused on saving energy, which is the most constrained resource of 80 all. Other design constraints, such as a limited memory capacity, 81 duty cycling of the LLN devices and low-power lossy transmissions, 82 derive from that primary concern. 84 The IETF produced the "Routing Protocol for Low Power and Lossy 85 Networks" [RFC6550] (RPL) to provide routing services within such 86 constraints. RPL is a Distance-Vector protocol, which, compared to 87 link-state protocols, limits the amount of topological knowledge that 88 needs to be installed and maintained in each node. In order to 89 operate in constrained networks, RPL allows a Routing Stretch (see 90 [RFC6687]), whereby routing is only performed along a DODAG as 91 opposed to straight along a shortest path between 2 peers, whatever 92 that would mean in a given LLN. This trades the quality of peer-to- 93 peer (P2P) paths for a vastly reduced amount of control traffic and 94 routing state that would be required to operate a any-to-any shortest 95 path protocol. Finally, broken routes may be fixed lazily and on- 96 demand, based on dataplane inconsistency discovery, which avoids 97 wasting energy in the proactive repair of unused paths. 99 In order to cope with lossy transmissions, RPL forms Direction- 100 Oriented Directed Acyclic Graphs (DODAGs) using DODAG Information 101 Solicitation (DIS) and DODAG Information Object (DIO) messages. For 102 most of the nodes, though not all, a DODAG provides multiple 103 forwarding solutions towards the Root of the topology via so-called 104 parents. RPL is designed to adapt to fuzzy connectivity, whereby the 105 physical topology cannot be expected to reach a stable state, with a 106 lazy control that creates routes proactively but only fixes them when 107 they are used by actual traffic. It results that RPL provides 108 reachability for most of the LLN nodes, most of the time, but does 109 not really converge in the classical sense. RPL provides unicast and 110 multicast routing services back to RPL-Aware nodes (RANs). A RAN 111 will inject routes to self using Destination Advertisement Object 112 (DAO) messages sent to either their parents in Storing Mode or to the 113 Root indicating their parent in Non-Storing mode. This process 114 effectively forms a DODAG back to the device that is a subset of the 115 DODAG to the Root with all links reversed. 117 When a routing protocol such as RPL is used to maintain reachability 118 within a Non-Broadcast Multi-Access (NBMA) subnet, some nodes may act 119 as routers and participate to the routing operations whereas others 120 may be plain hosts. In RPL terms, a plain host that does not 121 participate to the routing protocol is called a Leaf. It must be 122 noted that a 6LN could participate to RPL and inject DAO routes to 123 self, but refrain from advertising DIO and get children. In that 124 case, the 6LN is still a host but not a Leaf. 126 This specification enables a RPL-Unaware Leaf (RUL) to announce 127 itself as a host and demand that the 6LR that accepts the 128 registration also inject the relevant routing information for the 129 Registered Address in the RPL domain on its behalf. The unicast 130 packet forwarding operation by the 6LR serving a Leaf 6LN is 131 described in "When to use RFC 6553, 6554 and IPv6-in-IPv6" 132 [I-D.ietf-roll-useofrplinfo]. This document adds the capability by a 133 6LR to advertise the Global, Unique-Local and Multicast IPv6 134 address(es) of the 6LN in the RPL protocol. 136 Examples of routing-agnostic 6LN may include lightly-powered sensors 137 such as window smash sensor (alarm system), or the kinetically 138 powered light switch. Other application of this specification may 139 include a smart grid network that controls appliances - such as 140 washing machines or the heating system - in the home. Applicances 141 may not participate to the RPL protocol operated in the smart grid 142 network but can still receive control packet from the smart grid. 144 2. Terminology 146 2.1. BCP 14 148 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 149 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 150 "OPTIONAL" in this document are to be interpreted as described in BCP 151 14 [RFC2119][RFC8174] when, and only when, they appear in all 152 capitals, as shown here. 154 2.2. References 156 The Terminology used in this document is consistent with and 157 incorporates that described in Terms Used in Routing for Low-Power 158 and Lossy Networks (LLNs). [RFC7102]. 160 Other terms in use in LLNs are found in Terminology for Constrained- 161 Node Networks [RFC7228]. 163 A glossary of classical 6LoWPAN acronyms is given in Section 2.3. 165 The term "byte" is used in its now customary sense as a synonym for 166 "octet". 168 "RPL", "RPL Packet Information" (RPI) and "RPL Instance", DIO, DAO 169 and DIS messages are defined in the "RPL: IPv6 Routing Protocol for 170 Low-Power and Lossy Networks" [RFC6550] specification. 172 This document introduces the term RPL-Unaware Leaf (RUL) to refer to 173 a node that uses a RPL router (without necessarily knowing it) as 6LR 174 and depends on that router to obtain reachability for its addresses 175 inside the RPL domain. On the contrary, the term RPL-Aware Leaf 176 (RAL) is used to refer to a host or a router that participates to RPL 177 and advertises its addresses of prefixes by itself. 179 Other terms in use in LLNs are found in Terminology for Constrained- 180 Node Networks [RFC7228]. 182 Readers are expected to be familiar with all the terms and concepts 183 that are discussed in 185 o "Neighbor Discovery for IP version 6" [RFC4861], 187 o "IPv6 Stateless Address Autoconfiguration" [RFC4862], 189 o "Problem Statement and Requirements for IPv6 over Low-Power 190 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606], 192 o "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 193 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 195 o "Neighbor Discovery Optimization for Low-power and Lossy Networks" 196 [RFC6775], and 198 o "Registration Extensions for IPv6 over Low-Power Wireless Personal 199 Area Network (6LoWPAN) Neighbor Discovery" [RFC8505]. 201 2.3. Subset of a 6LoWPAN Glossary 203 This document often uses the following acronyms: 205 6BBR: 6LoWPAN Backbone Router (proxy for the registration) 207 6LBR: 6LoWPAN Border Router (authoritative on DAD) 209 6LN: 6LoWPAN Node 211 6LR: 6LoWPAN Router (relay to the registration process) 213 6CIO: Capability Indication Option 215 (E)ARO: (Extended) Address Registration Option 217 (E)DAR: (Extended) Duplicate Address Request 219 (E)DAC: (Extended) Duplicate Address Confirmation 221 DAD: Duplicate Address Detection 223 DODAG: Destination-Oriented Directed Acyclic Graph 225 LLN: Low-Power and Lossy Network (a typical IoT network) 227 NA: Neighbor Advertisement 229 NCE: Neighbor Cache Entry 231 ND: Neighbor Discovery 233 NDP: Neighbor Discovery Protocol 235 NS: Neighbor Solicitation 237 ROVR: Registration Ownership Verifier (pronounced rover) 239 RPL: IPv6 Routing Protocol for LLNs (pronounced ripple) 240 RA: Router Advertisement 242 RS: Router Solicitation 244 TSCH: Timeslotted Channel Hopping 246 TID: Transaction ID (a sequence counter in the EARO) 248 3. 6LoWPAN Neighbor Discovery 250 The IPv6 [RFC8200]Neighbor Discovery (IPv6 ND) Protocol (NDP) suite 251 [RFC4861] [RFC4862] defined for fast media such a Ethernet, relies 252 heavily on multicast operations for address discovery and duplicate 253 address detection (DAD). 255 "Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775] 256 (6LoWPAN ND) adapts IPv6 ND for operations over energy-constrained 257 LLNs. In particular, 6LoWPAN ND introduces a unicast host address 258 registration mechanism that contributes to reduce the use of 259 multicast messages that are present in the classical IPv6 ND 260 protocol. 6LoWPAN ND defines a new Address Registration Option (ARO) 261 that is carried in the unicast Neighbor Solicitation (NS) and 262 Neighbor Advertisement (NA) messages between the 6LoWPAN Node (6LN) 263 and the 6LoWPAN Router (6LR). 6LoWPAN ND also defines the Duplicate 264 Address Request (DAR) and Duplicate Address Confirmation (DAC) 265 messages between the 6LR and the 6LoWPAN Border Router (6LBR). In an 266 LLN, the 6LBR is the central repository of all the Registered 267 Addresses in its domain. 269 "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505] 270 updates the behavior of RFC 6775 to enable a generic registration to 271 routing services and defines an Extended ARO (EARO). The format of 272 the EARO is shown in Figure 1: 274 0 1 2 3 275 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 1 276 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 277 | Type | Length | Status | Opaque | 278 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 279 | Rsvd | I |R|T| TID | Registration Lifetime | 280 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 281 | | 282 ... Registration Ownership Verifier ... 283 | | 284 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 286 Figure 1: EARO Option Format 288 The 'R' flag that is set if the Registering Node expects that the 6LR 289 ensures reachability for the Registered Address, e.g., by means of 290 routing or proxying ND. 292 The EARO also includes a sequence counter called Transaction ID 293 (TID), which maps to the Path Sequence Field found in Transit Options 294 in RPL DAO messages. It is a prerequisite for this specification. 296 Finally, the EARO transports an Opaque field and an 'I' field that 297 describes what the Opaque field transports and how to use it. This 298 specification requires that the I field is left to 0 and to use the 299 Opaque field to carry the RPL InstanceID if one is known, else to 300 leave the Opaque field to zero. 302 4. Updating RFC 6550 304 This document specifies a new behavior whereby a 6LR injects DAO 305 messages for unicast addresses registered through the updated 6LoWPAN 306 ND [RFC8505] on behalf of 6LN nodes that are not RPL-aware. 308 Upon the renewal of a 6LoWPAN ND registration, this specification 309 changes the behavior of the 6LR as follows. If the 'R' flag is set, 310 the 6LR injects a DAO targeting the Registered Address, and refrains 311 from sending a DAR message. the DAR/DAC exchange that refreshes the 312 state in the 6LBR happens instead between the RPL Root and the 6LBR. 313 In that flow, the RPL Root acts as a proxy on behalf of the 6LR upon 314 the reception of the DAO propagation initiated at the 6LR. 316 5. Updating RFC 8505 318 The behavior defined in this specification whereby the 6LR that 319 processes the registration advertises the Registered Address in DAO 320 messages and bypasses the DAR/DAC process for the renewal of a 321 registration, is only triggered by an NS(EARO) that has the 'R' flag 322 set. If the 'R' flag is not set, then the Registering Node is 323 expected to be a RAN router that handles the reachability of the 324 Registered Address by itself. 326 This document also specifies a keep-alive EDAR message that the RPL 327 Root may use to maintain an existing state in the 6LBR upon receiving 328 DAO messages. The keep-alive EDAR message may only act as a 329 refresher and can only update the Lifetime and the TID of the state 330 in the 6LBR. 332 This document similarly specifies a keep-alive NS(EARO) message that 333 the RPL Root may use to maintain an existing state in a 6BBR upon 334 receiving DAO messages. The keep-alive NS(EARO) message may only act 335 as a refresher and can only update the Lifetime and the TID of the 336 state in the 6BBR. 338 As prescribed by [RFC8505], a RPL router SHOULD NOT set the 'R' flag. 340 6. Dependencies on the 6LN 342 This document provides RPL routing for a 6LN acting as a plain host 343 and not aware of RPL. Still, a minimal RPL-independent functionality 344 is expected from the 6LN in order to operate properly as a RLU; in 345 particular: 347 o the 6LN MUST implement [RFC8505] and set the 'R' flag in the EARO 348 option. The 'R' flag is used to determine whether the Registering 349 Node is a RUL, not aware of the RPL operation in the network, and 350 thus does not participate to it. A 6LN is considered to be a RUL 351 if and only if it sets the 'R' flag in the EARO. 353 o RPL data packets are often encapsulated using IP in IP and in non- 354 storing mode, packets going down will carry an SRH as well. RPL 355 data packets also typically carry a Hop-by-Hop Header to transport 356 a RPL Packet Information (RPI) [RFC6550]. These additional 357 headers are called RPL artifacts. 359 o When IP-in-IP is used and the outter headers terminate at the 6LR 360 that generated the DAO, then the 6LR decapsulates the packet to 361 the 6LN. In that case the 6LN gets a packet that is free of RPL 362 artifacts. IP-in-IP to the 6LR MUST be used if the 6LN cannot 363 handle the RPL artifacts or the way they are compressed [RFC8138]. 364 It SHOULD be used it there is a particular bandwidth or power 365 constraint at the 6LN. 367 o In order to save the IP-in-IP encapsulation and to suport storing 368 mode of operation, it is preferred that the 6LN can ignore an RPI 369 and consume a routing header in both the native and compressed 370 forms. In order to enable IP-in-IP to a 6LN in non storing mode, 371 it is also of interest that the 6LN supports decapsulating IP-in- 372 IP in both forms. But since the preferred behaviour when using 373 IP-in-IP is that the outter headers terminate at the 6LR, 374 supporting this capability is secondary. 376 7. Protocol Operations for Unicast Addresses 378 7.1. General Flow 380 This specification enables to save the exchange of Extended Duplicate 381 Address messages, EDAR and EDAC, from a 6LN all the way to the 6LBR 382 across a RPL mesh, for the sole purpose of refreshing an existing 383 state in the 6LBR. Instead, the EDAR/EDAC exchange is proxied by the 384 RPL Root upon a DAO message that refreshes the RPL routing state. To 385 achieve this, the lifetimes and sequence counters in 6LoWPAN ND and 386 RPL are aligned. In other words, the Path Sequence and the Path 387 Lifetime in the DAO message are derived from the Transaction ID and 388 the registration lifetime in the NS(EARO) message from the 6LN. 390 From the perspective of the 6LN, the registration flow happens 391 transparently; it is not delayed by the proxy RPL operation, so the 392 device does not need to wait more whether RPL proxy operation happens 393 or not. The flows below are RPL Non-Storing Mode examples. In 394 Storing Mode, the DAO ACK may not be present, and the DAO messages 395 cascade from child to parent all the way to the DODAG Root. 397 On the first registration, illustrated in Figure 2, from the 398 perspective of the 6LR in non-storing mode, the Extended Duplicate 399 Address message takes place as prescribed by [RFC8505]. When 400 successful, the flow creates a Neighbor Cache Entry (NCE) in the 6LR, 401 and the 6LR injects the Registered Address in RPL using DAO/DAO-ACK 402 exchanges all the way to the RPL DODAG Root. The protocol does not 403 carry a specific information that the Extended Duplicate Address 404 messages were already exchanged, so the Root proxies them anyway. 405 Note that in Storing Mode the DAO ACK is generated from the parent 406 that does not necessary wait for the grand parent to acknowledge, so 407 the DAO-ACK is no guarantee that the keep-alive EDAR succeeded. On 408 the other hand, th eflows can be nested in non storing mode, and it 409 is possible to carry information such as an updated lifetime from the 410 6LBR all the way to the 6LN. 412 6LN 6LR Root 6LBR 413 | | | | 414 | NS(EARO) | | | 415 |--------------->| | 416 | | Extended DAR | 417 | |-------------------------------->| 418 | | | 419 | | Extended DAC | 420 | |<--------------------------------| 421 | | DAO | | 422 | |-------------->| | 423 | | | keep-alive EDAR | 424 | | |---------------->| 425 | | | EDAC | 426 | | |<----------------| 427 | | DAO ACK | | 428 | |<--------------| | 429 | NA(EARO) | | 430 |<---------------| | | 431 | | | | 433 Figure 2: First Registration Flow 435 A re-registration is performed by the 6LN to maintain the NCE in the 436 6LR alive before lifetime expires. Upon a re-registration, as 437 illustrated in Figure 3, the 6LR redistributes the Registered Address 438 NS(EARO) in RPL. This causes the RPL DODAG Root to refresh the state 439 in the 6LBR with a keep-alive EDAC message. The keep-alive EDAC 440 lacks the Registration Ownership Verifier (ROVR) information, since 441 it is not present in RPL DAO messages, but the EDAC message sent in 442 response by the 6LBR contains the actual value of the ROVR field for 443 that registration. This enables the RPL Root to perform the proxy- 444 registration for the Registered Address and attract traffic captured 445 over the backbone by the 6BBR and route it back to the device. 447 6LN 6LR Root 6LBR 6BBR 448 | | | | | 449 | NS(EARO) | | | | 450 |--------------->| | | | 451 | NA(EARO) | | | | 452 |<---------------| | | | 453 | | | | | 454 | | DAO | | | 455 | |-------------->| | | 456 | | | | | 457 | | | keep-alive EDAR | | 458 | | |---------------->| | 459 | | | EDAC(ROVR) | | 460 | | |<----------------| | 461 | | | | | 462 | | | proxy NS(EARO) | 463 | | |-------------------------------->| 464 | | | proxy NA(EARO) | 465 | | |<--------------------------------| 466 | | | | | 467 | | DAO ACK | | | 468 | |<--------------| | | 469 | | | | | 471 Figure 3: Next Registration Flow 473 Note that any of the functions 6LR, Root and 6LBR might be collapsed 474 in a single node, in which case the flow above happens internally, 475 and possibly through internal API calls as opposed to messaging. 477 7.2. 6LN Operation 479 This specification does not alter the operation of a 6LoWPAN ND- 480 compliant 6LN, which is expected to operate as follows: 482 o The 6LN obtains an IPv6 global address, for instance using 483 autoconfiguration [RFC4862] based on a Prefix Information Option 484 (PIO) [RFC4861] found in a Router Advertisement message or by some 485 other means such as DHCPv6 [RFC3315]. 487 o Once it has formed an address, the 6LN (re)registers its address 488 periodically, within the Lifetime of the previous registration, as 489 prescribed by [RFC8505]. 491 o Upon each consecutive registration, the 6LN MUST increase the TID 492 field. 494 o If the 6LN is aware of the RPL Instance the packet should be 495 injected into, then it SHOULD set the Opaque field to the 496 InstanceID, else it MUST leave the Opaque field to zero. In any 497 fashion the 6LN MUST set the 'I' field to zero. 499 o A 6LN acting as a RUL MUST set the 'R' flag in the EARO whereas a 500 6LN acting as a RAN SHOULD NOT set the 'R' flag. 502 o The 6LN MAY register to more than one 6LR at the same time. In 503 that case, a same value of TID is used for each registration. 505 o The 6LN MAY use any of the 6LRs to which it register to forward 506 its packets. 508 o the 6LN is not expected to be aware of RPL so it is not expected 509 to produce RPL artifacts in the data packets. 511 7.3. 6LR Operation 513 Also as prescribed by [RFC8505], the 6LR generates a DAR message upon 514 reception of a valid NS(EARO) message for the registration of a new 515 IPv6 Address by a 6LN. If the Duplicate Address exchange succeeds, 516 then the 6LR installs a Neighbor Cache Entry (NCE). If the 'R' flag 517 was set in the EARO of the NS message, and this 6LR can manage the 518 reachability of Registered Address, then the 6LR sets the 'R' flag in 519 the ARO of the response NA message. 521 From then on, the 6LN periodically sends a new NS(EARO) to refresh 522 the NCE state before the lifetime indicated in the EARO expires, with 523 TID that is incremented each time till it wraps in a lollipop 524 fashion. As long as the 'R' flag is set and this router can still 525 manage the reachability of Registered Address, the 6LR keeps setting 526 the 'R' flag in the EARO of the response NA message, but the exchange 527 of Extended Duplicate Address messages is skipped. 529 The Opaque field in the EARO hints the 6LR on the RPL Instance that 530 should be used for the DAO advertisements, and for the forwarding of 531 packets sourced at the registered address when there is no RPL Packet 532 Information (RPI) in the packet, in which case the 6LR SHOULD add one 533 to the packet. if the 'I' field is not zero, then the 6LR MUST 534 consider that the Opaque field is left to zero. If the Opaque field 535 is not set to zero, then it should carry a RPL InstanceID for the 536 Instance suggested by the 6LN. If the 6LR does not participate to 537 the associated Instance, then the 6LR MUST consider that the Opaque 538 field is left to zero. If the Opaque field left to zero, the 6LR is 539 free to use the default Instance (zero) for the registered address or 540 to select an Instance of its choice; else, that is if the 6LR 541 participates to the suggested Instance, then the 6LR SHOULD use that 542 Instance for the registered address. 544 Upon a successful NS/NA(EARO) exchange: if the 'R' flag was set in 545 the EARO of the NS message, then the 6LR SHOULD inject the Registered 546 Address in RPL by sending a DAO message on behalf of the 6LN; else 547 the 6LR MUST NOT inject the Registered Address into RPL. 549 The DAO message advertising the Registered Address MUST be 550 constructed as follows: 552 o The Registered Address is placed in a RPL Target Option in the DAO 553 message as the Target Prefix, and the Prefix Length is set to 128 555 o the External 'E' flag in the Transit Information Option (TIO) 556 associated to the Target Option is set to indicate that the 6LR 557 redistributes an external target into the RPL network. This is 558 how the root knows in non-storing mode to use IP-in-IP and 559 terminate the outters headers at the 6LR that generated the DAO. 561 o the Path Lifetime in the TIO is computed from the Lifetime in the 562 EARO Option to adapt it to the Lifetime Units used in the RPL 563 operation. Note that if the lifetime is 0, then the 6LR generates 564 a No-Path DAO message that cleans up the routes down to the 565 Address of the 6LN. 567 o the Path Sequence in the TIO is set to the TID value found in the 568 EARO option. 570 o Additionally, in Non-Storing Mode the 6LR indicates one of its 571 global IPv6 unicast addresses as the Parent Address in the TIO. 573 If a 6LR receives a valid NS(EARO) message with the 'R' flag reset 574 and the 6LR was redistributing the Registered Address due to previous 575 NS(EARO) messages with the flag set, then it MUST stop injecting the 576 address. It is up to the Registering Node to maintain the 577 corresponding route from then on, either keeping it active by sending 578 further DAO messages, or destroying it using a No-Path DAO. 580 7.4. RPL Root Operation 582 In RPL Storing Mode of Operation (MOP), the DAO message is propagated 583 from child to parent all the way to the Root along the DODAG, 584 populating routing state as it goes. In Non-Storing Mode, The DAO 585 message is sent directly to the route. Upon reception of a DAO 586 message that creates or updates an existing RPL state: 588 o the Root notifies the 6LBR using an internal API if they are 589 collocated, or performs a keep-alive DAR/DAC exchange on behalf of 590 the registering node if they are separated. 592 o In an extended topology with a Backbone Link, the Root notifies 593 the 6LBR by proxying a keep-alive NS(EARO) on behalf of the 6LN 594 that owns the address indicated in the Target Option. 596 The keep-alive EDAR and the NS(EARO) messages MUST be constructed as 597 follows: 599 o The Target IPv6 address from in the RPL Target Option is placed in 600 the Registered Address field of the EDAR message and in the Target 601 field of the NS message, respectively 603 o the ROVR field in the keep-alive EDAR is set to 64-bits of all 604 ones to indicate that it is not provided and this is a keep-alive 605 EDAR. The actual value of the ROVR for that registration is 606 returned by the 6LBR in an EDAC, and used in the proxy NS(EARO). 608 o the Registration Lifetime is adapted from the Path Lifetime in the 609 TIO by converting the Lifetime Units used in RPL into units of 60 610 seconds used in the 6LoWPAN ND messages. 612 o The RPL Root indicates its own MAC Address as Source Link Layer 613 Address (SLLA) in the NS(EARO). 615 o the TID value is set to the Path Sequence in the TIO. The 'T' 616 flag and an ICMP code of 1 are used in the NS(EARO) and the DAR 617 message, respectively. 619 Upon a status in a DAC message that is not "Success", the Root MAY 620 destroy the formed paths using a No-Path DAO downwards as specified 621 in [I-D.ietf-roll-efficient-npdao]. 623 In Non-Storing Mode, the outer IPv6 header that is used by the Root 624 to transport the source routing information in data packets down the 625 DODAG has the 6LR that serves the 6LN as final destination. This 626 way, when the final 6LR decapsulates the outer header, it also 627 removes all the RPL artifacts from the packet. 629 7.5. 6LBR Operation 631 Upon reception of a DAR message with the Owner Unique ID field is set 632 to all ones, the 6LBR checks whether an entry exists for the and 633 computes whether the TID in the DAR message is fresher than that in 634 the entry as prescribed in section 4.2.1. of [RFC8505]. 636 If the entry does not exist, the 6LBR does not create the entry, and 637 answers with a Status "Removed" in the DAC message. 639 If the entry exists but is not fresher, the 6LBR does not update the 640 entry, and answers with a Status "Success" in the DAC message. 642 If the entry exists and the TID in the DAR message is fresher, the 643 6LBR updates the TID in the entry, and if the lifetime of the entry 644 is extended by the Registration Lifetime in the DAR message, it also 645 updates the lifetime of the entry. In that case, the 6LBR replies 646 with a Status "Success" in the DAC message. 648 8. Protocol Operations for Multicast Addresses 650 Section 12 of [RFC6550] details the RPL support for multicast flows. 651 This support is not source-specific and only operates as an extension 652 to the Storing Mode of Operation for unicast packets. Note that it 653 is the RPL model that the multicast packet is passed as a Layer-2 654 unicast to each if the interested children. This remains true when 655 forwarding between the 6LR and the listener 6LN. 657 "Multicast Listener Discovery (MLD) for IPv6" [RFC2710] and its 658 updated version "Multicast Listener Discovery Version 2 (MLDv2) for 659 IPv6" [RFC3810] provide an interface for a listener to register to 660 multicast flows. MLDv2 is backwards compatible with MLD, and adds in 661 particular the capability to filter the sources via black lists and 662 white lists. In the MLD model, the router is a "querier" and the 663 host is a multicast listener that registers to the querier to obtain 664 copies of the particular flows it is interested in. 666 On the first registration, as illustrated in Figure 4, the 6LN, as an 667 MLD listener, sends an unsolicited Report to the 6LR in order to 668 start receiving the flow immediately. Since multicast Layer-2 669 messages are avoided, it is important that the asynchronous messages 670 for unsolicited Report and Done are sent reliably, for instance using 671 an Layer-2 acknoledgement, or attempted multiple times. 673 The 6LR acts as a generic MLD querier and generates a DAO for the 674 multicast target. The lifetime of the DAO is set to be in the order 675 of the Query Interval, yet larger to account for variable propagation 676 delays. 678 The root proxies the MLD echange as listener with the 6BBR acting as 679 the querier, so as to get packets from a source external to the RPL 680 domain. Upon a DAO with a multicast target, the RPL root checks if 681 it is already registered as a listener for that address, and if not, 682 it performs its own unsolicited Report for the multicast target. 684 6LN 6LR Root 6LBR 685 | | | | 686 | unsolicited Report | | | 687 |------------------->| | | 688 | | | | 689 | | DAO | | 690 | |-------------->| | 691 | | DAO ACK | | 692 | |<--------------| | 693 | | | | 694 | | | unsolicited Report | 695 | | |------------------->| 696 | | | | 697 | | | | 699 Figure 4: First Multicast Registration Flow 701 A re-registration is pulled by 6LR acting as querier. Note that the 702 message may sent unicast to all the known individual listeners. Upon 703 a time out of the Query Interval, the 6LR sends a Query to each of 704 its listeners, and gets a Report back that is mapped into a DAO, as 705 illustrated in Figure 5, 707 6LN 6LR Root 6LBR 708 | | | | 709 | Query | | | 710 |<-------------------| | | 711 | Report | | | 712 |------------------->| | | 713 | | DAO | | 714 | |-------------->| | 715 | | DAO ACK | | 716 | |<--------------| | 717 | | | | 718 | | | Query | 719 | | |<-------------------| 720 | | | Report | 721 | | |------------------->| 722 | | | | 723 | | | | 725 Figure 5: Next Registration Flow 727 Note that any of the functions 6LR, Root and 6LBR might be collapsed 728 in a single node, in which case the flow above happens internally, 729 and possibly through internal API calls as opposed to messaging. 731 9. Implementation Status 733 10. Security Considerations 735 The LLN nodes depend on the 6LBR and the RPL participants for their 736 operation. A trust model must be put in place to ensure that the 737 right devices are acting in these roles, so as to avoid threats such 738 as black-holing, or bombing attack whereby an impersonated 6LBR would 739 destroy state in the network by using the "Removed" Status code. 740 This trust model could be at a minimum based on a Layer-2 access 741 control, or could provide role validation as well. This is a generic 742 6LoWPAN requirement, see Req5.1 in Appendix of [RFC8505]. 744 The keep-alive EDAR message does not carry a valid Registration 745 Unique ID [RFC8505] and it cannot be used to create a binding state 746 in the 6LBR. The 6LBR MUST NOT create an entry based on a keep-alive 747 EDAR that does not match an existing entry. All it can do is refresh 748 the lifetime and the TID of an existing entry. 750 11. IANA Considerations 752 This specification has no requirement on IANA. 754 12. Acknowledgments 756 The author wishes to thank Michael Richardson and Georgios 757 Papadopoulos for their early reviews of and contributions to this 758 document 760 13. References 762 13.1. Normative References 764 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 765 Requirement Levels", BCP 14, RFC 2119, 766 DOI 10.17487/RFC2119, March 1997, 767 . 769 [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast 770 Listener Discovery (MLD) for IPv6", RFC 2710, 771 DOI 10.17487/RFC2710, October 1999, 772 . 774 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 775 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 776 DOI 10.17487/RFC3810, June 2004, 777 . 779 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 780 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 781 DOI 10.17487/RFC4861, September 2007, 782 . 784 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 785 Address Autoconfiguration", RFC 4862, 786 DOI 10.17487/RFC4862, September 2007, 787 . 789 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 790 over Low-Power Wireless Personal Area Networks (6LoWPANs): 791 Overview, Assumptions, Problem Statement, and Goals", 792 RFC 4919, DOI 10.17487/RFC4919, August 2007, 793 . 795 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 796 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 797 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 798 Low-Power and Lossy Networks", RFC 6550, 799 DOI 10.17487/RFC6550, March 2012, 800 . 802 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 803 Statement and Requirements for IPv6 over Low-Power 804 Wireless Personal Area Network (6LoWPAN) Routing", 805 RFC 6606, DOI 10.17487/RFC6606, May 2012, 806 . 808 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 809 Bormann, "Neighbor Discovery Optimization for IPv6 over 810 Low-Power Wireless Personal Area Networks (6LoWPANs)", 811 RFC 6775, DOI 10.17487/RFC6775, November 2012, 812 . 814 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 815 "IPv6 over Low-Power Wireless Personal Area Network 816 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 817 April 2017, . 819 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 820 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 821 May 2017, . 823 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 824 (IPv6) Specification", STD 86, RFC 8200, 825 DOI 10.17487/RFC8200, July 2017, 826 . 828 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 829 Perkins, "Registration Extensions for IPv6 over Low-Power 830 Wireless Personal Area Network (6LoWPAN) Neighbor 831 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 832 . 834 13.2. Informative References 836 [I-D.ietf-6lo-ap-nd] 837 Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 838 "Address Protected Neighbor Discovery for Low-power and 839 Lossy Networks", draft-ietf-6lo-ap-nd-12 (work in 840 progress), April 2019. 842 [I-D.ietf-roll-efficient-npdao] 843 Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient 844 Route Invalidation", draft-ietf-roll-efficient-npdao-11 845 (work in progress), May 2019. 847 [I-D.ietf-roll-useofrplinfo] 848 Robles, I., Richardson, M., and P. Thubert, "Using RPL 849 Option Type, Routing Header for Source Routes and IPv6-in- 850 IPv6 encapsulation in the RPL Data Plane", draft-ietf- 851 roll-useofrplinfo-29 (work in progress), May 2019. 853 [IEEEstd802154] 854 IEEE standard for Information Technology, "IEEE Standard 855 for Local and metropolitan area networks-- Part 15.4: Low- 856 Rate Wireless Personal Area Networks (LR-WPANs)". 858 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 859 C., and M. Carney, "Dynamic Host Configuration Protocol 860 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 861 2003, . 863 [RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur, 864 Ed., "Performance Evaluation of the Routing Protocol for 865 Low-Power and Lossy Networks (RPL)", RFC 6687, 866 DOI 10.17487/RFC6687, October 2012, 867 . 869 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 870 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 871 2014, . 873 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 874 Constrained-Node Networks", RFC 7228, 875 DOI 10.17487/RFC7228, May 2014, 876 . 878 Author's Address 880 Pascal Thubert (editor) 881 Cisco Systems, Inc 882 Building D 883 45 Allee des Ormes - BP1200 884 MOUGINS - Sophia Antipolis 06254 885 FRANCE 887 Phone: +33 497 23 26 34 888 Email: pthubert@cisco.com