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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-30) exists of draft-ietf-6tisch-architecture-29 == Outdated reference: A later version (-09) exists of draft-pthubert-raw-architecture-04 == Outdated reference: A later version (-44) exists of draft-ietf-roll-useofrplinfo-40 Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ROLL P. Thubert, Ed. 3 Internet-Draft Cisco Systems 4 Updates: 6550 (if approved) R.A. Jadhav 5 Intended status: Standards Track Huawei Tech 6 Expires: 25 March 2021 M. Gillmore 7 Itron 8 21 September 2020 10 Root initiated routing state in RPL 11 draft-ietf-roll-dao-projection-12 13 Abstract 15 This document enables a RPL Root to install and maintain Projected 16 Routes within its DODAG, along a selected set of nodes that may or 17 may not include self, for a chosen duration. This potentially 18 enables routes that are more optimized or resilient than those 19 obtained with the classical distributed operation of RPL, either in 20 terms of the size of a source-route header or in terms of path 21 length, which impacts both the latency and the packet delivery ratio. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at https://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on 25 March 2021. 40 Copyright Notice 42 Copyright (c) 2020 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 47 license-info) in effect on the date of publication of this document. 48 Please review these documents carefully, as they describe your rights 49 and restrictions with respect to this document. Code Components 50 extracted from this document must include Simplified BSD License text 51 as described in Section 4.e of the Trust Legal Provisions and are 52 provided without warranty as described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 58 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 59 2.2. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 5 60 2.3. Other Terms . . . . . . . . . . . . . . . . . . . . . . . 5 61 2.4. References . . . . . . . . . . . . . . . . . . . . . . . 6 62 3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 6 63 4. Identifying a Path . . . . . . . . . . . . . . . . . . . . . 7 64 5. New RPL Control Messages and Options . . . . . . . . . . . . 8 65 5.1. New P-DAO Request Control Message . . . . . . . . . . . . 8 66 5.2. New PDR-ACK Control Message . . . . . . . . . . . . . . . 9 67 5.3. Route Projection Options . . . . . . . . . . . . . . . . 10 68 5.4. Sibling Information Option . . . . . . . . . . . . . . . 13 69 6. Projected DAO . . . . . . . . . . . . . . . . . . . . . . . . 14 70 6.1. Requesting a Track . . . . . . . . . . . . . . . . . . . 16 71 6.2. Routing over a Track . . . . . . . . . . . . . . . . . . 16 72 6.3. Non-Storing Mode Projected Route . . . . . . . . . . . . 17 73 6.4. Storing-Mode Projected Route . . . . . . . . . . . . . . 18 74 7. Security Considerations . . . . . . . . . . . . . . . . . . . 21 75 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 76 8.1. New RPL Control Codes . . . . . . . . . . . . . . . . . . 21 77 8.2. New RPL Control Message Options . . . . . . . . . . . . . 21 78 8.3. SubRegistry for the Projected DAO Request Flags . . . . . 22 79 8.4. SubRegistry for the PDR-ACK Flags . . . . . . . . . . . . 22 80 8.5. Subregistry for the PDR-ACK Acceptance Status Values . . 22 81 8.6. Subregistry for the PDR-ACK Rejection Status Values . . . 23 82 8.7. SubRegistry for the Route Projection Options Flags . . . 23 83 8.8. SubRegistry for the Sibling Information Option Flags . . 24 84 8.9. Error in Projected Route ICMPv6 Code . . . . . . . . . . 24 85 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24 86 10. Normative References . . . . . . . . . . . . . . . . . . . . 24 87 11. Informative References . . . . . . . . . . . . . . . . . . . 25 88 Appendix A. Applications . . . . . . . . . . . . . . . . . . . . 26 89 A.1. Loose Source Routing . . . . . . . . . . . . . . . . . . 27 90 A.2. Transversal Routes . . . . . . . . . . . . . . . . . . . 28 91 Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 30 92 B.1. Using Storing Mode P-DAO in Non-Storing Mode MOP . . . . 30 93 B.2. Projecting a storing-mode transversal route . . . . . . . 31 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33 96 1. Introduction 98 RPL, the "Routing Protocol for Low Power and Lossy Networks" [RPL] 99 (LLNs), is a generic Distance Vector protocol that is well suited for 100 application in a variety of low energy Internet of Things (IoT) 101 networks. RPL forms Destination Oriented Directed Acyclic Graphs 102 (DODAGs) in which the Root often acts as the Border Router to connect 103 the RPL domain to the Internet. The Root is responsible to select 104 the RPL Instance that is used to forward a packet coming from the 105 Internet into the RPL domain and set the related RPL information in 106 the packets. The "6TiSCH Architecture" [6TiSCH-ARCHI] uses RPL for 107 its routing operations. 109 The 6TiSCH Architecture also leverages the "Deterministic Networking 110 Architecture" [RFC8655] centralized model whereby the device 111 resources and capabilities are exposed to an external controller 112 which installs routing states into the network based on some 113 objective functions that reside in that external entity. With DetNet 114 and 6TiSCH, the component of the controller that is responsible of 115 computing routes is called a Path Computation Element ([PCE]). 117 Based on heuristics of usage, path length, and knowledge of device 118 capacity and available resources such as battery levels and 119 reservable buffers, a PCE with a global visibility on the system can 120 compute P2P routes that are more optimized for the current needs as 121 expressed by the objective function. 123 This draft proposes protocol extensions to RPL that enable the Root 124 to install a limited amount of centrally-computed routes in a RPL 125 graph, on behalf of a PCE that may be collocated or separated from 126 the Root. Those extensions enable loose source routing down and 127 transversal routes inside the main DODAG running a base RPL Instance. 129 This specification expects that the base RPL Instance is operated in 130 RPL Non-Storing Mode of Operation (MOP) to sustain the exchanges with 131 the Root. In that Mode, the Root has enough information to build a 132 basic DODAG topology based on parents and children, but lacks the 133 knowledge of siblings. This document adds the capability for nodes 134 to advertise sibling information in order to improve the topological 135 awareness of the Root. 137 As opposed to the classical RPL operations where routes are injected 138 by the Target nodes, the protocol extensions enable the Root of a 139 DODAG to project the routes that are needed onto the nodes where they 140 should be installed. This specification uses the term Projected 141 Route to refer to those routes. 143 A Projected Route may be installed in either Storing and Non-Storing 144 Mode, potentially resulting in hybrid situations where the Mode of 145 the Projected Route is different from that of the main RPL Instance. 146 A Projected Route may be a stand-alone end-to-end path to a Target or 147 a Segment in a more complex forwarding graph called a Track. 149 The concept of a Track was introduced in the 6TiSCH architecture, as 150 a complex path to a Target destination with redundant forwarding 151 solutions along the way. A node at the ingress of more than one 152 Segment in a Track may use any combination of those Segments to 153 forward a packet towards the Target. 155 The "Reliable and Available Wireless (RAW) Architecture/Framework" 156 [RAW-ARCHI] enables a dynamic path selection within the Track to 157 increase the transmission diversity and combat diverse causes of 158 packet loss. 160 To that effect, RAW defines the Path Selection Engine (PSE) as a 161 complement of the PCE operating in the dataplane. The PSE controls 162 the use of the Packet ARQ, Replication, Elimination, and Overhearing 163 (PAREO) functions over the Track segments. 165 While the time scale at which the PCE (re)computes the Track can be 166 long, for an operation based on long-term statistical metrics to 167 perform global optimizations at the scale of the whole network, the 168 PSE makes forwarding decision at the time scale of one or a small 169 collection of packets, using a knowledge that is changing rapidly but 170 limited in scope of the Track itself. This way, the PSE can provide 171 a dynamic balance between the reliability and availability 172 requirements of the flows and the need to conserve energy and 173 spectrum. 175 Projected Routes must be used with the parsimony to limit the amount 176 of state that is installed in each device to fit within the device 177 resources, and to maintain the amount of rerouted traffic within the 178 capabilities of the transmission links. The methods used to learn 179 the node capabilities and the resources that are available in the 180 devices and in the network are out of scope for this document. 182 This specification uses the RPL Root as a proxy to the PCE. The PCE 183 may be collocated with the Root, or may reside in an external 184 Controller. In that case, the PCE exchanges control messages with 185 the Root over a Southbound API, that is out of scope for this 186 specification. The algorithm to compute the paths and the protocol 187 used by an external PCE to obtain the topology of the network from 188 the Root are also out of scope. 190 2. Terminology 192 2.1. Requirements Language 194 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 195 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 196 "OPTIONAL" in this document are to be interpreted as described in BCP 197 14 [RFC2119][RFC8174] when, and only when, they appear in all 198 capitals, as shown here. 200 2.2. Glossary 202 This document often uses the following acronyms: 204 CMO: Control Message Option 205 DAO: Destination Advertisement Object 206 DAG: Directed Acyclic Graph 207 DODAG: Destination-Oriented Directed Acyclic Graph; A DAG with only 208 one vertice (i.e., node) that has no outgoing edge (i.e., link) 209 LLN: Low-Power and Lossy Network 210 MOP: RPL Mode of Operation 211 P-DAO: Projected DAO 212 PDR: P-DAO Request 213 RAN: RPL-Aware Node (either a RPL Router or a RPL-Aware Leaf) 214 RAL: RPL-Aware Leaf 215 RPI: RPL Packet Information 216 RPL: IPv6 Routing Protocol for LLNs [RPL] 217 RPO: A Route Projection Option; it can be a VIO or an SRVIO. 218 RTO: RPL Target Option 219 RUL: RPL-Unaware Leaf 220 SIO: RPL Sibling Information Option 221 SRVIO: A Source-Routed Via Information Option, used in Non-Storing 222 Mode P-DAO messages. 223 SubDAG: A DODAG rooted at a node which is a child of that node and a 224 subset of a larger DAG 225 TIO: RPL Transit Information Option 226 VIO: A Via Information Option, used in Storing Mode P-DAO messages. 228 2.3. Other Terms 230 Projected Route: A Projected Route is a serial path that is 231 computed, installed and maintained remotely by a RPL Root. 232 Projected DAO: A DAO message used to install a Projected Route. 233 Track: A complex path with redundant Segments to a destination. 234 TrackID: A RPL Local InstanceID with the 'D' bit set. The TrackId 235 is associated with a Target address that is the Track destination. 237 2.4. References 239 In this document, readers will encounter terms and concepts that are 240 discussed in the "Routing Protocol for Low Power and Lossy Networks" 241 [RPL] and "Terminology in Low power And Lossy Networks" [RFC7102]. 243 3. Updating RFC 6550 245 This specification introduces two new RPL Control Messages to enable 246 a RPL Aware Node (RAN) to request the establisment of a Track from 247 self to a Target. The RAN makes its request by sending a new P-DAO 248 Request (PDR) Message to the Root. The Root confirms with a new PDR- 249 ACK message back to the requester RAN, see Section 5.1 for more. 251 Section 6.7 of [RPL] specifies the RPL Control Message Options (CMO) 252 to be placed in RPL messages such as the Destination Advertisement 253 Object (DAO) message. The RPL Target Option (RTO) and the Transit 254 Information Option (TIO) are such options. 256 In Non-Storing Mode, the TIO option is used in the DAO message to 257 inform the root of the parent-child relationships within the DODAG, 258 and the Root has a full knowledge of the DODAG structure. The TIO 259 applies to the RTOs that preceed it immediately in the message. 260 Options may be factorized; multiple TIOs may be present to indicate 261 multiple routes to the one or more contiguous addresses indicated in 262 the RTOs that immediately precede the TIOs in the RPL message. 264 This specification introduces two new CMOs referred to as Route 265 Projection Options (RPO) to install Projected Routes. One RPO is the 266 Via Information Option (VIO) and the other is the Source-Routed VIO 267 (SRVIO). The VIO installs a route on each hop along a Projected 268 Route (in a fashion analogous to RPL Storing Mode) whereas the SRVIO 269 installs a source-routing state at the ingress node, which uses that 270 state to encapsulate a packet with an IPv6 Routing Header in a 271 fashion similar to RPL Non-Storing Mode. 273 Like the TIO, the RPOs MUST be preceded by exactly one RTO to which 274 they apply, and SRVIOs MAY be factorized, though VIOs MUST NOT be. 275 Factorized contiguous SRVIOs indicate alternate paths to the Target, 276 more in Section 5.3. 278 This specification also introduces a new CMO to enable a RAN to 279 advertise a selection of its candidate neighbors as siblings to the 280 Root, using a new Sibling Information Option (SIO) as specified in 281 Section 5.4. 283 4. Identifying a Path 285 It must be noted that RPL has a concept of Instance to represent 286 different routing topologies but does not have a concept of an 287 administrative distance, which exists in certain proprietary 288 implementations to sort out conflicts between multiple sources of 289 routing information within one routing topology. 291 This draft conforms the Instance model as follows: 293 * If the PCE needs to influence a particular Instance to add better 294 routes in conformance with the routing objectives in that 295 Instance, it may do so as long as it does not create a loop. A 296 Projected Route is always preferred over a route that is learned 297 via RPL. 299 * The PCE may use P-DAOs to install a specific (say, Traffic 300 Engineered) and possibly complex path, that we refer to as a 301 Track, towards a particular Target. In that case it MUST use a 302 Local RPL Instance (see section 5 of [RPL]) associated to that 303 Target to identify the Track. 305 We refer to the local RPLInstanceID as TrackID. The TrackID MUST 306 be unique for a particular Target IPv6 address. The Track is 307 uniquely identified within the RPL domain by the tuple (Target 308 address, TrackID) where the TrackID is always represented with the 309 'D' flag set. 311 The Track where a packet is placed is signaled by a RPL Packet 312 Information (RPI) (see [USEofRPLinfo]) in the outer chain of IPv6 313 Headers. The RPI contains the TrackID as RPLInstanceID and the 314 'D' flag is set to indicate that the destination address in the 315 IPv6 header is the Target that is used to identify the Track, more 316 in Section 6.2. 318 * The PCE may also install a projected Route as a complement to the 319 main DODAG, e.g., using the Storing-Mode Mode along a Source- 320 Routed path in order to enable loose source routing and reduce the 321 Routing Header. In that case, the global RPLInstanceID of the 322 main DODAG is signaled in place of the TrackId on the P-DAO, and 323 the RPI in the packet indicates the global RPLInstanceID, more in 324 Appendix A.1. 326 * A packet that is routed over the RPL Instance associated to a 327 Track MUST NOT be placed over a different RPL Instance again. 328 Conversely, a packet that is placed on a Global Instance MAY be 329 injected in a Local Instance based on a network policy and the 330 Local Instance configuration. 332 A Projected Route is a serial path that may represent the end-to-end 333 route or only a Segment in a complex Track, in which case multiple 334 Projected Routes are installed with the same tuple (Target address, 335 TrackID) and a different Segment ID each. 337 All properties of a Track operations are inherited form the main 338 instance that is used to install the Track. For instance, the use of 339 compression per [RFC8138] is determined by whether it is used in the 340 main instance, e.g., by setting the "T" flag [TURN-ON_RFC8138] in the 341 RPL configuration option. 343 5. New RPL Control Messages and Options 345 5.1. New P-DAO Request Control Message 347 The P-DAO Request (PDR) message is sent to the Root to request a new 348 that the PCE establishes a new a projected route from self ot the 349 Target indicated in the Target Option as a full path of a collection 350 of Segments in a Track. Exactly one Target Option MUST be present, 351 more in Section 6.1. 353 The RPL Control Code for the PDR is 0x09, to be confirmed by IANA. 354 The format of PDR Base Object is as follows: 356 0 1 2 3 357 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 1 358 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 359 | TrackID |K|R| Flags | ReqLifetime | PDRSequence | 360 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 361 | Option(s)... 362 +-+-+-+-+-+-+-+-+ 364 Figure 1: New P-DAO Request Format 366 TrackID: 8-bit field indicating the RPLInstanceID associated with 367 the Track. It is set to zero upon the first request for a new 368 Track and then to the TrackID once the Track was created, to 369 either renew it of destroy it. 371 K: The 'K' flag is set to indicate that the recipient is expected to 372 send a PDR-ACK back. 374 R: The 'R' flag is set to indicate that the Requested path should be 375 redundant. 377 Flags: Reserved. The Flags field MUST initialized to zero by the 378 sender and MUST be ignored by the receiver 380 ReqLifetime: 8-bit unsigned integer. 382 The requested lifetime for the Track expressed in Lifetime Units 383 (obtained from the DODAG Configuration option). 385 A PDR with a fresher PDRSequence refreshes the lifetime, and a 386 PDRLifetime of 0 indicates that the track should be destroyed. 388 PDRSequence: 8-bit wrapping sequence number, obeying the operation 389 in section 7.2 of [RPL]. 391 The PDRSequence is used to correlate a PDR-ACK message with the 392 PDR message that triggeted it. It is incremented at each PDR 393 message and echoed in the PDR-ACK by the Root. 395 5.2. New PDR-ACK Control Message 397 The new PDR-ACK is sent as a response to a PDR message with the 'K' 398 flag set. The RPL Control Code for the PDR-ACK is 0x0A, to be 399 confirmed by IANA. Its format is as follows: 401 0 1 2 3 402 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 1 403 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 404 | TrackID | Flags | Track Lifetime| PDRSequence | 405 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 406 | PDR-ACK Status| Reserved | 407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 408 | Option(s)... 409 +-+-+-+-+-+-+-+ 411 Figure 2: New PDR-ACK Control Message Format 413 TrackID: The RPLInstanceID of the Track that was created. The value 414 of 0x00 is used to when no Track was created. 416 Flags: Reserved. The Flags field MUST initialized to zero by the 417 sender and MUST be ignored by the receiver 419 Track Lifetime: Indicates that remaining Lifetime for the Track, 420 expressed in Lifetime Units; a value of zero (0x00) indicates that 421 the Track was destroyed or not created. 423 PDRSequence: 8-bit wrapping sequence number. It is incremented at 424 each PDR message and echoed in the PDR-ACK. 426 PDR-ACK Status: 8-bit field indicating the completion. 428 The PDR-ACK Status is substructured as indicated in Figure 3: 430 0 1 2 3 4 5 6 7 431 +-+-+-+-+-+-+-+-+ 432 |E|R| Value | 433 +-+-+-+-+-+-+-+-+ 435 Figure 3: PDR-ACK status Format 437 E: 1-bit flag. Set to indicate a rejection. When not set, a 438 value of 0 indicates Success/Unqualified acceptance and other 439 values indicate "not an outright rejection". 441 R: 1-bit flag. Reserved, MUST be set to 0 by the sender and 442 ignored by the receiver. 444 Status Value: 6-bit unsigned integer. Values depending on the 445 setting of the 'E' flag as indicated respectively in Table 4 446 and Table 5. 448 Reserved: The Reserved field MUST initialized to zero by the sender 449 and MUST be ignored by the receiver 451 5.3. Route Projection Options 453 The RPOs indicate a series of IPv6 addresses that can be compressed 454 using the method defined in the "6LoWPAN Routing Header" [RFC8138] 455 specification using the address of the Root found in the DODAGID 456 field of DIO messages as Compression Reference. 458 An RPO indicates a Projected Route that can be a serial Track in full 459 or a Segment of a more complex Track. In Non-Storing Mode, multiple 460 RPO may be placed after a same Target Option to reflect different 461 Segments originated at this node. The Track is identified by a 462 TrackID that is a Local RPLInstanceID to the Target of the Track. 464 The format of RPOs is as follows: 466 0 1 2 3 467 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 1 468 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 469 | Type | Option Length |C| Flags | Reserved | 470 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 471 | TrackID | SegmentID |Segm. Sequence | Seg. Lifetime | 472 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 473 | | 474 + + 475 . . 476 . Via Address 1 . 477 . . 478 + + 479 | | 480 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 481 | | 482 . .... . 483 | | 484 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 485 | | 486 + + 487 . . 488 . Via Address n . 489 . . 490 + + 491 | | 492 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 494 Figure 4: Route Projection Option format (uncompressed form) 496 Option Type: 0x0B for VIO, 0x0C for SRVIO (to be confirmed by IANA) 498 Option Length: In bytes; variable, depending on the number of Via 499 Addresses. 501 C: 1-bit flag. Set to indicate that the following Via Addresses are 502 expressed as one or more SRH-6LoRH as defined in section 5.1 of 503 [RFC8138]. Figure 4 illustrates the case where the "C" flag is 504 not set, meaning that the Via Addresses are expressed in 128 bits. 506 Flags: Reserved. The Flags field MUST initialized to zero by the 507 sender and MUST be ignored by the receiver 509 Reserved: The Reserved field MUST initialized to zero by the sender 510 and MUST be ignored by the receiver 512 TrackID: 8-bit field indicating the topology Instance associated 513 with the Track. This field carries either a TrackID, such that 514 the tuple (Target Address, TrackID) forms a unique ID of the Track 515 in the RPL domain, or the glocal InstanceID of the main DODAG, in 516 which case the RPO adds a route to the main DODAG as an individual 517 Segment. 519 SegmentID: 8-bit field that identifies a Segment within a Track or 520 the main DODAG as indicated by the TrackId field. A Value of 0 is 521 used to signal a serial path, i.e., made of a single segment. 523 Segment Sequence: 8-bit unsigned integer. The Segment Sequence 524 obeys the operation in section 7.2 of [RPL] and the lollipop 525 starts at 255. When the Root of the DODAG needs to refresh or 526 update a Segment in a Track, it increments the Segment Sequence 527 individually for that Segment. The Segment information indicated 528 in the RTO deprecates any state for the Segment indicated by the 529 SegmentID within the indicated Track and sets up the new 530 information. A RTO with a Segment Sequence that is not as fresh 531 as the current one is ignored. a RTO for a given target with the 532 same (TrackID, SegmentID, Segment Sequence) indicates a retry; it 533 MUST NOT change the Segment and MUST be propagated or answered as 534 the first copy. 536 Segment Lifetime: 8-bit unsigned integer. The length of time in 537 Lifetime Units (obtained from the Configuration option) that the 538 Segment is usable. The period starts when a new Segment Sequence 539 is seen. A value of 255 (0xFF) represents infinity. A value of 540 zero (0x00) indicates a loss of reachability. A DAO message that 541 contains a Via Information option with a Segment Lifetime of zero 542 for a Target is referred as a No-Path (for that Target) in this 543 document. 545 Via Address: The collection of Via Addresses along one Segment, 546 indicated in the order of the path from the ingress to the egress 547 nodes. If the "C" flag is set, the fields Via Address 1 .. Via 548 Address n in Figure 4 are replaced by one or more of the headers 549 illustrated in Fig. 6 of [RFC8138]. In the case of a VIO, or if 550 [RFC8138] is turned off, then the Root MUST use only one SRH- 551 6LoRH, and the compression is the same for all addresses. If 552 [RFC8138] is turned on, then the Root SHOULD optimize the size of 553 the SRVIO; in that case, more than one SRH-6LoRH are needed if the 554 compression of the addresses change inside the Segment and 555 different SRH-6LoRH Types are used. 557 An RPO MUST contain at least one Via Address, and a Via Address MUST 558 NOT be present more than once, otherwise the RPO MUST be ignored. 560 5.4. Sibling Information Option 562 The Sibling Information Option (SIO) provides indication on siblings 563 that could be used by the Root to form Projected Routes. The format 564 of SIOs is as follows: 566 0 1 2 3 567 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 1 568 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 569 | Type | Option Length |Comp.|B|D|Flags| Opaque | 570 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 571 | Step of Rank | Reserved | 572 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 573 | | 574 + + 575 . . 576 . Sibling DODAGID (if 'D' flag not set) . 577 . . 578 + + 579 | | 580 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 581 | | 582 + + 583 . . 584 . Sibling Address . 585 . . 586 + + 587 | | 588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 590 Figure 5: Sibling Information Option Format 592 Option Type: 0x0D (to be confirmed by IANA) 594 Option Length: In bytes; variable, depending on the number of Via 595 Addresses. 597 Compression Type: 3-bit unsigned integer. This is the SRH-6LoRH 598 Type as defined in figure 7 in section 5.1 of [RFC8138] that 599 corresponds to the compression used for the Sibling Address. 601 Reserved for Flags: MUST be set to zero by the sender and MUST be 602 ignored by the receiver. 604 B: 1-bit flag that is set to indicate that the connectivity to the 605 sibling is bidirectional and roughly symmetrical. In that case, 606 only one of the siblings may report the SIO for the hop. If 'B' 607 is not set then the SIO only indicates connectivity from the 608 sibling to this node, and does not provide information on the hop 609 from this node to the sibling. 611 D: 1-bit flag that is set to indicate that sibling belongs to the 612 same DODAG. When not set, the Sibling DODAGID is indicated. 614 Flags: Reserved. The Flags field MUST initialized to zero by the 615 sender and MUST be ignored by the receiver 617 Opaque: MAY be used to carry information that the node and the Root 618 understand, e.g., a particular representation of the Link 619 properties such as a proprietary Link Quality Information for 620 packets received from the sibling. An industraial Alliance that 621 uses RPL for a particular use / environment MAY redefine the use 622 of this field to fit its needs. 624 Step of Rank: 16-bit unsigned integer. This is the Step of Rank 625 [RPL] as computed by the Objective Function between this node and 626 the sibling. 628 Reserved: The Reserved field MUST initialized to zero by the sender 629 and MUST be ignored by the receiver 631 Sibling DODAGID: 2 to 16 bytes, the DODAGID of the sibling in a 632 [RFC8138] compressed form as indicated by the Compression Type 633 field. This field is present when the 'D' flag is not set. 635 Sibling Address: 2 to 16 bytes, the IPv6 Address of the sibling in a 636 [RFC8138] compressed form as indicated by the Compression Type 637 field. 639 An SIO MAY be immediately followed by a DAG Metric Container. In 640 that case the DAG Metric Container provides additional metrics for 641 the hop from the Sibling to this node. 643 6. Projected DAO 645 This draft adds a capability to RPL whereby the Root of a DODAG 646 projects a route by sending one or more extended DAO message called 647 Projected-DAO (P-DAO) messages to an arbitrary router in the DODAG, 648 indicating one or more sequence(s) of routers inside the DODAG via 649 which the Target(s) indicated in the RPL Target Option(s) (RTO) can 650 be reached. 652 A P-DAO is sent from a global address of the Root to a global address 653 of the recipient, and MUST be confirmed by a DAO-ACK, which is sent 654 back to a global address of the Root. 656 A P-DAO message MUST contain exactly one RTO and either one VIO or 657 one or more SRVIOs following it. There can be at most one such 658 sequence of RTOs and then RPOs. 660 Like a classical DAO message, a P-DAO causes a change of state only 661 if it is "new" per section 9.2.2. "Generation of DAO Messages" of 662 the RPL specification [RPL]; this is determined using the Segment 663 Sequence information from the RPO as opposed to the Path Sequence 664 from a TIO. Also, a Segment Lifetime of 0 in an RPO indicates that 665 the projected route associated to the Segment is to be removed. 667 There are two kinds of operation for the Projected Routes, the 668 Storing Mode and the Non-Storing Mode. 670 * The Non-Storing Mode is discussed in Section 6.3. It uses an 671 SRVIO that carries a list of Via Addresses to be used as a source- 672 routed path to the Target. The recipient of the P-DAO is the 673 ingress router of the source-routed path. Upon a Non-Storing Mode 674 P-DAO, the ingress router installs a source-routed state to the 675 Target and replies to the Root directly with a DAO-ACK message. 677 * The Storing Mode is discussed in Section 6.4. It uses a VIO with 678 one Via Address per consecutive hop, from the ingress to the 679 egress of the path, including the list of all intermediate routers 680 in the data path order. The Via Addresses indicate the routers in 681 which the routing state to the Target have to be installed via the 682 next Via Address in the VIO. In normal operations, the P-DAO is 683 propagated along the chain of Via Routers from the egress router 684 of the path till the ingress one, which confirms the installation 685 to the Root with a DAO-ACK message. Note that the Root may be the 686 ingress and it may be the egress of the path, that it can also be 687 neither but it cannot be both. 689 In case of a forwarding error along a Projected Route, an ICMP error 690 is sent to the Root with a new Code "Error in Projected Route" (See 691 Section 8.9). The Root can then modify or remove the Projected 692 Route. The "Error in Projected Route" message has the same format as 693 the "Destination Unreachable Message", as specified in RFC 4443 694 [RFC4443]. The portion of the invoking packet that is sent back in 695 the ICMP message SHOULD record at least up to the routing header if 696 one is present, and the routing header SHOULD be consumed by this 697 node so that the destination in the IPv6 header is the next hop that 698 this node could not reach. if a 6LoWPAN Routing Header (6LoRH) 700 [RFC8138] is used to carry the IPv6 routing information in the outter 701 header then that whole 6LoRH information SHOULD be present in the 702 ICMP message. The sender and exact operation depend on the Mode and 703 is described in Section 6.3 and Section 6.4 respectively. 705 6.1. Requesting a Track 707 A Node is free to ask the Root for a new Track with a PDR message, 708 for a duration indicated in a Requested Lifetime field. Upon that 709 Request, the Root install the necessary Segments and answers with a 710 PDR-ACK indicated the granted Track Lifetime. When the Track 711 Lifetime returned in the PDR-ACK is close to elapse, the resquesting 712 Node needs to resend a PDR using the TrackID in the PDR-ACK to get 713 the lifetime of the Track prolonged, else the Track will time out and 714 the Root will tear down the whole structure. 716 The Segment Lifetime in the P-DAO messages does not need to be 717 aligned to the Requested Lifetime in the PDR, or between P-DAO 718 messages for different Segments. The Root may use shorter lifetimes 719 for the Segments and renew them faster than the Track is, or longer 720 lifetimes in which case it will need to tear down the Segments if the 721 Track is not renewed. 723 The Root is free to install which ever Segments it wants, and change 724 them overtime, to serve the Track as needed, without notifying the 725 resquesting Node. If the Track fails and cannot be reestablished, 726 the Root notifies the resquesting Node asynchronously with a PDR-ACK 727 with a Track Lifetime of 0, indicating that the Track has failed, and 728 a PDR-ACK Status indicating the reason of the fault. 730 All the Segments MUST be of a same mode, either Storing or Non- 731 Storing. All the Segments MUST be created with the same TrackId and 732 Target in the P-DAO. 734 6.2. Routing over a Track 736 Sending a packet over a Track implies the addition of a RPI to 737 indicate the Track, in association with the IPv6 destination. In 738 case of a Non-Storing Mode Projected Route, a Source Routing Header 739 is needed as well. 741 The Destination IPv6 Address of a packet that is place in a Track 742 MUST be that of the Target of Track. The outer header of the packet 743 MUST contain an RPI that indicates the TrackId as RPL Instance ID. 745 If the Track Ingress is the originator of the packet and the Track 746 Egress (i.e., the Target) is the destination of the packet, there is 747 no need of an encapsulation. Else, i.e., if the Track Ingress is 748 forwarding a packet into the Track, or if the the final destination 749 is reached via is not the Target, but reached over the Track via the 750 Track Egress, then an IP-in-IP encapsulation is needed. 752 6.3. Non-Storing Mode Projected Route 754 As illustrated in Figure 6, a P-DAO that carries an SRVIO enables the 755 Root to install a source-routed path towards a Target in any 756 particular router; with this path information the router can add a 757 source routed header reflecting the Projected Route to any packet for 758 which the current destination either is the said Target or can be 759 reached via the Target. 761 ------+--------- 762 | Internet 763 | 764 +-----+ 765 | | Border Router 766 | | (RPL Root) 767 +-----+ | P ^ | 768 | | DAO | ACK | Loose 769 o o o o router V | | Source 770 o o o o o o o o o | P-DAO . Route 771 o o o o o o o o o o | Source . Path 772 o o o o o o o o o | Route . From 773 o o o o o o o o | Path . Root 774 o o o o o Target V . To 775 o o o o | Desti- 776 o o o o | nation 777 destination V 779 LLN 781 Figure 6: Projecting a Non-Storing Route 783 A route indicated by an SRVIO may be loose, meaning that the node 784 that owns the next listed Via Address is not necessarily a neighbor. 785 Without proper loop avoidance mechanisms, the interaction of loose 786 source routing and other mechanisms may effectively cause loops. In 787 order to avoid those loops, if the router that installs a Projected 788 Route does not have a connected route (a direct adjacency) to the 789 next soure routed hop and fails to locate it as a neighbor or a 790 neighbor of a neighbor, then it MUST ensure that it has another 791 Projected Route to the next loose hop under the control of the same 792 route computation system, otherwise the P-DAO is rejected. 794 When forwarding a packet to a destination for which the router 795 determines that routing happens via the Target, the router inserts 796 the source routing header in the packet to reach the Target. In 797 order to add a source-routing header, the router encapsulates the 798 packet with an IP-in-IP header and a Non-Storing Mode source routing 799 header (SRH) [RFC6554]. In the uncompressed form the source of the 800 packet would be self, the destination would be the first Via Address 801 in the SRVIO, and the SRH would contain the list of the remaining Via 802 Addresses and then the Target. 804 In the case of a loose source-routed path, there MUST be either a 805 neighbor that is adjacent to the loose next hop, on which case the 806 packet is forwarded to that neighbor, or a source-routed path to the 807 loose next hop; in the latter case, another encapsulation takes place 808 and the process possibly recurses; otherwise the packet is dropped. 810 In practice, the router will normally use the "IPv6 over Low-Power 811 Wireless Personal Area Network (6LoWPAN) Paging Dispatch" [RFC8025] 812 to compress the RPL artifacts as indicated in [RFC8138]. In that 813 case, the router indicates self as encapsulator in an IP-in-IP 6LoRH 814 Header, and places the list of Via Addresses in the order of the VIO 815 and then the Target in the SRH 6LoRH Header. 817 In case of a forwarding error along a Source Route path, the node 818 that fails to forward SHOULD send an ICMP error with a code "Error in 819 Source Routing Header" back to the source of the packet, as described 820 in section 11.2.2.3. of [RPL]. Upon this message, the encapsulating 821 node SHOULD stop using the source route path for a period of time and 822 it SHOULD send an ICMP message with a Code "Error in Projected Route" 823 to the Root. Failure to follow these steps may result in packet loss 824 and wasted resources along the source route path that is broken. 826 6.4. Storing-Mode Projected Route 828 As illustrated in Figure 7, the Storing Mode route projection is used 829 by the Root to install a routing state towards a Target in the 830 routers along a Segment between an ingress and an egress router; this 831 enables the routers to forward along that Segment any packet for 832 which the next loose hop is the said Target, for Instance a loose 833 source routed packet for which the next loose hop is the Target, or a 834 packet for which the router has a routing state to the final 835 destination via the Target. 837 ------+--------- 838 | Internet 839 | 840 +-----+ 841 | | Border Router 842 | | (RPL Root) 843 +-----+ | ^ | 844 | | DAO | ACK | 845 o o o o | | | 846 o o o o o o o o o | ^ | Projected . 847 o o o o o o o o o o | | DAO | Route . 848 o o o o o o o o o | ^ | . 849 o o o o o o o o v | DAO v . 850 o o LLN o o o | 851 o o o o o Loose Source Route Path | 852 o o o o From Root To Destination v 854 Figure 7: Projecting a route 856 In order to install the relevant routing state along the Segment 857 between an ingress and an egress routers, the Root sends a unicast 858 P-DAO message to the egress router of the routing Segment that must 859 be installed. The P-DAO message contains the ordered list of hops 860 along the Segment as a direct sequence of Via Information options 861 that are preceded by one or more RPL Target options to which they 862 relate. Each Via Information option contains a Segment Lifetime for 863 which the state is to be maintained. 865 The Root sends the P-DAO directly to the egress node of the Segment. 866 In that P-DAO, the destination IP address matches the Via Address in 867 the last VIO. This is how the egress recognizes its role. In a 868 similar fashion, the ingress node recognizes its role as it matches 869 Via Address in the first VIO. 871 The egress node of the Segment is the only node in the path that does 872 not install a route in response to the P-DAO; it is expected to be 873 already able to route to the Target(s) on its own. It may either be 874 the Target, or may have some existing information to reach the 875 Target(s), such as a connected route or an already installed 876 Projected Route. If one of the Targets cannot be located, the node 877 MUST answer to the Root with a negative DAO-ACK listing the Target(s) 878 that could not be located (suggested status 10 to be confirmed by 879 IANA). 881 If the egress node can reach all the Targets, then it forwards the 882 P-DAO with unchanged content to its loose predecessor in the Segment 883 as indicated in the list of Via Information options, and recursively 884 the message is propagated unchanged along the sequence of routers 885 indicated in the P-DAO, but in the reverse order, from egress to 886 ingress. 888 The address of the predecessor to be used as destination of the 889 propagated DAO message is found in the Via Information option the 890 precedes the one that contain the address of the propagating node, 891 which is used as source of the packet. 893 Upon receiving a propagated DAO, an intermediate router as well as 894 the ingress router install a route towards the DAO Target(s) via its 895 successor in the P-DAO; the router locates the VIO that contains its 896 address, and uses as next hop the address found in the Via Address 897 field in the following VIO. The router MAY install additional routes 898 towards the addresses that are located in VIOs that are after the 899 next one, if any, but in case of a conflict or a lack of resource, a 900 route to a Target installed by the Root has precedence. 902 The process recurses till the P-DAO is propagated to ingress router 903 of the Segment, which answers with a DAO-ACK to the Root. 905 Also, the path indicated in a P-DAO may be loose, in which case the 906 reachability to the next hop has to be asserted. Each router along 907 the path indicated in a P-DAO is expected to be able to reach its 908 successor, either with a connected route (direct neighbor), or by 909 routing, for Instance following a route installed previously by a DAO 910 or a P-DAO message. If that route is not connected then a recursive 911 lookup may take place at packet forwarding time to find the next hop 912 to reach the Target(s). If it does not and cannot reach the next 913 router in the P-DAO, the router MUST answer to the Root with a 914 negative DAO-ACK indicating the successor that is unreachable 915 (suggested status 11 to be confirmed by IANA). 917 A Segment Lifetime of 0 in a Via Information option is used to clean 918 up the state. The P-DAO is forwarded as described above, but the DAO 919 is interpreted as a No-Path DAO and results in cleaning up existing 920 state as opposed to refreshing an existing one or installing a new 921 one. 923 In case of a forwarding error along a Storing Mode Projected Route, 924 the node that fails to forward SHOULD send an ICMP error with a code 925 "Error in Projected Route" to the Root. Failure to do so may result 926 in packet loss and wasted resources along the Projected Route that is 927 broken. 929 7. Security Considerations 931 This draft uses messages that are already present in RPL [RPL] with 932 optional secured versions. The same secured versions may be used 933 with this draft, and whatever security is deployed for a given 934 network also applies to the flows in this draft. 936 TODO: should probably consider how P-DAO messages could be abused by 937 a) rogue nodes b) via replay of messages c) if use of P-DAO messages 938 could in fact deal with any threats? 940 8. IANA Considerations 942 8.1. New RPL Control Codes 944 This document extends the IANA Subregistry created by RFC 6550 for 945 RPL Control Codes as indicated in Table 1: 947 +======+=============================+===============+ 948 | Code | Description | Reference | 949 +======+=============================+===============+ 950 | 0x09 | Projected DAO Request (PDR) | This document | 951 +------+-----------------------------+---------------+ 952 | 0x0A | PDR-ACK | This document | 953 +------+-----------------------------+---------------+ 955 Table 1: New RPL Control Codes 957 8.2. New RPL Control Message Options 959 This document extends the IANA Subregistry created by RFC 6550 for 960 RPL Control Message Options as indicated in Table 2: 962 +=======+======================================+===============+ 963 | Value | Meaning | Reference | 964 +=======+======================================+===============+ 965 | 0x0B | Via Information option | This document | 966 +-------+--------------------------------------+---------------+ 967 | 0x0C | Source-Routed Via Information option | This document | 968 +-------+--------------------------------------+---------------+ 969 | 0x0D | Sibling Information option | This document | 970 +-------+--------------------------------------+---------------+ 972 Table 2: RPL Control Message Options 974 8.3. SubRegistry for the Projected DAO Request Flags 976 IANA is required to create a registry for the 8-bit Projected DAO 977 Request (PDR) Flags field. Each bit is tracked with the following 978 qualities: 980 * Bit number (counting from bit 0 as the most significant bit) 982 * Capability description 984 * Reference 986 Registration procedure is "Standards Action" [RFC8126]. The initial 987 allocation is as indicated in Table 3: 989 +============+========================+===============+ 990 | Bit number | Capability description | Reference | 991 +============+========================+===============+ 992 | 0 | PDR-ACK request (K) | This document | 993 +------------+------------------------+---------------+ 994 | 1 | Requested path should | This document | 995 | | be redundant (R) | | 996 +------------+------------------------+---------------+ 998 Table 3: Initial PDR Flags 1000 8.4. SubRegistry for the PDR-ACK Flags 1002 IANA is required to create an subregistry for the 8-bit PDR-ACK Flags 1003 field. Each bit is tracked with the following qualities: 1005 * Bit number (counting from bit 0 as the most significant bit) 1007 * Capability description 1009 * Reference 1011 Registration procedure is "Standards Action" [RFC8126]. No bit is 1012 currently defined for the PDR-ACK Flags. 1014 8.5. Subregistry for the PDR-ACK Acceptance Status Values 1016 IANA is requested to create a Subregistry for the PDR-ACK Acceptance 1017 Status values. 1019 * Possible values are 6-bit unsigned integers (0..63). 1021 * Registration procedure is "Standards Action" [RFC8126]. 1023 * Initial allocation is as indicated in Table 4: 1025 +-------+------------------------+---------------+ 1026 | Value | Meaning | Reference | 1027 +-------+------------------------+---------------+ 1028 | 0 | Unqualified acceptance | This document | 1029 +-------+------------------------+---------------+ 1031 Table 4: Acceptance values of the PDR-ACK Status 1033 8.6. Subregistry for the PDR-ACK Rejection Status Values 1035 IANA is requested to create a Subregistry for the PDR-ACK Rejection 1036 Status values. 1038 * Possible values are 6-bit unsigned integers (0..63). 1040 * Registration procedure is "Standards Action" [RFC8126]. 1042 * Initial allocation is as indicated in Table 5: 1044 +-------+-----------------------+---------------+ 1045 | Value | Meaning | Reference | 1046 +-------+-----------------------+---------------+ 1047 | 0 | Unqualified rejection | This document | 1048 +-------+-----------------------+---------------+ 1050 Table 5: Rejection values of the PDR-ACK Status 1052 8.7. SubRegistry for the Route Projection Options Flags 1054 IANA is requested to create a Subregistry for the 5-bit Route 1055 Projection Options (RPO) Flags field. Each bit is tracked with the 1056 following qualities: 1058 * Bit number (counting from bit 0 as the most significant bit) 1060 * Capability description 1062 * Reference 1064 Registration procedure is "Standards Action" [RFC8126]. No bit is 1065 currently defined for the Route Projection Options (RPO) Flags. 1067 8.8. SubRegistry for the Sibling Information Option Flags 1069 IANA is required to create a registry for the 5-bit Sibling 1070 Information Option (SIO) Flags field. Each bit is tracked with the 1071 following qualities: 1073 * Bit number (counting from bit 0 as the most significant bit) 1075 * Capability description 1077 * Reference 1079 Registration procedure is "Standards Action" [RFC8126]. The initial 1080 allocation is as indicated in Table 6: 1082 +============+===================================+===============+ 1083 | Bit number | Capability description | Reference | 1084 +============+===================================+===============+ 1085 | 0 | Connectivity is bidirectional (B) | This document | 1086 +------------+-----------------------------------+---------------+ 1088 Table 6: Initial SIO Flags 1090 8.9. Error in Projected Route ICMPv6 Code 1092 In some cases RPL will return an ICMPv6 error message when a message 1093 cannot be forwarded along a Projected Route. This ICMPv6 error 1094 message is "Error in Projected Route". 1096 IANA has defined an ICMPv6 "Code" Fields Registry for ICMPv6 Message 1097 Types. ICMPv6 Message Type 1 describes "Destination Unreachable" 1098 codes. This specification requires that a new code is allocated from 1099 the ICMPv6 Code Fields Registry for ICMPv6 Message Type 1, for "Error 1100 in Projected Route", with a suggested code value of 8, to be 1101 confirmed by IANA. 1103 9. Acknowledgments 1105 The authors wish to acknowledge JP Vasseur, Remy Liubing, James 1106 Pylakutty and Patrick Wetterwald for their contributions to the ideas 1107 developed here. 1109 10. Normative References 1111 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1112 Requirement Levels", BCP 14, RFC 2119, 1113 DOI 10.17487/RFC2119, March 1997, 1114 . 1116 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 1117 Control Message Protocol (ICMPv6) for the Internet 1118 Protocol Version 6 (IPv6) Specification", STD 89, 1119 RFC 4443, DOI 10.17487/RFC4443, March 2006, 1120 . 1122 [RPL] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1123 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1124 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1125 Low-Power and Lossy Networks", RFC 6550, 1126 DOI 10.17487/RFC6550, March 2012, 1127 . 1129 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1130 Routing Header for Source Routes with the Routing Protocol 1131 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1132 DOI 10.17487/RFC6554, March 2012, 1133 . 1135 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1136 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1137 May 2017, . 1139 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1140 Writing an IANA Considerations Section in RFCs", BCP 26, 1141 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1142 . 1144 11. Informative References 1146 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1147 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1148 2014, . 1150 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and 1151 J. Martocci, "Reactive Discovery of Point-to-Point Routes 1152 in Low-Power and Lossy Networks", RFC 6997, 1153 DOI 10.17487/RFC6997, August 2013, 1154 . 1156 [6TiSCH-ARCHI] 1157 Thubert, P., "An Architecture for IPv6 over the TSCH mode 1158 of IEEE 802.15.4", Work in Progress, Internet-Draft, 1159 draft-ietf-6tisch-architecture-29, 27 August 2020, 1160 . 1163 [RAW-ARCHI] 1164 Thubert, P., Papadopoulos, G., and R. Buddenberg, 1165 "Reliable and Available Wireless Architecture/Framework", 1166 Work in Progress, Internet-Draft, draft-pthubert-raw- 1167 architecture-04, 6 July 2020, 1168 . 1171 [TURN-ON_RFC8138] 1172 Thubert, P. and L. Zhao, "Configuration option for RFC 1173 8138", Work in Progress, Internet-Draft, draft-thubert- 1174 roll-turnon-rfc8138-03, 8 July 2019, 1175 . 1178 [RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas, 1179 "Deterministic Networking Architecture", RFC 8655, 1180 DOI 10.17487/RFC8655, October 2019, 1181 . 1183 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1184 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1185 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1186 . 1188 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1189 "IPv6 over Low-Power Wireless Personal Area Network 1190 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1191 April 2017, . 1193 [USEofRPLinfo] 1194 Robles, I., Richardson, M., and P. Thubert, "Using RPI 1195 Option Type, Routing Header for Source Routes and IPv6-in- 1196 IPv6 encapsulation in the RPL Data Plane", Work in 1197 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-40, 1198 25 June 2020, . 1201 [PCE] IETF, "Path Computation Element", 1202 . 1204 Appendix A. Applications 1205 A.1. Loose Source Routing 1207 A RPL implementation operating in a very constrained LLN typically 1208 uses the Non-Storing Mode of Operation as represented in Figure 8. 1209 In that mode, a RPL node indicates a parent-child relationship to the 1210 Root, using a Destination Advertisement Object (DAO) that is unicast 1211 from the node directly to the Root, and the Root typically builds a 1212 source routed path to a destination down the DODAG by recursively 1213 concatenating this information. 1215 ------+--------- 1216 | Internet 1217 | 1218 +-----+ 1219 | | Border Router 1220 | | (RPL Root) 1221 +-----+ ^ | | 1222 | | DAO | ACK | 1223 o o o o | | | Strict 1224 o o o o o o o o o | | | Source 1225 o o o o o o o o o o | | | Route 1226 o o o o o o o o o | | | 1227 o o o o o o o o | v v 1228 o o o o 1229 LLN 1231 Figure 8: RPL Non-Storing Mode of operation 1233 Based on the parent-children relationships expressed in the non- 1234 storing DAO messages,the Root possesses topological information about 1235 the whole network, though this information is limited to the 1236 structure of the DODAG for which it is the destination. A packet 1237 that is generated within the domain will always reach the Root, which 1238 can then apply a source routing information to reach the destination 1239 if the destination is also in the DODAG. Similarly, a packet coming 1240 from the outside of the domain for a destination that is expected to 1241 be in a RPL domain reaches the Root. 1243 It results that the Root, or then some associated centralized 1244 computation engine such as a PCE, can determine the amount of packets 1245 that reach a destination in the RPL domain, and thus the amount of 1246 energy and bandwidth that is wasted for transmission, between itself 1247 and the destination, as well as the risk of fragmentation, any 1248 potential delays because of a paths longer than necessary (shorter 1249 paths exist that would not traverse the Root). 1251 As a network gets deep, the size of the source routing header that 1252 the Root must add to all the downward packets becomes an issue for 1253 nodes that are many hops away. In some use cases, a RPL network 1254 forms long lines and a limited amount of well-Targeted routing state 1255 would allow to make the source routing operation loose as opposed to 1256 strict, and save packet size. Limiting the packet size is directly 1257 beneficial to the energy budget, but, mostly, it reduces the chances 1258 of frame loss and/or packet fragmentation, which is highly 1259 detrimental to the LLN operation. Because the capability to store a 1260 routing state in every node is limited, the decision of which route 1261 is installed where can only be optimized with a global knowledge of 1262 the system, a knowledge that the Root or an associated PCE may 1263 possess by means that are outside of the scope of this specification. 1265 This specification enables to store source-routed or Storing Mode 1266 state in intermediate routers, which enables to limit the excursion 1267 of the source route headers in deep networks. Once a P-DAO exchange 1268 has taken place for a given Target, if the Root operates in non 1269 Storing Mode, then it may elide the sequence of routers that is 1270 installed in the network from its source route headers to destination 1271 that are reachable via that Target, and the source route headers 1272 effectively become loose. 1274 A.2. Transversal Routes 1276 RPL is optimized for Point-to-Multipoint (P2MP) and Multipoint-to- 1277 Point (MP2P), whereby routes are always installed along the RPL DODAG 1278 respectively from and towards the DODAG Root. Transversal Peer to 1279 Peer (P2P) routes in a RPL network will generally suffer from some 1280 elongated (stretched) path versus the best possible path, since 1281 routing between 2 nodes always happens via a common parent, as 1282 illustrated in Figure 9: 1284 * In Storing Mode, unless the destination is a child of the source, 1285 the packets will follow the default route up the DODAG as well. 1286 If the destination is in the same DODAG, they will eventually 1287 reach a common parent that has a route to the destination; at 1288 worse, the common parent may also be the Root. From that common 1289 parent, the packet will follow a path down the DODAG that is 1290 optimized for the Objective Function that was used to build the 1291 DODAG. 1293 * in Non-Storing Mode, all packets routed within the DODAG flow all 1294 the way up to the Root of the DODAG. If the destination is in the 1295 same DODAG, the Root must encapsulate the packet to place a 1296 Routing Header that has the strict source route information down 1297 the DODAG to the destination. This will be the case even if the 1298 destination is relatively close to the source and the Root is 1299 relatively far off. 1301 ------+--------- 1302 | Internet 1303 | 1304 +-----+ 1305 | | Border Router 1306 | | (RPL Root) 1307 +-----+ 1308 X 1309 ^ v o o 1310 ^ o o v o o o o o 1311 ^ o o o v o o o o o 1312 ^ o o v o o o o o 1313 S o o o D o o o 1314 o o o o 1315 LLN 1317 Figure 9: Routing Stretch between S and D via common parent X 1319 It results that it is often beneficial to enable transversal P2P 1320 routes, either if the RPL route presents a stretch from shortest 1321 path, or if the new route is engineered with a different objective, 1322 and that it is even more critical in Non-Storing Mode than it is in 1323 Storing Mode, because the routing stretch is wider. For that reason, 1324 earlier work at the IETF introduced the "Reactive Discovery of 1325 Point-to-Point Routes in Low Power and Lossy Networks" [RFC6997], 1326 which specifies a distributed method for establishing optimized P2P 1327 routes. This draft proposes an alternate based on a centralized 1328 route computation. 1330 ------+--------- 1331 | Internet 1332 | 1333 +-----+ 1334 | | Border Router 1335 | | (RPL Root) 1336 +-----+ 1337 | 1338 o o o o 1339 o o o o o o o o o 1340 o o o o o o o o o o 1341 o o o o o o o o o 1342 S>>A>>>B>>C>>>D o o o 1343 o o o o 1344 LLN 1346 Figure 10: Projected Transversal Route 1348 This specification enables to store source-routed or Storing Mode 1349 state in intermediate routers, which enables to limit the stretch of 1350 a P2P route and maintain the characteristics within a given SLA. An 1351 example of service using this mechanism oculd be a control loop that 1352 would be installed in a network that uses classical RPL for 1353 asynchronous data collection. In that case, the P2P path may be 1354 installed in a different RPL Instance, with a different objective 1355 function. 1357 Appendix B. Examples 1359 B.1. Using Storing Mode P-DAO in Non-Storing Mode MOP 1361 In Non-Storing Mode, the DAG Root maintains the knowledge of the 1362 whole DODAG topology, so when both the source and the destination of 1363 a packet are in the DODAG, the Root can determine the common parent 1364 that would have been used in Storing Mode, and thus the list of nodes 1365 in the path between the common parent and the destination. For 1366 Instance in the diagram shown in Figure 11, if the source is node 41 1367 and the destination is node 52, then the common parent is node 22. 1369 ------+--------- 1370 | Internet 1371 | 1372 +-----+ 1373 | | Border Router 1374 | | (RPL Root) 1375 +-----+ 1376 | \ \____ 1377 / \ \ 1378 o 11 o 12 o 13 1379 / | / \ 1380 o 22 o 23 o 24 o 25 1381 / \ | \ \ 1382 o 31 o 32 o o o 35 1383 / / | \ | \ 1384 o 41 o 42 o o o 45 o 46 1385 | | | | \ | 1386 o 51 o 52 o 53 o o 55 o 56 1388 LLN 1390 Figure 11: Example DODAG forming a logical tree topology 1392 With this draft, the Root can install a Storing Mode routing states 1393 along a Segment that is either from itself to the destination, or 1394 from one or more common parents for a particular source/destination 1395 pair towards that destination (in this particular example, this would 1396 be the Segment made of nodes 22, 32, 42). 1398 In the example below, say that there is a lot of traffic to nodes 55 1399 and 56 and the Root decides to reduce the size of routing headers to 1400 those destinations. The Root can first send a DAO to node 45 1401 indicating Target 55 and a Via Segment (35, 45), as well as another 1402 DAO to node 46 indicating Target 56 and a Via Segment (35, 46). This 1403 will save one entry in the routing header on both sides. The Root 1404 may then send a DAO to node 35 indicating Targets 55 and 56 a Via 1405 Segment (13, 24, 35) to fully optimize that path. 1407 Alternatively, the Root may send a DAO to node 45 indicating Target 1408 55 and a Via Segment (13, 24, 35, 45) and then a DAO to node 46 1409 indicating Target 56 and a Via Segment (13, 24, 35, 46), indicating 1410 the same DAO Sequence. 1412 B.2. Projecting a storing-mode transversal route 1414 In this example, say that a PCE determines that a path must be 1415 installed between node S and node D via routers A, B and C, in order 1416 to serve the needs of a particular application. 1418 The Root sends a P-DAO with a Target option indicating the 1419 destination D and a sequence Via Information option, one for S, which 1420 is the ingress router of the Segment, one for A and then for B, which 1421 are an intermediate routers, and one for C, which is the egress 1422 router. 1424 ------+--------- 1425 | Internet 1426 | 1427 +-----+ 1428 | | Border Router 1429 | | (RPL Root) 1430 +-----+ 1431 | P-DAO message to C 1432 o | o o 1433 o o o | o o o o o 1434 o o o | o o o o o o 1435 o o V o o o o o o 1436 S A B C D o o o 1437 o o o o 1438 LLN 1440 Figure 12: P-DAO from Root 1442 Upon reception of the P-DAO, C validates that it can reach D, e.g. 1443 using IPv6 Neighbor Discovery, and if so, propagates the P-DAO 1444 unchanged to B. 1446 B checks that it can reach C and of so, installs a route towards D 1447 via C. Then it propagates the P-DAO to A. 1449 The process recurses till the P-DAO reaches S, the ingress of the 1450 Segment, which installs a route to D via A and sends a DAO-ACK to the 1451 Root. 1453 ------+--------- 1454 | Internet 1455 | 1456 +-----+ 1457 | | Border Router 1458 | | (RPL Root) 1459 +-----+ 1460 ^ P-DAO-ACK from S 1461 / o o o 1462 / o o o o o o o 1463 | o o o o o o o o o 1464 | o o o o o o o o 1465 S A B C D o o o 1466 o o o o 1467 LLN 1469 Figure 13: P-DAO-ACK to Root 1471 As a result, a transversal route is installed that does not need to 1472 follow the DODAG structure. 1474 ------+--------- 1475 | Internet 1476 | 1477 +-----+ 1478 | | Border Router 1479 | | (RPL Root) 1480 +-----+ 1481 | 1482 o o o o 1483 o o o o o o o o o 1484 o o o o o o o o o o 1485 o o o o o o o o o 1486 S>>A>>>B>>C>>>D o o o 1487 o o o o 1488 LLN 1490 Figure 14: Projected Transversal Route 1492 Authors' Addresses 1494 Pascal Thubert (editor) 1495 Cisco Systems, Inc 1496 Building D 1497 45 Allee des Ormes - BP1200 1498 06254 Mougins - Sophia Antipolis 1499 France 1500 Phone: +33 497 23 26 34 1501 Email: pthubert@cisco.com 1503 Rahul Arvind Jadhav 1504 Huawei Tech 1505 Kundalahalli Village, Whitefield, 1506 Bangalore 560037 1507 Karnataka 1508 India 1510 Phone: +91-080-49160700 1511 Email: rahul.ietf@gmail.com 1513 Matthew Gillmore 1514 Itron, Inc 1515 Building D 1516 2111 N Molter Road 1517 Liberty Lake, 99019 1518 United States 1520 Phone: +1.800.635.5461 1521 Email: matthew.gillmore@itron.com