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Thubert, Ed. 3 Internet-Draft Cisco Systems 4 Intended status: Standards Track R.A. Jadhav 5 Expires: 31 March 2022 Huawei Tech 6 M. Gillmore 7 Itron 8 27 September 2021 10 Root initiated routing state in RPL 11 draft-ietf-roll-dao-projection-21 13 Abstract 15 This document extends RFC 6550, RFC 6553,and RFC 8138 to enable a RPL 16 Root to install and maintain Projected Routes within its DODAG, along 17 a selected set of nodes that may or may not include self, for a 18 chosen duration. This potentially enables routes that are more 19 optimized or resilient than those obtained with the classical 20 distributed operation of RPL, either in terms of the size of a 21 Routing Header or in terms of path length, which impacts both the 22 latency and the packet delivery ratio. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at https://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on 31 March 2022. 41 Copyright Notice 43 Copyright (c) 2021 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 48 license-info) in effect on the date of publication of this document. 49 Please review these documents carefully, as they describe your rights 50 and restrictions with respect to this document. Code Components 51 extracted from this document must include Simplified BSD License text 52 as described in Section 4.e of the Trust Legal Provisions and are 53 provided without warranty as described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 60 2.2. References . . . . . . . . . . . . . . . . . . . . . . . 4 61 2.3. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 4 62 2.4. Domain Terms . . . . . . . . . . . . . . . . . . . . . . 5 63 3. Context and Goal . . . . . . . . . . . . . . . . . . . . . . 6 64 3.1. RPL Applicability . . . . . . . . . . . . . . . . . . . . 7 65 3.2. RPL Routing Modes . . . . . . . . . . . . . . . . . . . . 8 66 3.3. Requirements . . . . . . . . . . . . . . . . . . . . . . 9 67 3.3.1. Loose Source Routing . . . . . . . . . . . . . . . . 9 68 3.3.2. East-West Routes . . . . . . . . . . . . . . . . . . 10 69 3.4. On Tracks . . . . . . . . . . . . . . . . . . . . . . . . 12 70 3.5. Serial Track Signaling . . . . . . . . . . . . . . . . . 13 71 3.5.1. Using Storing Mode Segments . . . . . . . . . . . . . 14 72 3.5.2. Using Non-Storing Mode joining Tracks . . . . . . . . 20 73 3.6. Complex Tracks . . . . . . . . . . . . . . . . . . . . . 27 74 3.7. Scope and Expectations . . . . . . . . . . . . . . . . . 29 75 4. Extending existing RFCs . . . . . . . . . . . . . . . . . . . 31 76 4.1. Extending RFC 6550 . . . . . . . . . . . . . . . . . . . 31 77 4.1.1. Projected DAO . . . . . . . . . . . . . . . . . . . . 31 78 4.1.2. Via Information Option . . . . . . . . . . . . . . . 33 79 4.1.3. Sibling Information Option . . . . . . . . . . . . . 33 80 4.1.4. P-DAO Request . . . . . . . . . . . . . . . . . . . . 33 81 4.1.5. Extending the RPI . . . . . . . . . . . . . . . . . . 33 82 4.2. Extending RFC 6553 . . . . . . . . . . . . . . . . . . . 34 83 4.3. Extending RFC 8138 . . . . . . . . . . . . . . . . . . . 35 84 5. New RPL Control Messages and Options . . . . . . . . . . . . 36 85 5.1. New P-DAO Request Control Message . . . . . . . . . . . . 36 86 5.2. New PDR-ACK Control Message . . . . . . . . . . . . . . . 37 87 5.3. Via Information Options . . . . . . . . . . . . . . . . . 39 88 5.4. Sibling Information Option . . . . . . . . . . . . . . . 42 89 6. Root Initiated Routing State . . . . . . . . . . . . . . . . 44 90 6.1. Requesting a Track . . . . . . . . . . . . . . . . . . . 44 91 6.2. Identifying a Track . . . . . . . . . . . . . . . . . . . 45 92 6.3. Installing a Track . . . . . . . . . . . . . . . . . . . 46 93 6.3.1. Signaling a Projected Route . . . . . . . . . . . . . 47 94 6.3.2. Installing a Track Segment with a Storing Mode 95 P-Route . . . . . . . . . . . . . . . . . . . . . . . 48 97 6.3.3. Installing a Track Leg with a Non-Storing Mode 98 P-Route . . . . . . . . . . . . . . . . . . . . . . . 50 99 6.4. Tearing Down a P-Route . . . . . . . . . . . . . . . . . 52 100 6.5. Maintaining a Track . . . . . . . . . . . . . . . . . . . 52 101 6.5.1. Maintaining a Track Segment . . . . . . . . . . . . . 53 102 6.5.2. Maintaining a Track Leg . . . . . . . . . . . . . . . 53 103 6.6. Encapsulating and Forwarding Along a Track . . . . . . . 54 104 6.7. Compression of the RPL Artifacts . . . . . . . . . . . . 56 105 7. Lesser Constrained Variations . . . . . . . . . . . . . . . . 58 106 7.1. Storing Mode Main DODAG . . . . . . . . . . . . . . . . . 58 107 7.2. A Track as a Full DODAG . . . . . . . . . . . . . . . . . 60 108 8. Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . 61 109 9. Security Considerations . . . . . . . . . . . . . . . . . . . 63 110 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 63 111 10.1. New Elective 6LoWPAN Routing Header Type . . . . . . . . 64 112 10.2. New Critical 6LoWPAN Routing Header Type . . . . . . . . 64 113 10.3. New Subregistry For The RPL Option Flags . . . . . . . . 64 114 10.4. New RPL Control Codes . . . . . . . . . . . . . . . . . 65 115 10.5. New RPL Control Message Options . . . . . . . . . . . . 65 116 10.6. SubRegistry for the Projected DAO Request Flags . . . . 66 117 10.7. SubRegistry for the PDR-ACK Flags . . . . . . . . . . . 66 118 10.8. Subregistry for the PDR-ACK Acceptance Status Values . . 66 119 10.9. Subregistry for the PDR-ACK Rejection Status Values . . 67 120 10.10. SubRegistry for the Via Information Options Flags . . . 67 121 10.11. SubRegistry for the Sibling Information Option Flags . . 68 122 10.12. New destination Advertisement Object Flag . . . . . . . 68 123 10.13. New ICMPv6 Error Code . . . . . . . . . . . . . . . . . 68 124 10.14. New RPL Rejection Status values . . . . . . . . . . . . 69 125 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 69 126 12. Normative References . . . . . . . . . . . . . . . . . . . . 69 127 13. Informative References . . . . . . . . . . . . . . . . . . . 71 128 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 73 130 1. Introduction 132 RPL, the "Routing Protocol for Low Power and Lossy Networks" [RPL] 133 (LLNs), is an anisotropic Distance Vector protocol that is well- 134 suited for application in a variety of low energy Internet of Things 135 (IoT) networks where stretched P2P paths are acceptable vs. the 136 signaling and state overhead involved in maintaining shortest paths 137 across. 139 RPL forms destination Oriented Directed Acyclic Graphs (DODAGs) in 140 which the Root often acts as the Border router to connect the RPL 141 domain to the IP backbone and routes along that graph up, towards the 142 Root, and down towards the nodes. 144 With this specification, a Path Computation Element [PCE] in an 145 external controller interacts with the RPL Root to compute centrally 146 shorter Peer to Peer (P2P) paths within a pre-existing RPL Main 147 DODAG. The topological information that is passed to the PCE is 148 derived from the DODAG that is already available at the Root in RPL 149 Non-Storing Mode. This specification introduces protocol extensions 150 that enrich the topological information that is available at the Root 151 and passed to the PCE. 153 Based on usage, path length, and knowledge of available resources 154 such as battery levels and reservable buffers in the nodes, the PCE 155 with a global visibility on the system can optimize the computed 156 routes for the application needs, including the capability to provide 157 path redundancy. This specification also introduces protocol 158 extensions that enable the Root to translates the computed paths into 159 RPL and install them as Projected Routes (aka P-Routes) inside the 160 DODAG on behalf of a PCE. 162 2. Terminology 164 2.1. Requirements Language 166 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 167 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 168 "OPTIONAL" in this document are to be interpreted as described in BCP 169 14 [RFC2119][RFC8174] when, and only when, they appear in all 170 capitals, as shown here. 172 2.2. References 174 In this document, readers will encounter terms and concepts that are 175 discussed in the "Routing Protocol for Low Power and Lossy Networks" 176 [RPL], the "6TiSCH Architecture" [6TiSCH-ARCHI], the "Deterministic 177 Networking Architecture" [RFC8655], the "Reliable and Available 178 Wireless (RAW) Architecture/Framework" [RAW-ARCHI], and "Terminology 179 in Low power And Lossy Networks" [RFC7102]. 181 2.3. Glossary 183 This document often uses the following acronyms: 185 CMO: Control Message Option 186 DAO: destination Advertisement Object 187 DAG: Directed Acyclic Graph 188 DODAG: destination-Oriented Directed Acyclic Graph; A DAG with only 189 one vertex (i.e., node) that has no outgoing edge (i.e., link) 190 GUA: IPv6 Global Unicast Address 191 LLN: Low-Power and Lossy Network 192 MOP: RPL Mode of Operation 193 P-DAO: Projected DAO 194 P-Route: Projected Route 195 PDR: P-DAO Request 196 RAN: RPL-Aware Node (either a RPL router or a RPL-Aware Leaf) 197 RAL: RPL-Aware Leaf 198 RH: Routing Header 199 RPI: RPL Packet Information 200 RTO: RPL Target Option 201 RUL: RPL-Unaware Leaf 202 SIO: RPL Sibling Information Option 203 ULA: IPv6 Unique Local Address 204 NSM-VIO: A Source-Routed Via Information Option, used in Non-Storing 205 Mode P-DAO messages. 206 SLO: Service Level Objective 207 TIO: RPL Transit Information Option 208 SM-VIO: A strict Via Information Option, used in Storing Mode P-DAO 209 messages. 210 VIO: A Via Information Option; it can be a SM-VIO or an NSM-VIO. 212 2.4. Domain Terms 214 Projected Route: A RPL P-Route is a RPL route that is computed 215 remotely by a PCE, and installed and maintained by a RPL Root on 216 behalf of the PCE. It is installed as a state that signals that 217 destinations (aka Targets) are reachable along a sequence of 218 nodes. 219 Projected DAO: A DAO message used to install a P-Route. 220 Path: Quoting section 1.1.3 of [INT-ARCHI]: "At a given moment, all 221 the IP datagrams from a particular source host to a particular 222 destination host will typically traverse the same sequence of 223 gateways. We use the term "path" for this sequence. Note that a 224 path is uni-directional; it is not unusual to have different paths 225 in the two directions between a given host pair.". 226 Section 2 of [I-D.irtf-panrg-path-properties] points to a longer, 227 more modern definition of path, which begins as follows: " A 228 sequence of adjacent path elements over which a packet can be 229 transmitted, starting and ending with a node. A path is 230 unidirectional. Paths are time-dependent, i.e., the sequence of 231 path elements over which packets are sent from one node to another 232 may change. A path is defined between two nodes. " 233 It follows that the general acceptance of a path is a linear 234 sequence of nodes, as opposed to a multi-dimensional graph. In 235 the context of this document, a path is observed by following one 236 copy of a packet that is injected in a Track and possibly 237 replicated within. 238 Track: A networking graph that can be followed to transport packets 239 with equivalent treatment; as opposed to the definition of a path 240 above, a Track Track is not necessarily linear. It may contain 241 multiple paths that may fork and rejoin, and may enable the RAW 242 Packet ARQ, Replication, Elimination, and Overhearing (PAREO) 243 operations. 244 This specification builds Tracks that are DODAGs oriented towards 245 a Track Ingress, and the forward direction for packets is East- 246 West from the Track Ingress to one of the possibly multiple Track 247 Egress Nodes, which is also down the DODAG. 248 The Track may be strictly connected, meaning that the vertices are 249 adjacent, or loosely connected, meaning that the vertices are 250 connected using Segments that are associated to the same Track. 251 TrackID: A RPL Local InstanceID that identifies a Track using the 252 namespace owned ny the Track Ingress. The TrackID is associated 253 with the IPv6 Address of the Track Ingress that is used as 254 DODAGID, and together they form a unique identification of the 255 Track (see the definition of DODAGID in section 2 of [RPL]. 256 Serial Track: A Track that has only one path. 257 Stand-Alone: A single P-DAO that fully defines a Track, e.g., a 258 Serial Track installed with a single Storing Mode Via Information 259 option (SM-VIO). 260 subTrack: A Track within a Track. As the Non-Storing Mode Via 261 Information option (NSM-VIO) can only signal a loose sequence of 262 nodes, it takes a number of them to signal a complex Track. Each 263 NSM-VIO for the same TrackId but a different Segment ID signals a 264 different subTracks that the Track Ingress adds to the topology. 265 Track Leg: An end-to-end East-West serial path that can be a Track 266 by itself or a subTrack of a complex Track. With this 267 specification, a Leg is is installed by the Root of the main DODAG 268 using Non-Storing Mode P-DAO messages, and it is expressed as a 269 loose sequence of nodes that are joined by Track Segments. 270 Track Segment: A serial path formed by a strict sequence of nodes, 271 along which a P-Route is installed. With this specification, a 272 Segment is typically installed by the Root of the main DODAG using 273 Storing Mode P-DAO messages. A Segment used as the topological 274 edge of a Track. Since this specification builds only DODAGs, all 275 Segments are oriented from Ingress (East) to Egress (West), as 276 opposed to the general RAW model, which allows North/South 277 Segments that can be bidirectional. 279 3. Context and Goal 280 3.1. RPL Applicability 282 RPL is optimized for situations where the power is scarce, the 283 bandwidth constrained and the transmissions unreliable. This matches 284 the use case of an IoT LLN where RPL is typically used today, but 285 also situations of high relative mobility between the nodes in the 286 network (aka swarming), e.g., within a variable set of vehicles with 287 a similar global motion, or a toon of drones. 289 To reach this goal, RPL is primarily designed to minimize the control 290 plane activity, that is the relative amount of routing protocol 291 exchanges vs. data traffic, and the amount of state that is 292 maintained in each node. RPL does not need converge, and provides 293 connectivity to most nodes most of the time. 295 RPL may form multiple topologies called instances. Instances can be 296 created to enforce various optimizations through objective functions, 297 or to reach out through different Root Nodes. The concept of 298 objective function allows to adapt the activity of the routing 299 protocol to the use case, e.g., type, speed, and quality of the LLN 300 links. 302 RPL instances operate as ships in the night, unbeknownst of one 303 another. The RPL Root is responsible to select the RPL Instance that 304 is used to forward a packet coming from the Backbone into the RPL 305 domain and set the related RPL information in the packets. 6TiSCH 306 leverages RPL for its distributed routing operations. 308 To reduce the routing exchanges, RPL leverages an anisotropic 309 Distance Vector approach, which does not need a global knowledge of 310 the topology, and only optimizes the routes to and from the RPL Root, 311 allowing P2P paths to be stretched. Although RPL installs its routes 312 proactively, it only maintains them lazily, in reaction to actual 313 traffic, or as a slow background activity. 315 This is simple and efficient in situations where the traffic is 316 mostly directed from or to a central node, such as the control 317 traffic between routers and a controller of a Software Defined 318 Networking (SDN) infrastructure or an Autonomic Control Plane (ACP). 320 But stretch in P2P routing is counter-productive to both reliability 321 and latency as it introduces additional delay and chances of loss. 322 As a result, [RPL] is not a good fit for the use cases listed in the 323 RAW use cases document [USE-CASES], which demand high availability 324 and reliability, and as a consequence require both short and diverse 325 paths. 327 3.2. RPL Routing Modes 329 RPL first forms a default route in each node towards the a Root, and 330 those routes together coalesce as a Directed Acyclic Graph upwards. 331 RPL then constructs routes to so-called Targets in the reverse 332 direction, down the same DODAG. So do so, a RPL Instance can be 333 operated either in RPL Storing or Non-Storing Mode of Operation (MOP) 334 The default route towards the Root is maintained aggressively and may 335 change while a packet progresses without causing loops, so the packet 336 will still reach the Root. 338 In Non-Storing Mode, each node advertises itself as a Target directly 339 to the Root, indicating the parents that may be used to reach self. 340 Recursively, the Root builds and maintains an image of the whole 341 DODAG in memory, and leverages that abstraction to compute source 342 route paths for the packets to their destinations down the DODAG. 343 When a node changes its point(s) of attachment to the DODAG, it takes 344 single unicast packet to the Root along the default route to update 345 it, and the connectivity is restored immediately; this mode is 346 preferable for use cases where internet connectivity is dominant, or 347 when, like here, the Root controls the network activity in the nodes. 349 In Storing Mode, the routing information percolates upwards, and each 350 node maintains the routes to the subDAG of its descendants down the 351 DODAG. The maintenance is lazy, either reactive upon traffic or as a 352 slow background process. Packets flow via the common parent and the 353 routing stretch is reduced vs. Non-Storing, for a better P2P 354 connectivity, while the internet connectivity is restored more 355 slowly, time for the DV operation to operate hop-by-hop. 357 Either way, the RPL routes are injected by the Target nodes, in a 358 distributed fashion. To complement RPL and eliminate routing 359 stretch, this specification introduces an hybrid mode that combines 360 Storing and Non-Storing operations to build and project routes onto 361 the nodes where they should be installed. This specification uses 362 the term P-Route to refer to those routes. 364 A P-Route may be installed in either Storing and Non-Storing Mode, 365 potentially resulting in hybrid situations where the Mode of the P- 366 Route is different from that of the RPL Main DODAG. P-Routes can be 367 used as stand-alone segments to reduce the size of the source routing 368 headers with loose source routing operations down the main RPL DODAG. 369 P-Routes can also be combined with other P-Routes to form a more 370 complex forwarding graph called a Track. 372 3.3. Requirements 374 3.3.1. Loose Source Routing 376 A RPL implementation operating in a very constrained LLN typically 377 uses the Non-Storing Mode of Operation as represented in Figure 1. 378 In that mode, a RPL node indicates a parent-child relationship to the 379 Root, using a destination Advertisement Object (DAO) that is unicast 380 from the node directly to the Root, and the Root typically builds a 381 source routed path to a destination down the DODAG by recursively 382 concatenating this information. 384 +-----+ 385 | | Border router 386 | | (RPL Root) 387 +-----+ ^ | | 388 | | DAO | ACK | 389 o o o o | | | Strict 390 o o o o o o o o o | | | Source 391 o o o o o o o o o o | | | Route 392 o o o o o o o o o | | | 393 o o o o o o o o | v v 394 o o o o 395 LLN 397 Figure 1: RPL Non-Storing Mode of operation 399 Based on the parent-children relationships expressed in the Non- 400 Storing DAO messages,the Root possesses topological information about 401 the whole network, though this information is limited to the 402 structure of the DODAG for which it is the destination. A packet 403 that is generated within the domain will always reach the Root, which 404 can then apply a source routing information to reach the destination 405 if the destination is also in the DODAG. Similarly, a packet coming 406 from the outside of the domain for a destination that is expected to 407 be in a RPL domain reaches the Root. 409 It results that the Root, or then some associated centralized 410 computation engine such as a PCE, can determine the amount of packets 411 that reach a destination in the RPL domain, and thus the amount of 412 energy and bandwidth that is wasted for transmission, between itself 413 and the destination, as well as the risk of fragmentation, any 414 potential delays because of a paths longer than necessary (shorter 415 paths exist that would not traverse the Root). 417 As a network gets deep, the size of the source routing header that 418 the Root must add to all the downward packets becomes an issue for 419 nodes that are many hops away. In some use cases, a RPL network 420 forms long lines and a limited amount of well-targeted routing state 421 would allow to make the source routing operation loose as opposed to 422 strict, and save packet size. Limiting the packet size is directly 423 beneficial to the energy budget, but, mostly, it reduces the chances 424 of frame loss and/or packet fragmentation, which is highly 425 detrimental to the LLN operation. Because the capability to store a 426 routing state in every node is limited, the decision of which route 427 is installed where can only be optimized with a global knowledge of 428 the system, a knowledge that the Root or an associated PCE may 429 possess by means that are outside of the scope of this specification. 431 This requirement is to store a routing state associated with the Main 432 DODAG in selected RPL routers, to limit the excursion of the source 433 route headers in deep networks. The Root may elide the sequence of 434 routers that is installed in the network from its source route 435 header, which becomes loose while it is strict in [RPL]. 437 3.3.2. East-West Routes 439 RPL is optimized for INternet access, with Point-to-Multipoint (P2MP) 440 and Multipoint-to-Point (MP2P), whereby routes are always installed 441 North-South (aka up/down) along the RPL DODAG respectively from and 442 towards the Border Router that also serves as DODAG Root. Peer to 443 Peer (P2P) East-West routes in a RPL network will generally suffer 444 from some elongated (stretched) path versus a direct (optimized) 445 path, since routing between two nodes always happens via a common 446 parent, as illustrated in Figure 2: 448 ------+--------- 449 | Internet 450 +-----+ 451 | | Border router 452 | | (RPL Root) 453 +-----+ 454 X 455 ^ v o o 456 ^ o o v o o o o o 457 ^ o o o v o o o o o 458 ^ o o v o o o o o 459 S o o o D o o o 460 o o o o 461 LLN 463 Figure 2: Routing Stretch between S and D via common parent X 464 along North-South Paths 466 The amount of stretch depends on the Mode of Operation: 468 * in Non-Storing Mode, all packets routed within the DODAG flow all 469 the way up to the Root of the DODAG. If the destination is in the 470 same DODAG, the Root must encapsulate the packet to place an RH 471 that has the strict source route information down the DODAG to the 472 destination. This will be the case even if the destination is 473 relatively close to the source and the Root is relatively far off. 475 * In Storing Mode, unless the destination is a child of the source, 476 the packets will follow the default route up the DODAG as well. 477 If the destination is in the same DODAG, they will eventually 478 reach a common parent that has a route to the destination; at 479 worse, the common parent may also be the Root. From that common 480 parent, the packet will follow a path down the DODAG that is 481 optimized for the Objective Function that was used to build the 482 DODAG. 484 It results that it is often beneficial to enable East-West P2P 485 routes, either if the RPL route presents a stretch from shortest 486 path, or if the new route is engineered with a different objective, 487 and that it is even more critical in Non-Storing Mode than it is in 488 Storing Mode, because the routing stretch is wider. For that reason, 489 earlier work at the IETF introduced the "Reactive Discovery of 490 Point-to-Point Routes in Low Power and Lossy Networks" [RFC6997], 491 which specifies a distributed method for establishing optimized P2P 492 routes. This draft proposes an alternate based on a centralized 493 route computation. 495 +-----+ 496 | | Border router 497 | | (RPL Root) 498 +-----+ 499 | 500 o o o o 501 o o o o o o o o o 502 o o o o o o o o o o 503 o o o o o o o o o 504 S>>A>>>B>>C>>>D o o o 505 o o o o 506 LLN 508 Figure 3: More direct East-West Route between S and D 510 The requirement is to install additional routes in the RPL routers, 511 to reduce the stretch of some P2P routes and maintain the 512 characteristics within a given SLO, e.g., in terms of latency and/or 513 reliability. 515 3.4. On Tracks 517 A Track is typically a collection of parallel loose source routed 518 sequences of nodes from Ingress to Egress, forming so-called Track 519 Legs, that are joined with strict Segments of other nodes. The Legs 520 are expressed in RPL Non-Storing Modes and require an encapsulation 521 to add a Source Route Header, whereas the Segments are expressed in 522 Storing Mode. 524 A Serial Track comprises provides only one path between Ingress and 525 Egress. It comprises at most one Leg. A Stand-Alone Segment defines 526 implicitly a Serial Track from its Ingress to Egress. 528 A complex Track forms a graph that provides a collection of potential 529 paths to provide redundancy for the packets, either as a collection 530 of Legs that may be parallel or cross at certain points, or as a more 531 generic DODAG. 533 The concept of a Track was introduced in the "6TiSCH Architecture" 534 [6TiSCH-ARCHI], as a collection of potential paths that leverage 535 redundant forwarding solutions along the way. With this 536 specification, a Track forms DODAG that is directed towards a Track 537 Ingress. If there is a single Track Egress, then the Track is 538 reversible to form another DODAG by reversing the direction of each 539 edge. A node at the Ingress of more than one Segment in a Track may 540 use one or more of these Segments to forward a packet inside the 541 Track. 543 Section 5.1. of [RPL] describes the RPL Instance and its encoding. 544 There can be up to 128 global RPL Instances, for which there can be 545 one or more DODAGs, and there can be 64 local RPL Instances, with a 546 namespace that is indexed by a DODAGID, where the DODAGID is a Unique 547 Local Address (ULA) or a Global Unicast Address (GUA) of the Root of 548 the DODAG. 550 A Track is normally associated with a Local RPL Instance which 551 RPLInstanceID is used as the TrackID, more in Section 6.2. A Track 552 Leg may also be used as a subTrack that extends the RPL main DODAG. 553 In that case, the TrackID is set to the global RPLInstanceID of the 554 main DODAG, which suffices to identify the routing topology. As 555 opposed to local RPL instances, the Track Ingress that encapsulates 556 the packets over a subtrack is not Root, and that the source address 557 of the encapsulated packet is not used to determine the Track. 559 3.5. Serial Track Signaling 561 This specification enables to set up a P-Route along either a Track 562 Leg or a Segment. A P-Route is installed and maintained using an 563 extended RPL DAO message called a Projected DAO (P-DAO), and a Track 564 is composed of the combination of one or more P-Routes. 566 A P-DAO message for a Track signals the TrackID in the RPLInstanceID 567 field. In the case of a local RPL Instance, the address of the Track 568 Ingress is used as source to encapsulated packets along the Track is 569 signaled in the DODAGID field of the Projected DAO Base Object, see 570 Figure 6. 572 This specification introduces the Via Information Option (VIO) to 573 signal a sequence of hops in a Leg or a Segment in the P-DAO 574 messages, either in Storing Mode (SM-VIO) or NON-Storing Mode (NSM- 575 VIO). One P-DAO messages contains a single VIO, associated to one or 576 more RPL Target Options that signal the destination IPv6 addresses 577 that can reached along the Track, more in Section 5.3. 579 Before diving deeper into Track Legs and Segments signaling and 580 operation, this section provides examples of what how route 581 projection works through variations of a simple example. This simple 582 example illustrates the case of host routes, though RPL Targets can 583 be prefixes. 585 Say we want to build a Serial Track from node A to E in Figure 4, so 586 A can route packets to E's neighbors F and G along A, B, C, D and E 587 as opposed to via the Root: 589 /===> F 590 A ===> B ===> C ===> D===> E < 591 \===> G 593 Figure 4: Reference Track 595 Conventionally we use ==> to represent a strict hop and --> for a 596 loose hop. We use -to- like in C==>D==>E-to-F to represent coma- 597 separated Targets, e.g., F is a Target for Segment C==>D==>E. In 598 this example, A is Track Ingress, E is Track Egress. C is a 599 stitching point. F and G are "external" Targets for the Track, and 600 become reachable from A via the Track A(ingress) to E (Egress and 601 implicit Target in Non-Storing Mode) leading to F and G (explicit 602 Targets). 604 In a general manner the desired outcome is as follows: 606 * Targets are E, F, and G 608 * P-DAO 1 signals C==>D==>E 610 * P-DAO 2 signals A==>B==>C 612 * P-DAO 3 signals F and G via the A-->E Track 614 P-DAO 3 may be ommitted if P-DAO 1 and 2 signal F and G as Targets. 616 Loose sequences of hops must be expressed in Non-Storing Mode, so 617 P-DAO 3 contains a NSM-VIO. With this specification, the DODAGID to 618 be used by the Ingress as source address is signaled if needed in the 619 DAO base object, the via list starts at the first loose hop and 620 matches the source route header, and the Egress of a Non-Storing Mode 621 P-DAO is an implicit Target that is not listed in the RTO. 623 3.5.1. Using Storing Mode Segments 625 A==>B==>C and C==>D==>E are segments of a same Track. Note that the 626 Storing Mode signaling imposes strict continuity in a segment, since 627 the P-DAO is passed hop by hop, as a classical DAO is, along the 628 reverse datapath that it signals. One benefit of strict routing is 629 that loops are avoided along the Track. 631 3.5.1.1. Stitched Segments 633 In this formulation: 635 * P-DAO 1 signals C==>D==>E-to-F,G 637 * P-DAO 2 signals A==>B==>C-to-F,G 639 Storing Mode P-DAO 1 is sent to E and when it is succesfully 640 acknowledged, Storing Mode P-DAO 2 is sent to C, as follows: 642 +====================+==============+==============+ 643 | Field | P-DAO 1 to E | P-DAO 2 to C | 644 +====================+==============+==============+ 645 | Mode | Storing | Storing | 646 +--------------------+--------------+--------------+ 647 | Track Ingress | A | A | 648 +--------------------+--------------+--------------+ 649 | (DODAGID, TrackID) | (A, 129) | (A, 129) | 650 +--------------------+--------------+--------------+ 651 | SegmentID | 1 | 2 | 652 +--------------------+--------------+--------------+ 653 | VIO | C, D, E | A, B, C | 654 +--------------------+--------------+--------------+ 655 | Targets | F, G | F, G | 656 +--------------------+--------------+--------------+ 658 Table 1: P-DAO Messages 660 As a result the RIBs are set as follows: 662 +======+=============+=========+=============+==========+ 663 | Node | destination | Origin | Next Hop(s) | TrackID | 664 +======+=============+=========+=============+==========+ 665 | E | F, G | P-DAO 1 | Neighbor | (A, 129) | 666 +------+-------------+---------+-------------+----------+ 667 | D | E | P-DAO 1 | Neighbor | (A, 129) | 668 +------+-------------+---------+-------------+----------+ 669 | " | F, G | P-DAO 1 | E | (A, 129) | 670 +------+-------------+---------+-------------+----------+ 671 | C | D | P-DAO 1 | Neighbor | (A, 129) | 672 +------+-------------+---------+-------------+----------+ 673 | " | F, G | P-DAO 1 | D | (A, 129) | 674 +------+-------------+---------+-------------+----------+ 675 | B | C | P-DAO 2 | Neighbor | (A, 129) | 676 +------+-------------+---------+-------------+----------+ 677 | " | F, G | P-DAO 2 | C | (A, 129) | 678 +------+-------------+---------+-------------+----------+ 679 | A | B | P-DAO 2 | Neighbor | (A, 129) | 680 +------+-------------+---------+-------------+----------+ 681 | " | F, G | P-DAO 2 | B | (A, 129) | 682 +------+-------------+---------+-------------+----------+ 684 Table 2: RIB setting 686 Packets originated by A to F or G do not require an encapsulation as 687 the RPI can be placed in the native header chain. For packets that 688 it routes, A must encapsulate to add the RPI that signals the 689 trackID; the outer headers of the packets that are forwarded along 690 the Track have the following settings: 692 +========+===================+===================+================+ 693 | Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI | 694 +========+===================+===================+================+ 695 | Outer | A | F or G | (A, 129) | 696 +--------+-------------------+-------------------+----------------+ 697 | Inner | X != A | F or G | N/A | 698 +--------+-------------------+-------------------+----------------+ 700 Table 3: Packet Header Settings 702 As an example, say that A has a packet for F. Using the RIB above: 704 * From P-DAO 2: A forwards to B and B forwards to C. 706 * From P-DAO 1: C forwards to D and D forwards to E. 708 * From Neighbor Cache Entry: C delivers the packet to F. 710 3.5.1.2. External routes 712 In this example, we consider F and G as destinations that are 713 external to the Track as a DODAG, as discussed in section 4.1.1. of 714 [RFC9008]. We then apply the directives for encapsulating in that 715 case, more in Section 6.6. 717 In this formulation, we set up the Track Leg explicitly, which 718 creates less routing state in intermediate hops at the expense of 719 larger packets to accommodate source routing: 721 * P-DAO 1 signals C==>D==>E-to-E 723 * P-DAO 2 signals A==>B==>C-to-E 725 * P-DAO 3 signals F and G via the A-->E-to-F,G Track 727 Storing Mode P-DAO 1 and 2, and Non-Storing Mode P-DAO 3, are sent to 728 E, C and A, respectively, as follows: 730 +====================+==============+==============+==============+ 731 | | P-DAO 1 to E | P-DAO 2 to C | P-DAO 3 to A | 732 +====================+==============+==============+==============+ 733 | Mode | Storing | Storing | Non-Storing | 734 +--------------------+--------------+--------------+--------------+ 735 | Track Ingress | A | A | A | 736 +--------------------+--------------+--------------+--------------+ 737 | (DODAGID, TrackID) | (A, 129) | (A, 129) | (A, 129) | 738 +--------------------+--------------+--------------+--------------+ 739 | SegmentID | 1 | 2 | 3 | 740 +--------------------+--------------+--------------+--------------+ 741 | VIO | C, D, E | A, B, C | E | 742 +--------------------+--------------+--------------+--------------+ 743 | Targets | E | E | F, G | 744 +--------------------+--------------+--------------+--------------+ 746 Table 4: P-DAO Messages 748 Note in the above that E is not an implicit Target in Storing mode, 749 so it must be added in the RTO. 751 As a result the RIBs are set as follows: 753 +======+=============+=========+=============+==========+ 754 | Node | destination | Origin | Next Hop(s) | TrackID | 755 +======+=============+=========+=============+==========+ 756 | E | F, G | P-DAO 1 | Neighbor | (A, 129) | 757 +------+-------------+---------+-------------+----------+ 758 | D | E | P-DAO 1 | Neighbor | (A, 129) | 759 +------+-------------+---------+-------------+----------+ 760 | C | D | P-DAO 1 | Neighbor | (A, 129) | 761 +------+-------------+---------+-------------+----------+ 762 | " | E | P-DAO 1 | D | (A, 129) | 763 +------+-------------+---------+-------------+----------+ 764 | B | C | P-DAO 2 | Neighbor | (A, 129) | 765 +------+-------------+---------+-------------+----------+ 766 | " | E | P-DAO 2 | C | (A, 129) | 767 +------+-------------+---------+-------------+----------+ 768 | A | B | P-DAO 2 | Neighbor | (A, 129) | 769 +------+-------------+---------+-------------+----------+ 770 | " | E | P-DAO 2 | B | (A, 129) | 771 +------+-------------+---------+-------------+----------+ 772 | " | F, G | P-DAO 3 | E | (A, 129) | 773 +------+-------------+---------+-------------+----------+ 775 Table 5: RIB setting 777 Packets from A to E do not require an encapsulation. The outer 778 headers of the packets that are forwarded along the Track have the 779 following settings: 781 +========+===================+====================+================+ 782 | Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI | 783 +========+===================+====================+================+ 784 | Outer | A | E | (A, 129) | 785 +--------+-------------------+--------------------+----------------+ 786 | Inner | X | E (X != A), F or G | N/A | 787 +--------+-------------------+--------------------+----------------+ 789 Table 6: Packet Header Settings 791 As an example, say that A has a packet for F. Using the RIB above: 793 * From P-DAO 3: A encapsulates the packet the Track signaled by 794 P-DAO 3, with the outer header above. Now the packet destination 795 is E. 797 * From P-DAO 2: A forwards to B and B forwards to C. 799 * From P-DAO 1: C forwards to D and D forwards to E; E decapsulates 800 the packet. 802 * From Neighbor Cache Entry: C delivers packets to F or G. 804 3.5.1.3. Segment Routing 806 In this formulation leverages Track Legs to combine Segments and form 807 a Graph. The packets are source routed from a Segment to the next to 808 adapt the path. As such, this can be seen as a form of Segment 809 Routing [RFC8402]: 811 * P-DAO 1 signals C==>D==>E-to-E 813 * P-DAO 2 signals A==>B-to-B,C 815 * P-DAO 3 signals F and G via the A-->C-->E-to-F,G Track 817 Storing Mode P-DAO 1 and 2, and Non-Storing Mode P-DAO 3, are sent to 818 E, B and A, respectively, as follows: 820 +====================+==============+==============+==============+ 821 | | P-DAO 1 to E | P-DAO 2 to B | P-DAO 3 to A | 822 +====================+==============+==============+==============+ 823 | Mode | Storing | Storing | Non-Storing | 824 +--------------------+--------------+--------------+--------------+ 825 | Track Ingress | A | A | A | 826 +--------------------+--------------+--------------+--------------+ 827 | (DODAGID, TrackID) | (A, 129) | (A, 129) | (A, 129) | 828 +--------------------+--------------+--------------+--------------+ 829 | SegmentID | 1 | 2 | 3 | 830 +--------------------+--------------+--------------+--------------+ 831 | VIO | C, D, E | A, B | C, E | 832 +--------------------+--------------+--------------+--------------+ 833 | Targets | E | C | F, G | 834 +--------------------+--------------+--------------+--------------+ 836 Table 7: P-DAO Messages 838 Note in the above that the Segment can terminate at the loose hop as 839 used in the example of P-DAO 1 or at the previous hop as done with 840 P-DAO 2. Both methods are possible on any Segment joined by a loose 841 Track Leg. P-DAO 1 generates more signaling since E is the Segment 842 Egress when D could be, but has the benefit that it validates that 843 the connectivity between D and E still exists. 845 As a result the RIBs are set as follows: 847 +======+=============+=========+=============+==========+ 848 | Node | destination | Origin | Next Hop(s) | TrackID | 849 +======+=============+=========+=============+==========+ 850 | E | F, G | P-DAO 1 | Neighbor | (A, 129) | 851 +------+-------------+---------+-------------+----------+ 852 | D | E | P-DAO 1 | Neighbor | (A, 129) | 853 +------+-------------+---------+-------------+----------+ 854 | C | D | P-DAO 1 | Neighbor | (A, 129) | 855 +------+-------------+---------+-------------+----------+ 856 | " | E | P-DAO 1 | D | (A, 129) | 857 +------+-------------+---------+-------------+----------+ 858 | B | C | P-DAO 2 | Neighbor | (A, 129) | 859 +------+-------------+---------+-------------+----------+ 860 | A | B | P-DAO 2 | Neighbor | (A, 129) | 861 +------+-------------+---------+-------------+----------+ 862 | " | C | P-DAO 2 | B | (A, 129) | 863 +------+-------------+---------+-------------+----------+ 864 | " | E, F, G | P-DAO 3 | C, E | (A, 129) | 865 +------+-------------+---------+-------------+----------+ 867 Table 8: RIB setting 869 Packets originated at A to E do not require an encapsulation, but 870 carry a SRH via C. The outer headers of the packets that are 871 forwarded along the Track have the following settings: 873 +========+===================+====================+================+ 874 | Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI | 875 +========+===================+====================+================+ 876 | Outer | A | C till C then E | (A, 129) | 877 +--------+-------------------+--------------------+----------------+ 878 | Inner | X | E (X != A), F or G | N/A | 879 +--------+-------------------+--------------------+----------------+ 881 Table 9: Packet Header Settings 883 As an example, say that A has a packet for F. Using the RIB above: 885 * From P-DAO 3: A encapsulates the packet the Track signaled by 886 P-DAO 3, with the outer header above. Now the destination in the 887 IPv6 Header is C, and a SRH signals the final destination is E. 889 * From P-DAO 2: A forwards to B and B forwards to C. 891 * From P-DAO 3: C processes the SRH and sets the destination in the 892 IPv6 Header to E. 894 * From P-DAO 1: C forwards to D and D forwards to E; E decapsulates 895 the packet. 897 * From the Neighbor Cache Entry: C delivers packets to F or G. 899 3.5.2. Using Non-Storing Mode joining Tracks 901 In this formulation: 903 * P-DAO 1 signals C==>D==>E-to-F,G 905 * P-DAO 2 signals A==>B==>C-to-C,F,G 907 A==>B==>C and C==>D==>E are Tracks expressed as Non-Storing P-DAOs. 909 3.5.2.1. Stitched Tracks 911 Non-Storing Mode P-DAO 1 and 2 are sent to C and A respectively, as 912 follows: 914 +====================+==============+==============+ 915 | | P-DAO 1 to C | P-DAO 2 to A | 916 +====================+==============+==============+ 917 | Mode | Non-Storing | Non-Storing | 918 +--------------------+--------------+--------------+ 919 | Track Ingress | C | A | 920 +--------------------+--------------+--------------+ 921 | (DODAGID, TrackID) | (C, 131) | (A, 131) | 922 +--------------------+--------------+--------------+ 923 | SegmentID | 1 | 1 | 924 +--------------------+--------------+--------------+ 925 | VIO | D, E | B, C | 926 +--------------------+--------------+--------------+ 927 | Targets | F, G | E, F, G | 928 +--------------------+--------------+--------------+ 930 Table 10: P-DAO Messages 932 As a result the RIBs are set as follows: 934 +======+=============+=========+=============+==========+ 935 | Node | destination | Origin | Next Hop(s) | TrackID | 936 +======+=============+=========+=============+==========+ 937 | E | F, G | ND | Neighbor | Any | 938 +------+-------------+---------+-------------+----------+ 939 | D | E | ND | Neighbor | Any | 940 +------+-------------+---------+-------------+----------+ 941 | C | D | ND | Neighbor | Any | 942 +------+-------------+---------+-------------+----------+ 943 | " | E, F, G | P-DAO 1 | D, E | (C, 131) | 944 +------+-------------+---------+-------------+----------+ 945 | B | C | ND | Neighbor | Any | 946 +------+-------------+---------+-------------+----------+ 947 | A | B | ND | Neighbor | Any | 948 +------+-------------+---------+-------------+----------+ 949 | " | C, E, F, G | P-DAO 2 | B, C | (A, 131) | 950 +------+-------------+---------+-------------+----------+ 952 Table 11: RIB setting 954 Packets originated at A to E, F and G do not require an 955 encapsulation, though it is preferred that A encapsulates and C 956 decapsulates. Either way, they carry a SRH via B and C, and C needs 957 to encapsulate to E, F, or G to add an SRH via D and E. The 958 encapsulating headers of packets that are forwarded along the Track 959 between C and E have the following settings: 961 +========+===================+===================+================+ 962 | Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI | 963 +========+===================+===================+================+ 964 | Outer | C | D till D then E | (C, 131) | 965 +--------+-------------------+-------------------+----------------+ 966 | Inner | X | E, F, or G | N/A | 967 +--------+-------------------+-------------------+----------------+ 969 Table 12: Packet Header Settings between C and E 971 As an example, say that A has a packet for F. Using the RIB above: 973 * From P-DAO 2: A encapsulates the packet with destination of F in 974 the Track signaled by P-DAO 2. The outer header has source A, 975 destination B, an SRH that indicates C as the next loose hop, and 976 a RPI indicating a TrackId of 131 from A's namespace, which is 977 distinct from TrackId of 131 from C's. 979 * From the SRH: Packets forwarded by B have source A, destination C, 980 a consumed SRH, and a RPI indicating a TrackId of 131 from A's 981 namespace. C decapsulates. 983 * From P-DAO 1: C encapsulates the packet with destination of F in 984 the Track signaled by P-DAO 1. The outer header has source C, 985 destination D, an SRH that indicates E as the next loose hop, and 986 a RPI indicating a TrackId of 131 from C's namespace. E 987 decapsulates. 989 3.5.2.2. External routes 991 In this formulation: 993 * P-DAO 1 signals C==>D==>E-to-E 995 * P-DAO 2 signals A==>B==>C-to-C,E 997 * P-DAO 3 signals F and G via the A-->E-to-F,G Track 999 Non-Storing Mode P-DAO 1 is sent to C and Non-Storing Mode P-DAO 2 1000 and 3 are sent A, as follows: 1002 +====================+==============+==============+==============+ 1003 | | P-DAO 1 to C | P-DAO 2 to A | P-DAO 3 to A | 1004 +====================+==============+==============+==============+ 1005 | Mode | Non-Storing | Non-Storing | Non-Storing | 1006 +--------------------+--------------+--------------+--------------+ 1007 | Track Ingress | C | A | A | 1008 +--------------------+--------------+--------------+--------------+ 1009 | (DODAGID, TrackID) | (C, 131) | (A, 129) | (A, 141) | 1010 +--------------------+--------------+--------------+--------------+ 1011 | SegmentID | 1 | 1 | 1 | 1012 +--------------------+--------------+--------------+--------------+ 1013 | VIO | D, E | B, C | E | 1014 +--------------------+--------------+--------------+--------------+ 1015 | Targets | E | E | F, G | 1016 +--------------------+--------------+--------------+--------------+ 1018 Table 13: P-DAO Messages 1020 As a result the RIBs are set as follows: 1022 +======+=============+=========+=============+==========+ 1023 | Node | destination | Origin | Next Hop(s) | TrackID | 1024 +======+=============+=========+=============+==========+ 1025 | E | F, G | ND | Neighbor | Any | 1026 +------+-------------+---------+-------------+----------+ 1027 | D | E | ND | Neighbor | Any | 1028 +------+-------------+---------+-------------+----------+ 1029 | C | D | ND | Neighbor | Any | 1030 +------+-------------+---------+-------------+----------+ 1031 | " | E | P-DAO 1 | D, E | (C, 131) | 1032 +------+-------------+---------+-------------+----------+ 1033 | B | C | ND | Neighbor | Any | 1034 +------+-------------+---------+-------------+----------+ 1035 | A | B | ND | Neighbor | Any | 1036 +------+-------------+---------+-------------+----------+ 1037 | " | C, E | P-DAO 2 | B, C | (A, 129) | 1038 +------+-------------+---------+-------------+----------+ 1039 | " | F, G | P-DAO 3 | E | (A, 141) | 1040 +------+-------------+---------+-------------+----------+ 1042 Table 14: RIB setting 1044 The encapsulating headers of packets that are forwarded along the 1045 Track between C and E have the following settings: 1047 +========+===================+===================+================+ 1048 | Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI | 1049 +========+===================+===================+================+ 1050 | Outer | C | D till D then E | (C, 131) | 1051 +--------+-------------------+-------------------+----------------+ 1052 | Middle | A | E | (A, 141) | 1053 +--------+-------------------+-------------------+----------------+ 1054 | Inner | X | E, F or G | N/A | 1055 +--------+-------------------+-------------------+----------------+ 1057 Table 15: Packet Header Settings 1059 As an example, say that A has a packet for F. Using the RIB above: 1061 * From P-DAO 3: A encapsulates the packet with destination of F in 1062 the Track signaled by P-DAO 3. The outer header has source A, 1063 destination E, and a RPI indicating a TrackId of 141 from A's 1064 namespace. This recurses with: 1066 * From P-DAO 2: A encapsulates the packet with destination of E in 1067 the Track signaled by P-DAO 2. The outer header has source A, 1068 destination B, an SRH that indicates C as the next loose hop, and 1069 a RPI indicating a TrackId of 129 from A's namespace. 1071 * From the SRH: Packets forwarded by B have source A, destination C 1072 , a consumed SRH, and a RPI indicating a TrackId of 129 from A's 1073 namespace. C decapsulates. 1075 * From P-DAO 1: C encapsulates the packet with destination of E in 1076 the Track signaled by P-DAO 1. The outer header has source C, 1077 destination D, an SRH that indicates E as the next loose hop, and 1078 a RPI indicating a TrackId of 131 from C's namespace. E 1079 decapsulates. 1081 3.5.2.3. Segment Routing 1083 In this formulation: 1085 * P-DAO 1 signals C==>D==>E-to-E 1087 * P-DAO 2 signals A==>B-to-C 1089 * P-DAO 3 signals F and G via the A-->C-->E-to-F,G Track 1091 Non-Storing Mode P-DAO 1 is sent to C and Non-Storing Mode P-DAO 2 1092 and 3 are sent A, as follows: 1094 +====================+==============+==============+==============+ 1095 | | P-DAO 1 to C | P-DAO 2 to A | P-DAO 3 to A | 1096 +====================+==============+==============+==============+ 1097 | Mode | Non-Storing | Non-Storing | Non-Storing | 1098 +--------------------+--------------+--------------+--------------+ 1099 | Track Ingress | C | A | A | 1100 +--------------------+--------------+--------------+--------------+ 1101 | (DODAGID, TrackID) | (C, 131) | (A, 129) | (A, 141) | 1102 +--------------------+--------------+--------------+--------------+ 1103 | SegmentID | 1 | 1 | 1 | 1104 +--------------------+--------------+--------------+--------------+ 1105 | VIO | D, E | B | C, E | 1106 +--------------------+--------------+--------------+--------------+ 1107 | Targets | | C | F, G | 1108 +--------------------+--------------+--------------+--------------+ 1110 Table 16: P-DAO Messages 1112 As a result the RIBs are set as follows: 1114 +======+=============+=========+=============+==========+ 1115 | Node | destination | Origin | Next Hop(s) | TrackID | 1116 +======+=============+=========+=============+==========+ 1117 | E | F, G | ND | Neighbor | Any | 1118 +------+-------------+---------+-------------+----------+ 1119 | D | E | ND | Neighbor | Any | 1120 +------+-------------+---------+-------------+----------+ 1121 | C | D | ND | Neighbor | Any | 1122 +------+-------------+---------+-------------+----------+ 1123 | " | E | P-DAO 1 | D, E | (C, 131) | 1124 +------+-------------+---------+-------------+----------+ 1125 | B | C | ND | Neighbor | Any | 1126 +------+-------------+---------+-------------+----------+ 1127 | A | B | ND | Neighbor | Any | 1128 +------+-------------+---------+-------------+----------+ 1129 | " | C | P-DAO 2 | B, C | (A, 129) | 1130 +------+-------------+---------+-------------+----------+ 1131 | " | E, F, G | P-DAO 3 | C, E | (A, 141) | 1132 +------+-------------+---------+-------------+----------+ 1134 Table 17: RIB setting 1136 The encapsulating headers of packets that are forwarded along the 1137 Track between A and B have the following settings: 1139 +========+===================+===================+================+ 1140 | Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI | 1141 +========+===================+===================+================+ 1142 | Outer | A | B till D then E | (A, 129) | 1143 +--------+-------------------+-------------------+----------------+ 1144 | Middle | A | C | (A, 141) | 1145 +--------+-------------------+-------------------+----------------+ 1146 | Inner | X | E, F or G | N/A | 1147 +--------+-------------------+-------------------+----------------+ 1149 Table 18: Packet Header Settings 1151 The encapsulating headers of packets that are forwarded along the 1152 Track between B and C have the following settings: 1154 +========+===================+===================+================+ 1155 | Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI | 1156 +========+===================+===================+================+ 1157 | Outer | A | C | (A, 141) | 1158 +--------+-------------------+-------------------+----------------+ 1159 | Inner | X | E, F or G | N/A | 1160 +--------+-------------------+-------------------+----------------+ 1162 Table 19: Packet Header Settings 1164 The encapsulating headers of packets that are forwarded along the 1165 Track between C and E have the following settings: 1167 +========+===================+===================+================+ 1168 | Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI | 1169 +========+===================+===================+================+ 1170 | Outer | C | D till D then E | (C, 131) | 1171 +--------+-------------------+-------------------+----------------+ 1172 | Middle | A | E | (A, 141) | 1173 +--------+-------------------+-------------------+----------------+ 1174 | Inner | X | E, F or G | N/A | 1175 +--------+-------------------+-------------------+----------------+ 1177 Table 20: Packet Header Settings 1179 As an example, say that A has a packet for F. Using the RIB above: 1181 * From P-DAO 3: A encapsulates the packet with destination of F in 1182 the Track signaled by P-DAO 3. The outer header has source A, 1183 destination C, an SRH that indicates E as the next loose hop, and 1184 a RPI indicating a TrackId of 141 from A's namespace. This 1185 recurses with: 1187 * From P-DAO 2: A encapsulates the packet with destination of C in 1188 the Track signaled by P-DAO 2. The outer header has source A, 1189 destination B, and a RPI indicating a TrackId of 129 from A's 1190 namespace. B decapsulates forwards to C based on a sibling 1191 connected route. 1193 * From the SRH: C consumes the SRH and makes the destination E. 1195 * From P-DAO 1: C encapsulates the packet with destination of E in 1196 the Track signaled by P-DAO 1. The outer header has source C, 1197 destination D, an SRH that indicates E as the next loose hop, and 1198 a RPI indicating a TrackId of 131 from C's namespace. E 1199 decapsulates. 1201 3.6. Complex Tracks 1203 To increase the reliability of the P2P transmission, this 1204 specification enables to build a collection of Legs between the same 1205 Ingress and Egress Nodes and combine them with the same TrackID, as 1206 shown in Figure 5. Legs may cross at loose hops edges or remain 1207 parallel. 1209 The Segments that join the loose hops of a Leg are installed with the 1210 same TrackID as the Leg. But each individual Leg and Segment has its 1211 own P-RouteID which allows to manage it separately. When Legs cross 1212 within respsective Segment, the next loose hop (the current 1213 destination of the packet) indicates which Leg is being followed and 1214 a Segment that can reach that next loose hop is selected. 1216 CPF CPF CPF CPF 1218 Southbound API 1220 _-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._- 1221 _-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._- 1223 +----------+ 1224 | RPL Root | 1225 +----------+ 1226 ( ) 1227 ( ) 1228 ( DODAG ) 1229 ( ) 1230 ( ) 1231 ) 1232 <- Leg 1 B, E -> 1233 <--- Segment 1 A,B ---> <------- Segment 2 C,D,E -------> 1235 FWD --z Relay --z FWD --z FWD Target 1 1236 z-- Node z-- Node z-- Node z-- Node --z / 1237 --z (A) (B) \ (C) (D) z-- / 1238 Track \ Track 1239 Ingress Segment 5 Egress - Tgt 2 1240 (I) \ (E) 1241 --z \ z-- \ 1242 z-- FWD --z FWD --z Relay --z FWD --z \ 1243 Node z-- Node z-- Node z-- Node Target 3 1244 (F) (G) (H) (J) 1246 <------ Segment 3 F,G,H ------> <---- Segment 4 J,E ----> 1247 <- Leg 2 H, E -> 1249 <--- Segment 1 A,B ---> <- S5-> <---- Segment 4 J,E ----> 1250 <- Leg 3 B, H, E -> 1251 ) 1252 ( 1253 ( ) 1255 Figure 5: Segments and Tracks 1257 Note that while this specification enables to build both Segments 1258 inside a Leg (aka East-West), such as Segment 2 above which is within 1259 Leg 1, and Inter-Leg Segments (aka North-South), such as Segment 2 1260 above which joins Leg 1 and Leg 2, it does not signal to the Ingress 1261 which Inter-Leg Segments are available, so the use of North-South 1262 Segments and associated PAREO functions is curently limited. The 1263 only possibility available at this time is to define overlapping Legs 1264 as illustrated in Figure 5, with Leg 3 that is congruent with Leg 1 1265 till node B and congruent with Leg 2 from node H on, abstracting 1266 Segment 5 as an East-West Segment. 1268 DetNet Forwarding Nodes only understand the simple 1-to-1 forwarding 1269 sublayer transport operation along a segment whereas the more 1270 sophisticated Relay nodes can also provide service sublayer functions 1271 such as Replication and Elimination. One possible mapping between 1272 DetNet and this specification is to signal the Relay Nodes as the 1273 hops of a Leg and the forwarding Nodes as the hops in a Segment that 1274 join the Relay nodes as illustrated in Figure 5. 1276 3.7. Scope and Expectations 1278 This specification expects that the RPL Main DODAG is operated in RPL 1279 Non-Storing Mode to sustain the exchanges with the Root. Based on 1280 its comprehensive knowledge of the parent-child relationship, the 1281 Root can form an abstracted view of the whole DODAG topology. This 1282 document adds the capability for nodes to advertise additional 1283 sibling information to complement the topological awareness of the 1284 Root to be passed on to the PCE, and enable the PCE to build more / 1285 better paths that traverse those siblings. 1287 P-Routes require resources such as routing table space in the routers 1288 and bandwidth on the links; the amount of state that is installed in 1289 each node must be computed to fit within the node's memory, and the 1290 amount of rerouted traffic must fit within the capabilities of the 1291 transmission links. The methods used to learn the node capabilities 1292 and the resources that are available in the devices and in the 1293 network are out of scope for this document. The method to capture 1294 and report the LLN link capacity and reliability statistics are also 1295 out of scope. They may be fetched from the nodes through network 1296 management functions or other forms of telemetry such as OAM. 1298 The "6TiSCH Architecture" [6TiSCH-ARCHI] leverages a centralized 1299 model that is similar to that of "Deterministic Networking 1300 Architecture" [RFC8655], whereby the device resources and 1301 capabilities are exposed to an external controller which installs 1302 routing states into the network based on its own objective functions 1303 that reside in that external entity. With DetNet and 6TiSCH, the 1304 component of the controller that is responsible of computing routes 1305 is a PCE. The PCE computes its routes based on its own objective 1306 functions such as described in [RFC4655], and typically controls the 1307 routes using the PCE Protocol (PCEP) by [RFC5440]. While this 1308 specification expects a PCE and while PCEP might effectively be used 1309 between the Root and the PCE, the control protocol between the PCE 1310 and the Root is out of scope. 1312 This specification expects a single PCE with a full view of the 1313 network. Distributing the PCE function for a large network is out of 1314 scope. This specification uses the RPL Root as a proxy to the PCE. 1315 The PCE may be collocated with the Root, or may reside in an external 1316 Controller. In that case, the protocol between the Root and the PCE 1317 is out of scope and abstracted by / mapped to RPL inside the DODAG; 1318 one possibility is for the Root to transmit the RPL DAOs with the 1319 SIOs that detail the parent/child and sibling information. 1321 The algorithm to compute the paths and the protocol used by the PCE 1322 and the metrics and link statistics involved in the computation are 1323 also out of scope. The effectiveness of the route computation by the 1324 PCE depends on the quality of the metrics that are reported from the 1325 RPL network. Which metrics are used and how they are reported is out 1326 of scope, but the expectation is that they are mostly of long-term, 1327 statistical nature, and provide visibility on link throughput, 1328 latency, stability and availability over relatively long periods. 1330 The "Reliable and Available Wireless (RAW) Architecture/Framework" 1331 [RAW-ARCHI] extends the definition of Track, as being composed of 1332 East-West directional segments and North-South bidirectional 1333 segments, to enable additional path diversity, using Packet ARQ, 1334 Replication, Elimination, and Overhearing (PAREO) functions over the 1335 available paths, to provide a dynamic balance between the reliability 1336 and availability requirements of the flows and the need to conserve 1337 energy and spectrum. This specification prepares for RAW by setting 1338 up the Tracks, but only forms DODAGs, which are composed of 1339 aggregated end-to-end loose source routed Legs, joined by strict 1340 routed Segments, all oriented East-West. 1342 The RAW Architecture defines a dataplane extension of the PCE called 1343 the Path Selection Engine (PSE), that adapts the use of the path 1344 redundancy within a Track to defeat the diverse causes of packet 1345 loss. The PSE controls the forwarding operation of the packets 1346 within a Track This specification can use but does not impose a PSE 1347 and does not provide the policies that wouldselect which packets are 1348 routed through which path within a Track, IOW, how the PSE may use 1349 the path redundancy within the Track. By default, the use of the 1350 available redundancy is limited to simple load balancing, and all the 1351 segments are East-West unidirectional only. 1353 A Track may be set up to reduce the load around the Root, or to 1354 enable urgent traffic to flow more directly. This specification does 1355 not provide the policies that would decide which flows are routed 1356 through which Track. In a Non-Storing Mode RPL Instance, the Main 1357 DODAG provides a default route via the Root, and the Tracks provide 1358 more specific routes to the Track Targets. 1360 4. Extending existing RFCs 1362 4.1. Extending RFC 6550 1364 This specification extends RPL [RPL] to enable the Root to install 1365 East-West routes inside a Main DODAG that is operated as non-Storing 1366 Mode. A Projected DAO (P-DAO) message (see Section 4.1.1) contains a 1367 new Via Information Option that installs a strict or a loose sequence 1368 of hops to form respectively a Track Segment or a Track Leg. A new 1369 P-DAO Request (PDR) message (see Section 5.1) enables a Track Ingress 1370 to request the Track from the Root for which it is the Root and it 1371 owns the address that serves as TrackID, as well as the associated 1372 namespace from which it selects the TrackID. In the context of this 1373 specification, the installed route appears as a more specific route 1374 to the Track Targets, and the Track Ingress routes the packets 1375 towards the Targets via the Track using the longest match as usual. 1377 To ensure that the PDR and P-DAO messages can flow at most times, it 1378 is RECOMMENDED that the nodes involved in a Track mantain multiple 1379 parents in the Main DODAG, advertise them all to the Root, and use 1380 them in turn to retry similar packets. It is also RECOMMENDED that 1381 the Root uses diverse source route paths to retry similar messages ot 1382 the nodes in the Track. 1384 4.1.1. Projected DAO 1386 Section 6 of [RPL] introduces the RPL Control Message Options (CMO), 1387 including the RPL Target Option (RTO) and Transit Information Option 1388 (TIO), which can be placed in RPL messages such as the destination 1389 Advertisement Object (DAO). A DAO message signals routing 1390 information to one or more Targets indicated in RTOs, providing one 1391 hop information at a time in the TIO. A Projected DAO (P-DAO) is a 1392 special DAO message generated by the Root to install a P-Route formed 1393 of multiple hops in its DODAG. This provides a RPL-based method to 1394 install the Tracks as expected by the 6TiSCH Architecture 1395 [6TiSCH-ARCHI] as a collection of multiple P-Routes. 1397 The P-DAO is signaled with a new "Projected DAO" (P) flag, see 1398 Figure 6. The 'P' flag is encoded in bit position 2 (to be confirmed 1399 by IANA) of the Flags field in the DAO Base Object. The Root MUST 1400 set it to 1 in a Projected DAO message. Otherwise it MUST be set to 1401 0. It is set to 0 in Legacy implementations as specified 1402 respectively in Sections 20.11 and 6.4 of [RPL] 1404 The P-DAO is control plane signaling and should not be stuck behind 1405 high traffic levels. The expectation is that the P-DAO message is 1406 sent as high QoS level, above that of data traffic, typically with 1407 the Network Control precedence. 1409 0 1 2 3 1410 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 1411 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1412 | TrackID |K|D|P| Flags | Reserved | DAOSequence | 1413 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1414 | | 1415 + + 1416 | DODAGID field set to the | 1417 + IPv6 Address of the Track Ingress + 1418 | used to source encapsulated packets | 1419 + + 1420 | | 1421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1422 | Option(s)... 1423 +-+-+-+-+-+-+-+-+ 1425 Figure 6: Projected DAO Base Object 1427 New fields: 1429 TrackID: The local or global RPLInstanceID of the DODAG that serves 1430 as Track, more in Section 6.2 1432 P: 1-bit flag (position to be confirmed by IANA). 1434 The 'P' flag is set to 1 by the Root to signal a Projected DAO, 1435 and it is set to 0 otherwise. 1437 In RPL Non-Storing Mode, the TIO and RTO are combined in a DAO 1438 message to inform the DODAG Root of all the edges in the DODAG, which 1439 are formed by the directed parent-child relationships. Options may 1440 be factorized; multiple RTOs may be present to signal a collection of 1441 children that can be reached via the parent(s) indicated in the 1442 TIO(s) that follows the RTOs. This specification generalizes the 1443 case of a parent that can be used to reach a child with that of a 1444 whole Track through which children and siblings of the Track Egress 1445 are reachable. 1447 4.1.2. Via Information Option 1449 New CMOs called the Via Information Options (VIO) are introduced for 1450 use in P-DAO messages as a multihop alternative to the TIO, more in 1451 Section 5.3. One VIO is the stateful Storing Mode VIO (SM-VIO); an 1452 SM-VIO installs a strict hop-by-hop P-Route called a Track Segment. 1453 The other is the Non-Storing Mode VIO (NSM-VIO); the NSM-VIO installs 1454 a loose source-routed P-Route called a Track Leg at the Track 1455 Ingress, which uses that state to encapsulate a packet IPv6_in_IPv6 1456 with a new Routing Header (RH) to the Track Egress, more in 1457 Section 6.6. 1459 A P-DAO contains one or more RTOs to indicate the Target 1460 (destinations) that can be reached via the P-Route, followed by 1461 exactly one VIO that signals the sequence of nodes to be followed, 1462 more in Section 6. There are two modes of operation for the 1463 P-Routes, the Storing Mode and the Non-Storing Mode, see 1464 Section 6.3.2 and Section 6.3.3 respectively for more. 1466 4.1.3. Sibling Information Option 1468 This specification adds another CMO called the Sibling Information 1469 Option (SIO) that is used by a RPL Aware Node (RAN) to advertise a 1470 selection of its candidate neighbors as siblings to the Root, more in 1471 Section 5.4. The SIO is placed in DAO messages that are sent 1472 directly to the Root of the main DODAG. 1474 4.1.4. P-DAO Request 1476 Two new RPL Control Messages are also introduced, to enable a RPL- 1477 Aware Node to request the establishment of a Track between self as 1478 the Track Ingress Node and a Track Egress. The node makes its 1479 request by sending a new P-DAO Request (PDR) Message to the Root. 1480 The Root confirms with a new PDR-ACK message back to the requester 1481 RAN, see Section 5.1 for more. 1483 4.1.5. Extending the RPI 1485 Sending a Packet within a RPL Local Instance requires the presence of 1486 the abstract RPL Packet Information (RPI) described in section 11.2. 1487 of [RPL] in the outer IPv6 Header chain (see [RFC9008]). The RPI 1488 carries a local RPLInstanceID which, in association with either the 1489 source or the destination address in the IPv6 Header, indicates the 1490 RPL Instance that the packet follows. 1492 This specification extends [RPL] to create a new flag that signals 1493 that a packet is forwarded along a P-Route. 1495 Projected-Route 'P': 1-bit flag. It is set to 1 in the RPI that is 1496 added in the encapsulation when a packet is sent over a Track. It 1497 is set to 0 when a packet is forwarded along the main Track, 1498 including when the packet follows a Segment that joins loose hops 1499 of the Main DODAG. The flag is not mutable en-route. 1501 The encoding of the 'P' flag in native format is shown in Section 4.2 1502 while the compressed format is indicated in Section 4.3. 1504 4.2. Extending RFC 6553 1506 "The RPL Option for Carrying RPL Information in Data-Plane Datagrams" 1507 [RFC6553]describes the RPL Option for use among RPL routers to 1508 include the abstract RPL Packet Information (RPI) described in 1509 section 11.2. of [RPL] in data packets. 1511 The RPL Option is commonly referred to as the RPI though the RPI is 1512 really the abstract information that is transported in the RPL 1513 Option. [RFC9008] updated the Option Type from 0x63 to 0x23. 1515 This specification modifies the RPL Option to encode the 'P' flag as 1516 follows: 1518 0 1 2 3 1519 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 1520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1521 | Option Type | Opt Data Len | 1522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1523 |O|R|F|P|0|0|0|0| RPLInstanceID | SenderRank | 1524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1525 | (sub-TLVs) | 1526 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1528 Figure 7: Extended RPL Option Format 1530 Option Type: 0x23 or 0x63, see [RFC9008] 1532 Opt Data Len: See [RFC6553] 1534 'O', 'R' and 'F' flags: See [RFC6553]. Those flags MUST be set to 0 1535 by the sender and ignored by the receiver if the 'P' flag is set. 1537 Projected-Route 'P': 1-bit flag as defined in Section 4.1.5. 1539 RPLInstanceID: See [RFC6553]. Indicates the TrackId if the 'P' flag 1540 is set, as discussed in Section 4.1.1. 1542 SenderRank: See [RFC6553]. This field MUST be set to 0 by the 1543 sender and ignored by the receiver if the 'P'flag is set. 1545 4.3. Extending RFC 8138 1547 The 6LoWPAN Routing Header [RFC8138] specification introduces a new 1548 IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) 1549 [RFC6282] dispatch type for use in 6LoWPAN route-over topologies, 1550 which initially covers the needs of RPL data packet compression. 1552 Section 4 of [RFC8138] presents the generic formats of the 6LoWPAN 1553 Routing Header (6LoRH) with two forms, one Elective that can be 1554 ignored and skipped when the router does not understand it, and one 1555 Critical which causes the packet to be dropped when the router cannot 1556 process it. The 'E' Flag in the 6LoRH indicates its form. In order 1557 to skip the Elective 6LoRHs, their format imposes a fixed expression 1558 of the size, whereas the size of a Critical 6LoRH may be signaled in 1559 variable forms to enable additional optimizations. 1561 When the [RFC8138] compression is used, the Root of the Main DODAG 1562 that sets up the Track also constructs the compressed routing header 1563 (SRH-6LoRH) on behalf of the Track Ingress, which saves the 1564 complexities of optimizing the SRH-6LoRH encoding in constrained 1565 code. The SRH-6LoRH is signaled in the NSM-VIO, in a fashion that it 1566 is ready to be placed as is in the packet encapsulation by the Track 1567 Ingress. 1569 Section 6.3 of [RFC8138] presents the formats of the 6LoWPAN Routing 1570 Header of type 5 (RPI-6LoRH) that compresses the RPI for normal RPL 1571 operation. The format of the RPI-6LoRH is not suited for P-Routes 1572 since the O,R,F flags are not used and the Rank is unknown and 1573 ignored. 1575 This specification introduces a new 6LoRH, the P-RPI-6LoRH that can 1576 be used in either Elective or Critical 6LoRH form, see Table 21 and 1577 Table 22 respectively. The new 6LoRH MUST be used as a Critical 1578 6LoRH, unless an SRH-6LoRH is present and controls the routing 1579 decision, in which case it MAY be used in Elective form. 1581 The P-RPI-6LoRH is designed to compress the RPI along RPL P-Routes. 1582 Its format is as follows: 1584 0 1 2 1585 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 1586 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1587 |1|0|E| Length | 6LoRH Type | RPLInstanceID | 1588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1589 Figure 8: P-RPI-6LoRH Format 1591 Type: IANA is requested to define the same value of the type for 1592 both Elective and Critical forms. A type of 8 is suggested. 1594 Elective 'E': See [RFC8138]. The 'E' flag is set to 1 to indicate 1595 an Elective 6LoRH, meaning that it can be ignored when forwarding. 1597 RPLInstanceID : In the context of this specification, the 1598 RPLInstanceID field signals the TrackID, see Section 3.4 and 1599 Section 6.2 . 1601 Section 6.7 details how a a Track Ingress leverages the P-RPI-6LoRH 1602 Header as part of the encapsulation of a packet to place it into a 1603 Track. 1605 5. New RPL Control Messages and Options 1607 5.1. New P-DAO Request Control Message 1609 The P-DAO Request (PDR) message is sent by a Node in the Main DODAG 1610 to the Root. It is a request to establish or refresh a Track where 1611 this node is Track Ingress, and signals whether an acknowledgment 1612 called PDR-ACK is requested or not. A positive PDR-ACK indicates 1613 that the Track was built and that the Roots commits to maintain the 1614 Track for the negotiated lifetime. 1616 The Root may use an asynchronous PDR-ACK with an negative status to 1617 indicate that the Track was terminated before its time. A status of 1618 "Transient Failure" (see Section 10.9) is an indication that the PDR 1619 may be retried after a reasonable time that depends on the 1620 deployment. Other negative status values indicate a permanent error; 1621 the tentative must be abandoned until a corrective action is taken at 1622 the application layer or through network management. 1624 The source IPv6 address of the PDR signals the Track Ingress to-be of 1625 the requested Track, and the TrackID is indicated in the message 1626 itself. One and only one RPL Target Option MUST be present in the 1627 message. The RTO signals the Track Egress, more in Section 6.1. 1629 The RPL Control Code for the PDR is 0x09, to be confirmed by IANA. 1630 The format of PDR Base Object is as follows: 1632 0 1 2 3 1633 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 1634 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1635 | TrackID |K|R| Flags | ReqLifetime | PDRSequence | 1636 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1637 | Option(s)... 1638 +-+-+-+-+-+-+-+-+ 1640 Figure 9: New P-DAO Request Format 1642 TrackID: 8-bit field. In the context of this specification, the 1643 TrackID field signals the RPLInstanceID of the DODAG formed by the 1644 Track, see Section 3.4 and Section 6.2. To allocate a new Track, 1645 the Ingress Node must provide a value that is not in use at this 1646 time. 1648 K: The 'K' flag is set to indicate that the recipient is expected to 1649 send a PDR-ACK back. 1651 R: The 'R' flag is set to request a Complex Track for redundancy. 1653 Flags: Reserved. The Flags field MUST initialized to zero by the 1654 sender and MUST be ignored by the receiver 1656 ReqLifetime: 8-bit unsigned integer. The requested lifetime for the 1657 Track expressed in Lifetime Units (obtained from the DODAG 1658 Configuration option). 1660 A PDR with a fresher PDRSequence refreshes the lifetime, and a 1661 PDRLifetime of 0 indicates that the Track should be destroyed, 1662 e.g., when the application that requested the Track terminates. 1664 PDRSequence: 8-bit wrapping sequence number, obeying the operation 1665 in section 7.2 of [RPL]. The PDRSequence is used to correlate a 1666 PDR-ACK message with the PDR message that triggered it. It is 1667 incremented at each PDR message and echoed in the PDR-ACK by the 1668 Root. 1670 5.2. New PDR-ACK Control Message 1672 The new PDR-ACK is sent as a response to a PDR message with the 'K' 1673 flag set. The RPL Control Code for the PDR-ACK is 0x0A, to be 1674 confirmed by IANA. Its format is as follows: 1676 0 1 2 3 1677 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 1678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1679 | TrackID | Flags | Track Lifetime| PDRSequence | 1680 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1681 | PDR-ACK Status| Reserved | 1682 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1683 | Option(s)... 1684 +-+-+-+-+-+-+-+ 1686 Figure 10: New PDR-ACK Control Message Format 1688 TrackID: Set to the TrackID indicated in the TrackID field of the 1689 PDR messages that this replies to. 1691 Flags: Reserved. The Flags field MUST initialized to zero by the 1692 sender and MUST be ignored by the receiver 1694 Track Lifetime: Indicates that remaining Lifetime for the Track, 1695 expressed in Lifetime Units; the value of zero (0x00) indicates 1696 that the Track was destroyed or not created. 1698 PDRSequence: 8-bit wrapping sequence number. It is incremented at 1699 each PDR message and echoed in the PDR-ACK. 1701 PDR-ACK Status: 8-bit field indicating the completion. The PDR-ACK 1702 Status is substructured as indicated in Figure 11: 1704 0 1 2 3 4 5 6 7 1705 +-+-+-+-+-+-+-+-+ 1706 |E|R| Value | 1707 +-+-+-+-+-+-+-+-+ 1709 Figure 11: PDR-ACK status Format 1711 E: 1-bit flag. Set to indicate a rejection. When not set, the 1712 value of 0 indicates Success/Unqualified Acceptance and other 1713 values indicate "not an outright rejection". 1714 R: 1-bit flag. Reserved, MUST be set to 0 by the sender and 1715 ignored by the receiver. 1716 Status Value: 6-bit unsigned integer. Values depending on the 1717 setting of the 'E' flag, see Table 27 and Table 28. 1719 Reserved: The Reserved field MUST initialized to zero by the sender 1720 and MUST be ignored by the receiver 1722 5.3. Via Information Options 1724 A VIO signals the ordered list of IPv6 Via Addresses that constitutes 1725 the hops of either a Leg (using Non-Storing Mode) a Segment (using 1726 storing mode) of a Track. A Storing Mode P-DAO contains one Storing 1727 Mode VIO (SM-VIO) whereas a Non-Storing Mode P-DAO contains one Non- 1728 Storing Mode VIO (NSM-VIO) 1730 The duration of the validity of a VIO is indicated in a Segment 1731 Lifetime field. A P-DAO message that contains a VIO with a Segment 1732 Lifetime of zero is referred as a No-Path P-DAO. 1734 The VIO contains one or more SRH-6LoRH header(s), each formed of a 1735 SRH-6LoRH head and a collection of compressed Via Addresses, except 1736 in the case of a Non-Storing Mode No-Path P-DAO where the SRH-6LoRH 1737 header is not present. 1739 In the case of a SM-VIO, or if [RFC8138] is not used in the data 1740 packets, then the Root MUST use only one SRH-6LoRH per Via 1741 Information Option, and the compression is the same forall the 1742 addresses, as shown in Figure 12, for simplicity. 1744 In case of an NSM-VIO and if [RFC8138] is in use in the Main DODAG, 1745 the Root SHOULD optimize the size of the NSM-VIO if using different 1746 SRH-6LoRH Types make the VIO globally shorter; this means that more 1747 than one SRH-6LoRH may be present. 1749 The format of the Via Information Options is as follows: 1751 0 1 2 3 1752 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 1753 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1754 | Type | Option Length | Flags | P-RouteID | 1755 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1756 |Segm. Sequence | Seg. Lifetime | SRH-6LoRH head | 1757 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1758 | | 1759 . Via Address 1 (compressed by RFC 8138) . 1760 | | 1761 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1762 | | 1763 . .... . 1764 | | 1765 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1766 | | 1767 . Via Address n (compressed by RFC 8138) . 1768 | | 1769 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1770 | | 1771 . Additional SRH-6LoRH Header(s) . 1772 | | 1773 . .... . 1775 Figure 12: VIO format (uncompressed form) 1777 Option Type: 0x0E for SM-VIO, 0x0F for NSM-VIO (to be confirmed by 1778 IANA), see =Table 25 1780 Option Length: 8-bit unsigned integer, representing the length in 1781 octets of the option, not including the Option Type and Length 1782 fields, see section 6.7.1. of [RPL]; the Option Length is 1783 variable, depending on the number of Via Addresses and the 1784 compression applied. 1786 P-RouteID: 8-bit field that identifies a component of a Track or the 1787 Main DODAG as indicated by the TrackID field. The value of 0 is 1788 used to signal a Serial Track, i.e., made of a single segment/Leg. 1789 In an SM-VIO, the P-RouteID indicates an actual Segment. In an an 1790 NSM-VIO, it indicates a Leg, that is a serial subTrack that is 1791 added to the overall topology of the Track. 1793 Segment Sequence: 8-bit unsigned integer. The Segment Sequence 1794 obeys the operation in section 7.2 of [RPL] and the lollipop 1795 starts at 255. 1797 When the Root of the DODAG needs to refresh or update a Segment in 1798 a Track, it increments the Segment Sequence individually for that 1799 Segment. 1801 The Segment information indicated in the VIO deprecates any state 1802 for the Segment indicated by the P-RouteID within the indicated 1803 Track and sets up the new information. 1805 A VIO with a Segment Sequence that is not as fresh as the current 1806 one is ignored. 1808 A VIO for a given DODAGID with the same (TrackID, P-RouteID, 1809 Segment Sequence) indicates a retry; it MUST NOT change the 1810 Segment and MUST be propagated or answered as the first copy. 1812 Segment Lifetime: 8-bit unsigned integer. The length of time in 1813 Lifetime Units (obtained from the Configuration option) that the 1814 Segment is usable. 1816 The period starts when a new Segment Sequence is seen. The value 1817 of 255 (0xFF) represents infinity. The value of zero (0x00) 1818 indicates a loss of reachability. 1820 SRH-6LoRH head: The first 2 bytes of the (first) SRH-6LoRH as shown 1821 in Figure 6 of [RFC8138]. As an example, a 6LoRH Type of 4 means 1822 that the VIA Addresses are provided in full with no compression. 1824 Via Address: An IPv6 ULA or GUA of a node along the Segment. The 1825 VIO contains one or more IPv6 Via Addresses listed in the datapath 1826 order from Ingress to Egress. The list is expressed in a 1827 compressed form as signaled by the preceding SRH-6LoRH header. 1829 In a Storing Mode P-DAO that updates or removes a section of an 1830 already existing Segment, the list in the SM-VIO may represent 1831 only the section of the Segment that is being updated; at the 1832 extreme, the SM-VIO updates only one node, in which case it 1833 contains only one IPv6 address. In all other cases, the list in 1834 the VIO MUST be complete. 1836 In the case of an SM-VIO, the list indicates a sequential (strict) 1837 path through direct neighbors, the complete list starts at Ingress 1838 and ends at Egress, and the nodes listed in the VIO, including the 1839 Egress, MAY be considered as implicit Targets. 1841 In the case of an NSM-VIO, the complete list can be loose and 1842 excludes the Ingress node, starting at the first loose hop and 1843 ending at a Track Egress; the Track Egress MUST be considered as 1844 an implicit Target, so it MUST NOT be signaled in a RPL Target 1845 Option. 1847 5.4. Sibling Information Option 1849 The Sibling Information Option (SIO) provides indication on siblings 1850 that could be used by the Root to form P-Routes. One or more SIO(s) 1851 may be placed in the DAO messages that are sent to the Root in Non- 1852 Storing Mode. 1854 To advertise a neighbor node, the router MUST have an active Address 1855 Registration from that sibling using [RFC8505], for an address (ULA 1856 or GUA) that serves as identifier for the node. If this router also 1857 registers an address to that sibling, and the link has similar 1858 properties in both directions, only the router with the lowest 1859 Interface ID in its registered address needs report the SIO, and the 1860 Root will assume symmetry. 1862 The format of the SIO is as follows: 1864 0 1 2 3 1865 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 1866 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1867 | Type | Option Length |S| Flags |Comp.| Opaque | 1868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1869 | Step of Rank | Reserved | 1870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1871 | | 1872 + + 1873 . . 1874 . Sibling DODAGID (if the D flag not set) . 1875 . . 1876 + + 1877 | | 1878 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1879 | | 1880 + + 1881 . . 1882 . Sibling Address . 1883 . . 1884 + + 1885 | | 1886 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1888 Figure 13: Sibling Information Option Format 1890 Option Type: 0x10 for SIO (to be confirmed by IANA), see =Table 25 1892 Option Length: 8-bit unsigned integer, representing the length in 1893 octets of the option, not including the Option Type and Length 1894 fields, see section 6.7.1. of [RPL]. 1896 Reserved for Flags: MUST be set to zero by the sender and MUST be 1897 ignored by the receiver. 1899 S: 1-bit flag that is set to indicate that sibling belongs to the 1900 same DODAG. When not set, the Sibling DODAGID is indicated. 1902 Flags: Reserved. The Flags field MUST initialized to zero by the 1903 sender and MUST be ignored by the receiver 1905 Opaque: MAY be used to carry information that the node and the Root 1906 understand, e.g., a particular representation of the Link 1907 properties such as a proprietary Link Quality Information for 1908 packets received from the sibling. An industrial Alliance that 1909 uses RPL for a particular use / environment MAY redefine the use 1910 of this field to fit its needs. 1912 Compression Type: 3-bit unsigned integer. This is the SRH-6LoRH 1913 Type as defined in figure 7 in section 5.1 of [RFC8138] that 1914 corresponds to the compression used for the Sibling Address and 1915 its DODAGID if resent. The Compression reference is the Root of 1916 the Main DODAG. 1918 Step of Rank: 16-bit unsigned integer. This is the Step of Rank 1919 [RPL] as computed by the Objective Function between this node and 1920 the sibling. 1922 Reserved: The Reserved field MUST initialized to zero by the sender 1923 and MUST be ignored by the receiver 1925 Sibling DODAGID: 2 to 16 bytes, the DODAGID of the sibling in a 1926 [RFC8138] compressed form as indicated by the Compression Type 1927 field. This field is present if and only if the D flag is not 1928 set. 1930 Sibling Address: 2 to 16 bytes, an IPv6 Address of the sibling, with 1931 a scope that MUST be make it reachable from the Root, e.g., it 1932 cannot be a Link Local Address. The IPv6 address is encoded in 1933 the [RFC8138] compressed form indicated by the Compression Type 1934 field. 1936 An SIO MAY be immediately followed by a DAG Metric Container. In 1937 that case the DAG Metric Container provides additional metrics for 1938 the hop from the Sibling to this node. 1940 6. Root Initiated Routing State 1942 6.1. Requesting a Track 1944 This specification introduces the PDR message, used by an LLN node to 1945 request the formation of a new Track for which this node is Ingress. 1946 Note that the namespace for the TrackID is owned by the Ingress node, 1947 and in the absence of a PDR, there must be some procedure for the 1948 Root to assign TrackIDs in that namespace while avoiding collisions, 1949 more in Section 6.2. 1951 The PDR signals the desired TrackID and the duration for which the 1952 Track should be established. Upon a PDR, the Root MAY install the 1953 Track as requested, in which case it answers with a PDR-ACK 1954 indicating the granted Track Lifetime. All the Segments MUST be of a 1955 same mode, either Storing or Non-Storing. All the Segments MUST be 1956 created with the same TrackID and the same DODAGID signaled in the 1957 P-DAO. 1959 The Root designs the Track as it sees best, and updates / changes the 1960 Segments overtime to serve the Track as needed. There is no 1961 notification to the requesting node when those changes happen. The 1962 Segment Lifetime in the P-DAO messages does not need to be aligned to 1963 the Requested Lifetime in the PDR, or between P-DAO messages for 1964 different Segments. The Root may use shorter lifetimes for the 1965 Segments and renew them faster than the Track is, or longer lifetimes 1966 in which case it will need to tear down the Segments if the Track is 1967 not renewed. 1969 When the Track Lifetime that was returned in the PDR-ACK is close to 1970 elapse - vs. the trip time from the node to the Root, the requesting 1971 node SHOULD resend a PDR using the TrackID in the PDR-ACK to extend 1972 the lifetime of the Track, else the Track will time out and the Root 1973 will tear down the whole structure. 1975 If the Track fails and cannot be restored, the Root notifies the 1976 requesting node asynchronously with a PDR-ACK with a Track Lifetime 1977 of 0, indicating that the Track has failed, and a PDR-ACK Status 1978 indicating the reason of the fault. 1980 6.2. Identifying a Track 1982 RPL defines the concept of an Instance to signal an individual 1983 routing topology, and multiple topologies can coexist in the same 1984 network. The RPLInstanceID is tagged in the RPI of every packet to 1985 signal which topology the packet actually follows. 1987 This draft leverages the RPL Instance model as follows: 1989 * The Root MAY use P-DAO messages to add better routes in the main 1990 (Global) RPL Instance in conformance with the routing objectives 1991 in that Instance. 1993 To achieve this, the Root MAY install a Segment along a path down 1994 the main Non-Storing Mode DODAG. This enables a loose source 1995 routing and reduces the size of the Routing Header, see 1996 Section 3.3.1. The Root MAY also install a Track Leg across the 1997 Main DODAG to complement the routing topology. 1999 When adding a P-Route to the RPL Main DODAG, the Root MUST set the 2000 RPLInstanceID field of the P-DAO Base Object (see section 6.4.1. 2001 of [RPL]) to the RPLInstanceID of the Main DODAG, and MUST NOT use 2002 the DODAGID field. A P-Route provides a longer match to the 2003 Target Address than the default route via the Root, so it is 2004 preferred. 2006 * The Root MAY also use P-DAO messages to install a Track as an 2007 independent routing topology (say, Traffic Engineered) to achieve 2008 particular routing characteristics from an Ingress to an Egress 2009 Endpoints. To achieve this, the Root MUST set up a local RPL 2010 Instance (see section 5 of [RPL]), and the Local RPLInstanceID 2011 serves as TrackID. The TrackID MUST be unique for the IPv6 ULA or 2012 GUA of the Track Ingress that serves as DODAGID for the Track. 2014 This way, a Track is uniquely identified by the tuple (DODAGID, 2015 TrackID) where the TrackID is always represented with the D flag 2016 set to 0 (see also section 5.1. of [RPL]), indicating when used in 2017 an RPI that the source address of the IPv6 packet signals the 2018 DODAGID. 2020 The P-DAO Base Object MUST indicate the tuple (DODAGID, TrackID) 2021 that identifies the Track as shown in Figure 6, and the P-RouteID 2022 that identifies the P-Route MUST be signaled in the VIO as shown 2023 in Figure 12. 2025 The Track Ingress is the root of the DODAG ID formed by the local 2026 RPL Instance. It owns the namespace of its TrackIDs, so it can 2027 pick any unused value to request a new Track with a PDR. In a 2028 particular deployment where PDR are not used, the namespace can be 2029 delegated to the main Root, which can assign the TrackIDs for the 2030 Tracks it creates without collision. 2032 With this specification, the Root is aware of all the active 2033 Tracks, so it can also pick any unused value to form Tracks 2034 without a PDR. To avoid a collision of the Root and the Track 2035 Ingress picking the same value at the same time, it is RECOMMENDED 2036 that the Track Ingress starts allocating the ID value of the Local 2037 RPLInstanceID (see section 5.1. of [RPL]) used as TrackIDs with 2038 the value 0 incrementing, while the Root starts with 63 2039 decrementing. 2041 6.3. Installing a Track 2043 A Serial Track can be installed by a single P-Route that signals the 2044 sequence of consecutive nodes, either in Storing Mode as a single- 2045 Segment Track, or in Non-Storing Mode as a single-Leg Track. A 2046 single-Leg Track can be installed as a loose Non-Storing Mode 2047 P-Route, in which case the next loose entry must recursively be 2048 reached over a Serial Track. 2050 A Complex Track can be installed as a collection of P-Routes with the 2051 same DODAGID and Track ID. The Ingress of a Non-Storing Mode P-Route 2052 is the owner and Root of the DODAGID. The Ingress of a Storing Mode 2053 P-Route must be either the owner of the DODAGID, or a hop of a Leg of 2054 the same Track. In the latter case, the Targets of the P-Route must 2055 include the next hop of the Leg if there is one, to ensure forwarding 2056 continuity. In the case of a Complex Track, each Segment is 2057 maintained independently and asynchronously by the Root, with its own 2058 lifetime that may be shorter, the same, or longer than that of the 2059 Track. 2061 A route along a Track for which the TrackID is not the RPLInstanceID 2062 of the Main DODAG MUST be installed with a higher precedence than the 2063 routes along the Main DODAG, meaning that: 2065 * Longest match MUST be the prime comparison for routing. 2067 * In case of equal length match, the route along the Track MUST be 2068 preferred vs. the one along the Main DODAG. 2070 * There SHOULD NOT be 2 different Tracks leading to the same Target 2071 from same Ingress node, unless there's a policy for selecting 2072 which packets use which Track; such policy is out of scope. 2074 * A packet that was routed along a Track MUST NOT be routed along 2075 the main DODAG again; if the destination is not reachable as a 2076 neighbor by the node where the packet exits the Track then the 2077 packet MUST be dropped. 2079 6.3.1. Signaling a Projected Route 2081 This draft adds a capability whereby the Root of a main RPL DODAG 2082 installs a Track as a collection of P-Routes, using a Projected-DAO 2083 (P-DAO) message for each individual Track Leg or Segment. The P-DAO 2084 signals a collection of Targets in the RPL Target Option(s) (RTO). 2085 Those Targets can be reached via a sequence of routers indicated in a 2086 VIO. 2088 Like a classical DAO message, a P-DAO causes a change of state only 2089 if it is "new" per section 9.2.2. "Generation of DAO Messages" of 2090 the RPL specification [RPL]; this is determined using the Segment 2091 Sequence information from the VIO as opposed to the Path Sequence 2092 from a TIO. Also, a Segment Lifetime of 0 in a VIO indicates that 2093 the P-Route associated to the Segment is to be removed. There are 2094 two Modes of operation for the P-Routes, the Storing and the Non- 2095 Storing Modes. 2097 A P-DAO message MUST be sent from the address of the Root that serves 2098 as DODAGID for the Main DODAG. It MUST contain either exactly one 2099 sequence of one or more RTOs followed one VIO, or any number of 2100 sequences of one or more RTOs followed by one or more TIOs. The 2101 former is the normal expression for this specification, where as the 2102 latter corresponds to the variation for lesser constrained 2103 environments described in Section 7.2. 2105 A P-DAO that creates or updates a Track Leg MUST be sent to a GUA or 2106 a ULA of the Ingress of the Leg; it must contain the full list of 2107 hops in the Leg unless the Leg is being removed. A P-DAO that 2108 creates a new Track Segment MUST be sent to a GUA or a ULA of the 2109 Segment Egress and MUST signal the full list of hops in Segment; a 2110 P-DAO that updates (including deletes) a section of a Segment MUST be 2111 sent to the first node after the modified Segment and signal the full 2112 list of hops in the section starting at the node that immediately 2113 precedes the modified section. 2115 In Non-Storing Mode, as discussed in Section 6.3.3, the Root sends 2116 the P-DAO to the Track Ingress where the source-routing state is 2117 applied, whereas in Storing Mode, the P-DAO is sent to the last node 2118 on the installed path and forwarded in the reverse direction, 2119 installing a Storing Mode state at each hop, as discussed in 2120 Section 6.3.2. In both cases the Track Ingress is the owner of the 2121 Track, and it generates the P-DAO-ACK when the installation is 2122 successful. 2124 If the 'K' Flag is present in the P-DAO, the P-DAO must be 2125 acknowledged using a DAO-ACK that is sent back to the address of the 2126 Root from which the P-DAO was received. In most cases, the first 2127 node of the Leg, Segment, or updated section of the Segment is the 2128 node that sends the acknowledgment. The exception to the rule is 2129 when an intermediate node in a Segment fails to forward a Storing 2130 Mode P-DAO to the previous node in the SM-VIO. 2132 In a No-Path Non-Storing Mode P-DAO, the SRH-6LoRH MUST NOT be 2133 present in the NSM-VIO; the state in the Ingress is erased 2134 regardless. In all other cases, a VIO MUST contain at least one Via 2135 Address, and a Via Address MUST NOT be present more than once, which 2136 would create a loop. 2138 A node that processes a VIO MAY verify whether one of these 2139 conditions happen, and when so, it MUST ignore the P-DAO and reject 2140 it with a RPL Rejection Status of "Error in VIO" in the DAO-ACK, see 2141 Section 10.14. 2143 Other errors than those discussed explicitely that prevent the 2144 installing the route are acknowledged with a RPL Rejection Status of 2145 "Unqualified Rejection" in the DAO-ACK. 2147 6.3.2. Installing a Track Segment with a Storing Mode P-Route 2149 As illustrated in Figure 14, a Storing Mode P-DAO installs a route 2150 along the Segment signaled by the SM-VIO towards the Targets 2151 indicated in the Target Options. The Segment is to be included in a 2152 DODAG indicated by the P-DAO Base Object, that may be the one formed 2153 by the RPL Main DODAG, or a Track associated with a local RPL 2154 Instance. 2156 ------+--------- 2157 | Internet 2158 | 2159 +-----+ 2160 | | Border router 2161 | | (RPL Root) 2162 +-----+ | ^ | 2163 | | DAO | ACK | 2164 o o o o | | | 2165 o o o o o o o o o | ^ | Projected . 2166 o o o o o o o o o o | | DAO | Route . 2167 o o o o o o o o o | ^ | . 2168 o o o o o o o o v | DAO v . 2169 o o LLN o o o | 2170 o o o o o Loose Source Route Path | 2171 o o o o v 2173 Figure 14: Projecting a route 2175 In order to install the relevant routing state along the Segment , 2176 the Root sends a unicast P-DAO message to the Track Egress router of 2177 the routing Segment that is being installed. The P-DAO message 2178 contains a SM-VIO with the strict sequence of Via Addresses. The SM- 2179 VIO follows one or more RTOs indicating the Targets to which the 2180 Track leads. The SM-VIO contains a Segment Lifetime for which the 2181 state is to be maintained. 2183 The Root sends the P-DAO directly to the Egress node of the Segment. 2184 In that P-DAO, the destination IP address matches the last Via 2185 Address in the SM-VIO. This is how the Egress recognizes its role. 2186 In a similar fashion, the Segment Ingress node recognizes its role as 2187 it matches first Via Address in the SM-VIO. 2189 The Egress node of the Segment is the only node in the path that does 2190 not install a route in response to the P-DAO; it is expected to be 2191 already able to route to the Target(s) based on its existing tables. 2192 If one of the Targets is not known, the node MUST answer to the Root 2193 with a DAO-ACK listing the unreachable Target(s) in an RTO and a 2194 rejection status of "Unreachable Target". 2196 If the Egress node can reach all the Targets, then it forwards the 2197 P-DAO with unchanged content to its predecessor in the Segment as 2198 indicated in the list of Via Information options, and recursively the 2199 message is propagated unchanged along the sequence of routers 2200 indicated in the P-DAO, but in the reverse order, from Egress to 2201 Ingress. 2203 The address of the predecessor to be used as destination of the 2204 propagated DAO message is found in the Via Address the precedes the 2205 one that contain the address of the propagating node, which is used 2206 as source of the message. 2208 Upon receiving a propagated DAO, all except the Egress router MUST 2209 install a route towards the DAO Target(s) via their successor in the 2210 SM-VIO. A router that cannot store the routes to all the Targets in 2211 a P-DAO MUST reject the P-DAO by sending a DAO-ACK to the Root with a 2212 Rejection Status of "Out of Resources" as opposed to forwarding the 2213 DAO to its predecessor in the list. The router MAY install 2214 additional routes towards the VIA Addresses that are the SM-VIO after 2215 self, if any, but in case of a conflict or a lack of resource, the 2216 route(s) to the Target(s) are the ones that must be installed in 2217 priority. 2219 If a router cannot reach its predecessor in the SM-VIO, the router 2220 MUST send the DAO-ACK to the Root with a Rejection Status of 2221 "Predecessor Unreachable". 2223 The process continues till the P-DAO is propagated to Ingress router 2224 of the Segment, which answers with a DAO-ACK to the Root. The Root 2225 always expects a DAO-ACK, either from the Track Ingress with a 2226 positive status or from any node along the segment with a negative 2227 status. If the DAO-ACK is not received, the Root may retry the DAO 2228 with the same TID, or tear down the route. 2230 6.3.3. Installing a Track Leg with a Non-Storing Mode P-Route 2232 As illustrated in Figure 15, a Non-Storing Mode P-DAO installs a 2233 source-routed path within the Track indicated by the P-DAO Base 2234 Object, towards the Targets indicated in the Target Options. The 2235 source-routed path requires a Source-Routing header which implies an 2236 IP-in-IP encapsulation to add the SRH to an existing packet. It is 2237 sent to the Track Ingress which creates a tunnel associated with the 2238 Track, and connected routes over the tunnel to the Targets in the 2239 RTO. The tunnel encapsulation MUST incorporate a routing header via 2240 the list addresses listed in the VIO in the same order. The content 2241 of the NSM-VIO starting at the first SRH-6LoRH header MUST be used 2242 verbatim by the Track Ingress when it encapsulates a packet to 2243 forward it over the Track. 2245 ------+--------- 2246 | Internet 2247 | 2248 +-----+ 2249 | | Border router 2250 | | (RPL Root) 2251 +-----+ | P ^ ACK 2252 | Track | DAO | 2253 o o o o Ingress X V | X 2254 o o o o o o o X o X Source 2255 o o o o o o o o X o o X Routed 2256 o o ° o o o o X o X Segment 2257 o o o o o o o o X Egress X 2258 o o o o o | 2259 Target 2260 o o LLN o o 2261 o o o o 2263 Figure 15: Projecting a Non-Storing Route 2265 The next entry in the source-routed path must be either a neighbor of 2266 the previous entry, or reachable as a Target via another P-Route, 2267 either Storing or Non-Storing, which implies that the nested P-Route 2268 has to be installed before the loose sequence is, and that P-Routes 2269 must be installed from the last to the first along the datapath. For 2270 instance, a Segment of a Track must be installed before the Leg(s) of 2271 the same Track that use it, and stitched Segments must be installed 2272 in order from the last that reaches to the Targets to the first. 2274 If the next entry in the loose sequence is reachable over a Storing 2275 Mode P-Route, it MUST be the Target of a Segment and the Ingress of a 2276 next segment, both already setup; the segments are associated with 2277 the same Track, which avoids the need of an additional encapsulation. 2278 For instance, in Section 3.5.1.3, Segments A==>B-to-C and 2279 C==>D==>E-to-F must be installed with Storing Mode P-DAO messages 1 2280 and 2 before the Track A-->C-->E-to-F that joins them can be 2281 installed with Non-Storing Mode P-DAO 3. 2283 Conversely, if it is reachable over a Non-Storing Mode P-Route, the 2284 next loose source-routed hop of the inner Track is a Target of a 2285 previously installed Track and the Ingress of a next Track, which 2286 requires a de- and a re-encapsulation when switching the outer Tracks 2287 that join the loose hops. This is examplified in Section 3.5.2.3 2288 where Non-Storing Mode P-DAO 1 and 2 install strict Tracks that Non- 2289 Storing Mode P-DAO 3 joins as a super Track. In such a case, packets 2290 are subject to double IP-in-IP encapsulation. 2292 6.4. Tearing Down a P-Route 2294 A P-DAO with a lifetime of 0 is interpreted as a No-Path DAO and 2295 results in cleaning up existing state as opposed to refreshing an 2296 existing one or installing a new one. To tear down a Track, the Root 2297 must tear down all the Track Segments and Legs that compose it one by 2298 one. 2300 Since the state about a Leg of a Track is located only the Ingress 2301 Node, the Root cleans up the Leg by sending an NSM-VIO to the Ingress 2302 indicating the TrackID and the P-RouteID of the Leg being removed, a 2303 Segment Lifetime of 0 and a newer Segment Sequence. The SRH-6LoRH 2304 with the Via Addresses in the NSM-VIO are not needed and MUST be 2305 omitted. Upon that NSM-VIO, the Ingress node removes all state for 2306 that Track if any, and replies positively anyway. 2308 The Root cleans up a section of a Segment by sending an SM-VIO to the 2309 last node of the Segment, with the TrackID and the P-RouteID of the 2310 Segment being updated, a Segment Lifetime of zero (0) and a newer 2311 Segment Sequence. The Via Addresses in the SM-VIO indicates the 2312 section of the Segment being modified, from the first to the last 2313 node that is impacted. This can be the whole Segment if it is 2314 totally removed, or a sequence of one or more nodes that have been 2315 bypassed by a Segment update. 2317 The No-Path P-DAO is forwarded normally along the reverse list, even 2318 if the intermediate node does not find a Segment state to clean up. 2319 This results in cleaning up the existing Segment state if any, as 2320 opposed to refreshing an existing one or installing a new one. 2322 6.5. Maintaining a Track 2324 Repathing a Track Segment or Leg may cause jitter and packet 2325 misordering. For critical flows that require timely and/or in-order 2326 delivery, it might be necessary to deploy the PAREO functions 2327 [RAW-ARCHI] over a highly redundant Track. This specification allows 2328 to use more than one Leg for a Track, and 1+N packet redundancy. 2330 This section provides the steps to ensure that no packet is lost due 2331 to the operation itself. This is ensured by installing the new 2332 section from its last node to the first, so when an intermediate node 2333 installs a route along the new section, all the downstream nodes in 2334 the section have already installed their own. The disabled section 2335 is removed when the packets in-flight are forwarded along the new 2336 section as well. 2338 6.5.1. Maintaining a Track Segment 2340 To modify a section of a Segment between a first node and a second, 2341 downstream node (which can be the Ingress and Egress), while 2342 conserving those nodes in the Segment, the Root sends an SM-VIO to 2343 the second node indicating the sequence of nodes in the new section 2344 of the Segment. The SM-VIO indicates the TrackID and the P-RouteID 2345 of the Segment being updated, and a newer Segment Sequence. The 2346 P-DAO is propagated from the second to the first node and on the way, 2347 it updates the state on the nodes that are common to the old and the 2348 new section of the Segment and creates a state in the new nodes. 2350 When the state is updated in an intermediate node, that node might 2351 still receive packets that were in flight from the Ingress to self 2352 over the old section of the Segment. Since the remainder of the 2353 Segment is already updated, the packets are forwarded along the new 2354 version of the Segment from that node on. 2356 After a reasonable time to enable the deprecated sections to empty, 2357 the root tears down the remaining section(s) of the old segments are 2358 teared down as described in Section 6.4. 2360 6.5.2. Maintaining a Track Leg 2362 This specification allows to add Legs to a Track by sending a Non- 2363 Storing Mode P-DAO to the Ingress associated to the same TrackID, and 2364 a new Segment ID. If the Leg is loose, then the Segments that join 2365 the hops must be created first. It makes sense to add a new Leg 2366 before removing one that is misbehaving, and switch to the new Leg 2367 before removing the old. 2369 It is also possible to update a Track Leg by sending a Non-Storing 2370 Mode P-DAO to the Ingress with the same Segment ID, an incremented 2371 Segment Sequence, and the new complete listy of hops in the NSM-VIO. 2372 Updating a live Leg means changing one or more of the intermediate 2373 loose hops, and involves laying out new Segments from and to the new 2374 loose hops before the NSM-VIO for the new Leg is issued. 2376 Packets that are in flight over the old version of the Track Leg 2377 still follow the old source route path over the old Segments. After 2378 a reasonable time to enable the deprecated Segments to empty, the 2379 root tears down those Segments as described in Section 6.4. 2381 6.6. Encapsulating and Forwarding Along a Track 2383 When forwarding a packet to a destination for which a router 2384 determines that routing happens via a Track for which it is Ingress, 2385 the router must encapsulated the packet using IP-in-IP to add the 2386 Source Routing Header with the final destination set to the Track 2387 Egress. Though fragmentation is possible in a 6LoWPAN LLN, e.g., 2388 using [6LoWPAN], [RFC8930], and/or [RFC8931], it is RECOMMENDED to 2389 allow an MTU that is larger than 1280 in the main DODAG and allows 2390 for the additional headers while exposing only 1280 to the 6LoWPAN 2391 Nodes as indicated by section 4 of [6LoWPAN]. 2393 All properties of a Track operations are inherited form the main RPL 2394 Instance that is used to install the Track. For instance, the use of 2395 compression per [RFC8138] is determined by whether it is used in the 2396 RPL Main DODAG, e.g., by setting the "T" flag [TURN-ON_RFC8138] in 2397 the RPL configuration option. 2399 The Track Ingress that places a packet in a Track encapsulates it 2400 with an IP-in-IP header, a Routing Header, and an IPv6 Hop-by-Hop 2401 Option Header that contains the RPL Packet Information (RPI) as 2402 follows: 2404 * In the uncompressed form the source of the packet is the address 2405 that this router uses as DODAGID for the Track, the destination is 2406 the first Via Address in the NSM-VIO, and the RH is a Source 2407 Routing Header (SRH) [RFC6554] that contains the list of the 2408 remaining Via Addresses terminating by the Track Egress. 2410 * The preferred alternate in a network where 6LoWPAN Header 2411 Compression [RFC6282] is used is to leverage "IPv6 over Low-Power 2412 Wireless Personal Area Network (6LoWPAN) Paging Dispatch" 2413 [RFC8025] to compress the RPL artifacts as indicated in [RFC8138]. 2415 In that case, the source routed header is the exact copy of the 2416 (chain of) SRH-6LoRH found in the NSM-VIO, also terminating by the 2417 Track Egress. The RPI-6LoRH is appended next, followed by an IP- 2418 in-IP 6LoRH Header that indicates the Ingress router in the 2419 Encapsulator Address field, see as a similar case Figure 20 of 2420 [TURN-ON_RFC8138]. 2422 To signal the Track in the packet, this specification leverages the 2423 RPL Forwarding model follows: 2425 * In the data packets, the Track DODAGID and the TrackID MUST be 2426 respectively signaled as the IPv6 Source Address and the 2427 RPLInstanceID field of the RPI that MUST be placed in the outer 2428 chain of IPv6 Headers. 2430 The RPI carries a local RPLInstanceID called the TrackID, which, 2431 in association with the DODAGID, indicates the Track along which 2432 the packet is forwarded. 2434 The D flag in the RPLInstanceID MUST be set to 0 to indicate that 2435 the source address in the IPv6 header is set ot the DODAGID, more 2436 in Section 6.2. 2438 * This draft conforms to the principles of [RFC9008] with regards to 2439 packet forwarding and encapsulation along a Track, as follows: 2441 - With this draft, the Track is a RPL DODAG. From the 2442 perspective of that DODAG, the Track Ingress is the Root, the 2443 Track Egress is a RPL-Aware 6LR, and neighbors of the Track 2444 Egress that can be reached via the Track, but are external to 2445 it, are external destinations and treated as RPL-Unaware Leaves 2446 (RULs). The encapsulation rules in [RFC9008] apply. 2448 - If the Track Ingress is the originator of the packet and the 2449 Track Egress is the destination of the packet, there is no need 2450 for an encapsulation. 2452 - So the Track Ingress must encapsulate the traffic that it did 2453 not originate, and add an RPI. 2455 A packet that is being routed over the RPL Instance associated to 2456 a first Non-Storing Mode Track MAY be placed (encapsulated) in a 2457 second Track to cover one loose hop of the first Track as 2458 discussed in more details Section 3.5.2.3. On the other hand, a 2459 Storing Mode Track must be strict and a packet that it placed in a 2460 Storing Mode Track MUST follow that Track till the Track Egress. 2462 The forwarding of a packet along a track will fail if the Track 2463 continuity is broken,e.g.: 2465 * In the case of a strict path along a Segment, if the next strict 2466 hop is not reachable, the packet is dropped. 2468 * In the case of a loose source-routed path, when the loose next hop 2469 is not a neighbor, there must be a Segment of the same Track to 2470 that loose next hop. When that is the case the packet is 2471 forwarded to the next hop along that segment, or a common neighbor 2472 with the loose next hop, on which case the packet is forwarded to 2473 that neighbor, or another Track to the loose next hop for which 2474 this node or a neighbor is Ingress; in the last case, another 2475 encapsulation takes place and the process possibly recurses; 2476 otherwise the packet is dropped. 2478 * When a Track Egress extracts a packet from a Track (decapsulates 2479 the packet), the destination of the inner packet must be either 2480 this node or a direct neighbor, or a Target of another Segment of 2481 the same Track for which this node is Ingress, otherwise the 2482 packet MUST be dropped. 2484 In case of a failure forwarding a packet along a Segment, e.g., the 2485 next hop is unreachable, the node that discovers the fault MUST send 2486 an ICMPv6 Error message [RFC4443] to the Root, with a new Code "Error 2487 in P-Route" (See Section 10.13). The Root can then repair by 2488 updating the broken Segment and/or Tracks, and in the case of a 2489 broken Segment, remove the leftover sections of the segment using SM- 2490 VIOs with a lifetime of 0 indicating the section ot one or more nodes 2491 being removed (See Section 6.5). 2493 In case of a permanent forwarding error along a Source Route path, 2494 the node that fails to forward SHOULD send an ICMP error with a code 2495 "Error in Source Routing Header" back to the source of the packet, as 2496 described in section 11.2.2.3. of [RPL]. Upon this message, the 2497 encapsulating node SHOULD stop using the source route path for a 2498 reasonable period of time which duration depends on the deployment, 2499 and it SHOULD send an ICMP message with a Code "Error in P-Route" to 2500 the Root. Failure to follow these steps may result in packet loss 2501 and wasted resources along the source route path that is broken. 2503 Either way, the ICMP message MUST be throttled in case of consecutive 2504 occurrences. It MUST be sourced at the ULA or a GUA that is used in 2505 this Track for the source node, so the Root can establish where the 2506 error happened. 2508 The portion of the invoking packet that is sent back in the ICMP 2509 message SHOULD record at least up to the RH if one is present, and 2510 this hop of the RH SHOULD be consumed by this node so that the 2511 destination in the IPv6 header is the next hop that this node could 2512 not reach. if a 6LoWPAN Routing Header (6LoRH) [RFC8138] is used to 2513 carry the IPv6 routing information in the outer header then that 2514 whole 6LoRH information SHOULD be present in the ICMP message. 2516 6.7. Compression of the RPL Artifacts 2518 When using [RFC8138] in the Main DODAG operated in Non-Storing Mode 2519 in a 6LoWPAN LLN, a typical packet that circulates in the Main DODAG 2520 is formatted as shown in Figure 16, representing the case where : 2522 +-+ ... -+- ... -+- ... -+-+- ... +-+-+-+ ... +-+-+ ... -+ ... +-... 2523 |11110001| SRH- | RPI- | IP-in-IP | NH=1 |11110CPP| UDP | UDP 2524 | Page 1 | 6LoRH | 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 2525 +-+ ... -+- ... -+- ... -+-+- ... +-+-+-+ ... +-+-+ ... -+ ... +-... 2526 <= RFC 6282 => 2527 <================ Inner packet ==================== = = 2529 Figure 16: A Packet as Forwarded along the Main DODAG 2531 Since there is no page switch between the encapsulated packet and the 2532 encapsulation, the first octet of the compressed packet that acts as 2533 page selector is actually removed at encapsulation, so the inner 2534 packet used in the descriptions below start with the SRH-6LoRH, and 2535 is verbatim the packet represented in Figure 16 from the second octet 2536 on. 2538 When encapsulating that inner packet to place it in the Track, the 2539 first header that the Ingress appends at the head of the inner packet 2540 is an IP-in-IP 6LoRH Header; in that header, the encapsulator 2541 address, which maps to the IPv6 source address in the uncompressed 2542 form, contains a GUA or ULA IPv6 address of the Ingress node that 2543 serves as DODAG ID for the Track, expressed in the compressed form 2544 and using the DODAGID of the Main DODAG as compression reference. If 2545 the address is compressed to 2 bytes, the resulting value for the 2546 Length field shown in Figure 17 is 3, meaning that the SRH-6LoRH as a 2547 whole is 5-octets long. 2549 0 1 2 2550 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 2551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 2552 |1|0|1| Length | 6LoRH Type 6 | Hop Limit | Track DODAGID | 2553 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 2555 Figure 17: The IP-in-IP 6LoRH Header 2557 At the head of the resulting sequence of bytes, the track Ingress 2558 then adds the RPI that carries the TrackID as RPLinstanceID as a P- 2559 RPI-6LoRH Header, as illustrated in Figure 8, using the TrackID as 2560 RPLInstanceID. Combined with the IP-in-IP 6LoRH Header, this allows 2561 to identify the Track without ambiguity. 2563 The SRH-6LoRH is then added at the head of the resulting sequence of 2564 bytes as a verbatim copy of the content of the SR-VIO that signaled 2565 the selected Track Leg. 2567 0 1 2568 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 .. .. .. 2569 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+- -+ ... +- -+ 2570 |1|0|0| Size |6LoRH Type 0..4| Hop1 | Hop2 | | HopN | 2571 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+- -+ ... +- -+ 2572 Where N = Size + 1 2574 Figure 18: The SRH 6LoRH Header 2576 The format of the resulting encapsulated packet in [RFC8138] 2577 compressed form is illustrated in Figure 19: 2579 +-+ ... -+-+-+- ... -+-+-+- ... -+-+-+-+-+- ... +-+-+-+-+-+-+- ... 2580 | Page 1 | SRH-6LoRH | P-RPI-6LoRH | IP-in-IP 6LoRH | Inner Packet 2581 +-+ ... -+-+-+- ... -+-+-+- ... -+-+-+-+-+- ... +-+-+-+-+-+-+- ... 2583 Signals : Loose Hops : TrackID : Track DODAGID : 2585 Figure 19: A Packet as Forwarded along a Track 2587 7. Lesser Constrained Variations 2589 7.1. Storing Mode Main DODAG 2591 This specification expects that the Main DODAG is operated in Non- 2592 Storing Mode. The reasons for that limitation are mostly related to 2593 LLN operations, power and spectrum conservation: 2595 * In Non-Storing Mode The Root already possesses the DODAG topology, 2596 so the additional topological information is reduced to the 2597 siblings. 2599 * The downwards routes are updated with unicast messages to the 2600 Root, which ensures that the Root can reach back to the LLN nodes 2601 after a repair faster than in the case of Storing Mode. Also the 2602 Root can control the use of the path diversity in the DODAG to 2603 reach to the LLN nodes. For both reasons, Non-Storing Mode 2604 provides better capabilities for the Root to maintain the 2605 P-Routes. 2607 * When the Main DODAG is operated in Non-Storing Mode, P-Routes 2608 enable loose Source Routing, which is only an advantage in that 2609 mode. Storing Mode does not use Source Routing Headers, and does 2610 not derive the same benefits from this capability. 2612 On the other hand, since RPL is a Layer-3 routing protocol, its 2613 applicability extends beyond LLNs to a generic IP network. RPL 2614 requires fewer resources than alternative IGPs like OSPF, ISIS, 2615 EIGRP, BABEL or RIP at the expense of a route stretch vs. the 2616 shortest path routes to a destination that those protocols compute. 2617 P-Routes add the capability to install shortest and/or constrained 2618 routes to special destinations such as discussed in section A.9.4. of 2619 the ANIMA ACP [RFC8994]. 2621 In a powered and wired network, when enough memory to store the 2622 needed routes is available, the RPL Storing Mode proposes a better 2623 trade-off than the Non-Storing, as it reduces the route stretch and 2624 lowers the load on the Root. In that case, the control path between 2625 the Root and the LLN nodes is highly available compared to LLNs, and 2626 the nodes can be reached to maintain the P-Routes at most times. 2628 This section specifies the additions that are needed to support 2629 Projected Routes when the Main DODAG is operated in Storing Mode. As 2630 long as the RPI can be processed adequately by the dataplane, the 2631 changes to this specification are limited to the DAO message. The 2632 Track structure, routes and forwarding operations remain the same. 2634 In Storing Mode, the Root misses the Child to Parent relationship 2635 that forms the Main DODAG, as well as the sibling information. To 2636 provide that knowledge the nodes in the network MUST send additional 2637 DAO messages that are unicast to the Root as Non-Storing DAO messages 2638 are. 2640 In the DAO message, the originating router advertises a set of 2641 neighbor nodes using Sibling Information Options (SIO)s, regardless 2642 of the relative position in the DODAG of the advertised node vs. this 2643 router. 2645 The DAO message MUST be formed as follows: 2647 * The originating router is identified by the source address of the 2648 DAO. That address MUST be the one that this router registers to 2649 neighbor routers so the Root can correlate the DAOs from those 2650 routers when they advertise this router as their neighbor. The 2651 DAO contains one or more sequences of one Transit Information 2652 Option and one or more Sibling Information Options. There is no 2653 RPL Target Option so the Root is not confused into adding a 2654 Storing Mode route to the Target. 2656 * The TIO is formed as in Storing Mode, and the Parent Address is 2657 not present. The Path Sequence and Path Lifetime fields are 2658 aligned with the values used in the Address Registration of the 2659 node(s) advertised in the SIO, as explained in Section 9.1. of 2660 [RFC9010]. Having similar values in all nodes allows to factorise 2661 the TIO for multiple SIOs as done with [RPL]. 2663 * The TIO is followed by one or more SIOs that provide an address 2664 (ULA or GUA) of the advertised neighbor node. 2666 But the RPL routing information headers may not be supported on all 2667 type of routed network infrastructures, especially not in high-speed 2668 routers. When the RPI is not be supported in the dataplane, there 2669 cannot be local RPL Instances and RPL can only operate as a single 2670 topology (the Main DODAG). The RPL Instance is that of the Main 2671 DODAG and the Ingress node that encapsulates is not the Root. The 2672 routes along the Tracks are alternate routes to those available along 2673 the Main DODAG. They MAY conflict with routes to children and MUST 2674 take precedence in the routing table. The Targets MUST be adjacent 2675 to the Track Egress to avoid loops that may form if the packet is 2676 reinjected in the Main DODAG. 2678 7.2. A Track as a Full DODAG 2680 This specification builds parallel or crossing Track Legs as opposed 2681 to a more complex DODAG with interconnections at any place desirable. 2682 The reason for that limitation is related to constrained node 2683 operations, and capability to store large amount of topological 2684 information and compute complex paths: 2686 * With this specification, the node in the LLN has no topological 2687 awareness, and does not need to maintain dynamic information about 2688 the link quality and availability. 2690 * The Root has a complete topological information and statistical 2691 metrics that allow it or its PCE to perform a global optimization 2692 of all Tracks in its DODAG. Based on that information, the Root 2693 computes the Track Leg and predigest the source route paths. 2695 * The node merely selects one of the proposed paths and applies the 2696 associated pre-computed routing header in the encapsulation. This 2697 alleviates both the complexity of computing a path and the 2698 compressed form of the routing header. 2700 The "Reliable and Available Wireless (RAW) Architecture/Framework" 2701 [RAW-ARCHI] actually expects the PSE at the Track Ingress to react to 2702 changes in the forwarding conditions along the Track, and reroute 2703 packets to maintain the required degree of reliability. To achieve 2704 this, the PSE need the full richness of a DODAG to form any path that 2705 could make meet the Service Level Objective (SLO). 2707 This section specifies the additions that are needed to turn the 2708 Track into a full DODAG and enable the main Root to provide the 2709 necessary topological information to the Track Ingress. The 2710 expectation is that the metrics that the PSE uses are of an order 2711 other than that of the PCE, because of the difference of time scale 2712 between routing and forwarding, mor e in [RAW-ARCHI]. It follows 2713 that the PSE will learn the metrics it needs from an alternate 2714 source, e.g., OAM frames. 2716 To pass the topological information to the Ingress, the Root uses a 2717 P-DAO messages that contains sequences of Target and Transit 2718 Information options that collectively represent the Track, expressed 2719 in the same fashion as in classical Non-Storing Mode. The difference 2720 as that the Root is the source as opposed to the destination, and can 2721 report information on many Targets, possibly the full Track, with one 2722 P-DAO. 2724 Note that the Path Sequence and Lifetime in the TIO are selected by 2725 the Root, and that the Target/Transit information tupples in the 2726 P-DAO are not those received by the Root in the DAO messages about 2727 the said Targets. The Track may follow sibling routes and does not 2728 need to be congruent with the Main DODAG. 2730 8. Profiles 2732 This document provides a set of tools that may or may not be needed 2733 by an implementation depending on the type of application it serves. 2734 This sections described profiles that can be implemented separately 2735 and can be used to discriminate what an implementation can and cannot 2736 do. This section describes profiles that enable to implement only a 2737 portion of this specification to meet a particular use case. 2739 Profiles 0 to 2 operate in the Main RPL Instance and do not require 2740 the support of local RPL Instances or the indication of the RPL 2741 Instance in the data plane. Profile 3 and above leverage Local RPL 2742 Instances to build arbitrary Tracks rooted at the Track Ingress and 2743 using its namespace for TrackID. 2745 Profiles 0 and 1 are REQUIRED by all implementations that may be used 2746 in LLNs; this enables to use Storing Mode to reduce the size of the 2747 Source Route Header in the most common LLN deployments. Profile 2 is 2748 RECOMMENDED in high speed / wired environment to enable traffic 2749 Engineering and network automation. All the other profile / 2750 environment combinations are OPTIONAL. 2752 Profile 0 Profile 0 is the Legacy support of [RPL] Non-Storing Mode, 2753 with default routing Northwards (up) and strict source routing 2754 Southwards (down the main DOAG). It provides the minimal common 2755 functionality that must be implemented as a prerequisite to all 2756 the Track-supporting profiles. The other Profiles extend Profile 2757 0 with selected capabilities that this specification introduces on 2758 top. 2760 Profile 1 (Storing Mode P-Route Segments along the Main DODAG) Profi 2761 le 1 does not create new paths; compared to Profile 0, it combines 2762 Storing and Non-Storing Modes to balance the size of the Routing 2763 Header in the packet and the amount of state in the intermediate 2764 routers in a Non-Storing Mode RPL DODAG. 2766 Profile 2 (Non-Storing Mode P-Route Segments along the Main DODAG) P 2767 rofile 2 extends Profile 0 with Strict Source-Routing Non-Storing 2768 Mode P-Routes along the Main DODAG, which is the same as Profile 1 2769 but using NSM VIOs as opposed to SM VIOs. Profile 2 provides the 2770 same capability to compress the SRH in packets down the Main DODAG 2771 as Profile 1, but it require an encapsulation, in order to insert 2772 an additional SRH between the loose source routing hops. In that 2773 case, the Tracks MUST be installed as subTracks of the Main DODAG, 2774 the main RPL Instance MUST be used as TrackID, and the Ingress 2775 node that encapsulates is not the Root as it does not own the 2776 DODAGID. 2778 Profile 3 In order to form the best path possible, those Profiles 2779 require the support of Sibling Information Option to inform the 2780 Root of additional possible hops. Profile 3 extends Profile 1 2781 with additional Storing Mode P-Routes that install segments that 2782 do not follow the Main DODAG. If the Segment Ingress (in the SM- 2783 VIO) is the same as the IPv6 Address of the Track Ingress (in the 2784 projected DAO base Object), the P-DAO creates an implicit Track 2785 between the Segment Ingress and the Segment Egress. 2787 Profile 4 Profile 4 extends Profile 2 with Strict Source-Routing 2788 Non-Storing Mode P-Routes to form East-West Tracks that are inside 2789 the Main DODAG but do not necessarily follow it. A Track is 2790 formed as one or more strict source source routed paths between 2791 the Root that is the Track Ingress, and the Track Egress that is 2792 the last node. 2794 Profile 5 Profile 5 Combines Profile 4 with Profile 1 and enables to 2795 loose source routing between the Ingress and the Egress of the 2796 Track. As in Profile 1, Storing Mode P-Routes connect the dots in 2797 the loose source route. 2799 Profile 6 Profile 6 Combines Profile 4 with Profile 2 and also 2800 enables to loose source routing between the Ingress and the Egress 2801 of the Track. 2803 Profile 7 Profile 7 implements profile 5 in a Main DODAG that is 2804 operated in Storing Mode as presented in Section 7.1. As in 2805 Profile 1 and 2, the TrackID is the RPLInstanceID of the Main 2806 DODAG. Longest match rules decide whether a packet is sent along 2807 the Main DODAG or rerouted in a track. 2809 Profile 8 Profile 8 is offered in preparation of the RAW work, and 2810 for use cases where an arbitrary node in the network can afford 2811 the same code complexity as the RPL Root in a traditional 2812 deployment. It offers a full DODAG visibility to the Track 2813 Ingress as specified in Section 7.2 in a Non-Storing Mode Main 2814 DODAG. 2816 Profile 9 Profile 9 combines profiles 7 and 8, operating the Track 2817 as a full DODAG within a Storing Mode Main DODAG, using only the 2818 Main DODAG RPLInstanceID as TrackID. 2820 9. Security Considerations 2822 It is worth noting that with [RPL], every node in the LLN is RPL- 2823 aware and can inject any RPL-based attack in the network. This draft 2824 uses messages that are already present in RPL [RPL] with optional 2825 secured versions. The same secured versions may be used with this 2826 draft, and whatever security is deployed for a given network also 2827 applies to the flows in this draft. 2829 The LLN nodes depend on the 6LBR and the RPL participants for their 2830 operation. A trust model must be put in place to ensure that the 2831 right devices are acting in these roles, so as to avoid threats such 2832 as black-holing, (see [RFC7416] section 7). This trust model could 2833 be at a minimum based on a Layer-2 Secure joining and the Link-Layer 2834 security. This is a generic 6LoWPAN requirement, see Req5.1 in 2835 Appendix B.5 of [RFC8505]. 2837 In a general manner, the Security Considerations in [RPL], and 2838 [RFC7416] apply to this specification as well. The Link-Layer 2839 security is needed in particular to prevent Denial-Of-Service attacks 2840 whereby a rogue router creates a high churn in the RPL network by 2841 constantly injected forged P-DAO messages and using up all the 2842 available storage in the attacked routers. 2844 Additionally, the trust model could include a role validation (e.g., 2845 using a role-based authorization) to ensure that the node that claims 2846 to be a RPL Root is entitled to do so. That trust should propagate 2847 from Egress to Ingress in the case of a Storing Mode P-DAO. 2849 This specification suggests some validation of the VIO to prevent 2850 basic loops by avoiding that a node appears twice. But that is only 2851 a minimal protection. Arguably, an attacker tha can inject P-DAOs 2852 can reroute any traffic and deplete critical resources such as 2853 spectrum and battery in the LLN rapidly. 2855 10. IANA Considerations 2856 10.1. New Elective 6LoWPAN Routing Header Type 2858 This document updates the IANA registry titled "Elective 6LoWPAN 2859 Routing Header Type" that was created for [RFC8138] and assigns the 2860 following value: 2862 +===============+=============+===============+ 2863 | Value | Description | Reference | 2864 +===============+=============+===============+ 2865 | 8 (Suggested) | P-RPI-6LoRH | This document | 2866 +---------------+-------------+---------------+ 2868 Table 21: New Elective 6LoWPAN Routing 2869 Header Type 2871 10.2. New Critical 6LoWPAN Routing Header Type 2873 This document updates the IANA registry titled "Critical 6LoWPAN 2874 Routing Header Type" that was created for [RFC8138] and assigns the 2875 following value: 2877 +===============+=============+===============+ 2878 | Value | Description | Reference | 2879 +===============+=============+===============+ 2880 | 8 (Suggested) | P-RPI-6LoRH | This document | 2881 +---------------+-------------+---------------+ 2883 Table 22: New Critical 6LoWPAN Routing 2884 Header Type 2886 10.3. New Subregistry For The RPL Option Flags 2888 IANA is required to create a subregistry for the 8-bit RPL Option 2889 Flags field, as detailed in Figure 7, under the "Routing Protocol for 2890 Low Power and Lossy Networks (RPL)" registry. The bits are indexed 2891 from 0 (leftmost) to 7. Each bit is Tracked with the following 2892 qualities: 2894 * Bit number (counting from bit 0 as the most significant bit) 2896 * Indication When Set 2898 * Reference 2900 Registration procedure is "Standards Action" [RFC8126]. The initial 2901 allocation is as indicated in Table 26: 2903 +===============+======================+===============+ 2904 | Bit number | Indication When Set | Reference | 2905 +===============+======================+===============+ 2906 | 0 | Down 'O' | [RFC6553] | 2907 +---------------+----------------------+---------------+ 2908 | 1 | Rank-Error (R) | [RFC6553] | 2909 +---------------+----------------------+---------------+ 2910 | 2 | Forwarding-Error (F) | [RFC6553] | 2911 +---------------+----------------------+---------------+ 2912 | 3 (Suggested) | Projected-Route (P) | This document | 2913 +---------------+----------------------+---------------+ 2915 Table 23: Initial PDR Flags 2917 10.4. New RPL Control Codes 2919 This document extends the IANA Subregistry created by RFC 6550 for 2920 RPL Control Codes as indicated in Table 24: 2922 +==================+=============================+===============+ 2923 | Code | Description | Reference | 2924 +==================+=============================+===============+ 2925 | 0x09 (Suggested) | Projected DAO Request (PDR) | This document | 2926 +------------------+-----------------------------+---------------+ 2927 | 0x0A (Suggested) | PDR-ACK | This document | 2928 +------------------+-----------------------------+---------------+ 2930 Table 24: New RPL Control Codes 2932 10.5. New RPL Control Message Options 2934 This document extends the IANA Subregistry created by RFC 6550 for 2935 RPL Control Message Options as indicated in Table 25: 2937 +==================+=============================+===============+ 2938 | Value | Meaning | Reference | 2939 +==================+=============================+===============+ 2940 | 0x0E (Suggested) | Stateful VIO (SM-VIO) | This document | 2941 +------------------+-----------------------------+---------------+ 2942 | 0x0F (Suggested) | Source-Routed VIO (NSM-VIO) | This document | 2943 +------------------+-----------------------------+---------------+ 2944 | 0x10 (Suggested) | Sibling Information option | This document | 2945 +------------------+-----------------------------+---------------+ 2947 Table 25: RPL Control Message Options 2949 10.6. SubRegistry for the Projected DAO Request Flags 2951 IANA is required to create a registry for the 8-bit Projected DAO 2952 Request (PDR) Flags field. Each bit is Tracked with the following 2953 qualities: 2955 * Bit number (counting from bit 0 as the most significant bit) 2957 * Capability description 2959 * Reference 2961 Registration procedure is "Standards Action" [RFC8126]. The initial 2962 allocation is as indicated in Table 26: 2964 +============+========================+===============+ 2965 | Bit number | Capability description | Reference | 2966 +============+========================+===============+ 2967 | 0 | PDR-ACK request (K) | This document | 2968 +------------+------------------------+---------------+ 2969 | 1 | Requested path should | This document | 2970 | | be redundant (R) | | 2971 +------------+------------------------+---------------+ 2973 Table 26: Initial PDR Flags 2975 10.7. SubRegistry for the PDR-ACK Flags 2977 IANA is required to create an subregistry for the 8-bit PDR-ACK Flags 2978 field. Each bit is Tracked with the following qualities: 2980 * Bit number (counting from bit 0 as the most significant bit) 2982 * Capability description 2984 * Reference 2986 Registration procedure is "Standards Action" [RFC8126]. No bit is 2987 currently defined for the PDR-ACK Flags. 2989 10.8. Subregistry for the PDR-ACK Acceptance Status Values 2991 IANA is requested to create a Subregistry for the PDR-ACK Acceptance 2992 Status values. 2994 * Possible values are 6-bit unsigned integers (0..63). 2996 * Registration procedure is "Standards Action" [RFC8126]. 2998 * Initial allocation is as indicated in Table 27: 3000 +-------+------------------------+---------------+ 3001 | Value | Meaning | Reference | 3002 +-------+------------------------+---------------+ 3003 | 0 | Unqualified Acceptance | This document | 3004 +-------+------------------------+---------------+ 3006 Table 27: Acceptance values of the PDR-ACK Status 3008 10.9. Subregistry for the PDR-ACK Rejection Status Values 3010 IANA is requested to create a Subregistry for the PDR-ACK Rejection 3011 Status values. 3013 * Possible values are 6-bit unsigned integers (0..63). 3015 * Registration procedure is "Standards Action" [RFC8126]. 3017 * Initial allocation is as indicated in Table 28: 3019 +-------+-----------------------+---------------+ 3020 | Value | Meaning | Reference | 3021 +-------+-----------------------+---------------+ 3022 | 0 | Unqualified Rejection | This document | 3023 +-------+-----------------------+---------------+ 3024 | 1 | Transient Failure | This document | 3025 +-------+-----------------------+---------------+ 3027 Table 28: Rejection values of the PDR-ACK Status 3029 10.10. SubRegistry for the Via Information Options Flags 3031 IANA is requested to create a Subregistry for the 5-bit Via 3032 Information Options (Via Information Option) Flags field. Each bit 3033 is Tracked with the following qualities: 3035 * Bit number (counting from bit 0 as the most significant bit) 3037 * Capability description 3039 * Reference 3041 Registration procedure is "Standards Action" [RFC8126]. No bit is 3042 currently defined for the Via Information Options (Via Information 3043 Option) Flags. 3045 10.11. SubRegistry for the Sibling Information Option Flags 3047 IANA is required to create a registry for the 5-bit Sibling 3048 Information Option (SIO) Flags field. Each bit is Tracked with the 3049 following qualities: 3051 * Bit number (counting from bit 0 as the most significant bit) 3053 * Capability description 3055 * Reference 3057 Registration procedure is "Standards Action" [RFC8126]. The initial 3058 allocation is as indicated in Table 29: 3060 +===============+========================+===========+ 3061 | Bit number | Capability description | Reference | 3062 +===============+========================+===========+ 3063 | 0 (Suggested) | "S" flag: Sibling in | This | 3064 | | same DODAG as Self | document | 3065 +---------------+------------------------+-----------+ 3067 Table 29: Initial SIO Flags 3069 10.12. New destination Advertisement Object Flag 3071 This document modifies the "destination Advertisement Object (DAO) 3072 Flags" registry initially created in Section 20.11 of [RPL] . 3074 Section 4.1.1 also defines one new entry in the Registry as follows: 3076 +---------------+------------------------+-----------+ 3077 | Bit Number | Capability Description | Reference | 3078 +---------------+------------------------+-----------+ 3079 | 2 (Suggested) | Projected DAO (P) | THIS RFC | 3080 +---------------+------------------------+-----------+ 3082 Table 30: New destination Advertisement Object 3083 (DAO) Flag 3085 10.13. New ICMPv6 Error Code 3087 In some cases RPL will return an ICMPv6 error message when a message 3088 cannot be forwarded along a P-Route. 3090 IANA has defined an ICMPv6 "Code" Fields Registry for ICMPv6 Message 3091 Types. ICMPv6 Message Type 1 describes "destination Unreachable" 3092 codes. This specification requires that a new code is allocated from 3093 the ICMPv6 Code Fields Registry for ICMPv6 Message Type 1, for "Error 3094 in P-Route", with a suggested code value of 8, to be confirmed by 3095 IANA. 3097 10.14. New RPL Rejection Status values 3099 This specification updates the Subregistry for the "RPL Rejection 3100 Status" values under the RPL registry, as follows: 3102 +---------------+-------------------------+-----------+ 3103 | Value | Meaning | Reference | 3104 +---------------+-------------------------+-----------+ 3105 | 2 (Suggested) | Out of Resources | THIS RFC | 3106 +---------------+-------------------------+-----------+ 3107 | 3 (Suggested) | Error in VIO | THIS RFC | 3108 +---------------+-------------------------+-----------+ 3109 | 4 (Suggested) | Predecessor Unreachable | THIS RFC | 3110 +---------------+-------------------------+-----------+ 3111 | 5 (Suggested) | Unreachable Target | THIS RFC | 3112 +---------------+-------------------------+-----------+ 3113 | 6..63 | Unassigned | | 3114 +---------------+-------------------------+-----------+ 3116 Table 31: Rejection values of the RPL Status 3118 11. Acknowledgments 3120 The authors wish to acknowledge JP Vasseur, Remy Liubing, James 3121 Pylakutty, and Patrick Wetterwald for their contributions to the 3122 ideas developed here. Many thanks to Dominique Barthel and SVR Anand 3123 for their global contribution to 6TiSCH, RAW and this document, as 3124 well as text suggestions that were incorporated, and to Michael 3125 Richardson for his useful recommendations based on his global view of 3126 the system. Also special thanks Toerless Eckert for his deep review, 3127 with many excellent suggestions that improved the readability and 3128 well as the content of the specification. 3130 12. Normative References 3132 [INT-ARCHI] 3133 Braden, R., Ed., "Requirements for Internet Hosts - 3134 Communication Layers", STD 3, RFC 1122, 3135 DOI 10.17487/RFC1122, October 1989, 3136 . 3138 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3139 Requirement Levels", BCP 14, RFC 2119, 3140 DOI 10.17487/RFC2119, March 1997, 3141 . 3143 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3144 Control Message Protocol (ICMPv6) for the Internet 3145 Protocol Version 6 (IPv6) Specification", STD 89, 3146 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3147 . 3149 [RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path 3150 Computation Element (PCE)-Based Architecture", RFC 4655, 3151 DOI 10.17487/RFC4655, August 2006, 3152 . 3154 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 3155 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 3156 DOI 10.17487/RFC5440, March 2009, 3157 . 3159 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 3160 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 3161 DOI 10.17487/RFC6282, September 2011, 3162 . 3164 [RPL] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 3165 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 3166 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 3167 Low-Power and Lossy Networks", RFC 6550, 3168 DOI 10.17487/RFC6550, March 2012, 3169 . 3171 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 3172 Power and Lossy Networks (RPL) Option for Carrying RPL 3173 Information in Data-Plane Datagrams", RFC 6553, 3174 DOI 10.17487/RFC6553, March 2012, 3175 . 3177 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 3178 Routing Header for Source Routes with the Routing Protocol 3179 for Low-Power and Lossy Networks (RPL)", RFC 6554, 3180 DOI 10.17487/RFC6554, March 2012, 3181 . 3183 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3184 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3185 May 2017, . 3187 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 3188 Writing an IANA Considerations Section in RFCs", BCP 26, 3189 RFC 8126, DOI 10.17487/RFC8126, June 2017, 3190 . 3192 13. Informative References 3194 [6LoWPAN] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 3195 "Transmission of IPv6 Packets over IEEE 802.15.4 3196 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, 3197 . 3199 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 3200 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 3201 2014, . 3203 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and 3204 J. Martocci, "Reactive Discovery of Point-to-Point Routes 3205 in Low-Power and Lossy Networks", RFC 6997, 3206 DOI 10.17487/RFC6997, August 2013, 3207 . 3209 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 3210 and M. Richardson, Ed., "A Security Threat Analysis for 3211 the Routing Protocol for Low-Power and Lossy Networks 3212 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 3213 . 3215 [6TiSCH-ARCHI] 3216 Thubert, P., Ed., "An Architecture for IPv6 over the Time- 3217 Slotted Channel Hopping Mode of IEEE 802.15.4 (6TiSCH)", 3218 RFC 9030, DOI 10.17487/RFC9030, May 2021, 3219 . 3221 [RAW-ARCHI] 3222 Thubert, P., Papadopoulos, G. Z., and L. Berger, "Reliable 3223 and Available Wireless Architecture/Framework", Work in 3224 Progress, Internet-Draft, draft-ietf-raw-architecture-01, 3225 28 July 2021, . 3228 [USE-CASES] 3229 Papadopoulos, G. Z., Thubert, P., Theoleyre, F., and C. J. 3230 Bernardos, "RAW use cases", Work in Progress, Internet- 3231 Draft, draft-ietf-raw-use-cases-02, 12 July 2021, 3232 . 3235 [TURN-ON_RFC8138] 3236 Thubert, P., Ed. and L. Zhao, "A Routing Protocol for Low- 3237 Power and Lossy Networks (RPL) Destination-Oriented 3238 Directed Acyclic Graph (DODAG) Configuration Option for 3239 the 6LoWPAN Routing Header", RFC 9035, 3240 DOI 10.17487/RFC9035, April 2021, 3241 . 3243 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 3244 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 3245 RFC 8025, DOI 10.17487/RFC8025, November 2016, 3246 . 3248 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 3249 "IPv6 over Low-Power Wireless Personal Area Network 3250 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 3251 April 2017, . 3253 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 3254 Perkins, "Registration Extensions for IPv6 over Low-Power 3255 Wireless Personal Area Network (6LoWPAN) Neighbor 3256 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 3257 . 3259 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3260 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3261 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3262 July 2018, . 3264 [RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas, 3265 "Deterministic Networking Architecture", RFC 8655, 3266 DOI 10.17487/RFC8655, October 2019, 3267 . 3269 [RFC8930] Watteyne, T., Ed., Thubert, P., Ed., and C. Bormann, "On 3270 Forwarding 6LoWPAN Fragments over a Multi-Hop IPv6 3271 Network", RFC 8930, DOI 10.17487/RFC8930, November 2020, 3272 . 3274 [RFC8931] Thubert, P., Ed., "IPv6 over Low-Power Wireless Personal 3275 Area Network (6LoWPAN) Selective Fragment Recovery", 3276 RFC 8931, DOI 10.17487/RFC8931, November 2020, 3277 . 3279 [RFC8994] Eckert, T., Ed., Behringer, M., Ed., and S. Bjarnason, "An 3280 Autonomic Control Plane (ACP)", RFC 8994, 3281 DOI 10.17487/RFC8994, May 2021, 3282 . 3284 [RFC9008] Robles, M.I., Richardson, M., and P. Thubert, "Using RPI 3285 Option Type, Routing Header for Source Routes, and IPv6- 3286 in-IPv6 Encapsulation in the RPL Data Plane", RFC 9008, 3287 DOI 10.17487/RFC9008, April 2021, 3288 . 3290 [RFC9010] Thubert, P., Ed. and M. Richardson, "Routing for RPL 3291 (Routing Protocol for Low-Power and Lossy Networks) 3292 Leaves", RFC 9010, DOI 10.17487/RFC9010, April 2021, 3293 . 3295 [I-D.irtf-panrg-path-properties] 3296 Enghardt, T. and C. Krähenbühl, "A Vocabulary of Path 3297 Properties", Work in Progress, Internet-Draft, draft-irtf- 3298 panrg-path-properties-03, 9 July 2021, 3299 . 3302 [PCE] IETF, "Path Computation Element", 3303 . 3305 Authors' Addresses 3307 Pascal Thubert (editor) 3308 Cisco Systems, Inc 3309 Building D 3310 45 Allee des Ormes - BP1200 3311 06254 Mougins - Sophia Antipolis 3312 France 3314 Phone: +33 497 23 26 34 3315 Email: pthubert@cisco.com 3317 Rahul Arvind Jadhav 3318 Huawei Tech 3319 Kundalahalli Village, Whitefield, 3320 Bangalore 560037 3321 Karnataka 3322 India 3324 Phone: +91-080-49160700 3325 Email: rahul.ietf@gmail.com 3327 Matthew Gillmore 3328 Itron, Inc 3329 Building D 3330 2111 N Molter Road 3331 Liberty Lake, 99019 3332 United States 3334 Phone: +1.800.635.5461 3335 Email: matthew.gillmore@itron.com