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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-30) exists of draft-ietf-6tisch-architecture-29 == Outdated reference: A later version (-09) exists of draft-pthubert-raw-architecture-04 == Outdated reference: A later version (-44) exists of draft-ietf-roll-useofrplinfo-40 Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ROLL P. Thubert, Ed. 3 Internet-Draft Cisco Systems 4 Updates: 6550 (if approved) R.A. Jadhav 5 Intended status: Standards Track Huawei Tech 6 Expires: 2 April 2021 M. Gillmore 7 Itron 8 29 September 2020 10 Root initiated routing state in RPL 11 draft-ietf-roll-dao-projection-13 13 Abstract 15 This document updates RFC 6550 to enable a RPL Root to install and 16 maintain Projected Routes within its DODAG, along a selected set of 17 nodes that may or may not include self, for a chosen duration. This 18 potentially enables routes that are more optimized or resilient than 19 those obtained with the classical distributed operation of RPL, 20 either in terms of the size of a source-route header or in terms of 21 path length, which impacts both the latency and the packet delivery 22 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 2 April 2021. 41 Copyright Notice 43 Copyright (c) 2020 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 . . . . . . . . . . . . . . . . . . . . . . . . . 5 59 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 60 2.2. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 5 61 2.3. Other Terms . . . . . . . . . . . . . . . . . . . . . . . 5 62 2.4. References . . . . . . . . . . . . . . . . . . . . . . . 6 63 3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 6 64 4. Identifying a Track . . . . . . . . . . . . . . . . . . . . . 8 65 5. New RPL Control Messages and Options . . . . . . . . . . . . 9 66 5.1. New P-DAO Request Control Message . . . . . . . . . . . . 9 67 5.2. New PDR-ACK Control Message . . . . . . . . . . . . . . . 10 68 5.3. Route Projection Options . . . . . . . . . . . . . . . . 12 69 5.4. Sibling Information Option . . . . . . . . . . . . . . . 14 70 6. Projected DAO . . . . . . . . . . . . . . . . . . . . . . . . 16 71 6.1. Requesting a Track . . . . . . . . . . . . . . . . . . . 17 72 6.2. Routing over a Track . . . . . . . . . . . . . . . . . . 18 73 6.3. Non-Storing Mode Projected Route . . . . . . . . . . . . 18 74 6.4. Storing Mode Projected Route . . . . . . . . . . . . . . 20 75 7. Security Considerations . . . . . . . . . . . . . . . . . . . 22 76 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 77 8.1. New RPL Control Codes . . . . . . . . . . . . . . . . . . 22 78 8.2. New RPL Control Message Options . . . . . . . . . . . . . 22 79 8.3. SubRegistry for the Projected DAO Request Flags . . . . . 23 80 8.4. SubRegistry for the PDR-ACK Flags . . . . . . . . . . . . 23 81 8.5. Subregistry for the PDR-ACK Acceptance Status Values . . 24 82 8.6. Subregistry for the PDR-ACK Rejection Status Values . . . 24 83 8.7. SubRegistry for the Route Projection Options Flags . . . 24 84 8.8. SubRegistry for the Sibling Information Option Flags . . 25 85 8.9. Error in Projected Route ICMPv6 Code . . . . . . . . . . 25 86 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25 87 10. Normative References . . . . . . . . . . . . . . . . . . . . 26 88 11. Informative References . . . . . . . . . . . . . . . . . . . 26 89 Appendix A. Applications . . . . . . . . . . . . . . . . . . . . 28 90 A.1. Loose Source Routing . . . . . . . . . . . . . . . . . . 28 91 A.2. Transversal Routes . . . . . . . . . . . . . . . . . . . 29 92 Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 31 93 B.1. Using Storing Mode P-DAO in Non-Storing Mode MOP . . . . 31 94 B.2. Projecting a Storing Mode transversal route . . . . . . . 32 95 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 97 1. Introduction 99 RPL, the "Routing Protocol for Low Power and Lossy Networks" [RPL] 100 (LLNs), is a generic Distance Vector protocol that is well suited for 101 application in a variety of low energy Internet of Things (IoT) 102 networks. RPL forms Destination Oriented Directed Acyclic Graphs 103 (DODAGs) in which the Root often acts as the Border Router to connect 104 the RPL domain to the Internet. The Root is responsible to select 105 the RPL Instance that is used to forward a packet coming from the 106 Internet into the RPL domain and set the related RPL information in 107 the packets. 6TiSCH uses RPL for its routing operations. 109 The "6TiSCH Architecture" [6TiSCH-ARCHI] also leverages the 110 "Deterministic Networking Architecture" [RFC8655] centralized model 111 whereby the device resources and capabilities are exposed to an 112 external controller which installs routing states into the network 113 based on some objective functions that reside in that external 114 entity. With DetNet and 6TiSCH, the component of the controller that 115 is responsible of computing routes is called a Path Computation 116 Element ([PCE]). 118 Based on heuristics of usage, path length, and knowledge of device 119 capacity and available resources such as battery levels and 120 reservable buffers, the PCE with a global visibility on the system 121 can compute direct Peer to Peer (P2P) routes that are optimized for 122 the needs expressed by an objective function. This document 123 specifies protocol extensions to RPL [RPL] that enable the Root of a 124 main DODAG to install centrally-computed routes inside the DODAG on 125 behalf of a PCE. 127 This specification expects that the main RPL Instance is operated in 128 RPL Non-Storing Mode of Operation (MOP) to sustain the exchanges with 129 the Root. In that Mode, the Root has enough information to build a 130 basic DODAG topology based on parents and children, but lacks the 131 knowledge of siblings. This document adds the capability for nodes 132 to advertise sibling information in order to improve the topological 133 awareness of the Root. 135 As opposed to the classical RPL operations where routes are injected 136 by the Target nodes, the protocol extensions enable the Root of a 137 DODAG to project the routes that are needed onto the nodes where they 138 should be installed. This specification uses the term Projected 139 Route to refer to those routes. Projected Routes can be used to 140 reduce the size of the source routing headers with loose source 141 routing operations down the main RPL DODAG. Projected Routes can 142 also be used to build transversal routes for route optimization and 143 Traffic Engineering purposes, between nodes of the DODAG. 145 A Projected Route may be installed in either Storing and Non-Storing 146 Mode, potentially resulting in hybrid situations where the Mode of 147 the Projected Route is different from that of the main RPL Instance. 148 A Projected Route may be a stand-alone end-to-end path or a Segment 149 in a more complex forwarding graph called a Track. 151 The concept of a Track was introduced in the 6TiSCH architecture, as 152 a potentially complex path with redundant forwarding solutions along 153 the way. A node at the ingress of more than one Segment in a Track 154 may use any combination of those Segments to forward a packet towards 155 the Track Egress. 157 The "Reliable and Available Wireless (RAW) Architecture/Framework" 158 [RAW-ARCHI] defines the Path Selection Engine (PSE) that adapts the 159 use of the path redundancy within a Track to defeat the diverse 160 causes of packet loss. 162 The PSE is a dataplane extension of the PCE; it controls the 163 forwarding operation of the packets within a Track, using Packet ARQ, 164 Replication, Elimination, and Overhearing (PAREO) functions over the 165 Track segments, to provide a dynamic balance between the reliability 166 and availability requirements of the flows and the need to conserve 167 energy and spectrum. 169 The time scale at which the PCE (re)computes the Track can be long, 170 using long-term statistical metrics to perform global optimizations 171 at the scale of the whole network. Conversely, the PSE makes 172 forwarding decisions at the time scale of one or a small collection 173 of packets, based on a knowledge that is limited in scope to the 174 Track itself, so it can be refreshed at a fast pace. 176 Projected Routes must be used with the parsimony to limit the amount 177 of state that is installed in each device to fit within the device 178 resources, and to maintain the amount of rerouted traffic within the 179 capabilities of the transmission links. The methods used to learn 180 the node capabilities and the resources that are available in the 181 devices and in the network are out of scope for this document. 183 This specification uses the RPL Root as a proxy to the PCE. The PCE 184 may be collocated with the Root, or may reside in an external 185 Controller. 187 In that case, the PCE exchanges control messages with the Root over a 188 Southbound API that is out of scope for this specification. The 189 algorithm to compute the paths and the protocol used by an external 190 PCE to obtain the topology of the network from the Root are also out 191 of scope. 193 2. Terminology 195 2.1. Requirements Language 197 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 198 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 199 "OPTIONAL" in this document are to be interpreted as described in BCP 200 14 [RFC2119][RFC8174] when, and only when, they appear in all 201 capitals, as shown here. 203 2.2. Glossary 205 This document often uses the following acronyms: 207 CMO: Control Message Option 208 DAO: Destination Advertisement Object 209 DAG: Directed Acyclic Graph 210 DODAG: Destination-Oriented Directed Acyclic Graph; A DAG with only 211 one vertex (i.e., node) that has no outgoing edge (i.e., link) 212 LLN: Low-Power and Lossy Network 213 MOP: RPL Mode of Operation 214 P-DAO: Projected DAO 215 PDR: P-DAO Request 216 RAN: RPL-Aware Node (either a RPL Router or a RPL-Aware Leaf) 217 RAL: RPL-Aware Leaf 218 RPI: RPL Packet Information 219 RPL: IPv6 Routing Protocol for LLNs [RPL] 220 RPO: A Route Projection Option; it can be a VIO or an SRVIO. 221 RTO: RPL Target Option 222 RUL: RPL-Unaware Leaf 223 SIO: RPL Sibling Information Option 224 SRVIO: A Source-Routed Via Information Option, used in Non-Storing 225 Mode P-DAO messages. 226 SubDAG: A DODAG rooted at a node which is a child of that node and a 227 subset of a larger DAG 228 TIO: RPL Transit Information Option 229 VIO: A Via Information Option, used in Storing Mode P-DAO messages. 231 2.3. Other Terms 233 Projected Route: A Projected Route is a path segment that is 234 computed remotely, and installed and maintained by a RPL Root. 235 Projected DAO: A DAO message used to install a Projected Route. 236 Track: A complex path with redundant Segments to a destination. 237 TrackID: A RPL Local InstanceID with the 'D' bit set. The TrackID 238 is associated with a IPv6 Address to the Track Egress Node. 240 2.4. References 242 In this document, readers will encounter terms and concepts that are 243 discussed in the "Routing Protocol for Low Power and Lossy Networks" 244 [RPL] and "Terminology in Low power And Lossy Networks" [RFC7102]. 246 3. Updating RFC 6550 248 Section 6 of [RPL] introduces the RPL Control Message Options (CMO), 249 including the RPL Target Option (RTO) and Transit Information Option 250 (TIO), which can be placed in RPL messages such as the Destination 251 Advertisement Object (DAO). This specification extends the DAO 252 message with the Projected DAO (P-DAO); a P-DAO message signals a 253 Projected Route using new CMOs presented therein. 255 A Projected Route can be an additional route of higher precedence 256 within the main DODAG, in which case it is installed with the 257 RPLInstanceID and DODAGID of the main DODAG. 259 A Projected Route can also be a Segment within a Track. A stand- 260 alone Segment can be used as a Serial (end-to-end) Track. Segments 261 can also be combined to form a Complex Track. The Root uses a local 262 RPL Instance rooted at the Track Egress to establish and maintain the 263 Track. The local RPLInstanceID of the Track is called the TrackID, 264 more in Section 4. 266 0 1 2 3 267 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 1 268 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 269 | TrackID |K|D| Flags | Reserved | DAOSequence | 270 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 271 | | 272 + + 273 | | 274 + IPv6 Address of the Track Egress + 275 | | 276 + + 277 | | 278 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 279 | Option(s)... 280 +-+-+-+-+-+-+-+-+ 282 Figure 1: Projected DAO Format for a Track 284 A P-DAO message signals the IPv6 Address of the Track Egress in the 285 DODAGID field of the DAO Base Object, and the TrackID in the 286 RPLInstanceID field, as shown in Figure 1. 288 In RPL Non-Storing Mode, the TIO and RTO are combined in a DAO 289 message to inform the DODAG Root of all the edges in the DODAG, which 290 are formed by the directed parent-child relationships. Options may 291 be factorized; multiple RTOs may be present to signal a collection of 292 children that can be reached via the parent(s) indicated in the 293 TIO(s) that follows the RTOs. 295 This specification generalizes the case of a parent that can be used 296 to reach a child with that of a whole Track through which both 297 children and siblings may be reached. 299 New CMOs called the Route Projection Options (RPO) are introduced for 300 use in P-DAO messages as a multihop alternative to the TIO. One RPO 301 is the Via Information Option (VIO); the VIO installs a state at each 302 hop along a Storing Mode Projected Route. The other is the Source- 303 Routed VIO (SRVIO); the SRVIO installs a source-routing state at the 304 Segment ingress, which uses that state to encapsulate a packet with a 305 Source-Routing Header along a Non-Storing Mode Projected Route. 307 Like in a DAO message, the RTOs can be factorized in a P-DAO, but the 308 CMOs cannot. A P-DAO contains one or more RTOs that indicate the 309 destinations that can be reached via the Track, and either one SRVIO 310 or one VIO signal the sequence of hops between the Track Ingress and 311 the (penultimate) node before the Track Egress. In Non-Storing Mode, 312 the Root sends the P-DAO to the Track Ingress where the source- 313 routing state is stored. In Storing Mode, the P-DAO is sent to the 314 Track Egress and forwarded along the Segment in the reverse 315 direction, installing a Storing Mode state at each hop. 317 This specification adds another CMO called the Sibling Information 318 Option (SIO) that is used by a RPL Aware Node (RAN) to advertise a 319 selection of its candidate neighbors as siblings to the Root, more in 320 Section 5.4. The sibling selection process is out of scope. 322 Two new RPL Control Messages are also introduced, to enable a RAN to 323 request the establishment of a Track between self as the Track 324 Ingress Node and a Track Egress. The RAN makes its request by 325 sending a new P-DAO Request (PDR) Message to the Root. The Root 326 confirms with a new PDR-ACK message back to the requester RAN, see 327 Section 5.1 for more. A positive PDR-ACK indicates that the Track 328 was built and that the Roots commits to maintain the Track for a 329 negotiated lifetime. 331 In the case of a complex Track, each Segment is maintained 332 independently and asynchronously by the Root, with its own lifetime 333 that may be shorter, the same, or longer than that of the Track. The 334 Root may use an asynchronous PDR-ACK with an negative status to 335 indicate that the Track was terminated before its time. 337 4. Identifying a Track 339 RPL defines the concept of an Instance to signal an individual 340 routing topology but does not have a concept of an administrative 341 distance, which exists in certain proprietary implementations to sort 342 out conflicts between multiple sources of routing information within 343 one routing topology. 345 This draft conforms the RPL Instance model as follows: 347 * The PCE MAY use P-DAO messages to add better routes in the main 348 (Global) Instance in conformance with the routing objectives in 349 that Instance. To achieve this, the PCE MAY install a Storing 350 Mode Projected Route along a path down the main (Non-Storing Mode) 351 DODAG. This enables a loose source routing and reduces the size 352 of the Source Routing Header, see Appendix A.1. 354 When adding a Storing Mode Projected Route to the main RPL 355 Instance, the Root MUST set the RPLInstanceID field of the DAO 356 message (see section 6.4.1. of [RPL]) to the RPLInstanceID of the 357 main DODAG, and set the DODAGID field to the Segment Egress. The 358 Projected Route provides a longer match to the Egress than the 359 default route via the Root, so it is preferred. Once the 360 Projected Route is installed, the intermediate nodes listed in the 361 VIO between the first (excluded) and the last (included) can be 362 elided in a Source-Route Header that signals that Segment. 364 * The Root MAY also use P-DAO messages to install a specific (say, 365 Traffic Engineered) path as a Serial of a Complex Track, to a 366 particular endpoint that is the Track Egress. In that case, the 367 Root MUST use a Local RPL Instance (see section 5 of [RPL]) as 368 TrackID. 370 The TrackID MUST be unique for the Global Unique IPv6 Address 371 (GUA) or Unique-Local Address (ULA) of the Track Egress that 372 serves as DODAGID for the Track. This way, a Track is uniquely 373 identified by the tuple (Track Egress Address, TrackID) where the 374 TrackID is always represented with the 'D' flag set. The Track 375 Egress Address and the TrackID are signaled in the P-DAO message 376 as shown in Figure 1. 378 * In the data packets, the Track Egress Address and the TrackID are 379 respectively signaled in IPv6 Address of the final destination and 380 the RPLInstanceID field of the RPL Packet Information (RPI) (see 381 [USEofRPLinfo]) in the outer chain of IPv6 Headers. 383 If the outer chain of IPv6 Headers contains a Source-Routing 384 Header that is not fully consumed, then the final destination is 385 the last entry in the Source-Routing Header; else it is the 386 Destination Address in the IPv6 Header. When using the [RFC8138] 387 compression, it is the last hop of the last SRH-6LoRH of the outer 388 header in either case. 390 The 'D' flag in the RPLInstanceID MUST be set to indicate that the 391 final destination address in the IPv6 header owns the local 392 RPLInstanceID, more in Section 6.2. 394 * A packet that is being routed over the RPL Instance associated to 395 a first Non-Storing Mode Track MAY be placed (encapsulated) in a 396 second Track to cover one loose hop of the first Track. On the 397 other hand, a Storing Mode Track must be strict and a packet that 398 it placed in a Storing Mode Track MUST follow that Track till the 399 Track Egress. 401 When a Track Egress extracts a packet from a Track (decapsulates 402 the packet), the Destination of the inner packet MUST be either 403 this node or a direct neighbor, otherwise the packet MUST be 404 dropped. That Destination may be the next Hop in a Non-Storing 405 Mode Track. 407 All properties of a Track operations are inherited form the main RPL 408 Instance that is used to install the Track. For instance, the use of 409 compression per [RFC8138] is determined by whether it is used in the 410 main instance, e.g., by setting the "T" flag [TURN-ON_RFC8138] in the 411 RPL configuration option. 413 5. New RPL Control Messages and Options 415 5.1. New P-DAO Request Control Message 417 The P-DAO Request (PDR) message is sent to the Root to request a new 418 that the PCE establishes a new a projected route from self to the 419 Track Egress indicated in the TIO as a full path of a collection of 420 Segments in a Track. Exactly one TIO MUST be present, more in 421 Section 6.1. 423 The RPL Control Code for the PDR is 0x09, to be confirmed by IANA. 424 The format of PDR Base Object is as follows: 426 0 1 2 3 427 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 429 | TrackID |K|R| Flags | ReqLifetime | PDRSequence | 430 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 431 | Option(s)... 432 +-+-+-+-+-+-+-+-+ 434 Figure 2: New P-DAO Request Format 436 TrackID: 8-bit field indicating the RPLInstanceID associated with 437 the Track. It is set to zero upon the first request for a new 438 Track and then to the TrackID once the Track was created, to 439 either renew it of destroy it. 441 K: The 'K' flag is set to indicate that the recipient is expected to 442 send a PDR-ACK back. 444 R: The 'R' flag is set to indicate that the Requested path should be 445 redundant. 447 Flags: Reserved. The Flags field MUST initialized to zero by the 448 sender and MUST be ignored by the receiver 450 ReqLifetime: 8-bit unsigned integer. 452 The requested lifetime for the Track expressed in Lifetime Units 453 (obtained from the DODAG Configuration option). 455 A PDR with a fresher PDRSequence refreshes the lifetime, and a 456 PDRLifetime of 0 indicates that the track should be destroyed. 458 PDRSequence: 8-bit wrapping sequence number, obeying the operation 459 in section 7.2 of [RPL]. 461 The PDRSequence is used to correlate a PDR-ACK message with the 462 PDR message that triggered it. It is incremented at each PDR 463 message and echoed in the PDR-ACK by the Root. 465 5.2. New PDR-ACK Control Message 467 The new PDR-ACK is sent as a response to a PDR message with the 'K' 468 flag set. The RPL Control Code for the PDR-ACK is 0x0A, to be 469 confirmed by IANA. Its format is as follows: 471 0 1 2 3 472 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 1 473 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 474 | TrackID | Flags | Track Lifetime| PDRSequence | 475 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 476 | PDR-ACK Status| Reserved | 477 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 478 | Option(s)... 479 +-+-+-+-+-+-+-+ 481 Figure 3: New PDR-ACK Control Message Format 483 TrackID: The RPLInstanceID of the Track that was created. The value 484 of 0x00 is used to when no Track was created. 486 Flags: Reserved. The Flags field MUST initialized to zero by the 487 sender and MUST be ignored by the receiver 489 Track Lifetime: Indicates that remaining Lifetime for the Track, 490 expressed in Lifetime Units; a value of zero (0x00) indicates that 491 the Track was destroyed or not created. 493 PDRSequence: 8-bit wrapping sequence number. It is incremented at 494 each PDR message and echoed in the PDR-ACK. 496 PDR-ACK Status: 8-bit field indicating the completion. 498 The PDR-ACK Status is substructured as indicated in Figure 4: 500 0 1 2 3 4 5 6 7 501 +-+-+-+-+-+-+-+-+ 502 |E|R| Value | 503 +-+-+-+-+-+-+-+-+ 505 Figure 4: PDR-ACK status Format 507 E: 1-bit flag. Set to indicate a rejection. When not set, a 508 value of 0 indicates Success/Unqualified acceptance and other 509 values indicate "not an outright rejection". 511 R: 1-bit flag. Reserved, MUST be set to 0 by the sender and 512 ignored by the receiver. 514 Status Value: 6-bit unsigned integer. Values depending on the 515 setting of the 'E' flag as indicated respectively in Table 4 516 and Table 5. 518 Reserved: The Reserved field MUST initialized to zero by the sender 519 and MUST be ignored by the receiver 521 5.3. Route Projection Options 523 The RPOs indicate a series of IPv6 addresses that can be compressed 524 using the method defined in the "6LoWPAN Routing Header" [RFC8138] 525 specification using the address of the Root found in the DODAGID 526 field of DIO messages as Compression Reference. 528 An RPO indicates a Projected Route that can be a Serial Track in full 529 or a Segment of a more Complex Track. In Non-Storing Mode, multiple 530 RPO may be placed after a TIO to reflect different Segments 531 originated at this node. The Track is identified by a TrackID that 532 is a Local RPLInstanceID to the Track Egress of the Track. 534 The format of RPOs is as follows: 536 0 1 2 3 537 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 1 538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 539 | Type | Option Length | Flags | SegmentID | 540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 541 |Segm. Sequence | Seg. Lifetime | SRH-6LoRH header | 542 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 543 | | 544 + + 545 . . 546 . Via Address 1 . 547 . . 548 + + 549 | | 550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 551 | | 552 . .... . 553 | | 554 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 555 | | 556 + + 557 . . 558 . Via Address n . 559 . . 560 + + 561 | | 562 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 564 Figure 5: Route Projection Option format (uncompressed form) 566 Option Type: 0x0B for VIO, 0x0C for SRVIO (to be confirmed by IANA) 568 Option Length: In bytes; variable, depending on the number of Via 569 Addresses and the compression. 571 Flags: Reserved. The Flags field MUST initialized to zero by the 572 sender and MUST be ignored by the receiver 574 SegmentID: 8-bit field that identifies a Segment within a Track or 575 the main DODAG as indicated by the TrackID field. A Value of 0 is 576 used to signal a Serial Track, i.e., made of a single segment. 578 Segment Sequence: 8-bit unsigned integer. The Segment Sequence 579 obeys the operation in section 7.2 of [RPL] and the lollipop 580 starts at 255. When the Root of the DODAG needs to refresh or 581 update a Segment in a Track, it increments the Segment Sequence 582 individually for that Segment. The Segment information indicated 583 in the RTO deprecates any state for the Segment indicated by the 584 SegmentID within the indicated Track and sets up the new 585 information. A RTO with a Segment Sequence that is not as fresh 586 as the current one is ignored. a RTO for a given Track Egress 587 with the same (TrackID, SegmentID, Segment Sequence) indicates a 588 retry; it MUST NOT change the Segment and MUST be propagated or 589 answered as the first copy. 591 Segment Lifetime: 8-bit unsigned integer. The length of time in 592 Lifetime Units (obtained from the Configuration option) that the 593 Segment is usable. The period starts when a new Segment Sequence 594 is seen. A value of 255 (0xFF) represents infinity. A value of 595 zero (0x00) indicates a loss of reachability. A DAO message that 596 contains a Via Information option with a Segment Lifetime of zero 597 for a Track Egress is referred as a No-Path (for that Track 598 Egress) in this document. 600 SRH-6LoRH header: The first 2 bytes of the SRH-6LoRH as shown in 601 Figure 6 of [RFC8138]. A 6LoRH Type of 4 means that the VIA 602 Addresses are provided in full with no compression. 604 Via Address: A Luistof Via Addresses along one Segment, indicated in 605 the order of the path from the ingress to the egress nodes. 607 In a VIO, the list is a strict path between direct neighbors, 608 whereas for an SRVIO, the list may be loose, provided that each 609 listed node has a path to the next listed node, e.g., via another 610 Track. 612 In the case of a VIO, or if [RFC8138] is turned off, then the Root 613 MUST use only one SRH-6LoRH per RPO, and the compression is the 614 same for all the addresses, as shown in Figure 5. 616 If [RFC8138] is turned on, then the Root SHOULD optimize the size 617 of the SRVIO; in that case, more than one SRH-6LoRH may be needed 618 if the compression of the addresses changes inside the Segment and 619 different SRH-6LoRH Types are used. 621 An RPO MUST contain at least one Via Address, and a Via Address MUST 622 NOT be present more than once, otherwise the RPO MUST be ignored. 624 5.4. Sibling Information Option 626 The Sibling Information Option (SIO) provides indication on siblings 627 that could be used by the Root to form Projected Routes. The format 628 of SIOs is as follows: 630 0 1 2 3 631 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 1 632 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 633 | Type | Option Length |Comp.|B|D|Flags| Opaque | 634 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 635 | Step of Rank | Reserved | 636 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 637 | | 638 + + 639 . . 640 . Sibling DODAGID (if 'D' flag not set) . 641 . . 642 + + 643 | | 644 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 645 | | 646 + + 647 . . 648 . Sibling Address . 649 . . 650 + + 651 | | 652 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 654 Figure 6: Sibling Information Option Format 656 Option Type: 0x0D (to be confirmed by IANA) 658 Option Length: In bytes; variable, depending on the number of Via 659 Addresses. 661 Compression Type: 3-bit unsigned integer. This is the SRH-6LoRH 662 Type as defined in figure 7 in section 5.1 of [RFC8138] that 663 corresponds to the compression used for the Sibling Address. 665 Reserved for Flags: MUST be set to zero by the sender and MUST be 666 ignored by the receiver. 668 B: 1-bit flag that is set to indicate that the connectivity to the 669 sibling is bidirectional and roughly symmetrical. In that case, 670 only one of the siblings may report the SIO for the hop. If 'B' 671 is not set then the SIO only indicates connectivity from the 672 sibling to this node, and does not provide information on the hop 673 from this node to the sibling. 675 D: 1-bit flag that is set to indicate that sibling belongs to the 676 same DODAG. When not set, the Sibling DODAGID is indicated. 678 Flags: Reserved. The Flags field MUST initialized to zero by the 679 sender and MUST be ignored by the receiver 681 Opaque: MAY be used to carry information that the node and the Root 682 understand, e.g., a particular representation of the Link 683 properties such as a proprietary Link Quality Information for 684 packets received from the sibling. An industraial Alliance that 685 uses RPL for a particular use / environment MAY redefine the use 686 of this field to fit its needs. 688 Step of Rank: 16-bit unsigned integer. This is the Step of Rank 689 [RPL] as computed by the Objective Function between this node and 690 the sibling. 692 Reserved: The Reserved field MUST initialized to zero by the sender 693 and MUST be ignored by the receiver 695 Sibling DODAGID: 2 to 16 bytes, the DODAGID of the sibling in a 696 [RFC8138] compressed form as indicated by the Compression Type 697 field. This field is present when the 'D' flag is not set. 699 Sibling Address: 2 to 16 bytes, the IPv6 Address of the sibling in a 700 [RFC8138] compressed form as indicated by the Compression Type 701 field. 703 An SIO MAY be immediately followed by a DAG Metric Container. In 704 that case the DAG Metric Container provides additional metrics for 705 the hop from the Sibling to this node. 707 6. Projected DAO 709 This draft adds a capability to RPL whereby the Root of a DODAG 710 projects a Track by sending one or more extended DAO message called 711 Projected-DAO (P-DAO) messages to chosen routers in the DODAG, 712 indicating one or more sequence(s) of routers inside the DODAG via 713 which the Target(s) indicated in the RPL Target Option(s) (RTO) can 714 be reached. 716 A P-DAO is sent from a global address of the Root to a global address 717 of the recipient, and MUST be confirmed by a DAO-ACK, which is sent 718 back to a global address of the Root. 720 A P-DAO message MUST contain exactly one RTO and either one VIO or 721 one or more SRVIOs following it. There can be at most one such 722 sequence of RTOs and then RPOs. 724 Like a classical DAO message, a P-DAO causes a change of state only 725 if it is "new" per section 9.2.2. "Generation of DAO Messages" of 726 the RPL specification [RPL]; this is determined using the Segment 727 Sequence information from the RPO as opposed to the Path Sequence 728 from a TIO. Also, a Segment Lifetime of 0 in an RPO indicates that 729 the projected route associated to the Segment is to be removed. 731 There are two kinds of operation for the Projected Routes, the 732 Storing Mode and the Non-Storing Mode. 734 * The Non-Storing Mode is discussed in Section 6.3. It uses an 735 SRVIO that carries a list of Via Addresses to be used as a source- 736 routed Segment to the Track Egress. The recipient of the P-DAO is 737 the ingress router of the source-routed Segment. Upon a Non- 738 Storing Mode P-DAO, the ingress router installs a source-routed 739 state to the Track Egress and replies to the Root directly with a 740 DAO-ACK message. 742 * The Storing Mode is discussed in Section 6.4. It uses a single 743 VIO, within which are signaled one Via Address per consecutive 744 hop, from the ingress to the egress of the path, including the 745 list of all intermediate routers in the data path order. The Via 746 Addresses indicate the routers in which the routing state to the 747 Track Egress have to be installed via the next Via Address in the 748 VIO. In normal operations, the P-DAO is propagated along the 749 chain of Via Routers from the egress router of the path till the 750 ingress one, which confirms the installation to the Root with a 751 DAO-ACK message. Note that the Root may be the ingress and it may 752 be the egress of the path, that it can also be neither but it 753 cannot be both. 755 In case of a forwarding error along a Projected Route, an ICMP error 756 is sent to the Root with a new Code "Error in Projected Route" (See 757 Section 8.9). The Root can then modify or remove the Projected 758 Route. The "Error in Projected Route" message has the same format as 759 the "Destination Unreachable Message", as specified in RFC 4443 760 [RFC4443]. The portion of the invoking packet that is sent back in 761 the ICMP message SHOULD record at least up to the routing header if 762 one is present, and the routing header SHOULD be consumed by this 763 node so that the destination in the IPv6 header is the next hop that 764 this node could not reach. if a 6LoWPAN Routing Header (6LoRH) 765 [RFC8138] is used to carry the IPv6 routing information in the outter 766 header then that whole 6LoRH information SHOULD be present in the 767 ICMP message. The sender and exact operation depend on the Mode and 768 is described in Section 6.3 and Section 6.4 respectively. 770 6.1. Requesting a Track 772 A Node is free to ask the Root for a new Track with a PDR message, 773 for a duration indicated in a Requested Lifetime field. Upon that 774 Request, the Root install the necessary Segments and answers with a 775 PDR-ACK indicated the granted Track Lifetime. When the Track 776 Lifetime returned in the PDR-ACK is close to elapse, the resquesting 777 Node needs to resend a PDR using the TrackID in the PDR-ACK to get 778 the lifetime of the Track prolonged, else the Track will time out and 779 the Root will tear down the whole structure. 781 The Segment Lifetime in the P-DAO messages does not need to be 782 aligned to the Requested Lifetime in the PDR, or between P-DAO 783 messages for different Segments. The Root may use shorter lifetimes 784 for the Segments and renew them faster than the Track is, or longer 785 lifetimes in which case it will need to tear down the Segments if the 786 Track is not renewed. 788 The Root is free to install which ever Segments it wants, and change 789 them overtime, to serve the Track as needed, without notifying the 790 resquesting Node. If the Track fails and cannot be reestablished, 791 the Root notifies the resquesting Node asynchronously with a PDR-ACK 792 with a Track Lifetime of 0, indicating that the Track has failed, and 793 a PDR-ACK Status indicating the reason of the fault. 795 All the Segments MUST be of a same mode, either Storing or Non- 796 Storing. All the Segments MUST be created with the same TrackID and 797 Track Egress in the P-DAO. 799 6.2. Routing over a Track 801 Sending a packet over a Track implies the addition of a RPI to 802 indicate the Track, in association with the IPv6 destination. In 803 case of a Non-Storing Mode Projected Route, a Source Routing Header 804 is needed as well. 806 The Destination IPv6 Address of a packet that is placed in a Track 807 MUST be that of the Track Egress of Track. The outer header of the 808 packet MUST contain an RPI that indicates the TrackID as RPL Instance 809 ID. 811 If the Track Ingress is the originator of the packet and the Track 812 Egress is the destination of the packet, there is no need for an 813 encapsulation. Else, i.e., if the Track Ingress is forwarding a 814 packet into the Track, or if the the final destination is reached via 815 is not the Track Egress, but reached over the Track via the Track 816 Egress, then an IP-in-IP encapsulation is needed. 818 6.3. Non-Storing Mode Projected Route 820 As illustrated in Figure 7, a P-DAO that carries an SRVIO enables the 821 Root to install a source-routed path towards a Track Egress in any 822 particular router; with this path information the router can add a 823 source routed header reflecting the Projected Route to any packet for 824 which the current destination either is the said Track Egress or can 825 be reached via the Track Egress. 827 ------+--------- 828 | Internet 829 | 830 +-----+ 831 | | Border Router 832 | | (RPL Root) 833 +-----+ | P ^ | 834 | | DAO | ACK | Loose 835 o o o o router V | | Source 836 o o o o o o o o o | P-DAO . Route 837 o o o o o o o o o o | Source . Path 838 o o o o o o o o o | Route . From 839 o o o o o o o o | Path . Root 840 o o o o o Track Egress V . To 841 o o o o | Desti- 842 o o o o | nation 843 destination V 845 LLN 847 Figure 7: Projecting a Non-Storing Route 849 A route indicated by an SRVIO may be loose, meaning that the node 850 that owns the next listed Via Address is not necessarily a neighbor. 851 Without proper loop avoidance mechanisms, the interaction of loose 852 source routing and other mechanisms may effectively cause loops. In 853 order to avoid those loops, if the router that installs a Projected 854 Route does not have a connected route (a direct adjacency) to the 855 next soure routed hop and fails to locate it as a neighbor or a 856 neighbor of a neighbor, then it MUST ensure that it has another 857 Projected Route to the next loose hop under the control of the same 858 route computation system, otherwise the P-DAO is rejected. 860 When forwarding a packet to a destination for which the router 861 determines that routing happens via the Track Egress, the router 862 inserts the source routing header in the packet with the destination 863 set to the Track Egress. In order to add a source-routing header, 864 the router encapsulates the packet with an IP-in-IP header and a Non- 865 Storing Mode source routing header (SRH) [RFC6554]. In the 866 uncompressed form the source of the packet would be self, the 867 destination would be the first Via Address in the SRVIO, and the SRH 868 would contain the list of the remaining Via Addresses and then the 869 Track Egress. 871 In the case of a loose source-routed path, there MUST be either a 872 neighbor that is adjacent to the loose next hop, on which case the 873 packet is forwarded to that neighbor, or a source-routed path to the 874 loose next hop; in the latter case, another encapsulation takes place 875 and the process possibly recurses; otherwise the packet is dropped. 877 In practice, the router will normally use the "IPv6 over Low-Power 878 Wireless Personal Area Network (6LoWPAN) Paging Dispatch" [RFC8025] 879 to compress the RPL artifacts as indicated in [RFC8138]. In that 880 case, the router indicates self as encapsulator in an IP-in-IP 6LoRH 881 Header, and places the list of Via Addresses in the order of the 882 SRVIO and then the Track Egress in the SRH 6LoRH Header. 884 In case of a forwarding error along a Source Route path, the node 885 that fails to forward SHOULD send an ICMP error with a code "Error in 886 Source Routing Header" back to the source of the packet, as described 887 in section 11.2.2.3. of [RPL]. Upon this message, the encapsulating 888 node SHOULD stop using the source route path for a period of time and 889 it SHOULD send an ICMP message with a Code "Error in Projected Route" 890 to the Root. Failure to follow these steps may result in packet loss 891 and wasted resources along the source route path that is broken. 893 6.4. Storing Mode Projected Route 895 As illustrated in Figure 8, the Storing Mode route projection is used 896 by the Root to install a routing state in the routers along a Segment 897 between an Ingress and an Egress router this enables the routers to 898 forward along that Segment any packet for which the next loose hop is 899 the Egress node, for instance a loose source routed packet for which 900 the next loose hop is the Egress node, or a packet for which the 901 router has a routing state to the final destination via the Egress 902 node. 904 ------+--------- 905 | Internet 906 | 907 +-----+ 908 | | Border Router 909 | | (RPL Root) 910 +-----+ | ^ | 911 | | DAO | ACK | 912 o o o o | | | 913 o o o o o o o o o | ^ | Projected . 914 o o o o o o o o o o | | DAO | Route . 915 o o o o o o o o o | ^ | . 916 o o o o o o o o v | DAO v . 917 o o LLN o o o | 918 o o o o o Loose Source Route Path | 919 o o o o From Root To Destination v 921 Figure 8: Projecting a route 923 In order to install the relevant routing state along the Segment 924 between an ingress and an egress routers, the Root sends a unicast 925 P-DAO message to the egress router of the routing Segment that must 926 be installed. The P-DAO message contains the ordered list of hops 927 along the Segment as a direct sequence of Via Information options 928 that are preceded by one or more RPL Target options to which they 929 relate. Each Via Information option contains a Segment Lifetime for 930 which the state is to be maintained. 932 The Root sends the P-DAO directly to the egress node of the Segment. 933 In that P-DAO, the destination IP address matches the last Via 934 Address in the VIO. This is how the egress recognizes its role. In 935 a similar fashion, the ingress node recognizes its role as it matches 936 first Via Address in the VIO. 938 The Egress node of the Segment is the only node in the path that does 939 not install a route in response to the P-DAO; it is expected to be 940 already able to route to the Target(s) on its own. It may either be 941 the Target, or may have some existing information to reach the 942 Target(s), such as a connected route or an already installed 943 Projected Route. If one of the Targets cannot be located, the node 944 MUST answer to the Root with a negative DAO-ACK listing the Target(s) 945 that could not be located (suggested status 10 to be confirmed by 946 IANA). 948 If the egress node can reach all the Targets, then it forwards the 949 P-DAO with unchanged content to its loose predecessor in the Segment 950 as indicated in the list of Via Information options, and recursively 951 the message is propagated unchanged along the sequence of routers 952 indicated in the P-DAO, but in the reverse order, from egress to 953 ingress. 955 The address of the predecessor to be used as destination of the 956 propagated DAO message is found in the Via Information option the 957 precedes the one that contain the address of the propagating node, 958 which is used as source of the packet. 960 Upon receiving a propagated DAO, an intermediate router as well as 961 the ingress router install a route towards the DAO Target(s) via its 962 successor in the P-DAO; the router locates its address in the VIO, 963 and uses as next hop the address found in the previous Via Address 964 field in the VIO. The router MAY install additional routes towards 965 the VIA Addresses that are the VIO after the next one, if any, but in 966 case of a conflict or a lack of resource, the route(s) to the 967 Target(s) have precedence. 969 The process recurses till the P-DAO is propagated to ingress router 970 of the Segment, which answers with a DAO-ACK to the Root. 972 Also, the path indicated in a P-DAO may be loose, in which case the 973 reachability to the next hop has to be asserted. Each router along 974 the path indicated in a P-DAO is expected to be able to reach its 975 successor, either with a connected route (direct neighbor), or by 976 routing, for Instance following a route installed previously by a DAO 977 or a P-DAO message. If that route is not connected then a recursive 978 lookup may take place at packet forwarding time to find the next hop 979 to reach the Target(s). If it does not and cannot reach the next 980 router in the P-DAO, the router MUST answer to the Root with a 981 negative DAO-ACK indicating the successor that is unreachable 982 (suggested status 11 to be confirmed by IANA). 984 A Segment Lifetime of 0 in a Via Information option is used to clean 985 up the state. The P-DAO is forwarded as described above, but the DAO 986 is interpreted as a No-Path DAO and results in cleaning up existing 987 state as opposed to refreshing an existing one or installing a new 988 one. 990 In case of a forwarding error along a Storing Mode Projected Route, 991 the node that fails to forward SHOULD send an ICMP error with a code 992 "Error in Projected Route" to the Root. Failure to do so may result 993 in packet loss and wasted resources along the Projected Route that is 994 broken. 996 7. Security Considerations 998 This draft uses messages that are already present in RPL [RPL] with 999 optional secured versions. The same secured versions may be used 1000 with this draft, and whatever security is deployed for a given 1001 network also applies to the flows in this draft. 1003 TODO: should probably consider how P-DAO messages could be abused by 1004 a) rogue nodes b) via replay of messages c) if use of P-DAO messages 1005 could in fact deal with any threats? 1007 8. IANA Considerations 1009 8.1. New RPL Control Codes 1011 This document extends the IANA Subregistry created by RFC 6550 for 1012 RPL Control Codes as indicated in Table 1: 1014 +======+=============================+===============+ 1015 | Code | Description | Reference | 1016 +======+=============================+===============+ 1017 | 0x09 | Projected DAO Request (PDR) | This document | 1018 +------+-----------------------------+---------------+ 1019 | 0x0A | PDR-ACK | This document | 1020 +------+-----------------------------+---------------+ 1022 Table 1: New RPL Control Codes 1024 8.2. New RPL Control Message Options 1026 This document extends the IANA Subregistry created by RFC 6550 for 1027 RPL Control Message Options as indicated in Table 2: 1029 +=======+======================================+===============+ 1030 | Value | Meaning | Reference | 1031 +=======+======================================+===============+ 1032 | 0x0B | Via Information option | This document | 1033 +-------+--------------------------------------+---------------+ 1034 | 0x0C | Source-Routed Via Information option | This document | 1035 +-------+--------------------------------------+---------------+ 1036 | 0x0D | Sibling Information option | This document | 1037 +-------+--------------------------------------+---------------+ 1039 Table 2: RPL Control Message Options 1041 8.3. SubRegistry for the Projected DAO Request Flags 1043 IANA is required to create a registry for the 8-bit Projected DAO 1044 Request (PDR) Flags field. Each bit is tracked with the following 1045 qualities: 1047 * Bit number (counting from bit 0 as the most significant bit) 1049 * Capability description 1051 * Reference 1053 Registration procedure is "Standards Action" [RFC8126]. The initial 1054 allocation is as indicated in Table 3: 1056 +============+========================+===============+ 1057 | Bit number | Capability description | Reference | 1058 +============+========================+===============+ 1059 | 0 | PDR-ACK request (K) | This document | 1060 +------------+------------------------+---------------+ 1061 | 1 | Requested path should | This document | 1062 | | be redundant (R) | | 1063 +------------+------------------------+---------------+ 1065 Table 3: Initial PDR Flags 1067 8.4. SubRegistry for the PDR-ACK Flags 1069 IANA is required to create an subregistry for the 8-bit PDR-ACK Flags 1070 field. Each bit is tracked with the following qualities: 1072 * Bit number (counting from bit 0 as the most significant bit) 1074 * Capability description 1076 * Reference 1077 Registration procedure is "Standards Action" [RFC8126]. No bit is 1078 currently defined for the PDR-ACK Flags. 1080 8.5. Subregistry for the PDR-ACK Acceptance Status Values 1082 IANA is requested to create a Subregistry for the PDR-ACK Acceptance 1083 Status values. 1085 * Possible values are 6-bit unsigned integers (0..63). 1087 * Registration procedure is "Standards Action" [RFC8126]. 1089 * Initial allocation is as indicated in Table 4: 1091 +-------+------------------------+---------------+ 1092 | Value | Meaning | Reference | 1093 +-------+------------------------+---------------+ 1094 | 0 | Unqualified acceptance | This document | 1095 +-------+------------------------+---------------+ 1097 Table 4: Acceptance values of the PDR-ACK Status 1099 8.6. Subregistry for the PDR-ACK Rejection Status Values 1101 IANA is requested to create a Subregistry for the PDR-ACK Rejection 1102 Status values. 1104 * Possible values are 6-bit unsigned integers (0..63). 1106 * Registration procedure is "Standards Action" [RFC8126]. 1108 * Initial allocation is as indicated in Table 5: 1110 +-------+-----------------------+---------------+ 1111 | Value | Meaning | Reference | 1112 +-------+-----------------------+---------------+ 1113 | 0 | Unqualified rejection | This document | 1114 +-------+-----------------------+---------------+ 1116 Table 5: Rejection values of the PDR-ACK Status 1118 8.7. SubRegistry for the Route Projection Options Flags 1120 IANA is requested to create a Subregistry for the 5-bit Route 1121 Projection Options (RPO) Flags field. Each bit is tracked with the 1122 following qualities: 1124 * Bit number (counting from bit 0 as the most significant bit) 1125 * Capability description 1127 * Reference 1129 Registration procedure is "Standards Action" [RFC8126]. No bit is 1130 currently defined for the Route Projection Options (RPO) Flags. 1132 8.8. SubRegistry for the Sibling Information Option Flags 1134 IANA is required to create a registry for the 5-bit Sibling 1135 Information Option (SIO) Flags field. Each bit is tracked with the 1136 following qualities: 1138 * Bit number (counting from bit 0 as the most significant bit) 1140 * Capability description 1142 * Reference 1144 Registration procedure is "Standards Action" [RFC8126]. The initial 1145 allocation is as indicated in Table 6: 1147 +============+===================================+===============+ 1148 | Bit number | Capability description | Reference | 1149 +============+===================================+===============+ 1150 | 0 | Connectivity is bidirectional (B) | This document | 1151 +------------+-----------------------------------+---------------+ 1153 Table 6: Initial SIO Flags 1155 8.9. Error in Projected Route ICMPv6 Code 1157 In some cases RPL will return an ICMPv6 error message when a message 1158 cannot be forwarded along a Projected Route. This ICMPv6 error 1159 message is "Error in Projected Route". 1161 IANA has defined an ICMPv6 "Code" Fields Registry for ICMPv6 Message 1162 Types. ICMPv6 Message Type 1 describes "Destination Unreachable" 1163 codes. This specification requires that a new code is allocated from 1164 the ICMPv6 Code Fields Registry for ICMPv6 Message Type 1, for "Error 1165 in Projected Route", with a suggested code value of 8, to be 1166 confirmed by IANA. 1168 9. Acknowledgments 1170 The authors wish to acknowledge JP Vasseur, Remy Liubing, James 1171 Pylakutty and Patrick Wetterwald for their contributions to the ideas 1172 developed here. 1174 10. Normative References 1176 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1177 Requirement Levels", BCP 14, RFC 2119, 1178 DOI 10.17487/RFC2119, March 1997, 1179 . 1181 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 1182 Control Message Protocol (ICMPv6) for the Internet 1183 Protocol Version 6 (IPv6) Specification", STD 89, 1184 RFC 4443, DOI 10.17487/RFC4443, March 2006, 1185 . 1187 [RPL] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1188 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1189 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1190 Low-Power and Lossy Networks", RFC 6550, 1191 DOI 10.17487/RFC6550, March 2012, 1192 . 1194 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1195 Routing Header for Source Routes with the Routing Protocol 1196 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1197 DOI 10.17487/RFC6554, March 2012, 1198 . 1200 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1201 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1202 May 2017, . 1204 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1205 Writing an IANA Considerations Section in RFCs", BCP 26, 1206 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1207 . 1209 11. Informative References 1211 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1212 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1213 2014, . 1215 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and 1216 J. Martocci, "Reactive Discovery of Point-to-Point Routes 1217 in Low-Power and Lossy Networks", RFC 6997, 1218 DOI 10.17487/RFC6997, August 2013, 1219 . 1221 [6TiSCH-ARCHI] 1222 Thubert, P., "An Architecture for IPv6 over the TSCH mode 1223 of IEEE 802.15.4", Work in Progress, Internet-Draft, 1224 draft-ietf-6tisch-architecture-29, 27 August 2020, 1225 . 1228 [RAW-ARCHI] 1229 Thubert, P., Papadopoulos, G., and R. Buddenberg, 1230 "Reliable and Available Wireless Architecture/Framework", 1231 Work in Progress, Internet-Draft, draft-pthubert-raw- 1232 architecture-04, 6 July 2020, 1233 . 1236 [TURN-ON_RFC8138] 1237 Thubert, P. and L. Zhao, "Configuration option for RFC 1238 8138", Work in Progress, Internet-Draft, draft-thubert- 1239 roll-turnon-rfc8138-03, 8 July 2019, 1240 . 1243 [RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas, 1244 "Deterministic Networking Architecture", RFC 8655, 1245 DOI 10.17487/RFC8655, October 2019, 1246 . 1248 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1249 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1250 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1251 . 1253 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1254 "IPv6 over Low-Power Wireless Personal Area Network 1255 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1256 April 2017, . 1258 [USEofRPLinfo] 1259 Robles, I., Richardson, M., and P. Thubert, "Using RPI 1260 Option Type, Routing Header for Source Routes and IPv6-in- 1261 IPv6 encapsulation in the RPL Data Plane", Work in 1262 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-40, 1263 25 June 2020, . 1266 [PCE] IETF, "Path Computation Element", 1267 . 1269 Appendix A. Applications 1271 A.1. Loose Source Routing 1273 A RPL implementation operating in a very constrained LLN typically 1274 uses the Non-Storing Mode of Operation as represented in Figure 9. 1275 In that mode, a RPL node indicates a parent-child relationship to the 1276 Root, using a Destination Advertisement Object (DAO) that is unicast 1277 from the node directly to the Root, and the Root typically builds a 1278 source routed path to a destination down the DODAG by recursively 1279 concatenating this information. 1281 ------+--------- 1282 | Internet 1283 | 1284 +-----+ 1285 | | Border Router 1286 | | (RPL Root) 1287 +-----+ ^ | | 1288 | | DAO | ACK | 1289 o o o o | | | Strict 1290 o o o o o o o o o | | | Source 1291 o o o o o o o o o o | | | Route 1292 o o o o o o o o o | | | 1293 o o o o o o o o | v v 1294 o o o o 1295 LLN 1297 Figure 9: RPL Non-Storing Mode of operation 1299 Based on the parent-children relationships expressed in the non- 1300 storing DAO messages,the Root possesses topological information about 1301 the whole network, though this information is limited to the 1302 structure of the DODAG for which it is the destination. A packet 1303 that is generated within the domain will always reach the Root, which 1304 can then apply a source routing information to reach the destination 1305 if the destination is also in the DODAG. Similarly, a packet coming 1306 from the outside of the domain for a destination that is expected to 1307 be in a RPL domain reaches the Root. 1309 It results that the Root, or then some associated centralized 1310 computation engine such as a PCE, can determine the amount of packets 1311 that reach a destination in the RPL domain, and thus the amount of 1312 energy and bandwidth that is wasted for transmission, between itself 1313 and the destination, as well as the risk of fragmentation, any 1314 potential delays because of a paths longer than necessary (shorter 1315 paths exist that would not traverse the Root). 1317 As a network gets deep, the size of the source routing header that 1318 the Root must add to all the downward packets becomes an issue for 1319 nodes that are many hops away. In some use cases, a RPL network 1320 forms long lines and a limited amount of well-Targeted routing state 1321 would allow to make the source routing operation loose as opposed to 1322 strict, and save packet size. Limiting the packet size is directly 1323 beneficial to the energy budget, but, mostly, it reduces the chances 1324 of frame loss and/or packet fragmentation, which is highly 1325 detrimental to the LLN operation. Because the capability to store a 1326 routing state in every node is limited, the decision of which route 1327 is installed where can only be optimized with a global knowledge of 1328 the system, a knowledge that the Root or an associated PCE may 1329 possess by means that are outside of the scope of this specification. 1331 This specification enables to store source-routed or Storing Mode 1332 state in intermediate routers, which enables to limit the excursion 1333 of the source route headers in deep networks. Once a P-DAO exchange 1334 has taken place for a given Target, if the Root operates in non 1335 Storing Mode, then it may elide the sequence of routers that is 1336 installed in the network from its source route headers to destination 1337 that are reachable via that Target, and the source route headers 1338 effectively become loose. 1340 A.2. Transversal Routes 1342 RPL is optimized for Point-to-Multipoint (P2MP) and Multipoint-to- 1343 Point (MP2P), whereby routes are always installed along the RPL DODAG 1344 respectively from and towards the DODAG Root. Transversal Peer to 1345 Peer (P2P) routes in a RPL network will generally suffer from some 1346 elongated (stretched) path versus the best possible path, since 1347 routing between 2 nodes always happens via a common parent, as 1348 illustrated in Figure 10: 1350 * In Storing Mode, unless the destination is a child of the source, 1351 the packets will follow the default route up the DODAG as well. 1352 If the destination is in the same DODAG, they will eventually 1353 reach a common parent that has a route to the destination; at 1354 worse, the common parent may also be the Root. From that common 1355 parent, the packet will follow a path down the DODAG that is 1356 optimized for the Objective Function that was used to build the 1357 DODAG. 1359 * in Non-Storing Mode, all packets routed within the DODAG flow all 1360 the way up to the Root of the DODAG. If the destination is in the 1361 same DODAG, the Root must encapsulate the packet to place a 1362 Routing Header that has the strict source route information down 1363 the DODAG to the destination. This will be the case even if the 1364 destination is relatively close to the source and the Root is 1365 relatively far off. 1367 ------+--------- 1368 | Internet 1369 | 1370 +-----+ 1371 | | Border Router 1372 | | (RPL Root) 1373 +-----+ 1374 X 1375 ^ v o o 1376 ^ o o v o o o o o 1377 ^ o o o v o o o o o 1378 ^ o o v o o o o o 1379 S o o o D o o o 1380 o o o o 1381 LLN 1383 Figure 10: Routing Stretch between S and D via common parent X 1385 It results that it is often beneficial to enable transversal P2P 1386 routes, either if the RPL route presents a stretch from shortest 1387 path, or if the new route is engineered with a different objective, 1388 and that it is even more critical in Non-Storing Mode than it is in 1389 Storing Mode, because the routing stretch is wider. For that reason, 1390 earlier work at the IETF introduced the "Reactive Discovery of 1391 Point-to-Point Routes in Low Power and Lossy Networks" [RFC6997], 1392 which specifies a distributed method for establishing optimized P2P 1393 routes. This draft proposes an alternate based on a centralized 1394 route computation. 1396 ------+--------- 1397 | Internet 1398 | 1399 +-----+ 1400 | | Border Router 1401 | | (RPL Root) 1402 +-----+ 1403 | 1404 o o o o 1405 o o o o o o o o o 1406 o o o o o o o o o o 1407 o o o o o o o o o 1408 S>>A>>>B>>C>>>D o o o 1409 o o o o 1410 LLN 1412 Figure 11: Projected Transversal Route 1414 This specification enables to store source-routed or Storing Mode 1415 state in intermediate routers, which enables to limit the stretch of 1416 a P2P route and maintain the characteristics within a given SLA. An 1417 example of service using this mechanism oculd be a control loop that 1418 would be installed in a network that uses classical RPL for 1419 asynchronous data collection. In that case, the P2P path may be 1420 installed in a different RPL Instance, with a different objective 1421 function. 1423 Appendix B. Examples 1425 B.1. Using Storing Mode P-DAO in Non-Storing Mode MOP 1427 In Non-Storing Mode, the DAG Root maintains the knowledge of the 1428 whole DODAG topology, so when both the source and the destination of 1429 a packet are in the DODAG, the Root can determine the common parent 1430 that would have been used in Storing Mode, and thus the list of nodes 1431 in the path between the common parent and the destination. For 1432 Instance in the diagram shown in Figure 12, if the source is node 41 1433 and the destination is node 52, then the common parent is node 22. 1435 ------+--------- 1436 | Internet 1437 | 1438 +-----+ 1439 | | Border Router 1440 | | (RPL Root) 1441 +-----+ 1442 | \ \____ 1443 / \ \ 1444 o 11 o 12 o 13 1445 / | / \ 1446 o 22 o 23 o 24 o 25 1447 / \ | \ \ 1448 o 31 o 32 o o o 35 1449 / / | \ | \ 1450 o 41 o 42 o o o 45 o 46 1451 | | | | \ | 1452 o 51 o 52 o 53 o o 55 o 56 1454 LLN 1456 Figure 12: Example DODAG forming a logical tree topology 1458 With this draft, the Root can install a Storing Mode routing states 1459 along a Segment that is either from itself to the destination, or 1460 from one or more common parents for a particular source/destination 1461 pair towards that destination (in this particular example, this would 1462 be the Segment made of nodes 22, 32, 42). 1464 In the example below, say that there is a lot of traffic to nodes 55 1465 and 56 and the Root decides to reduce the size of routing headers to 1466 those destinations. The Root can first send a DAO to node 45 1467 indicating Target 55 and a Via Segment (35, 45), as well as another 1468 DAO to node 46 indicating Target 56 and a Via Segment (35, 46). This 1469 will save one entry in the routing header on both sides. The Root 1470 may then send a DAO to node 35 indicating Targets 55 and 56 a Via 1471 Segment (13, 24, 35) to fully optimize that path. 1473 Alternatively, the Root may send a DAO to node 45 indicating Target 1474 55 and a Via Segment (13, 24, 35, 45) and then a DAO to node 46 1475 indicating Target 56 and a Via Segment (13, 24, 35, 46), indicating 1476 the same DAO Sequence. 1478 B.2. Projecting a Storing Mode transversal route 1480 In this example, say that a PCE determines that a path must be 1481 installed between node I and node D via routers A, B and E, in order 1482 to serve the needs of a particular application. 1484 The Root sends a P-DAO to node E, with an RTO indicating the 1485 destination D, a TIO optionally indicating the Track Egress in the 1486 Parent Address field, and a sequence of Via Information options 1487 indicating the hops, one for S, which is the ingress router of the 1488 Segment, one for A, and then one for B, which are respectively the 1489 intermediate and penultimate routers. 1491 ------+--------- 1492 | Internet 1493 | 1494 +-----+ 1495 | | Border Router 1496 | | (RPL Root) 1497 +-----+ 1498 | P-DAO message to C 1499 o | o o 1500 o o o | o o o o o 1501 o o o | o o o o o o 1502 o o V o o o o o o 1503 S A B E D o o o 1504 o o o o 1505 LLN 1507 Figure 13: P-DAO from Root 1509 Upon reception of the P-DAO, C validates that it can reach D, e.g. 1510 using IPv6 Neighbor Discovery, and if so, propagates the P-DAO 1511 unchanged to B. 1513 B checks that it can reach C and of so, installs a route towards D 1514 via C. Then it propagates the P-DAO to A. 1516 The process recurses till the P-DAO reaches S, the ingress of the 1517 Segment, which installs a route to D via A and sends a DAO-ACK to the 1518 Root. 1520 ------+--------- 1521 | Internet 1522 | 1523 +-----+ 1524 | | Border Router 1525 | | (RPL Root) 1526 +-----+ 1527 ^ P-DAO-ACK from S 1528 / o o o 1529 / o o o o o o o 1530 | o o o o o o o o o 1531 | o o o o o o o o 1532 S A B C D o o o 1533 o o o o 1534 LLN 1536 Figure 14: P-DAO-ACK to Root 1538 As a result, a transversal route is installed that does not need to 1539 follow the DODAG structure. 1541 ------+--------- 1542 | Internet 1543 | 1544 +-----+ 1545 | | Border Router 1546 | | (RPL Root) 1547 +-----+ 1548 | 1549 o o o o 1550 o o o o o o o o o 1551 o o o o o o o o o o 1552 o o o o o o o o o 1553 S>>A>>>B>>C>>>D o o o 1554 o o o o 1555 LLN 1557 Figure 15: Projected Transversal Route 1559 Authors' Addresses 1561 Pascal Thubert (editor) 1562 Cisco Systems, Inc 1563 Building D 1564 45 Allee des Ormes - BP1200 1565 06254 Mougins - Sophia Antipolis 1566 France 1567 Phone: +33 497 23 26 34 1568 Email: pthubert@cisco.com 1570 Rahul Arvind Jadhav 1571 Huawei Tech 1572 Kundalahalli Village, Whitefield, 1573 Bangalore 560037 1574 Karnataka 1575 India 1577 Phone: +91-080-49160700 1578 Email: rahul.ietf@gmail.com 1580 Matthew Gillmore 1581 Itron, Inc 1582 Building D 1583 2111 N Molter Road 1584 Liberty Lake, 99019 1585 United States 1587 Phone: +1.800.635.5461 1588 Email: matthew.gillmore@itron.com