idnits 2.17.1 draft-ietf-roll-dao-projection-10.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- -- The draft header indicates that this document updates RFC6550, but the abstract doesn't seem to mention this, which it should. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (11 May 2020) is 1445 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-30) exists of draft-ietf-6tisch-architecture-28 == Outdated reference: A later version (-09) exists of draft-pthubert-raw-architecture-01 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ROLL P. Thubert, Ed. 3 Internet-Draft Cisco Systems 4 Updates: 6550 (if approved) R.A. Jadhav 5 Intended status: Standards Track Huawei Tech 6 Expires: 12 November 2020 M. Gillmore 7 Itron 8 11 May 2020 10 Root initiated routing state in RPL 11 draft-ietf-roll-dao-projection-10 13 Abstract 15 This document enables a RPL Root to install and maintain Projected 16 Routes within its DODAG, along a selected set of nodes that may or 17 may not include self, for a chosen duration. This potentially 18 enables routes that are more optimized or resilient than those 19 obtained with the classical distributed operation of RPL, either in 20 terms of the size of a source-route header or in terms of path 21 length, which impacts both the latency and the packet delivery ratio. 22 Projected Routes may be installed in either Storing and Non-Storing 23 Modes Instances of the classical RPL operation, resulting in 24 potentially hybrid situations where the mode of some Projected Routes 25 is different from that of the other routes in the RPL Instance. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at https://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on 12 November 2020. 44 Copyright Notice 46 Copyright (c) 2020 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 51 license-info) in effect on the date of publication of this document. 52 Please review these documents carefully, as they describe your rights 53 and restrictions with respect to this document. Code Components 54 extracted from this document must include Simplified BSD License text 55 as described in Section 4.e of the Trust Legal Provisions and are 56 provided without warranty as described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 61 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 62 2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 4 63 2.2. References . . . . . . . . . . . . . . . . . . . . . . . 5 64 2.3. Other Terms . . . . . . . . . . . . . . . . . . . . . . . 5 65 2.4. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 5 66 3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 6 67 4. Identifying a Path . . . . . . . . . . . . . . . . . . . . . 7 68 5. New RPL Control Messages and Options . . . . . . . . . . . . 8 69 5.1. New P-DAO Request Control Message . . . . . . . . . . . . 8 70 5.2. New PDR-ACK Control Message . . . . . . . . . . . . . . . 8 71 5.3. Route Projection Options . . . . . . . . . . . . . . . . 10 72 5.4. Sibling Information Option . . . . . . . . . . . . . . . 12 73 6. Projected DAO . . . . . . . . . . . . . . . . . . . . . . . . 14 74 6.1. Non-Storing Mode Projected Route . . . . . . . . . . . . 15 75 6.2. Storing-Mode Projected Route . . . . . . . . . . . . . . 17 76 7. Security Considerations . . . . . . . . . . . . . . . . . . . 19 77 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 78 8.1. New RPL Control Codes . . . . . . . . . . . . . . . . . . 19 79 8.2. New RPL Control Message Options . . . . . . . . . . . . . 19 80 8.3. New SubRegistry for the Projected DAO Request (PDR) 81 Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 20 82 8.4. New SubRegistry for the PDR-ACK Flags . . . . . . . . . . 20 83 8.5. New Subregistry for the PDR-ACK Acceptance Status 84 values . . . . . . . . . . . . . . . . . . . . . . . . . 21 85 8.6. New Subregistry for the PDR-ACK Rejection Status 86 values . . . . . . . . . . . . . . . . . . . . . . . . . 21 87 8.7. New SubRegistry for the Route Projection Options (RPO) 88 Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 21 89 8.8. New SubRegistry for the Sibling Information Option (SIO) 90 Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 22 91 8.9. Error in Projected Route ICMPv6 Code . . . . . . . . . . 22 92 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22 93 10. Normative References . . . . . . . . . . . . . . . . . . . . 23 94 11. Informative References . . . . . . . . . . . . . . . . . . . 23 95 Appendix A. Applications . . . . . . . . . . . . . . . . . . . . 24 96 A.1. Loose Source Routing in Non-storing Mode . . . . . . . . 25 97 A.2. Transversal Routes in storing and non-storing modes . . . 26 98 Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 28 99 B.1. Using storing mode P-DAO in non-storing mode MOP . . . . 28 100 B.2. Projecting a storing-mode transversal route . . . . . . . 29 101 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 103 1. Introduction 105 RPL, the "Routing Protocol for Low Power and Lossy Networks" [RPL] 106 (LLNs), is a generic Distance Vector protocol that is well suited for 107 application in a variety of low energy Internet of Things (IoT) 108 networks. RPL forms Destination Oriented Directed Acyclic Graphs 109 (DODAGs) in which the Root often acts as the Border Router to connect 110 the RPL domain to the Internet. The Root is responsible to select 111 the RPL Instance that is used to forward a packet coming from the 112 Internet into the RPL domain and set the related RPL information in 113 the packets. 115 The "6TiSCH architecture" [6TiSCH-ARCHI] leverages RPL for its 116 routing operations and considers the Deterministic Networking 117 Architecture [RFC8655] as one possible model whereby the device 118 resources and capabilities are exposed to an external controller 119 which installs routing states into the network based on some 120 objective functions that reside in that external entity. With DetNet 121 and 6TiSCH, the component of the controller that is responsible of 122 computing routes is called a Path Computation Element ([PCE]). 124 Based on heuristics of usage, path length, and knowledge of device 125 capacity and available resources such as battery levels and 126 reservable buffers, a PCE with a global visibility on the system can 127 compute P2P routes that are more optimized for the current needs as 128 expressed by the objective function. This draft proposes a protocol 129 extension to RPL that enables the Root to install a limited amount of 130 centrally-computed routes in a RPL graph, on behalf of a PCE that may 131 be collocated or separated from the Root. Those extensions enable 132 loose source routing down in RPL Non-Storing Mode and transversal 133 routes inside the DODAG regardless of the RPL Mode of Operation 134 (MOP). 136 The 6TiSCH architecture also introduces the concept of a Track that 137 is a complex path with possibly redundant forwarding solutions along 138 the way, exploiting Packet ARQ, Replication, Elimination, and 139 Overhearing (PAREO) functions. The "Reliable and Available Wireless 140 (RAW) Architecture/Framework" [RAW-ARCHI] separates the time scale at 141 which the PCE computes the Track (slow, globally optimized, with 142 statistical metrics) and the time scale at which the forwarding 143 decision is made for a packet or a small collection of packets (fast, 144 at the scale of the Track), to leverage the PAREO functions 145 dynamically and provide the required reliability and availability 146 while conserving energy and spectrum. 148 As opposed to the classical RPL operations where routes are injected 149 by the Target nodes, the protocol extension enables the Root of a 150 DODAG to project the routes that are needed onto the nodes where they 151 should be installed. This specification uses the term Projected 152 Route to refer to those routes. A Projected Route may be a stand- 153 alone end-to-end path to a Target or a segment in a more complex 154 Track. 156 Projected Routes must be used with the parsimony to limit the amount 157 of state that is installed in each device to fit within its 158 resources, and to limit the amount of rerouted traffic to fit within 159 the capabilities of the transmission links. The method to learn the 160 node capabilities and the resources that are available in the devices 161 and in the network are out of scope for this document. 163 In RPL Non-Storing Mode, the Root has enough information to build a 164 basic DODAG topology. This document adds the capability for nodes to 165 advertise sibling information in order to improve the topological 166 awareness of the Root. This specification uses the RPL Root as a 167 proxy to the PCE. The algorithm to compute the paths and the 168 protocol used by an external PCE to obtain the topology of the 169 network from the Root are out of scope for this document. 171 2. Terminology 173 2.1. BCP 14 175 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 176 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 177 "OPTIONAL" in this document are to be interpreted as described in BCP 178 14 [RFC2119][RFC8174] when, and only when, they appear in all 179 capitals, as shown here. 181 2.2. References 183 In this document, readers will encounter terms and concepts that are 184 discussed in the following documents: 186 * "Routing Protocol for Low Power and Lossy Networks" [RPL], and 187 * "Terminology in Low power And Lossy Networks" [RFC7102]. 189 2.3. Other Terms 191 Projected Route: A Projected Route is a serial path that is computed 192 and installed remotely by a RPL Root. 193 Track: The term Track is used in this document to refer to a complex 194 path, e.g., a DODAG, that incorporates redundant Projected Routes 195 towards a destination using diversity to increase the reliability. 197 2.4. Glossary 199 This document often uses the following acronyms: 201 6BBR: 6LoWPAN Backbone Router 202 6LBR: 6LoWPAN Border Router 203 6LN: 6LoWPAN Node 204 6LR: 6LoWPAN Router 205 CMO: Control Message Option 206 DAD: Duplicate Address Detection 207 DAO: Destination Advertisement Object 208 DODAG: Destination-Oriented Directed Acyclic Graph 209 LLN: Low-Power and Lossy Network 210 MOP: RPL Mode of Operation 211 NA: Neighbor Advertisement 212 NCE: Neighbor Cache Entry 213 ND: Neighbor Discovery 214 NDP: Neighbor Discovery Protocol 215 NS: Neighbor Solicitation 216 P-DAO: A Projected DAO is a DAO message sent by the RPL Root to 217 install a Projected Route. 218 PDR P-DAO Request 219 RA: Router Advertisement 220 RAN: RPL-Aware Node 221 RS: Router Solicitation 222 RPL: IPv6 Routing Protocol for LLNs [RPL] 223 RPO: A Route Projection Option; it can be a VIO or an SRVIO. 224 RTO: RPL Target Option 225 SIO: RPL Sibling Information Option 226 SRVIO: A Source-Routed Via Information Option, used in Non-Storing 227 Mode P-DAO messages. 228 TIO: RPL Transit Information Option 229 VIO: A Via Information Option, used in Storing Mode P-DAO messages. 231 3. Updating RFC 6550 233 This specification introduces two new RPL Control Messages to enable 234 a RPL Aware Node (RAN) to request the establisment of a path from 235 self to a Target. A RAN may request the installation of a path by 236 sending a new P-DAO Request (PDR) Message to the Root. The Root 237 confirms with a new PDR-ACK message back to the requester RAN with a 238 completion status once it is done installing the path. See 239 Section 5.1 for more. 241 Section 6.7 of [RPL] specifies the RPL Control Message Options (CMO) 242 to be placed in RPL messages such as the Destination Advertisement 243 Object (DAO) message. The RPL Target Option (RTO) and the Transit 244 Information Option (TIO) are such options. In Non-Storing Mode, the 245 TIO option is used in the DAO message to indicate a parent within a 246 DODAG. The TIO applies to the RTOs that immedially preceed it in the 247 message. Options may be factorized; multiple TIOs may be present to 248 indicate multiple routes to the one or more contiguous addresses 249 indicated in the RTOs that immediately precede the TIOs in the RPL 250 message. 252 This specification introduces two new CMOs referred to as Route 253 Projection Options (RPO) to install Projected Routes. One RPO is the 254 Via Information Option (VIO) and the other is the Source-Routed VIO 255 (SRVIO). The VIO installs a route on each hop along a Projected 256 Route (in a fashion analogous to RPL Storing Mode) whereas the SRVIO 257 installs a source-routing state at the ingress node, which uses that 258 state to encapsulate a packet with an IPv6 Routing Header in a 259 fashion similar to RPL Non-Storing Mode. Like the TIO, the RPOs MUST 260 be preceded by exactly one RTO to which they apply, and they can be 261 factorized: multiple contiguous RPOs indicate alternate paths to the 262 Target, more in Section 5.3. 264 This specification also introduces a new CMO to enable a RAN to 265 advertise a selection of its candidate neighbors as siblings to the 266 Root, using a new Sibling Information Option (SIO) as specified in 267 Section 5.4. 269 4. Identifying a Path 271 It must be noted that RPL has a concept of Instance to represent 272 different routing topologies but does not have a concept of an 273 administrative distance, which exists in certain proprietary 274 implementations to sort out conflicts between multiple sources of 275 routing information within one routing topology. 277 This draft conforms the Instance model as follows: 279 * If the PCE needs to influence a particular Instance to add better 280 routes in conformance with the routing objectives in that 281 Instance, it may do so as long as it does not create a loop. A 282 Projected Route is always preferred over a route that is learned 283 via RPL. 285 * A PCE that installs a more specific (say, Traffic Engineered) and 286 possibly complex path (aka a Track) towards a particular Target 287 MUST use a Local RPL Instance (see section 5 of [RPL]) associated 288 to that Target to identify the path. We refer to that Local 289 RPLInstanceID as TrackID. A projected path is uniquely identified 290 within the RPL domain by the tuple (Target address, TrackID). 291 When packet is placed on a Track, a RPL Packet Information (RPI) 292 is added with the TrackID as RPLInstanceID. The RPLInstanceID has 293 the 'D' flag set, indicating that the destination address in the 294 IPv6 header is the Target that is used to identify the Track. 296 * A packet that is routed over a projected path MUST NOT be placed 297 over a different RPL Instance again. A packet that is placed on a 298 Global Instance MAY be injected in a Local Instance based on a 299 network policy and the Local Instance configuration. 301 A Projected Route is a serial path that may represent the end-to-end 302 route or only a segment in a complex Track, in which case multiple 303 Projected Routes are installed with the same tuple (Target address, 304 TrackID) and a different segment ID. A node that is present on more 305 than one segment in a Track may be able to use either of the 306 Projected Routes to forward towards the Target. The selection of the 307 best route in a Track at forwarding time is out of scope for this 308 document, but [RAW-ARCHI] elaborates on that particular problem. 310 All properties of a Track operations are inherited form the main 311 instance that is used to install the Track. For instance, the use of 312 compression per [RFC8138] is determined by whether it is used in the 313 main instance, e.g., by setting the "T" flag [TURN-ON_RFC8138] in the 314 RPL configuration option. 316 5. New RPL Control Messages and Options 318 5.1. New P-DAO Request Control Message 320 The PDR is sent to the Root to request a new Path. Exactly one 321 Target Options MUST be present. 323 The format of P-DAO Request (PDR) Base Object is as follows: 325 0 1 2 3 326 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 1 327 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 328 | TrackID |K|R| Flags | PDRLifetime | PDRSequence | 329 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 330 | Option(s)... 331 +-+-+-+-+-+-+-+-+ 333 Figure 1: New P-DAO Request Format 335 TrackID: 8-bit field indicating the RPLInstanceID associated with 336 the Track. It is set to zero upon the first request for a new 337 Track and then to the TrackID once the Track was created, to 338 either renew it of destroy it. 340 K: The 'K' flag is set to indicate that the recipient is expected to 341 send a PDR-ACK back. 343 R: The 'R' flag is set to indicate that the Requested path should be 344 redundant. 346 PDRLifetime: 8-bit unsigned integer. The requested lifetime for the 347 Track expressed in Lifetime Units (obtained from the Configuration 348 option). A PDR with a fresher PDRSequence refreshes the lifetime, 349 and a PDRLifetime of 0 indicates that the track should be 350 destroyed. 352 PDRSequence: 8-bit wrapping sequence number. The PDRSequence obeys 353 the operation in section 7.2 of [RPL]. It is incremented at each 354 PDR message and echoed in the PDR-ACK by the Root. The 355 PDRSequence is used to correlate a PDR-ACK message with the PDR 356 message that triggeted it. 358 5.2. New PDR-ACK Control Message 360 The new PDR-ACK is sent as a response to a PDR message with the 'K' 361 flag set. Its format is as follows: 363 0 1 2 3 364 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 1 365 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 366 | TrackID | PDR-ACK Status| Flags | Track Lifetime| 367 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 368 | PDRSequence | Reserved | 369 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 370 | Option(s)... 371 +-+-+-+-+-+-+-+ 373 Figure 2: New PDR-ACK Control Message Format 375 TrackID: The RPLInstanceID of the Track that was created. Set to 0 376 when no Track is created. 378 PDR-ACK Status: Indicates the completion. Substructured as 379 indicated in Figure 3. 381 Track Lifetime: Indicates that remaining Lifetime for the Track, 0 382 if the Track was destroyed or not created. 384 PDRSequence: 8-bit wrapping sequence number. It is incremented at 385 each PDR message and echoed in the PDR-ACK. 387 The PDR-ACK Status is further substructured as follows: 389 0 390 0 1 2 3 4 5 6 7 391 +-+-+-+-+-+-+-+-+ 392 |E|R| Value | 393 +-+-+-+-+-+-+-+-+ 395 Figure 3: PDR-ACK status Format 397 The PDR-ACK Status subfields are: 399 E: 1-bit flag. Set to indicate a rejection. When not set, a value 400 of 0 indicates Success/Unqualified acceptance and other values 401 indicate "not an outright rejection". 403 R: 1-bit flag. Reserved, MUST be set to 0 by the sender and ignored 404 by the receiver. 406 Status Value: 6-bit unsigned integer. Values depedning on the 407 setting of the 'E' flag as indicated respectively in Table 4 and 408 Table 5. 410 5.3. Route Projection Options 412 The RPOs indicate a series of IPv6 addresses that can be compressed 413 using the method defined in the "6LoWPAN Routing Header" [RFC8138] 414 specification using the address of the Root found in the DODAGID 415 field of DIO messages as Compression Reference. 417 An RPO indicates a Projected Route that can be a serial Track in full 418 or a segment of a more complex Track. In the latter case, multiple 419 RPO may be placed after a same Target Option. The Track is 420 identified by a TrackID that is a Local RPLInstanceID to the Target 421 of the Track. 423 The format of RPOs is as follows: 425 0 1 2 3 426 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 428 | Type | Option Length |Comp.| Flags | TrackID | 429 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 430 | Track Sequence| Track Lifetime| SegmentID |Segm. Sequence | 431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 432 | | 433 + + 434 . . 435 . Via Address 1 . 436 . . 437 + + 438 | | 439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 440 | | 441 . .... . 442 | | 443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 444 | | 445 + + 446 . . 447 . Via Address n . 448 . . 449 + + 450 | | 451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 453 Figure 4: Via Information option format 455 Option Type: 0x0A for VIO, 0x0B for SRVIO (to be confirmed by IANA) 456 Option Length: In bytes; variable, depending on the number of Via 457 Addresses. 459 Compression Type: 3-bit unsigned integer. This is the SRH-6LoRH 460 Type as defined in figure 7 in section 5.1 of [RFC8138] that 461 corresponds to the compression used for all the Via Addresses. 463 TrackID: 8-bit field indicating the topology Instance associated 464 with the Track. The tuple (Target Address, TrackID) forms a 465 unique ID of the Track in the RPL domain. 467 Track Sequence: 8-bit unsigned integer. The Track Sequence obeys 468 the operation in section 7.2 of [RPL] and the lollipop starts at 469 255. The Track Sequence is set by the Root and incremented each 470 time the Root refreshes that Track globally. A Track Sequence 471 that is fresher than the current on deprecates any state for the 472 Track. A Track Sequence that is current adds to any state that 473 was learned for that Track Sequence. A RTO with a Track Sequence 474 that is not as fresh as the current one is ignored. 476 Track Lifetime: 8-bit unsigned integer. The length of time in 477 Lifetime Units (obtained from the Configuration option) that the 478 Track is usable. The period starts when a new Track Sequence is 479 seen. A value of 255 (0xFF) represents infinity. A value of zero 480 (0x00) indicates a loss of reachability. A DAO message that 481 contains a Via Information option with a Path Lifetime of zero for 482 a Target is referred as a No-Path (for that Target) in this 483 document. 485 SegmentID: 8-bit field that identifies a segment within a Track. A 486 Value of 0 is used to signal a serial Track. 488 Segment Sequence: 8-bit unsigned integer. The Segment Sequence 489 obeys the operation in section 7.2 of [RPL] and the lollipop 490 starts at 255. When the Root of the DODAG needs to update a 491 single segment in a Track, but does not need to modify the rest of 492 the Track, it increments the Segment Sequence but not the Track 493 Sequence. The segment information indicated in the RTO deprecates 494 any state for the segment indicated by the SegmentID within the 495 indicated Track and sets up the new information. A RTO with a 496 Segment Sequence that is not as fresh as the current one is 497 ignored. a RTO for a given target with the same (TrackID, Track 498 Sequence, SegmentID, Segment Sequence) indicates a retry; it MUST 499 NOT change the segment and MUST be propagated or answered as the 500 first copy. 502 Via Address: 2 to 16 bytes, a compressed IPv6 Address. A Via 503 Address indicates the next hop within the path towards the 504 destination(s) that is indicated in the Target option that 505 immediately precede the RPO in the DAO message. Via Addresses are 506 indicated in the order of the path from the ingress to the egress 507 nodes. All Via addresses are expressed in the same size as 508 indicated by the Compression Type. 510 An RPO MUST contain at least one Via Address, and a Via Address MUST 511 NOT be present more than once, otherwise the RPO MUST be ignored. 513 5.4. Sibling Information Option 515 The Sibling Information Option (SIO) provides indication on siblings 516 that could be used by the Root to form Projected Routes. The format 517 of SIOs is as follows: 519 0 1 2 3 520 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 1 521 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 522 | Type | Option Length |Comp.|B|D|Flags| Opaque | 523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 524 | Step of Rank | Sibling Rank | 525 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 526 | | 527 + + 528 . . 529 . Sibling DODAGID (if 'D' flag not set) . 530 . . 531 + + 532 | | 533 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 534 | | 535 + + 536 . . 537 . Sibling Address . 538 . . 539 + + 540 | | 541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 543 Figure 5: Sibling Information Option Format 545 Option Type: 0x0C (to be confirmed by IANA) 547 Option Length: In bytes; variable, depending on the number of Via 548 Addresses. 550 Compression Type: 3-bit unsigned integer. This is the SRH-6LoRH 551 Type as defined in figure 7 in section 5.1 of [RFC8138] that 552 corresponds to the compression used for the Sibling Address. 554 Reserved for Flags: MUST be set to zero by the sender and MUST be 555 ignored by the receiver. 557 B: 1-bit flag that is set to indicate that the connectivity to the 558 sibling is bidirectional and roughly symmetrical. In that case, 559 only one of the siblings may report the SIO for the hop. If 'B' 560 is not set then the SIO only indicates connectivity from the 561 sibling to this node, and does not provide information on the hop 562 from this node to the sibling. 564 D: 1-bit flag that is set to indicate that sibling belongs to the 565 same DODAG. When not set, the Sibling DODAGID is indicated. 567 Opaque: MAY be used to carry information that the node and the Root 568 understand, e.g., a particular representation of the Link 569 properties such as a proprietary Link Quality Information for 570 packets received from the sibling. An industraial Alliance that 571 uses RPL for a particular use / environment MAY redefine the use 572 of this field to fit its needs. 574 Step of Rank: 16-bit unsigned integer. This is the Step of Rank 575 [RPL] as computed by the Objective Function between this node and 576 the sibling. 578 Sibling Rank: 16-bit unsigned integer. When non-zero, this is the 579 Rank [RPL] as exposed by the sibling in DIO messages. 581 Sibling DODAGID: 2 to 16 bytes, the DODAGID of the sibling in a 582 [RFC8138] compressed form as indicated by the Compression Type 583 field. This field is present when the 'D' flag is not set. 585 Sibling Address: 2 to 16 bytes, the IPv6 Address of the sibling in a 586 [RFC8138] compressed form as indicated by the Compression Type 587 field. 589 An SIO MAY be immediately followed by a DAG Metric Container. In 590 that case the DAG Metric Container provides additional metrics for 591 the hop from the Sibling to this node. 593 6. Projected DAO 595 This draft adds a capability to RPL whereby the Root of a DODAG 596 projects a route by sending an extended DAO message called one or 597 more Projected-DAO (P-DAO) messages to an arbitrary router in the 598 DODAG, indicating one or more sequence(s) of routers inside the DODAG 599 via which the Target(s) indicated in the RPL Target Option(s) (RTO) 600 can be reached. 602 A P-DAO is sent from a global address of the Root to a global address 603 of the recipient, and MUST be confirmed by a DAO-ACK, which is sent 604 back to a global address of the Root. 606 A P-DAO message MUST contain at least one RTO and at least one RPO 607 following it. There can be at most one such sequence of RTOs and 608 then RPOs. 610 Like a classical DAO message, a P-DAO causes a change of state only 611 if it is "new" per section 9.2.2. "Generation of DAO Messages" of 612 the RPL specification [RPL]; this is determined using the Track 613 Sequence and the Segment Sequence information from the RPO as opposed 614 to the Path Sequence from a TIO. Also, a Path Lifetime of 0 in an 615 RPO indicates that a route is to be removed. 617 There are two kinds of operation for the Projected Routes, the 618 Storing Mode and the Non-Storing Mode. 620 * The Non-Storing Mode is discussed in Section 6.1. It uses an 621 SRVIO that carries a list of Via Addresses to be used as a source- 622 routed path to the Target. The recipient of the P-DAO is the 623 ingress router of the source-routed path. Upon a Non-Storing Mode 624 P-DAO, the ingress router installs a source-routed state to the 625 Target and replies to the Root directly with a DAO-ACK message. 627 * The Storing Mode is discussed in Section 6.2. It uses a VIO with 628 one Via Address per consecutive hop, from the ingress to the 629 egress of the path, including the list of all intermediate routers 630 in the data path order. The Via Addresses indicate the routers in 631 which the routing state to the Target have to be installed via the 632 next Via Address in the VIO. In normal operations, the P-DAO is 633 propagated along the chain of Via Routers from the egress router 634 of the path till the ingress one, which confirms the installation 635 to the Root with a DAO-ACK message. Note that the Root may be the 636 ingress and it may be the egress of the path, that it can also be 637 neither but it cannot be both. 639 In case of a forwarding error along a Projected Route, an ICMP error 640 is sent to the Root with a new Code "Error in Projected Route" (See 641 Section 8.9). The Root can then modify or remove the Projected 642 Route. The "Error in Projected Route" message has the same format as 643 the "Destination Unreachable Message", as specified in RFC 4443 644 [RFC4443]. The portion of the invoking packet that is sent back in 645 the ICMP message SHOULD record at least up to the routing header if 646 one is present, and the routing header SHOULD be consumed by this 647 node so that the destination in the IPv6 header is the next hop that 648 this node could not reach. if a 6LoWPAN Routing Header (6LoRH) 649 [RFC8138] is used to carry the IPv6 routing information in the outter 650 header then that whole 6LoRH information SHOULD be present in the 651 ICMP message. The sender and exact operation depend on the Mode and 652 is described in Section 6.1 and Section 6.2 respectively. 654 6.1. Non-Storing Mode Projected Route 656 As illustrated in Figure 6, a P-DAO that carries an SRVIO enables the 657 Root to install a source-routed path towards a Target in any 658 particular router; with this path information the router can add a 659 source routed header reflecting the Projected Route to any packet for 660 which the current destination either is the said Target or can be 661 reached via the Target. 663 ------+--------- 664 | Internet 665 | 666 +-----+ 667 | | Border Router 668 | | (RPL Root) 669 +-----+ | P ^ | 670 | | DAO | ACK | Loose 671 o o o o router V | | Source 672 o o o o o o o o o | P-DAO . Route 673 o o o o o o o o o o | Source . Path 674 o o o o o o o o o | Route . From 675 o o o o o o o o | Path . Root 676 o o o o o Target V . To 677 o o o o | Desti- 678 o o o o | nation 679 destination V 681 LLN 683 Figure 6: Projecting a Non-Storing Route 685 A route indicated by an SRVIO may be loose, meaning that the node 686 that owns the next listed Via Address is not necessarily a neighbor. 687 Without proper loop avoidance mechanisms, the interaction of loose 688 source routing and other mechanisms may effectively cause loops. In 689 order to avoid those loops, if the router that installs a Projected 690 Route does not have a connected route (a direct adjacency) to the 691 next soure routed hop and fails to locate it as a neighbor or a 692 neighbor of a neighbor, then it MUST ensure that it has another 693 Projected Route to the next loose hop under the control of the same 694 route computation system, otherwise the P-DAO is rejected. 696 When forwarding a packet to a destination for which the router 697 determines that routing happens via the Target, the router inserts 698 the source routing header in the packet to reach the Target. In 699 order to add a source-routing header, the router encapsulates the 700 packet with an IP-in-IP header and a non-storing mode source routing 701 header (SRH) [RFC6554]. In the uncompressed form the source of the 702 packet would be self, the destination would be the first Via Address 703 in the SRVIO, and the SRH would contain the list of the remaining Via 704 Addresses and then the Target. 706 In the case of a loose source-routed path, there MUST be either a 707 neighbor that is adjacent to the loose next hop, on which case the 708 packet is forwarded to that neighbor, or a source-routed path to the 709 loose next hop; in the latter case, another encapsulation takes place 710 and the process possibly recurses; otherwise the packet is dropped. 712 In practice, the router will normally use the "IPv6 over Low-Power 713 Wireless Personal Area Network (6LoWPAN) Paging Dispatch" [RFC8025] 714 to compress the RPL artifacts as indicated in [RFC8138]. In that 715 case, the router indicates self as encapsulator in an IP-in-IP 6LoRH 716 Header, and places the list of Via Addresses in the order of the VIO 717 and then the Target in the SRH 6LoRH Header. 719 In case of a forwarding error along a Source Route path, the node 720 that fails to forward SHOULD send an ICMP error with a code "Error in 721 Source Routing Header" back to the source of the packet, as described 722 in section 11.2.2.3. of [RPL]. Upon this message, the encapsulating 723 node SHOULD stop using the source route path for a period of time and 724 it SHOULD send an ICMP message with a Code "Error in Projected Route" 725 to the Root. Failure to follow these steps may result in packet loss 726 and wasted resources along the source route path that is broken. 728 6.2. Storing-Mode Projected Route 730 As illustrated in Figure 7, the Storing Mode route projection is used 731 by the Root to install a routing state towards a Target in the 732 routers along a segment between an ingress and an egress router; this 733 enables the routers to forward along that segment any packet for 734 which the next loose hop is the said Target, for Instance a loose 735 source routed packet for which the next loose hop is the Target, or a 736 packet for which the router has a routing state to the final 737 destination via the Target. 739 ------+--------- 740 | Internet 741 | 742 +-----+ 743 | | Border Router 744 | | (RPL Root) 745 +-----+ | ^ | 746 | | DAO | ACK | 747 o o o o | | | 748 o o o o o o o o o | ^ | Projected . 749 o o o o o o o o o o | | DAO | Route . 750 o o o o o o o o o | ^ | . 751 o o o o o o o o v | DAO v . 752 o o LLN o o o | 753 o o o o o Loose Source Route Path | 754 o o o o From Root To Destination v 756 Figure 7: Projecting a route 758 In order to install the relevant routing state along the segment 759 between an ingress and an egress routers, the Root sends a unicast 760 P-DAO message to the egress router of the routing segment that must 761 be installed. The P-DAO message contains the ordered list of hops 762 along the segment as a direct sequence of Via Information options 763 that are preceded by one or more RPL Target options to which they 764 relate. Each Via Information option contains a Path Lifetime for 765 which the state is to be maintained. 767 The Root sends the P-DAO directly to the egress node of the segment. 768 In that P-DAO, the destination IP address matches the Via Address in 769 the last VIO. This is how the egress recognizes its role. In a 770 similar fashion, the ingress node recognizes its role as it matches 771 Via Address in the first VIO. 773 The egress node of the segment is the only node in the path that does 774 not install a route in response to the P-DAO; it is expected to be 775 already able to route to the Target(s) on its own. It may either be 776 the Target, or may have some existing information to reach the 777 Target(s), such as a connected route or an already installed 778 Projected Route. If one of the Targets cannot be located, the node 779 MUST answer to the Root with a negative DAO-ACK listing the Target(s) 780 that could not be located (suggested status 10 to be confirmed by 781 IANA). 783 If the egress node can reach all the Targets, then it forwards the 784 P-DAO with unchanged content to its loose predecessor in the segment 785 as indicated in the list of Via Information options, and recursively 786 the message is propagated unchanged along the sequence of routers 787 indicated in the P-DAO, but in the reverse order, from egress to 788 ingress. 790 The address of the predecessor to be used as destination of the 791 propagated DAO message is found in the Via Information option the 792 precedes the one that contain the address of the propagating node, 793 which is used as source of the packet. 795 Upon receiving a propagated DAO, an intermediate router as well as 796 the ingress router install a route towards the DAO Target(s) via its 797 successor in the P-DAO; the router locates the VIO that contains its 798 address, and uses as next hop the address found in the Via Address 799 field in the following VIO. The router MAY install additional routes 800 towards the addresses that are located in VIOs that are after the 801 next one, if any, but in case of a conflict or a lack of resource, a 802 route to a Target installed by the Root has precedence. 804 The process recurses till the P-DAO is propagated to ingress router 805 of the segment, which answers with a DAO-ACK to the Root. 807 Also, the path indicated in a P-DAO may be loose, in which case the 808 reachability to the next hop has to be asserted. Each router along 809 the path indicated in a P-DAO is expected to be able to reach its 810 successor, either with a connected route (direct neighbor), or by 811 routing, for Instance following a route installed previously by a DAO 812 or a P-DAO message. If that route is not connected then a recursive 813 lookup may take place at packet forwarding time to find the next hop 814 to reach the Target(s). If it does not and cannot reach the next 815 router in the P-DAO, the router MUST answer to the Root with a 816 negative DAO-ACK indicating the successor that is unreachable 817 (suggested status 11 to be confirmed by IANA). 819 A Path Lifetime of 0 in a Via Information option is used to clean up 820 the state. The P-DAO is forwarded as described above, but the DAO is 821 interpreted as a No-Path DAO and results in cleaning up existing 822 state as opposed to refreshing an existing one or installing a new 823 one. 825 In case of a forwarding error along a Storing Mode Projected Route, 826 the node that fails to forward SHOULD send an ICMP error with a code 827 "Error in Projected Route" to the Root. Failure to do so may result 828 in packet loss and wasted resources along the Projected Route that is 829 broken. 831 7. Security Considerations 833 This draft uses messages that are already present in RPL [RPL] with 834 optional secured versions. The same secured versions may be used 835 with this draft, and whatever security is deployed for a given 836 network also applies to the flows in this draft. 838 TODO: should probably consider how P-DAO messages could be abused by 839 a) rogue nodes b) via replay of messages c) if use of P-DAO messages 840 could in fact deal with any threats? 842 8. IANA Considerations 844 8.1. New RPL Control Codes 846 This document extends the IANA Subregistry created by RFC 6550 for 847 RPL Control Codes as indicated in Table 1: 849 +------+-----------------------------+---------------+ 850 | Code | Description | Reference | 851 +======+=============================+===============+ 852 | 0x09 | Projected DAO Request (PDR) | This document | 853 +------+-----------------------------+---------------+ 854 | 0x0A | PDR-ACK | This document | 855 +------+-----------------------------+---------------+ 857 Table 1: New RPL Control Codes 859 8.2. New RPL Control Message Options 861 This document extends the IANA Subregistry created by RFC 6550 for 862 RPL Control Message Options as indicated in Table 2: 864 +-------+--------------------------------------+---------------+ 865 | Value | Meaning | Reference | 866 +=======+======================================+===============+ 867 | 0x0B | Via Information option | This document | 868 +-------+--------------------------------------+---------------+ 869 | 0x0C | Source-Routed Via Information option | This document | 870 +-------+--------------------------------------+---------------+ 871 | 0x0D | Sibling Information option | This document | 872 +-------+--------------------------------------+---------------+ 874 Table 2: RPL Control Message Options 876 8.3. New SubRegistry for the Projected DAO Request (PDR) Flags 878 IANA is required to create a registry for the 8-bit Projected DAO 879 Request (PDR) Flags field. Each bit is tracked with the following 880 qualities: 882 * Bit number (counting from bit 0 as the most significant bit) 884 * Capability description 886 * Reference 888 Registration procedure is "Standards Action" [RFC8126]. The initial 889 allocation is as indicated in Table 3: 891 +------------+------------------------+---------------+ 892 | Bit number | Capability description | Reference | 893 +============+========================+===============+ 894 | 0 | PDR-ACK request (K) | This document | 895 +------------+------------------------+---------------+ 896 | 1 | Requested path should | This document | 897 | | be redundant (R) | | 898 +------------+------------------------+---------------+ 900 Table 3: Initial PDR Flags 902 8.4. New SubRegistry for the PDR-ACK Flags 904 IANA is required to create an subregistry for the 8-bit PDR-ACK Flags 905 field. Each bit is tracked with the following qualities: 907 * Bit number (counting from bit 0 as the most significant bit) 909 * Capability description 911 * Reference 912 Registration procedure is "Standards Action" [RFC8126]. No bit is 913 currently defined for the PDR-ACK Flags. 915 8.5. New Subregistry for the PDR-ACK Acceptance Status values 917 IANA is requested to create a new subregistry for the PDR-ACK 918 Acceptance Status values. 920 * Possible values are 6-bit unsigned integers (0..63). 922 * Registration procedure is "Standards Action" [RFC8126]. 924 * Initial allocation is as indicated in Table 4: 926 +-------+------------------------+---------------+ 927 | Value | Meaning | Reference | 928 +=======+========================+===============+ 929 | 0 | Unqualified acceptance | This document | 930 +-------+------------------------+---------------+ 932 Table 4: Acceptance values of the PDR-ACK Status 934 8.6. New Subregistry for the PDR-ACK Rejection Status values 936 IANA is requested to create a new subregistry for the PDR-ACK 937 Rejection Status values. 939 * Possible values are 6-bit unsigned integers (0..63). 941 * Registration procedure is "Standards Action" [RFC8126]. 943 * Initial allocation is as indicated in Table 5: 945 +-------+-----------------------+---------------+ 946 | Value | Meaning | Reference | 947 +=======+=======================+===============+ 948 | 0 | Unqualified rejection | This document | 949 +-------+-----------------------+---------------+ 951 Table 5: Rejection values of the PDR-ACK Status 953 8.7. New SubRegistry for the Route Projection Options (RPO) Flags 955 IANA is requested to create a new subregistry for the 5-bit Route 956 Projection Options (RPO) Flags field. Each bit is tracked with the 957 following qualities: 959 * Bit number (counting from bit 0 as the most significant bit) 960 * Capability description 962 * Reference 964 Registration procedure is "Standards Action" [RFC8126]. No bit is 965 currently defined for the Route Projection Options (RPO) Flags. 967 8.8. New SubRegistry for the Sibling Information Option (SIO) Flags 969 IANA is required to create a registry for the 5-bit Sibling 970 Information Option (SIO) Flags field. Each bit is tracked with the 971 following qualities: 973 * Bit number (counting from bit 0 as the most significant bit) 975 * Capability description 977 * Reference 979 Registration procedure is "Standards Action" [RFC8126]. The initial 980 allocation is as indicated in Table 6: 982 +------------+-----------------------------------+---------------+ 983 | Bit number | Capability description | Reference | 984 +============+===================================+===============+ 985 | 0 | Connectivity is bidirectional (B) | This document | 986 +------------+-----------------------------------+---------------+ 988 Table 6: Initial SIO Flags 990 8.9. Error in Projected Route ICMPv6 Code 992 In some cases RPL will return an ICMPv6 error message when a message 993 cannot be forwarded along a Projected Route. This ICMPv6 error 994 message is "Error in Projected Route". 996 IANA has defined an ICMPv6 "Code" Fields Registry for ICMPv6 Message 997 Types. ICMPv6 Message Type 1 describes "Destination Unreachable" 998 codes. This specification requires that a new code is allocated from 999 the ICMPv6 Code Fields Registry for ICMPv6 Message Type 1, for "Error 1000 in Projected Route", with a suggested code value of 8, to be 1001 confirmed by IANA. 1003 9. Acknowledgments 1005 The authors wish to acknowledge JP Vasseur, Remy Liubing, James 1006 Pylakutty and Patrick Wetterwald for their contributions to the ideas 1007 developed here. 1009 10. Normative References 1011 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1012 Requirement Levels", BCP 14, RFC 2119, 1013 DOI 10.17487/RFC2119, March 1997, 1014 . 1016 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 1017 Control Message Protocol (ICMPv6) for the Internet 1018 Protocol Version 6 (IPv6) Specification", STD 89, 1019 RFC 4443, DOI 10.17487/RFC4443, March 2006, 1020 . 1022 [RPL] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1023 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1024 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1025 Low-Power and Lossy Networks", RFC 6550, 1026 DOI 10.17487/RFC6550, March 2012, 1027 . 1029 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1030 Routing Header for Source Routes with the Routing Protocol 1031 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1032 DOI 10.17487/RFC6554, March 2012, 1033 . 1035 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1036 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1037 May 2017, . 1039 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1040 Writing an IANA Considerations Section in RFCs", BCP 26, 1041 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1042 . 1044 11. Informative References 1046 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1047 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1048 2014, . 1050 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and 1051 J. Martocci, "Reactive Discovery of Point-to-Point Routes 1052 in Low-Power and Lossy Networks", RFC 6997, 1053 DOI 10.17487/RFC6997, August 2013, 1054 . 1056 [6TiSCH-ARCHI] 1057 Thubert, P., "An Architecture for IPv6 over the TSCH mode 1058 of IEEE 802.15.4", Work in Progress, Internet-Draft, 1059 draft-ietf-6tisch-architecture-28, 29 October 2019, 1060 . 1063 [RAW-ARCHI] 1064 Thubert, P. and G. Papadopoulos, "Reliable and Available 1065 Wireless Architecture/Framework", Work in Progress, 1066 Internet-Draft, draft-pthubert-raw-architecture-01, 2 1067 April 2020, . 1070 [TURN-ON_RFC8138] 1071 Thubert, P. and L. Zhao, "Configuration option for RFC 1072 8138", Work in Progress, Internet-Draft, draft-thubert- 1073 roll-turnon-rfc8138-03, 8 July 2019, 1074 . 1077 [RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas, 1078 "Deterministic Networking Architecture", RFC 8655, 1079 DOI 10.17487/RFC8655, October 2019, 1080 . 1082 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1083 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1084 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1085 . 1087 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1088 "IPv6 over Low-Power Wireless Personal Area Network 1089 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1090 April 2017, . 1092 [PCE] IETF, "Path Computation Element", 1093 . 1095 Appendix A. Applications 1096 A.1. Loose Source Routing in Non-storing Mode 1098 A RPL implementation operating in a very constrained LLN typically 1099 uses the Non-Storing Mode of Operation as represented in Figure 8. 1100 In that mode, a RPL node indicates a parent-child relationship to the 1101 Root, using a Destination Advertisement Object (DAO) that is unicast 1102 from the node directly to the Root, and the Root typically builds a 1103 source routed path to a destination down the DODAG by recursively 1104 concatenating this information. 1106 ------+--------- 1107 | Internet 1108 | 1109 +-----+ 1110 | | Border Router 1111 | | (RPL Root) 1112 +-----+ ^ | | 1113 | | DAO | ACK | 1114 o o o o | | | Strict 1115 o o o o o o o o o | | | Source 1116 o o o o o o o o o o | | | Route 1117 o o o o o o o o o | | | 1118 o o o o o o o o | v v 1119 o o o o 1120 LLN 1122 Figure 8: RPL non-storing mode of operation 1124 Based on the parent-children relationships expressed in the non- 1125 storing DAO messages,the Root possesses topological information about 1126 the whole network, though this information is limited to the 1127 structure of the DODAG for which it is the destination. A packet 1128 that is generated within the domain will always reach the Root, which 1129 can then apply a source routing information to reach the destination 1130 if the destination is also in the DODAG. Similarly, a packet coming 1131 from the outside of the domain for a destination that is expected to 1132 be in a RPL domain reaches the Root. 1134 It results that the Root, or then some associated centralized 1135 computation engine such as a PCE, can determine the amount of packets 1136 that reach a destination in the RPL domain, and thus the amount of 1137 energy and bandwidth that is wasted for transmission, between itself 1138 and the destination, as well as the risk of fragmentation, any 1139 potential delays because of a paths longer than necessary (shorter 1140 paths exist that would not traverse the Root). 1142 As a network gets deep, the size of the source routing header that 1143 the Root must add to all the downward packets becomes an issue for 1144 nodes that are many hops away. In some use cases, a RPL network 1145 forms long lines and a limited amount of well-Targeted routing state 1146 would allow to make the source routing operation loose as opposed to 1147 strict, and save packet size. Limiting the packet size is directly 1148 beneficial to the energy budget, but, mostly, it reduces the chances 1149 of frame loss and/or packet fragmentation, which is highly 1150 detrimental to the LLN operation. Because the capability to store a 1151 routing state in every node is limited, the decision of which route 1152 is installed where can only be optimized with a global knowledge of 1153 the system, a knowledge that the Root or an associated PCE may 1154 possess by means that are outside of the scope of this specification. 1156 This specification enables to store source-routed or storing mode 1157 state in intermediate routers, which enables to limit the excursion 1158 of the source route headers in deep networks. Once a P-DAO exchange 1159 has taken place for a given Target, if the Root operates in non 1160 storing mode, then it may elide the sequence of routers that is 1161 installed in the network from its source route headers to destination 1162 that are reachable via that Target, and the source route headers 1163 effectively become loose. 1165 A.2. Transversal Routes in storing and non-storing modes 1167 RPL is optimized for Point-to-Multipoint (P2MP) and Multipoint-to- 1168 Point (MP2P), whereby routes are always installed along the RPL DODAG 1169 respectively from and towards the DODAG Root. Transversal Peer to 1170 Peer (P2P) routes in a RPL network will generally suffer from some 1171 elongated (stretched) path versus the best possible path, since 1172 routing between 2 nodes always happens via a common parent, as 1173 illustrated in Figure 9: 1175 * in non-storing mode, all packets routed within the DODAG flow all 1176 the way up to the Root of the DODAG. If the destination is in the 1177 same DODAG, the Root must encapsulate the packet to place a 1178 Routing Header that has the strict source route information down 1179 the DODAG to the destination. This will be the case even if the 1180 destination is relatively close to the source and the Root is 1181 relatively far off. 1183 * In storing mode, unless the destination is a child of the source, 1184 the packets will follow the default route up the DODAG as well. 1185 If the destination is in the same DODAG, they will eventually 1186 reach a common parent that has a route to the destination; at 1187 worse, the common parent may also be the Root. From that common 1188 parent, the packet will follow a path down the DODAG that is 1189 optimized for the Objective Function that was used to build the 1190 DODAG. 1192 ------+--------- 1193 | Internet 1194 | 1195 +-----+ 1196 | | Border Router 1197 | | (RPL Root) 1198 +-----+ 1199 X 1200 ^ v o o 1201 ^ o o v o o o o o 1202 ^ o o o v o o o o o 1203 ^ o o v o o o o o 1204 S o o o D o o o 1205 o o o o 1206 LLN 1208 Figure 9: Routing Stretch between S and D via common parent X 1210 It results that it is often beneficial to enable transversal P2P 1211 routes, either if the RPL route presents a stretch from shortest 1212 path, or if the new route is engineered with a different objective. 1213 For that reason, earlier work at the IETF introduced the "Reactive 1214 Discovery of Point-to-Point Routes in Low Power and Lossy Networks" 1215 [RFC6997], which specifies a distributed method for establishing 1216 optimized P2P routes. This draft proposes an alternate based on a 1217 centralized route computation. 1219 ------+--------- 1220 | Internet 1221 | 1222 +-----+ 1223 | | Border Router 1224 | | (RPL Root) 1225 +-----+ 1226 | 1227 o o o o 1228 o o o o o o o o o 1229 o o o o o o o o o o 1230 o o o o o o o o o 1231 S>>A>>>B>>C>>>D o o o 1232 o o o o 1233 LLN 1235 Figure 10: Projected Transversal Route 1237 This specification enables to store source-routed or storing mode 1238 state in intermediate routers, which enables to limit the stretch of 1239 a P2P route and maintain the characteristics within a given SLA. An 1240 example of service using this mechanism oculd be a control loop that 1241 would be installed in a network that uses classical RPL for 1242 asynchronous data collection. In that case, the P2P path may be 1243 installed in a different RPL Instance, with a different objective 1244 function. 1246 Appendix B. Examples 1248 B.1. Using storing mode P-DAO in non-storing mode MOP 1250 In non-storing mode, the DAG Root maintains the knowledge of the 1251 whole DODAG topology, so when both the source and the destination of 1252 a packet are in the DODAG, the Root can determine the common parent 1253 that would have been used in storing mode, and thus the list of nodes 1254 in the path between the common parent and the destination. For 1255 Instance in the diagram shown in Figure 11, if the source is node 41 1256 and the destination is node 52, then the common parent is node 22. 1258 ------+--------- 1259 | Internet 1260 | 1261 +-----+ 1262 | | Border Router 1263 | | (RPL Root) 1264 +-----+ 1265 | \ \____ 1266 / \ \ 1267 o 11 o 12 o 13 1268 / | / \ 1269 o 22 o 23 o 24 o 25 1270 / \ | \ \ 1271 o 31 o 32 o o o 35 1272 / / | \ | \ 1273 o 41 o 42 o o o 45 o 46 1274 | | | | \ | 1275 o 51 o 52 o 53 o o 55 o 56 1277 LLN 1279 Figure 11: Example DODAG forming a logical tree topology 1281 With this draft, the Root can install a storing mode routing states 1282 along a segment that is either from itself to the destination, or 1283 from one or more common parents for a particular source/destination 1284 pair towards that destination (in this particular example, this would 1285 be the segment made of nodes 22, 32, 42). 1287 In the example below, say that there is a lot of traffic to nodes 55 1288 and 56 and the Root decides to reduce the size of routing headers to 1289 those destinations. The Root can first send a DAO to node 45 1290 indicating Target 55 and a Via segment (35, 45), as well as another 1291 DAO to node 46 indicating Target 56 and a Via segment (35, 46). This 1292 will save one entry in the routing header on both sides. The Root 1293 may then send a DAO to node 35 indicating Targets 55 and 56 a Via 1294 segment (13, 24, 35) to fully optimize that path. 1296 Alternatively, the Root may send a DAO to node 45 indicating Target 1297 55 and a Via segment (13, 24, 35, 45) and then a DAO to node 46 1298 indicating Target 56 and a Via segment (13, 24, 35, 46), indicating 1299 the same DAO Sequence. 1301 B.2. Projecting a storing-mode transversal route 1303 In this example, say that a PCE determines that a path must be 1304 installed between node S and node D via routers A, B and C, in order 1305 to serve the needs of a particular application. 1307 The Root sends a P-DAO with a Target option indicating the 1308 destination D and a sequence Via Information option, one for S, which 1309 is the ingress router of the segment, one for A and then for B, which 1310 are an intermediate routers, and one for C, which is the egress 1311 router. 1313 ------+--------- 1314 | Internet 1315 | 1316 +-----+ 1317 | | Border Router 1318 | | (RPL Root) 1319 +-----+ 1320 | P-DAO message to C 1321 o | o o 1322 o o o | o o o o o 1323 o o o | o o o o o o 1324 o o V o o o o o o 1325 S A B C D o o o 1326 o o o o 1327 LLN 1329 Figure 12: P-DAO from Root 1331 Upon reception of the P-DAO, C validates that it can reach D, e.g. 1332 using IPv6 Neighbor Discovery, and if so, propagates the P-DAO 1333 unchanged to B. 1335 B checks that it can reach C and of so, installs a route towards D 1336 via C. Then it propagates the P-DAO to A. 1338 The process recurses till the P-DAO reaches S, the ingress of the 1339 segment, which installs a route to D via A and sends a DAO-ACK to the 1340 Root. 1342 ------+--------- 1343 | Internet 1344 | 1345 +-----+ 1346 | | Border Router 1347 | | (RPL Root) 1348 +-----+ 1349 ^ P-DAO-ACK from S 1350 / o o o 1351 / o o o o o o o 1352 | o o o o o o o o o 1353 | o o o o o o o o 1354 S A B C D o o o 1355 o o o o 1356 LLN 1358 Figure 13: P-DAO-ACK to Root 1360 As a result, a transversal route is installed that does not need to 1361 follow the DODAG structure. 1363 ------+--------- 1364 | Internet 1365 | 1366 +-----+ 1367 | | Border Router 1368 | | (RPL Root) 1369 +-----+ 1370 | 1371 o o o o 1372 o o o o o o o o o 1373 o o o o o o o o o o 1374 o o o o o o o o o 1375 S>>A>>>B>>C>>>D o o o 1376 o o o o 1377 LLN 1379 Figure 14: Projected Transversal Route 1381 Authors' Addresses 1383 Pascal Thubert (editor) 1384 Cisco Systems, Inc 1385 Building D 1386 45 Allee des Ormes - BP1200 1387 06254 Mougins - Sophia Antipolis 1388 France 1389 Phone: +33 497 23 26 34 1390 Email: pthubert@cisco.com 1392 Rahul Arvind Jadhav 1393 Huawei Tech 1394 Kundalahalli Village, Whitefield, 1395 Bangalore 560037 1396 Karnataka 1397 India 1399 Phone: +91-080-49160700 1400 Email: rahul.ietf@gmail.com 1402 Matthew Gillmore 1403 Itron, Inc 1404 Building D 1405 2111 N Molter Road 1406 Liberty Lake, 99019 1407 United States 1409 Phone: +1.800.635.5461 1410 Email: matthew.gillmore@itron.com