idnits 2.17.1 draft-ietf-roll-p2p-rpl-09.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 : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (March 6, 2012) is 4432 days in the past. Is this intentional? Checking references for intended status: Experimental ---------------------------------------------------------------------------- == Missing Reference: 'NH' is mentioned on line 1016, but not defined == Outdated reference: A later version (-10) exists of draft-ietf-roll-p2p-measurement-03 == Outdated reference: A later version (-13) exists of draft-ietf-roll-terminology-06 Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force M. Goyal, Ed. 3 Internet-Draft University of Wisconsin 4 Intended status: Experimental Milwaukee 5 Expires: September 7, 2012 E. Baccelli 6 M. Philipp 7 INRIA 8 A. Brandt 9 Sigma Designs 10 J. Martocci 11 Johnson Controls 12 March 6, 2012 14 Reactive Discovery of Point-to-Point Routes in Low Power and Lossy 15 Networks 16 draft-ietf-roll-p2p-rpl-09 18 Abstract 20 This document specifies a point-to-point route discovery mechanism, 21 complementary to the RPL core functionality. This mechanism allows 22 an IPv6 router to discover "on demand" routes to one or more IPv6 23 routers in the LLN such that the discovered routes meets specified 24 metrics constraints. 26 Status of this Memo 28 This Internet-Draft is submitted to IETF in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on September 7, 2012. 43 Copyright Notice 45 Copyright (c) 2012 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 61 2. The Use Cases . . . . . . . . . . . . . . . . . . . . . . . . 3 62 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 63 4. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 5 64 5. Functional Overview . . . . . . . . . . . . . . . . . . . . . 5 65 6. P2P Route Discovery Mode Of Operation . . . . . . . . . . . . 8 66 6.1. Setting a P2P Mode DIO . . . . . . . . . . . . . . . . . . 8 67 7. New RPL Control Message Options . . . . . . . . . . . . . . . 11 68 7.1. P2P Route Discovery Option (P2P-RDO) . . . . . . . . . . . 11 69 7.2. Data Option . . . . . . . . . . . . . . . . . . . . . . . 14 70 8. The Discovery Reply Object (DRO) . . . . . . . . . . . . . . . 14 71 8.1. Secure DRO . . . . . . . . . . . . . . . . . . . . . . . . 16 72 8.2. Setting a P2P-RDO Carried in a Discovery Reply Object . . 16 73 9. P2P-RPL Route Discovery By Creating a Temporary DAG . . . . . 17 74 9.1. Joining a Temporary DAG . . . . . . . . . . . . . . . . . 17 75 9.2. Trickle Operation For P2P Mode DIOs . . . . . . . . . . . 18 76 9.3. Processing a P2P Mode DIO . . . . . . . . . . . . . . . . 19 77 9.4. Additional Processing of a P2P Mode DIO At An 78 Intermediate Router . . . . . . . . . . . . . . . . . . . 20 79 9.5. Additional Processing of a P2P Mode DIO At The Target . . 21 80 9.6. Processing a DRO At An Intermediate Router . . . . . . . . 22 81 9.7. Processing a DRO At The Origin . . . . . . . . . . . . . . 23 82 10. The Discovery Reply Object Acknowledgement (DRO-ACK) . . . . . 24 83 11. Packet Forwarding Along a Route Discovered Using P2P-RPL . . . 24 84 12. Constants . . . . . . . . . . . . . . . . . . . . . . . . . . 25 85 13. Interoperability with Core RPL . . . . . . . . . . . . . . . . 25 86 14. Security Considerations . . . . . . . . . . . . . . . . . . . 26 87 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 88 15.1. Additions to DIO Mode of Operation . . . . . . . . . . . . 26 89 15.2. Additions to RPL Control Message Options . . . . . . . . . 27 90 15.3. Additions to RPL Control Codes . . . . . . . . . . . . . . 27 91 16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27 92 17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 93 17.1. Normative References . . . . . . . . . . . . . . . . . . . 28 94 17.2. Informative References . . . . . . . . . . . . . . . . . . 28 95 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 97 1. Introduction 99 Targeting Low power and Lossy Networks (LLNs), the RPL routing 100 protocol [I-D.ietf-roll-rpl] provides paths along a Directed Acyclic 101 Graph (DAG) rooted at a single router in the network. Establishment 102 and maintenance of a DAG is performed by routers in the LLN using 103 DODAG Information Object (DIO) messages. When two arbitrary routers 104 (neither of which is the DAG's root) need to communicate, the data 105 packets are restricted to travel only along the links in the DAG. 106 Such point-to-point (P2P) routing functionality may not be sufficient 107 for several Home and Building Automation applications [RFC5826] 108 [RFC5867] due to the following reasons: 110 o The need to pre-establish routes: each potential destination in 111 the network must declare itself as such ahead of the time a source 112 needs to reach it. 114 o The need to route only along the links in the DAG: A DAG is built 115 to optimize the routing cost to reach the root. Restricting P2P 116 routes to use only the in-DAG links may result in significantly 117 suboptimal routes and severe traffic congestion near the DAG root. 119 This document describes an extension to core RPL that enables an IPv6 120 router in the LLN to discover routes to one or more IPv6 routers in 121 the LLN "on demand", such that the discovered routes meet the 122 specified metrics constraints, without necessarily going along the 123 links in an existing DAG. This reactive P2P route discovery 124 mechanism is henceforth referred to as P2P-RPL. P2P-RPL does not 125 guarantee discovery of a route. Also, the discovered routes may not 126 be the best available. However, any discovered routes are guaranteed 127 to satisfy the desired constraints in terms of the routing metrics 128 and are thus considered "good enough" from the application's 129 perspective. 131 A mechanism to measure the end-to-end cost of an existing route has 132 been specified in [I-D.ietf-roll-p2p-measurement]. As discussed in 133 Section 4, measuring the end-to-end cost of an existing route may 134 help decide whether to initiate the discovery of a better route using 135 P2P-RPL and the metric constraints to be used for this purpose. 137 2. The Use Cases 139 One use case, common in home and commercial building environments, 140 involves a device (say a remote control or an airduct controller) 141 that suddenly needs to communicate with another device (say a lamp or 142 a humidity sensor) to which it does not already have a route. In 143 this case, the remote control (or the airduct controller) must be 144 able to discover a route to the lamp (or the humidity sensor) "on 145 demand". 147 Another use case, common in a commercial building environment, 148 involves a large LLN deployment where P2P communication along a 149 particular DAG among hundreds (or thousands) of routers creates 150 severe traffic congestion near that DAG's root, and thus routes 151 across this DAG are desirable. 153 Other use cases involve scenarios where energy or latency constraints 154 are not satisfied by the P2P routes along an existing DAG because 155 they involve traversing many more intermediate routers than necessary 156 to reach the destination. 158 3. Terminology 160 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 161 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 162 "OPTIONAL" in this document are to be interpreted as described in 163 [RFC2119]. 165 Additionally, this document uses terminology from 166 [I-D.ietf-roll-terminology] and [I-D.ietf-roll-rpl]. This document 167 introduces the following terms: 169 Origin : The IPv6 router initiating the P2P-RPL route discovery. 171 Target : The IPv6 router at the other end point of the P2P route(s) 172 to be discovered. A P2P-RPL route discovery can discover routes to 173 multiple targets at the same time. 175 Intermediate Router: An IPv6 router that is neither the origin nor a 176 target. 178 Forward Route: A route in the forward direction, i.e., from the 179 origin to the target. 181 Backward Route: A route in the backward direction, i.e., from the 182 target to the origin. 184 Bidirectional Route: A route that can be used in both forward and 185 backward directions. 187 Source Route: A complete and ordered list of routers that can be used 188 by a packet to travel from a source to a destination node. 190 Hop-by-hop Route: The route characterized by each router on the route 191 using its routing table to determine the next hop on the route. 193 4. Applicability 195 A route discovery using P2P-RPL may be performed by an origin when no 196 route exists between itself and the target(s) or when the existing 197 routes do not satisfy the application requirements. P2P-RPL is 198 designed to discover hop-by-hop or source routes to one or more 199 targets such that the discovered routes meet the specified 200 constraints. In some application contexts, the constraints that the 201 discovered routes must satisfy are intrinsically known or can be 202 specified by the application. For example, an origin that expects 203 its targets to be less than 5 hops away may use "hop-count < 5" as 204 the constraint. In other application contexts, the origin may need 205 to measure the cost of the existing route to a target to determine 206 the constraints. For example, an origin that measures the total ETX 207 along its current route to a target to be 20 may use "ETX < x*20", 208 where x is a fraction that the origin decides, as the constraint. A 209 mechanism to measure the cost of an existing route between two IPv6 210 routers is specified in [I-D.ietf-roll-p2p-measurement]. If there is 211 no existing route between the origin and the target(s) or the cost 212 measurement for the existing routes fails, the origin will have to 213 guess the constraints to be used in the initial route discovery. 214 Once, the initial route discovery succeeds or fails, the origin will 215 have a better estimate for the constraints to be used in the 216 subsequent route discovery. 218 P2P-RPL may result in discovery of better P2P routes than the ones 219 available along a DAG designed to optimize routing cost to the DAG's 220 root. The improvement in route quality depends on a number of 221 factors including the network topology, the routing metrics in use 222 and the prevalent conditions in the network. A network designer may 223 take into consideration both the benefits (potentially better routes; 224 no need to maintain routes proactively) and costs (control messages 225 generated during the route discovery process) when using P2P-RPL. 227 5. Functional Overview 229 This section contains a high level description of P2P-RPL. 231 A P2P-RPL route discovery takes place by forming a DAG rooted at the 232 origin. As is the case with core RPL, P2P-RPL uses IPv6 link-local 233 multicast DIO messages to establish a DAG. However, unlike core RPL, 234 this DAG is temporary in nature and routers in the DAG leave once the 235 DAG's life time is over. The sole purpose of DAG creation is to 236 discover routes to the target(s) and DIOs serve as the route 237 discovery messages. Each router joining the DAG determines a rank 238 for itself in the DAG and ignores the subsequent DIOs received from 239 lower (higher in numerical value) ranked neighbors. Thus, the route 240 discovery messages propagate away from the origin rather than return 241 back to it. As in core RPL, DIO generation at a router is controlled 242 by a Trickle timer [RFC6206] that allows a router to avoid generating 243 unnecessary messages while providing protection against unreliable 244 wireless communication. P2P-RPL also uses the routing metrics 245 [I-D.ietf-roll-routing-metrics], objective functions and packet 246 forwarding framework 247 [I-D.ietf-6man-rpl-routing-header][I-D.ietf-6man-rpl-option] 248 developed for core RPL. 250 An origin may use P2P-RPL to discover routes to one or more targets 251 identified by one or more unicast/multicast addresses. P2P-RPL 252 allows for the discovery of one hop-by-hop route or upto four source 253 routes per target. P2P-RPL allows an origin to piggyback time- 254 critical application data on the DIO messages for delivery to the 255 target(s). P2P-RPL does not guarantee discovery of a route to a 256 target. Also, the discovered routes may not be the best available. 257 However, any discovered routes are guaranteed to satisfy the desired 258 constraints in terms of the routing metrics and are thus considered 259 "good enough" from the application's perspective. 261 A P2P-RPL route discovery takes place by forming a temporary DAG 262 rooted at the origin. The DIOs, used to create the temporary DAG, 263 are identified by a new Mode of Operation (P2P Route Discovery mode 264 defined in Section 6). The DIOs, listing the P2P Route Discovery 265 mode as the Mode of Operation, are henceforth referred to as the P2P 266 mode DIOs. A P2P mode DIO always carries one P2P Route Discovery 267 Option (defined in Section 7.1) in which the origin specifies the 268 following information: 270 o The IPv6 address of a target. This could be a unicast address or 271 a multicast one. Any additional targets may be specified by 272 including one or more RPL Target Options [I-D.ietf-roll-rpl] 273 inside the DIO. 275 o The nature of the route(s) to be discovered: hop-by-hop or source 276 routes. This specification allows for the discovery of one hop- 277 by-hop route or up to four source routes per target. 279 o The desired number of routes (if source routes are being 280 discovered). 282 o Whether the target(s) should send Discovery Reply Object (DRO) 283 messages (defined in Section 8) back to the origin on receiving a 284 DIO message. A DRO message carries a discovered source route back 285 to the origin or establishes a hop-by-hop route between the origin 286 and the target. By not allowing the generation of DRO messages, 287 an origin can use P2P-RPL as purely a mechanism to deliver time- 288 critical application data to the target(s). 290 A P2P Route Discovery Option also accumulates a route from the origin 291 to a target as the routers join the temporary DAG. 293 A P2P mode DIO MAY also carry: 295 o One or more Metric Container Options to specify: 297 * The relevant routing metrics. 299 * The constraints that the discovered route must satisfy. These 300 constraints also limit how far the DIOs message may travel. 302 o One or more RPL Target options to specify additional unicast or 303 multicast targets. 305 o One or more Data Options (defined in Section 7.2) to carry time- 306 critical application-level data to be delivered to the target(s). 308 As the routers join the temporary DAG, they keep track of the best 309 (partial) route(s) they have seen and advertise these routes, along 310 with the corresponding routing metrics, in their P2P mode DIOs. A 311 router, including the target(s), discards a received P2P mode DIO if 312 the aggregated routing metrics on the route advertised by the DIO do 313 not satisfy the listed constraints. These constraints can be used to 314 limit the propagation of P2P mode DIO messages. A router may also 315 discard a received P2P mode DIO if it does not wish to be a part of 316 the discovered route due to limited resources or due to policy 317 reasons. 319 When a target receives a P2P mode DIO, it forwards the data in any 320 Data Options to the higher layer. The target may remember the 321 discovered route for use as a source route to reach the origin. If 322 the origin has requested DRO messages to be sent back, the target may 323 select the route contained in the received DIO for further processing 324 as described next. This document does not specify a particular 325 method for the target to use to select a route for further 326 processing. Example methods include selecting any route that meets 327 the constraints or selecting the best route(s) discovered over a 328 certain time period. 330 If one or more source routes are being discovered, the target sends 331 the selected source routes to the origin via DRO messages with one 332 DRO message carrying one discovered route. On receiving a DRO 333 message, the origin stores the discovered route in its memory. If a 334 hop-by-hop route is being discovered, the target sends a DRO message 335 containing the selected route to the origin. The DRO message travels 336 back to the origin along the selected route, establishing state for 337 this route in the routers on the path. The target may include one or 338 more Data Options in a DRO message to deliver any time-critical 339 application data to the origin. 341 The target may request the origin to acknowledge the receipt of a DRO 342 message by sending back a DRO Acknowledgement (DRO-ACK) message 343 (defined in Section 10). The origin unicasts a DRO-ACK message to 344 the target. When the target does not receive the requested DRO-ACK 345 within a certain time interval of sending a DRO, it resends the DRO 346 message (up to a certain number of times) carrying the same route as 347 before. 349 The use of trickle timers to delay the propagation of DIO messages 350 may cause some nodes to generate these messages even when the desired 351 routes have already been discovered. In order to preempt the 352 generation of such unnecessary messages, the target may set a "stop" 353 flag in the DRO message to let the nodes in the LLN know about the 354 completion of the route discovery process. The routers receiving 355 such a DRO should not generate any more DIOs for this temporary DAG. 356 Neither should they process any received DIOs for this temporary DAG 357 in future. However, such routers must still process the DROs 358 received for this temporary DAG. 360 6. P2P Route Discovery Mode Of Operation 362 This section specifies a new RPL Mode of Operation (MOP), P2P Route 363 Discovery mode (or P2P mode, for short), with value 4 (to be 364 confirmed by IANA). A DIO message, listing P2P mode as the MOP, is 365 identified as performing a P2P-RPL route discovery by creating a 366 temporary DAG. A P2P mode DIO MUST carry one and only one P2P Route 367 Discovery Option (specified in Section 7.1). 369 6.1. Setting a P2P Mode DIO 371 The Base Object in a P2P mode DIO message MUST be set in the 372 following manner: 374 o RPLInstanceID: RPLInstanceID MUST be a local value as described in 375 Section 5.1 of [I-D.ietf-roll-rpl]. The origin MUST NOT use the 376 same RPLInstanceID in two or more concurrent route discoveries. 378 o Version Number: MUST be set to zero. The temporary DAG used for 379 P2P-RPL route discovery does not exist long enough to have new 380 versions. 382 o Grounded (G) Flag: MUST be set to zero since this DAG is temporary 383 in nature, is created solely for the purpose of P2P-RPL route 384 discovery and MUST NOT be used for packet routing. 386 o Mode of Operation (MOP): MUST be set to 4, corresponding to P2P 387 Route Discovery mode. 389 o DTSN: MUST be set to zero on transmission and ignored on 390 reception. 392 o DODAGPreference (Prf): This field MUST be set to zero (least 393 preferred). 395 o DODAGID: This field MUST be set to an IPv6 address of the origin. 397 o The other fields in the DIO Base Object can be set in the desired 398 fashion as per the rules described in [I-D.ietf-roll-rpl]. 400 The DODAG Configuration Option, inside a P2P mode DIO MUST be set in 401 the following manner: 403 o MaxRankIncrease: This field MUST be set to zero to disable local 404 repair of the temporary DAG. 406 o Trickle parameters (DIOIntervalDoublings, DIOIntervalMin, 407 DIORedundancyConstant) SHOULD be set as described in Section 9.2. 409 o The Default Lifetime and Lifetime Unit parameters in DODAG 410 Configuration option indicate the life time of the state the 411 routers maintain for a hop-by-hop route established using P2P-RPL 412 and may be set as desired. 414 o The other fields in the DODAG Configuration Option, including the 415 OCP identifying the Objective function, can be set in the desired 416 fashion as per the rules described in [I-D.ietf-roll-rpl]. 418 A default DODAG Configuration Option comes in effect if a P2P mode 419 DIO does not carry an explicit one. The default DODAG Configuration 420 Option has the following parameter values: 422 o Authentication Enabled: 0 424 o DIOIntervalMin: 6, which translates to 64ms as the value for Imin 425 parameter in Trickle operation. 427 o DIORedundancyConstant: 1 429 o MaxRankIncrease: 0 431 o Default Lifetime: 0xFF 433 o Lifetime Unit: 0xFFFF 435 o Objective Code Point: 0, i.e., OF0 [I-D.ietf-roll-of0] is the 436 default objective function. 438 o The remaining parameters have default values as specified in 439 [I-D.ietf-roll-rpl]. 441 The routing metrics and constraints [I-D.ietf-roll-routing-metrics] 442 used in P2P-RPL route discovery are included in one or more Metric 443 Container Options [I-D.ietf-roll-rpl] inside the P2P mode DIO. Note 444 that a DIO need not include a Metric Container if OF0 is the 445 objective function in effect. In that case, a P2P mode DIO may still 446 specify an upper limit on the maximum rank, that a router may have in 447 the temporary DAG, inside the P2P Route Discovery Option (described 448 in Section 7.1). 450 A P2P mode DIO: 452 o MUST carry one (and only one) P2P Route Discovery Option 453 (described in Section 7.1). The P2P Route Discovery Option allows 454 for the specification of one unicast or multicast address for the 455 target. 457 o MAY carry one or more RPL Target Options to specify additional 458 unicast/multicast addresses for the target. 460 o MAY carry one or more Metric Container Options to specify routing 461 metrics and constraints. 463 o MAY carry one or more Data Options (described in Section 7.2) 464 containing time-critical application data to be delivered to the 465 target(s). 467 o MAY carry one or more Route Information or Prefix Information 468 Options (described in [I-D.ietf-roll-rpl]). 470 A router MUST discard a received P2P mode DIO if it violates any of 471 the rules listed above. 473 7. New RPL Control Message Options 475 This document defines two new RPL control message options: the P2P 476 Route Discovery Option and the Data Option. 478 7.1. P2P Route Discovery Option (P2P-RDO) 480 - 481 0 1 2 3 482 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 1 483 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 484 | Type = 10 | Option Length |R|H| N | Compr | L |MaxRank/NH | 485 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 486 | | 487 | Target | 488 | | 489 | | 490 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 491 | | 492 | Address[1..n] | 493 | | 494 | | 495 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 497 Figure 1: Format of P2P Route Discovery Option (P2P-RDO) 499 The format of a P2P Route Discovery Option (P2P-RDO) is illustrated 500 in Figure 1. A P2P mode DIO and a DRO (defined in Section 8) message 501 MUST carry one and at most one P2P-RDO. A P2P-RDO consists of the 502 following fields: 504 o Option Type: 0x0A (to be confirmed by IANA). 506 o Option Length: 8-bit unsigned integer, representing the length in 507 octets of the option, not including the Option Type and Option 508 Length fields. 510 o Reply (R): The origin sets this flag to one to allow the target(s) 511 to send DRO messages back to the origin. If this flag is zero, a 512 target MUST NOT generate any DRO message. 514 o Hop-by-hop (H): This flag is valid only if the R flag is set to 515 one. The origin sets this flag to one if it desires hop-by-hop 516 routes. The origin sets this flag to zero if it desires source 517 routes. This specification allows for the establishment of one 518 hop-by-hop route or up to four source routes per target. The hop- 519 by-hop route is established in the forward direction, i.e. from 520 the origin to the target. This specification does not allow for 521 the establishment of hop-by-hop routes in the backward direction. 523 o Number of Routes (N): This flag is valid only if the R flag is one 524 and H flag is zero, i.e. the targets are allowed to generate DRO 525 messages carrying discovered source routes back to the origin. In 526 this case, the value in the N field plus one indicates the number 527 of source routes that each target should convey to the origin. 528 When hop-by-hop routes are being discovered, the N field MUST be 529 set to zero on transmission and ignored on reception. 531 o Compr: 4-bit unsigned integer indicating the number of prefix 532 octets that are elided from the Target field and the Address 533 vector. For example, Compr value will be zero if full IPv6 534 addresses are carried in the Target field and the Address vector. 536 o Life Time (L): A 2-bit field that indicates the suggested life 537 time of the temporary DAG, i.e., the suggested duration a router 538 joining the temporary DAG SHOULD maintain its membership in the 539 DAG. The mapping between the values in this field and the life 540 time of the temporary DAG is as follows: 542 * 0x00: 1 second; 544 * 0x01: 4 seconds; 546 * 0x02: 16 seconds; 548 * 0x03: 64 seconds; 550 The origin sets this field based on its expectation regarding the 551 time required for the DIOs to reach the target(s). 553 o MaxRank/NH: 555 * When a P2P-RDO is included in a P2P mode DIO, this field 556 indicates the upper limit on the integer portion of the rank 557 (calculated using the DAGRank() macro defined in 558 [I-D.ietf-roll-rpl]) that a router may have in the temporary 559 DAG being created. An intermediate router MUST NOT join a 560 temporary DAG being created by a P2P mode DIO if the integer 561 portion of its rank would be equal to or higher (in numerical 562 value) than the MaxRank limit. A target can join the temporary 563 DAG at a rank whose integer portion is equal to the MaxRank. A 564 router MUST discard a received P2P mode DIO if the integer part 565 of the advertized rank equals or exceeds the MaxRank limit. A 566 value 0 in this field indicates that the MaxRank is infinity. 568 * When a P2P-RDO is included in a DRO message, this field 569 indicates the index of the next hop address inside the Address 570 vector. 572 o Target: An IPv6 address of the target after eliding Compr number 573 of prefix octets. When the P2P-RDO is included in a P2P mode DIO, 574 this field may contain a unicast address or a multicast one. Any 575 additional target addresses can be specified by including one or 576 more RPL Target Options [I-D.ietf-roll-rpl] in the DIO. When the 577 P2P-RDO is included in a DRO, this field MUST contain a unicast 578 IPv6 address of the target generating the DRO. 580 o Address[1..n]: A vector of IPv6 addresses representing a (partial) 581 route in the forward direction: 583 * Each element in the Address vector has size (16 - Compr) octets 584 and MUST contain a valid IPv6 address with first Compr octets 585 elided. 587 * The total number of elements inside the Address vector is given 588 by n = (Option Length - 2 - (16 - Compr))/(16 - Compr). 590 * The IPv6 addresses in the Address vector MUST be reachable in 591 both forward and backward directions. Reachability in the 592 backward direction allows a DRO message to use the route 593 accumulated in the Address vector to travel from the target to 594 the origin. 596 * The Address vector MUST carry the accumulated route in the 597 forward direction, i.e., the first element in the Address 598 vector must contain the IPv6 address of the router next to the 599 origin and so on. 601 * The origin and target addresses MUST NOT be included in the 602 Address vector. 604 * A router adding its address to the vector MUST ensure that its 605 address does not already exist in the vector. A router 606 specifying a complete route in the Address vector MUST ensure 607 that the vector does not contain any address more than once. 609 * The Address vector MUST NOT contain any multicast addresses. 611 7.2. Data Option 613 0 1 2 3 614 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 1 615 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 616 | Type = 11 | Option Length | Data | 617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+... | 619 Figure 2: Format of Data Option 621 The format of a Data Option is illustrated in Figure 2. A P2P mode 622 DIO and a DRO (defined in Section 8) message MAY carry one or more 623 Data Options. A P2P-RDO consists of the following fields: 625 o Option Type: 0x0B (to be confirmed by IANA). 627 o Option Length: 8-bit unsigned integer, representing the length in 628 octets of the option, not including the Option Type and Option 629 Length fields. 631 o Data: If the Data Option is contained in a DIO, this field 632 contains application data to be delivered to the target(s). If 633 the Data Option is contained in a DRO, this field contains 634 application data to be delivered to the origin. 636 8. The Discovery Reply Object (DRO) 638 This section defines two new RPL Control Message types, the Discovery 639 Reply Object (DRO), with code 0x04 (to be confirmed by IANA), and the 640 Secure DRO, with code 0x84 (to be confirmed by IANA). A DRO serves 641 one of the following functions: 643 o Carry a discovered source route from a target to the origin; 645 o Establish a hop-by-hop route as it travels from a target to the 646 origin. 648 A DRO message MAY serve the function of letting the routers in the 649 LLN know that a P2P-RPL route discovery is complete and no more DIO 650 messages need to be generated for the corresponding temporary DAG. A 651 DRO message MAY also carry time-critical application data from the 652 target to the origin in one or more Data Options. A DRO message MUST 653 carry one P2P-RDO whose Target field MUST contain a unicast IPv6 654 address of the target that generated the DRO. A DRO message travels 655 from the target to the origin via link-local multicast along the 656 route specified inside the Address vector in the P2P-RDO. 658 0 1 2 3 659 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 1 660 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 661 | RPLInstanceID | Version |S|A|Seq| Reserved | 662 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 663 | | 664 | DODAGID | 665 | | 666 | | 667 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 668 | Option(s)... 669 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+... 671 Figure 3: Format of the base Discovery Reply Object (DRO) 673 The format of the base Discovery Reply Object (DRO) is shown in 674 Figure 3. A base DRO consists of the following fields: 676 o RPLInstanceID: The RPLInstanceID of the temporary DAG used for 677 route discovery. 679 o Version: The Version of the temporary DAG used for route 680 discovery. Since a temporary DAG always has value zero for the 681 Version, this field MUST always be set to zero. 683 o Stop (S): This flag, when set to one by a target, indicates that 684 the P2P-RPL route discovery is over. All the routers receiving 685 such a DRO, including the ones not listed in the route carried 686 inside P2P-RDO, 688 * SHOULD NOT process any more DIOs received for this temporary 689 DAG; 691 * SHOULD NOT generate any more DIOs for this temporary DAG; 693 * SHOULD cancel any pending DIO transmission for this temporary 694 DAG. 696 Note that the stop flag serves to stop further DIO generation/ 697 processing for a P2P-RPL route discovery but it does not affect 698 the processing of DRO messages at either the origin or the 699 intermediate routers. In other words, a router (the origin or an 700 intermediate router) MUST continue to process the DRO messages 701 even if an earlier DRO message (with same RPLInstanceID and 702 DODAGID fields) had the stop flag set to one. 704 o Ack Required (A): This flag, when set to one by the target, 705 indicates that the origin MUST unicast a DRO-ACK message (defined 706 in Section 10) to the target when it receives the DRO. 708 o Sequence Number (Seq): This 2-bit field indicates the sequence 709 number for the DRO. This field is relevant when the A flag is set 710 to one, i.e., the target requests an acknowledgement from the 711 origin for a received DRO. The origin includes the RPLInstanceID, 712 the DODAGID and the Sequence Number of the received DRO inside the 713 DRO-ACK message it sends back to the target. 715 o Reserved: These bits are reserved for future use. These bits MUST 716 be set to zero on transmission and MUST be ignored on reception. 718 o DODAGID: The DODAGID of the temporary DAG used for route 719 discovery. The DODAGID also identifies the origin. The 720 RPLInstanceID, the Version and the DODAGID together uniquely 721 identify the temporary DAG used for route discovery and can be 722 copied from the DIO message advertizing the temporary DAG. 724 o Options: The DRO message: 726 * MUST carry one P2P-RDO that MUST specify a complete route 727 between the target and the origin; 729 * MAY carry one or more Metric Container Options that contains 730 the aggregated routing metrics values for the route specified 731 in P2P-RDO; 733 * MAY carry one or more Data Options to carry any time-critical 734 application data to the origin. 736 8.1. Secure DRO 738 A Secure DRO message follows the format in Figure 7 of 739 [I-D.ietf-roll-rpl], where the base format is the base DRO shown in 740 Figure 3. 742 8.2. Setting a P2P-RDO Carried in a Discovery Reply Object 744 A Discovery Reply Object MUST carry one P2P-RDO, which MUST be set as 745 defined in Section 7.1. Specifically, the following fields MUST be 746 set as specified next: 748 o Reply (R): This flag MUST be set to zero on transmission and 749 ignored on reception. 751 o Hop-by-Hop (H): The H flag in the P2P-RDO included in a DRO 752 message MUST have the same value as the H flag in the P2P-RDO 753 inside the corresponding DIO message. 755 o Number of Routes (N): This field MUST be set to zero on 756 transmission and ignored on reception. 758 o Life Time (L): This field MUST be set to zero on transmission and 759 ignored on reception. 761 o MaxRank/NH: This field indicates the index of the next hop address 762 in the Address vector. When a target generates a DRO message, the 763 NH field is set to n = (Option Length - 2 - (16 - Compr))/(16 - 764 Compr). 766 o Target: This field MUST contain a unicast IPv6 address of the 767 target generating the DRO. 769 o Address[1..n]: The Address vector MUST contain a complete route 770 between the origin and the target such that the first element in 771 the vector contains the IPv6 address of the router next to the 772 origin and the last element contains the IPv6 address of the 773 router next to the target. 775 9. P2P-RPL Route Discovery By Creating a Temporary DAG 777 This section details the P2P-RPL route discovery operation. 779 9.1. Joining a Temporary DAG 781 All the routers participating in a P2P-RPL route discovery, including 782 the origin and the target(s), MUST join the temporary DAG being 783 created for the purpose. When a router joins a temporary DAG 784 advertized by a P2P mode DIO, it SHOULD maintain its membership in 785 the temporary DAG for the suggested Life Time duration listed in the 786 P2P-RDO. The only purpose of a temporary DAG's existence is to 787 facilitate the P2P-RPL route discovery process. The temporary DAG 788 MUST NOT be used to route packets. A router SHOULD detach from the 789 temporary DAG once the duration of its membership in the DAG has 790 exceeded the DAG's suggested life time. After receiving a DRO with 791 the stop flag set to one, a router SHOULD NOT send or receive any 792 more DIOs for this temporary DAG and SHOULD also cancel any pending 793 DIO transmission. 795 9.2. Trickle Operation For P2P Mode DIOs 797 An RPL router uses a Trickle timer [RFC6206] to control DIO 798 transmissions. The Trickle control of DIO transmissions provides 799 quick resolution of any "inconsistency" while avoiding redundant DIO 800 transmissions. The Trickle algorithm also imparts protection against 801 loss of DIOs due to inherent lack of reliability in wireless 802 communication. When controlling the transmissions of a P2P mode DIO, 803 a Trickle timer SHOULD follow the following rules: 805 o The receipt of a P2P mode DIO, that allows the router to advertise 806 a better route (in terms of the routing metrics and the OF in use) 807 than before, is considered "inconsistent" and hence resets the 808 Trickle timer. Note that the first receipt of a P2P mode DIO 809 advertising a particular temporary DAG is always considered an 810 "inconsistent" event. 812 o The receipt of a P2P mode DIO from a parent in the temporary DAG 813 is considered neither "consistent" nor "inconsistent" if it does 814 not allow the router to advertise a better route than before. 815 Thus, the receipt of such DIOs has no impact on the Trickle 816 operation. Note that this document does not impose any 817 requirements on how a router might choose its parents in the 818 temporary DAG. 820 o The receipt of a P2P mode DIO is considered "consistent" if the 821 source of the DIO is not a parent in the temporary DAG and either 822 of the following conditions is true: 824 * The DIO advertises a better route than the router but does not 825 allow the router to advertise a better route itself; or 827 * The DIO advertises a route as good as the route (to be) 828 advertised by the router. 830 Note that Trickle algorithm's DIO suppression rules are in effect 831 at all times. Hence, a P2P-RPL router may suppress a DIO 832 transmission even if it has not made any DIO transmission yet. 834 o The receipt of a P2P mode DIO, that advertises a worse route than 835 what the router advertises (or would advertise when it gets a 836 chance to generate its DIO), is considered neither "consistent" 837 nor "inconsistent", i.e., the receipt of such a DIO has no impact 838 on the Trickle operation. 840 o The Imin parameter SHOULD be set taking in account the 841 connectivity within the network. For highly connected networks, a 842 small Imin value (of the order of the typical transmission delay 843 for a DIO) may lead to congestion in the network as a large number 844 of routers reset their Trickle timers in response to the first 845 receipt of a DIO from the origin. These routers would generate 846 their DIOs within Imin interval and cause additional routers to 847 reset their trickle timers and generate more DIOs. Thus, for 848 highly connected networks, the Imin parameter SHOULD be set to a 849 value at least one order of magnitude larger than the typical 850 transmission delay for a DIO. For sparsely connected networks, 851 the Imin parameter can be set to a value that is a small multiple 852 of the typical transmission delay for a DIO. Note that the Imin 853 value has a direct impact on the time required for a P2P-RPL route 854 discovery to complete. In general, the time required for a P2P- 855 RPL route discovery would increase approximately linearly with the 856 value of the Imin parameter. 858 o The Imax parameter SHOULD be set to a large value (several orders 859 of magnitude higher than the Imin value) and is unlikely to be 860 critical for P2P-RPL operation. This is because the first receipt 861 of a P2P mode DIO for a particular temporary DAG is considered an 862 inconsistent event and would lead to resetting of Trickle timer 863 duration to the Imin value. Given the temporary nature of the 864 DAGs used in P2P-RPL, Trickle timer may not get a chance to 865 increase much. 867 o The recommended value of redundancy constant "k" is 1. With this 868 value of "k", a DIO transmission will be suppressed if the router 869 receives even a single "consistent" DIO during a timer interval. 870 This setting for the redundancy constant is designed to reduce the 871 number of messages generated during a route discovery process and 872 is suitable for environments with low or moderate packet loss 873 rates. In environments with high packet loss rates, a higher 874 value for the redundancy constant may be more suitable. 876 9.3. Processing a P2P Mode DIO 878 The rules for DIO processing and transmission, described in Section 8 879 of RPL [I-D.ietf-roll-rpl], apply to P2P mode DIOs as well except as 880 modified in this document. 882 The following rules for processing a received P2P mode DIO apply to 883 both intermediate routers and the target. 885 A router SHOULD discard a received P2P mode DIO with no further 886 processing if it does not have bidirectional reachability with the 887 neighbor that generated the received DIO. Note that bidirectional 888 reachability does not mean that the link must have the same values 889 for a routing metric in both directions. A router SHOULD calculate 890 the values of the link-level routing metrics included in the received 891 DIO taking in account the metric's value in both forward and backward 892 directions. Bidirectional reachability along a discovered route 893 allows the target to use this route to reach the origin. In 894 particular, the DRO messages travel from the target to the origin 895 along a discovered route. 897 A router MUST discard a received P2P mode DIO with no further 898 processing: 900 o If the DIO advertises INFINITE_RANK as defined in 901 [I-D.ietf-roll-rpl]. 903 o If the integer part of the rank advertised in the DIO equals or 904 exceeds the MaxRank limit listed in the P2P Route Discovery 905 Option. 907 o If the router cannot evaluate the mandatory route constraints 908 listed in the DIO or if the routing metric values do not satisfy 909 one or more of the mandatory constraints. 911 o If the router previously received a DRO message with same 912 RPLInstanceID and DODAGID as the received DIO and with the stop 913 flag set to one. 915 The router MUST check the target addresses listed in the P2P-RDO and 916 any RPL Target Options included in the received DIO. If one of its 917 IPv6 addresses is listed as a target address or if it belongs to the 918 multicast group specified as one of the target addresses, the router 919 considers itself a target and processes the received DIO as specified 920 in Section 9.5. Otherwise, the router considers itself an 921 intermediate router and processes the received DIO as specified in 922 Section 9.4. 924 9.4. Additional Processing of a P2P Mode DIO At An Intermediate Router 926 An intermediate router MUST discard a received P2P mode DIO with no 927 further processing if the router cannot elide Compr (as specified in 928 the P2P-RDO) prefix octets from its IPv6 address. 930 On receiving a P2P mode DIO, an intermediate router MUST determine 931 whether this DIO advertises a better route than the router itself and 932 whether the receipt of the DIO would allow the router to advertise a 933 better route than before. Accordingly, the router SHOULD consider 934 this DIO as consistent/inconsistent from Trickle perspective as 935 described in Section 9.2. Note that the route comparison in a P2P- 936 RPL route discovery is performed using the parent selection rules of 937 the OF in use as specified in Section 14 of RPL [I-D.ietf-roll-rpl]. 938 If the received DIO would allow the router to advertise a better 939 route, the router MUST remember the route advertised (inside the P2P- 940 RDO) in the DIO (after adding its own IPv6 address to the route) as 941 well as any Data Options for inclusion in its future DIOs. When an 942 intermediate router adds itself to a route, it MUST ensure that the 943 IPv6 address added to the route is reachable in both forward and 944 backward directions. To improve the diversity of the routes being 945 discovered, an intermediate router SHOULD keep track of multiple 946 partial routes to be advertised in the P2P-RDO inside its DIO. When 947 the router generates its DIO, it SHOULD randomly select the partial 948 route to be included in the P2P-RDO. 950 9.5. Additional Processing of a P2P Mode DIO At The Target 952 The target MUST deliver the data contained in any Data Options in the 953 received DIO to the application layer. The target MAY store the 954 route contained in the P2P-RDO in the received DIO for use as a 955 source route to reach the origin. If the Reply flag inside the P2P- 956 RDO is zero, the target MUST discard the received DIO with no further 957 processing. Otherwise, the target MAY select the route contained in 958 the P2P-RDO to send a DRO message back to the origin. If the H flag 959 inside the P2P-RDO is one, the target needs to select one route and 960 send a DRO message along this route back to the origin. If the H 961 flag is zero, the number of routes to be selected (and the number of 962 DRO messages to be sent back) is given by one plus the value of the N 963 field in the P2P-RDO. This document does not prescribe a particular 964 method for the target to select the routes. Example methods include 965 selecting each route that meets the specified routing constraints 966 until the desired number have been selected or selecting the best 967 routes discovered over a certain time period. If multiple routes are 968 to be selected, the target SHOULD avoid selecting routes that have 969 large segments in common. 971 If the target selects the route contained in the P2P-RDO in the 972 received DIO, it sends a DRO message back to the origin (identified 973 by the DODAGID field in the DIO). The DRO message MUST include a 974 P2P-RDO that contains the selected route inside the Address vector. 975 Various fields inside the P2P-RDO MUST be set as specified in 976 Section 8.2. The target MAY set the A flag inside the DRO message to 977 one if it desires the origin to send back a DRO-ACK message on 978 receiving the DRO. In this case, the target waits for 979 DRO_ACK_WAIT_TIME duration for the DRO-ACK message to arrive. 980 Failure to receive the DRO-ACK message within this time duration 981 causes the target to retransmit the DRO message. The target MAY 982 retransmit the DRO message in this fashion up to 983 MAX_DRO_RETRANSMISSIONS times. The values of DRO_ACK_WAIT_TIME and 984 MAX_DRO_RETRANSMISSIONS are defined in Section 12. 986 The target MAY set the stop flag inside the DRO message to one if 987 o this router is the only target specified in the corresponding DIO, 988 i.e., the corresponding DIO specified a unicast address of the 989 router as the Target inside the P2P-RDO with no additional targets 990 specified via RPL Target Options; and 992 o the target has already selected the desired number of routes. 994 The target MAY include a Metric Container Option in the DRO message. 995 This Metric Container contains the end-to-end routing metric values 996 for the route specified in the P2P-RDO. The target MAY include one 997 or more Data Options in the DRO message to carry time-critical 998 application data for the origin. The target MUST transmit the DRO 999 message via a link-local multicast. 1001 A target MUST NOT forward a P2P mode DIO any further. 1003 9.6. Processing a DRO At An Intermediate Router 1005 When a router receives a DRO message that does not list its IPv6 1006 address in the DODAGID field, the router MUST process the received 1007 message in the following manner: 1009 o If the stop flag inside the received DRO is set to one, the router 1010 SHOULD NOT send or receive any more DIOs for this temporary DAG 1011 and SHOULD cancel any pending DIO transmission. 1013 o An intermediate router MUST ignore any Metric Container and Data 1014 Options contained in the DRO message. 1016 o If Address[NH] element inside the Route Discovery Option lists the 1017 router's own IPv6 address, the router is a part of the route 1018 carried in the P2P-RDO. In this case, the router MUST do the 1019 following: 1021 * If the H flag inside the P2P-RDO is one, the router MUST store 1022 the state for the forward hop-by-hop route carried inside the 1023 P2P-RDO. This state consists of: 1025 + The RPLInstanceID and the DODAGID fields of the DRO. 1027 + The route's destination, the target (identified by Target 1028 field inside P2P-RDO). 1030 + The IPv6 address of the next hop, Address[NH+1] (unless NH 1031 value equals the number of elements in the Address vector, 1032 in which case the target itself is the next hop). 1034 * If the router already maintains a hop-by-hop state listing the 1035 target as the destination and carrying same RPLInstanceID and 1036 DODAGID fields as the received DRO and the next hop information 1037 in the state does not match the next hop indicated in the 1038 received DRO, the router MUST drop the DRO message with no 1039 further processing. 1041 * The router MUST decrement the NH field inside the P2P-RDO and 1042 send the DRO further via link-local multicast. 1044 9.7. Processing a DRO At The Origin 1046 When a router receives a DRO message that lists its IPv6 address in 1047 the DODAGID field, the router recognizes itself as the origin for the 1048 corresponding P2P-RPL route discovery and processes the message in 1049 the following manner. 1051 The origin MUST deliver data in any Data Options in the received DRO 1052 to the application layer. 1054 If the stop flag inside the received DRO is set to one, the origin 1055 SHOULD NOT generate any more DIOs for this temporary DAG and SHOULD 1056 cancel any pending DIO transmission. 1058 If the P2P-RDO inside the DRO identifies the discovered route as a 1059 source route (H=0), the origin MUST store in its memory the 1060 discovered route contained in the Address vector. 1062 If the P2P-RDO inside the DRO identifies the discovered route as a 1063 hop-by-hop route (H=1), the origin MUST store in its memory the state 1064 for the discovered route in the manner described in Section 9.6. 1066 If the received DRO message contains one or more Metric Container 1067 Options, the origin MAY store the values of the routing metrics 1068 associated with the discovered route in its memory. This information 1069 may be useful in formulating the constraints for any future P2P-RPL 1070 route discovery to the target. 1072 If the A flag is set to one in the received DRO message, the origin 1073 MUST generate a DRO-ACK message as described in Section 10 and 1074 unicast the message to the target (identified by the Target field 1075 inside the P2P-RDO). The origin MAY use the route just discovered to 1076 send the DRO-ACK message to the target. Section 11 describes how a 1077 packet may be forwarded along a source/hop-by-hop route discovered 1078 using P2P-RPL. 1080 10. The Discovery Reply Object Acknowledgement (DRO-ACK) 1082 0 1 2 3 1083 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 1084 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1085 | RPLInstanceID | Version |Seq| Reserved | 1086 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1087 | | 1088 | DODAGID | 1089 | | 1090 | | 1091 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1093 Figure 4: Format of the base Discovery Reply Object Acknowledgement 1094 (DRO-ACK) 1096 A DRO message may fail to reach the origin due to a number of 1097 reasons. Unlike the DIO messages that benefit from Trickle- 1098 controlled retransmissions, the DRO messages are prone to loss due to 1099 unreliable wireless communication. Since a DRO message travels via 1100 link-local multicast, it cannot use link-level acknowledgements to 1101 improve the reliability of its transmission. Also, an intermediate 1102 router may drop the DRO message (e.g., because of its inability to 1103 store the state for the hop-by-hop route the DRO is establishing). 1104 To protect against the potential failure of a DRO message to reach 1105 the origin, the target MAY request the origin to send back a DRO 1106 Acknowledgement (DRO-ACK) message on receiving a DRO message. 1107 Failure to receive such an acknowledgement within the 1108 DRO_ACK_WAIT_TIME interval of sending the DRO message forces the 1109 target to resend the message. 1111 This section defines two new RPL Control Message types: DRO 1112 Acknowledgement (DRO-ACK; with code 0x05; to be confirmed by IANA) 1113 and Secure DRO-ACK (with code 0x85; to be confirmed by IANA). A DRO- 1114 ACK message MUST travel as a unicast message from the origin to the 1115 target. The format of a base DRO-ACK message is shown in Figure 4. 1116 Various fields in a DRO-ACK message MUST have the same values as the 1117 corresponding fields in the DRO message. The field marked as 1118 "Reserved" MUST be set to zero on transmission and MUST be ignored on 1119 reception. A Secure DRO-ACK message follows the format in Figure 7 1120 of [I-D.ietf-roll-rpl], where the base format is same as the base 1121 DRO-ACK shown in Figure 4. 1123 11. Packet Forwarding Along a Route Discovered Using P2P-RPL 1125 An origin MAY use a Source Routing Header (SRH) 1127 [I-D.ietf-6man-rpl-routing-header] to send a packet along a source 1128 route discovered using P2P-RPL. 1130 Travel along a hop-by-hop route, established using P2P-RPL, requires 1131 specifying the RPLInstanceID and the DODAGID (of the temporary DAG 1132 used for the route discovery) to identify the route. This is because 1133 a P2P-RPL route discovery does not use globally unique RPLInstanceID 1134 values and hence both the RPLInstanceID (a local value assigned by 1135 the origin) and the DODAGID (an IPv6 address of the origin) are 1136 required to uniquely identify a P2P-RPL hop-by-hop route to a 1137 particular destination. 1139 An origin MAY include an RPL option [I-D.ietf-6man-rpl-option] inside 1140 the IPv6 hop-by-hop options header of a packet to send it along a 1141 hop-by-hop route established using P2P-RPL. For this purpose, the 1142 origin MUST set the DODAGID of the temporary DAG used for the route 1143 discovery as the source IPv6 address of the packet. Further, the 1144 origin MUST specify inside the RPL option the RPLInstanceID of the 1145 temporary DAG used for the route discovery and set the O flag inside 1146 the RPL option to one. On receiving this packet, an intermediate 1147 router checks the O flag and correctly infer the source IPv6 address 1148 of the packet as the DODAGID of the hop-by-hop route. The router 1149 then uses the DODAGID, the RPLInstanceID and the destination address 1150 to identify the routing state to be used to forward the packet 1151 further. 1153 12. Constants 1155 This document defines the following constants: 1157 o DRO_ACK_WAIT_TIME: The time duration a target waits for the DRO- 1158 ACK before retransmitting a DRO message. DRO_ACK_WAIT_TIME has a 1159 value of 1 second. 1161 o MAX_DRO_RETRANSMISSIONS: The maximum number of times a DRO message 1162 may be retransmitted if the target does not receive a DRO-ACK in 1163 response. MAX_DRO_RETRANSMISSIONS has a value 2. 1165 13. Interoperability with Core RPL 1167 This section describes how RPL routers that implement P2P-RPL 1168 interact with RPL routers that do not. In general, P2P-RPL operation 1169 does not affect core RPL operation and vice versa. However, core RPL 1170 does allow a router to join a DAG as a leaf node even if it does not 1171 understand the Mode of Operation (MOP) used in the DAG. Thus, an RPL 1172 router that does not implement P2P-RPL may conceivably join a 1173 temporary DAG being created for a P2P-RPL route discovery as a leaf 1174 node and maintain its membership even though the DAG no longer 1175 exists. This may impose a drain on the router's memory. However, 1176 such RPL-only leaf nodes do not interfere with P2P-RPL route 1177 discovery since a leaf node may only generate a DIO advertising an 1178 INFINITE_RANK and all routers implementing P2P-RPL are required to 1179 discard such DIOs. Note that core RPL does not require a router to 1180 join a DAG whose MOP it does not understand. Moreover, RPL routers 1181 in a particular deployment may have strict restrictions on the DAGs 1182 they may join, thereby mitigating the problem. 1184 The P2P-RPL mechanism described in this document works best when all 1185 the RPL routers in the LLN implement P2P-RPL. In general, the 1186 ability to discover routes as well as the quality of discovered 1187 routes would deteriorate with the fraction of RPL routers that 1188 implement P2P-RPL. 1190 14. Security Considerations 1192 The security considerations for the operation of P2P-RPL are similar 1193 to the ones for the operation of RPL (as described in Section 19 of 1194 [I-D.ietf-roll-rpl]). Section 10 of RPL specification 1195 [I-D.ietf-roll-rpl] describes a variety of security mechanisms that 1196 provide data confidentiality, authentication, replay protection and 1197 delay protection services. Each RPL control message has a secure 1198 version that allows the specification of the level of security and 1199 the algorithms used to secure the message. The mechanism defined in 1200 this document is based on the use of DIOs to form a temporary DAG and 1201 discover P2P routes. These DIOs can be used in their secure versions 1202 if desired. New RPL control messages defined in this document (DRO 1203 and DRO-ACK) have secure versions as well. Thus, a particular P2P- 1204 RPL deployment can analyze its security requirements and use the 1205 appropriate set of RPL security mechanisms that meet those 1206 requirements. 1208 15. IANA Considerations 1210 15.1. Additions to DIO Mode of Operation 1212 IANA is requested to allocate a new value in the "DIO Mode of 1213 Operation" registry for the "P2P Route Discovery Mode" described in 1214 this document. 1216 +----------+-----------------------------------------+--------------+ 1217 | MOP | Description | Reference | 1218 | Value | | | 1219 +----------+-----------------------------------------+--------------+ 1220 | 4 | Reactive P2P route discovery mode of | This | 1221 | | operation | document | 1222 +----------+-----------------------------------------+--------------+ 1224 DIO Mode of Operation 1226 15.2. Additions to RPL Control Message Options 1228 IANA is requested to allocate new values in the "RPL Control Message 1229 Options" registry for the "P2P Route Discovery Option" and the "Data 1230 Option" described in this document. 1232 +-------+---------------------+---------------+ 1233 | Value | Meaning | Reference | 1234 +-------+---------------------+---------------+ 1235 | 10 | P2P Route Discovery | This document | 1236 | 11 | Data | This document | 1237 +-------+---------------------+---------------+ 1239 RPL Control Message Options 1241 15.3. Additions to RPL Control Codes 1243 IANA is requested to allocate new code points in the "RPL Control 1244 Codes" registry for the "Discovery Reply Object" and "Discovery Reply 1245 Object Acknowledgement" (and their secure versions) described in this 1246 document. 1248 +------+--------------------------------------------+---------------+ 1249 | Code | Description | Reference | 1250 +------+--------------------------------------------+---------------+ 1251 | 0x04 | Discovery Reply Object | This document | 1252 | 0x05 | Discovery Reply Object Acknowledgement | This document | 1253 | 0x84 | Secure Discovery Reply Object | This document | 1254 | 0x85 | Secure Discovery Reply Object | This document | 1255 | | Acknowledgement | | 1256 +------+--------------------------------------------+---------------+ 1258 RPL Control Codes 1260 16. Acknowledgements 1262 Authors gratefully acknowledge the contributions of the following 1263 individuals (in alphabetical order) in the development of this 1264 document: Dominique Barthel, Jakob Buron, Thomas Clausen, Richard 1265 Kelsey, Phil Levis, Zach Shelby, Pascal Thubert, Hristo Valev and JP 1266 Vasseur. 1268 17. References 1270 17.1. Normative References 1272 [I-D.ietf-roll-routing-metrics] 1273 Barthel, D., Vasseur, J., Pister, K., Kim, M., and N. 1274 Dejean, "Routing Metrics used for Path Calculation in Low 1275 Power and Lossy Networks", 1276 draft-ietf-roll-routing-metrics-19 (work in progress), 1277 March 2011. 1279 [I-D.ietf-roll-rpl] 1280 Brandt, A., Vasseur, J., Hui, J., Pister, K., Thubert, P., 1281 Levis, P., Struik, R., Kelsey, R., Clausen, T., and T. 1282 Winter, "RPL: IPv6 Routing Protocol for Low power and 1283 Lossy Networks", draft-ietf-roll-rpl-19 (work in 1284 progress), March 2011. 1286 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1287 Requirement Levels", BCP 14, RFC 2119, March 1997. 1289 [RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko, 1290 "The Trickle Algorithm", RFC 6206, March 2011. 1292 17.2. Informative References 1294 [I-D.ietf-6man-rpl-option] 1295 Hui, J. and J. Vasseur, "RPL Option for Carrying RPL 1296 Information in Data-Plane Datagrams", 1297 draft-ietf-6man-rpl-option-06 (work in progress), 1298 December 2011. 1300 [I-D.ietf-6man-rpl-routing-header] 1301 Culler, D., Hui, J., Vasseur, J., and V. Manral, "An IPv6 1302 Routing Header for Source Routes with RPL", 1303 draft-ietf-6man-rpl-routing-header-07 (work in progress), 1304 December 2011. 1306 [I-D.ietf-roll-of0] 1307 Thubert, P., "RPL Objective Function Zero", 1308 draft-ietf-roll-of0-20 (work in progress), September 2011. 1310 [I-D.ietf-roll-p2p-measurement] 1311 Goyal, M., Baccelli, E., Brandt, A., and J. Martocci, "A 1312 Mechanism to Measure the Quality of a Point-to-point Route 1313 in a Low Power and Lossy Network", 1314 draft-ietf-roll-p2p-measurement-03 (work in progress), 1315 March 2012. 1317 [I-D.ietf-roll-terminology] 1318 Vasseur, J., "Terminology in Low power And Lossy 1319 Networks", draft-ietf-roll-terminology-06 (work in 1320 progress), September 2011. 1322 [RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation 1323 Routing Requirements in Low-Power and Lossy Networks", 1324 RFC 5826, April 2010. 1326 [RFC5867] Martocci, J., De Mil, P., Riou, N., and W. Vermeylen, 1327 "Building Automation Routing Requirements in Low-Power and 1328 Lossy Networks", RFC 5867, June 2010. 1330 Authors' Addresses 1332 Mukul Goyal (editor) 1333 University of Wisconsin Milwaukee 1334 3200 N Cramer St 1335 Milwaukee, WI 53201 1336 USA 1338 Phone: +1 414 2295001 1339 Email: mukul@uwm.edu 1341 Emmanuel Baccelli 1342 INRIA 1344 Phone: +33-169-335-511 1345 Email: Emmanuel.Baccelli@inria.fr 1346 URI: http://www.emmanuelbaccelli.org/ 1348 Matthias Philipp 1349 INRIA 1351 Phone: +33-169-335-511 1352 Email: Matthias.Philipp@inria.fr 1353 Anders Brandt 1354 Sigma Designs 1355 Emdrupvej 26A, 1. 1356 Copenhagen, Dk-2100 1357 Denmark 1359 Phone: +45-29609501 1360 Email: abr@sdesigns.dk 1362 Jerald Martocci 1363 Johnson Controls 1364 507 E Michigan St 1365 Milwaukee, WI 53202 1366 USA 1368 Phone: +1 414-524-4010 1369 Email: jerald.p.martocci@jci.com