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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Experimental RFC: RFC 3561 ** Downref: Normative reference to an Experimental RFC: RFC 6998 Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ROLL S. Anamalamudi 3 Internet-Draft SRM University-AP 4 Intended status: Standards Track M. Zhang 5 Expires: November 8, 2020 Huawei Technologies 6 C. Perkins 7 Deep Blue Sky Networks 8 S.V.R.Anand 9 Indian Institute of Science 10 B. Liu 11 Huawei Technologies 12 May 7, 2020 14 AODV based RPL Extensions for Supporting Asymmetric P2P Links in Low- 15 Power and Lossy Networks 16 draft-ietf-roll-aodv-rpl-08 18 Abstract 20 Route discovery for symmetric and asymmetric Point-to-Point (P2P) 21 traffic flows is a desirable feature in Low power and Lossy Networks 22 (LLNs). For that purpose, this document specifies a reactive P2P 23 route discovery mechanism for both hop-by-hop routing and source 24 routing: Ad Hoc On-demand Distance Vector Routing (AODV) based RPL 25 protocol (AODV-RPL). Paired Instances are used to construct 26 directional paths, in case some of the links between source and 27 target node are asymmetric. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at https://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on November 8, 2020. 46 Copyright Notice 48 Copyright (c) 2020 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (https://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 65 3. Overview of AODV-RPL . . . . . . . . . . . . . . . . . . . . 5 66 4. AODV-RPL DIO Options . . . . . . . . . . . . . . . . . . . . 6 67 4.1. AODV-RPL RREQ Option . . . . . . . . . . . . . . . . . . 6 68 4.2. AODV-RPL RREP Option . . . . . . . . . . . . . . . . . . 8 69 4.3. AODV-RPL Target Option . . . . . . . . . . . . . . . . . 10 70 5. Symmetric and Asymmetric Routes . . . . . . . . . . . . . . . 11 71 6. AODV-RPL Operation . . . . . . . . . . . . . . . . . . . . . 13 72 6.1. Route Request Generation . . . . . . . . . . . . . . . . 13 73 6.2. Receiving and Forwarding RREQ messages . . . . . . . . . 14 74 6.2.1. General Processing . . . . . . . . . . . . . . . . . 14 75 6.2.2. Additional Processing for Multiple Targets . . . . . 15 76 6.3. Generating Route Reply (RREP) at TargNode . . . . . . . . 16 77 6.3.1. RREP-DIO for Symmetric route . . . . . . . . . . . . 16 78 6.3.2. RREP-DIO for Asymmetric Route . . . . . . . . . . . . 16 79 6.3.3. RPLInstanceID Pairing . . . . . . . . . . . . . . . . 17 80 6.4. Receiving and Forwarding Route Reply . . . . . . . . . . 17 81 7. Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . . 19 82 8. Operation of Trickle Timer . . . . . . . . . . . . . . . . . 19 83 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 84 9.1. New Mode of Operation: AODV-RPL . . . . . . . . . . . . . 20 85 9.2. AODV-RPL Options: RREQ, RREP, and Target . . . . . . . . 20 86 10. Security Considerations . . . . . . . . . . . . . . . . . . . 20 87 11. Link State Determination . . . . . . . . . . . . . . . . . . 21 88 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 89 12.1. Normative References . . . . . . . . . . . . . . . . . . 21 90 12.2. Informative References . . . . . . . . . . . . . . . . . 22 91 Appendix A. Example: ETX/RSSI Values to select S bit . . . . . . 23 92 Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . 24 93 B.1. Changes from version 07 to version 08 . . . . . . . . . . 24 94 B.2. Changes from version 06 to version 07 . . . . . . . . . . 24 95 B.3. Changes from version 05 to version 06 . . . . . . . . . . 25 96 B.4. Changes from version 04 to version 05 . . . . . . . . . . 25 97 B.5. Changes from version 03 to version 04 . . . . . . . . . . 25 98 B.6. Changes from version 02 to version 03 . . . . . . . . . . 25 99 Appendix C. Contributors . . . . . . . . . . . . . . . . . . . . 26 100 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 102 1. Introduction 104 RPL [RFC6550] (Routing Protocol for Low-Power and Lossy Networks) is 105 an IPv6 distance vector routing protocol designed to support multiple 106 traffic flows through a root-based Destination-Oriented Directed 107 Acyclic Graph (DODAG). Typically, a router does not have routing 108 information for most other routers. Consequently, for traffic 109 between routers within the DODAG (i.e., Point-to-Point (P2P) traffic) 110 data packets either have to traverse the root in non-storing mode, or 111 traverse a common ancestor in storing mode. Such P2P traffic is 112 thereby likely to traverse longer routes and may suffer severe 113 congestion near the DAG root (for more information see [RFC6997], 114 [RFC6998]). 116 The route discovery process in AODV-RPL is modeled on the analogous 117 procedure specified in AODV [RFC3561]. The on-demand nature of AODV 118 route discovery is natural for the needs of peer-to-peer routing in 119 RPL-based LLNs. AODV terminology has been adapted for use with AODV- 120 RPL messages, namely RREQ for Route Request, and RREP for Route 121 Reply. AODV-RPL currently omits some features compared to AODV -- in 122 particular, flagging Route Errors, blacklisting unidirectional links, 123 multihoming, and handling unnumbered interfaces. 125 AODV-RPL reuses and provides a natural extension to the core RPL 126 functionality to support routes with birectional asymmetric links. 127 It retains RPL's DODAG formation, RPL Instance and the associated 128 Objective Function, trickle timers, and support for storing and non- 129 storing modes. AODV adds basic messages RREQ and RREP as part of RPL 130 DIO (DODAG Information Object) control messages, and does not utilize 131 the DAO message of RPL. AODV-RPL specifies a new MOP running in a 132 seperate instance dedicating to discover P2P routes, which may differ 133 from the P2MP routes discoverable by native RPL. AODV-RPL can be 134 operated whether or not native RPL is running otherwise. 136 2. Terminology 138 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 139 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 140 "OPTIONAL" in this document are to be interpreted as described in BCP 141 14 [RFC2119] [RFC8174] when, and only when, they appear in all 142 capitals, as shown here. 144 AODV 145 Ad Hoc On-demand Distance Vector Routing[RFC3561]. 147 AODV-RPL Instance 148 Either the RREQ-Instance or RREP-Instance 150 Asymmetric Route 151 The route from the OrigNode to the TargNode can traverse different 152 nodes than the route from the TargNode to the OrigNode. An 153 asymmetric route may result from the asymmetry of links, such that 154 only one direction of the series of links satisfies the Objective 155 Function during route discovery. 157 Bi-directional Asymmetric Link 158 A link that can be used in both directions but with different link 159 characteristics. 161 DIO 162 DODAG Information Object 164 DODAG RREQ-Instance (or simply RREQ-Instance) 165 RPL Instance built using the DIO with RREQ option; used for 166 control message transmission from OrigNode to TargNode, thus 167 enabling data transmission from TargNode to OrigNode. 169 DODAG RREP-Instance (or simply RREP-Instance) 170 RPL Instance built using the DIO with RREP option; used for 171 control message transmission from TargNode to OrigNode thus 172 enabling data transmission from OrigNode to TargNode. 174 Downward Direction 175 The direction from the OrigNode to the TargNode. 177 Downward Route 178 A route in the downward direction. 180 hop-by-hop routing 181 Routing when each node stores routing information about the next 182 hop. 184 on-demand routing 185 Routing in which a route is established only when needed. 187 OrigNode 188 The IPv6 router (Originating Node) initiating the AODV-RPL route 189 discovery to obtain a route to TargNode. 191 Paired DODAGs 192 Two DODAGs for a single route discovery process between OrigNode 193 and TargNode. 195 P2P 196 Point-to-Point -- in other words, not constrained a priori to 197 traverse a common ancestor. 199 reactive routing 200 Same as "on-demand" routing. 202 RREQ-DIO message 203 An AODV-RPL MOP DIO message containing the RREQ option. The 204 RPLInstanceID in RREQ-DIO is assigned locally by the OrigNode. 206 RREP-DIO message 207 An AODV-RPL MOP DIO message containing the RREP option. The 208 RPLInstanceID in RREP-DIO is typically paired to the one in the 209 associated RREQ-DIO message. 211 Source routing 212 A mechanism by which the source supplies the complete route 213 towards the target node along with each data packet [RFC6550]. 215 Symmetric route 216 The upstream and downstream routes traverse the same routers. 218 TargNode 219 The IPv6 router (Target Node) for which OrigNode requires a route 220 and initiates Route Discovery within the LLN network. 222 Upward Direction 223 The direction from the TargNode to the OrigNode. 225 Upward Route 226 A route in the upward direction. 228 ART option 229 AODV-RPL Target option: a target option defined in this document. 231 3. Overview of AODV-RPL 233 With AODV-RPL, routes from OrigNode to TargNode within the LLN 234 network are established "on-demand". In other words, the route 235 discovery mechanism in AODV-RPL is invoked reactively when OrigNode 236 has data for delivery to the TargNode but existing routes do not 237 satisfy the application's requirements. AODV-RPL is thus functional 238 without requiring the use of RPL or any other routing protocol. 240 The routes discovered by AODV-RPL are not constrained to traverse a 241 common ancestor. AODV-RPL can enable asymmetric communication paths 242 in networks with bidirectional asymmetric links. For this purpose, 243 AODV-RPL enables discovery of two routes: namely, one from OrigNode 244 to TargNode, and another from TargNode to OrigNode. When possible, 245 AODV-RPL also enables symmetric route discovery along Paired DODAGs 246 (see Section 5). 248 In AODV-RPL, routes are discovered by first forming a temporary DAG 249 rooted at the OrigNode. Paired DODAGs (Instances) are constructed 250 according to the AODV-RPL Mode of Operation (MOP) during route 251 formation between the OrigNode and TargNode. The RREQ-Instance is 252 formed by route control messages from OrigNode to TargNode whereas 253 the RREP-Instance is formed by route control messages from TargNode 254 to OrigNode. Intermediate routers join the Paired DODAGs based on 255 the Rank as calculated from the DIO message. Henceforth in this 256 document, the RREQ-DIO message means the AODV-RPL mode DIO message 257 from OrigNode to TargNode, containing the RREQ option (see 258 Section 4.1). Similarly, the RREP-DIO message means the AODV-RPL 259 mode DIO message from TargNode to OrigNode, containing the RREP 260 option (see Section 4.2). The route discovered in the RREQ-Instance 261 is used for transmitting data from TargNode to OrigNode, and the 262 route discovered in RREP-Instance is used for transmitting data from 263 OrigNode to TargNode. 265 4. AODV-RPL DIO Options 267 4.1. AODV-RPL RREQ Option 269 OrigNode sets its IPv6 address in the DODAGID field of the RREQ-DIO 270 message. A RREQ-DIO message MUST carry exactly one RREQ option, 271 otherwise it SHOULD be dropped. 273 0 1 2 3 274 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 1 275 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 276 | Option Type | Option Length |S|H|X| Compr | L | MaxRank | 277 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 278 | Orig SeqNo | | 279 +-+-+-+-+-+-+-+-+ | 280 | | 281 | | 282 | Address Vector (Optional, Variable Length) | 283 | | 284 | | 285 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 287 Figure 1: Format for AODV-RPL RREQ Option 289 OrigNode supplies the following information in the RREQ option: 291 Option Type 292 TBD2 294 Option Length 295 The length of the option in octets, excluding the Type and Length 296 fields. Variable due to the presence of the address vector and 297 the number of octets elided according to the Compr value. 299 S 300 Symmetric bit indicating a symmetric route from the OrigNode to 301 the router transmitting this RREQ-DIO. 303 H 304 Set to one for a hop-by-hop route. Set to zero for a source 305 route. This flag controls both the downstream route and upstream 306 route. 308 X 309 Reserved. 311 Compr 312 4-bit unsigned integer. Number of prefix octets that are elided 313 from the Address Vector. The octets elided are shared with the 314 IPv6 address in the DODAGID. This field is only used in source 315 routing mode (H=0). In hop-by-hop mode (H=1), this field MUST be 316 set to zero and ignored upon reception. 318 L 319 2-bit unsigned integer determining the duration that a node is 320 able to belong to the temporary DAG in RREQ-Instance, including 321 the OrigNode and the TargNode. Once the time is reached, a node 322 MUST leave the DAG and stop sending or receiving any more DIOs for 323 the temporary DODAG. 325 * 0x00: No time limit imposed. 326 * 0x01: 16 seconds 327 * 0x02: 64 seconds 328 * 0x03: 256 seconds 330 L is independent from the route lifetime, which is defined in the 331 DODAG configuration option. The route entries in hop-by-hop 332 routing and states of source routing can still be maintained even 333 after the node no longer maintains DAG connectivity or messaging. 335 MaxRank 336 This field indicates the upper limit on the integer portion of the 337 Rank (calculated using the DAGRank() macro defined in [RFC6550]). 338 A value of 0 in this field indicates the limit is infinity. 340 Orig SeqNo 341 Sequence Number of OrigNode. See Section 6.1. 343 Address Vector 344 A vector of IPv6 addresses representing the route that the RREQ- 345 DIO has passed. It is only present when the H bit is set to 0. 346 The prefix of each address is elided according to the Compr field. 348 TargNode can join the RREQ instance at a Rank whose integer portion 349 is equal to the MaxRank. Other nodes MUST NOT join a RREQ instance 350 if its own Rank would be equal to or higher than MaxRank. A router 351 MUST discard a received RREQ if the integer part of the advertised 352 Rank equals or exceeds the MaxRank limit. 354 4.2. AODV-RPL RREP Option 356 TargNode sets its IPv6 address in the DODAGID field of the RREP-DIO 357 message. A RREP-DIO message MUST carry exactly one RREP option, 358 otherwise the message SHOULD be dropped. TargNode supplies the 359 following information in the RREP option: 361 0 1 2 3 362 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 1 363 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 364 | Option Type | Option Length |G|H|X| Compr | L | MaxRank | 365 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 366 | Shift |Rsv| | 367 +-+-+-+-+-+-+-+-+ | 368 | | 369 | | 370 | Address Vector (Optional, Variable Length) | 371 . . 372 . . 373 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 375 Figure 2: Format for AODV-RPL RREP option 377 Option Type 378 TBD3 380 Option Length 381 The length of the option in octets, excluding the Type and Length 382 fields. Variable due to the presence of the address vector and 383 the number of octets elided according to the Compr value. 385 G 386 Gratuitous route (see Section 7). 388 H 389 Requests either source routing (H=0) or hop-by-hop (H=1) for the 390 downstream route. It MUST be set to be the same as the H bit in 391 RREQ option. 393 X 394 Reserved. 396 Compr 397 4-bit unsigned integer. Same definition as in RREQ option. 399 L 400 2-bit unsigned integer defined as in RREQ option. 402 MaxRank 403 Similarly to MaxRank in the RREQ message, this field indicates the 404 upper limit on the integer portion of the Rank. A value of 0 in 405 this field indicates the limit is infinity. 407 Shift 408 6-bit unsigned integer. This field is used to recover the 409 original RPLInstanceID (see Section 6.3.3); 0 indicates that the 410 original RPLInstanceID is used. 412 Rsv 413 MUST be initialized to zero and ignored upon reception. 415 Address Vector 416 Only present when the H bit is set to 0. For an asymmetric route, 417 the Address Vector represents the IPv6 addresses of the route that 418 the RREP-DIO has passed. For a symmetric route, it is the Address 419 Vector when the RREQ-DIO arrives at the TargNode, unchanged during 420 the transmission to the OrigNode. 422 4.3. AODV-RPL Target Option 424 The AODV-RPL Target (ART) Option is based on the Target Option in 425 core RPL [RFC6550]. The Flags field is replaced by the Destination 426 Sequence Number of the TargNode and the Prefix Length field is 427 reduced to 7 bits so that the value is limited to be no greater than 428 127. 430 A RREQ-DIO message MUST carry at least one ART Option. A RREP-DIO 431 message MUST carry exactly one ART Option. Otherwise, the message 432 SHOULD be dropped. 434 OrigNode can include multiple TargNode addresses via multiple AODV- 435 RPL Target Options in the RREQ-DIO, for routes that share the same 436 requirement on metrics. This reduces the cost to building only one 437 DODAG. 439 0 1 2 3 440 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 1 441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 442 | Option Type | Option Length | Dest SeqNo |r|Prefix Length| 443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 444 | | 445 + | 446 | Target Prefix / Address (Variable Length) | 447 . . 448 . . 449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 451 Figure 3: Target option format for AODV-RPL MOP 453 Option Type 454 TBD4 456 Option Length 457 Length of the option in octets excluding the Type and Length 458 fields 460 Dest SeqNo 462 In RREQ-DIO, if nonzero, it is the last known Sequence Number for 463 TargNode for which a route is desired. In RREP-DIO, it is the 464 destination sequence number associated to the route. 466 r 467 A one-bit reserved field. This field MUST be initialized to zero 468 by the sender and MUST be ignored by the receiver. 470 Prefix Length 471 7-bit unsigned integer. Number of valid leading bits in the IPv6 472 Prefix. If Prefix Length is 0, then the value in the Target 473 Prefix / Address field represents an IPv6 address, not a prefix. 475 Target Prefix / Address 476 (variable-length field) An IPv6 destination address or prefix. 477 The Prefix Length field contains the number of valid leading bits 478 in the prefix. The length of the field is the least number of 479 octets that can contain all of the bits of the Prefix, in other 480 words Floor((7+(Prefix Length))/8) octets. The remaining bits in 481 the Target Prefix / Address field after the prefix length (if any) 482 MUST be set to zero on transmission and MUST be ignored on 483 receipt. 485 5. Symmetric and Asymmetric Routes 487 In Figure 4 and Figure 5, BR is the Border Router, O is the OrigNode, 488 R is an intermediate router, and T is the TargNode. If the RREQ-DIO 489 arrives over an interface that is known to be symmetric, and the S 490 bit is set to 1, then it remains as 1, as illustrated in Figure 4. 491 If an intermediate router sends out RREQ-DIO with the S bit set to 1, 492 then all the one-hop links on the route from the OrigNode O to this 493 router meet the requirements of route discovery, and the route can be 494 used symmetrically. 496 BR 497 /----+----\ 498 / | \ 499 / | \ 500 R R R 501 _/ \ | / \ 502 / \ | / \ 503 / \ | / \ 504 R -------- R --- R ----- R -------- R 505 / \ <--S=1--> / \ <--S=1--> / \ 506 <--S=1--> \ / \ / <--S=1--> 507 / \ / \ / \ 508 O ---------- R ------ R------ R ----- R ----------- T 509 / \ / \ / \ / \ 510 / \ / \ / \ / \ 511 / \ / \ / \ / \ 512 R ----- R ----------- R ----- R ----- R ----- R ---- R----- R 514 >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> 515 <---- RREP-Instance (Control: T-->O; Data: O-->T) -------< 517 Figure 4: AODV-RPL with Symmetric Paired Instances 519 Upon receiving a RREQ-DIO with the S bit set to 1, a node determines 520 whether this one-hop link can be used symmetrically, i.e., both the 521 two directions meet the requirements of data transmission. If the 522 RREQ-DIO arrives over an interface that is not known to be symmetric, 523 or is known to be asymmetric, the S bit is set to 0. If the S bit 524 arrives already set to be '0', it is set to be '0' on retransmission 525 (Figure 5). For an asymmetric route, there is at least one hop which 526 doesn't satisfy the Objective Function. Based on the S bit received 527 in RREQ-DIO, TargNode T determines whether or not the route is 528 symmetric before transmitting the RREP-DIO message upstream towards 529 the OrigNode O. 531 The criteria used to determine whether or not each link is symmetric 532 is beyond the scope of the document, and may be implementation- 533 specific. For instance, intermediate routers can use local 534 information (e.g., bit rate, bandwidth, number of cells used in 535 6tisch), a priori knowledge (e.g. link quality according to previous 536 communication) or use averaging techniques as appropriate to the 537 application. 539 Appendix A describes an example method using the ETX and RSSI to 540 estimate whether the link is symmetric in terms of link quality is 541 given in using an averaging technique. 543 BR 544 /----+----\ 545 / | \ 546 / | \ 547 R R R 548 / \ | / \ 549 / \ | / \ 550 / \ | / \ 551 R --------- R --- R ---- R --------- R 552 / \ --S=1--> / \ --S=0--> / \ 553 --S=1--> \ / \ / --S=0--> 554 / \ / \ / \ 555 O ---------- R ------ R------ R ----- R ----------- T 556 / \ / \ / \ / \ 557 / <--S=0-- / \ / \ / <--S=0-- 558 / \ / \ / \ / \ 559 R ----- R ----------- R ----- R ----- R ----- R ---- R----- R 560 <--S=0-- <--S=0-- <--S=0-- <--S=0-- <--S=0-- 562 >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> 563 <---- RREP-Instance (Control: T-->O; Data: O-->T) -------< 565 Figure 5: AODV-RPL with Asymmetric Paired Instances 567 6. AODV-RPL Operation 569 6.1. Route Request Generation 571 The route discovery process is initiated when an application at the 572 OrigNode has data to be transmitted to the TargNode, but does not 573 have a route that satisfies the Objective Function for the target of 574 the data transmission. In this case, the OrigNode builds a local 575 RPLInstance and a DODAG rooted at itself. Then it transmits a DIO 576 message containing exactly one RREQ option (see Section 4.1) via 577 link-local multicast. The DIO MUST contain at least one ART Option 578 (see Section 4.3). The S bit in RREQ-DIO sent out by the OrigNode is 579 set to 1. 581 Each node maintains a sequence number; the operation is specified in 582 section 7.2 of [RFC6550]. When the OrigNode initiates a route 583 discovery process, it MUST increase its own sequence number to avoid 584 conflicts with previously established routes. The sequence number is 585 carried in the Orig SeqNo field of the RREQ option. 587 The address in the ART Option can be a unicast IPv6 address or a 588 prefix. The OrigNode can initiate the route discovery process for 589 multiple targets simultaneously by including multiple ART Options, 590 and within a RREQ-DIO the requirements for the routes to different 591 TargNodes MUST be the same. 593 OrigNode can maintain different RPLInstances to discover routes with 594 different requirements to the same targets. Using the InstanceID 595 pairing mechanism (see Section 6.3.3), route replies (RREP-DIOs) for 596 different RPLInstances can be distinguished. 598 The transmission of RREQ-DIO obeys the Trickle timer [RFC6206]. If 599 the duration specified by the L bit has elapsed, the OrigNode MUST 600 leave the DODAG and stop sending RREQ-DIOs in the related 601 RPLInstance. 603 6.2. Receiving and Forwarding RREQ messages 605 6.2.1. General Processing 607 Upon receiving a RREQ-DIO, a router goes through the steps below. If 608 the router does not belong to the RREQ-Instance, then the maximum 609 useful rank (MaxUseRank) is MaxRank. Otherwise, MaxUseRank is set to 610 be the Rank value that was stored when the router processed the best 611 previous RREQ for the DODAG with the given RREQ-Instance. 613 Step 1: 615 If the S bit in the received RREQ-DIO is set to 1, the router MUST 616 determine whether each direction of the link (by which the RREQ- 617 DIO is received) satisfies the Objective Function. In case that 618 the downward (i.e. towards the TargNode) direction of the link 619 does not satisfy the Objective Function, the link can't be used 620 symmetrically, thus the S bit of the RREQ-DIO to be sent out MUST 621 be set as 0. If the S bit in the received RREQ-DIO is set to 0, 622 the router MUST only check into the upward direction (towards the 623 OrigNode) of the link. 625 If the upward direction of the link can satisfy the Objective 626 Function (defined in [RFC6551]), and the router's Rank would not 627 exceed the MaxUseRank limit, the router joins the DODAG of the 628 RREQ-Instance. The router that transmitted the received RREQ-DIO 629 is selected as the preferred parent. Otherwise, if the Objective 630 Function is not satisfied or the MaxUseRank limit is exceeded, the 631 router MUST discard the received RREQ-DIO and MUST NOT join the 632 DODAG. 634 Step 2: 636 Then the router checks if one of its addresses is included in one 637 of the ART Options. If so, this router is one of the TargNodes. 638 Otherwise, it is an intermediate router. 640 Step 3: 642 If the H bit is set to 1, then the router (TargNode or 643 intermediate) MUST build an upward route entry towards OrigNode 644 which MUST include at least the following items: Source Address, 645 InstanceID, Destination Address, Next Hop, Lifetime, and Sequence 646 Number. The Destination Address and the InstanceID respectively 647 can be learned from the DODAGID and the RPLInstanceID of the RREQ- 648 DIO, and the Source Address is the address used by the local 649 router to send data to the OrigNode. The Next Hop is the 650 preferred parent. The lifetime is set according to DODAG 651 configuration (i.e., not the L bit) and can be extended when the 652 route is actually used. The sequence number represents the 653 freshness of the route entry, and it is copied from the Orig SeqNo 654 field of the RREQ option. A route entry with the same source and 655 destination address, same InstanceID, but stale sequence number, 656 MUST be deleted. 658 Step 4: 660 If the router is an intermediate router, then it transmits a RREQ- 661 DIO via link-local multicast; if the H bit is set to 0, the 662 intermediate router MUST include the address of the interface 663 receiving the RREQ-DIO into the address vector.. Otherwise, if 664 the router (i.e., TargNode) was not already associated with the 665 RREQ-Instance, it prepares a RREP-DIO Section 6.3. If, on the 666 other hand TargNode was already associated with the RREQ-Instance, 667 it takes no further action and does not send an RREP-DIO. 669 6.2.2. Additional Processing for Multiple Targets 671 If the OrigNode tries to reach multiple TargNodes in a single RREQ- 672 Instance, one of the TargNodes can be an intermediate router to the 673 others, therefore it MUST continue sending RREQ-DIO to reach other 674 targets. In this case, before rebroadcasting the RREQ-DIO, a 675 TargNode MUST delete the Target Option encapsulating its own address, 676 so that downstream routers with higher Rank values do not try to 677 create a route to this TargetNode. 679 An intermediate router could receive several RREQ-DIOs from routers 680 with lower Rank values in the same RREQ-Instance but have different 681 lists of Target Options. When rebroadcasting the RREQ-DIO, the 682 intersection of these lists MUST be included. For example, suppose 683 two RREQ-DIOs are received with the same RPLInstance and OrigNode. 685 Suppose further that the first RREQ has (T1, T2) as the targets, and 686 the second one has (T2, T4) as targets. Then only T2 needs to be 687 included in the generated RREQ-DIO. If the intersection is empty, it 688 means that all the targets have been reached, and the router MUST NOT 689 send out any RREQ-DIO. For the purposes of determining the 690 intersection with previous incoming RREQ-DIOs, the intermediate 691 router maintains a record of the targets that have been requested 692 associated with the RREQ-Instance. Any RREQ-DIO message with 693 different ART Options coming from a router with higher Rank is 694 ignored. 696 6.3. Generating Route Reply (RREP) at TargNode 698 6.3.1. RREP-DIO for Symmetric route 700 If a RREQ-DIO arrives at TargNode with the S bit set to 1, there is a 701 symmetric route along which both directions satisfy the Objective 702 Function. Other RREQ-DIOs might later provide asymmetric upward 703 routes (i.e. S=0). Selection between a qualified symmetric route 704 and an asymmetric route that might have better performance is 705 implementation-specific and out of scope. If the implementation 706 selects the symmetric route, and the L bit is not 0, the TargNode MAY 707 delay transmitting the RREP-DIO for duration RREP_WAIT_TIME to await 708 a symmetric route with a lower Rank. The value of RREP_WAIT_TIME is 709 set by default to 1/4 of the time duration determined by the L bit. 711 For a symmetric route, the RREP-DIO message is unicast to the next 712 hop according to the accumulated address vector (H=0) or the route 713 entry (H=1). Thus the DODAG in RREP-Instance does not need to be 714 built. The RPLInstanceID in the RREP-Instance is paired as defined 715 in Section 6.3.3. In case the H bit is set to 0, the address vector 716 received in the RREQ-DIO MUST be included in the RREP-DIO. TargNode 717 increments its current sequence number and uses the incremented 718 result in the Dest SeqNo in the ART option of the RREQ-DIO. The 719 address of the OrigNode MUST be encapsulated in the ART Option and 720 included in this RREP-DIO message. 722 6.3.2. RREP-DIO for Asymmetric Route 724 When a RREQ-DIO arrives at a TargNode with the S bit set to 0, the 725 TargNode MUST build a DODAG in the RREP-Instance rooted at itself in 726 order to discover the downstream route from the OrigNode to the 727 TargNode. The RREP-DIO message MUST be re-transmitted via link-local 728 multicast until the OrigNode is reached or MaxRank is exceeded. The 729 TargNode MAY delay transmitting the RREP-DIO for duration 730 RREP_WAIT_TIME to await a route with a lower Rank. The value of 731 RREP_WAIT_TIME is set by default to 1/4 of the time duration 732 determined by the L bit. 734 The settings of the fields in RREP option and ART option are the same 735 as for the symmetric route, except for the S bit. 737 6.3.3. RPLInstanceID Pairing 739 Since the RPLInstanceID is assigned locally (i.e., there is no 740 coordination between routers in the assignment of RPLInstanceID), the 741 tuple (OrigNode, TargNode, RPLInstanceID) is needed to uniquely 742 identify a discovered route. It is possible that multiple route 743 discoveries with dissimilar Objective Functions are initiated 744 simultaneously. Thus between the same pair of OrigNode and TargNode, 745 there can be multiple AODV-RPL route discovery instances. To avoid 746 any mismatch, the RREQ-Instance and the RREP-Instance in the same 747 route discovery MUST be paired using the RPLInstanceID. 749 When preparing the RREP-DIO, a TargNode could find the RPLInstanceID 750 to be used for the RREP-Instance is already occupied by another RPL 751 Instance from an earlier route discovery operation which is still 752 active. In other words, it might happen that two distinct OrigNodes 753 need routes to the same TargNode, and they happen to use the same 754 RPLInstanceID for RREQ-Instance. In this case, the occupied 755 RPLInstanceID MUST NOT be used again. Then the second RPLInstanceID 756 MUST be shifted into another integer so that the two RREP-instances 757 can be distinguished. In RREP option, the Shift field indicates the 758 shift to be applied to original RPLInstanceID. When the new 759 InstanceID after shifting exceeds 63, it rolls over starting at 0. 760 For example, the original InstanceID is 60, and shifted by 6, the new 761 InstanceID will be 2. Related operations can be found in 762 Section 6.4. 764 6.4. Receiving and Forwarding Route Reply 766 Upon receiving a RREP-DIO, a router which does not belong to the 767 RREQ-Instance goes through the following steps: 769 Step 1: 771 If the S bit is set to 1, the router MUST proceed to step 2. 773 If the S bit of the RREP-DIO is set to 0, the router MUST check 774 the downward direction of the link (towards the TargNode) over 775 which the RREP-DIO is received. If the downward direction of the 776 link can satisfy the Objective Function, and the router's Rank 777 would not exceed the MaxRank limit, the router joins the DODAG of 778 the RREP-Instance. The router that transmitted the received RREP- 779 DIO is selected as the preferred parent. Afterwards, other RREP- 780 DIO messages can be received. 782 If the Objective Function is not satisfied, the router MUST NOT 783 join the DODAG; the router MUST discard the RREQ-DIO, and does not 784 execute the remaining steps in this section. 786 Step 2: 788 The router next checks if one of its addresses is included in the 789 ART Option. If so, this router is the OrigNode of the route 790 discovery. Otherwise, it is an intermediate router. 792 Step 3: 794 If the H bit is set to 1, then the router (OrigNode or 795 intermediate) MUST build a downward route entry. The route entry 796 MUST include at least the following items: OrigNode Address, 797 InstanceID, TargNode Address as destination, Next Hop, Lifetime 798 and Sequence Number. For a symmetric route, the Next Hop in the 799 route entry is the router from which the RREP-DIO is received. 800 For an asymmetric route, the Next Hop is the preferred parent in 801 the DODAG of RREQ-Instance. The InstanceID in the route entry 802 MUST be the original RPLInstanceID (after subtracting the Shift 803 field value). The source address is learned from the ART Option, 804 and the destination address is learned from the DODAGID. The 805 lifetime is set according to DODAG configuration and can be 806 extended when the route is actually used. The sequence number 807 represents the freshness of the route entry, and is copied from 808 the Dest SeqNo field of the ART option of the RREP-DIO. A route 809 entry with same source and destination address, same InstanceID, 810 but stale sequence number, SHOULD be deleted. 812 If the H bit is set to 0, for an asymmetric route, an intermediate 813 router MUST include the address of the interface receiving the 814 RREP-DIO into the address vector; for a symmetric route, there is 815 nothing to do in this step. 817 Step 4: 819 If the receiver is the OrigNode, it can start transmitting the 820 application data to TargNode along the path as provided in RREP- 821 Instance, and processing for the RREP-DIO is complete. Otherwise, 822 in case of an asymmetric route, the intermediate router transmits 823 the RREP-DIO via link-local multicast. In case of a symmetric 824 route, the RREP-DIO message is unicast to the Next Hop according 825 to the address vector in the RREP-DIO (H=0) or the local route 826 entry (H=1). The RPLInstanceID in the transmitted RREP-DIO is the 827 same as the value in the received RREP-DIO. The local knowledge 828 for the TargNode's sequence number SHOULD be updated. 830 Upon receiving a RREP-DIO, a router which already belongs to the 831 RREQ-Instance SHOULD drop the RREP-DIO. 833 7. Gratuitous RREP 835 In some cases, an Intermediate router that receives a RREQ-DIO 836 message MAY transmit a "Gratuitous" RREP-DIO message back to OrigNode 837 instead of continuing to multicast the RREQ-DIO towards TargNode. 838 The intermediate router effectively builds the RREP-Instance on 839 behalf of the actual TargNode. The G bit of the RREP option is 840 provided to distinguish the Gratuitous RREP-DIO (G=1) sent by the 841 Intermediate node from the RREP-DIO sent by TargNode (G=0). 843 The gratuitous RREP-DIO can be sent out when an intermediate router 844 receives a RREQ-DIO for a TargNode, and the router has a more recent 845 (larger destination sequence number) pair of downward and upward 846 routes to the TargNode which also satisfy the Objective Function. 848 In case of source routing, the intermediate router MUST unicast the 849 received RREQ-DIO to TargNode including the address vector between 850 the OrigNode and the router. Thus the TargNode can have a complete 851 upward route address vector from itself to the OrigNode. Then the 852 router MUST send out the gratuitous RREP-DIO including the address 853 vector from the router itself to the TargNode. 855 In case of hop-by-hop routing, the intermediate router MUST unicast 856 the received RREQ-DIO to the Next Hop on the route. The Next Hop 857 router along the route MUST build new route entries with the related 858 RPLInstanceID and DODAGID in the downward direction. The above 859 process will happen recursively until the RREQ-DIO arrives at the 860 TargNode. Then the TargNode MUST unicast recursively the RREP-DIO 861 hop-by-hop to the intermediate router, and the routers along the 862 route SHOULD build new route entries in the upward direction. Upon 863 receiving the unicast RREP-DIO, the intermediate router sends the 864 gratuitous RREP-DIO to the OrigNode as defined in Section 6.3. 866 8. Operation of Trickle Timer 868 The trickle timer operation to control RREQ-Instance/RREP-Instance 869 multicast uses [RFC6206] to control RREQ-DIO and RREP-DIO 870 transmissions. The Trickle control of these DIO transmissions follow 871 the procedures described in the Section 8.3 of [RFC6550] entitled 872 "DIO Transmission". 874 9. IANA Considerations 876 9.1. New Mode of Operation: AODV-RPL 878 IANA is asked to assign a new Mode of Operation, named "AODV-RPL" for 879 Point-to-Point(P2P) hop-by-hop routing from the "Mode of Operation" 880 Registry [RFC6550]. 882 +-------------+---------------+---------------+ 883 | Value | Description | Reference | 884 +-------------+---------------+---------------+ 885 | TBD1 (5) | AODV-RPL | This document | 886 +-------------+---------------+---------------+ 888 Figure 6: Mode of Operation 890 9.2. AODV-RPL Options: RREQ, RREP, and Target 892 IANA is asked to assign three new AODV-RPL options "RREQ", "RREP" and 893 "ART", as described in Figure 7 from the "RPL Control Message 894 Options" Registry [RFC6550]. 896 +-------------+------------------------+---------------+ 897 | Value | Meaning | Reference | 898 +-------------+------------------------+---------------+ 899 | TBD2 (0x0A) | RREQ Option | This document | 900 +-------------+------------------------+---------------+ 901 | TBD3 (0x0B) | RREP Option | This document | 902 +-------------+------------------------+---------------+ 903 | TBD4 (0x0C) | ART Option | This document | 904 +-------------+------------------------+---------------+ 906 Figure 7: AODV-RPL Options 908 10. Security Considerations 910 In general, the security considerations for the operation of AODV-RPL 911 are similar to those for the operation of RPL (as described in 912 Section 19 of the RPL specification [RFC6550]). Sections 6.1 and 10 913 of [RFC6550] describe RPL's security framework, which provides data 914 confidentiality, authentication, replay protection, and delay 915 protection services. 917 A router can join a temporary DAG created for a secure AODV-RPL route 918 discovery only if it can support the Security Configuration in use, 919 which also specifies the key in use. It does not matter whether the 920 key is preinstalled or dynamically acquired. The router must have 921 the key in use before it can join the DAG being created for a secure 922 P2P-RPL route discovery. 924 If a rogue router knows the key for the Security Configuration in 925 use, it can join the secure AODV-RPL route discovery and cause 926 various types of damage. Such a rogue router could advertise false 927 information in its DIOs in order to include itself in the discovered 928 route(s). It could generate bogus RREQ-DIO, and RREP-DIO messages 929 carrying bad routes or maliciously modify genuine RREP-DIO messages 930 it receives. A rogue router acting as the OrigNode could launch 931 denial-of-service attacks against the LLN deployment by initiating 932 fake AODV-RPL route discoveries. In this type of scenario, RPL's 933 authenticated mode of operation, where a node can obtain the key to 934 use for a P2P-RPL route discovery only after proper authentication, 935 SHOULD be used. 937 When RREQ-DIO message uses source routing option with 'H' set to 0, 938 some of the security concerns that led to the deprecation of Type 0 939 routing headers [RFC5095] may apply. To avoid the possibility of a 940 RREP-DIO message traveling in a routing loop, if one of its addresses 941 are present as part of the Source Route listed inside the message, 942 the Intermediate Router MUST NOT forward the message. 944 11. Link State Determination 946 This document specifies that links are considered symmetric until 947 additional information is collected. Other link metric information 948 can be acquired before AODV-RPL operation, by executing evaluation 949 procedures; for instance test traffic can be generated between nodes 950 of the deployed network. During AODV-RPL operation, OAM techniques 951 for evaluating link state (see([RFC7548], [RFC7276], [co-ioam]) MAY 952 be used (at regular intervals appropriate for the LLN). The 953 evaluation procedures are out of scope for AODV-RPL. 955 12. References 957 12.1. Normative References 959 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 960 Requirement Levels", BCP 14, RFC 2119, 961 DOI 10.17487/RFC2119, March 1997, 962 . 964 [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- 965 Demand Distance Vector (AODV) Routing", RFC 3561, 966 DOI 10.17487/RFC3561, July 2003, 967 . 969 [RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation 970 of Type 0 Routing Headers in IPv6", RFC 5095, 971 DOI 10.17487/RFC5095, December 2007, 972 . 974 [RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko, 975 "The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206, 976 March 2011, . 978 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 979 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 980 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 981 Low-Power and Lossy Networks", RFC 6550, 982 DOI 10.17487/RFC6550, March 2012, 983 . 985 [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., 986 and D. Barthel, "Routing Metrics Used for Path Calculation 987 in Low-Power and Lossy Networks", RFC 6551, 988 DOI 10.17487/RFC6551, March 2012, 989 . 991 [RFC6998] Goyal, M., Ed., Baccelli, E., Brandt, A., and J. Martocci, 992 "A Mechanism to Measure the Routing Metrics along a Point- 993 to-Point Route in a Low-Power and Lossy Network", 994 RFC 6998, DOI 10.17487/RFC6998, August 2013, 995 . 997 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 998 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 999 May 2017, . 1001 12.2. Informative References 1003 [co-ioam] Ballamajalu, Rashmi., S.V.R., Anand., and Malati. Hegde, 1004 "Co-iOAM: In-situ Telemetry Metadata Transport for 1005 Resource Constrained Networks within IETF Standards 1006 Framework", 2018 10th International Conference on 1007 Communication Systems & Networks (COMSNETS) pp.573-576, 1008 Jan 2018. 1010 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and 1011 J. Martocci, "Reactive Discovery of Point-to-Point Routes 1012 in Low-Power and Lossy Networks", RFC 6997, 1013 DOI 10.17487/RFC6997, August 2013, 1014 . 1016 [RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y. 1017 Weingarten, "An Overview of Operations, Administration, 1018 and Maintenance (OAM) Tools", RFC 7276, 1019 DOI 10.17487/RFC7276, June 2014, 1020 . 1022 [RFC7548] Ersue, M., Ed., Romascanu, D., Schoenwaelder, J., and A. 1023 Sehgal, "Management of Networks with Constrained Devices: 1024 Use Cases", RFC 7548, DOI 10.17487/RFC7548, May 2015, 1025 . 1027 Appendix A. Example: ETX/RSSI Values to select S bit 1029 The combination of Received Signal Strength Indication(downstream) 1030 (RSSI) and Expected Number of Transmissions(upstream)" (ETX) has been 1031 tested to determine whether a link is symmetric or asymmetric at 1032 intermediate nodes. ETX and RSSI values may be used in conjunction 1033 as explained below: 1035 Source---------->NodeA---------->NodeB------->Destination 1037 Figure 8: Communication link from Source to Destination 1039 +-------------------------+----------------------------------------+ 1040 | RSSI at NodeA for NodeB | Expected ETX at NodeA for NodeB->NodeA | 1041 +-------------------------+----------------------------------------+ 1042 | > -60 | 150 | 1043 | -70 to -60 | 192 | 1044 | -80 to -70 | 226 | 1045 | -90 to -80 | 662 | 1046 | -100 to -90 | 993 | 1047 +-------------------------+----------------------------------------+ 1049 Table 1: Selection of S bit based on Expected ETX value 1051 We tested the operations in this specification by making the 1052 following experiment, using the above parameters. In our experiment, 1053 a communication link is considered as symmetric if the ETX value of 1054 NodeA->NodeB and NodeB->NodeA (see Figure 8) are within, say, a 1:3 1055 ratio. This ratio should be understood as determining the link's 1056 symmetric/asymmetric nature. NodeA can typically know the ETX value 1057 in the direction of NodeA -> NodeB but it has no direct way of 1058 knowing the value of ETX from NodeB->NodeA. Using physical testbed 1059 experiments and realistic wireless channel propagation models, one 1060 can determine a relationship between RSSI and ETX representable as an 1061 expression or a mapping table. Such a relationship in turn can be 1062 used to estimate ETX value at nodeA for link NodeB--->NodeA from the 1063 received RSSI from NodeB. Whenever nodeA determines that the link 1064 towards the nodeB is bi-directional asymmetric then the S bit is set 1065 to 0. Later on, the link from NodeA to Destination is asymmetric 1066 with S bit remains set to 0. 1068 Appendix B. Changelog 1070 Note to the RFC Editor: please remove this section before 1071 publication. 1073 B.1. Changes from version 07 to version 08 1075 o Instead of describing the need for routes to "fulfill the 1076 requirements", specify that routes need to "satisfy the Objective 1077 Function". 1079 o Removed all normative dependencies on [RFC6997] 1081 o Rewrote Section 10 to avoid duplication of language in cited 1082 specifications. 1084 o Added Section 11 with text and citations to more fully describe 1085 how implementations determine whether links are symmetric. 1087 o Modified text comparing AODV-RPL to other protocols to emphasize 1088 the need for AODV-RPL instead of the problems with the other 1089 protocols. 1091 o Clarified that AODV-RPL uses some of the base RPL specification 1092 but does not require an instance of RPL to run. 1094 o Improved capitalization, quotation, and spelling variations. 1096 o Specified behavior upon reception of a RREQ-DIO or RREP-DIO 1097 message for an already existing DODAGID (e.g, Section 6.4). 1099 o Fixed numerous language issues in IANA Considerations Section 9. 1101 o For consistency, adjusted several mandates from SHOULD to MUST and 1102 from SHOULD NOT to MUST NOT. 1104 o Numerous editorial improvements and clarificaions. 1106 B.2. Changes from version 06 to version 07 1108 o Added definitions for all fields of the ART option (see 1109 Section 4.3). Modified definition of Prefix Length to prohibit 1110 Prefix Length values greater than 127. 1112 o Modified the language from [RFC6550] Target Option definition so 1113 that the trailing zero bits of the Prefix Length are no longer 1114 described as "reserved". 1116 o Reclassified [RFC3561] and [RFC6998] as Informative. 1118 o Added citation for [RFC8174] to Terminology section. 1120 B.3. Changes from version 05 to version 06 1122 o Added Security Considerations based on the security mechanisms 1123 defined in [RFC6550]. 1125 o Clarified the nature of improvements due to P2P route discovery 1126 versus bidirectional asymmetric route discovery. 1128 o Editorial improvements and corrections. 1130 B.4. Changes from version 04 to version 05 1132 o Add description for sequence number operations. 1134 o Extend the residence duration L in section 4.1. 1136 o Change AODV-RPL Target option to ART option. 1138 B.5. Changes from version 03 to version 04 1140 o Updated RREP option format. Remove the T bit in RREP option. 1142 o Using the same RPLInstanceID for RREQ and RREP, no need to update 1143 [RFC6550]. 1145 o Explanation of Shift field in RREP. 1147 o Multiple target options handling during transmission. 1149 B.6. Changes from version 02 to version 03 1151 o Include the support for source routing. 1153 o Import some features from [RFC6997], e.g., choice between hop-by- 1154 hop and source routing, the L bit which determines the duration of 1155 residence in the DAG, MaxRank, etc. 1157 o Define new target option for AODV-RPL, including the Destination 1158 Sequence Number in it. Move the TargNode address in RREQ option 1159 and the OrigNode address in RREP option into ADOV-RPL Target 1160 Option. 1162 o Support route discovery for multiple targets in one RREQ-DIO. 1164 o New InstanceID pairing mechanism. 1166 Appendix C. Contributors 1168 Abdur Rashid Sangi 1169 Huaiyin Institute of Technology 1170 No.89 North Beijing Road, Qinghe District 1171 Huaian 223001 1172 P.R. China 1173 Email: sangi_bahrian@yahoo.com 1175 Authors' Addresses 1177 Satish Anamalamudi 1178 SRM University-AP 1179 Amaravati Campus 1180 Amaravati, Andhra Pradesh 522 502 1181 India 1183 Email: satishnaidu80@gmail.com 1185 Mingui Zhang 1186 Huawei Technologies 1187 No. 156 Beiqing Rd. Haidian District 1188 Beijing 100095 1189 China 1191 Email: zhangmingui@huawei.com 1193 Charles E. Perkins 1194 Deep Blue Sky Networks 1195 Saratoga 95070 1196 United States 1198 Email: charliep@computer.org 1199 S.V.R Anand 1200 Indian Institute of Science 1201 Bangalore 560012 1202 India 1204 Email: anand@ece.iisc.ernet.in 1206 Bing Liu 1207 Huawei Technologies 1208 No. 156 Beiqing Rd. Haidian District 1209 Beijing 100095 1210 China 1212 Email: remy.liubing@huawei.com