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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) No issues found here. Summary: 0 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 C. Perkins 5 Expires: March 20, 2022 Lupin Lodge 6 S.V.R.Anand 7 Indian Institute of Science 8 B. Liu 9 Huawei Technologies 10 September 16, 2021 12 Supporting Asymmetric Links in Low Power Networks: AODV-RPL 13 draft-ietf-roll-aodv-rpl-11 15 Abstract 17 Route discovery for symmetric and asymmetric Peer-to-Peer (P2P) 18 traffic flows is a desirable feature in Low power and Lossy Networks 19 (LLNs). For that purpose, this document specifies a reactive P2P 20 route discovery mechanism for both hop-by-hop routing and source 21 routing: Ad Hoc On-demand Distance Vector Routing (AODV) based RPL 22 protocol (AODV-RPL). Paired Instances are used to construct 23 directional paths, for cases where there are asymmetric links between 24 source and target nodes. 26 Status of This Memo 28 This Internet-Draft is submitted 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 https://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 March 20, 2022. 43 Copyright Notice 45 Copyright (c) 2021 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 (https://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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 62 3. Overview of AODV-RPL . . . . . . . . . . . . . . . . . . . . 6 63 4. AODV-RPL DIO Options . . . . . . . . . . . . . . . . . . . . 6 64 4.1. AODV-RPL RREQ Option . . . . . . . . . . . . . . . . . . 6 65 4.2. AODV-RPL RREP Option . . . . . . . . . . . . . . . . . . 8 66 4.3. AODV-RPL Target Option . . . . . . . . . . . . . . . . . 10 67 5. Symmetric and Asymmetric Routes . . . . . . . . . . . . . . . 11 68 6. AODV-RPL Operation . . . . . . . . . . . . . . . . . . . . . 13 69 6.1. Route Request Generation . . . . . . . . . . . . . . . . 13 70 6.2. Receiving and Forwarding RREQ messages . . . . . . . . . 14 71 6.2.1. General Processing . . . . . . . . . . . . . . . . . 14 72 6.2.2. Additional Processing for Multiple Targets . . . . . 16 73 6.3. Generating Route Reply (RREP) at TargNode . . . . . . . . 16 74 6.3.1. RREP-DIO for Symmetric route . . . . . . . . . . . . 16 75 6.3.2. RREP-DIO for Asymmetric Route . . . . . . . . . . . . 17 76 6.3.3. RPLInstanceID Pairing . . . . . . . . . . . . . . . . 17 77 6.4. Receiving and Forwarding Route Reply . . . . . . . . . . 18 78 7. Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . . 19 79 8. Operation of Trickle Timer . . . . . . . . . . . . . . . . . 20 80 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 81 9.1. New Mode of Operation: AODV-RPL . . . . . . . . . . . . . 20 82 9.2. AODV-RPL Options: RREQ, RREP, and Target . . . . . . . . 21 83 10. Security Considerations . . . . . . . . . . . . . . . . . . . 21 84 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 85 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 86 12.1. Normative References . . . . . . . . . . . . . . . . . . 22 87 12.2. Informative References . . . . . . . . . . . . . . . . . 23 88 Appendix A. Example: Using ETX/RSSI Values to determine value of 89 S bit . . . . . . . . . . . . . . . . . . . . . . . 24 90 Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . 26 91 B.1. Changes from version 10 to version 11 . . . . . . . . . . 26 92 B.2. Changes from version 09 to version 10 . . . . . . . . . . 27 93 B.3. Changes from version 08 to version 09 . . . . . . . . . . 27 94 B.4. Changes from version 07 to version 08 . . . . . . . . . . 28 95 B.5. Changes from version 06 to version 07 . . . . . . . . . . 29 96 B.6. Changes from version 05 to version 06 . . . . . . . . . . 29 97 B.7. Changes from version 04 to version 05 . . . . . . . . . . 29 98 B.8. Changes from version 03 to version 04 . . . . . . . . . . 29 99 B.9. Changes from version 02 to version 03 . . . . . . . . . . 29 100 Appendix C. Contributors . . . . . . . . . . . . . . . . . . . . 30 101 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30 103 1. Introduction 105 Routing Protocol for Low-Power and Lossy Networks (RPL) [RFC6550] is 106 an IPv6 distance vector routing protocol designed to support multiple 107 traffic flows through a root-based Destination-Oriented Directed 108 Acyclic Graph (DODAG). Typically, a router does not have routing 109 information for most other routers. Consequently, for traffic 110 between routers within the DODAG (i.e., Peer-to-Peer (P2P) traffic) 111 data packets either have to traverse the root in non-storing mode, or 112 traverse a common ancestor in storing mode. Such P2P traffic is 113 thereby likely to traverse longer routes and may suffer severe 114 congestion near the root (for more information see [RFC6997], 115 [RFC6998]). The network environment that is considered in this 116 document is assumed to be the same as described in Section 1 of 117 [RFC6550]. 119 The route discovery process in AODV-RPL is modeled on the analogous 120 procedure specified in AODV [RFC3561]. The on-demand nature of AODV 121 route discovery is natural for the needs of peer-to-peer routing in 122 RPL-based LLNs. AODV terminology has been adapted for use with AODV- 123 RPL messages, namely RREQ for Route Request, and RREP for Route 124 Reply. AODV-RPL currently omits some features compared to AODV -- in 125 particular, flagging Route Errors, "blacklisting" unidirectional 126 links ([RFC3561]), multihoming, and handling unnumbered interfaces. 128 AODV-RPL reuses and extends the core RPL functionality to support 129 routes with bidirectional asymmetric links. It retains RPL's DODAG 130 formation, RPL Instance and the associated Objective Function 131 (defined in [RFC6551]), trickle timers, and support for storing and 132 non-storing modes. AODV-RPL adds basic messages RREQ and RREP as 133 part of RPL DODAG Information Object (DIO) control message, which go 134 in separate (paired) RPL instances. AODV-RPL does not utilize the 135 Destination Advertisement Object (DAO) control message of RPL. AODV- 136 RPL specifies a new Mode of Operation (MOP) running in a separate 137 instance dedicated to discover P2P routes, which may differ from 138 routes discoverable by native RPL. AODV-RPL can be operated whether 139 or not native RPL is running otherwise. 141 2. Terminology 143 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 144 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 145 "OPTIONAL" in this document are to be interpreted as described in BCP 146 14 [RFC2119] [RFC8174] when, and only when, they appear in all 147 capitals, as shown here. 149 AODV-RPL reuses names for messages and data structures, including 150 Rank, DODAG and DODAGID, as defined in RPL [RFC6550]. 152 AODV 153 Ad Hoc On-demand Distance Vector Routing[RFC3561]. 155 Asymmetric Route 156 The route from the OrigNode to the TargNode can traverse different 157 nodes than the route from the TargNode to the OrigNode. An 158 asymmetric route may result from the asymmetry of links, such that 159 only one direction of the series of links satisfies the Objective 160 Function during route discovery. 162 Bi-directional Asymmetric Link 163 A link that can be used in both directions but with different link 164 characteristics. 166 DIO 167 DODAG Information Object 169 DODAG RREQ-Instance (or simply RREQ-Instance) 170 RPL Instance built using the DIO with RREQ option; used for 171 control message transmission from OrigNode to TargNode, thus 172 enabling data transmission from TargNode to OrigNode. 174 DODAG RREP-Instance (or simply RREP-Instance) 175 RPL Instance built using the DIO with RREP option; used for 176 control message transmission from TargNode to OrigNode thus 177 enabling data transmission from OrigNode to TargNode. 179 Downward Direction 180 The direction from the OrigNode to the TargNode. 182 Downward Route 183 A route in the downward direction. 185 hop-by-hop routing 186 Routing when each node stores routing information about the next 187 hop. 189 on-demand routing 190 Routing in which a route is established only when needed. 192 OrigNode 193 The IPv6 router (Originating Node) initiating the AODV-RPL route 194 discovery to obtain a route to TargNode. 196 Paired DODAGs 197 Two DODAGs for a single route discovery process between OrigNode 198 and TargNode. 200 P2P 201 Peer-to-Peer -- in other words, not constrained a priori to 202 traverse a common ancestor. 204 reactive routing 205 Same as "on-demand" routing. 207 RREQ-DIO message 208 An AODV-RPL MOP DIO message containing the RREQ option. The 209 RPLInstanceID in RREQ-DIO is assigned locally by the OrigNode. 210 The RREQ-DIO message has a secure variant as noted in [RFC6550]. 212 RREP-DIO message 213 An AODV-RPL MOP DIO message containing the RREP option. The 214 RPLInstanceID in RREP-DIO MUST be paired to the one in the 215 associated RREQ-DIO message as described in Section 6.3.2. The 216 RREP-DIO message has a secure variant as noted in [RFC6550]. 218 Source routing 219 A mechanism by which the source supplies the complete route 220 towards the target node along with each data packet [RFC6550]. 222 Symmetric route 223 The upstream and downstream routes traverse the same routers and 224 over the same links. 226 TargNode 227 The IPv6 router (Target Node) for which OrigNode requires a route 228 and initiates Route Discovery within the LLN network. 230 Upward Direction 231 The direction from the TargNode to the OrigNode. 233 Upward Route 234 A route in the upward direction. 236 ART option 237 AODV-RPL Target option: a target option defined in this document. 239 3. Overview of AODV-RPL 241 With AODV-RPL, routes from OrigNode to TargNode within the LLN 242 network are established "on-demand". In other words, the route 243 discovery mechanism in AODV-RPL is invoked reactively when OrigNode 244 has data for delivery to the TargNode but existing routes do not 245 satisfy the application's requirements. AODV-RPL is thus functional 246 without requiring the use of RPL or any other routing protocol. 248 The routes discovered by AODV-RPL are not constrained to traverse a 249 common ancestor. AODV-RPL can enable asymmetric communication paths 250 in networks with bidirectional asymmetric links. For this purpose, 251 AODV-RPL enables discovery of two routes: namely, one from OrigNode 252 to TargNode, and another from TargNode to OrigNode. When possible, 253 AODV-RPL also enables symmetric route discovery along Paired DODAGs 254 (see Section 5). 256 In AODV-RPL, routes are discovered by first forming a temporary DAG 257 rooted at the OrigNode. Paired DODAGs (Instances) are constructed 258 according to the AODV-RPL Mode of Operation (MOP) during route 259 formation between the OrigNode and TargNode. The RREQ-Instance is 260 formed by route control messages from OrigNode to TargNode whereas 261 the RREP-Instance is formed by route control messages from TargNode 262 to OrigNode. Intermediate routers join the Paired DODAGs based on 263 the Rank [RFC6550] as calculated from the DIO message. Henceforth in 264 this document, the RREQ-DIO message means the AODV-RPL mode DIO 265 message from OrigNode to TargNode, containing the RREQ option (see 266 Section 4.1). Similarly, the RREP-DIO message means the AODV-RPL 267 mode DIO message from TargNode to OrigNode, containing the RREP 268 option (see Section 4.2). The route discovered in the RREQ-Instance 269 is used for transmitting data from TargNode to OrigNode, and the 270 route discovered in RREP-Instance is used for transmitting data from 271 OrigNode to TargNode. 273 4. AODV-RPL DIO Options 275 4.1. AODV-RPL RREQ Option 277 OrigNode selects one of its IPv6 addresses and sets it in the DODAGID 278 field of the RREQ-DIO message. Exactly one RREQ option MUST be 279 present in a RREQ-DIO message, otherwise the message MUST be dropped. 281 0 1 2 3 282 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 1 283 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 284 | Option Type | Option Length |S|H|X| Compr | L | MaxRank | 285 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 286 | Orig SeqNo | | 287 +-+-+-+-+-+-+-+-+ | 288 | | 289 | | 290 | Address Vector (Optional, Variable Length) | 291 | | 292 | | 293 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 295 Figure 1: Format for AODV-RPL RREQ Option 297 OrigNode supplies the following information in the RREQ option: 299 Option Type 300 TBD2 302 Option Length 303 The length of the option in octets, excluding the Type and Length 304 fields. Variable due to the presence of the address vector and 305 the number of octets elided according to the Compr value. 307 S 308 Symmetric bit indicating a symmetric route from the OrigNode to 309 the router transmitting this RREQ-DIO. See Section 5. 311 H 312 Set to one for a hop-by-hop route. Set to zero for a source 313 route. This flag controls both the downstream route and upstream 314 route. 316 X 317 Reserved. MUST be set to zero. 319 Compr 320 4-bit unsigned integer. Number of prefix octets that are elided 321 from the Address Vector. The octets elided are shared with the 322 IPv6 address in the DODAGID. This field is only used in source 323 routing mode (H=0). In hop-by-hop mode (H=1), this field MUST be 324 set to zero and ignored upon reception. 326 L 327 2-bit unsigned integer determining the length of time that a node 328 is able to belong to the RREQ-Instance (a temporary DAG including 329 the OrigNode and the TargNode). Once the time is reached, a node 330 MUST leave the RREQ-Instance and stop sending or receiving any 331 more DIOs for the RREQ-Instance. This naturally depends on the 332 node's ability to keep track of the time. 334 * 0x00: No time limit imposed. 335 * 0x01: 16 seconds 336 * 0x02: 64 seconds 337 * 0x03: 256 seconds 339 L is independent from the route lifetime, which is defined in the 340 DODAG configuration option. 342 MaxRank 343 This field indicates the upper limit on the integer portion of the 344 Rank (calculated using the DAGRank() macro defined in [RFC6550]). 345 A value of 0 in this field indicates the limit is infinity. 347 Orig SeqNo 348 Sequence Number of OrigNode. See Section 6.1. 350 Address Vector 351 A vector of IPv6 addresses representing the route that the RREQ- 352 DIO has passed. It is only present when the H bit is set to 0. 353 The prefix of each address is elided according to the Compr field. 355 TargNode can join the RREQ instance at a Rank whose integer portion 356 is less than or equal to the MaxRank. Other nodes MUST NOT join a 357 RREQ instance if its own Rank would be equal to or higher than 358 MaxRank. A router MUST discard a received RREQ if the integer part 359 of the advertised Rank equals or exceeds the MaxRank limit. 361 4.2. AODV-RPL RREP Option 363 TargNode sets one of its IPv6 addresses in the DODAGID field of the 364 RREP-DIO message. Exactly one RREP option MUST be present in a RREP- 365 DIO message, otherwise the message MUST be dropped. TargNode 366 supplies the following information in the RREP option: 368 0 1 2 3 369 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 1 370 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 371 | Option Type | Option Length |G|H|X| Compr | L | MaxRank | 372 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 373 | Shift |X X| | 374 +-+-+-+-+-+-+-+-+ | 375 | | 376 | | 377 | Address Vector (Optional, Variable Length) | 378 . . 379 . . 380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 382 Figure 2: Format for AODV-RPL RREP option 384 Option Type 385 TBD3 387 Option Length 388 The length of the option in octets, excluding the Type and Length 389 fields. Variable due to the presence of the address vector and 390 the number of octets elided according to the Compr value. 392 G 393 Gratuitous route (see Section 7). 395 H 396 The H bit in the RREP option MUST be set to be the same as the H 397 bit in RREQ option. It requests either source routing (H=0) or 398 hop-by-hop (H=1) for the downstream route. 400 X 401 Reserved. MUST be set to zero. 403 Compr 404 4-bit unsigned integer. Same definition as in RREQ option. 406 L 407 2-bit unsigned integer defined as in RREQ option. 409 MaxRank 410 Similarly to MaxRank in the RREQ message, this field indicates the 411 upper limit on the integer portion of the Rank. A value of 0 in 412 this field indicates the limit is infinity. 414 Shift 415 6-bit unsigned integer. This field is used to recover the 416 original RPLInstanceID (see Section 6.3.3); 0 indicates that the 417 original RPLInstanceID is used. 419 X X 420 MUST be initialized to zero and ignored upon reception. 422 Address Vector 423 Only present when the H bit is set to 0. For an asymmetric route, 424 the Address Vector represents the IPv6 addresses of the path 425 through the network the RREP-DIO has passed. For a symmetric 426 route, it is the Address Vector when the RREQ-DIO arrives at the 427 TargNode, unchanged during the transmission to the OrigNode. 429 4.3. AODV-RPL Target Option 431 The AODV-RPL Target (ART) Option is based on the Target Option in 432 core RPL [RFC6550]. The Flags field is replaced by the Destination 433 Sequence Number of the TargNode and the Prefix Length field is 434 reduced to 7 bits so that the value is limited to be no greater than 435 127. 437 A RREQ-DIO message MUST carry at least one ART Option. A RREP-DIO 438 message MUST carry exactly one ART Option. Otherwise, the message 439 MUST be dropped. 441 OrigNode can include multiple TargNode addresses via multiple AODV- 442 RPL Target Options in the RREQ-DIO, for routes that share the same 443 requirement on metrics. This reduces the cost to building only one 444 DODAG. 446 0 1 2 3 447 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 1 448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 449 | Option Type | Option Length | Dest SeqNo |X|Prefix Length| 450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 451 | | 452 + | 453 | Target Prefix / Address (Variable Length) | 454 . . 455 . . 456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 458 Figure 3: ART Option format for AODV-RPL MOP 460 Option Type 461 TBD4 463 Option Length 464 Length of the option in octets excluding the Type and Length 465 fields. 467 Dest SeqNo 469 In RREQ-DIO, if nonzero, it is the Sequence Number for the last 470 route that OrigNode stored to the TargNode for which a route is 471 desired. In RREP-DIO, it is the destination sequence number 472 associated to the route. Zero is used if there is no known 473 information about the sequence number of TargNode, and not used 474 otherwise. 476 X 477 A one-bit reserved field. This field MUST be initialized to zero 478 by the sender and MUST be ignored by the receiver. 480 Prefix Length 481 7-bit unsigned integer. Number of valid leading bits in the IPv6 482 Prefix. If Prefix Length is 0, then the value in the Target 483 Prefix / Address field represents an IPv6 address, not a prefix. 485 Target Prefix / Address 486 (variable-length field) An IPv6 destination address or prefix. 487 The Prefix Length field contains the number of valid leading bits 488 in the prefix. The Target Prefix / Address field contains the 489 least number of octets that can represent all of the bits of the 490 Prefix, in other words Ceil(Prefix Length/8) octets. The initial 491 bits in the Target Prefix / Address field preceding the prefix 492 length (if any) MUST be set to zero on transmission and MUST be 493 ignored on receipt. If Prefix Length is zero, the Address field 494 is 128 bits for IPv6 addresses. 496 5. Symmetric and Asymmetric Routes 498 Links are considered symmetric until indication to the contrary is 499 received. In Figure 4 and Figure 5, BR is the Border Router, O is 500 the OrigNode, each R is an intermediate router, and T is the 501 TargNode. If the RREQ-DIO arrives over an interface that is known to 502 be symmetric, and the S bit is set to 1, then it remains as 1, as 503 illustrated in Figure 4. If an intermediate router sends out RREQ- 504 DIO with the S bit set to 1, then each link en route from the 505 OrigNode O to this router has met the requirements of route 506 discovery, and the route can be used symmetrically. 508 BR 509 /----+----\ 510 / | \ 511 / | \ 512 R R R 513 _/ \ | / \ 514 / \ | / \ 515 / \ | / \ 516 R -------- R --- R ----- R -------- R 517 / \ <--S=1--> / \ <--S=1--> / \ 518 <--S=1--> \ / \ / <--S=1--> 519 / \ / \ / \ 520 O ---------- R ------ R------ R ----- R ----------- T 521 / \ / \ / \ / \ 522 / \ / \ / \ / \ 523 / \ / \ / \ / \ 524 R ----- R ----------- R ----- R ----- R ----- R ---- R----- R 526 >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> 527 <---- RREP-Instance (Control: T-->O; Data: O-->T) -------< 529 Figure 4: AODV-RPL with Symmetric Paired Instances 531 Upon receiving a RREQ-DIO with the S bit set to 1, a node determines 532 whether this link can be used symmetrically, i.e., both directions 533 meet the requirements of data transmission. If the RREQ-DIO arrives 534 over an interface that is not known to be symmetric, or is known to 535 be asymmetric, the S bit is set to 0. If the S bit arrives already 536 set to be '0', it is set to be '0' when the RREQ-DIO is propagated 537 (Figure 5). For an asymmetric route, there is at least one hop which 538 doesn't satisfy the Objective Function. Based on the S bit received 539 in RREQ-DIO, TargNode T determines whether or not the route is 540 symmetric before transmitting the RREP-DIO message upstream towards 541 the OrigNode O. 543 The criteria used to determine whether or not each link is symmetric 544 is beyond the scope of the document. For instance, intermediate 545 routers can use local information (e.g., bit rate, bandwidth, number 546 of cells used in 6tisch [RFC9030]), a priori knowledge (e.g., link 547 quality according to previous communication) or use averaging 548 techniques as appropriate to the application. Other link metric 549 information can be acquired before AODV-RPL operation, by executing 550 evaluation procedures; for instance test traffic can be generated 551 between nodes of the deployed network. During AODV-RPL operation, 552 OAM techniques for evaluating link state (see [RFC7548], [RFC7276], 553 [co-ioam]) MAY be used (at regular intervals appropriate for the 554 LLN). The evaluation procedures are out of scope for AODV-RPL. 556 Appendix A describes an example method using the upstream Expected 557 Number of Transmissions (ETX) and downstream Received Signal Strength 558 Indicator (RSSI) to estimate whether the link is symmetric in terms 559 of link quality using an averaging technique. 561 BR 562 /----+----\ 563 / | \ 564 / | \ 565 R R R 566 / \ | / \ 567 / \ | / \ 568 / \ | / \ 569 R --------- R --- R ---- R --------- R 570 / \ --S=1--> / \ --S=0--> / \ 571 --S=1--> \ / \ / --S=0--> 572 / \ / \ / \ 573 O ---------- R ------ R------ R ----- R ----------- T 574 / \ / \ / \ / \ 575 / <--S=0-- / \ / \ / <--S=0-- 576 / \ / \ / \ / \ 577 R ----- R ----------- R ----- R ----- R ----- R ---- R----- R 578 <--S=0-- <--S=0-- <--S=0-- <--S=0-- <--S=0-- 580 >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> 581 <---- RREP-Instance (Control: T-->O; Data: O-->T) -------< 583 Figure 5: AODV-RPL with Asymmetric Paired Instances 585 As illustrated in Figure 5, an intermediate router determines the S 586 bit value that the RREQ-DIO should carry using link asymmetry 587 detection methods as discussed earlier in this section. In many 588 cases the intermediate router has already made the link asymmetry 589 decision by the time RREQ-DIO arrives. 591 6. AODV-RPL Operation 593 6.1. Route Request Generation 595 The route discovery process is initiated when an application at the 596 OrigNode has data to be transmitted to the TargNode, but does not 597 have a route that satisfies the Objective Function for the target of 598 the data transmission. In this case, the OrigNode builds a local 599 RPLInstance and a DODAG rooted at itself. Then it transmits a DIO 600 message containing exactly one RREQ option (see Section 4.1) via 601 link-local multicast. The DIO MUST contain at least one ART Option 602 (see Section 4.3). The required ART Option indicates the TargNode. 603 The S bit in RREQ-DIO sent out by the OrigNode is set to 1. 605 Each node maintains a sequence number; the operation is specified in 606 section 7.2 of [RFC6550]. When the OrigNode initiates a route 607 discovery process, it MUST increase its own sequence number to avoid 608 conflicts with previously established routes. The sequence number is 609 carried in the Orig SeqNo field of the RREQ option. 611 The address in the ART Option can be a unicast IPv6 address or a 612 prefix. The OrigNode can initiate the route discovery process for 613 multiple targets simultaneously by including multiple ART Options. 614 Within a RREQ-DIO the requirements for the routes to different 615 TargNodes MUST be the same. 617 OrigNode can maintain different RPLInstances to discover routes with 618 different requirements to the same targets. Using the RPLInstanceID 619 pairing mechanism (see Section 6.3.3), route replies (RREP-DIOs) for 620 different RPLInstances can be generated. 622 The transmission of RREQ-DIO obeys the Trickle timer [RFC6206]. If 623 the length of time specified by the L field has elapsed, the OrigNode 624 MUST leave the DODAG and stop sending RREQ-DIOs in the related 625 RPLInstance. 627 6.2. Receiving and Forwarding RREQ messages 629 6.2.1. General Processing 631 Upon receiving a RREQ-DIO, a router goes through the steps below. If 632 the router has not joined the RREQ-Instance, then the maximum useful 633 rank (MaxUseRank) is MaxRank. Otherwise, MaxUseRank is set to be the 634 Rank value that was stored when the router processed the best 635 previous RREQ for the DODAG with the given RREQ-Instance. 637 Step 1: 639 The router MUST first determine whether to propagate the RREQ-DIO. 640 It does this by determining whether or not the downstream 641 direction of the incoming link satisfies the Objective Function 642 (OF). If not the RREQ-DIO MUST be dropped, and the following 643 steps are not processed. Otherwise, the router MUST join the 644 RREQ-Instance and prepare to propagate the RREQ-DIO. The upstream 645 neighbor router that transmitted the received RREQ-DIO is selected 646 as the preferred parent. 648 Step 2: 650 If the H bit is set to 1, then the router (TargNode or 651 intermediate) MUST build an upward route entry towards OrigNode 652 which includes at least the following items: Source Address, 653 RPLInstanceID, Destination Address, Next Hop, Lifetime, and 654 Sequence Number. The Destination Address and the RPLInstanceID 655 respectively can be learned from the DODAGID and the RPLInstanceID 656 of the RREQ-DIO, and the Source Address is the address used by the 657 local router to send data to the Next Hop, i.e., the preferred 658 parent. The lifetime is set according to DODAG configuration (not 659 the L field) and can be extended when the route is actually used. 660 The sequence number represents the freshness of the route entry, 661 and it is copied from the Orig SeqNo field of the RREQ option. A 662 route entry with the same source and destination address, same 663 RPLInstanceID, but stale sequence number, MUST be deleted. 665 Step 3: 667 If the S bit of the incoming RREQ-DIO is 0, then the route cannot 668 be symmetric, and the S bit of the RREQ-DIO to be transmitted is 669 set to 0. Otherwise, the router MUST determine whether the 670 downward (i.e., towards the TargNode) direction of the incoming 671 link satisfies the OF. If so, the S bit of the RREQ-DIO to be 672 transmitted is set to 1. Otherwise the S bit of the RREQ-DIO to 673 be transmitted is set to 0. 675 When a router joins the RREQ-Instance, it also associates within 676 its data structure for the RREQ-Instance the information about 677 whether or not the RREQ-DIO to be transmitted has the S-bit set to 678 1. This information associated to RREQ-Instance is known as the 679 S-bit of the RREQ-Instance. It will be used later during the 680 RREP-DIO message processing Section 6.3.2 for RPLInstance pairing 681 as described in Section 6.4. 683 Step 4: 685 The router checks whether one of its addresses is included in one 686 of the ART Options. If so, this router is one of the TargNodes. 687 Otherwise, it is an intermediate router. 689 If the router is an intermediate router, then it transmits the 690 RREQ-DIO via link-local multicast; if the H bit is set to 0, the 691 intermediate router MUST include the address of the interface 692 receiving the RREQ-DIO into the address vector. Otherwise, the 693 router is TargNode; if it was not already associated with the 694 RREQ-Instance, it prepares and transmits a RREP-DIO (Section 6.3). 695 If, on the other hand, TargNode was already associated with the 696 RREQ-Instance, it takes no further action and does not send an 697 RREP-DIO. 699 6.2.2. Additional Processing for Multiple Targets 701 If the OrigNode tries to reach multiple TargNodes in a single RREQ- 702 Instance, one of the TargNodes can be an intermediate router to the 703 others, therefore it MUST continue sending RREQ-DIO to reach other 704 targets. In this case, before transmitting the RREQ-DIO via link- 705 local multicast, a TargNode MUST delete the Target Option 706 encapsulating its own address, so that downstream routers with higher 707 Rank values do not try to create a route to this TargNode. 709 An intermediate router could receive several RREQ-DIOs from routers 710 with lower Rank values in the same RREQ-Instance with different lists 711 of Target Options. When transmitting the RREQ-DIO, the intersection 712 of all received lists MUST be included. For example, suppose two 713 RREQ-DIOs are received with the same RPLInstance and OrigNode. 714 Suppose further that the first RREQ has (T1, T2) as the targets, and 715 the second one has (T2, T4) as targets. Then only T2 needs to be 716 included in the generated RREQ-DIO. If the intersection is empty, it 717 means that all the targets have been reached, and the router MUST NOT 718 transmit any RREQ-DIO. For the purposes of determining the 719 intersection with previous incoming RREQ-DIOs, the intermediate 720 router maintains a record of the targets that have been requested for 721 a given RREQ-Instance. Any incoming RREQ-DIO message having multiple 722 ART Options coming from a router with higher Rank than the Rank of 723 the stored targets is ignored. 725 6.3. Generating Route Reply (RREP) at TargNode 727 When H=1 in the incoming RREQ, the TargNode MUST NOT generate a RREP 728 if one of its addresses is present in the Address Vector. If the 729 implementation selects the symmetric route, and the L field is not 0, 730 the TargNode MAY delay transmitting the RREP-DIO for duration 731 RREP_WAIT_TIME to await a route with a lower Rank. The value of 732 RREP_WAIT_TIME is set by default to 1/4 of the duration determined by 733 the L field. For L == 0, RREP_WAIT_TIME is set by default to 0. 734 Depending upon the application, RREP_WAIT_TIME may be set to other 735 values. Smaller values enable quicker formation for the P2P route. 736 Larger values enable formation of P2P routes with better Rank values. 738 6.3.1. RREP-DIO for Symmetric route 740 If a RREQ-DIO arrives at TargNode with the S bit set to 1, there is a 741 symmetric route both of whose directions satisfy the Objective 742 Function. Other RREQ-DIOs might later provide better upward routes. 743 The method of selection between a qualified symmetric route and an 744 asymmetric route that might have better performance is 745 implementation-specific and out of scope. 747 For a symmetric route, the RREP-DIO message is unicast to the next 748 hop according to the accumulated address vector (H=0) or the route 749 entry (H=1). Thus the DODAG in RREP-Instance does not need to be 750 built. The RPLInstanceID in the RREP-Instance is paired as defined 751 in Section 6.3.3. In case the H bit is set to 0, the address vector 752 received in the RREQ-DIO MUST be included in the RREP-DIO. TargNode 753 increments its current sequence number and uses the incremented 754 result in the Dest SeqNo in the ART option of the RREQ-DIO. The 755 address of the OrigNode MUST be encapsulated in the ART Option and 756 included in this RREP-DIO message. 758 6.3.2. RREP-DIO for Asymmetric Route 760 When a RREQ-DIO arrives at a TargNode with the S bit set to 0, the 761 TargNode MUST build a DODAG in the RREP-Instance corresponding to the 762 RREQ-DIO, rooted at itself in order to discover the downstream route 763 from the OrigNode to the TargNode. The RREP-DIO message MUST be 764 transmitted via link-local multicast until the OrigNode is reached or 765 MaxRank is exceeded. 767 The settings of the fields in RREP option and ART option are the same 768 as for the symmetric route, except for the value of the S bit 769 associated with the RREP-instance. 771 6.3.3. RPLInstanceID Pairing 773 Since the RPLInstanceID is assigned locally (i.e., there is no 774 coordination between routers in the assignment of RPLInstanceID), the 775 tuple (OrigNode, TargNode, RPLInstanceID) is needed to uniquely 776 identify a discovered route. It is possible that multiple route 777 discoveries with dissimilar Objective Functions are initiated 778 simultaneously. Thus between the same pair of OrigNode and TargNode, 779 there can be multiple AODV-RPL route discovery instances. To avoid 780 any mismatch, the RREQ-Instance and the RREP-Instance in the same 781 route discovery MUST be paired using the RPLInstanceID. 783 When preparing the RREP-DIO, a TargNode could find the RPLInstanceID 784 candidate for the RREP-Instance is already occupied by another RPL 785 Instance from an earlier route discovery operation which is still 786 active. This unlikely case might happen if two distinct OrigNodes 787 need routes to the same TargNode, and they happen to use the same 788 RPLInstanceID for RREQ-Instance. In such cases, the original 789 RPLInstanceID of an already active RREP-Instance MUST NOT be used 790 again for assigning RPLInstanceID for the later RREP-Instance. 791 Reusing the same RPLInstanceID for two distinct DODAGs originated 792 with the same DODAGID (TargNode address) would prevent intermediate 793 routers to distinguish between these DODAGs (and their associated 794 Objective Functions). Instead, the RPLInstanceID MUST be replaced by 795 another value so that the two RREP-instances can be distinguished. 796 In RREP-DIO option, the Shift field of the RREP-DIO message(Figure 2) 797 indicates the shift to be applied to original RPLInstanceID to obtain 798 the replacement RPLInstanceID. When the new RPLInstanceID after 799 shifting exceeds 255, it rolls over starting at 0. For example, if 800 the original RPLInstanceID is 252, and shifted by 6, the new 801 RPLInstanceID will be 2. Related operations can be found in 802 Section 6.4. RPLInstanceID collisions do not occur across RREQ-DIOs; 803 the DODAGID equals the OrigNode address and is sufficient to 804 disambiguate between DODAGs. 806 6.4. Receiving and Forwarding Route Reply 808 Upon receiving a RREP-DIO, a router performs the following steps: 810 Step 1: 812 If the Objective Function is not satisfied, the router MUST NOT 813 join the DODAG; the router MUST discard the RREQ-DIO, and does not 814 execute the remaining steps in this section. An Intermediate 815 Router MUST NOT forward a RREP if one of its addresses is present 816 in the Address Vector, and does not execute the remaining steps in 817 this section. 819 If the S bit of the associated RREQ-Instance is set to 1, the 820 router MUST proceed to step 2. 822 If the S-bit of the RREQ-Instance is set to 0, the router MUST 823 determine whether the downward direction of the link (towards the 824 TargNode) over which the RREP-DIO is received satisfies the 825 Objective Function, and the router's Rank would not exceed the 826 MaxRank limit. If so, the router joins the DODAG of the RREP- 827 Instance. The router that transmitted the received RREP-DIO is 828 selected as the preferred parent. Afterwards, other RREP-DIO 829 messages can be received. 831 Step 2: 833 The router next checks if one of its addresses is included in the 834 ART Option. If so, this router is the OrigNode of the route 835 discovery. Otherwise, it is an intermediate router. 837 Step 3: 839 If the H bit is set to 1, then the router (OrigNode or 840 intermediate) MUST build a downward route entry towards TargNode 841 which includes at least the following items: OrigNode Address, 842 RPLInstanceID, TargNode Address as destination, Next Hop, Lifetime 843 and Sequence Number. For a symmetric route, the Next Hop in the 844 route entry is the router from which the RREP-DIO is received. 845 For an asymmetric route, the Next Hop is the preferred parent in 846 the DODAG of RREQ-Instance. The RPLInstanceID in the route entry 847 MUST be the original RPLInstanceID (after subtracting the Shift 848 field value). The source address is learned from the ART Option, 849 and the destination address is learned from the DODAGID. The 850 lifetime is set according to DODAG configuration (i.e., not the L 851 field) and can be extended when the route is actually used. The 852 sequence number represents the freshness of the route entry, and 853 is copied from the Dest SeqNo field of the ART option of the RREP- 854 DIO. A route entry with same source and destination address, same 855 RPLInstanceID, but stale sequence number (i.e., incoming sequence 856 number is less than the currently stored sequence number of the 857 route entry), MUST be deleted. 859 Step 4: 861 If the receiver is the OrigNode, it can start transmitting the 862 application data to TargNode along the path as provided in RREP- 863 Instance, and processing for the RREP-DIO is complete. Otherwise, 864 in case of an asymmetric route, the intermediate router MUST 865 include the address of the interface receiving the RREP-DIO into 866 the address vector, and then transmit the RREP-DIO via link-local 867 multicast. In case of a symmetric route, the RREP-DIO message is 868 unicast to the Next Hop according to the address vector in the 869 RREP-DIO (H=0) or the local route entry (H=1). The RPLInstanceID 870 in the transmitted RREP-DIO is the same as the value in the 871 received RREP-DIO. The local knowledge for the TargNode's 872 sequence number SHOULD be updated. 874 Upon receiving a RREP-DIO, a router which already belongs to the 875 RREP-Instance SHOULD drop the RREP-DIO. 877 7. Gratuitous RREP 879 In some cases, an Intermediate router that receives a RREQ-DIO 880 message MAY transmit a "Gratuitous" RREP-DIO message back to OrigNode 881 instead of continuing to multicast the RREQ-DIO towards TargNode. 882 The intermediate router effectively builds the RREP-Instance on 883 behalf of the actual TargNode. The G bit of the RREP option is 884 provided to distinguish the Gratuitous RREP-DIO (G=1) sent by the 885 Intermediate node from the RREP-DIO sent by TargNode (G=0). 887 The gratuitous RREP-DIO can be sent out when an intermediate router 888 receives a RREQ-DIO for a TargNode, and the router has a more recent 889 (larger destination sequence number) pair of downward and upward 890 routes to the TargNode which also satisfy the Objective Function. 892 In case of source routing, the intermediate router MUST unicast the 893 received RREQ-DIO to TargNode including the address vector between 894 the OrigNode and the router. Thus the TargNode can have a complete 895 upward route address vector from itself to the OrigNode. Then the 896 router MUST transmit the gratuitous RREP-DIO including the address 897 vector from the router itself to the TargNode. 899 In case of hop-by-hop routing, the intermediate router MUST unicast 900 the received RREQ-DIO to the Next Hop on the route. The Next Hop 901 router along the route MUST build new route entries with the related 902 RPLInstanceID and DODAGID in the downward direction. The above 903 process will happen recursively until the RREQ-DIO arrives at the 904 TargNode. Then the TargNode MUST unicast recursively the RREP-DIO 905 hop-by-hop to the intermediate router, and the routers along the 906 route SHOULD build new route entries in the upward direction. Upon 907 receiving the unicast RREP-DIO, the intermediate router sends the 908 gratuitous RREP-DIO to the OrigNode as defined in Section 6.3. 910 8. Operation of Trickle Timer 912 The trickle timer operation to control RREQ-Instance/RREP-Instance 913 multicast uses [RFC6206] to control RREQ-DIO and RREP-DIO 914 transmissions. The Trickle control of these DIO transmissions follow 915 the procedures described in the Section 8.3 of [RFC6550] entitled 916 "DIO Transmission". 918 9. IANA Considerations 920 Note to RFC editor: 922 The sentences "The parenthesized number 5 is only a suggestion." and 923 "The parenthesized numbers are only suggestions." are to be removed 924 prior publication. 926 A Subregistry in this section refers to a named sub-registry of the 927 "Routing Protocol for Low Power and Lossy Networks (RPL)" registry. 929 9.1. New Mode of Operation: AODV-RPL 931 IANA is asked to assign a new Mode of Operation, named "AODV-RPL" for 932 peer-to-peer hop-by-hop routing from the "Mode of Operation" 933 Subregistry. The parenthesized number 5 is only a suggestion. 935 +-------------+---------------+---------------+ 936 | Value | Description | Reference | 937 +-------------+---------------+---------------+ 938 | TBD1 (5) | AODV-RPL | This document | 939 +-------------+---------------+---------------+ 941 Figure 6: Mode of Operation 943 9.2. AODV-RPL Options: RREQ, RREP, and Target 945 IANA is asked to assign three new AODV-RPL options "RREQ", "RREP" and 946 "ART", as described in Figure 7 from the "RPL Control Message 947 Options" Subregistry. The parenthesized numbers are only 948 suggestions. 950 +-------------+------------------------+---------------+ 951 | Value | Meaning | Reference | 952 +-------------+------------------------+---------------+ 953 | TBD2 (0x0B) | RREQ Option | This document | 954 +-------------+------------------------+---------------+ 955 | TBD3 (0x0C) | RREP Option | This document | 956 +-------------+------------------------+---------------+ 957 | TBD4 (0x0D) | ART Option | This document | 958 +-------------+------------------------+---------------+ 960 Figure 7: AODV-RPL Options 962 10. Security Considerations 964 The security considerations for the operation of AODV-RPL are similar 965 to those for the operation of RPL (as described in Section 19 of the 966 RPL specification [RFC6550]). Sections 6.1 and 10 of [RFC6550] 967 describe RPL's optional security framework, which AODV-RPL relies on 968 to provide data confidentiality, authentication, replay protection, 969 and delay protection services. Additional analysis for the security 970 threats to RPL can be found in [RFC7416]. 972 A router can join a temporary DAG created for a secure AODV-RPL route 973 discovery only if it can support the security configuration in use 974 (see Section 6.1 of [RFC6550]), which also specifies the key in use. 975 It does not matter whether the key is preinstalled or dynamically 976 acquired. The router must have the key in use before it can join the 977 DAG being created for secure route discovery. 979 If a rogue router knows the key for the security configuration in 980 use, it can join the secure AODV-RPL route discovery and cause 981 various types of damage. Such a rogue router could advertise false 982 information in its DIOs in order to include itself in the discovered 983 route(s). It could generate bogus RREQ-DIO, and RREP-DIO messages 984 carrying bad routes or maliciously modify genuine RREP-DIO messages 985 it receives. A rogue router acting as the OrigNode could launch 986 denial-of-service attacks against the LLN deployment by initiating 987 fake AODV-RPL route discoveries. When rogue routers might be 988 present, RPL's preinstalled mode of operation, where the key to use 989 for route discovery is preinstalled, SHOULD be used. 991 When a RREQ-DIO message uses the source routing option by setting the 992 H bit to 0, a rogue router may populate the Address Vector field with 993 a set of addresses that may result in the RREP-DIO traveling in a 994 routing loop. 996 If a rogue router is able to forge a gratuitous RREP, significant 997 damage might result. 999 11. Acknowledgements 1001 The authors thank Pascal Thubert, Rahul Jadhav, and Lijo Thomas for 1002 their support and valuable inputs. The authors specially thank 1003 Lavanya H.M for implementing AODV-RPl in Contiki and conducting 1004 extensive simulation studies. 1006 The authors would like to acknowledge the review, feedback and 1007 comments from the following people, in alphabetical order: Roman 1008 Danyliw, Lars Eggert, Benjamin Kaduk, Tero Kivinen, Erik Kline, 1009 Murray Kucherawy, Warren Kumari, Francesca Palombini, Alvaro Retana, 1010 Ines Robles, John Scudder, Meral Shirazipour, Peter Van der Stok, 1011 Eric Vyncke, and Robert Wilton. 1013 12. References 1015 12.1. Normative References 1017 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1018 Requirement Levels", BCP 14, RFC 2119, 1019 DOI 10.17487/RFC2119, March 1997, 1020 . 1022 [RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko, 1023 "The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206, 1024 March 2011, . 1026 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1027 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1028 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1029 Low-Power and Lossy Networks", RFC 6550, 1030 DOI 10.17487/RFC6550, March 2012, 1031 . 1033 [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., 1034 and D. Barthel, "Routing Metrics Used for Path Calculation 1035 in Low-Power and Lossy Networks", RFC 6551, 1036 DOI 10.17487/RFC6551, March 2012, 1037 . 1039 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1040 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1041 May 2017, . 1043 12.2. Informative References 1045 [co-ioam] Ballamajalu, Rashmi., S.V.R., Anand., and Malati Hegde, 1046 "Co-iOAM: In-situ Telemetry Metadata Transport for 1047 Resource Constrained Networks within IETF Standards 1048 Framework", 2018 10th International Conference on 1049 Communication Systems & Networks (COMSNETS) pp.573-576, 1050 Jan 2018. 1052 [contiki] Contiki contributors, "The Contiki Open Source OS for the 1053 Internet of Things (Contiki Version 2.7)", Nov 2013, 1054 . 1056 [Contiki-ng] 1057 Contiki-NG contributors, "Contiki-NG: The OS for Next 1058 Generation IoT Devices (Contiki-NG Version 4.6)", Dec 1059 2020, . 1061 [cooja] Contiki/Cooja contributors, "Cooja Simulator for Wireless 1062 Sensor Networks (Contiki/Cooja Version 2.7)", Nov 2013, 1063 . 1066 [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- 1067 Demand Distance Vector (AODV) Routing", RFC 3561, 1068 DOI 10.17487/RFC3561, July 2003, 1069 . 1071 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and 1072 J. Martocci, "Reactive Discovery of Point-to-Point Routes 1073 in Low-Power and Lossy Networks", RFC 6997, 1074 DOI 10.17487/RFC6997, August 2013, 1075 . 1077 [RFC6998] Goyal, M., Ed., Baccelli, E., Brandt, A., and J. Martocci, 1078 "A Mechanism to Measure the Routing Metrics along a Point- 1079 to-Point Route in a Low-Power and Lossy Network", 1080 RFC 6998, DOI 10.17487/RFC6998, August 2013, 1081 . 1083 [RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y. 1084 Weingarten, "An Overview of Operations, Administration, 1085 and Maintenance (OAM) Tools", RFC 7276, 1086 DOI 10.17487/RFC7276, June 2014, 1087 . 1089 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1090 and M. Richardson, Ed., "A Security Threat Analysis for 1091 the Routing Protocol for Low-Power and Lossy Networks 1092 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1093 . 1095 [RFC7548] Ersue, M., Ed., Romascanu, D., Schoenwaelder, J., and A. 1096 Sehgal, "Management of Networks with Constrained Devices: 1097 Use Cases", RFC 7548, DOI 10.17487/RFC7548, May 2015, 1098 . 1100 [RFC9030] Thubert, P., Ed., "An Architecture for IPv6 over the Time- 1101 Slotted Channel Hopping Mode of IEEE 802.15.4 (6TiSCH)", 1102 RFC 9030, DOI 10.17487/RFC9030, May 2021, 1103 . 1105 Appendix A. Example: Using ETX/RSSI Values to determine value of S bit 1107 The combination of Received Signal Strength Indication(downstream) 1108 (RSSI) and Expected Number of Transmissions(upstream) (ETX) has been 1109 tested to determine whether a link is symmetric or asymmetric at 1110 intermediate nodes. We present two methods to obtain an ETX value 1111 from RSSI measurement. 1113 Method 1: In the first method, we constructed a table measuring RSSI 1114 vs ETX using the Cooja simulation [cooja] setup in the Contiki OS 1115 environment[contiki]. We used Contiki-2.7 running 6LoWPAN/RPL 1116 protocol stack for the simulations. For approximating the number 1117 of packet drops based on the RSSI values, we implemented simple 1118 logic that drops transmitted packets with certain pre-defined 1119 ratios before handing over the packets to the receiver. The 1120 packet drop ratio is implemented as a table lookup of RSSI ranges 1121 mapping to different packet drop ratios with lower RSSI ranges 1122 resulting in higher values. While this table has been defined for 1123 the purpose of capturing the overall link behavior, it is highly 1124 recommended to conduct physical radio measurement experiments, in 1125 general. By keeping the receiving node at different distances, we 1126 let the packets experience different packet drops as per the 1127 described method. The ETX value computation is done by another 1128 module which is part of RPL Objective Function implementation. 1129 Since ETX value is reflective of the extent of packet drops, it 1130 allowed us to prepare a useful ETX vs RSSI table. ETX versus RSSI 1131 values obtained in this way may be used as explained below: 1133 Source---------->NodeA---------->NodeB------->Destination 1135 Figure 8: Communication link from Source to Destination 1137 +-------------------------+----------------------------------------+ 1138 | RSSI at NodeA for NodeB | Expected ETX at NodeA for NodeB->NodeA | 1139 +-------------------------+----------------------------------------+ 1140 | > -60 | 150 | 1141 | -70 to -60 | 192 | 1142 | -80 to -70 | 226 | 1143 | -90 to -80 | 662 | 1144 | -100 to -90 | 3840 | 1145 +-------------------------+----------------------------------------+ 1147 Table 1: Selection of S bit based on Expected ETX value 1149 Method 2: One could also make use of the function 1150 guess_etx_from_rssi() defined in the 6LoWPAN/RPL protocol stack of 1151 Contiki-ng OS [Contiki-ng] to obtain RSSI-ETX mapping. This 1152 function outputs ETX value ranging between 128 and 3840 for -60 <= 1153 rssi <= -89. The function description is beyond the scope of this 1154 document. 1156 We tested the operations in this specification by making the 1157 following experiment, using the above parameters. In our experiment, 1158 a communication link is considered as symmetric if the ETX value of 1159 NodeA->NodeB and NodeB->NodeA (see Figure 8) are within, say, a 1:3 1160 ratio. This ratio should be understood as determining the link's 1161 symmetric/asymmetric nature. NodeA can typically know the ETX value 1162 in the direction of NodeA -> NodeB but it has no direct way of 1163 knowing the value of ETX from NodeB->NodeA. Using physical testbed 1164 experiments and realistic wireless channel propagation models, one 1165 can determine a relationship between RSSI and ETX representable as an 1166 expression or a mapping table. Such a relationship in turn can be 1167 used to estimate ETX value at nodeA for link NodeB--->NodeA from the 1168 received RSSI from NodeB. Whenever nodeA determines that the link 1169 towards the nodeB is bi-directional asymmetric then the S bit is set 1170 to 0. Afterwards, the link from NodeA to Destination remains 1171 designated as asymmetric and the S bit remains set to 0. 1173 Appendix B. Changelog 1175 Note to the RFC Editor: please remove this section before 1176 publication. 1178 B.1. Changes from version 10 to version 11 1180 o Numerous editorial improvements. 1182 o Replace Floor((7+(Prefix Length))/8) by Ceil(Prefix Length/8) for 1183 simplicity and ease of understanding. 1185 o Use "L field" instead of "L bit" since L is a two-bit field. 1187 o Improved the procedures in section 6.2.1. 1189 o Define the S bit of the data structure a node uses to represent 1190 whether or not the RREQ instance is for a symmetric or an 1191 asymmetric route. This replaces text in the document that was a 1192 holdover from earlier versions in which the RREP had an S bit for 1193 that purpose. 1195 o Quote terminology from AODV that has been identified as possibly 1196 originating in language reflecting various kinds of bias against 1197 certain cultures. 1199 o Clarified the relationship of AODV-RPL to RPL. 1201 o Eliminated the "Point-to-Point" terminology to avoid suggesting 1202 only a single link. 1204 o Modified certain passages to better reflect the possibility that a 1205 node might have multiple IP addresses. 1207 o "Rsv" replaced by "X X" for reserved field. 1209 o Added mandates for reserved fields, and replaces some ambiguous 1210 language phraseology by mandates. 1212 o Replaced "retransmit" terminology by more correct "propagate" 1213 terminology. 1215 o Added text about determining link symmetry near Figure 5. 1217 o Mandated checking the Address Vector to avoid routing loops. 1219 o Improved specification for use of the Shift value in 1220 Section 6.3.3. 1222 o Corrected the wrong use of RREQ-Instance to be RREP-Instance. 1224 o Referred to Subregistry values instead of Registry values in 1225 Section 9. 1227 o Sharpened language in Section 10, eliminated misleading use of 1228 capitalization in the words "Security Configuration". 1230 o Added acknowledgements and contributors. 1232 B.2. Changes from version 09 to version 10 1234 o Changed the title for brevity and to remove acronyms. 1236 o Added "Note to the RFC Editor" in Section 9. 1238 o Expanded DAO and P2MP in Section 1. 1240 o Reclassified [RFC6998] and [RFC7416] as Informational. 1242 o SHOULD changed to MUST in Section 4.1 and Section 4.2. 1244 o Several editorial improvements and clarifications. 1246 B.3. Changes from version 08 to version 09 1248 o Removed section "Link State Determination" and put some of the 1249 relevant material into Section 5. 1251 o Cited security section of [RFC6550] as part of the RREP-DIO 1252 message description in Section 2. 1254 o SHOULD has been changed to MUST in Section 4.2. 1256 o Expanded the terms ETX and RSSI in Section 5. 1258 o Section 6.4 has been expanded to provide a more precise 1259 explanation of the handling of route reply. 1261 o Added [RFC7416] in the Security Considerations (Section 10) for 1262 RPL security threats. Cited [RFC6550] for authenticated mode of 1263 operation. 1265 o Appendix A has been mostly re-written to describe methods to 1266 determine whether or not the S bit should be set to 1. 1268 o For consistency, adjusted several mandates from SHOULD to MUST and 1269 from SHOULD NOT to MUST NOT. 1271 o Numerous editorial improvements and clarifications. 1273 B.4. Changes from version 07 to version 08 1275 o Instead of describing the need for routes to "fulfill the 1276 requirements", specify that routes need to "satisfy the Objective 1277 Function". 1279 o Removed all normative dependencies on [RFC6997] 1281 o Rewrote Section 10 to avoid duplication of language in cited 1282 specifications. 1284 o Added a new section "Link State Determination" with text and 1285 citations to more fully describe how implementations determine 1286 whether links are symmetric. 1288 o Modified text comparing AODV-RPL to other protocols to emphasize 1289 the need for AODV-RPL instead of the problems with the other 1290 protocols. 1292 o Clarified that AODV-RPL uses some of the base RPL specification 1293 but does not require an instance of RPL to run. 1295 o Improved capitalization, quotation, and spelling variations. 1297 o Specified behavior upon reception of a RREQ-DIO or RREP-DIO 1298 message for an already existing DODAGID (e.g, Section 6.4). 1300 o Fixed numerous language issues in IANA Considerations Section 9. 1302 o For consistency, adjusted several mandates from SHOULD to MUST and 1303 from SHOULD NOT to MUST NOT. 1305 o Numerous editorial improvements and clarifications. 1307 B.5. Changes from version 06 to version 07 1309 o Added definitions for all fields of the ART option (see 1310 Section 4.3). Modified definition of Prefix Length to prohibit 1311 Prefix Length values greater than 127. 1313 o Modified the language from [RFC6550] Target Option definition so 1314 that the trailing zero bits of the Prefix Length are no longer 1315 described as "reserved". 1317 o Reclassified [RFC3561] and [RFC6998] as Informative. 1319 o Added citation for [RFC8174] to Terminology section. 1321 B.6. Changes from version 05 to version 06 1323 o Added Security Considerations based on the security mechanisms 1324 defined in [RFC6550]. 1326 o Clarified the nature of improvements due to P2P route discovery 1327 versus bidirectional asymmetric route discovery. 1329 o Editorial improvements and corrections. 1331 B.7. Changes from version 04 to version 05 1333 o Add description for sequence number operations. 1335 o Extend the residence duration L in section 4.1. 1337 o Change AODV-RPL Target option to ART option. 1339 B.8. Changes from version 03 to version 04 1341 o Updated RREP option format. Remove the T bit in RREP option. 1343 o Using the same RPLInstanceID for RREQ and RREP, no need to update 1344 [RFC6550]. 1346 o Explanation of Shift field in RREP. 1348 o Multiple target options handling during transmission. 1350 B.9. Changes from version 02 to version 03 1352 o Include the support for source routing. 1354 o Import some features from [RFC6997], e.g., choice between hop-by- 1355 hop and source routing, the L field which determines the duration 1356 of residence in the DAG, MaxRank, etc. 1358 o Define new target option for AODV-RPL, including the Destination 1359 Sequence Number in it. Move the TargNode address in RREQ option 1360 and the OrigNode address in RREP option into ADOV-RPL Target 1361 Option. 1363 o Support route discovery for multiple targets in one RREQ-DIO. 1365 o New RPLInstanceID pairing mechanism. 1367 Appendix C. Contributors 1369 Abdur Rashid Sangi 1370 Huaiyin Institute of Technology 1371 No.89 North Beijing Road, Qinghe District 1372 Huaian 223001 1373 P.R. China 1374 Email: sangi_bahrian@yahoo.com 1376 Malati Hegde 1377 Indian Institute of Science 1378 Bangalore 560012 1379 India 1380 Email: malati@iisc.ac.in 1382 Mingui Zhang 1383 Huawei Technologies 1384 No. 156 Beiqing Rd. Haidian District 1385 Beijing 100095 1386 P.R. China 1387 Email: zhangmingui@huawei.com 1389 Authors' Addresses 1391 Satish Anamalamudi 1392 SRM University-AP 1393 Amaravati Campus 1394 Amaravati, Andhra Pradesh 522 502 1395 India 1397 Email: satishnaidu80@gmail.com 1398 Charles E. Perkins 1399 Lupin Lodge 1400 Los Gatos 95033 1401 United States 1403 Email: charliep@computer.org 1405 S.V.R Anand 1406 Indian Institute of Science 1407 Bangalore 560012 1408 India 1410 Email: anandsvr@iisc.ac.in 1412 Bing Liu 1413 Huawei Technologies 1414 No. 156 Beiqing Rd. Haidian District 1415 Beijing 100095 1416 China 1418 Email: remy.liubing@huawei.com