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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 Informational RFC: RFC 5548 ** Downref: Normative reference to an Informational RFC: RFC 5673 ** Downref: Normative reference to an Informational RFC: RFC 5826 ** Downref: Normative reference to an Informational RFC: RFC 5867 ** Downref: Normative reference to an Experimental RFC: RFC 6998 Summary: 6 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: January 3, 2019 Huawei Technologies 6 AR. Sangi 7 Huaiyin Institute of Technology 8 C. Perkins 9 Futurewei 10 S.V.R.Anand 11 Indian Institute of Science 12 B. Liu 13 Huawei Technologies 14 July 2, 2018 16 Asymmetric AODV-P2P-RPL in Low-Power and Lossy Networks (LLNs) 17 draft-ietf-roll-aodv-rpl-04 19 Abstract 21 Route discovery for symmetric and asymmetric Point-to-Point (P2P) 22 traffic flows is a desirable feature in Low power and Lossy Networks 23 (LLNs). For that purpose, this document specifies a reactive P2P 24 route discovery mechanism for both hop-by-hop routing and source 25 routing: Ad Hoc On-demand Distance Vector Routing (AODV) based RPL 26 protocol. Paired Instances are used to construct directional paths, 27 in case some of the links between source and target node are 28 asymmetric. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on January 3, 2019. 47 Copyright Notice 49 Copyright (c) 2018 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 65 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 66 3. Overview of AODV-RPL . . . . . . . . . . . . . . . . . . . . 6 67 4. AODV-RPL DIO Options . . . . . . . . . . . . . . . . . . . . 7 68 4.1. AODV-RPL DIO RREQ Option . . . . . . . . . . . . . . . . 7 69 4.2. AODV-RPL DIO RREP Option . . . . . . . . . . . . . . . . 9 70 4.3. AODV-RPL DIO Target Option . . . . . . . . . . . . . . . 10 71 5. Symmetric and Asymmetric Routes . . . . . . . . . . . . . . . 11 72 6. AODV-RPL Operation . . . . . . . . . . . . . . . . . . . . . 13 73 6.1. Route Request Generation . . . . . . . . . . . . . . . . 13 74 6.2. Receiving and Forwarding RREQ messages . . . . . . . . . 14 75 6.2.1. General Processing . . . . . . . . . . . . . . . . . 14 76 6.2.2. Additional Processing for Multiple Targets . . . . . 15 77 6.3. Generating Route Reply (RREP) at TargNode . . . . . . . . 16 78 6.3.1. RREP-DIO for Symmetric route . . . . . . . . . . . . 16 79 6.3.2. RREP-DIO for Asymmetric Route . . . . . . . . . . . . 16 80 6.3.3. RPLInstanceID Pairing . . . . . . . . . . . . . . . . 16 81 6.4. Receiving and Forwarding Route Reply . . . . . . . . . . 17 82 7. Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . . 18 83 8. Operation of Trickle Timer . . . . . . . . . . . . . . . . . 19 84 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 85 9.1. New Mode of Operation: AODV-RPL . . . . . . . . . . . . . 19 86 9.2. AODV-RPL Options: RREQ, RREP, and Target . . . . . . . . 19 87 10. Security Considerations . . . . . . . . . . . . . . . . . . . 20 88 11. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 20 89 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 90 12.1. Normative References . . . . . . . . . . . . . . . . . . 20 91 12.2. Informative References . . . . . . . . . . . . . . . . . 21 92 Appendix A. Example: ETX/RSSI Values to select S bit . . . . . . 21 93 Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . 22 94 B.1. Changes to version 02 . . . . . . . . . . . . . . . . . . 22 95 B.2. Changes to version 03 . . . . . . . . . . . . . . . . . . 23 96 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 98 1. Introduction 100 RPL[RFC6550] is a IPv6 distance vector routing protocol for Low-power 101 and Lossy Networks (LLNs), and is designed to support multiple 102 traffic flows through a root-based Destination-Oriented Directed 103 Acyclic Graph (DODAG). Typically, a router does not have routing 104 information for most other routers. Consequently, for traffic 105 between routers within the DODAG (i.e., Point-to-Point (P2P) traffic) 106 data packets either have to traverse the root in non-storing mode, or 107 traverse a common ancestor in storing mode. Such P2P traffic is 108 thereby likely to traverse longer routes and may suffer severe 109 congestion near the DAG root [RFC6997], [RFC6998]. 111 To discover better paths for P2P traffic flows in RPL, P2P-RPL 112 [RFC6997] specifies a temporary DODAG where the source acts as a 113 temporary root. The source initiates DIOs encapsulating the P2P 114 Route Discovery option (P2P-RDO) with an address vector for both hop- 115 by-hop mode (H=1) and source routing mode (H=0). Subsequently, each 116 intermediate router adds its IP address and multicasts the P2P mode 117 DIOs, until the message reaches the target node (TargNode), which 118 then sends the "Discovery Reply" object. P2P-RPL is efficient for 119 source routing, but much less efficient for hop-by-hop routing due to 120 the extra address vector overhead. However, for symmetric links, 121 when the P2P mode DIO message is being multicast from the source hop- 122 by-hop, receiving nodes can infer a next hop towards the source. 123 When TargNode subsequently replies to the source along the 124 established forward route, receiving nodes determine the next hop 125 towards TargNode. For hop-by-hop routes (H=1) over symmetric links, 126 this would allow efficient use of routing tables for P2P-RDO messages 127 instead of the "Address Vector". 129 RPL and P2P-RPL both specify the use of a single DODAG in networks of 130 symmetric links, where the two directions of a link MUST both satisfy 131 the constraints of the objective function. This disallows the use of 132 asymmetric links which are qualified in one direction. But, 133 application-specific routing requirements as defined in IETF ROLL 134 Working Group [RFC5548], [RFC5673], [RFC5826] and [RFC5867] may be 135 satisfied by routing paths using bidirectional asymmetric links. For 136 this purpose, [I-D.thubert-roll-asymlink] described bidirectional 137 asymmetric links for RPL [RFC6550] with Paired DODAGs, for which the 138 DAG root (DODAGID) is common for two Instances. This can satisfy 139 application-specific routing requirements for bidirectional 140 asymmetric links in core RPL [RFC6550]. Using P2P-RPL twice with 141 Paired DODAGs, on the other hand, requires two roots: one for the 142 source and another for the target node due to temporary DODAG 143 formation. For networks composed of bidirectional asymmetric links 144 (see Section 5), AODV-RPL specifies P2P route discovery, utilizing 145 RPL with a new MoP. AODV-RPL makes use of two multicast messages to 146 discover possibly asymmetric routes, which can achieve higher route 147 diversity. AODV-RPL eliminates the need for address vector overhead 148 in hop-by-hop mode. This significantly reduces the control packet 149 size, which is important for Constrained LLN networks. Both 150 discovered routes (upward and downward) meet the application specific 151 metrics and constraints that are defined in the Objective Function 152 for each Instance [RFC6552]. 154 The route discovery process in AODV-RPL is modeled on the analogous 155 procedure specified in AODV [RFC3561]. The on-demand nature of AODV 156 route discovery is natural for the needs of peer-to-peer routing in 157 RPL-based LLNs. AODV terminology has been adapted for use with AODV- 158 RPL messages, namely RREQ for Route Request, and RREP for Route 159 Reply. AODV-RPL currently omits some features compared to AODV -- in 160 particular, flagging Route Errors, blacklisting unidirectional links, 161 multihoming, and handling unnumbered interfaces. 163 2. Terminology 165 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 166 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 167 "OPTIONAL" in this document are to be interpreted as described in 168 [RFC2119]. This document uses the following terms: 170 AODV 171 Ad Hoc On-demand Distance Vector Routing[RFC3561]. 173 AODV-RPL Instance 174 Either the RREQ-Instance or RREP-Instance 176 Asymmetric Route 177 The route from the OrigNode to the TargNode can traverse different 178 nodes than the route from the TargNode to the OrigNode. An 179 asymmetric route may result from the asymmetry of links, such that 180 only one direction of the series of links fulfills the constraints 181 in route discovery. 183 Bi-directional Asymmetric Link 184 A link that can be used in both directions but with different link 185 characteristics. 187 DIO 188 DODAG Information Object 190 DODAG RREQ-Instance (or simply RREQ-Instance) 191 RPL Instance built using the DIO with RREQ option; used for 192 control message transmission from OrigNode to TargNode, thus 193 enabling data transmission from TargNode to OrigNode. 195 DODAG RREP-Instance (or simply RREP-Instance) 196 RPL Instance built using the DIO with RREP option; used for 197 control message transmission from TargNode to OrigNode thus 198 enabling data transmission from OrigNode to TargNode. 200 Downward Direction 201 The direction from the OrigNode to the TargNode. 203 Downward Route 204 A route in the downward direction. 206 hop-by-hop routing 207 Routing when each node stores routing information about the next 208 hop. 210 on-demand routing 211 Routing in which a route is established only when needed. 213 OrigNode 214 The IPv6 router (Originating Node) initiating the AODV-RPL route 215 discovery to obtain a route to TargNode. 217 Paired DODAGs 218 Two DODAGs for a single route discovery process between OrigNode 219 and TargNode. 221 P2P 222 Point-to-Point -- in other words, not constrained a priori to 223 traverse a common ancestor. 225 reactive routing 226 Same as "on-demand" routing. 228 RREQ-DIO message 229 An AODV-RPL MoP DIO message containing the RREQ option. The 230 RPLInstanceID in RREQ-DIO is assigned locally by the OrigNode. 232 RREP-DIO message 233 An AODV-RPL MoP DIO message containing the RREP option. The 234 RPLInstanceID in RREP-DIO is typically paired to the one in the 235 associated RREQ-DIO message. 237 Source routing 238 A mechanism by which the source supplies the complete route 239 towards the target node along with each data packet [RFC6550]. 241 Symmetric route 242 The upstream and downstream routes traverse the same routers. 244 TargNode 245 The IPv6 router (Target Node) for which OrigNode requires a route 246 and initiates Route Discovery within the LLN network. 248 Upward Direction 249 The direction from the TargNode to the OrigNode. 251 Upward Route 252 A route in the upward direction. 254 3. Overview of AODV-RPL 256 With AODV-RPL, routes from OrigNode to TargNode within the LLN 257 network established are "on-demand". In other words, the route 258 discovery mechanism in AODV-RPL is invoked reactively when OrigNode 259 has data for delivery to the TargNode but existing routes do not 260 satisfy the application's requirements. The routes discovered by 261 AODV-RPL are not constrained to traverse a common ancestor. Unlike 262 RPL [RFC6550] and P2P-RPL [RFC6997], AODV-RPL can enable asymmetric 263 communication paths in networks with bidirectional asymmetric links. 264 For this purpose, AODV-RPL enables discovery of two routes: namely, 265 one from OrigNode to TargNode, and another from TargNode to OrigNode. 266 When possible, AODV-RPL also enables symmetric route discovery along 267 Paired DODAGs (see Section 5). 269 In AODV-RPL, routes are discovered by first forming a temporary DAG 270 rooted at the OrigNode. Paired DODAGs (Instances) are constructed 271 according to the AODV-RPL Mode of Operation (MoP) during route 272 formation between the OrigNode and TargNode. The RREQ-Instance is 273 formed by route control messages from OrigNode to TargNode whereas 274 the RREP-Instance is formed by route control messages from TargNode 275 to OrigNode. Intermediate routers join the Paired DODAGs based on 276 the rank as calculated from the DIO message. Henceforth in this 277 document, the RREQ-DIO message means the AODV-RPL mode DIO message 278 from OrigNode to TargNode, containing the RREQ option (see 279 Section 4.1). Similarly, the RREP-DIO message means the AODV-RPL 280 mode DIO message from TargNode to OrigNode, containing the RREP 281 option (see Section 4.2). The route discovered in the RREQ-Instance 282 is used for transmitting data from TargNode to OrigNode, and the 283 route discovered in RREP-Instance is used for transmitting data from 284 OrigNode to TargNode. 286 4. AODV-RPL DIO Options 288 4.1. AODV-RPL DIO RREQ Option 290 OrigNode sets its IPv6 address in the DODAGID field of the RREQ-DIO 291 message. A RREQ-DIO message MUST carry exactly one RREQ option. 293 0 1 2 3 294 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 1 295 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 296 | Type | Option Length |S|H|X| Compr | L | MaxRank | 297 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 298 | Orig SeqNo | | 299 +-+-+-+-+-+-+-+-+ | 300 | | 301 | | 302 | Address Vector (Optional, Variable Length) | 303 | | 304 | | 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 307 Figure 1: DIO RREQ option format for AODV-RPL MoP 309 OrigNode supplies the following information in the RREQ option: 311 Type 312 The type assigned to the RREQ option (see Section 9.2). 314 Option Length 315 The length of the option in octets, excluding the Type and Length 316 fields. Variable due to the presence of the address vector and 317 the number of octets elided according to the Compr value. 319 S 320 Symmetric bit indicating a symmetric route from the OrigNode to 321 the router transmitting this RREQ-DIO. 323 H 324 Set to one for a hop-by-hop route. Set to zero for a source 325 route. This flag controls both the downstream route and upstream 326 route. 328 X 329 Reserved. 331 Compr 332 4-bit unsigned integer. Number of prefix octets that are elided 333 from the Address Vector. The octets elided are shared with the 334 IPv6 address in the DODAGID. This field is only used in source 335 routing mode (H=0). In hop-by-hop mode (H=1), this field MUST be 336 set to zero and ignored upon reception. 338 L 340 2-bit unsigned integer determining the duration that a node is 341 able to belong to the temporary DAG in RREQ-Instance, including 342 the OrigNode and the TargNode. Once the time is reached, a node 343 MUST leave the DAG and stop sending or receiving any more DIOs for 344 the temporary DODAG. The definition for the "L" bit is similar to 345 that found in [RFC6997], except that the values are adjusted to 346 enable arbitrarily long route lifetime. 348 * 0x00: No time limit imposed. 349 * 0x01: 2 seconds 350 * 0x02: 16 seconds 351 * 0x03: 64 seconds 353 L is independent from the route lifetime, which is defined in the 354 DODAG configuration option. The route entries in hop-by-hop 355 routing and states of source routing can still be maintained even 356 after the DAG expires. 358 MaxRank 359 This field indicates the upper limit on the integer portion of the 360 rank (calculated using the DAGRank() macro defined in [RFC6550]). 361 A value of 0 in this field indicates the limit is infinity. 363 Orig SeqNo 364 Sequence Number of OrigNode, defined similarly as in AODV 365 [RFC3561]. 367 Address Vector 368 A vector of IPv6 addresses representing the route that the RREQ- 369 DIO has passed. It is only present when the 'H' bit is set to 0. 370 The prefix of each address is elided according to the Compr field. 372 A node MUST NOT join a RREQ instance if its own rank would equal to 373 or higher than MaxRank. Targnode can join the RREQ instance at a 374 rank whose integer portion is equal to the MaxRank. A router MUST 375 discard a received RREQ if the integer part of the advertised rank 376 equals or exceeds the MaxRank limit. This definition of MaxRank is 377 the same as that found in [RFC6997]. 379 4.2. AODV-RPL DIO RREP Option 381 TargNode sets its IPv6 address in the DODAGID field of the RREP-DIO 382 message. A RREP-DIO message MUST carry exactly one RREP option. 383 TargNode supplies the following information in the RREP option: 385 0 1 2 3 386 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 1 387 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 388 | Type | Option Length |G|H|X| Compr | L | MaxRank | 389 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 390 | Shift |Rsv| | 391 +-+-+-+-+-+-+-+-+ | 392 | | 393 | | 394 | Address Vector (Optional, Variable Length) | 395 . . 396 . . 397 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 399 Figure 2: DIO RREP option format for AODV-RPL MoP 401 Type 402 The type assigned to the RREP option (see Section 9.2) 404 Option Length 405 The length of the option in octets, excluding the Type and Length 406 fields. Variable due to the presence of the address vector and 407 the number of octets elided according to the Compr value. 409 G 410 Gratuitous route (see Section 7). 412 H 413 Requests either source routing (H=0) or hop-by-hop (H=1) for the 414 downstream route. It MUST be set to be the same as the 'H' bit in 415 RREQ option. 417 X 418 Reserved. 420 Compr 421 4-bit unsigned integer. Same definition as in RREQ option. 423 L 424 2-bit unsigned integer defined as in RREQ option. 426 MaxRank 427 Similarly to MaxRank in the RREQ message, this field indicates the 428 upper limit on the integer portion of the rank. A value of 0 in 429 this field indicates the limit is infinity. 431 Shift 432 6-bit unsigned integer. This field is used to recover the 433 original InstanceID (see Section 6.3.3); 0 indicates that the 434 original InstanceID is used. 436 Rsv 437 MUST be initialized to zero and ignored upon reception. 439 Address Vector 440 Only present when the 'H' bit is set to 0. For an asymmetric 441 route, the Address Vector represents the IPv6 addresses of the 442 route that the RREP-DIO has passed. For a symmetric route, it is 443 the Address Vector when the RREQ-DIO arrives at the TargNode, 444 unchanged during the transmission to the OrigNode. 446 4.3. AODV-RPL DIO Target Option 448 The AODV-RPL Target Option is defined based on the Target Option in 449 core RPL [RFC6550]: the Destination Sequence Number of the TargNode 450 is added. 452 A RREQ-DIO message MUST carry at least one AODV-RPL Target Options. 453 A RREP-DIO message MUST carry exactly one AODV-RPL Target Option. 455 OrigNode can include multiple TargNode addresses via multiple AODV- 456 RPL Target Options in the RREQ-DIO, for routes that share the same 457 constraints. This reduces the cost to building only one DODAG. 458 Furthermore, a single Target Option can be used for different 459 TargNode addresses if they share the same prefix; in that case the 460 use of the destination sequence number is not defined in this 461 document. 463 0 1 2 3 464 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 1 465 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 466 | Type | Option Length | Dest SeqNo | Prefix Length | 467 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 468 | | 469 + | 470 | Target Prefix (Variable Length) | 471 . . 472 . . 473 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 475 Figure 3: Target option format for AODV-RPL MoP 477 Type 478 The type assigned to the AODV-RPL Target Option 480 Dest SeqNo 482 In RREQ-DIO, if nonzero, it is the last known Sequence Number for 483 TargNode for which a route is desired. In RREP-DIO, it is the 484 destination sequence number associated to the route. 486 5. Symmetric and Asymmetric Routes 488 In Figure 4 and Figure 5, BR is the Border Router, O is the OrigNode, 489 R is an intermediate router, and T is the TargNode. If the RREQ-DIO 490 arrives over an interface that is known to be symmetric, and the 'S' 491 bit is set to 1, then it remains as 1, as illustrated in Figure 4. 492 If an intermediate router sends out RREQ-DIO with the 'S' bit set to 493 1, then all the one-hop links on the route from the OrigNode O to 494 this router meet the requirements of route discovery, and the route 495 can be used symmetrically. 497 BR 498 /----+----\ 499 / | \ 500 / | \ 501 R R R 502 _/ \ | / \ 503 / \ | / \ 504 / \ | / \ 505 R -------- R --- R ----- R -------- R 506 / \ <--S=1--> / \ <--S=1--> / \ 507 <--S=1--> \ / \ / <--S=1--> 508 / \ / \ / \ 509 O ---------- R ------ R------ R ----- R ----------- T 510 / \ / \ / \ / \ 511 / \ / \ / \ / \ 512 / \ / \ / \ / \ 513 R ----- R ----------- R ----- R ----- R ----- R ---- R----- R 515 >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> 516 <---- RREP-Instance (Control: T-->O; Data: O-->T) -------< 518 Figure 4: AODV-RPL with Symmetric Paired Instances 520 Upon receiving a RREQ-DIO with the 'S' bit set to 1, a node 521 determines whether this one-hop link can be used symmetrically, i.e., 522 both the two directions meet the requirements of data transmission. 523 If the RREQ-DIO arrives over an interface that is not known to be 524 symmetric, or is known to be asymmetric, the 'S' bit is set to 0. If 525 the 'S' bit arrives already set to be '0', it is set to be '0' on 526 retransmission (Figure 5). Therefore, for asymmetric route, there is 527 at least one hop which doesn't fulfill the constraints in the two 528 directions. Based on the 'S' bit received in RREQ-DIO, the TargNode 529 T determines whether or not the route is symmetric before 530 transmitting the RREP-DIO message upstream towards the OrigNode O. 532 The criteria used to determine whether or not each link is symmetric 533 is beyond the scope of the document, and may be implementation- 534 specific. For instance, intermediate routers MAY use local 535 information (e.g., bit rate, bandwidth, number of cells used in 536 6tisch), a priori knowledge (e.g. link quality according to previous 537 communication) or use averaging techniques as appropriate to the 538 application. 540 Appendix A describes an example method using the ETX and RSSI to 541 estimate whether the link is symmetric in terms of link quality is 542 given in using an averaging technique. 544 BR 545 /----+----\ 546 / | \ 547 / | \ 548 R R R 549 / \ | / \ 550 / \ | / \ 551 / \ | / \ 552 R --------- R --- R ---- R --------- R 553 / \ --S=1--> / \ --S=0--> / \ 554 --S=1--> \ / \ / --S=0--> 555 / \ / \ / \ 556 O ---------- R ------ R------ R ----- R ----------- T 557 / \ / \ / \ / \ 558 / <--S=0-- / \ / \ / <--S=0-- 559 / \ / \ / \ / \ 560 R ----- R ----------- R ----- R ----- R ----- R ---- R----- R 561 <--S=0-- <--S=0-- <--S=0-- <--S=0-- <--S=0-- 563 >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> 564 <---- RREP-Instance (Control: T-->O; Data: O-->T) -------< 566 Figure 5: AODV-RPL with Asymmetric Paired Instances 568 6. AODV-RPL Operation 570 6.1. Route Request Generation 572 The route discovery process is initiated when an application at the 573 OrigNode has data to be transmitted to the TargNode, but does not 574 have a route for the target that fulfills the requirements of the 575 data transmission. In this case, the OrigNode builds a local 576 RPLInstance and a DODAG rooted at itself. Then it transmits a DIO 577 message containing exactly one RREQ option (see Section 4.1) via 578 link-local multicast. The DIO MUST contain at least one AODV-RPL 579 Target Option (see Section 4.3). The 'S' bit in RREQ-DIO sent out by 580 the OrigNode is set to 1. 582 The OrigNode maintains its Sequence Number as defined in AODV 583 [RFC3561]. Namely, the OrigNode increments its Sequence number each 584 time it initiate a new route discovery operation by transmitting a 585 new RREQ message. Similarly, TargNode increments its Sequence number 586 each time it transmits a RREP message in response to a new RREQ 587 message (one with an incremented Sequence Number for OrigNode). 589 The address in the AODV-RPL Target Option can be a unicast IPv6 590 address, or a prefix. The OrigNode can initiate the route discovery 591 process for multiple targets simultaneously by including multiple 592 AODV-RPL Target Options, and within a RREQ-DIO the requirements for 593 the routes to different TargNodes MUST be the same. 595 OrigNode can maintain different RPLInstances to discover routes with 596 different requirements to the same targets. Using the InstanceID 597 pairing mechanism (see Section 6.3.3), route replies (RREP-DIOs) for 598 different RPLInstances can be distinguished. 600 The transmission of RREQ-DIO obeys the Trickle timer. If the 601 duration specified by the "L" bit has elapsed, the OrigNode MUST 602 leave the DODAG and stop sending RREQ-DIOs in the related 603 RPLInstance. 605 6.2. Receiving and Forwarding RREQ messages 607 6.2.1. General Processing 609 Upon receiving a RREQ-DIO, a router which does not belong to the 610 RREQ-instance goes through the following steps: 612 Step 1: 614 If the 'S' bit in the received RREQ-DIO is set to 1, the router 615 MUST check the two directions of the link by which the RREQ-DIO is 616 received. In case that the downward (i.e. towards the TargNode) 617 direction of the link can't fulfill the requirements, the link 618 can't be used symmetrically, thus the 'S' bit of the RREQ-DIO to 619 be sent out MUST be set as 0. If the 'S' bit in the received 620 RREQ-DIO is set to 0, the router only checks into the upward 621 direction (towards the OrigNode) of the link. 623 If the upward direction of the link can fulfill the requirements 624 indicated in the constraint option, and the router's rank would 625 not exceed the MaxRank limit, the router joins the DODAG of the 626 RREQ-Instance. The router that transmitted the received RREQ-DIO 627 is selected as the preferred parent. Later, other RREQ-DIO 628 messages might be received. How to maintain the parent set, 629 select the preferred parent, and update the router's rank obeys 630 the core RPL and the OFs defined in ROLL WG. In case that the 631 constraint or the MaxRank limit is not fulfilled, the router MUST 632 discard the received RREQ-DIO and MUST NOT join the DODAG. 634 Step 2: 636 Then the router checks if one of its addresses is included in one 637 of the AODV-RPL Target Options. If so, this router is one of the 638 TargNodes. 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 the upward route entry accordingly. The 644 route entry MUST include at least the following items: Source 645 Address, InstanceID, Destination Address, Next Hop and Lifetime. 646 The Destination Address and the InstanceID can be respectively 647 learned from the DODAGID and the RPLInstanceID of the RREQ-DIO, 648 and the Source Address is copied from the AODV-RPL Target Option. 649 The next hop is the preferred parent. And the lifetime is set 650 according to DODAG configuration and can be extended when the 651 route is actually used. 653 If the 'H' bit is set to 0, an intermediate router MUST include 654 the address of the interface receiving the RREQ-DIO into the 655 address vector. 657 Step 4: 659 An intermediate router transmits a RREQ-DIO via link-local 660 multicast. TargNode prepares a RREP-DIO. 662 6.2.2. Additional Processing for Multiple Targets 664 If the OrigNode tries to reach multiple TargNodes in a single RREQ- 665 instance, one of the TargNodes can be an intermediate router to the 666 others, therefore it SHOULD continue sending RREQ-DIO to reach other 667 targets. In this case, before rebroadcasting the RREQ-DIO, a 668 TargNode MUST delete the Target Option encapsulating its own address, 669 so that downstream routers with higher ranks do not try to create a 670 route to this TargetNode. 672 An intermediate router could receive several RREQ-DIOs from routers 673 with lower ranks in the same RREQ-instance but have different lists 674 of Target Options. When rebroadcasting the RREQ-DIO, the 675 intersection of these lists SHOULD be included. For example, suppose 676 two RREQ-DIOs are received with the same RPLInstance and OrigNode. 677 Suppose further that the first RREQ has (T1, T2) as the targets, and 678 the second one has (T2, T4) as targets. Then only T2 needs to be 679 included in the generated RREQ-DIO. If the intersection is empty, it 680 means that all the targets have been reached, and the router SHOULD 681 NOT send out any RREQ-DIO. Any RREQ-DIO message with different AODV- 682 RPL Target Options coming from a router with higher rank is ignored. 684 6.3. Generating Route Reply (RREP) at TargNode 686 6.3.1. RREP-DIO for Symmetric route 688 If a RREQ-DIO arrives at TargNode with the 'S' bit set to 1, there is 689 a symmetric route along which both directions can fulfill the 690 requirements. Other RREQ-DIOs might later provide asymmetric upward 691 routes (i.e. S=0). Selection between a qualified symmetric route 692 and an asymmetric route that might have better performance is 693 implementation-specific and out of scope. If the implementation uses 694 the symmetric route, the TargNode MAY delay transmitting the RREP-DIO 695 for duration RREP_WAIT_TIME to await a better symmetric route. 697 For a symmetric route, the RREP-DIO message is unicast to the next 698 hop according to the accumulated address vector (H=0) or the route 699 entry (H=1). Thus the DODAG in RREP-Instance does not need to be 700 built. The RPLInstanceID in the RREP-Instance is paired as defined 701 in Section 6.3.3. In case the 'H' bit is set to 0, the address 702 vector received in the RREQ-DIO MUST be included in the RREP-DIO. 703 The address of the OrigNode MUST be encapsulated in an AODV-RPL 704 Target Option and included in this RREP-DIO message, and the Dest 705 SeqNo is incremented, as is done in AODV [RFC3561]. 707 6.3.2. RREP-DIO for Asymmetric Route 709 When a RREQ-DIO arrives at a TargNode with the 'S' bit set to 0, the 710 TargNode MUST build a DODAG in the RREP-Instance rooted at itself in 711 order to discover the downstream route from the OrigNode to the 712 TargNode. The RREP-DIO message MUST be re-transmitted via link-local 713 multicast until the OrigNode is reached or MaxRank is exceeded. 715 The settings of the fields in RREP option are the same as in 716 symmetric route except for the 'S' bit. 718 6.3.3. RPLInstanceID Pairing 720 Since the RPLInstanceID is assigned locally (i.e., there is no 721 coordination between routers in the assignment of RPLInstanceID), the 722 tuple (OrigNode, TargNode, RPLInstanceID) is needed to uniquely 723 identify a discovered route. The upper layer applications may have 724 different requirements and they can initiate the route discoveries 725 simultaneously. Thus between the same pair of OrigNode and TargNode, 726 there can be multiple AODV-RPL instances. To avoid any mismatch, the 727 RREQ-Instance and the RREP-Instance in the same route discovery MUST 728 be paired somehow, e.g. using the RPLInstanceID. 730 When preparing the RREP-DIO, a TargNode could find the RPLInstanceID 731 to be used for the RREP-Instance is already occupied by another RPL 732 Instance from an earlier route discovery operation which is still 733 active. In other words, it might happen that two distinct OrigNodes 734 need routes to the same TargNode, and they happen to use the same 735 RPLInstanceID for RREQ-Instance. In this case, the occupied 736 RPLInstanceID MUST NOT be used again. Then the second RPLInstanceID 737 MUST be shifted into another integer so that the two RREP-instances 738 can be distinguished. In RREP option, the Shift field indicates the 739 shift to be applied to original RPLInstanceID. When the new 740 InstanceID after shifting exceeds 63, it rolls over starting at 0. 741 For example, the original InstanceID is 60, and shifted by 6, the new 742 InstanceID will be 2. Related operations can be found in 743 Section 6.4. 745 6.4. Receiving and Forwarding Route Reply 747 Upon receiving a RREP-DIO, a router which does not belong to the 748 RREQ-instance goes through the following steps: 750 Step 1: 752 If the 'S' bit is set to 1, the router proceeds to step 2. 754 If the 'S' bit of the RREP-DIO is set to 0, the router MUST check 755 the downward direction of the link (towards the TargNode) over 756 which the RREP-DIO is received. If the downward direction of the 757 link can fulfill the requirements indicated in the constraint 758 option, and the router's rank would not exceed the MaxRank limit, 759 the router joins the DODAG of the RREP-Instance. The router that 760 transmitted the received RREP-DIO is selected as the preferred 761 parent. Afterwards, other RREP-DIO messages can be received. How 762 to maintain the parent set, select the preferred parent, and 763 update the router's rank obeys the core RPL and the OFs defined in 764 ROLL WG. 766 If the constraints are not fulfilled, the router MUST NOT join the 767 DODAG; the router MUST discard the RREQ-DIO, and does not execute 768 the remaining steps in this section. 770 Step 2: 772 The router next checks if one of its addresses is included in the 773 AODV-RPL Target Option. If so, this router is the OrigNode of the 774 route discovery. Otherwise, it is an intermediate router. 776 Step 3: 778 If the 'H' bit is set to 1, then the router (OrigNode or 779 intermediate) MUST build a downward route entry. The route entry 780 SHOULD include at least the following items: OrigNode Address, 781 InstanceID, TargNode Address as destination, Next Hop and 782 Lifetime. For a symmetric route, the next hop in the route entry 783 is the router from which the RREP-DIO is received. For an 784 asymmetric route, the next hop is the preferred parent in the 785 DODAG of RREQ-Instance. The InstanceID in the route entry MUST be 786 the original RPLInstanceID (after subtracting the Shift field 787 value). The source address is learned from the AODV-RPL Target 788 Option, and the destination address is learned from the DODAGID. 789 The lifetime is set according to DODAG configuration and can be 790 extended when the route is actually used. 792 If the 'H' bit is set to 0, for an asymmetric route, an 793 intermediate router MUST include the address of the interface 794 receiving the RREP-DIO into the address vector; for a symmetric 795 route, there is nothing to do in this step. 797 Step 4: 799 If the receiver is the OrigNode, it can start transmitting the 800 application data to TargNode along the path as provided in RREP- 801 Instance, and processing for the RREP-DIO is complete. Otherwise, 802 in case of an asymmetric route, the intermediate router transmits 803 the RREP-DIO via link-local multicast. In case of a symmetric 804 route, the RREP-DIO message is unicast to the next hop according 805 to the address vector in the RREP-DIO (H=0) or the local route 806 entry (H=1). The RPLInstanceID in the transmitted RREP-DIO is the 807 same as the value in the received RREP-DIO. 809 7. Gratuitous RREP 811 In some cases, an Intermediate router that receives a RREQ-DIO 812 message MAY transmit a "Gratuitous" RREP-DIO message back to OrigNode 813 instead of continuing to multicast the RREQ-DIO towards TargNode. 814 The intermediate router effectively builds the RREP-Instance on 815 behalf of the actual TargNode. The 'G' bit of the RREP option is 816 provided to distinguish the Gratuitous RREP-DIO (G=1) sent by the 817 Intermediate node from the RREP-DIO sent by TargNode (G=0). 819 The gratuitous RREP-DIO can be sent out when an intermediate router R 820 receives a RREQ-DIO for a TargNode T, and R happens to have both 821 downward and upward routes to T which also fulfill the requirements. 823 In case of source routing, the intermediate router R MUST unicast the 824 received RREQ-DIO to TargNode T including the address vector between 825 the OrigNode O and the router R. Thus T can have a complete upward 826 route address vector from itself to O. Then R MUST send out the 827 gratuitous RREP-DIO including the address vector from R to T. 829 In case of hop-by-hop routing, R MUST unicast the received RREQ-DIO 830 to T. The routers along the route SHOULD build new route entries 831 with the related RPLInstanceID and DODAGID in the downward direction. 832 Then T MUST unicast the RREP-DIO to R, and the routers along the 833 route SHOULD build new route entries in the upward direction. Upon 834 received the unicast RREP-DIO, R sends the gratuitous RREP-DIO to the 835 OrigNode as the same way defined in Section 6.3. 837 8. Operation of Trickle Timer 839 The trickle timer operation to control RREQ-Instance/RREP-Instance 840 multicast is similar to that in P2P-RPL [RFC6997]. 842 9. IANA Considerations 844 9.1. New Mode of Operation: AODV-RPL 846 IANA is required to assign a new Mode of Operation, named "AODV-RPL" 847 for Point-to-Point(P2P) hop-by-hop routing under the RPL registry. 848 The value of TBD1 is assigned from the "Mode of Operation" space 849 [RFC6550]. 851 +-------------+---------------+---------------+ 852 | Value | Description | Reference | 853 +-------------+---------------+---------------+ 854 | TBD1 (5) | AODV-RPL | This document | 855 +-------------+---------------+---------------+ 857 Figure 6: Mode of Operation 859 9.2. AODV-RPL Options: RREQ, RREP, and Target 861 Three entries are required for new AODV-RPL options "RREQ", "RREP" 862 and "AODV-RPL Target" with values of TBD2 (0x0A), TBD3 (0x0B) and 863 TBD4 (0x0C) from the "RPL Control Message Options" space [RFC6550]. 865 +-------------+------------------------+---------------+ 866 | Value | Meaning | Reference | 867 +-------------+------------------------+---------------+ 868 | TBD2 (0x0A) | RREQ Option | This document | 869 +-------------+------------------------+---------------+ 870 | TBD3 (0x0B) | RREP Option | This document | 871 +-------------+------------------------+---------------+ 872 | TBD3 (0x0C) | AODV-RPL Target Option | This document | 873 +-------------+------------------------+---------------+ 875 Figure 7: AODV-RPL Options 877 10. Security Considerations 879 This document does not introduce additional security issues compared 880 to base RPL. For general RPL security considerations, see [RFC6550]. 882 11. Future Work 884 There has been some discussion about how to determine the initial 885 state of a link after an AODV-RPL-based network has begun operation. 886 The current draft operates as if the links are symmetric until 887 additional metric information is collected. The means for making 888 link metric information is considered out of scope for AODV-RPL. In 889 the future, RREQ and RREP messages could be equipped with new fields 890 for use in verifying link metrics. In particular, it is possible to 891 identify unidirectional links; an RREQ received across a 892 unidirectional link has to be dropped, since the destination node 893 cannot make use of the received DODAG to route packets back to the 894 source node that originated the route discovery operation. This is 895 roughly the same as considering a unidirectional link to present an 896 infinite cost metric that automatically disqualifies it for use in 897 the reverse direction. 899 12. References 901 12.1. Normative References 903 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 904 Requirement Levels", BCP 14, RFC 2119, 905 DOI 10.17487/RFC2119, March 1997, 906 . 908 [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- 909 Demand Distance Vector (AODV) Routing", RFC 3561, 910 DOI 10.17487/RFC3561, July 2003, 911 . 913 [RFC5548] Dohler, M., Ed., Watteyne, T., Ed., Winter, T., Ed., and 914 D. Barthel, Ed., "Routing Requirements for Urban Low-Power 915 and Lossy Networks", RFC 5548, DOI 10.17487/RFC5548, May 916 2009, . 918 [RFC5673] Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T. 919 Phinney, "Industrial Routing Requirements in Low-Power and 920 Lossy Networks", RFC 5673, DOI 10.17487/RFC5673, October 921 2009, . 923 [RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation 924 Routing Requirements in Low-Power and Lossy Networks", 925 RFC 5826, DOI 10.17487/RFC5826, April 2010, 926 . 928 [RFC5867] Martocci, J., Ed., De Mil, P., Riou, N., and W. Vermeylen, 929 "Building Automation Routing Requirements in Low-Power and 930 Lossy Networks", RFC 5867, DOI 10.17487/RFC5867, June 931 2010, . 933 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 934 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 935 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 936 Low-Power and Lossy Networks", RFC 6550, 937 DOI 10.17487/RFC6550, March 2012, 938 . 940 [RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing 941 Protocol for Low-Power and Lossy Networks (RPL)", 942 RFC 6552, DOI 10.17487/RFC6552, March 2012, 943 . 945 [RFC6998] Goyal, M., Ed., Baccelli, E., Brandt, A., and J. Martocci, 946 "A Mechanism to Measure the Routing Metrics along a Point- 947 to-Point Route in a Low-Power and Lossy Network", 948 RFC 6998, DOI 10.17487/RFC6998, August 2013, 949 . 951 12.2. Informative References 953 [I-D.thubert-roll-asymlink] 954 Thubert, P., "RPL adaptation for asymmetrical links", 955 draft-thubert-roll-asymlink-02 (work in progress), 956 December 2011. 958 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and 959 J. Martocci, "Reactive Discovery of Point-to-Point Routes 960 in Low-Power and Lossy Networks", RFC 6997, 961 DOI 10.17487/RFC6997, August 2013, 962 . 964 Appendix A. Example: ETX/RSSI Values to select S bit 966 We have tested the combination of "RSSI(downstream)" and "ETX 967 (upstream)" to determine whether the link is symmetric or asymmetric 968 at the intermediate nodes. The example of how the ETX and RSSI 969 values are used in conjuction is explained below: 971 Source---------->NodeA---------->NodeB------->Destination 973 Figure 8: Communication link from Source to Destination 975 +-------------------------+----------------------------------------+ 976 | RSSI at NodeA for NodeB | Expected ETX at NodeA for NodeB->NodeA | 977 +-------------------------+----------------------------------------+ 978 | > -15 | 150 | 979 | -25 to -15 | 192 | 980 | -35 to -25 | 226 | 981 | -45 to -35 | 662 | 982 | -55 to -45 | 993 | 983 +-------------------------+----------------------------------------+ 985 Table 1: Selection of 'S' bit based on Expected ETX value 987 We tested the operations in this specification by making the 988 following experiment, using the above parameters. In our experiment, 989 a communication link is considered as symmetric if the ETX value of 990 NodeA->NodeB and NodeB->NodeA (See Figure.8) are, say, within 1:3 991 ratio. This ratio should be taken as a notional metric for deciding 992 link symmetric/asymmetric nature, and precise definition of the ratio 993 is beyond the scope of the draft. In general, NodeA can only know 994 the ETX value in the direction of NodeA -> NodeB but it has no direct 995 way of knowing the value of ETX from NodeB->NodeA. Using physical 996 testbed experiments and realistic wireless channel propagation 997 models, one can determine a relationship between RSSI and ETX 998 representable as an expression or a mapping table. Such a 999 relationship in turn can be used to estimate ETX value at nodeA for 1000 link NodeB--->NodeA from the received RSSI from NodeB. Whenever 1001 nodeA determines that the link towards the nodeB is bi-directional 1002 asymmetric then the "S" bit is set to "S=0". Later on, the link from 1003 NodeA to Destination is asymmetric with "S" bit remains to "0". 1005 Appendix B. Changelog 1007 B.1. Changes to version 02 1009 o Include the support for source routing. 1011 o Import some features from [RFC6997], e.g., choice between hop-by- 1012 hop and source routing, the "L" bit which determines the duration 1013 of residence in the DAG, MaxRank, etc. 1015 o Define new target option for AODV-RPL, including the Destination 1016 Sequence Number in it. Move the TargNode address in RREQ option 1017 and the OrigNode address in RREP option into ADOV-RPL Target 1018 Option. 1020 o Support route discovery for multiple targets in one RREQ-DIO. 1022 o New InstanceID pairing mechanism. 1024 B.2. Changes to version 03 1026 o Updated RREP option format. Remove the 'T' bit in RREP option. 1028 o Using the same RPLInstanceID for RREQ and RREP, no need to update 1029 [RFC6550]. 1031 o Explanation of Shift field in RREP. 1033 o Multiple target options handling during transmission. 1035 Authors' Addresses 1037 Satish Anamalamudi 1038 SRM University-AP 1039 Amaravati Campus 1040 Amaravati, Andhra Pradesh 522 502 1041 India 1043 Email: satishnaidu80@gmail.com 1045 Mingui Zhang 1046 Huawei Technologies 1047 No. 156 Beiqing Rd. Haidian District 1048 Beijing 100095 1049 China 1051 Email: zhangmingui@huawei.com 1053 Abdur Rashid Sangi 1054 Huaiyin Institute of Technology 1055 No.89 North Beijing Road, Qinghe District 1056 Huaian 223001 1057 P.R. China 1059 Email: sangi_bahrian@yahoo.com 1060 Charles E. Perkins 1061 Futurewei 1062 2330 Central Expressway 1063 Santa Clara 95050 1064 Unites States 1066 Email: charliep@computer.org 1068 S.V.R Anand 1069 Indian Institute of Science 1070 Bangalore 560012 1071 India 1073 Email: anand@ece.iisc.ernet.in 1075 Bing Liu 1076 Huawei Technologies 1077 No. 156 Beiqing Rd. Haidian District 1078 Beijing 100095 1079 China 1081 Email: remy.liubing@huawei.com