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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) ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ROLL J. Hui 3 Internet-Draft Cisco 4 Intended status: Standards Track R. Kelsey 5 Expires: July 28, 2013 Silicon Labs 6 January 24, 2013 8 Multicast Protocol for Low power and Lossy Networks (MPL) 9 draft-ietf-roll-trickle-mcast-03 11 Abstract 13 This document specifies the Multicast Protocol for Low power and 14 Lossy Networks (MPL) that provides IPv6 multicast forwarding in 15 constrained networks. MPL avoids the need to construct or maintain 16 any multicast forwarding topology, disseminating messages to all MPL 17 forwarders in an MPL domain. MPL uses the Trickle algorithm to 18 manage message transmissions for both control and data-plane 19 messages. Different Trickle parameter configurations allow MPL to 20 trade between dissemination latency and transmission efficiency. 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on July 28, 2013. 39 Copyright Notice 41 Copyright (c) 2013 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 3. Applicability Statement . . . . . . . . . . . . . . . . . . . 5 59 4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6 60 4.1. Information Base Overview . . . . . . . . . . . . . . . . 6 61 4.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 6 62 4.3. Signaling Overview . . . . . . . . . . . . . . . . . . . . 7 63 5. MPL Constants . . . . . . . . . . . . . . . . . . . . . . . . 9 64 5.1. Multicast Addresses . . . . . . . . . . . . . . . . . . . 9 65 5.2. Message Types . . . . . . . . . . . . . . . . . . . . . . 9 66 5.3. MPL Forwarder Parameters . . . . . . . . . . . . . . . . . 9 67 5.4. Trickle Parameters . . . . . . . . . . . . . . . . . . . . 9 68 6. Protocol Message Formats . . . . . . . . . . . . . . . . . . . 11 69 6.1. MPL Option . . . . . . . . . . . . . . . . . . . . . . . . 11 70 6.2. MPL Control Message . . . . . . . . . . . . . . . . . . . 12 71 6.3. MPL Seed Info . . . . . . . . . . . . . . . . . . . . . . 13 72 7. Information Base . . . . . . . . . . . . . . . . . . . . . . . 15 73 7.1. Local Interface Set . . . . . . . . . . . . . . . . . . . 15 74 7.2. Domain Set . . . . . . . . . . . . . . . . . . . . . . . . 15 75 7.3. Seed Set . . . . . . . . . . . . . . . . . . . . . . . . . 15 76 7.4. Buffered Message Set . . . . . . . . . . . . . . . . . . . 15 77 8. MPL Domains . . . . . . . . . . . . . . . . . . . . . . . . . 17 78 9. MPL Seed Sequence Numbers . . . . . . . . . . . . . . . . . . 18 79 10. MPL Data Messages . . . . . . . . . . . . . . . . . . . . . . 19 80 10.1. MPL Data Message Generation . . . . . . . . . . . . . . . 19 81 10.2. MPL Data Message Transmission . . . . . . . . . . . . . . 19 82 10.3. MPL Data Message Processing . . . . . . . . . . . . . . . 20 83 11. MPL Control Messages . . . . . . . . . . . . . . . . . . . . . 22 84 11.1. MPL Control Message Generation . . . . . . . . . . . . . . 22 85 11.2. MPL Control Message Transmission . . . . . . . . . . . . . 22 86 11.3. MPL Control Message Processing . . . . . . . . . . . . . . 23 87 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25 88 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 89 13.1. MPL Option Type . . . . . . . . . . . . . . . . . . . . . 26 90 13.2. MPL ICMPv6 Type . . . . . . . . . . . . . . . . . . . . . 26 91 13.3. Well-known Multicast Addresses . . . . . . . . . . . . . . 26 92 14. Security Considerations . . . . . . . . . . . . . . . . . . . 27 93 15. Normative References . . . . . . . . . . . . . . . . . . . . . 28 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 96 1. Introduction 98 Low power and Lossy Networks typically operate with strict resource 99 constraints in communication, computation, memory, and energy. Such 100 resource constraints may preclude the use of existing IPv6 multicast 101 routing and forwarding mechanisms. Traditional IP multicast delivery 102 typically relies on topology maintenance mechanisms to discover and 103 maintain routes to all subscribers of a multicast group. However, 104 maintaining such topologies in LLNs is costly and may not be feasible 105 given the available resources. 107 Memory constraints may limit devices to maintaining links/routes to 108 one or a few neighbors. For this reason, the Routing Protocol for 109 LLNs (RPL) specifies both storing and non-storing modes [RFC6550]. 110 The latter allows RPL routers to maintain only one or a few default 111 routes towards a LLN Border Router (LBR) and use source routing to 112 forward messages away from the LBR. For the same reasons, a LLN 113 device may not be able to maintain a multicast routing topology when 114 operating with limited memory. 116 Furthermore, the dynamic properties of wireless networks can make the 117 cost of maintaining a multicast routing topology prohibitively 118 expensive. In wireless environments, topology maintenance may 119 involve selecting a connected dominating set used to forward 120 multicast messages to all nodes in an administrative domain. 121 However, existing mechanisms often require two-hop topology 122 information and the cost of maintaining such information grows 123 polynomially with network density. 125 This document specifies the Multicast Protocol for Low power and 126 Lossy Networks (MPL), which provides IPv6 multicast forwarding in 127 constrained networks. MPL avoids the need to construct or maintain 128 any multicast routing topology, disseminating multicast messages to 129 all MPL forwarders in an MPL domain. By using the Trickle algorithm 130 [RFC6206], MPL requires only small, constant state for each MPL 131 device that initiates disseminations. The Trickle algorithm also 132 allows MPL to be density-aware, allowing the communication rate to 133 scale logarithmically with density. 135 2. Terminology 137 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 138 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 139 "OPTIONAL" in this document are to be interpreted as described in 140 [RFC2119]. 142 The following terms are used throughout this document: 144 MPL Forwarder - A router that implements this protocol. A MPL 145 Forwarder is equipped with at least one MPL 146 Interface. 148 MPL Interface - An MPL Forwarder's attachment to a 149 communications medium, over which it transmits 150 and receives MPL Data Messages and MPL Control 151 Messages according to this specification. An MPL 152 Interface is assigned one or more unicast 153 addresses and is subscribed to one or more MPL 154 Domain Addresses. 156 MPL Domain Address - A multicast address that identifies the set of 157 MPL Interfaces within an MPL Domain. MPL Data 158 Messages disseminated in an MPL Domain have the 159 associated MPL Domain Address as their 160 destination address. 162 MPL Domain - A scope zone, as defined in [RFC4007], in which 163 MPL Interfaces subscribe to the same MPL Domain 164 Address and participate in disseminating MPL Data 165 Messages. 167 MPL Data Message - A multicast message that is used to communicate 168 a multicast payload between MPL Forwarders and 169 contains an MPL Option in the IPv6 header. A MPL 170 Data Message has its destination address set to 171 the MPL Domain Address. 173 MPL Control Message - A link-local multicast message that is used to 174 communicate information about recently received 175 MPL Data Messages to neighboring MPL Forwarders. 177 MPL Seed - An MPL Forwarder that generates MPL Data 178 Messages and serves as an entry point into an MPL 179 Domain. 181 3. Applicability Statement 183 This protocol is an IPv6 multicast forwarding protocol for Low-Power 184 and Lossy Networks. By implementing a controlled dissemination using 185 the Trickle algorithm, this protocol is designed for networks that 186 communicate using low-power and lossy links with widely varying 187 topologies in both the space and time dimensions. 189 4. Protocol Overview 191 The goal of MPL is to deliver multicast messages to all interfaces 192 that subscribe to the multicast messages' destination address within 193 an MPL Domain. 195 4.1. Information Base Overview 197 A node records necessary protocol state in the following information 198 sets: 200 o The Local Interface Set records the set of local MPL Interfaces 201 and the unicast addresses assigned to those MPL Interfaces. 203 o The Domain Set records the set of MPL Domain Addresses and the 204 local MPL Interfaces that subscribe to those addresses. 206 o The Seed Set records information about received MPL Data Messages 207 received from an MPL Seed. The Seed Set maintains the minimum 208 sequence number that the MPL Forwarder is willing to receive or 209 has buffered in its Buffered Message Set. MPL uses the Seed Set 210 and Buffered Message Set to determine when to accept an MPL Data 211 Message, process its payload, and retransmit it. 213 o The Buffered Message Set records recently received MPL Data 214 Messages from an MPL Seed. MPL Data Messages resident in the 215 Buffered Message Set have sequence numbers that are greater than 216 or equal to the minimum threshold maintained in the Seed Set. MPL 217 uses the Buffered Message Set to store MPL Data Messages that may 218 be transmitted by the MPL Forwarder for forwarding. 220 4.2. Overview 222 MPL achieves its goal by implementing a controlled flood that 223 attempts to disseminate the multicast data message to all interfaces 224 within an MPL Domain. MPL performs the following tasks to 225 disseminate a multicast message: 227 o When having a multicast message to forward into an MPL Domain, the 228 MPL Seed generates an MPL Data Message that includes the MPL Seed 229 Identifier, a newly generated sequence number, and the multicast 230 message. If the multicast destination address is not the MPL 231 Domain Address, IP-in-IP [RFC2473] is used to encapsulate the 232 multicast message in the MPL Data Message. 234 o Upon receiving an MPL Data Message, the MPL Forwarder extracts the 235 MPL Seed and sequence number and determines whether or not the MPL 236 Data Message was previously received using the Seed Set and 237 Buffered Message Set. 239 * If the sequence number is less than the lower-bound sequence 240 number maintained in the Seed Set or a message with the same 241 sequence number exists within the Buffered Message Set, the MPL 242 Forwarder marks the MPL Data Message as old. 244 * Otherwise, the MPL Forwarder marks the MPL Data Message as new. 246 o For each newly received MPL Data Message, an MPL Forwarder updates 247 the Seed Set, adds the MPL Data Message into the Buffered Message 248 Set, processes its payload, and multicasts the MPL Data Message a 249 number of times on all MPL Interfaces participating in the same 250 MPL Domain to forward the message. 252 o Each MPL Forwarder may periodically link-local multicast MPL 253 Control Messages on MPL Interfaces to communicate information 254 contained in the MPL Forwarder's Seed Set and Buffered Message 255 Sets. 257 o Upon receiving an MPL Control Message, an MPL Forwarder determines 258 whether there are any new MPL Data Messages that have yet to be 259 received by the MPL Control Message's source and multicasts those 260 MPL Data Messages. 262 MPL's configuration parameters allow two forwarding strategies for 263 disseminating MPL Data Messages. 265 Proactive Forwarding - With proactive forwarding, an MPL Forwarder 266 schedules transmissions of MPL Data Messages using the Trickle 267 algorithm, without any prior indication that neighboring nodes 268 have yet to receive the message. After transmitting the MPL Data 269 Message a limited number of times, the MPL forwarder may terminate 270 proactive forwarding for the MPL Data Message message. 272 Reactive Forwarding - With reactive forwarding, an MPL Forwarder 273 link-local multicasts MPL Control Messages using the Trickle 274 algorithm [RFC6206]. MPL Forwarders use MPL Control Messages to 275 discover new MPL Data Messages that have not yet been received. 276 When discovering that a neighboring MPL Forwarder has not yet 277 received a new MPL Data Message, the MPL Forwarder schedules those 278 MPL Data Messages for transmission using the Trickle algorithm. 280 4.3. Signaling Overview 282 This protocol generates and processes the following messages: 284 MPL Data Message - Generated by an MPL Seed to deliver a multicast 285 message across an MPL Domain. The MPL Data Message's source is an 286 address in the Local Interface Set of the MPL Seed that generated 287 the message and is valid within the MPL Domain. The MPL Data 288 Message's destination is the MPL Domain Address corresponding to 289 the MPL Domain. An MPL Data Message contains: 291 * The Seed Identifier of the MPL Seed that generated the MPL Data 292 Message. 294 * The sequence number of the MPL Seed that generated the MPL Data 295 Message. 297 * The original multicast message. 299 MPL Control Message - Generated by an MPL Forwarder to communicate 300 information contained in the Seed Set and Buffered Message Set to 301 neighboring MPL Forwarders. An MPL Control Message contains a 302 list of tuples for each entry in the Seed Set. Each tuple 303 contains: 305 * The minimum sequence number maintained in the Seed Set for the 306 MPL Seed. 308 * A bit-vector indicating the sequence numbers of MPL Data 309 Messages resident in the Buffered Message Set for the MPL Seed, 310 where the first bit represents a sequence number equal to the 311 minimum threshold maintained in the Seed Set. 313 * The length of the bit-vector. 315 5. MPL Constants 317 This section describes various program and networking constants used 318 by MPL. 320 5.1. Multicast Addresses 322 MPL makes use of MPL Domain Addresses to identify MPL Interfaces of 323 an MPL Domain. By default, MPL Forwarders subscribe to the 324 ALL_MPL_FORWARDERS multicast address with a scope value of 3 (subnet- 325 local). 327 For each MPL Domain Address that an MPL Interface subscribes to, the 328 MPL Interface MUST also subscribe to the MPL Domain Address with a 329 scope value of 2 (link-local) when reactive forwarding is in use. 330 MPL Forwarders use the link-scoped MPL Domain Address to communicate 331 MPL Control Messages to neighboring (i.e. on-link) MPL Forwarders. 333 5.2. Message Types 335 MPL defines an IPv6 Option for carrying an MPL Seed Identifier and a 336 sequence number within an MPL Data Message. The IPv6 Option Type has 337 value MPL_OPT_TYPE. 339 MPL defines an ICMPv6 Message (MPL Control Message) for communicating 340 information contained in its Seed Set and Buffered Message Set to 341 neighboring MPL Forwarders. The MPL Control Message has ICMPv6 Type 342 MPL_ICMP_TYPE. 344 5.3. MPL Forwarder Parameters 346 PROACTIVE_FORWARDING A boolean value that indicates whether the MPL 347 Forwarder should schedule MPL Data Message transmissions after 348 receiving them for the first time. 350 SEED_SET_LIFETIME The minimum lifetime for an entry in the Seed Set. 352 5.4. Trickle Parameters 354 As specified in [RFC6206], a Trickle timer runs for a defined 355 interval and has three configuration parameters: the minimum interval 356 size Imin, the maximum interval size Imax, and a redundancy constant 357 k. 359 This specification defines a fourth Trickle configuration parameter, 360 TimerExpirations, which indicates the number of Trickle timer 361 expiration events that occur before terminating the Trickle 362 algorithm. 364 Each MPL forwarder maintains a separate Trickle parameter set for MPL 365 Data Message and MPL Control Message transmissions. The Trickle 366 parameters are listed below: 368 DATA_MESSAGE_IMIN The minimum Trickle timer interval, as defined in 369 [RFC6206], for MPL Data Message transmissions. 371 DATA MESSAGE_IMAX The maximum Trickle timer interval, as defined in 372 [RFC6206], for MPL Data Message transmissions. 374 DATA_MESSAGE_K The redundancy constant, as defined in [RFC6206], for 375 MPL Data Message transmissions. 377 DATA_MESSAGE_TIMER_EXPIRATIONS The number of Trickle timer 378 expirations that occur before terminating the Trickle algorithm 379 for MPL Data Message transmissions. 381 CONTROL_MESSAGE_IMIN The minimum Trickle timer interval, as defined 382 in [RFC6206], for MPL Control Message transmissions. 384 CONTROL_MESSAGE_IMAX The maximum Trickle timer interval, as defined 385 in [RFC6206], for MPL Control Message transmissions. 387 CONTROL_MESSAGE_K The redundancy constant, as defined in [RFC6206], 388 for MPL Control Message transmissions. 390 CONTROL_MESSAGE_TIMER_EXPIRATIONS The number of Trickle timer 391 expirations that occur before terminating the Trickle algorithm 392 for MPL Control Message transmissions. 394 It is RECOMMENDED that all MPL Forwarder within an MPL Domain use the 395 same values for the Trickle Parameters above, as specified in 396 [RFC6206]. 398 6. Protocol Message Formats 400 The protocol messages generated and processed by an MPL Forwarder are 401 described in this section. 403 6.1. MPL Option 405 The MPL Option is carried in MPL Data Messages in an IPv6 Hop-by-Hop 406 Options header, immediately following the IPv6 header. The MPL 407 Option has the following format: 409 0 1 2 3 410 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 1 411 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 412 | Option Type | Opt Data Len | 413 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 414 | S |M|V| rsv | sequence | seed-id (optional) | 415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 417 Option Type MPL_OPT_TYPE 419 Opt Data Len Length of the Option Data field in octets. 421 S 2-bit unsigned integer. Identifies the length of 422 seed-id. 0 indicates that the seed-id is the IPv6 423 Source Address and not included in the MPL 424 Option. 1 indicates that the seed-id is a 16-bit 425 unsigned integer. 2 indicates that the seed-id is 426 a 64-bit unsigned integer. 3 indicates that the 427 seed-id is a 128-bit unsigned integer. 429 M 1-bit flag. 1 indicates that the value in 430 sequence is known to be the largest sequence 431 number that was received from the MPL Seed. 433 V 1-bit flag. 0 indicates that the MPL Option 434 conforms to this specification. MPL Options 435 received in which this flag is 1 MUST be dropped. 437 rsv 4-bit reserved field. MUST be set to 0 on 438 transmission and ignored on reception. 440 sequence 8-bit unsigned integer. Identifies relative 441 ordering of MPL Data Messages from the MPL Seed 442 identified by seed-id. 444 seed-id Uniquely identifies the MPL Seed that initiated 445 dissemination of the MPL Data Message. The size 446 of seed-id is indicated by the S field. 448 The Option Data (in particular the M flag) of the MPL Option is 449 updated by MPL Forwarders as the MPL Data Message is forwarded. 450 Nodes that do not understand the MPL Option MUST discard the MPL Data 451 Message. Thus, according to [RFC2460] the three high order bits of 452 the Option Type are set to '011'. The Option Data length is 453 variable. 455 The seed-id uniquely identifies an MPL Seed. When seed-id is 128 456 bits (S=3), the MPL seed MAY use an IPv6 address assigned to one of 457 its interfaces that is unique within the MPL domain. Managing MPL 458 Seed Identifiers is not within scope of this document. 460 The sequence field establishes a total ordering of MPL Data Messages 461 generated by an MPL Seed for an MPL Domain. The MPL Seed MUST 462 increment the sequence field's value on each new MPL Data Message 463 that it generates for an MPL Domain. Implementations MUST follow the 464 Serial Number Arithmetic as defined in [RFC1982] when incrementing a 465 sequence value or comparing two sequence values. 467 Future updates to this specification may define additional fields 468 following the seed-id field. 470 6.2. MPL Control Message 472 An MPL Forwarder uses ICMPv6 messages to communicate information 473 contained in its Seed Set and Buffered Message Set to neighboring MPL 474 Forwarders. The MPL Control Message has the following format: 476 0 1 2 3 477 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 1 478 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 479 | Type | Code | Checksum | 480 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 481 | | 482 . MPL Seed Info[1..n] . 483 . . 484 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 486 IP Fields: 488 Source Address A link-local address assigned to the sending 489 interface. 491 Destination Address The link-scoped MPL Domain Address corresponding 492 to the MPL Domain. 494 Hop Limit 255 496 ICMPv6 Fields: 498 Type MPL_ICMP_TYPE 500 Code 0 502 Checksum The ICMP checksum. See [RFC4443]. 504 MPL Seed Info[1..n] List of one or more MPL Seed Info entries. 506 The MPL Control Message indicates the sequence numbers of MPL Data 507 Messages that are within the Buffered Message Set. The MPL Control 508 Message also indicates the sequence numbers of MPL Data Messages that 509 an MPL Forwarder is willing to receive. The MPL Control Message 510 allows neighboring MPL Forwarders to determine whether there are any 511 new MPL Data Messages to exchange. 513 6.3. MPL Seed Info 515 An MPL Seed Info encodes the minimum sequence number for the MPL Seed 516 maintained in the Seed Set. The MPL Seed Info also indicates the 517 sequence numbers of MPL Data Messages generated by the MPL Seed 518 within the Buffered Message Set. The MPL Seed Info has the following 519 format: 521 0 1 2 3 522 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 1 523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 524 | min-seqno | bm-len | S | seed-id (0/2/8/16 octets) | 525 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 526 | | 527 . buffered-mpl-messages (variable length) . 528 . . 529 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 531 min-seqno 8-bit unsigned integer. The lower-bound sequence 532 number for the MPL Seed. 534 bm-len 6-bit unsigned integer. The size of buffered- 535 mpl-messages in octets. 537 S 2-bit unsigned integer. Identifies the length of 538 seed-id. 0 indicates that the seed-id value is 539 the IPv6 Source Address and not included in the 540 MPL Seed Info. 1 indicates that the seed-id value 541 is a 16-bit unsigned integer. 2 indicates that 542 the seed-id value is a 64-bit unsigned integer. 3 543 indicates that the seed-id is a 128-bit unsigned 544 integer. 546 seed-id Variable-length unsigned integer. Indicates the 547 MPL Seed associated with this MPL Seed Info. 549 buffered-mpl-messages Variable-length bit vector. Identifies the 550 sequence numbers of MPL Data Messages maintained 551 in the Buffered Message Set for the MPL Seed. 552 The sequence number is determined by min-seqno + 553 i, where i is the bit offset within buffered-mpl- 554 messages. 556 The MPL Seed Info does not have any octet alignment requirement. 558 7. Information Base 560 7.1. Local Interface Set 562 The Local Interface Set records the local MPL Interfaces of an MPL 563 Forwarder. The Local Interface Set consists of Local Interface 564 Tuples, one per MPL Interface: (AddressSet). 566 AddressSet - a set of unicast addresses assigned to the MPL 567 Interface. 569 7.2. Domain Set 571 The Domain Set records the MPL Interfaces that subscribe to each MPL 572 Domain Address. The Domain Set consists of MPL Domain Tuples, one 573 per MPL Domain: (MPLInterfaceSet). 575 MPLInterfaceSet - a set of MPL Interfaces that subscribe to the MPL 576 Domain Address that identifies the MPL Domain. 578 7.3. Seed Set 580 The Seed Set records a sliding window used to determine the sequence 581 numbers of MPL Data Messages that an MPL Forwarder is willing to 582 accept generated by the MPL Seed. It consists of MPL Seed Tuples: 583 (SeedID, MinSequence, Lifetime). 585 SeedID - the identifier for the MPL Seed. 587 MinSequence - a lower-bound sequence number that represents the 588 sequence number of the oldest MPL Data Message the MPL Forwarder 589 is willing to receive or transmit. An MPL Forwarder MUST ignore 590 any MPL Data Message that has sequence value less than than 591 MinSequence. 593 Lifetime - indicates the minimum lifetime of the Seed Set entry. An 594 MPL Forwarder MUST NOT free a Seed Set entry before its expires. 596 7.4. Buffered Message Set 598 The Buffered Message Set records recently received MPL Data Messages 599 from an MPL Seed. An MPL Forwarder uses the Buffered Message Set to 600 buffer MPL Data Messages while the MPL Forwarder is forwarding the 601 MPL Data Messages. The Buffered Message Set consists of Buffered 602 Message Tuples: (SeedID, SequenceNumber, DataMessage). 604 SeedID - the identifier for the MPL Seed that generated the MPL Data 605 Message. 607 SequenceNumber - the sequence number for the MPL Data Message. 609 DataMessage - the MPL Data Message. 611 All MPL Data Messages within the Buffered Message Set MUST have a 612 sequence number greater than or equal to MinSequence for the 613 corresponding SeedID. When increasing MinSequence for an MPL Seed, 614 the MPL Forwarder MUST delete any MPL Data Messages from the Buffered 615 Message Set that have sequence numbers less than MinSequence. 617 8. MPL Domains 619 An MPL Domain is a scope zone, as defined in [RFC4007], in which MPL 620 Interfaces subscribe to the same MPL Domain Address and participate 621 in disseminating MPL Data Messages. 623 By default, an MPL Forwarder MUST participate in an MPL Domain 624 identified by the ALL_MPL_FORWARDERS multicast address with a scope 625 value of 3 (subnet-local). 627 An MPL Forwarder MAY participate in additional MPL Domains identified 628 by other multicast addresses. An MPL Interface MUST subscribe to the 629 MPL Domain Addresses for the MPL Domains that it participates in. 630 The allocation of other multicast addresses is out of scope. 632 For each MPL Domain Address that an MPL Interface subscribes to, the 633 MPL Interface MUST also subscribe to the same MPL Domain Address with 634 a scope value of 2 (link-local) when reactive forwarding is in use 635 (i.e. when communicating MPL Control Messages). 637 9. MPL Seed Sequence Numbers 639 Each MPL Seed maintains a sequence number for each MPL Domain that it 640 serves. The sequence numbers are included in MPL Data Messages 641 generated by the MPL Seed. The MPL Seed MUST increment the sequence 642 number for each MPL Data Message that it generates for an MPL Domain. 643 Implementations MUST follow the Serial Number Arithmetic as defined 644 in [RFC1982] when incrementing a sequence value or comparing two 645 sequence values. This sequence number is used to establish a total 646 ordering of MPL Data Messages generated by an MPL Seed for an MPL 647 Domain. 649 10. MPL Data Messages 651 10.1. MPL Data Message Generation 653 MPL Data Messages are generated by MPL Seeds when they enter the MPL 654 Domain. All MPL Data messages have the following properties: 656 o The IPv6 Source Address MUST be an address in the AddressSet of a 657 corresponding MPL Interface and MUST be valid within the MPL 658 Domain. 660 o The IPv6 Destination Address MUST be set to the MPL Domain Address 661 corresponding to the MPL Domain. 663 o A MPL Data Message MUST contain an MPL Option in its IPv6 Header 664 to identify the MPL Seed that generated the message and the 665 ordering relative to other MPL Data Messages generated by the MPL 666 Seed. 668 When the source address is in the AddressList of an MPL Interface 669 corresponding to the MPL Domain Address and the destination address 670 is the MPL Domain Address, the application message and the MPL Data 671 Message MAY be identical. In other words, the MPL Data Message may 672 contain a single IPv6 header that includes the MPL Option. 674 Otherwise, IPv6-in-IPv6 encapsulation MUST be used to satisfy the MPL 675 Data Message requirements listed above [RFC2473]. The complete IPv6- 676 in-IPv6 message forms an MPL Data Message. The outer IPv6 header 677 conforms to the MPL Data Message requirements listed above. The 678 encapsulated IPv6 datagram encodes the multicast data message that is 679 communicated beyond the MPL Domain. 681 10.2. MPL Data Message Transmission 683 An MPL Forwarder manages transmission of MPL Data Messages in the 684 Buffered Message set using the Trickle algorithm [RFC6206]. An MPL 685 Forwarder MUST use a separate Trickle timer for each MPL Data Message 686 that it is actively forwarding. In accordance with Section 5 of RFC 687 6206 [RFC6206], this document defines the following: 689 o This document defines a "consistent" transmission as receiving an 690 MPL Data Message that has the same seed-id and sequence value as 691 the MPL Data Message managed by the Trickle timer. 693 o This document defines an "inconsistent" transmission as receiving 694 an MPL Data Message that has the same seed-id value and the M flag 695 set, but has a sequence value less than MPL Data Message managed 696 by the Trickle timer. 698 o This document does not define any external "events". 700 o This document defines MPL Data Messages as Trickle messages. 702 o The actions outside the Trickle algorithm that the protocol takes 703 involve managing Seed Set and Buffered Message Set 705 As specified in [RFC6206], a Trickle timer has three variables: the 706 current interval size I, a time within the current interval t, and a 707 counter c. MPL defines a fourth variable, e, which counts the number 708 of Trickle timer expiration events since the Trickle timer was last 709 reset. 711 After DATA_MESSAGE_TIMER_EXPIRATIONS Trickle timer events, the MPL 712 Forwarder MUST disable the Trickle timer. When a buffered MPL Data 713 Message does not have an associated Trickle timer, the MPL Forwarder 714 MAY delete the message from the Buffered Message Set by advancing 715 MinSequence of the corresponding MPL Seed in the Seed Set. When the 716 MPL Forwarder no longer buffers any messages for an MPL Seed, the MPL 717 Forwarder MUST NOT increment MinSequence for that MPL Seed. 719 When transmitting an MPL Data Message, the MPL Forwarder MUST either 720 set the M flag to zero or set it to a level that indicates whether or 721 not the message's sequence number is the largest value that has been 722 received from the MPL Seed. 724 10.3. MPL Data Message Processing 726 Upon receiving an MPL Data Message, the MPL Forwarder first processes 727 the MPL Option and updates the Trickle timer associated with the MPL 728 Data Message if one exists. 730 Upon receiving an MPL Data Message, an MPL Forwarder MUST perform one 731 of the following actions: 733 o Accept the message and enter the MPL Data Message in the Buffered 734 Message Set. 736 o Accept the message and update the corresponding MinSequence in the 737 Seed Set to 1 greater than the message's sequence number. 739 o Discard the message without any change to the MPL Information 740 Base. 742 If a Seed Set entry exists for the MPL Seed, the MPL Forwarder MUST 743 discard the MPL Data Message if its sequence number is less than 744 MinSequence or exists in the Buffered Message Set. 746 If a Seed Set entry does not exist for the MPL Seed, the MPL 747 Forwarder MUST create a new entry for the MPL Seed before accepting 748 the MPL Data Message. 750 If memory is limited, an MPL Forwarder SHOULD reclaim memory 751 resources by: 753 o Incrementing MinSequence entries in the Seed Set and deleting MPL 754 Data Messages in the Buffered Message Set that fall below the 755 corresponding MinSequence value. 757 o Deleting other Seed Set entries that have expired and the 758 corresponding MPL Data Messages in the Buffered Message Set. 760 If the MPL Forwarder accepts the MPL Data Message, the MPL Forwarder 761 MUST perform the following actions: 763 o If PROACTIVE_PROPAGATION is true, the MPL Forwarder MUST 764 initialize and start a Trickle timer for the MPL Data Message. 766 o If the MPL Control Message Trickle timer is not running and 767 CONTROL_MESSAGE_TIMER_EXPIRATIONS is non-zero, the MPL Forwarder 768 MUST initialize and start the MPL Control Message Trickle timer. 770 o If the MPL Control Message Trickle timer is running, the MPL 771 Forwarder MUST reset the MPL Control Message Trickle timer. 773 11. MPL Control Messages 775 11.1. MPL Control Message Generation 777 An MPL Forwarder generates MPL Control Messages to communicate its 778 Seed Set and Buffered Message Set to neighboring MPL Forwarders. 779 Each MPL Control Message is generated according to Section 6.2, with 780 an MPL Seed Info for each entry in Seed Set. Each MPL Seed Info entry 781 has the following content: 783 o S set to the size of the seed-id field in the MPL Seed Info entry. 785 o min-seqno set to MinSequence of the MPL Seed. 787 o bm-len set to the size of buffered-mpl-messages in octets. 789 o seed-id set to the MPL seed identifier. 791 o buffered-mpl-messages with each bit representing whether or not an 792 MPL Data Message with the corresponding sequence number exists in 793 the Buffered Message Set. The i'th bit represents a sequence 794 number of min-seqno + i. '0' indicates that the corresponding MPL 795 Data Message does not exist in the Buffered Message Set. '1' 796 indicates that the corresponding MPL Data Message does exist in 797 the Buffered Message Set. 799 11.2. MPL Control Message Transmission 801 An MPL Forwarder transmits MPL Control Messages using the Trickle 802 algorithm. A MPL forwarder maintains a single Trickle timer for each 803 MPL Domain. When CONTROL_MESSAGE_TIMER_EXPIRATIONS is 0, the MPL 804 Forwarder does not execute the Trickle algorithm and does not 805 transmit MPL Control Messages. In accordance with Section 5 of RFC 806 6206 [RFC6206], this document defines the following: 808 o This document defines a "consistent" transmission as receiving an 809 MPL Control Message that indicates neither the receiving nor 810 transmitting node has new MPL Data Message. 812 o This document defines an "inconsistent" transmission as receiving 813 an MPL Control Message that indicates either the receiving or 814 transmitting node has at least one new MPL Data Message to offer. 816 o This document defines an "event" as increasing MinSequence of any 817 entry in the Seed Set or adding a message to the Buffered Message 818 Set. 820 o This document defines an MPL Control Message as a Trickle message. 822 As specified in [RFC6206], a Trickle timer has three variables: the 823 current interval size I, a time within the current interval t, and a 824 counter c. MPL defines a fourth variable, e, which counts the number 825 of Trickle timer expiration events since the Trickle timer was last 826 reset. After CONTROL_MESSAGE_TIMER_EXPIRATIONS Trickle timer events, 827 the MPL Forwarder MUST disable the Trickle timer. 829 11.3. MPL Control Message Processing 831 An MPL Forwarder processes each MPL Control Message that it receives 832 to determine if it has any new MPL Data Messages to receive or offer. 834 An MPL Forwarder determines if a new MPL Data Message has not been 835 received from a neighboring node if any of the following conditions 836 hold true: 838 o The MPL Control Message includes an MPL Seed that does not exist 839 in the Seed Set. 841 o The MPL Control Message indicates that the neighbor has an MPL 842 Data Message in its Buffered Message Set with sequence number 843 greater than MinSequence (i.e. the i-th bit is set to 1 and min- 844 seqno + i > MinSequence) and is not included in the MPL 845 Forwarder's Buffered Message Set. 847 When an MPL Forwarder determines that it has not yet received an MPL 848 Data Message buffered by a neighboring device, the MPL Forwarder MUST 849 reset its Trickle timer associated with MPL Control Message 850 transmissions. If an MPL Control Message Trickle timer is not 851 running, the MPL Forwarder MUST initialize and start a new Trickle 852 timer. 854 An MPL Forwarder determines if an MPL Data Message in the Buffered 855 Message Set has not yet been received by a neighboring MPL Forwarder 856 if any of the following conditions hold true: 858 o The MPL Control Message does not include an MPL Seed for the MPL 859 Data Message. 861 o The MPL Data Message's sequence number is greater than or equal to 862 min-seqno and not included in the neighbor's Buffered Message Set 863 (i.e. the MPL Data Message's sequence number does not have a 864 corresponding bit in buffered-mpl-messages set to 1). 866 When an MPL Forwarder determines that it has at least one MPL Data 867 Message in its Buffered Message Set that has not yet been received by 868 a neighbor, the MPL Forwarder MUST reset the MPL Control Message 869 Trickle timer. Additionally, for each of those entries in the 870 Buffered Message Set, the MPL Forwarder MUST reset the Trickle timer 871 and reset e to 0. If a Trickle timer is not associated with the MPL 872 Data Message, the MPL Forwarder MUST initialize and start a new 873 Trickle timer. 875 12. Acknowledgements 877 The authors would like to acknowledge the helpful comments of Robert 878 Cragie, Esko Dijk, Ralph Droms, Paul Duffy, Ulrich Herberg, Owen 879 Kirby, Joseph Reddy, Don Sturek, Dario Tedeschi, and Peter van der 880 Stok, which greatly improved the document. 882 13. IANA Considerations 884 This document defines one IPv6 Option, a type that must be allocated 885 from the IPv6 "Destination Options and Hop-by-Hop Options" registry 886 of [RFC2780]. 888 This document defines one ICMPv6 Message, a type that must be 889 allocated from the "ICMPv6 "type" Numbers" registry of [RFC4443]. 891 This document registers two well-known multicast addresses from the 892 IPv6 multicast address space. 894 13.1. MPL Option Type 896 IANA is requested to allocate an IPv6 Option Type from the IPv6 897 "Destination Options and Hop-by-Hop Options" registry of [RFC2780], 898 as specified in Table 1 below: 900 +--------------+-----+-----+--------------+-------------+-----------+ 901 | Mnemonic | act | chg | rest | Description | Reference | 902 +--------------+-----+-----+--------------+-------------+-----------+ 903 | MPL_OPT_TYPE | 01 | 1 | TBD | MPL Option | This | 904 | | | | (suggested | | Document | 905 | | | | value 01101) | | | 906 +--------------+-----+-----+--------------+-------------+-----------+ 908 Table 1: IPv6 Option Type Allocation 910 13.2. MPL ICMPv6 Type 912 IANA is requested to allocate an ICMPv6 Type from the "ICMPv6 "type" 913 Numbers" registry of [RFC4443], as specified in Table 2 below: 915 +---------------+------+---------------------+---------------+ 916 | Mnemonic | Type | Name | Reference | 917 +---------------+------+---------------------+---------------+ 918 | MPL_ICMP_TYPE | TBD | MPL Control Message | This Document | 919 +---------------+------+---------------------+---------------+ 921 Table 2: IPv6 Option Type Allocation 923 13.3. Well-known Multicast Addresses 925 IANA is requested to allocate an IPv6 multicast address 926 "ALL_MPL_FORWARDERS" from the "Variable Scope Multicast Addresses" 927 sub-registry of the "INTERNET PROTOCOL VERSION 6 MULTICAST ADDRESSES" 928 registry. 930 14. Security Considerations 932 MPL uses sequence numbers to maintain a total ordering of MPL Data 933 Messages from an MPL Seed. The use of sequence numbers allows a 934 denial-of-service attack where an attacker can spoof a message with a 935 sufficiently large sequence number to: (i) flush messages from the 936 Buffered Message List and (ii) increase the MinSequence value for an 937 MPL Seed in the Seed Set. The former side effect allows an attacker 938 to halt the forwarding process of any MPL Data Messages being 939 disseminated. The latter side effect allows an attacker to prevent 940 MPL Forwarders from accepting new MPL Data Messages that an MPL Seed 941 generates while the sequence number is less than MinSequence. 943 More generally, the basic ability to inject messages into a Low-power 944 and Lossy Network can be used as a denial-of-service attack 945 regardless of what forwarding protocol is used. For these reasons, 946 Low-power and Lossy Networks typically employ link-layer security 947 mechanisms to disable an attacker's ability to inject messages. 949 To prevent attackers from injecting packets through an MPL Forwarder, 950 the MPL Forwarder MUST NOT accept or forward MPL Data Messages from a 951 communication interface that does not subscribe to the MPL Domain 952 Address identified in message's destination address. 954 MPL uses the Trickle algorithm to manage message transmissions and 955 the security considerations described in [RFC6206] apply. 957 15. Normative References 959 [RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, 960 August 1996. 962 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 963 Requirement Levels", BCP 14, RFC 2119, March 1997. 965 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 966 (IPv6) Specification", RFC 2460, December 1998. 968 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 969 IPv6 Specification", RFC 2473, December 1998. 971 [RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For 972 Values In the Internet Protocol and Related Headers", 973 BCP 37, RFC 2780, March 2000. 975 [RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and 976 B. Zill, "IPv6 Scoped Address Architecture", RFC 4007, 977 March 2005. 979 [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control 980 Message Protocol (ICMPv6) for the Internet Protocol 981 Version 6 (IPv6) Specification", RFC 4443, March 2006. 983 [RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko, 984 "The Trickle Algorithm", RFC 6206, March 2011. 986 [RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R., 987 Levis, P., Pister, K., Struik, R., Vasseur, JP., and R. 988 Alexander, "RPL: IPv6 Routing Protocol for Low-Power and 989 Lossy Networks", RFC 6550, March 2012. 991 Authors' Addresses 993 Jonathan W. Hui 994 Cisco 995 170 West Tasman Drive 996 San Jose, California 95134 997 USA 999 Phone: +408 424 1547 1000 Email: jonhui@cisco.com 1002 Richard Kelsey 1003 Silicon Labs 1004 25 Thomson Place 1005 Boston, Massachusetts 02210 1006 USA 1008 Phone: +617 951 1225 1009 Email: richard.kelsey@silabs.com