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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 6lo P. Thubert, Ed. 3 Internet-Draft Cisco 4 Updates: 4944 (if approved) C. Bormann 5 Intended status: Standards Track Uni Bremen TZI 6 Expires: January 3, 2016 L. Toutain 7 IMT-TELECOM Bretagne 8 R. Cragie 9 ARM 10 July 02, 2015 12 A Routing Header Dispatch for 6LoWPAN 13 draft-thubert-6lo-routing-dispatch-05 15 Abstract 17 This specification provides a new 6LoWPAN dispatch type for use in 18 Route-over and mixed Mesh-under and Route-over topologies, that 19 reuses the encoding of the mesh type defined in RFC 4944 for pure 20 Mesh-under topologies. This specification also defines a method to 21 compress RPL Option (RFC6553) information and Routing Header type 3 22 (RFC6554), an efficient IP-in-IP technique and opens the way for 23 further routing techniques. This extends 6LoWPAN Transmission of 24 IPv6 Packets (RFC4944), and is applicable to new link-layer types 25 where 6LoWPAN is being defined. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at http://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on January 3, 2016. 44 Copyright Notice 46 Copyright (c) 2015 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 62 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 63 3. Updating RFC 4944 . . . . . . . . . . . . . . . . . . . . . . 5 64 3.1. Reusing Mesh Header (or NALP) Dispatch Space . . . . . . 6 65 3.2. Add A New Dispatch . . . . . . . . . . . . . . . . . . . 6 66 3.3. Use Free Space the the FRAG range . . . . . . . . . . . . 7 67 4. Placement of 6LoRH . . . . . . . . . . . . . . . . . . . . . 7 68 5. General Format . . . . . . . . . . . . . . . . . . . . . . . 7 69 5.1. Elective Format . . . . . . . . . . . . . . . . . . . . . 8 70 5.2. Critical Format . . . . . . . . . . . . . . . . . . . . . 9 71 6. The Routing Header type 3 (RH3) 6LoRH . . . . . . . . . . . . 10 72 7. The RPL Packet Information 6LoRH . . . . . . . . . . . . . . 11 73 7.1. Compressing the RPLInstanceID . . . . . . . . . . . . . . 12 74 7.2. Compressing the SenderRank . . . . . . . . . . . . . . . 13 75 7.3. The Overall RPI-6LoRH encoding . . . . . . . . . . . . . 13 76 8. The IP-in-IP 6LoRH . . . . . . . . . . . . . . . . . . . . . 16 77 9. The Mesh Header 6LoRH . . . . . . . . . . . . . . . . . . . . 17 78 10. The BIER 6LoRH . . . . . . . . . . . . . . . . . . . . . . . 18 79 11. Security Considerations . . . . . . . . . . . . . . . . . . . 20 80 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 81 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20 82 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 83 14.1. Normative References . . . . . . . . . . . . . . . . . . 20 84 14.2. Informative References . . . . . . . . . . . . . . . . . 21 85 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 87 1. Introduction 89 The design of Low Power and Lossy Networks (LLNs) is generally 90 focused on saving energy, which is the most constrained resource of 91 all. The other constraints, such as the memory capacity and the duty 92 cycling of the LLN devices, derive from that primary concern. Energy 93 is often available from primary batteries that are expected to last 94 for years, or is scavenged from the environment in very limited 95 quantities. Any protocol that is intended for use in LLNs must be 96 designed with the primary concern of saving energy as a strict 97 requirement. 99 Controlling the amount of data transmission is one possible venue to 100 save energy. In a number of LLN standards, the frame size is limited 101 to much smaller values than the IPv6 maximum transmission unit (MTU) 102 of 1280 bytes. In particular, an LLN that relies on the classical 103 Physical Layer (PHY) of IEEE 802.14.5 [IEEE802154] is limited to 127 104 bytes per frame. The need to compress IPv6 packets over IEEE 105 802.14.5 led to the 6LoWPAN Header Compression [RFC6282] work 106 (6LoWPAN-HC). 108 Innovative Route-over techniques have been and are still being 109 developed for routing inside a LLN. In a general fashion, such 110 techniques require additional information in the packet to provide 111 loop prevention and to indicate information such as flow 112 identification, source routing information, etc. 114 For reasons such as security and the capability to send ICMP errors 115 back to the source, an original packet must not be tampered with, and 116 any information that must be inserted in or removed from an IPv6 117 packet must be placed in an extra IP-in-IP encapsulation. This is 118 the case when the additional routing information is inserted by a 119 router on the path of a packet, for instance a mesh root, as opposed 120 to the source node. This is also the case when some routing 121 information must be removed from a packet that will flow outside the 122 LLN. 124 As an example, the Routing Protocol for Low Power and Lossy Networks 125 [RFC6550] (RPL) is designed to optimize the routing operations in 126 constrained LLNs. As part of this optimization, RPL requires the 127 addition of RPL Packet Information (RPI) in every packet, as defined 128 in Section 11.2 of [RFC6550]. 130 The RPL Option for Carrying RPL Information in Data-Plane Datagrams 131 [RFC6553] specification indicates how the RPI can be placed in a RPL 132 Option for use in an IPv6 Hop-by-Hop header. This representation 133 demands a total of 8 bytes when in most cases the actual RPI payload 134 requires only 19 bits. Since the Hop-by-Hop header must not flow 135 outside of the RPL domain, it must be removed from packets that leave 136 the domain, and be inserted in packets entering the domain. In both 137 cases, this operation implies an IP-in-IP encapsulation. 139 ------+--------- ^ 140 | Internet | 141 | | Native IPv6 142 +-----+ | 143 | | Border Router (RPL Root) ^ | ^ 144 | | | | | 145 +-----+ | | | IPv6 in 146 | | | | IPv6 147 o o o o | | | + RPI 148 o o o o o o o o o | | | or RH3 149 o o o o o o o o o o | | | 150 o o o o o o o o o | | | 151 o o o o o o o o v v v 152 o o o o 153 LLN 155 Figure 1: IP-in-IP Encapsulation within the LLN 157 Additionally, in the case of the Non-Storing Mode of Operation (MOP), 158 RPL requires a Routing Header type 3 (RH3) as defined in the IPv6 159 Routing Header for Source Routes with RPL [RFC6554] specification, 160 for all packets that are routed down a RPL graph. With Non-Storing 161 RPL, even if the source is a node in the same LLN, the packet must 162 first reach up the graph to the root so that the root can insert the 163 RH3 to go down the graph. In any fashion, whether the packet was 164 originated in a node in the LLN or outside the LLN, and regardless of 165 whether the packet stays within the LLN or not, as long as the source 166 of the packet is not the root itself, the source-routing operation 167 also implies an IP-in-IP encapsulation at the root to insert the RH3. 169 6TiSCH [I-D.ietf-6tisch-architecture] specifies the operation of IPv6 170 over the TimeSlotted Channel Hopping [I-D.ietf-6tisch-tsch] (TSCH) 171 mode of operation of IEEE 802.14.5. The architecture requires the 172 use of both RPL and the 6lo adaptation layer framework ([RFC4944], 173 [RFC6282]) over IEEE 802.14.5. Because it inherits the constraints 174 on the frame size from the MAC layer, 6TiSCH cannot afford to spend 8 175 bytes per packet on the RPI. Hence the requirement for a 6LoWPAN 176 header compression of the RPI. 178 The type of information that needs to be present in a packet inside 179 the LLN but not outside of the LLN varies with the routing operation, 180 but there is overall a need for an extensible compression technique 181 that would simplify the IP-in-IP encapsulation, when needed, and 182 optimally compress existing routing artifacts found in LLNs. 184 This specification extends 6LoWPAN [RFC4944] and in particular reuses 185 the Mesh Header formats that are defined for the Mesh-under use cases 186 so as to carry routing information for Route-over use cases. The 187 specification includes the formats necessary for RPL and is 188 extensible for additional formats. 190 2. Terminology 192 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 193 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 194 "OPTIONAL" in this document are to be interpreted as described in 195 [RFC2119]. 197 The Terminology used in this document is consistent with and 198 incorporates that described in `Terminology in Low power And Lossy 199 Networks' [RFC7102] and [RFC6550]. 201 The terms Route-over and Mesh-under are defined in [RFC6775]. 203 Other terms in use in LLNs are found in [RFC7228]. 205 The term "byte" is used in its now customary sense as a synonym for 206 "octet". 208 3. Updating RFC 4944 210 This draft proposes 3 ways to adapt 6LoWPAN while maintaining 211 backward compatibility with IPv6 over IEEE 802.15.4 [RFC4944]. 213 Option 1 considers that a network where this specification applies 214 is physically separate from a network where the Mesh Header 215 defined in [RFC4944] is used. With that assumption, the Mesh 216 Header dispatch space can be reused. A variation is proposed 217 whereby the NALP pattern 00xxxxxx is reused instead of the Mesh 218 Header pattern. 220 Option 2 defines a new Separator Dispatch value that indicates 221 that no Mesh Header is present in the remainder of the packet. If 222 the 10xxxxxx pattern is found in the packet after this new 223 Separator Dispatch, then this specification applies. It is 224 suggested that the new Separator Dispatch would also enable to 225 reuse patterns 00xxxxxx and 11xxxxxx in the future. 227 Option 3 uses values in pattern 11xxxxxx that are free to this 228 date, avoiding patterns 11000xxx and 11100xxx that are used for 229 the Fragmentation Header as defined in [RFC4944]. 231 3.1. Reusing Mesh Header (or NALP) Dispatch Space 233 Section 5.1 of the IPv6 over IEEE 802.15.4 [RFC4944] specification 234 defines various Dispatch Types and Headers, and in particular a Mesh 235 Header that corresponds to a pattern 10xxxxxx and effectively 236 consumes one third of the whole 6LoWPAN dispatch space for Mesh-under 237 specific applications. 239 This specification reuses the Dispatch space for Route-over and mixed 240 operations. This means that a device that use the Mesh Header as 241 specified in [RFC4944] should not be placed in a same network as a 242 device which operates per this update. This is generally not a 243 problem since a network is classically either Mesh-under OR Route- 244 over. 246 A new implementation of Mesh-under MAY support both types of 247 encoding, and if so, it SHOULD provide a management toggle to enable 248 either mode and it SHOULD use this specification as the default mode. 250 A dispatch space of equivalent size to the Mesh Header was reserved 251 in [RFC4944] for external specifications Not A LowPan (NALP), hoping 252 that such specification could coexist harmlessly on a same network as 253 early 6LoWPAN. 255 It is unclear that this disposition was useful at some point and that 256 NALP was effectively used in a network where 6LoWPAN is deployed. A 257 variation of the suggestion above would be, to use pattern 10xxxxxx 258 instead of pattern 10xxxxxx If deemed necessary, it would be possible 259 to move NALP to some other (smaller) dispatch space. 261 3.2. Add A New Dispatch 263 The suggestion here is not to use the Escape Dispatch, which is not 264 entirely defined at this point, but to block one other dispatch value 265 (say 11111111) to indicate that from that point on, the parsing of 266 the packet should use this specification if the pattern 10xxxxxx is 267 found. 269 The expectation is that if there is a Mesh Header, it is placed early 270 in the packet and from there this specification will apply to any 271 other appearance of the 10xxxxxx pattern. On the other hand, if 272 there is no mesh header, there is a need to indicate so with this new 273 dispatch value, and then any appearance of the 10xxxxxx pattern will 274 be parsed per this specification. 276 It must be noted that the NALP space is really reserved for the first 277 dispatch in the 6LoWPAN packet. Once a packet is identified as a 278 6LoWPAN packet by a first dispatch, the NALP range could be used. 280 Finally, the specification indicates that Fragments Headers must 281 always preceed Routing header. 283 As a result, the 11111111 pattern could be considered a delimiminator 284 between a portion of the frame that is formatted per [RFC4944] on the 285 left, and a portion from which the space for Mesh Header, Fragment 286 Header and NALP can be reused, on the right. This specification 287 would reuse the Mesh Header or the NALP as discuused above, so the 288 text in this specification is not impacted. 290 3.3. Use Free Space the the FRAG range 292 With the third proposal, the 6LoRH uses free bit patterns that are 293 defined in [RFC4944] in the 11 xxxxxx range, avoiding FRAG1 of 11 294 000xxx and FRAGN of 11 100xxx. 296 The third bit, which differentiates FRAG1 from FRAGN in their 297 particular ranges, indicates Elective vs. Critical; the fourth bit is 298 always set to ensure that the 6LoRH does not collision with FRAG1 or 299 FRAGN. The net result is one bit less than in the other proposals 300 for the encoding space in the 6LoRH, which means only 4 bits to 301 encode the length in the Elective format, as discussed below, and 302 only 4 bits TSE. 304 The resulting formats and consequences are detailed in the relevant 305 sections. 307 4. Placement of 6LoRH 309 One or more 6LoRHs MAY be placed in a 6LoWPAN packet and MUST always 310 be placed before the LOWPAN_IPHC [RFC6282]. A 6LoRH MUST always be 311 placed after Fragmentation Header and Mesh Header [RFC6282]. 313 5. General Format 315 The 6LoWPAN Routing Header (6LoRH) may contain source routing 316 information such as a compressed form of RH3, or other sorts of 317 routing information such as the RPL RPI, source and/or destination 318 address, and is extensible for future uses, with the given example of 319 BIER bitmap encoding in Section 10. 321 There are two forms for 6LoRH: 323 Elective (6LoRHE) 325 Critical (6LoRHC) 327 This specification proposes several alternatives for the 6LoRH 328 encoding: 330 Reuse Mesh Header Space in route over mode 332 Same as above, signaled by an initial escape byte 334 a more complex encoding using other coding space that is still 335 free in the 6lo adaptation layer framework 337 The layout of the Elective and Critical forms depends on the encoding 338 of the 6LoRH itself. 340 With the Mesh Header reuse proposal, the 6LoRH reuses the bit 341 patterns that are defined in [RFC4944] for the Mesh Header, 342 specifically the Dispatch Value Bit Pattern of 10xxxxxx. 344 With the Escaped Mesh Header reuse, the 6LoRH also reuses the bit 345 patterns that are defined in [RFC4944] for the Mesh Header, but an 346 ESC dispatch, with a value of 11111111, must be placed before the 347 first 6LoRH. The ESC indicates that the parsing of the pattern of 348 10xxxxxx will now be performed following this specification. There 349 is no need to place an ESC before each 6LoRH, since the ESC 350 influences the parsing of the rest of the packet. 352 5.1. Elective Format 354 With the first and second proposals, the 6LoRHE uses the Dispatch 355 Value Bit Pattern of 101xxxxx. 356 A 6LoRHE may be ignored and skipped in parsing. 357 If it is ignored, the 6LoRHE is forwarded with no change inside the 358 LLN. 360 0 1 361 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 363 |1|0|1| Length | Type | | 364 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 365 <-- Length --> 367 Figure 2: Elective 6LoWPAN Routing Header 369 With the third proposal 6LoRHE uses the Dispatch Value Bit Pattern of 370 1111xxxx. 372 0 1 373 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 374 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 375 |1|1|1|1| Length| Type | | 376 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 377 <-- Length --> 379 Figure 3: Elective 6LoWPAN Routing Header 381 Length: 382 Length of the 6LoRHE expressed in bytes, excluding the first 2 383 bytes. This is done to enable a node to skip a 6LoRH that it does 384 not support and/or cannot parse, for instance if the Type is not 385 known. 387 Type: 388 Type of the 6LoRHE 390 5.2. Critical Format 392 With the first and second proposals, the 6LoRHC uses the Dispatch 393 Value Bit Pattern of 100xxxxx. 394 A node which does not support the 6LoRHC Type MUST silently discard 395 the packet (note that there is no provision for the exchange of error 396 messages; such a situation should be avoided by judicious use of 397 administrative control and/or capability indications). 399 0 1 400 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 401 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 402 |1|0|0| TSE | Type | | 403 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 404 <-- Length implied by Type/TSE --> 406 Figure 4: Critical 6LoWPAN Routing Header 408 With the third proposal 6LoRHE uses the Dispatch Value Bit Pattern of 409 1101xxxx. 411 0 1 412 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 413 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 414 |1|1|0|1| TSE | Type | | 415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 416 <-- Length implied by Type/TSE --> 418 TSE: 420 Type Specific Extension. The meaning depends on the Type, which 421 must be known in all of the nodes. The interpretation of the TSE 422 depends on the Type field that follows. For instance, it may be 423 used to transport control bits, the number of elements in an 424 array, or the length of the remainder of the 6LoRHC expressed in a 425 unit other than bytes. 427 Type: 428 Type of the 6LoRHC 430 6. The Routing Header type 3 (RH3) 6LoRH 432 The Routing Header type 3 (RH3) 6LoRH (RH3-6LoRH) is a Critical 433 6LoWPAN Routing Header that provides a compressed form for the RH3, 434 as defined in [RFC6554] for use by RPL routers. Routers that need to 435 forward a packet with a RH3-6LoRH are expected to be RPL routers and 436 expected to support this specification. If a non-RPL router receives 437 a packet with a RPI-6LoRH, this means that there was a routing error 438 and the packet should be dropped so the Type cannot be ignored. 440 0 1 441 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 442 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+- -+ ... +- -+ 443 |1|0|0| Size |6LoRH Type 0..4| Hop1 | Hop2 | | HopN | 444 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+- -+ ... +- -+ 446 Size indicates the number of compressed addresses 448 Figure 5: The RH3-6LoRH 450 The values for the RH3-6LoRH Type are an enumeration, 0 to 4. The 451 form of compression is indicated by the Type as follows: 453 +-----------+-----------+ 454 | Type | Size Unit | 455 +-----------+-----------+ 456 | 0 | 1 | 457 | 1 | 2 | 458 | 2 | 4 | 459 | 3 | 8 | 460 | 4 | 16 | 461 +-----------+-----------+ 463 Figure 6: The RH3-6LoRH Types 465 In the case of a RH3-6LoRH, the TSE field is used as a Size, which 466 encodes the number of hops minus 1; so a Size of 0 means one hop, and 467 the maximum that can be encoded is 32 hops. (If more than 32 hops 468 need to be expressed, a sequence of RH3-6LoRH can be employed.) 470 The next Hop is indicated in the first entry of the first RH3-6LoRH. 471 Upon reception, the entry is checked whether it refers to the 472 processing router itself. If it so, the entry is removed from the 473 RH3-6LoRH and the Size is decremented. If the Size is now zero, the 474 whole RH3-6LoRH is removed. If there is no more RH3-6LoRH, the 475 processing node is the last router on the way, which may or may not 476 be collocated with the final destination. 478 The last hop in the last RH3-6LoRH is the last router prior to the 479 destination in the LLN. So even when there is a RH3-6LoRH in the 480 frame, the address of the final destination is in the LoWPAN_IPHC 481 [RFC6282]. 483 If some bits of the first address in the RH3-6LoRH can be derived 484 from the final destination is in the LoWPAN_IPHC, then that address 485 may be compressed, otherwise is is expressed in full. Next addresses 486 only need to express the delta from the previous address. 488 All addresses in a RH3-6LoRH are compressed in a same fashion, down 489 to the same number of bytes per address. In order to get different 490 forms of compression, multiple consecutive RH3-6LoRH must be used. 492 7. The RPL Packet Information 6LoRH 494 [RFC6550], Section 11.2, specifies the RPL Packet Information (RPI) 495 as a set of fields that are to be added to the IP packets for the 496 purpose of Instance Identification, as well as Loop Avoidance and 497 Detection. 499 In particular, the SenderRank, which is the scalar metric computed by 500 an specialized Objective Function such as [RFC6552], indicates the 501 Rank of the sender and is modified at each hop. The SenderRank 502 allows to validate that the packet progresses in the expected 503 direction, either upwards or downwards, along the DODAG. 505 RPL defines the RPL Option for Carrying RPL Information in Data-Plane 506 Datagrams [RFC6553] to transport the RPI, which is carried in an IPv6 507 Hop-by-Hop Options Header [RFC2460], typically consuming eight bytes 508 per packet. 510 With [RFC6553], the RPL option is encoded as six Octets; it must be 511 placed in a Hop-by-Hop header that consumes two additional octets for 512 a total of eight. In order to limit its range to the inside the RPL 513 domain, the Hop-by-Hop header must be added to (or removed from) 514 packets that cross the border of the RPL domain. 516 The 8-bytes overhead is detrimental to the LLN operation, in 517 particular with regards to bandwidth and battery constraints. These 518 bytes may cause a containing frame to grow above maximum frame size, 519 leading to Layer 2 or 6LoWPAN [RFC4944] fragmentation, which in turn 520 cause even more energy spending and issues discussed in the LLN 521 Fragment Forwarding and Recovery 522 [I-D.thubert-6lo-forwarding-fragments]. 524 An additional overhead comes from the need, in certain cases, to add 525 an IP-in-IP encapsulation to carry the Hop-by-Hop header. This is 526 needed when the router that inserts the Hop-by-Hop header is not the 527 source of the packet, so that an error can be returned to the router. 528 This is also the case when a packet originated by a RPL node must be 529 stripped from the Hop-by-Hop header to be routed outside the RPL 530 domain. 532 This specification defines an IPinIP-6LoRH in Section 8 for that 533 purpose, but it must be noted that stripping a 6LoRH does not require 534 a manipulation of the packet in the LOWPAN_IPHC, and thus, if the 535 source address in the LOWPAN_IPHC is the node that inserted the 536 IPinIP-6LoRH then this alone does not mandate an IPinIP-6LoRH. 538 As a result, a RPL packet may bear only a RPI-6LoRH and no IPinIP- 539 6LoRH. In that case, the source and destination of the packet are 540 located in the LOWPAN_IPHC. 542 As with [RFC6553], the fields in the RPI include an 'O', an 'R', and 543 an 'F' bit, an 8-bit RPLInstanceID (with some internal structure), 544 and a 16-bit SenderRank. 546 The remainder of this section defines the RPI-6LoRH, a Critical 547 6LoWPAN Routing Header that is designed to transport the RPI in 548 6LoWPAN LLNs. 550 7.1. Compressing the RPLInstanceID 552 RPL Instances are discussed in [RFC6550], Section 5. A number of 553 simple use cases will not require more than one instance, and in such 554 a case, the instance is expected to be the global Instance 0. A 555 global RPLInstanceID is encoded in a RPLInstanceID field as follows: 557 0 1 2 3 4 5 6 7 558 +-+-+-+-+-+-+-+-+ 559 |0| ID | Global RPLInstanceID in 0..127 560 +-+-+-+-+-+-+-+-+ 562 Figure 7: RPLInstanceID Field Format for Global Instances 564 For the particular case of the global Instance 0, the RPLInstanceID 565 field is all zeros. This specification allows to elide a 566 RPLInstanceID field that is all zeros, and defines a I flag that, 567 when set, signals that the field is elided. 569 7.2. Compressing the SenderRank 571 The SenderRank is the result of the DAGRank operation on the rank of 572 the sender; here the DAGRank operation is defined in [RFC6550], 573 Section 3.5.1, as: 575 DAGRank(rank) = floor(rank/MinHopRankIncrease) 577 If MinHopRankIncrease is set to a multiple of 256, the least 578 significant 8 bits of the SenderRank will be all zeroes; by eliding 579 those, the SenderRank can be compressed into a single byte. This 580 idea is used in [RFC6550] by defining DEFAULT_MIN_HOP_RANK_INCREASE 581 as 256 and in [RFC6552] that defaults MinHopRankIncrease to 582 DEFAULT_MIN_HOP_RANK_INCREASE. 584 This specification allows to encode the SenderRank as either one or 585 two bytes, and defines a K flag that, when set, signals that a single 586 byte is used. 588 7.3. The Overall RPI-6LoRH encoding 590 The RPI-6LoRH provides a compressed form for the RPL RPI. Routers 591 that need to forward a packet with a RPI-6LoRH are expected to be RPL 592 routers and expected to support this specification. If a non-RPL 593 router receives a packet with a RPI-6LoRH, this means that there was 594 a routing error and the packet should be dropped so the Type cannot 595 be ignored. 597 Since the I flag is not set, the TSE field does not need to be a 598 length expressed in bytes. The field is fully reused for control 599 bits so as to encode the O, R and F flags from the RPI, and the I and 600 K flags that indicate the compression that is taking place. 602 The Type for the RPI-6LoRH is 5 with the first proposal and in the 603 range 5-8 with the third proposal. 605 The RPI-6LoRH is immediately followed by the RPLInstanceID field, 606 unless that field is fully elided, and then the SenderRank, which is 607 either compressed into one byte or fully in-lined as the whole 2 608 bytes. The I and K flags in the RPI-6LoRH indicate whether the 609 RPLInstanceID is elided and/or the SenderRank is compressed and 610 depending on these bits, the Length of the RPI-6LoRH may vary as 611 described hereafter. 613 0 1 2 614 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 615 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... -+-+-+ 616 |1|0|0|O|R|F|I|K| 6LoRH Type=5 | Compressed fields | 617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... -+-+-+ 619 Figure 8: The Generic RPI-6LoRH Format 621 O, R, and F bits: 622 The O, R, and F bits as defined in [RFC6550], Section 11.2. 624 I bit: 625 If it is set, the Instance ID is elided and the RPLInstanceID 626 is the Global RPLInstanceID 0. If it is not set, the octet 627 immediately following the type field contains the RPLInstanceID 628 as specified in [RFC6550] section 5.1. 630 K bit: 631 If it is set, the SenderRank is be compressed into one octet, 632 and the lowest significant octet is elided. If it is not set, 633 the SenderRank, is fully inlined as 2 octets. 635 In Figure 9, the RPLInstanceID is the Global RPLInstanceID 0, and the 636 MinHopRankIncrease is a multiple of 256 so the least significant byte 637 is all zeros and can be elided: 639 0 1 2 640 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 641 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 642 |1|0|0|O|R|F|1|1| 6LoRH Type=5 | SenderRank | 643 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 644 I=1, K=1 646 Figure 9: The most compressed RPI-6LoRH 648 In Figure 10, the RPLInstanceID is the Global RPLInstanceID 0, but 649 both bytes of the SenderRank are significant so it can not be 650 compressed: 652 0 1 2 3 653 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 1 654 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 655 |1|0|0|O|R|F|1|0| 6LoRH Type=5 | SenderRank | 656 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 657 I=1, K=0 659 Figure 10: Eliding the RPLInstanceID 661 In Figure 11, the RPLInstanceID is not the Global RPLInstanceID 0, 662 and the MinHopRankIncrease is a multiple of 256: 664 0 1 2 3 665 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 1 666 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 667 |1|0|0|O|R|F|0|1| 6LoRH Type=5 | RPLInstanceID | SenderRank | 668 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 669 I=0, K=1 671 Figure 11: Compressing SenderRank 673 In Figure 12, the RPLInstanceID is not the Global RPLInstanceID 0, 674 and both bytes of the SenderRank are significant: 676 0 1 2 3 677 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 1 678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 679 |1|0|0|O|R|F|0|0| 6LoRH Type=5 | RPLInstanceID | Sender-... 680 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 681 ...-Rank | 682 +-+-+-+-+-+-+-+-+ 683 I=0, K=0 685 Figure 12: Least compressed form of RPI-6LoRH 687 A typical packet in RPL non-storing mode going down the RPL graph 688 requires an IPinIP encapsulating the RH3, whereas the RPI is usually 689 omitted, unless it is important to indicate the RPLInstanceID. To 690 match this structure, an optimized IPinIP 6LoRH is defined in 691 Section 8. 693 With the third approach, the format becomes: 695 0 1 696 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 697 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 698 |1|1|0|1|O|R|F|r|6LoRH Type 5-8 | ... 699 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 700 r = reserved 702 Figure 13: Third encoding 704 And the types include the setting of I and K as follows: 706 +-----------+-------+-------+ 707 | Type | I | K | 708 +-----------+-------+-------+ 709 | 5 | 0 | 0 | 710 | 6 | 0 | 1 | 711 | 7 | 1 | 0 | 712 | 8 | 1 | 1 | 713 +-----------+-------+-------+ 715 Figure 14: The RPI-6LoRH Types 717 8. The IP-in-IP 6LoRH 719 The IP-in-IP 6LoRH (IPinIP-6LoRH) is an Elective 6LoWPAN Routing 720 Header that provides a compressed form for the encapsulating IPv6 721 Header in the case of an IP-in-IP encapsulation. 723 An IPinIP encapsulation is used to insert a field such as a Routing 724 Header or an RPI at a router that is not the source of the packet. 725 In order to send an error back regarding the inserted field, the 726 address of the router that performs the insertion must be provided. 728 The encapsulation can also enable a router down the path removing a 729 field such as the RPI, but this can be done in the compressed form by 730 removing the RPI-6LoRH, so an IPinIP-6LoRH encapsulation is not 731 required for that sole purpose. 733 This field is not critical for routing so the Type can be ignored, 734 and the TSE field contains the Length in bytes. 736 0 1 2 737 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 738 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 739 |1|0|1| Length | 6LoRH Type 9 | Hop Limit | Encaps. Address | 740 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 742 Figure 15: The IPinIP-6LoRH 744 The Length of an IPinIP-6LoRH is expressed in bytes and MUST be at 745 least 1, to indicate a Hop Limit (HL), that is decremented at each 746 hop. When the HL reaches 0, the packet is dropped per [RFC2460] 748 If the Length of an IPinIP-6LoRH is exactly 1, then the Encapsulator 749 Address is elided, which means that the Encapsulator is a well-known 750 router, for instance the root in a RPL graph. 752 If the Length of an IPinIP-6LoRH is strictly more than 1, then an 753 Encapsulator Address is placed in a compressed form after the Hop 754 Limit field. The value of the Length indicates which compression is 755 performed on the Encapsulator Address. For instance, a Size of 3 756 indicates that the Encapsulator Address is compressed to 2 bytes. 758 When it cannot be elided, the destination IP address of the IP-in-IP 759 header is transported in a RH3-6LoRH as the first address of the 760 list. 762 With RPL, the destination address in the IP-in-IP header is 763 implicitly the root in the RPL graph for packets going upwards, and 764 the destination address in the IPHC for packets going downwards. If 765 the implicit value is correct, the destination IP address of the IP- 766 in-IP encapsulation can be elided. 768 If the final destination of the packet is a leaf that does not 769 support this specification, then the chain of 6LoRH must be stripped 770 by the RPL/6LR router to which the leaf is attached. In that 771 example, the destination IP address of the IP-in-IP header cannot be 772 elided. 774 In the special case where the 6LoRH is used to route 6LoWPAN 775 fragments, the destination address is not accessible in the IPHC on 776 all fragments and can be elided only for the first fragment and for 777 packets going upwards. 779 9. The Mesh Header 6LoRH 781 The Mesh Header 6LoRH (MH-6LoRH) is an Elective 6LoWPAN Routing 782 Header that provides an alternate form for the Mesh Addressing Type 783 and Header defined in [RFC4944] with the same semantics. 785 The MH-6LoRH is introduced as replacement for use in potentially 786 mixed Route_Over and Mesh-under environments. LLN nodes that need to 787 forward a packet with a MH-6LoRH are expected to support this 788 specification. If a router that supports only Route-over receives a 789 packet with a MH-6LoRH, this means that there was a routing error and 790 the packet should be dropped, so the Type cannot be ignored. 792 The HopsLft field defined in [RFC4944] is encoded in the TSE, so this 793 specification doubles the potential number of hops vs. [RFC4944] in 794 the first proposal and is conserved in the third proposal. 796 The HopsLft value of 0x1F is reserved and signifies an 8-bit Deep 797 Hops Left field immediately following the Type, and allows a source 798 node to specify a hop limit greater than 30 hops. 800 0 1 801 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 802 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 803 |1|0|0| HopsLft |6LoRHType 11-14| originator address, final address | 804 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 806 Figure 16: The MH-6LoRH 808 The V and F flags defined in [RFC4944] are encoded in the MH-6LoRH 809 Type as follows: 811 +-----------+-------+-------+ 812 | Type | V | F | 813 +-----------+-------+-------+ 814 | 11 | 0 | 0 | 815 | 12 | 0 | 1 | 816 | 13 | 1 | 0 | 817 | 14 | 1 | 1 | 818 +-----------+-------+-------+ 820 Figure 17: The MH-6LoRH Types 822 10. The BIER 6LoRH 824 (Note that the current contents of this section is a proof of concept 825 only; the details for this encoding need to be developed in parallel 826 with defining the semantics of a constrained version of BIER.) 828 The Bit Index Explicit Replication (BIER) 6LoRH (BIER-6LoRH) is an 829 Elective 6LoWPAN Routing Header that provides a variable-size 830 container for a BIER Bitmap. BIER can be used to route downwards a 831 RPL graph towards one or more LLN node, as discussed in the BIER 832 Architecture [I-D.wijnands-bier-architecture] specification. The 833 capability to parse the BIER Bitmap is necessary to forward the 834 packet so the Type cannot be ignored. 836 0 1 837 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 838 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... -+-+-+- ... -+ 839 |1|0|0| Size |6LoRHType 15-19| Control Fields | bitmap | 840 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... -+-+-+- ... -+ 842 Figure 18: The BIER-6LoRH 844 The Type for a BIER-6LoRH indicates the size of words used to build 845 the bitmap and whether the bitmap is operated as an uncompressed bit- 846 by-bit mapping, or as a Bloom filter. 848 In the bit-by-bit case, each bit is mapped in an unequivocal fashion 849 with a single addressable resource in the network. This may rapidly 850 lead to large bitmaps, and BIER allows to divide a network into 851 groups that partition the network so that a given bitmap is locally 852 significant to one group only. This specification allows to encode a 853 1-byte Group ID in the BIER-6LoRH Control Fields. 855 A Bloom Filter can be seen as a compression technique for the bitmap. 856 A Bloom Filter may generate false positives, which, in the case of 857 BIER, result in undue forwarding of a packet down a path where no 858 listener exists. 860 As an example, the Constrained-Cast [I-D.bergmann-bier-ccast] 861 specification employs Bloom Filters as a compact representation of a 862 match or non-match for elements in a large set. 864 In the case of a Bloom Filter, a number of Hash functions must be run 865 to obtain a multi-bit signature of an encoded element. This 866 specification allows to signal an Identifier of the Hash functions 867 being used to generate a certain bitmap, so as to enable a migration 868 scenario where Hash functions are renewed. A Hash ID is signaled as 869 a 1-byte value, and, depending on the Type, there may be up to 2 or 870 up to 8 Hash IDs passed in the BIER-6LoRH Control Fields associated 871 with a Bloom Filter bitmap, as follows: 873 +-----------+--------------+------------------+-----------+ 874 | Type | encoding | Control Fields | Word Size | 875 +-----------+--------------+------------------+-----------+ 876 | 15 | bit-by-bit | none | 32 bits | 877 | 16 | Bloom filter | 2* 1-byte HashID | 32 bits | 878 | 17 | bit-by-bit | none | 128 bits | 879 | 18 | Bloom filter | 8* 1-byte HashID | 128 bits | 880 | 19 | bit-by-bit | 1-byte GroupID | 128 bits | 881 +-----------+--------------+------------------+-----------+ 883 Figure 19: The BIER-6LoRH Types 885 In order to address a potentially large number of devices, the bitmap 886 may grow very large. Yet, the maximum frame size for a given MAC 887 layer may limit the number of bits that can be dedicated to routing. 888 The Size indicates the number of words in the bitmap minus one, so a 889 size of 0 means one word, a Size of 1 means 64 2 words, up to a size 890 of 31 which means 32 words. 892 11. Security Considerations 894 The security considerations of [RFC4944], [RFC6282], and [RFC6553] 895 apply. 897 Using a compressed format as opposed to the full in-line format is 898 logically equivalent and does not create an opening for a new threat 899 when compared to [RFC6550], [RFC6553] and [RFC6554]. 901 12. IANA Considerations 903 This document creates a IANA registry for the 6LoWPAN Routing Header 904 Type, and assigns the following values: 906 0..4 : RH3-6LoRH [RFCthis] 908 5 : RPI-6LoRH [RFCthis] 910 9 : IPinIP-6LoRH [RFCthis] 912 11..14 : MH-6LoRH [RFCthis] 914 15..19 : BIER-6LoRH [RFCthis] 916 13. Acknowledgments 918 The authors wish to thank Martin Turon, James Woodyatt and Ralph 919 Droms for constructive reviews to the design in the 6lo Working 920 Group. The overall discussion involved participants to the 6MAN, 921 6TiSCH and ROLL WGs, thank you all. Special thanks to the chairs of 922 the ROLL WG, Michael Richardson and Ines Robles, and Brian Haberman, 923 Internet Area A-D, and Adrian Farrel, Routing Area A-D, for driving 924 this complex effort across Working Groups and Areas. 926 14. References 928 14.1. Normative References 930 [IEEE802154] 931 IEEE standard for Information Technology, "IEEE std. 932 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) 933 and Physical Layer (PHY) Specifications for Low-Rate 934 Wireless Personal Area Networks", 2015. 936 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 937 Requirement Levels", BCP 14, RFC 2119, March 1997. 939 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 940 (IPv6) Specification", RFC 2460, December 1998. 942 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 943 "Transmission of IPv6 Packets over IEEE 802.15.4 944 Networks", RFC 4944, September 2007. 946 [RFC6282] Hui, J. and P. Thubert, "Compression Format for IPv6 947 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 948 September 2011. 950 [RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R., 951 Levis, P., Pister, K., Struik, R., Vasseur, JP., and R. 952 Alexander, "RPL: IPv6 Routing Protocol for Low-Power and 953 Lossy Networks", RFC 6550, March 2012. 955 [RFC6552] Thubert, P., "Objective Function Zero for the Routing 956 Protocol for Low-Power and Lossy Networks (RPL)", RFC 957 6552, March 2012. 959 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 960 Power and Lossy Networks (RPL) Option for Carrying RPL 961 Information in Data-Plane Datagrams", RFC 6553, March 962 2012. 964 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 965 Routing Header for Source Routes with the Routing Protocol 966 for Low-Power and Lossy Networks (RPL)", RFC 6554, March 967 2012. 969 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 970 Lossy Networks", RFC 7102, January 2014. 972 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 973 Constrained-Node Networks", RFC 7228, May 2014. 975 14.2. Informative References 977 [I-D.bergmann-bier-ccast] 978 Bergmann, O., Bormann, C., and S. Gerdes, "Constrained- 979 Cast: Source-Routed Multicast for RPL", draft-bergmann- 980 bier-ccast-00 (work in progress), November 2014. 982 [I-D.ietf-6tisch-architecture] 983 Thubert, P., "An Architecture for IPv6 over the TSCH mode 984 of IEEE 802.15.4", draft-ietf-6tisch-architecture-08 (work 985 in progress), May 2015. 987 [I-D.ietf-6tisch-tsch] 988 Watteyne, T., Palattella, M., and L. Grieco, "Using 989 IEEE802.15.4e TSCH in an IoT context: Overview, Problem 990 Statement and Goals", draft-ietf-6tisch-tsch-06 (work in 991 progress), March 2015. 993 [I-D.thubert-6lo-forwarding-fragments] 994 Thubert, P. and J. Hui, "LLN Fragment Forwarding and 995 Recovery", draft-thubert-6lo-forwarding-fragments-02 (work 996 in progress), November 2014. 998 [I-D.wijnands-bier-architecture] 999 Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and 1000 S. Aldrin, "Multicast using Bit Index Explicit 1001 Replication", draft-wijnands-bier-architecture-05 (work in 1002 progress), March 2015. 1004 [RFC6775] Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann, 1005 "Neighbor Discovery Optimization for IPv6 over Low-Power 1006 Wireless Personal Area Networks (6LoWPANs)", RFC 6775, 1007 November 2012. 1009 Authors' Addresses 1011 Pascal Thubert (editor) 1012 Cisco Systems 1013 Village d'Entreprises Green Side 1014 400, Avenue de Roumanille 1015 Batiment T3 1016 Biot - Sophia Antipolis 06410 1017 FRANCE 1019 Phone: +33 4 97 23 26 34 1020 Email: pthubert@cisco.com 1022 Carsten Bormann 1023 Universitaet Bremen TZI 1024 Postfach 330440 1025 Bremen D-28359 1026 Germany 1028 Phone: +49-421-218-63921 1029 Email: cabo@tzi.org 1030 Laurent Toutain 1031 Institut MINES TELECOM; TELECOM Bretagne 1032 2 rue de la Chataigneraie 1033 CS 17607 1034 Cesson-Sevigne Cedex 35576 1035 France 1037 Email: Laurent.Toutain@telecom-bretagne.eu 1039 Robert Cragie 1040 ARM Ltd. 1041 110 Fulbourn Road 1042 Cambridge CB1 9NJ 1043 UK 1045 Email: robert.cragie@gridmerge.com