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'IEEE802154' ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) == Outdated reference: A later version (-30) exists of draft-ietf-6tisch-architecture-10 == Outdated reference: A later version (-44) exists of draft-ietf-roll-useofrplinfo-08 == Outdated reference: A later version (-08) exists of draft-thubert-6lo-forwarding-fragments-02 Summary: 3 errors (**), 0 flaws (~~), 6 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 roll P. Thubert, Ed. 3 Internet-Draft Cisco 4 Intended status: Standards Track C. Bormann 5 Expires: April 22, 2017 Uni Bremen TZI 6 L. Toutain 7 IMT-TELECOM Bretagne 8 R. Cragie 9 ARM 10 October 19, 2016 12 6LoWPAN Routing Header 13 draft-ietf-roll-routing-dispatch-02 15 Abstract 17 This specification introduces a new 6LoWPAN dispatch type for use in 18 6LoWPAN Route-Over topologies, that initially covers the needs of RPL 19 (RFC6550) data packets compression. Using this dispatch type, this 20 specification defines a method to compress RPL Option (RFC6553) 21 information and Routing Header type 3 (RFC6554), an efficient IP-in- 22 IP technique and is extensible for more applications. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on April 22, 2017. 41 Copyright Notice 43 Copyright (c) 2016 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 59 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 60 3. Using the Page Dispatch . . . . . . . . . . . . . . . . . . . 6 61 3.1. New Routing Header Dispatch (6LoRH) . . . . . . . . . . . 6 62 3.2. Placement Of 6LoRH headers . . . . . . . . . . . . . . . 7 63 3.2.1. Relative To Non-6LoRH Headers . . . . . . . . . . . . 7 64 3.2.2. Relative To Other 6LoRH Headers . . . . . . . . . . . 7 65 4. 6LoWPAN Routing Header General Format . . . . . . . . . . . . 8 66 4.1. Elective Format . . . . . . . . . . . . . . . . . . . . . 9 67 4.2. Critical Format . . . . . . . . . . . . . . . . . . . . . 9 68 4.3. Compressing Addresses . . . . . . . . . . . . . . . . . . 10 69 4.3.1. Coalescence . . . . . . . . . . . . . . . . . . . . . 10 70 4.3.2. DODAG Root Address Determination . . . . . . . . . . 11 71 5. The SRH 6LoRH Header . . . . . . . . . . . . . . . . . . . . 12 72 5.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . . 12 73 5.2. SRH-6LoRH General Operation . . . . . . . . . . . . . . . 13 74 5.2.1. Uncompressed SRH Operation . . . . . . . . . . . . . 13 75 5.2.2. 6LoRH-Compressed SRH Operation . . . . . . . . . . . 14 76 5.2.3. Inner LOWPAN_IPHC Compression . . . . . . . . . . . . 14 77 5.3. The Design Point of Popping Entries . . . . . . . . . . . 15 78 5.4. Compression Reference for SRH-6LoRH header entries . . . 16 79 5.5. Popping Headers . . . . . . . . . . . . . . . . . . . . . 17 80 5.6. Forwarding . . . . . . . . . . . . . . . . . . . . . . . 17 81 6. The RPL Packet Information 6LoRH . . . . . . . . . . . . . . 18 82 6.1. Compressing the RPLInstanceID . . . . . . . . . . . . . . 19 83 6.2. Compressing the SenderRank . . . . . . . . . . . . . . . 20 84 6.3. The Overall RPI-6LoRH encoding . . . . . . . . . . . . . 20 85 7. The IP-in-IP 6LoRH Header . . . . . . . . . . . . . . . . . . 23 86 8. Management Considerations . . . . . . . . . . . . . . . . . . 24 87 9. Security Considerations . . . . . . . . . . . . . . . . . . . 25 88 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 89 10.1. Reserving Space in 6LoWPAN Dispatch Page 1 . . . . . . . 25 90 10.2. New Critical 6LoWPAN Routing Header Type Registry . . . 26 91 10.3. New Elective 6LoWPAN Routing Header Type Registry . . . 26 92 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26 93 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 26 94 12.1. Normative References . . . . . . . . . . . . . . . . . . 26 95 12.2. Informative References . . . . . . . . . . . . . . . . . 28 96 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 28 97 A.1. Examples Compressing The RPI . . . . . . . . . . . . . . 28 98 A.2. Example Of Downward Packet In Non-Storing Mode . . . . . 30 99 A.3. Example of SRH-6LoRH life-cycle . . . . . . . . . . . . . 32 100 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 102 1. Introduction 104 The design of Low Power and Lossy Networks (LLNs) is generally 105 focused on saving energy, a very constrained resource in most cases. 106 The other constraints, such as the memory capacity and the duty 107 cycling of the LLN devices, derive from that primary concern. Energy 108 is often available from primary batteries that are expected to last 109 for years, or is scavenged from the environment in very limited 110 quantities. Any protocol that is intended for use in LLNs must be 111 designed with the primary concern of saving energy as a strict 112 requirement. 114 Controlling the amount of data transmission is one possible venue to 115 save energy. In a number of LLN standards, the frame size is limited 116 to much smaller values than the IPv6 maximum transmission unit (MTU) 117 of 1280 bytes. In particular, an LLN that relies on the classical 118 Physical Layer (PHY) of IEEE 802.15.4 [IEEE802154] is limited to 127 119 bytes per frame. The need to compress IPv6 packets over IEEE 120 802.15.4 led to the "6LoWPAN Header Compression" [RFC6282] work 121 (6LoWPAN_HC). 123 Innovative Route-over techniques have been and are still being 124 developed for routing inside a LLN. In a general fashion, such 125 techniques require additional information in the packet to provide 126 loop prevention and to indicate information such as flow 127 identification, source routing information, etc. 129 For reasons such as security and the capability to send ICMP errors 130 back to the source, an original packet must not be tampered with, and 131 any information that must be inserted in or removed from an IPv6 132 packet must be placed in an extra IP-in-IP encapsulation. 134 This is the case when the additional routing information is inserted 135 by a router on the path of a packet, for instance the root of a mesh, 136 as opposed to the source node, with the non-storing mode of the "IPv6 137 Routing Protocol for Low-Power and Lossy Networks" [RFC6550] (RPL). 139 This is also the case when some routing information must be removed 140 from a packet that flows outside the LLN. 142 "When to use RFC 6553, RFC 6554 and IPv6-in-IPv6" 143 [I-D.ietf-roll-useofrplinfo] details different cases where IPv6 144 headers defined in the "RPL Option for Carrying RPL Information in 145 Data-Plane Datagrams" [RFC6553] and the "Routing Header for Source 146 Routes with RPL" [RFC6554], and IPv6-in-IPv6 encapsulation, are 147 inserted or removed from packets in a LLN environments operating RPL. 149 When using RFC 6282 [RFC6282] the outer IP header of an IP-in-IP 150 encapsulation may be compressed down to 2 octets in stateless 151 compression and down to 3 octets in stateful compression when context 152 information must be added. 154 0 1 155 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 156 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 157 | 0 | 1 | 1 | TF |NH | HLIM |CID|SAC| SAM | M |DAC| DAM | 158 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 160 Figure 1: LOWPAN_IPHC base Encoding (RFC6282). 162 The Stateless Compression of an IPv6 addresses can only happen if the 163 IPv6 address can de deduced from the MAC addresses, meaning that the 164 IP end point is also the MAC-layer endpoint. This is generally not 165 the case in a RPL network which is generally a multi-hop route-over 166 (i.e., operated at Layer-3) network. A better compression, which 167 does not involve variable compressions depending on the hop in the 168 mesh, can be achieved based on the fact that the outer encapsulation 169 is usually between the source (or destination) of the inner packet 170 and the root. Also, the inner IP header can only be compressed by 171 RFC 6282 [RFC6282] if all the fields preceding it are also 172 compressed. This specification makes the inner IP header the first 173 header to be compressed by RFC 6282 [RFC6282], and keeps the inner 174 packet encoded the same way whether it is encapsulated or not, thus 175 preserving existing implementations. 177 As an example, RPL [RFC6550] is designed to optimize the routing 178 operations in constrained LLNs. As part of this optimization, RPL 179 requires the addition of RPL Packet Information (RPI) in every 180 packet, as defined in Section 11.2 of RFC 6550 [RFC6550]. 182 The "RPL Option for Carrying RPL Information in Data-Plane Datagrams" 183 [RFC6553] specification indicates how the RPI can be placed in a RPL 184 Option (RPL-OPT) that is placed in an IPv6 Hop-by-Hop header. 186 This representation demands a total of 8 bytes, while in most cases 187 the actual RPI payload requires only 19 bits. Since the Hop-by-Hop 188 header must not flow outside of the RPL domain, it must be inserted 189 in packets entering the domain and be removed from packets that leave 190 the domain. In both cases, this operation implies an IP-in-IP 191 encapsulation. 193 Additionally, in the case of the Non-Storing Mode of Operation (MOP), 194 RPL requires a Source Routing Header (SRH) in all packets that are 195 routed down a RPL graph. for that purpose, the "IPv6 Routing Header 196 for Source Routes with RPL" [RFC6554] specification defines the type 197 3 Routing Header for IPv6 (RH3). 199 ------+--------- ^ 200 | Internet | 201 | | Native IPv6 202 +-----+ | 203 | | Border Router (RPL Root) ^ | ^ 204 | | | | | 205 +-----+ | | | IPv6 in 206 | | | | IPv6 207 o o o o | | | plus 208 o o o o o o o o o | | | RPL SRH 209 o o o o o o o o o o | | | 210 o o o o o o o o o | | | 211 o o o o o o o o v v v 212 o o o o 213 LLN 215 Figure 2: IP-in-IP Encapsulation within the LLN. 217 With Non-Storing RPL, even if the source is a node in the same LLN, 218 the packet must first reach up the graph to the root so that the root 219 can insert the SRH to go down the graph. In any fashion, whether the 220 packet was originated in a node in the LLN or outside the LLN, and 221 regardless of whether the packet stays within the LLN or not, as long 222 as the source of the packet is not the root itself, the source- 223 routing operation also implies an IP-in-IP encapsulation at the root 224 in order to insert the SRH. 226 "The 6TiSCH Architecture" [I-D.ietf-6tisch-architecture] specifies 227 the operation of IPv6 over the "TimeSlotted Channel Hopping" 228 [RFC7554] (TSCH) mode of operation of IEEE 802.15.4. The 229 architecture requires the use of both RPL and the 6lo adaptation 230 layer over IEEE 802.15.4. Because it inherits the constraints on 231 frame size from the MAC layer, 6TiSCH cannot afford to allocate 8 232 bytes per packet on the RPI. Hence the requirement for 6LoWPAN 233 header compression of the RPI. 235 An extensible compression technique is required that simplifies IP- 236 in-IP encapsulation when it is needed, and optimally compresses 237 existing routing artifacts found in RPL LLNs. 239 This specification extends the 6lo adaptation layer framework (RFC 240 4944 [RFC4944] and RFC 6282 [RFC6282]) so as to carry routing 241 information for route-over networks based on RPL. The specification 242 includes the formats necessary for RPL and is extensible for 243 additional formats. 245 2. Terminology 247 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 248 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 249 "OPTIONAL" in this document are to be interpreted as described in RFC 250 2119 [RFC2119]. 252 The Terminology used in this document is consistent with and 253 incorporates that described in Terminology in Low power And Lossy 254 Networks [RFC7102] and RPL [RFC6550]. 256 The terms Route-over and Mesh-under are defined in RFC 6775 257 [RFC6775]. 259 Other terms in use in LLNs are found in "Terminology for Constrained- 260 Node Networks" [RFC7228]. 262 The term "byte" is used in its now customary sense as a synonym for 263 "octet". 265 3. Using the Page Dispatch 267 The 6LoWPAN Paging Dispatch [I-D.ietf-6lo-paging-dispatch] 268 specification extends the 6lo adaptation layer framework (RFC 4944 269 [RFC4944] and RFC 6282 [RFC6282]) by introducing a concept of 270 "context" in the 6LoWPAN parser, a context being identified by a Page 271 number. The specification defines 16 Pages. 273 This draft operates within Page 1, which is indicated by a Dispatch 274 Value of binary 11110001. 276 3.1. New Routing Header Dispatch (6LoRH) 278 This specification introduces a new 6LoWPAN Routing Header (6LoRH) to 279 carry IPv6 routing information. The 6LoRH may contain source routing 280 information such as a compressed form of SRH, as well as other sorts 281 of routing information such as the RPI and IP-in-IP encapsulation. 283 The 6LoRH is expressed in a 6loWPAN packet as a Type-Length-Value 284 (TLV) field, which is extensible for future use. 286 It is expected that a router that does not recognize the 6LoRH 287 general format detailed in Section 4 will drop the packet when a 288 6LoRH is present. 290 This specification uses the bit pattern 10xxxxxx in Page 1 for the 291 new 6LoRH Dispatch. Section 4 describes how RPL artifacts in data 292 packets can be compressed as 6LoRH headers. 294 3.2. Placement Of 6LoRH headers 296 3.2.1. Relative To Non-6LoRH Headers 298 In a zone of a packet where Page 1 is active (that is, once the Page 299 1 Paging Dispatch is parsed, and until another Paging Dispatch is 300 parsed as described in the 6LoWPAN Paging Dispatch specification 301 [I-D.ietf-6lo-paging-dispatch]), the parsing of the packet MUST 302 follow this specification if the 6LoRH Bit Pattern (see Section 3.1) 303 is found. 305 With this specification, the 6LoRH Dispatch is only defined in Page 306 context is active. 308 Because a 6LoRH header requires a Page 1 context, it MUST always be 309 placed after any Fragmentation Header and/or Mesh Header as defined 310 in RFC 4944 [RFC4944]. 312 A 6LoRH header MUST always be placed before the LOWPAN_IPHC as 313 defined in RFC 6282 [RFC6282]. It is designed in such a fashion that 314 placing or removing a header that is encoded with 6LoRH does not 315 modify the part of the packet that is encoded with LOWPAN_IPHC, 316 whether there is an IP-in-IP encapsulation or not. For instance, the 317 final destination of the packet is always the one in the LOWPAN_IPHC 318 whether there is a Routing Header or not. 320 3.2.2. Relative To Other 6LoRH Headers 322 The "Internet Protocol, Version 6 (IPv6) Specification" [RFC2460] 323 defines chains of headers that are introduced by an IPv6 header and 324 terminated by either another IPv6 header (IP-in-IP) or an Upper Layer 325 Protocol (ULP) header. When an outer header is stripped from the 326 packet, the whole chain goes with it. When one or more header(s) are 327 inserted by an intermediate router, that router normally chains the 328 headers and encapsulates the result in IP-in-IP. 330 With this specification, the chains of headers MUST be compressed in 331 the same order as they appear in the uncompressed form of the packet. 332 This means that if there is more than one nested IP-in-IP 333 encapsulations, the first IP-in-IP encapsulation, with all its chain 334 of headers, is encoded first in the compressed form. 336 In the compressed form of a packet that has a Source Route or a Hop- 337 by-Hop (HbH) Options Header [RFC2460] after the inner IPv6 header 338 (e.g. if there is no IP-in-IP encapsulation), these headers are 339 placed in the 6LoRH form before the 6LOWPAN_IPHC that represents the 340 IPv6 header (see Section 3.2.1). If this packet gets encapsulated 341 and some other SRH or HbH Options Headers are added as part of the 342 encapsulation, placing the 6LoRH headers next to one another may 343 present an ambiguity on which header belong to which chain in the 344 uncompressed form. 346 In order to disambiguate the headers that follow the inner IPv6 347 header in the uncompressed form from the headers that follow the 348 outer IP-in-IP header, it is REQUIRED that the compressed IP-in-IP 349 header is placed last in the encoded chain. This means that the 350 6LoRH headers that are found after the last compressed IP-in-IP 351 header are to be inserted after the IPv6 header that is encoded with 352 the 6LOWPAN_IPHC when decompressing the packet. 354 With regards to the relative placement of the SRH and the RPI in the 355 compressed form, it is a design point for this specification that the 356 SRH entries are consumed as the packet progresses down the LLN (see 357 Section 5.3). In order to make this operation simpler in the 358 compressed form, it is REQUIRED that in the compressed form, the 359 addresses along the source route path are encoded in the order of the 360 path, and that the compressed SRH are placed before the compressed 361 RPI. 363 4. 6LoWPAN Routing Header General Format 365 The 6LoRH uses the Dispatch Value Bit Pattern of 10xxxxxx in Page 1. 367 The Dispatch Value Bit Pattern is split in two forms of 6LoRH: 369 Elective (6LoRHE) that may skipped if not understood 371 Critical (6LoRHC) that may not be ignored 373 For each form, a Type field is used to encode the type of 6LoRH. 375 Note that there is a different registry for the Type field of each 376 form of 6LoRH. 378 This means that a value for the Type that is defined for one form of 379 6LoRH may be redefined in the future for the other form. 381 4.1. Elective Format 383 The 6LoRHE uses the Dispatch Value Bit Pattern of 101xxxxx. A 6LoRHE 384 may be ignored and skipped in parsing. If it is ignored, the 6LoRHE 385 is forwarded with no change inside the LLN. 387 0 1 388 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 389 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 390 |1|0|1| Length | Type | | 391 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 392 <-- Length --> 394 Figure 3: Elective 6LoWPAN Routing Header. 396 Length: Length of the 6LoRHE expressed in bytes, excluding the first 397 2 bytes. This enables a node to skip a 6LoRHE header that it 398 does not support and/or cannot parse, for instance if the Type 399 is not recognized. 401 Type: Type of the 6LoRHE 403 4.2. Critical Format 405 The 6LoRHC uses the Dispatch Value Bit Pattern of 100xxxxx. 407 A node which does not support the 6LoRHC Type MUST silently discard 408 the packet. 410 Note: the situation where a node receives a message with a Critical 411 6LoWPAN Routing Header that it does not understand should not occur 412 and is an administrative error, see Section 8. 414 0 1 415 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 417 |1|0|0| TSE | Type | | 418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 419 <-- Length implied by Type/TSE --> 421 Figure 4: Critical 6LoWPAN Routing Header. 423 TSE: Type Specific Extension. The meaning depends on the Type, 424 which must be known in all of the nodes. The interpretation of 425 the TSE depends on the Type field that follows. For instance, 426 it may be used to transport control bits, the number of 427 elements in an array, or the length of the remainder of the 428 6LoRHC expressed in a unit other than bytes. 430 Type: Type of the 6LoRHC 432 4.3. Compressing Addresses 434 The general technique used in this draft to compress an address is 435 first to determine a reference that has a long prefix match with this 436 address, and then elide that matching piece. In order to reconstruct 437 the compressed address, the receiving node will perform the process 438 of coalescence described in Section 4.3.1. 440 One possible reference is the root of the RPL DODAG that is being 441 traversed. It is used by 6LoRH as the reference to compress an outer 442 IP header, in case of an IP-in-IP encapsulation. If the root is the 443 source of the packet, this technique allows to fully elide the source 444 address in the compressed form of the IP header. If the root is not 445 the encapsulator, then the encapsulator address may still be 446 compressed using the root as reference. How the address of the root 447 is determined is discussed in Section 4.3.2. 449 Once the address of the source of the packet is determined, it 450 becomes the reference for the compression of the addresses that are 451 located in compressed SRH headers that are present inside the IP-in- 452 IP encapsulation in the uncompressed form. 454 4.3.1. Coalescence 456 An IPv6 compressed address is coalesced with a reference address by 457 overriding the N rightmost bytes of the reference address with the 458 compressed address, where N is the length of the compressed address, 459 as indicated by the Type of the SRH-6LoRH header in Figure 7. 461 The reference address MAY be a compressed address as well, in which 462 case it MUST be compressed in a form that is of an equal or greater 463 length than the address that is being coalesced. 465 A compressed address is expanded by coalescing it with a reference 466 address. In the particular case of a Type 4 SRH-6LoRH, the address 467 is expressed in full and the coalescence is a complete override as 468 illustrated in Figure 5. 470 RRRRRRRRRRRRRRRRRRRR reference address, may be compressed or not 472 CCCCCCC compressed address, shorter or same as reference 474 RRRRRRRRRRRRRCCCCCCC Coalesced address, same compression as reference 476 Figure 5: Coalescing addresses. 478 4.3.2. DODAG Root Address Determination 480 Stateful Address compression requires that some state is installed in 481 the devices to store the compression information that is elided from 482 the packet. That state is stored in an abstract context table and 483 some form of index is found in the packet to obtain the compression 484 information from the context table. 486 With RFC 6282 [RFC6282], the state is provided to the stack by the 487 "6LoWPAN Neighbor Discovery Protocol (NDP)" [RFC6775]. NDP exchanges 488 the context through 6LoWPAN Context Option in Router Advertisement 489 (RA) messages. In the compressed form of the packet, the context can 490 be signaled in a Context Identifier Extension. 492 With this specification, the compression information is provided to 493 the stack by RPL, and RPL exchanges it through the DODAGID field in 494 the DAG Information Object (DIO) messages, as described in more 495 detail below. In the compressed form of the packet, the context can 496 be signaled in by the RPLInstanceID in the RPI. 498 With RPL [RFC6550], the address of the DODAG root is known from the 499 DODAGID field of the DIO messages. For a Global Instance, the 500 RPLInstanceID that is present in the RPI is enough information to 501 identify the DODAG that this node participates to and its associated 502 root. But for a Local Instance, the address of the root MUST be 503 explicit, either in some device configuration or signaled in the 504 packet, as the source or the destination address, respectively. 506 When implicit, the address of the DODAG root MUST be determined as 507 follows: 509 If the whole network is a single DODAG then the root can be well- 510 known and does not need to be signaled in the packets. But since RPL 511 does not expose that property, it can only be known by a 512 configuration applied to all nodes. 514 Else, the router that encapsulates the packet and compresses it with 515 this specification MUST also place an RPI in the packet as prescribed 516 by RPL to enable the identification of the DODAG. The RPI must be 517 present even in the case when the router also places an SRH header in 518 the packet. 520 It is expected that the RPL implementation maintains an abstract 521 context table, indexed by Global RPLInstanceID, that provides the 522 address of the root of the DODAG that this nodes participates to for 523 that particular RPL Instance. 525 5. The SRH 6LoRH Header 527 5.1. Encoding 529 A Source Routing Header 6LoRH (SRH-6LoRH) header provides a 530 compressed form for the SRH, as defined in RFC 6554 [RFC6554] for use 531 by RPL routers. 533 One or more SRH-6LoRH header(s) MAY be placed in a 6LoWPAN packet. 535 If a non-RPL router receives a packet with a SRH-6LoRH header, there 536 was a routing or a configuration error (see Section 8). 538 The desired reaction for the non-RPL router is to drop the packet as 539 opposed to skip the header and forward the packet. 541 The Dispatch Value Bit Pattern for the SRH-6LoRH header indicates 542 Critical. Routers that understand the 6LoRH general format detailed 543 in Section 4 cannot ignore a 6LoRH header of this type, and will drop 544 the packet if it is unknown to them. 546 0 1 547 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+- -+ ... +- -+ 549 |1|0|0| Size |6LoRH Type 0..4| Hop1 | Hop2 | | HopN | 550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+- -+ ... +- -+ 552 Where N = Size + 1 554 Figure 6: The SRH-6LoRH. 556 The 6LoRH Type of a SRH-6LoRH header indicates the compression level 557 used for that header. 559 The fields following the 6LoRH Type are compressed addresses 560 indicating the consecutive hops, and are ordered from the first to 561 the last hop. 563 All the addresses in a given SRH-6LoRH header MUST be compressed in 564 an identical fashion, so the Length of the compressed for is the same 565 for all. 567 In order to get different degrees of compression, multiple 568 consecutive SRH-6LoRH headers MUST be used. 570 Type 0 means that the address is compressed down to one byte, whereas 571 Type 4 means that the address is provided in full in the SRH-6LoRH 572 with no compression. The complete list of Types of SRH-6LoRH and the 573 corresponding compression level are provided in Figure 7: 575 +-----------+----------------------+ 576 | 6LoRH | Length of compressed | 577 | Type | IPv6 address (bytes) | 578 +-----------+----------------------+ 579 | 0 | 1 | 580 | 1 | 2 | 581 | 2 | 4 | 582 | 3 | 8 | 583 | 4 | 16 | 584 +-----------+----------------------+ 586 Figure 7: The SRH-6LoRH Types. 588 In the case of a SRH-6LoRH header, the TSE field is used as a Size, 589 which encodes the number of hops minus 1; so a Size of 0 means one 590 hop, and the maximum that can be encoded is 32 hops. (If more than 591 32 hops need to be expressed, a sequence of SRH-6LoRH elements can be 592 employed.) It results that the Length in bytes of a SRH-6LoRH header 593 is: 595 2 + Length_of_compressed_IPv6_address * (Size + 1) 597 5.2. SRH-6LoRH General Operation 599 5.2.1. Uncompressed SRH Operation 601 In the non-compressed form, when the root generates or forwards a 602 packet in non-Storing Mode, it needs to include a Source Routing 603 Header [RFC6554] to signal a strict source-route path to a final 604 destination down the DODAG. 606 All the hops along the path, but the first one, are encoded in order 607 in the SRH. The last entry in the SRH is the final destination and 608 the destination in the IPv6 header is the first hop along the source- 609 route path. The intermediate hops perform a swap and the Segment- 610 Left field indicates the active entry in the Routing Header 611 [RFC2460]. 613 The current destination of the packet, which is the termination of 614 the current segment, is indicated at all times by the destination 615 address of the IPv6 header. 617 5.2.2. 6LoRH-Compressed SRH Operation 619 The handling of the SRH-6LoRH is different: there is no swap, and a 620 forwarding router that corresponds to the first entry in the first 621 SRH-6LoRH upon reception of a packet effectively consumes that entry 622 when forwarding. This means that the size of a compressed source- 623 routed packet decreases as the packet progresses along its path and 624 that the routing information is lost along the way. This also means 625 that an SRH encoded with 6LoRH is not recoverable and cannot be 626 protected. 628 When compressed with this specification, all the remaining hops MUST 629 be encoded in order in one or more consecutive SRH-6LoRH headers. 630 Whether or not there is a SRH-6LoRH header present, the address of 631 the final destination is indicated in the LOWPAN_IPHC at all times 632 along the path. Examples of this are provided in Appendix A. 634 The current destination (termination of the current segment) for a 635 compressed source-routed packet is indicated in the first entry of 636 the first SRH-6LoRH. In strict source-routing, that entry MUST match 637 an address of the router that receives the packet. 639 The last entry in the last SRH-6LoRH is the last router on the way to 640 the final destination in the LLN. This router can be the final 641 destination if it is found desirable to carry a whole IP-in-IP 642 encapsulation all the way. Else, it is the RPL parent of the final 643 destination, or a router acting at 6LR [RFC6775] for the destination 644 host, and advertising the host as an external route to RPL. 646 If the SRH-6LoRH header is contained in an IP-in-IP encapsulation, 647 the last router removes the whole chain of headers. Otherwise, it 648 removes the SRH-6LoRH header only. 650 5.2.3. Inner LOWPAN_IPHC Compression 652 6LoWPAN ND [RFC6282] is designed to support more than one IPv6 653 address per node and per Interface Identifier (IID), an IID being 654 typically derived from a MAC address to optimize the LOWPAN_IPHC 655 compression. 657 Link local addresses are compressed with stateless address 658 compression (S/DAC=0). The other addresses are derived from 659 different prefixes and they can be compressed with stateful address 660 compression based on a context (S/DAC=1). 662 But stateless compression is only defined for the specific link-local 663 prefix as opposed to the prefix in an encapsulating header. And with 664 stateful compression, the compression reference is found in a 665 context, as opposed to an encapsulating header. 667 It results that in the case of an IP-in-IP encapsulation, it is 668 possible to compress an inner source (respectively destination) IP 669 address in a LOWPAN_IPHC based on the encapsulating IP header only if 670 stateful (context-based) compression is used. The compression will 671 operate only if the IID in the source (respectively the destination) 672 IP address in the outer and inner headers match, which usually means 673 that they refer to the same node . This is encoded as S/DAC = 1 and 674 S/AM=11. It must be noted that the outer destination address that is 675 used to compress the inner destination address is the last entry in 676 the last SRH-6LoRH header. 678 5.3. The Design Point of Popping Entries 680 In order to save energy and to optimize the chances of transmission 681 success on lossy media, it is a design point for this specification 682 that the entries in the SRH that have been used are removed from the 683 packet. This creates a discrepancy from the art of IPv6 where 684 Routing Header are mutable but recoverable. 686 With this specification, the packet can be expanded at any hop into a 687 valid IPv6 packet, including a SRH, and compressed back. But the 688 packet as decompressed along the way will not carry all the consumed 689 addresses that packet would have if it had been forwarded in the 690 uncompressed form. 692 It is noted that: 694 The value of keeping the whole RH in an IPv6 header is for the 695 receiver to reverse it to use the symmetrical path on the way 696 back. 698 It is generally not a good idea to reverse a routing header. The 699 RH may have been used to stay away from the shortest path for some 700 reason that is only valid on the way in (segment routing). 702 There is no use of reversing a RH in the present RPL 703 specifications. 705 P2P RPL reverses a path that was learned reactively, as a part of 706 the protocol operation, which is probably a cleaner way than a 707 reversed echo on the data path. 709 Reversing a header is discouraged by RFC 2460 [RFC2460] for RH0 710 unless it is authenticated, which requires an Authentication 711 Header (AH). There is no definition of an AH operation for SRH, 712 and there is no indication that the need exists in LLNs. 714 It is noted that AH does not protect the RH on the way. AH is a 715 validation at the receiver with the sole value of enabling the 716 receiver to reversing it. 718 A RPL domain is usually protected by L2 security and that secures 719 both RPL itself and the RH in the packets, at every hop. This is 720 a better security than that provided by AH. 722 In summary, the benefit of saving energy and lowering the chances of 723 loss by sending smaller frames over the LLN are seen as overwhelming 724 compared to the value of possibly reversing the header. 726 5.4. Compression Reference for SRH-6LoRH header entries 728 In order to optimize the compression of IP addresses present in the 729 SRH headers, this specification requires that the 6LoWPAN layer 730 identifies an address that is used as reference for the compression. 732 With this specification, the Compression Reference for the first 733 address found in an SRH header is the source of the IPv6 packet, and 734 then the reference for each subsequent entry is the address of its 735 predecessor once it is uncompressed. 737 With RPL [RFC6550], an SRH header may only be present in Non-Storing 738 mode, and it may only be placed in the packet by the root of the 739 DODAG, which must be the source of the resulting IPv6 packet 740 [RFC2460]. In this case, the address used as Compression Reference 741 is the address of the root. 743 The Compression Reference MUST be determined as follows: 745 The reference address may be obtained by configuration. The 746 configuration may indicate either the address in full, or the 747 identifier of a 6LoWPAN Context that carries the address [RFC6775], 748 for instance one of the 16 Context Identifiers used in LOWPAN_IPHC 749 [RFC6282]. 751 Else, and if there is no IP-in-IP encapsulation, the source address 752 in the IPv6 header that is compressed with LOWPAN_IPHC is the 753 reference for the compression. 755 Else, and if the IP-in-IP compression specified in this document is 756 used and the Encapsulator Address is provided, then the Encapsulator 757 Address is the reference. 759 Else, meaning that the IP-in-IP compression specified in this 760 document is used and the encapsulator is implicitly the root, the 761 address of the root is the reference. 763 5.5. Popping Headers 765 Upon reception, the router checks whether the address in the first 766 entry of the first SRH-6LoRH one of its own addresses. In that case, 767 router MUST consume that entry before forwarding, which is an action 768 of popping from a stack, where the stack is effectively the sequence 769 of entries in consecutive SRH-6LoRH headers. 771 Popping an entry of an SRH-6LoRH header is a recursive action 772 performed as follows: 774 If the Size of the SRH-6LoRH header is 1 or more, indicating that 775 there are at least 2 entries in the header, the router removes the 776 first entry and decrements the Size (by 1). 778 Else (meaning that this is the last entry in the SRH-6LoRH header), 779 and if there is no next SRH-6LoRH header after this then the SRH- 780 6LoRH is removed. 782 Else, if there is a next SRH-6LoRH of a Type with a larger or equal 783 value, meaning a same or lesser compression yielding same or larger 784 compressed forms, then the SRH-6LoRH is removed. 786 Else, the first entry of the next SRH-6LoRH is popped from the next 787 SRH-6LoRH and coalesced with the first entry of this SRH-6LoRH. 789 At the end of the process, if there is no more SRH-6LoRH in the 790 packet, then the processing node is the last router along the source 791 route path. 793 An example of this operation is provided in Appendix A.3. 795 5.6. Forwarding 797 When receiving a packet with a SRH-6LoRH, a router determines the 798 IPv6 address of the current segment endpoint. 800 If strict source routing is enforced and this router is not the 801 segment endpoint for the packet then this router MUST drop the 802 packet. 804 If this router is the current segment endpoint, then the router pops 805 its address as described in Section 5.5 and continues processing the 806 packet. 808 If there is still a SRH-6LoRH, then the router determines the new 809 segment endpoint and routes the packet towards that endpoint. 811 Otherwise the router uses the destination in the inner IP header to 812 forward or accept the packet. 814 The segment endpoint of a packet MUST be determined as follows: 816 The router first determines the Compression Reference as discussed in 817 Section 4.3.1. 819 The router then coalesces the Compression Reference with the first 820 entry of the first SRH-6LoRH header as discussed in Section 5.4. If 821 the type of the SRH-6LoRH header is type 4 then the coalescence is a 822 full override. 824 Since the Compression Reference is an uncompressed address, the 825 coalesced IPv6 address is also expressed in the full 128bits. 827 6. The RPL Packet Information 6LoRH 829 RPL [RFC6550], Section 11.2, specifies the RPL Packet Information 830 (RPI) as a set of fields that are placed by RPL routers in IP packets 831 to identify the RPL Instance, detect anomalies and trigger corrective 832 actions. 834 In particular, the SenderRank, which is the scalar metric computed by 835 a specialized Objective Function such as described in RFC 6552 836 [RFC6552], indicates the Rank of the sender and is modified at each 837 hop. The SenderRank field is used to validate that the packet 838 progresses in the expected direction, either upwards or downwards, 839 along the DODAG. 841 RPL defines the "RPL Option for Carrying RPL Information in Data- 842 Plane Datagrams" [RFC6553] to transport the RPI, which is carried in 843 an IPv6 Hop-by-Hop Options Header [RFC2460], typically consuming 844 eight bytes per packet. 846 With RFC 6553 [RFC6553], the RPL option is encoded as six octets, 847 which must be placed in a Hop-by-Hop header that consumes two 848 additional octets for a total of eight octets. To limit the header's 849 range to just the RPL domain, the Hop-by-Hop header must be added to 850 (or removed from) packets that cross the border of the RPL domain. 852 The 8-byte overhead is detrimental to LLN operation, in particular 853 with regards to bandwidth and battery constraints. These bytes may 854 cause a containing frame to grow above maximum frame size, leading to 855 Layer 2 or 6LoWPAN [RFC4944] fragmentation, which in turn leads to 856 even more energy expenditure and issues discussed in "LLN Fragment 857 Forwarding and Recovery" [I-D.thubert-6lo-forwarding-fragments]. 859 An additional overhead comes from the need, in certain cases, to add 860 an IP-in-IP encapsulation to carry the Hop-by-Hop header. This is 861 needed when the router that inserts the Hop-by-Hop header is not the 862 source of the packet, so that an error can be returned to the router. 863 This is also the case when a packet originated by a RPL node must be 864 stripped from the Hop-by-Hop header to be routed outside the RPL 865 domain. 867 For that reason, this specification defines an IP-in-IP-6LoRH header 868 in Section 7, but it must be noted that removal of a 6LoRH header 869 does not require manipulation of the packet in the LOWPAN_IPHC, and 870 thus, if the source address in the LOWPAN_IPHC is the node that 871 inserted the IP-in-IP-6LoRH header then this situation alone does not 872 mandate an IP-in-IP-6LoRH header. 874 Note: it was found that some implementations omit the RPI for packets 875 going down the RPL graph in Non-Storing Mode, even though RPL 876 indicates that the RPI should be placed in the packet. With this 877 specification, the RPI is important to indicate the RPLInstanceID so 878 the RPI should not be omitted. 880 As a result, a RPL packet may bear only an RPI-6LoRH header and no 881 IP-in-IP-6LoRH header. In that case, the source and destination of 882 the packet are specified by the LOWPAN_IPHC. 884 As with RFC 6553 [RFC6553], the fields in the RPI include an 'O', an 885 'R', and an 'F' bit, an 8-bit RPLInstanceID (with some internal 886 structure), and a 16-bit SenderRank. 888 The remainder of this section defines the RPI-6LoRH header, which is 889 a Critical 6LoWPAN Routing Header that is designed to transport the 890 RPI in 6LoWPAN LLNs. 892 6.1. Compressing the RPLInstanceID 894 RPL Instances are discussed in Section 5 of the RPL specification 895 [RFC6550]. A number of simple use cases do not require more than one 896 RPL Instance, and in such cases, the RPL Instance is expected to be 897 the Global Instance 0. A global RPLInstanceID is encoded in a 898 RPLInstanceID field as follows: 900 0 1 2 3 4 5 6 7 901 +-+-+-+-+-+-+-+-+ 902 |0| ID | Global RPLInstanceID in 0..127 903 +-+-+-+-+-+-+-+-+ 905 Figure 8: RPLInstanceID Field Format for Global Instances. 907 For the particular case of the Global Instance 0, the RPLInstanceID 908 field is all zeros. This specification allows to elide a 909 RPLInstanceID field that is all zeros, and defines a I flag that, 910 when set, signals that the field is elided. 912 6.2. Compressing the SenderRank 914 The SenderRank is the result of the DAGRank operation on the rank of 915 the sender; here the DAGRank operation is defined in Section 3.5.1 of 916 the RPL specification [RFC6550] as: 918 DAGRank(rank) = floor(rank/MinHopRankIncrease) 920 If MinHopRankIncrease is set to a multiple of 256, the least 921 significant 8 bits of the SenderRank will be all zeroes; by eliding 922 those, the SenderRank can be compressed into a single byte. This 923 idea is used in RFC 6550 [RFC6550] by defining 924 DEFAULT_MIN_HOP_RANK_INCREASE as 256 and in RFC 6552 [RFC6552] that 925 defaults MinHopRankIncrease to DEFAULT_MIN_HOP_RANK_INCREASE. 927 This specification allows to encode the SenderRank as either one or 928 two bytes, and defines a K flag that, when set, signals that a single 929 byte is used. 931 6.3. The Overall RPI-6LoRH encoding 933 The RPI-6LoRH header provides a compressed form for the RPL RPI. 934 Routers that need to forward a packet with a RPI-6LoRH header are 935 expected to be RPL routers that support this specification. 937 If a non-RPL router receives a packet with a RPI-6LoRH header, there 938 was a routing or a configuration error (see Section 8). 940 The desired reaction for the non-RPL router is to drop the packet as 941 opposed to skip the header and forward the packet, which could end up 942 forming loops by reinjecting the packet in the wrong RPL Instance. 944 The Dispatch Value Bit Pattern for the SRH-6LoRH header indicates 945 Critical. Routers that understand the 6LoRH general format detailed 946 in Section 4 cannot ignore a 6LoRH header of this type, and will drop 947 the packet if it is unknown to them. 949 Since the RPI-6LoRH header is a critical header, the TSE field does 950 not need to be a length expressed in bytes. In that case the field 951 is fully reused for control bits that encode the O, R and F flags 952 from the RPI, as well as the I and K flags that indicate the 953 compression format. 955 The Type for the RPI-6LoRH is 5. 957 The RPI-6LoRH header is immediately followed by the RPLInstanceID 958 field, unless that field is fully elided, and then the SenderRank, 959 which is either compressed into one byte or fully in-lined as two 960 bytes. The I and K flags in the RPI-6LoRH header indicate whether 961 the RPLInstanceID is elided and/or the SenderRank is compressed. 962 Depending on these bits, the Length of the RPI-6LoRH may vary as 963 described hereafter. 965 0 1 2 966 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 967 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... -+-+-+ 968 |1|0|0|O|R|F|I|K| 6LoRH Type=5 | Compressed fields | 969 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... -+-+-+ 971 Figure 9: The Generic RPI-6LoRH Format. 973 O, R, and F bits: The O, R, and F bits are defined in section 11.2 974 of RFC 6550 [RFC6550]. 976 I flag: If it is set, the RPLInstanceID is elided and the 977 RPLInstanceID is the Global RPLInstanceID 0. If it is not set, 978 the octet immediately following the type field contains the 979 RPLInstanceID as specified in section 5.1 of RFC 6550 980 [RFC6550],. 982 K flag: If it is set, the SenderRank is compressed into one octet, 983 with the least significant octet elided. If it is not set, the 984 SenderRank, is fully inlined as two octets. 986 In Figure 10, the RPLInstanceID is the Global RPLInstanceID 0, and 987 the MinHopRankIncrease is a multiple of 256 so the least significant 988 byte is all zeros and can be elided: 990 0 1 2 991 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 992 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 993 |1|0|0|O|R|F|1|1| 6LoRH Type=5 | SenderRank | 994 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 995 I=1, K=1 997 Figure 10: The most compressed RPI-6LoRH. 999 In Figure 11, the RPLInstanceID is the Global RPLInstanceID 0, but 1000 both bytes of the SenderRank are significant so it can not be 1001 compressed: 1003 0 1 2 3 1004 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 1005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1006 |1|0|0|O|R|F|1|0| 6LoRH Type=5 | SenderRank | 1007 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1008 I=1, K=0 1010 Figure 11: Eliding the RPLInstanceID. 1012 In Figure 12, the RPLInstanceID is not the Global RPLInstanceID 0, 1013 and the MinHopRankIncrease is a multiple of 256: 1015 0 1 2 3 1016 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 1017 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1018 |1|0|0|O|R|F|0|1| 6LoRH Type=5 | RPLInstanceID | SenderRank | 1019 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1020 I=0, K=1 1022 Figure 12: Compressing SenderRank. 1024 In Figure 13, the RPLInstanceID is not the Global RPLInstanceID 0, 1025 and both bytes of the SenderRank are significant: 1027 0 1 2 3 1028 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 1029 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1030 |1|0|0|O|R|F|0|0| 6LoRH Type=5 | RPLInstanceID | Sender-... 1031 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1032 ...-Rank | 1033 +-+-+-+-+-+-+-+-+ 1034 I=0, K=0 1036 Figure 13: Least compressed form of RPI-6LoRH. 1038 7. The IP-in-IP 6LoRH Header 1040 The IP-in-IP 6LoRH (IP-in-IP-6LoRH) header is an Elective 6LoWPAN 1041 Routing Header that provides a compressed form for the encapsulating 1042 IPv6 Header in the case of an IP-in-IP encapsulation. 1044 An IP-in-IP encapsulation is used to insert a field such as a Routing 1045 Header or an RPI at a router that is not the source of the packet. 1046 In order to send an error back regarding the inserted field, the 1047 address of the router that performs the insertion must be provided. 1049 The encapsulation can also enable the last router prior to 1050 Destination to remove a field such as the RPI, but this can be done 1051 in the compressed form by removing the RPI-6LoRH, so an IP-in-IP- 1052 6LoRH encapsulation is not required for that sole purpose. 1054 The Dispatch Value Bit Pattern for the SRH-6LoRH header indicates 1055 Elective. This field is not critical for routing since it does not 1056 indicate the destination of the packet, which is either encoded in a 1057 SRH-6LoRH header or in the inner IP header. A 6LoRH header of this 1058 type can be skipped if not understood (per Section 4), and the 6LoRH 1059 header indicates the Length in bytes. 1061 0 1 2 1062 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 1063 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 1064 |1|0|1| Length | 6LoRH Type 6 | Hop Limit | Encaps. Address | 1065 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 1067 Figure 14: The IP-in-IP-6LoRH. 1069 The Length of an IP-in-IP-6LoRH header is expressed in bytes and MUST 1070 be at least 1, to indicate a Hop Limit (HL), that is decremented at 1071 each hop. When the HL reaches 0, the packet is dropped per RFC 2460 1072 [RFC2460]. 1074 If the Length of an IP-in-IP-6LoRH header is exactly 1, then the 1075 Encapsulator Address is elided, which means that the Encapsulator is 1076 a well-known router, for instance the root in a RPL graph. 1078 The most efficient compression of an IP-in-IP encapsulation that can 1079 be achieved with this specification is obtained when an endpoint of 1080 the packet is the root of the RPL DODAG associated to the RPL 1081 Instance that is used to forward the packet, and the root address is 1082 known implicitly as opposed to signaled explicitly in the data 1083 packets. 1085 If the Length of an IP-in-IP-6LoRH header is greater than 1, then an 1086 Encapsulator Address is placed in a compressed form after the Hop 1087 Limit field. The value of the Length indicates which compression is 1088 performed on the Encapsulator Address. For instance, a Length of 3 1089 indicates that the Encapsulator Address is compressed to 2 bytes. 1090 The reference for the compression is the address of the root of the 1091 DODAG. The way the address of the root is determined is discussed in 1092 Section 4.3.2. 1094 With RPL, the destination address in the IP-in-IP header is 1095 implicitly the root in the RPL graph for packets going upwards, and, 1096 in storing mode, it is the destination address in the LOWPAN_IPHC for 1097 packets going downwards. In non-storing mode, there is no implicit 1098 value for packets going downwards. 1100 If the implicit value is correct, the destination IP address of the 1101 IP-in-IP encapsulation can be elided. Else, the destination IP 1102 address of the IP-in-IP header is transported in a SRH-6LoRH header 1103 as the first entry of the first of these headers. 1105 If the final destination of the packet is a leaf that does not 1106 support this specification, then the chain of 6LoRH headers must be 1107 stripped by the RPL/6LR router to which the leaf is attached. In 1108 that example, the destination IP address of the IP-in-IP header 1109 cannot be elided. 1111 In the special case where a 6LoRH header is used to route 6LoWPAN 1112 fragments, the destination address is not accessible in the 1113 LOWPAN_IPHC on all fragments and can be elided only for the first 1114 fragment and for packets going upwards. 1116 8. Management Considerations 1118 Though it is possible to decompress a packet at any hop, this 1119 specification is optimized to enable that a packet is forwarded in 1120 its compressed form all the way, and it makes sense to deploy 1121 homogeneous networks, where all nodes, or no node at all, use the 1122 compression technique detailed therein. 1124 This specification does not provide a method to discover the 1125 capability by a next-hop device to support the compression technique, 1126 or the incremental addition of 6LoWPAN Routing Header as new 1127 specifications are published, considering that such extraneous code 1128 would overburden many constrained devices. This specification does 1129 not require extraneous code to exchange and handle error messages for 1130 mismatch situations, either. 1132 It is thus critical to keep the network homogeneous, or at least 1133 provide in forwarding nodes the knowledge of the support by the next 1134 hops. This is either a deployment issue, by deploying only devices 1135 with a same capability, or a management issue, by configuring all 1136 devices to either use, or not use, a certain level of this 1137 compression technique and its future additions. 1139 In particular, the situation where a node receives a message with a 1140 Critical 6LoWPAN Routing Header that it does not understand is an 1141 administrative error whereby the wrong device is placed in a network, 1142 or the device is mis-configured. 1144 When a mismatch situation is detected, it is expected that the device 1145 raises some management alert, indicating the issue, e.g. that it has 1146 to drop a packet with a Critical 6LoRH. 1148 9. Security Considerations 1150 The security considerations of RFC 4944 [RFC4944], RFC 6282 1151 [RFC6282], and RFC 6553 [RFC6553] apply. 1153 Using a compressed format as opposed to the full in-line format is 1154 logically equivalent and is believed to not create an opening for a 1155 new threat when compared to RFC 6550 [RFC6550], RFC 6553 [RFC6553] 1156 and RFC 6554 [RFC6554], noting that, even though intermediate hops 1157 are removed from the SRH header as they are consumed, a node may 1158 still identify that the rest of the source routed path includes a 1159 loop or not (see Security section of RFC 6554). It must be noted 1160 that if the attacker is not part of the loop, then there is always a 1161 node at the beginning of the loop that can detect it and remove it. 1163 10. IANA Considerations 1165 This specification reserves Dispatch Value Bit Patterns within the 1166 6LoWPAN Dispatch Page 1 as follows: 1168 101xxxxx: for Elective 6LoWPAN Routing Headers 1170 100xxxxx: for Critical 6LoWPAN Routing Headers. 1172 Additionally this document creates two IANA registries, one for the 1173 Critical 6LoWPAN Routing Header Type and one for the Elective 6LoWPAN 1174 Routing Header Type, each with 32 possible values from 0 to 31, as 1175 described below. 1177 Future assignments in these registries are to be coordinated via IANA 1178 under the policy of "RFC Required" (per RFC 5226 [RFC5226]) to enable 1179 any type of RFC to obtain a value in the registry. 1181 10.2. New Critical 6LoWPAN Routing Header Type Registry 1183 This document creates an IANA registry for the Critical 6LoWPAN 1184 Routing Header Type, and assigns the following values: 1186 0..4: SRH-6LoRH [RFCthis] 1188 5: RPI-6LoRH [RFCthis] 1190 10.3. New Elective 6LoWPAN Routing Header Type Registry 1192 This document creates an IANA registry for the Elective 6LoWPAN 1193 Routing Header Type, and assigns the following value: 1195 6: IP-in-IP-6LoRH [RFCthis] 1197 11. Acknowledgments 1199 The authors wish to thank Tom Phinney, Thomas Watteyne, Tengfei 1200 Chang, Martin Turon, James Woodyatt, Samita Chakrabarti, Jonathan 1201 Hui, Gabriel Montenegro and Ralph Droms for constructive reviews to 1202 the design in the 6lo Working Group. The overall discussion involved 1203 participants to the 6MAN, 6TiSCH and ROLL WGs, thank you all. 1204 Special thanks to the chairs of the ROLL WG, Michael Richardson and 1205 Ines Robles, Brian Haberman, Internet Area A-D, and Alvaro Retana and 1206 Adrian Farrel, Routing Area A-Ds, for driving this complex effort 1207 across Working Groups and Areas. 1209 12. References 1211 12.1. Normative References 1213 [I-D.ietf-6lo-paging-dispatch] 1214 Thubert, P. and R. Cragie, "6LoWPAN Paging Dispatch", 1215 draft-ietf-6lo-paging-dispatch-05 (work in progress), 1216 October 2016. 1218 [IEEE802154] 1219 IEEE standard for Information Technology, "IEEE std. 1220 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) 1221 and Physical Layer (PHY) Specifications for Low-Rate 1222 Wireless Personal Area Networks", 2015. 1224 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1225 Requirement Levels", BCP 14, RFC 2119, 1226 DOI 10.17487/RFC2119, March 1997, 1227 . 1229 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1230 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 1231 December 1998, . 1233 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 1234 "Transmission of IPv6 Packets over IEEE 802.15.4 1235 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, 1236 . 1238 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1239 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1240 DOI 10.17487/RFC5226, May 2008, 1241 . 1243 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1244 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1245 DOI 10.17487/RFC6282, September 2011, 1246 . 1248 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1249 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1250 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1251 Low-Power and Lossy Networks", RFC 6550, 1252 DOI 10.17487/RFC6550, March 2012, 1253 . 1255 [RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing 1256 Protocol for Low-Power and Lossy Networks (RPL)", 1257 RFC 6552, DOI 10.17487/RFC6552, March 2012, 1258 . 1260 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1261 Power and Lossy Networks (RPL) Option for Carrying RPL 1262 Information in Data-Plane Datagrams", RFC 6553, 1263 DOI 10.17487/RFC6553, March 2012, 1264 . 1266 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1267 Routing Header for Source Routes with the Routing Protocol 1268 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1269 DOI 10.17487/RFC6554, March 2012, 1270 . 1272 12.2. Informative References 1274 [I-D.ietf-6tisch-architecture] 1275 Thubert, P., "An Architecture for IPv6 over the TSCH mode 1276 of IEEE 802.15.4", draft-ietf-6tisch-architecture-10 (work 1277 in progress), June 2016. 1279 [I-D.ietf-roll-useofrplinfo] 1280 Robles, I., Richardson, M., and P. Thubert, "When to use 1281 RFC 6553, 6554 and IPv6-in-IPv6", draft-ietf-roll- 1282 useofrplinfo-08 (work in progress), September 2016. 1284 [I-D.thubert-6lo-forwarding-fragments] 1285 Thubert, P. and J. Hui, "LLN Fragment Forwarding and 1286 Recovery", draft-thubert-6lo-forwarding-fragments-02 (work 1287 in progress), November 2014. 1289 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1290 Bormann, "Neighbor Discovery Optimization for IPv6 over 1291 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1292 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1293 . 1295 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1296 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1297 2014, . 1299 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1300 Constrained-Node Networks", RFC 7228, 1301 DOI 10.17487/RFC7228, May 2014, 1302 . 1304 [RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using 1305 IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the 1306 Internet of Things (IoT): Problem Statement", RFC 7554, 1307 DOI 10.17487/RFC7554, May 2015, 1308 . 1310 Appendix A. Examples 1312 A.1. Examples Compressing The RPI 1314 The example in Figure 15 illustrates the 6LoRH compression of a 1315 classical packet in Storing Mode in all directions, as well as in 1316 non-Storing mode for a packet going up the DODAG following the 1317 default route to the root. In this particular example, a 1318 fragmentation process takes place per RFC 4944 [RFC4944], and the 1319 fragment headers must be placed in Page 0 before switching to Page 1: 1321 +- ... -+- ... -+-+ ... -+- ... +-+-+ ... -+-+-+-+-+-+-+-+-+-+... 1322 |Frag type|Frag hdr |11110001| RPI- |IP-in-IP| LOWPAN_IPHC | ... 1323 |RFC 4944 |RFC 4944 | Page 1 | 6LoRH | 6LoRH | | 1324 +- ... -+- ... -+-+ ... -+- ... +-+-+ ... -+-+-+-+-+-+-+-+-+-+... 1325 <- RFC 6282 -> 1326 No RPL artifact 1328 +- ... -+- ... -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+... 1329 |Frag type|Frag hdr | 1330 |RFC 4944 |RFC 4944 | Payload (cont) 1331 +- ... -+- ... -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+... 1333 +- ... -+- ... -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+... 1334 |Frag type|Frag hdr | 1335 |RFC 4944 |RFC 4944 | Payload (cont) 1336 +- ... -+- ... -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+... 1338 Figure 15: Example Compressed Packet with RPI. 1340 In Storing Mode, if the packet stays within the RPL domain, then it 1341 is possible to save the IP-in-IP encapsulation, in which case only 1342 the RPI is compressed with a 6LoRH, as illustrated in Figure 16 in 1343 the case of a non-fragmented ICMP packet: 1345 +- ... -+-+- ... -+-+-+-+ ... -+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+... 1346 |11110001| RPI-6LoRH | NH = 0 | NH = 58 | ICMP message ... 1347 |Page 1 | type 5 | 6LOWPAN_IPHC | (ICMP) | (no compression) 1348 +- ... -+-+- ... -+-+-+-+ ... -+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+... 1349 <- RFC 6282 -> 1350 No RPL artifact 1352 Figure 16: Example ICMP Packet with RPI in Storing Mode. 1354 The format in Figure 16 is logically equivalent to the non-compressed 1355 format illustrated in Figure 17: 1357 +-+-+-+- ... -+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+... 1358 | IPv6 Header | Hop-by-Hop | RPI in | ICMP message ... 1359 | NH = 58 | Header | RPL Option | 1360 +-+-+-+- ... -+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+... 1362 Figure 17: Uncompressed ICMP Packet with RPI. 1364 For a UDP packet, the transport header can be compressed with 6LoWPAN 1365 HC [RFC6282] as illustrated in Figure 18: 1367 +-+ ... -+-+-...-+-+- ... -+-+-+-+ ... -+-+-+ ... -+-+-+-+-+... 1368 |11110001| RPI- | NH=1 |11110CPP| Compressed | UDP 1369 |Page 1 | 6LoRH | LOWPAN_IPHC | UDP | UDP header | Payload 1370 +-+ ... -+-+-...-+-+- ... -+-+-+-+ ... -+-+-+ ... -+-+-+-+-+... 1371 <- RFC 6282 -> 1372 No RPL artifact 1374 Figure 18: Uncompressed ICMP Packet with RPI. 1376 If the packet is received from the Internet in Storing Mode, then the 1377 root is supposed to encapsulate the packet to insert the RPI. The 1378 resulting format would be as represented in Figure 19: 1380 +-+ ... -+-+-...-+-+-- ... -+-+-+-+- ... -+-+ ... -+-+-+ ... -+-+-+... 1381 |11110001| RPI- | IP-in-IP | NH=1 |11110CPP| Compressed | UDP 1382 |Page 1 | 6LoRH | 6LoRH | LOWPAN_IPHC | UDP | UDP header | Payld 1383 +-+ ... -+-+-...-+-+-- ... -+-+-+-+- ... -+-+ ... -+-+-+ ... -+-+-+... 1384 <- RFC 6282 -> 1385 No RPL artifact 1387 Figure 19: RPI inserted by the root in Storing Mode. 1389 A.2. Example Of Downward Packet In Non-Storing Mode 1391 The example illustrated in Figure 20 is a classical packet in non- 1392 Storing mode for a packet going down the DODAG following a source 1393 routed path from the root. Say that we have 4 forwarding hops to 1394 reach a destination. In the non-compressed form, when the root 1395 generates the packet, the last 3 hops are encoded in a Routing Header 1396 type 3 (SRH) and the first hop is the destination of the packet. The 1397 intermediate hops perform a swap and the hop count indicates the 1398 current active hop as defiend in RFC 2460 [RFC2460] and RFC 6554 1399 [RFC6554]. 1401 When compressed with this specification, the 4 hops are encoded in 1402 SRH-6LoRH when the root generates the packet, and the final 1403 destination is left in the LOWPAN_IPHC. There is no swap, and the 1404 forwarding node that corresponds to the first entry effectively 1405 consumes it when forwarding, which means that the size of the encoded 1406 packet decreases and that the hop information is lost. 1408 If the last hop in a SRH-6LoRH is not the final destination then it 1409 removes the SRH-6LoRH before forwarding. 1411 In the particular example illustrated in Figure 20, all addresses in 1412 the DODAG are assigned from a same /112 prefix and the last 2 octets 1413 encoding an identifier such as a IEEE 802.15.4 short address. In 1414 that case, all addresses can be compressed to 2 octets, using the 1415 root address as reference. There will be one SRH_6LoRH header, with, 1416 in this example, 3 compressed addresses: 1418 +-+-+-+-+-+-+- ... +-+-+- ... -+-+-- ... -+-+- ... -+-+-+-+-+ ... +-... 1419 |11110001 |SRH-6LoRH | RPI-6LoRH | IP-in-IP | NH=1 |11110CPP| UDP | UDP 1420 |Page 1 |Type1 S=2 | | 6LoRH |LOWPAN_IPHC | UDP | hdr |load 1421 +-+-+-+-+-+-+- ... +-+-+- ... -+-+-- ... -+-+- ... -+-+-+-+-+ ... +-... 1422 <-8bytes-> <- RFC 6282 -> 1423 No RPL artifact 1425 Figure 20: Example Compressed Packet with SRH. 1427 One may note that the RPI is provided. This is because the address 1428 of the root that is the source of the IP-in-IP header is elided and 1429 inferred from the RPLInstanceID in the RPI. Once found from a local 1430 context, that address is used as Compression Reference to expand 1431 addresses in the SRH-6LoRH. 1433 With the RPL specifications available at the time of writing this 1434 draft, the root is the only node that may incorporate a SRH in an IP 1435 packet. When the root forwards a packet that it did not generate, it 1436 has to encapsulate the packet with IP-in-IP. 1438 But if the root generates the packet towards a node in its DODAG, 1439 then it should avoid the extra IP-in-IP as illustrated in Figure 21: 1441 +- ... -+-+-+ ... +-+-+-+ ... -+-+-+-+-+-+-+-++-+- ... -+-+-+-+-+... 1442 |11110001| SRH-6LoRH | NH=1 | 11110CPP | Compressed | UDP 1443 |Page 1 | Type1 S=3 | LOWPAN_IPHC| LOWPAN-NHC| UDP header | Payload 1444 +- ... -+-+-+ ... +-+-+-+ ... -+-+-+-+-+-+-+-++-+- ... -+-+-+-+-+... 1445 <- RFC 6282 -> 1447 Figure 21: compressed SRH 4*2bytes entries sourced by root. 1449 Note: the RPI is not represented though RPL [RFC6550] generally 1450 expects it. In this particular case, since the Compression Reference 1451 for the SRH-6LoRH is the source address in the LOWPAN_IPHC, and the 1452 routing is strict along the source route path, the RPI does not 1453 appear to be absolutely necessary. 1455 In Figure 21, all the nodes along the source route path share a same 1456 /112 prefix. This is typical of IPv6 addresses derived from an 1457 IEEE802.15.4 short address, as long as all the nodes share a same 1458 PAN-ID. In that case, a type-1 SRH-6LoRH header can be used for 1459 encoding. The IPv6 address of the root is taken as reference, and 1460 only the last 2 octets of the address of the intermediate hops is 1461 encoded. The Size of 3 indicates 4 hops, resulting in a SRH-6LoRH of 1462 10 bytes. 1464 A.3. Example of SRH-6LoRH life-cycle 1466 This section illustrates the operation specified in Section 5.6 of 1467 forwarding a packet with a compressed SRH along an A->B->C->D source 1468 route path. The operation of popping addresses is exemplified at 1469 each hop. 1471 Packet as received by node A 1472 ---------------------------- 1473 Type 3 SRH-6LoRH Size = 0 AAAA AAAA AAAA AAAA 1474 Type 1 SRH-6LoRH Size = 0 BBBB 1475 Type 2 SRH-6LoRH Size = 1 CCCC CCCC 1476 DDDD DDDD 1478 Step 1 popping BBBB the first entry of the next SRH-6LoRH 1479 Step 2 next is if larger value (2 vs. 1) the SRH-6LoRH is removed 1481 Type 3 SRH-6LoRH Size = 0 AAAA AAAA AAAA AAAA 1482 Type 2 SRH-6LoRH Size = 1 CCCC CCCC 1483 DDDD DDDD 1485 Step 3: recursion ended, coalescing BBBB with the first entry 1486 Type 3 SRH-6LoRH Size = 0 AAAA AAAA AAAA BBBB 1488 Step 4: routing based on next segment endpoint to B 1490 Figure 22: Processing at Node A. 1492 Packet as received by node B 1493 ---------------------------- 1494 Type 3 SRH-6LoRH Size = 0 AAAA AAAA AAAA BBBB 1495 Type 2 SRH-6LoRH Size = 1 CCCC CCCC 1496 DDDD DDDD 1498 Step 1 popping CCCC CCCC, the first entry of the next SRH-6LoRH 1499 Step 2 removing the first entry and decrementing the Size (by 1) 1501 Type 3 SRH-6LoRH Size = 0 AAAA AAAA AAAA BBBB 1502 Type 2 SRH-6LoRH Size = 0 DDDD DDDD 1504 Step 3: recursion ended, coalescing CCCC CCCC with the first entry 1505 Type 3 SRH-6LoRH Size = 0 AAAA AAAA CCCC CCCC 1507 Step 4: routing based on next segment endpoint to C 1509 Figure 23: Processing at Node B. 1511 Packet as received by node C 1512 ---------------------------- 1514 Type 3 SRH-6LoRH Size = 0 AAAA AAAA CCCC CCCC 1515 Type 2 SRH-6LoRH Size = 0 DDDD DDDD 1517 Step 1 popping DDDD DDDD, the first entry of the next SRH-6LoRH 1518 Step 2 the SRH-6LoRH is removed 1520 Type 3 SRH-6LoRH Size = 0 AAAA AAAA CCCC CCCC 1522 Step 3: recursion ended, coalescing DDDD DDDDD with the first entry 1523 Type 3 SRH-6LoRH Size = 0 AAAA AAAA DDDD DDDD 1525 Step 4: routing based on next segment endpoint to D 1527 Figure 24: Processing at Node C. 1529 Packet as received by node D 1530 ---------------------------- 1531 Type 3 SRH-6LoRH Size = 0 AAAA AAAA DDDD DDDD 1533 Step 1 the SRH-6LoRH is removed. 1534 Step 2 no more header, routing based on inner IP header. 1536 Figure 25: Processing at Node D. 1538 Authors' Addresses 1540 Pascal Thubert (editor) 1541 Cisco Systems 1542 Building D - Regus 1543 45 Allee des Ormes 1544 BP1200 1545 MOUGINS - Sophia Antipolis 06254 1546 FRANCE 1548 Phone: +33 4 97 23 26 34 1549 Email: pthubert@cisco.com 1551 Carsten Bormann 1552 Universitaet Bremen TZI 1553 Postfach 330440 1554 Bremen D-28359 1555 Germany 1557 Phone: +49-421-218-63921 1558 Email: cabo@tzi.org 1560 Laurent Toutain 1561 Institut MINES TELECOM; TELECOM Bretagne 1562 2 rue de la Chataigneraie 1563 CS 17607 1564 Cesson-Sevigne Cedex 35576 1565 France 1567 Email: Laurent.Toutain@telecom-bretagne.eu 1568 Robert Cragie 1569 ARM Ltd. 1570 110 Fulbourn Road 1571 Cambridge CB1 9NJ 1572 UK 1574 Email: robert.cragie@gridmerge.com