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Hinden 5 Intended status: Standards Track Check Point Software 6 Expires: June 18, 2016 December 16, 2015 8 Internet Protocol, Version 6 (IPv6) Specification 9 draft-ietf-6man-rfc2460bis-02 11 Abstract 13 This document specifies version 6 of the Internet Protocol (IPv6), 14 also sometimes referred to as IP Next Generation or IPng. It 15 obsoletes RFC2460 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at http://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on June 18, 2016. 34 Copyright Notice 36 Copyright (c) 2015 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 This document may contain material from IETF Documents or IETF 50 Contributions published or made publicly available before November 51 10, 2008. The person(s) controlling the copyright in some of this 52 material may not have granted the IETF Trust the right to allow 53 modifications of such material outside the IETF Standards Process. 54 Without obtaining an adequate license from the person(s) controlling 55 the copyright in such materials, this document may not be modified 56 outside the IETF Standards Process, and derivative works of it may 57 not be created outside the IETF Standards Process, except to format 58 it for publication as an RFC or to translate it into languages other 59 than English. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 3. IPv6 Header Format . . . . . . . . . . . . . . . . . . . . . 5 66 4. IPv6 Extension Headers . . . . . . . . . . . . . . . . . . . 6 67 4.1. Extension Header Order . . . . . . . . . . . . . . . . . 8 68 4.2. Options . . . . . . . . . . . . . . . . . . . . . . . . . 9 69 4.3. Hop-by-Hop Options Header . . . . . . . . . . . . . . . . 12 70 4.4. Routing Header . . . . . . . . . . . . . . . . . . . . . 13 71 4.5. Fragment Header . . . . . . . . . . . . . . . . . . . . . 14 72 4.6. Destination Options Header . . . . . . . . . . . . . . . 21 73 4.7. No Next Header . . . . . . . . . . . . . . . . . . . . . 22 74 4.8. Defining New Extension Headers and Options . . . . . . . 22 75 5. Packet Size Issues . . . . . . . . . . . . . . . . . . . . . 23 76 6. Flow Labels . . . . . . . . . . . . . . . . . . . . . . . . . 24 77 7. Traffic Classes . . . . . . . . . . . . . . . . . . . . . . . 24 78 8. Upper-Layer Protocol Issues . . . . . . . . . . . . . . . . . 25 79 8.1. Upper-Layer Checksums . . . . . . . . . . . . . . . . . . 25 80 8.2. Maximum Packet Lifetime . . . . . . . . . . . . . . . . . 26 81 8.3. Maximum Upper-Layer Payload Size . . . . . . . . . . . . 27 82 8.4. Responding to Packets Carrying Routing Headers . . . . . 27 83 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 84 10. Security Considerations . . . . . . . . . . . . . . . . . . . 28 85 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28 86 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 87 12.1. Normative References . . . . . . . . . . . . . . . . . . 28 88 12.2. Informative References . . . . . . . . . . . . . . . . . 29 89 Appendix A. Formatting Guidelines for Options . . . . . . . . . 30 90 Appendix B. CHANGES SINCE RFC2460 . . . . . . . . . . . . . . . 33 91 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37 93 1. Introduction 95 IP version 6 (IPv6) is a new version of the Internet Protocol, 96 designed as the successor to IP version 4 (IPv4) [RFC0791]. The 97 changes from IPv4 to IPv6 fall primarily into the following 98 categories: 100 o Expanded Addressing Capabilities 102 IPv6 increases the IP address size from 32 bits to 128 bits, to 103 support more levels of addressing hierarchy, a much greater 104 number of addressable nodes, and simpler auto-configuration of 105 addresses. The scalability of multicast routing is improved by 106 adding a "scope" field to multicast addresses. And a new type 107 of address called an "anycast address" is defined, used to send 108 a packet to any one of a group of nodes. 110 o Header Format Simplification 112 Some IPv4 header fields have been dropped or made optional, to 113 reduce the common-case processing cost of packet handling and 114 to limit the bandwidth cost of the IPv6 header. 116 o Improved Support for Extensions and Options 118 Changes in the way IP header options are encoded allows for 119 more efficient forwarding, less stringent limits on the length 120 of options, and greater flexibility for introducing new options 121 in the future. 123 o Flow Labeling Capability 125 A new capability is added to enable the labeling of sequences 126 of packets for which the sender requests to be treated in the 127 network as a single flow. 129 o Authentication and Privacy Capabilities 131 Extensions to support authentication, data integrity, and 132 (optional) data confidentiality are specified for IPv6. 134 This document specifies the basic IPv6 header and the initially- 135 defined IPv6 extension headers and options. It also discusses packet 136 size issues, the semantics of flow labels and traffic classes, and 137 the effects of IPv6 on upper-layer protocols. The format and 138 semantics of IPv6 addresses are specified separately in 140 [I-D.hinden-6man-rfc4291bis]. The IPv6 version of ICMP, which all 141 IPv6 implementations are required to include, is specified in 142 [RFC4443] 144 The data transmission order for IPv6 is the same as for IPv4 as 145 defined in Appendix B of [RFC0791]. 147 Note: As this document obsoletes [RFC2460], any document referenced 148 in this document that includes pointers to RFC2460, should be 149 interpreted as referencing this document. 151 2. Terminology 153 node a device that implements IPv6. 155 router a node that forwards IPv6 packets not explicitly 156 addressed to itself. [See Note below]. 158 host any node that is not a router. [See Note below]. 160 upper layer a protocol layer immediately above IPv6. Examples are 161 transport protocols such as TCP and UDP, control 162 protocols such as ICMP, routing protocols such as OSPF, 163 and internet or lower-layer protocols being "tunneled" 164 over (i.e., encapsulated in) IPv6 such as IPX, 165 AppleTalk, or IPv6 itself. 167 link a communication facility or medium over which nodes can 168 communicate at the link layer, i.e., the layer 169 immediately below IPv6. Examples are Ethernets (simple 170 or bridged); PPP links; X.25, Frame Relay, or ATM 171 networks; and internet (or higher) layer "tunnels", such 172 as tunnels over IPv4 or IPv6 itself. 174 neighbors nodes attached to the same link. 176 interface a node's attachment to a link. 178 address an IPv6-layer identifier for an interface or a set of 179 interfaces. 181 packet an IPv6 header plus payload. 183 link MTU the maximum transmission unit, i.e., maximum packet size 184 in octets, that can be conveyed over a link. 186 path MTU the minimum link MTU of all the links in a path between 187 a source node and a destination node. 189 Note: it is possible, though unusual, for a device with multiple 190 interfaces to be configured to forward non-self-destined packets 191 arriving from some set (fewer than all) of its interfaces, and to 192 discard non-self-destined packets arriving from its other interfaces. 193 Such a device must obey the protocol requirements for routers when 194 receiving packets from, and interacting with neighbors over, the 195 former (forwarding) interfaces. It must obey the protocol 196 requirements for hosts when receiving packets from, and interacting 197 with neighbors over, the latter (non-forwarding) interfaces. 199 3. IPv6 Header Format 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 202 |Version| Traffic Class | Flow Label | 203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 204 | Payload Length | Next Header | Hop Limit | 205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 206 | | 207 + + 208 | | 209 + Source Address + 210 | | 211 + + 212 | | 213 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 214 | | 215 + + 216 | | 217 + Destination Address + 218 | | 219 + + 220 | | 221 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 223 Version 4-bit Internet Protocol version number = 6. 225 Traffic Class 8-bit traffic class field. See section 7. 227 Flow Label 20-bit flow label. See section 6. 229 Payload Length 16-bit unsigned integer. Length of the IPv6 230 payload, i.e., the rest of the packet 231 following this IPv6 header, in octets. (Note 232 that any extension headers [section 4] present 233 are considered part of the payload, i.e., 234 included in the length count.) 236 Next Header 8-bit selector. Identifies the type of header 237 immediately following the IPv6 header. Uses 238 the same values as the IPv4 Protocol field 239 [IANA-PN]. 241 Hop Limit 8-bit unsigned integer. Decremented by 1 by 242 each node that forwards the packet. The 243 packet is discarded if Hop Limit is 244 decremented to zero, or is received with a 245 zero Hop Limit. 247 Source Address 128-bit address of the originator of the 248 packet. See [I-D.hinden-6man-rfc4291bis]. 250 Destination Address 128-bit address of the intended recipient of 251 the packet (possibly not the ultimate 252 recipient, if a Routing header is present). 253 See [I-D.hinden-6man-rfc4291bis] and section 254 4.4. 256 4. IPv6 Extension Headers 258 In IPv6, optional internet-layer information is encoded in separate 259 headers that may be placed between the IPv6 header and the upper- 260 layer header in a packet. There are a small number of such extension 261 headers, each identified by a distinct Next Header value. As 262 illustrated in these examples, an IPv6 packet may carry zero, one, or 263 more extension headers, each identified by the Next Header field of 264 the preceding header: 266 +---------------+------------------------ 267 | IPv6 header | TCP header + data 268 | | 269 | Next Header = | 270 | TCP | 271 +---------------+------------------------ 273 +---------------+----------------+------------------------ 274 | IPv6 header | Routing header | TCP header + data 275 | | | 276 | Next Header = | Next Header = | 277 | Routing | TCP | 278 +---------------+----------------+------------------------ 280 +---------------+----------------+-----------------+----------------- 281 | IPv6 header | Routing header | Fragment header | fragment of TCP 282 | | | | header + data 283 | Next Header = | Next Header = | Next Header = | 284 | Routing | Fragment | TCP | 285 +---------------+----------------+-----------------+----------------- 287 Extension headers must never be inserted by any node other than the 288 source of the packet. IP Encapsulation must be used to meet any 289 requirement for inserting headers, for example, as defined in 290 [RFC2473]. 292 With one exception, extension headers are not processed by any node 293 along a packet's delivery path, until the packet reaches the node (or 294 each of the set of nodes, in the case of multicast) identified in the 295 Destination Address field of the IPv6 header. Note: If an 296 intermediate forwarding node examines an extension header for any 297 reason, it must do so in accordance with the provisions of [RFC7045]. 298 At the Destination node, normal demultiplexing on the Next Header 299 field of the IPv6 header invokes the module to process the first 300 extension header, or the upper-layer header if no extension header is 301 present. The contents and semantics of each extension header 302 determine whether or not to proceed to the next header. Therefore, 303 extension headers must be processed strictly in the order they appear 304 in the packet; a receiver must not, for example, scan through a 305 packet looking for a particular kind of extension header and process 306 that header prior to processing all preceding ones. 308 The exception referred to in the preceding paragraph is the Hop-by- 309 Hop Options header, which carries information that should be examined 310 and processed by every node along a packet's delivery path, including 311 the source and destination nodes. The Hop-by-Hop Options header, 312 when present, must immediately follow the IPv6 header. Its presence 313 is indicated by the value zero in the Next Header field of the IPv6 314 header. 316 It should be noted that due to performance restrictions nodes may 317 ignore the Hop-by-Hop Option header, drop packets containing a hop- 318 by-hop option header, or assign packets containing a hop-by-hop 319 option header to a slow processing path. Designers planning to use a 320 hop-by-hop option need to be aware of this likely behaviour. 322 If, as a result of processing a header, a node is required to proceed 323 to the next header but the Next Header value in the current header is 324 unrecognized by the node, it should discard the packet and send an 325 ICMP Parameter Problem message to the source of the packet, with an 326 ICMP Code value of 1 ("unrecognized Next Header type encountered") 327 and the ICMP Pointer field containing the offset of the unrecognized 328 value within the original packet. The same action should be taken if 329 a node encounters a Next Header value of zero in any header other 330 than an IPv6 header. 332 Each extension header is an integer multiple of 8 octets long, in 333 order to retain 8-octet alignment for subsequent headers. Multi- 334 octet fields within each extension header are aligned on their 335 natural boundaries, i.e., fields of width n octets are placed at an 336 integer multiple of n octets from the start of the header, for n = 1, 337 2, 4, or 8. 339 A full implementation of IPv6 includes implementation of the 340 following extension headers: 342 Hop-by-Hop Options 343 Fragment 344 Destination Options 345 Authentication 346 Encapsulating Security Payload 348 The first three are specified in this document; the last two are 349 specified in [RFC4302] and [RFC4303], respectively. 351 4.1. Extension Header Order 353 When more than one extension header is used in the same packet, it is 354 recommended that those headers appear in the following order: 356 IPv6 header 357 Hop-by-Hop Options header 358 Destination Options header (note 1) 359 Routing header 360 Fragment header 361 Authentication header (note 2) 362 Encapsulating Security Payload header (note 2) 363 Destination Options header (note 3) 364 upper-layer header 366 note 1: for options to be processed by the first destination that 367 appears in the IPv6 Destination Address field plus 368 subsequent destinations listed in the Routing header. 370 note 2: additional recommendations regarding the relative order of 371 the Authentication and Encapsulating Security Payload 372 headers are given in [RFC4303]. 374 note 3: for options to be processed only by the final destination 375 of the packet. 377 Each extension header should occur at most once, except for the 378 Destination Options header which should occur at most twice (once 379 before a Routing header and once before the upper-layer header). 381 If the upper-layer header is another IPv6 header (in the case of IPv6 382 being tunneled over or encapsulated in IPv6), it may be followed by 383 its own extension headers, which are separately subject to the same 384 ordering recommendations. 386 If and when other extension headers are defined, their ordering 387 constraints relative to the above listed headers must be specified. 389 IPv6 nodes must accept and attempt to process extension headers in 390 any order and occurring any number of times in the same packet, 391 except for the Hop-by-Hop Options header which is restricted to 392 appear immediately after an IPv6 header only. Nonetheless, it is 393 strongly advised that sources of IPv6 packets adhere to the above 394 recommended order until and unless subsequent specifications revise 395 that recommendation. 397 4.2. Options 399 Two of the currently-defined extension headers -- the Hop-by-Hop 400 Options header and the Destination Options header -- carry a variable 401 number of type-length-value (TLV) encoded "options", of the following 402 format: 404 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 405 | Option Type | Opt Data Len | Option Data 406 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 407 Option Type 8-bit identifier of the type of option. 409 Opt Data Len 8-bit unsigned integer. Length of the Option 410 Data field of this option, in octets. 412 Option Data Variable-length field. Option-Type-specific 413 data. 415 The sequence of options within a header must be processed strictly in 416 the order they appear in the header; a receiver must not, for 417 example, scan through the header looking for a particular kind of 418 option and process that option prior to processing all preceding 419 ones. 421 The Option Type identifiers are internally encoded such that their 422 highest-order two bits specify the action that must be taken if the 423 processing IPv6 node does not recognize the Option Type: 425 00 - skip over this option and continue processing the header. 427 01 - discard the packet. 429 10 - discard the packet and, regardless of whether or not the 430 packet's Destination Address was a multicast address, send an 431 ICMP Parameter Problem, Code 2, message to the packet's 432 Source Address, pointing to the unrecognized Option Type. 434 11 - discard the packet and, only if the packet's Destination 435 Address was not a multicast address, send an ICMP Parameter 436 Problem, Code 2, message to the packet's Source Address, 437 pointing to the unrecognized Option Type. 439 The third-highest-order bit of the Option Type specifies whether or 440 not the Option Data of that option can change en-route to the 441 packet's final destination. When an Authentication header is present 442 in the packet, for any option whose data may change en-route, its 443 entire Option Data field must be treated as zero-valued octets when 444 computing or verifying the packet's authenticating value. 446 0 - Option Data does not change en-route 448 1 - Option Data may change en-route 450 The three high-order bits described above are to be treated as part 451 of the Option Type, not independent of the Option Type. That is, a 452 particular option is identified by a full 8-bit Option Type, not just 453 the low-order 5 bits of an Option Type. 455 The same Option Type numbering space is used for both the Hop-by-Hop 456 Options header and the Destination Options header. However, the 457 specification of a particular option may restrict its use to only one 458 of those two headers. 460 Individual options may have specific alignment requirements, to 461 ensure that multi-octet values within Option Data fields fall on 462 natural boundaries. The alignment requirement of an option is 463 specified using the notation xn+y, meaning the Option Type must 464 appear at an integer multiple of x octets from the start of the 465 header, plus y octets. For example: 467 2n means any 2-octet offset from the start of the header. 468 8n+2 means any 8-octet offset from the start of the header, plus 2 469 octets. 471 There are two padding options which are used when necessary to align 472 subsequent options and to pad out the containing header to a multiple 473 of 8 octets in length. These padding options must be recognized by 474 all IPv6 implementations: 476 Pad1 option (alignment requirement: none) 478 +-+-+-+-+-+-+-+-+ 479 | 0 | 480 +-+-+-+-+-+-+-+-+ 482 NOTE! the format of the Pad1 option is a special case -- it does 483 not have length and value fields. 485 The Pad1 option is used to insert one octet of padding into the 486 Options area of a header. If more than one octet of padding is 487 required, the PadN option, described next, should be used, rather 488 than multiple Pad1 options. 490 PadN option (alignment requirement: none) 491 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 492 | 1 | Opt Data Len | Option Data 493 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 495 The PadN option is used to insert two or more octets of padding 496 into the Options area of a header. For N octets of padding, the 497 Opt Data Len field contains the value N-2, and the Option Data 498 consists of N-2 zero-valued octets. 500 Appendix A contains formatting guidelines for designing new options. 502 4.3. Hop-by-Hop Options Header 504 The Hop-by-Hop Options header is used to carry optional information 505 that should be examined by every node along a packet's delivery path. 506 The Hop-by-Hop Options header is identified by a Next Header value of 507 0 in the IPv6 header, and has the following format: 509 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 510 | Next Header | Hdr Ext Len | | 511 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 512 | | 513 . . 514 . Options . 515 . . 516 | | 517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 519 Next Header 8-bit selector. Identifies the type of header 520 immediately following the Hop-by-Hop Options 521 header. Uses the same values as the IPv4 522 Protocol field [IANA-PN]. 524 Hdr Ext Len 8-bit unsigned integer. Length of the Hop-by- 525 Hop Options header in 8-octet units, not 526 including the first 8 octets. 528 Options Variable-length field, of length such that the 529 complete Hop-by-Hop Options header is an 530 integer multiple of 8 octets long. Contains 531 one or more TLV-encoded options, as described 532 in section 4.2. 534 The only hop-by-hop options defined in this document are the Pad1 and 535 PadN options specified in section 4.2. 537 4.4. Routing Header 539 The Routing header is used by an IPv6 source to list one or more 540 intermediate nodes to be "visited" on the way to a packet's 541 destination. This function is very similar to IPv4's Loose Source 542 and Record Route option. The Routing header is identified by a Next 543 Header value of 43 in the immediately preceding header, and has the 544 following format: 546 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 547 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 549 | | 550 . . 551 . type-specific data . 552 . . 553 | | 554 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 556 Next Header 8-bit selector. Identifies the type of header 557 immediately following the Routing header. 558 Uses the same values as the IPv4 Protocol 559 field [IANA-PN]. 561 Hdr Ext Len 8-bit unsigned integer. Length of the Routing 562 header in 8-octet units, not including the 563 first 8 octets. 565 Routing Type 8-bit identifier of a particular Routing 566 header variant. 568 Segments Left 8-bit unsigned integer. Number of route 569 segments remaining, i.e., number of explicitly 570 listed intermediate nodes still to be visited 571 before reaching the final destination. 573 type-specific data Variable-length field, of format determined by 574 the Routing Type, and of length such that the 575 complete Routing header is an integer multiple 576 of 8 octets long. 578 If, while processing a received packet, a node encounters a Routing 579 header with an unrecognized Routing Type value, the required behavior 580 of the node depends on the value of the Segments Left field, as 581 follows: 583 If Segments Left is zero, the node must ignore the Routing header 584 and proceed to process the next header in the packet, whose type 585 is identified by the Next Header field in the Routing header. 587 If Segments Left is non-zero, the node must discard the packet and 588 send an ICMP Parameter Problem, Code 0, message to the packet's 589 Source Address, pointing to the unrecognized Routing Type. 591 If, after processing a Routing header of a received packet, an 592 intermediate node determines that the packet is to be forwarded onto 593 a link whose link MTU is less than the size of the packet, the node 594 must discard the packet and send an ICMP Packet Too Big message to 595 the packet's Source Address. 597 The currently defined IPv6 Routing Headers and their status can be 598 found at [IANA-RH]. Allocation guidelines for IPv6 Routing Headers 599 can be found in [RFC5871]. 601 4.5. Fragment Header 603 The Fragment header is used by an IPv6 source to send a packet larger 604 than would fit in the path MTU to its destination. (Note: unlike 605 IPv4, fragmentation in IPv6 is performed only by source nodes, not by 606 routers along a packet's delivery path -- see section 5.) The 607 Fragment header is identified by a Next Header value of 44 in the 608 immediately preceding header, and has the following format: 610 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 611 | Next Header | Reserved | Fragment Offset |Res|M| 612 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 613 | Identification | 614 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 616 Next Header 8-bit selector. Identifies the initial header 617 type of the Fragmentable Part of the original 618 packet (defined below). Uses the same values 619 as the IPv4 Protocol field [IANA-PN]. 621 Reserved 8-bit reserved field. Initialized to zero for 622 transmission; ignored on reception. 624 Fragment Offset 13-bit unsigned integer. The offset, in 625 8-octet units, of the data following this 626 header, relative to the start of the 627 Fragmentable Part of the original packet. 629 Res 2-bit reserved field. Initialized to zero for 630 transmission; ignored on reception. 632 M flag 1 = more fragments; 0 = last fragment. 634 Identification 32 bits. See description below. 636 In order to send a packet that is too large to fit in the MTU of the 637 path to its destination, a source node may divide the packet into 638 fragments and send each fragment as a separate packet, to be 639 reassembled at the receiver. 641 For every packet that is to be fragmented, the source node generates 642 an Identification value. The Identification must be different than 643 that of any other fragmented packet sent recently* with the same 644 Source Address and Destination Address. If a Routing header is 645 present, the Destination Address of concern is that of the final 646 destination. 648 * "recently" means within the maximum likely lifetime of a 649 packet, including transit time from source to destination and 650 time spent awaiting reassembly with other fragments of the same 651 packet. However, it is not required that a source node know 652 the maximum packet lifetime. Rather, it is assumed that the 653 requirement can be met by maintaining the Identification value 654 as a simple, 32-bit, "wrap-around" counter, incremented each 655 time a packet must be fragmented. It is an implementation 656 choice whether to maintain a single counter for the node or 657 multiple counters, e.g., one for each of the node's possible 658 source addresses, or one for each active (source address, 659 destination address) combination. 661 The initial, large, unfragmented packet is referred to as the 662 "original packet", and it is considered to consist of three parts, as 663 illustrated: 665 original packet: 667 +------------------+-------------------------+---//----------------+ 668 | Per-Fragment | Extension & Upper-Layer | Fragmentable | 669 | Headers | Headers | Part | 670 +------------------+-------------------------+---//----------------+ 672 The Per-Fragment Headers consists of the IPv6 header plus any 673 extension headers that must be processed by nodes en route to the 674 destination, that is, all headers up to and including the Routing 675 header if present, else the Hop-by-Hop Options header if present, 676 else no extension headers. 678 The Extension Headers are all other extension headers that are not 679 included in the Per-Fragment headers part of the packet. For this 680 purpose, the Encapsulating Security Payload (ESP) is not 681 considered an extension headers. The Upper-Layer Header is the 682 first upper-layer header that is not an IPv6 extension header. 683 Examples of upper-layer headers include TCP, UDP, IPv4, IPv6, 684 ICMPv6, and as noted ESP. 686 The Fragmentable Part consists of the rest of the packet after the 687 upper-layer header or after any header (i.e., initial IPv6 header 688 or extension header) that contains a Next Header value of No Next 689 Header. 691 The Fragmentable Part of the original packet is divided into 692 fragments. The lengths of the fragments must be chosen such that the 693 resulting fragment packets fit within the MTU of the path to the 694 packets' destination(s). Each complete fragment, except possibly the 695 last ("rightmost") one, being an integer multiple of 8 octets long. 697 The fragments are transmitted in separate "fragment packets" as 698 illustrated: 700 original packet: 702 +-----------------+-----------------+--------+--------+-//-+--------+ 703 | Per-Fragment |Ext & Upper-Layer| first | second | | last | 704 | Headers | Headers |fragment|fragment|....|fragment| 705 +-----------------+-----------------+--------+--------+-//-+--------+ 707 fragment packets: 709 +------------------+---------+-------------------+----------+ 710 | Per-Fragment |Fragment | Ext & Upper-Layer | first | 711 | Headers | Header | Headers | fragment | 712 +------------------+---------+-------------------+----------+ 714 +------------------+--------+-------------------------------+ 715 | Per-Fragment |Fragment| second | 716 | Headers | Header | fragment | 717 +------------------+--------+-------------------------------+ 718 o 719 o 720 o 721 +------------------+--------+----------+ 722 | Per-Fragment |Fragment| last | 723 | Headers | Header | fragment | 724 +------------------+--------+----------+ 726 The first fragment packet is composed of: 728 (1) The Per-Fragment Headers of the original packet, with the 729 Payload Length of the original IPv6 header changed to contain the 730 length of this fragment packet only (excluding the length of the 731 IPv6 header itself), and the Next Header field of the last header 732 of the Per-Fragment Headers changed to 44. 734 (2) A Fragment header containing: 736 The Next Header value that identifies the first header after 737 the Per-Fragment Headers of the original packet. 739 A Fragment Offset containing the offset of the fragment, in 740 8-octet units, relative to the start of the Fragmentable Part 741 of the original packet. The Fragment Offset of the first 742 ("leftmost") fragment is 0. 744 An M flag value of 1 as this is the first fragment. 746 The Identification value generated for the original packet. 748 (3) Extension Headers, if any, and the Upper-Layer header. These 749 headers must be in the first fragment. Note: This restricts the 750 size of the headers through the Upper-Layer header to the MTU of 751 the path to the packets' destinations(s). 753 (4) The first fragment. 755 The subsequent fragment packets are composed of: 757 (1) The Per-Fragment Headers of the original packet, with the 758 Payload Length of the original IPv6 header changed to contain the 759 length of this fragment packet only (excluding the length of the 760 IPv6 header itself), and the Next Header field of the last header 761 of the Per-Fragment Headers changed to 44. 763 (2) A Fragment header containing: 765 The Next Header value that identifies the first header after 766 the Per-Fragment Headers of the original packet. 768 A Fragment Offset containing the offset of the fragment, in 769 8-octet units, relative to the start of the Fragmentable part 770 of the original packet. 772 An M flag value of 0 if the fragment is the last ("rightmost") 773 one, else an M flag value of 1. 775 The Identification value generated for the original packet. 777 (3) The fragment itself. 779 Fragments must not be created that overlap with any other fragments 780 created from the original packet. 782 At the destination, fragment packets are reassembled into their 783 original, unfragmented form, as illustrated: 785 reassembled original packet: 787 +---------------+-----------------+---------+--------+-//--+--------+ 788 | Per-Fragment |Ext & Upper-Layer| first | second | | last | 789 | Headers | Headers |frag data|fragment|.....|fragment| 790 +---------------+-----------------+---------+--------+-//--+--------+ 792 The following rules govern reassembly: 794 An original packet is reassembled only from fragment packets that 795 have the same Source Address, Destination Address, and Fragment 796 Identification. 798 The Per-Fragment Headers of the reassembled packet consists of all 799 headers up to, but not including, the Fragment header of the first 800 fragment packet (that is, the packet whose Fragment Offset is 801 zero), with the following two changes: 803 The Next Header field of the last header of the Per-Fragment 804 Headers is obtained from the Next Header field of the first 805 fragment's Fragment header. 807 The Payload Length of the reassembled packet is computed from 808 the length of the Per-Fragment Headers and the length and 809 offset of the last fragment. For example, a formula for 810 computing the Payload Length of the reassembled original packet 811 is: 813 PL.orig = PL.first - FL.first - 8 + (8 * FO.last) + FL.last 815 where 816 PL.orig = Payload Length field of reassembled packet. 817 PL.first = Payload Length field of first fragment packet. 818 FL.first = length of fragment following Fragment header of 819 first fragment packet. 820 FO.last = Fragment Offset field of Fragment header of last 821 fragment packet. 822 FL.last = length of fragment following Fragment header of 823 last fragment packet. 825 The Fragmentable Part of the reassembled packet is constructed 826 from the fragments following the Fragment headers in each of 827 the fragment packets. The length of each fragment is computed 828 by subtracting from the packet's Payload Length the length of 829 the headers between the IPv6 header and fragment itself; its 830 relative position in Fragmentable Part is computed from its 831 Fragment Offset value. 833 The Fragment header is not present in the final, reassembled 834 packet. 836 If any of the fragments being reassembled overlaps with any 837 other fragments being reassembled for the same packet, 838 reassembly of that packet must be abandoned and all the 839 fragments that have been received for that packet must be 840 discarded. 842 It should be noted that fragments may be duplicated in the 843 network. These exact duplicate fragments will be treated as 844 overlapping fragments and handled as described in the previous 845 paragraph. An implementation may choose to detect this case 846 and not drop the other fragments of the same packet. 848 If the fragment is a whole datagram (that is, both the Fragment 849 Offset field and the M flag are zero), then it does not need 850 any further reassembly and should be processed as a fully 851 reassembled packet (i.e., updating Next Header, adjust Payload 852 Length, removing the Fragmentation Header, etc.). Any other 853 fragments that match this packet (i.e., the same IPv6 Source 854 Address, IPv6 Destination Address, and Fragment Identification) 855 should be processed independently. 857 The following error conditions may arise when reassembling fragmented 858 packets: 860 If insufficient fragments are received to complete reassembly of a 861 packet within 60 seconds of the reception of the first-arriving 862 fragment of that packet, reassembly of that packet must be 863 abandoned and all the fragments that have been received for that 864 packet must be discarded. If the first fragment (i.e., the one 865 with a Fragment Offset of zero) has been received, an ICMP Time 866 Exceeded -- Fragment Reassembly Time Exceeded message should be 867 sent to the source of that fragment. 869 If the length of a fragment, as derived from the fragment packet's 870 Payload Length field, is not a multiple of 8 octets and the M flag 871 of that fragment is 1, then that fragment must be discarded and an 872 ICMP Parameter Problem, Code 0, message should be sent to the 873 source of the fragment, pointing to the Payload Length field of 874 the fragment packet. 876 If the length and offset of a fragment are such that the Payload 877 Length of the packet reassembled from that fragment would exceed 878 65,535 octets, then that fragment must be discarded and an ICMP 879 Parameter Problem, Code 0, message should be sent to the source of 880 the fragment, pointing to the Fragment Offset field of the 881 fragment packet. 883 If the first fragment does not include all headers through an 884 Upper-Layer header, then that fragment should be discarded and an 885 ICMP Parameter Problem, Code 3, message should be sent to the 886 source of the fragment, with the Pointer field set to zero. 888 The following conditions are not expected to occur, but are not 889 considered errors if they do: 891 The number and content of the headers preceding the Fragment 892 header of different fragments of the same original packet may 893 differ. Whatever headers are present, preceding the Fragment 894 header in each fragment packet, are processed when the packets 895 arrive, prior to queueing the fragments for reassembly. Only 896 those headers in the Offset zero fragment packet are retained in 897 the reassembled packet. 899 The Next Header values in the Fragment headers of different 900 fragments of the same original packet may differ. Only the value 901 from the Offset zero fragment packet is used for reassembly. 903 4.6. Destination Options Header 905 The Destination Options header is used to carry optional information 906 that need be examined only by a packet's destination node(s). The 907 Destination Options header is identified by a Next Header value of 60 908 in the immediately preceding header, and has the following format: 910 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 911 | Next Header | Hdr Ext Len | | 912 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 913 | | 914 . . 915 . Options . 916 . . 917 | | 918 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 920 Next Header 8-bit selector. Identifies the type of header 921 immediately following the Destination Options 922 header. Uses the same values as the IPv4 923 Protocol field [IANA-PN]. 925 Hdr Ext Len 8-bit unsigned integer. Length of the 926 Destination Options header in 8-octet units, 927 not including the first 8 octets. 929 Options Variable-length field, of length such that the 930 complete Destination Options header is an 931 integer multiple of 8 octets long. Contains 932 one or more TLV-encoded options, as described 933 in section 4.2. 935 The only destination options defined in this document are the Pad1 936 and PadN options specified in section 4.2. 938 Note that there are two possible ways to encode optional destination 939 information in an IPv6 packet: either as an option in the Destination 940 Options header, or as a separate extension header. The Fragment 941 header and the Authentication header are examples of the latter 942 approach. Which approach can be used depends on what action is 943 desired of a destination node that does not understand the optional 944 information: 946 o If the desired action is for the destination node to discard 947 the packet and, only if the packet's Destination Address is not 948 a multicast address, send an ICMP Unrecognized Type message to 949 the packet's Source Address, then the information may be 950 encoded either as a separate header or as an option in the 951 Destination Options header whose Option Type has the value 11 952 in its highest-order two bits. The choice may depend on such 953 factors as which takes fewer octets, or which yields better 954 alignment or more efficient parsing. 956 o If any other action is desired, the information must be encoded 957 as an option in the Destination Options header whose Option 958 Type has the value 00, 01, or 10 in its highest-order two bits, 959 specifying the desired action (see section 4.2). 961 4.7. No Next Header 963 The value 59 in the Next Header field of an IPv6 header or any 964 extension header indicates that there is nothing following that 965 header. If the Payload Length field of the IPv6 header indicates the 966 presence of octets past the end of a header whose Next Header field 967 contains 59, those octets must be ignored, and passed on unchanged if 968 the packet is forwarded. 970 4.8. Defining New Extension Headers and Options 972 No new extension headers that require hop-by-hop behavior should be 973 defined because as specified in Section 4 of this document, the only 974 Extension Header that has hop-by-hop behavior is the Hop-by-Hop 975 Options header. 977 New hop-by-hop options are not recommended because, due to 978 performance restrictions, nodes may ignore the Hop-by-Hop Option 979 header, drop packets containing a hop-by-hop header, or assign 980 packets containing a hop-by-hop header to a slow processing path. 981 Designers considering defining new hop-by-hop options need to be 982 aware of this likely behaviour. There has to a very clear 983 justification why any new hop-by-hop option is needed before it is 984 standardized. 986 Instead of defining new Extension Headers, it is recommended that the 987 Destination Options header is used to carry optional information that 988 need be examined only by a packet's destination node(s), because they 989 provide better handling and backward compatibility. Defining new 990 IPv6 extension headers is not recommended. There has to a very clear 991 justification why any new extension header is needed before it is 992 standardized. 994 If new Extension Headers are defined, they need to use the following 995 format: 997 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 998 | Next Header | Hdr Ext Len | | 999 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 1000 | | 1001 . . 1002 . Header Specific Data . 1003 . . 1004 | | 1005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1007 Next Header 8-bit selector. Identifies the type of 1008 header immediately following the extension 1009 header. Uses the same values as the IPv4 1010 Protocol field [IANA-PN]. 1012 Hdr Ext Len 8-bit unsigned integer. Length of the 1013 Destination Options header in 8-octet units, 1014 not including the first 8 octets. 1016 Header Specific Data Variable-length field, Fields specific to 1017 the extension header. 1019 5. Packet Size Issues 1021 IPv6 requires that every link in the internet have an MTU of 1280 1022 octets or greater. On any link that cannot convey a 1280-octet 1023 packet in one piece, link-specific fragmentation and reassembly must 1024 be provided at a layer below IPv6. 1026 Links that have a configurable MTU (for example, PPP links [RFC1661]) 1027 must be configured to have an MTU of at least 1280 octets; it is 1028 recommended that they be configured with an MTU of 1500 octets or 1029 greater, to accommodate possible encapsulations (i.e., tunneling) 1030 without incurring IPv6-layer fragmentation. 1032 From each link to which a node is directly attached, the node must be 1033 able to accept packets as large as that link's MTU. 1035 It is strongly recommended that IPv6 nodes implement Path MTU 1036 Discovery [RFC1981], in order to discover and take advantage of path 1037 MTUs greater than 1280 octets. However, a minimal IPv6 1038 implementation (e.g., in a boot ROM) may simply restrict itself to 1039 sending packets no larger than 1280 octets, and omit implementation 1040 of Path MTU Discovery. 1042 In order to send a packet larger than a path's MTU, a node may use 1043 the IPv6 Fragment header to fragment the packet at the source and 1044 have it reassembled at the destination(s). However, the use of such 1045 fragmentation is discouraged in any application that is able to 1046 adjust its packets to fit the measured path MTU (i.e., down to 1280 1047 octets). 1049 A node must be able to accept a fragmented packet that, after 1050 reassembly, is as large as 1500 octets. A node is permitted to 1051 accept fragmented packets that reassemble to more than 1500 octets. 1052 An upper-layer protocol or application that depends on IPv6 1053 fragmentation to send packets larger than the MTU of a path should 1054 not send packets larger than 1500 octets unless it has assurance that 1055 the destination is capable of reassembling packets of that larger 1056 size. 1058 6. Flow Labels 1060 The 20-bit Flow Label field in the IPv6 header is used by a source to 1061 label sequences of packets to be treated in the network as a single 1062 flow. 1064 The current definition of the IPv6 Flow Label can be found in 1065 [RFC6437]. 1067 7. Traffic Classes 1069 The 8-bit Traffic Class field in the IPv6 header is used by the 1070 network for traffic management. The value of the Traffic Class bits 1071 in a received packet might be different from the value sent by the 1072 packet's source. 1074 The current use of the Traffic Class field for Differentiated 1075 Services and Explicit Congestion Notification is specified in 1076 [RFC2474] and [RFC3168]. 1078 8. Upper-Layer Protocol Issues 1080 8.1. Upper-Layer Checksums 1082 Any transport or other upper-layer protocol that includes the 1083 addresses from the IP header in its checksum computation must be 1084 modified for use over IPv6, to include the 128-bit IPv6 addresses 1085 instead of 32-bit IPv4 addresses. In particular, the following 1086 illustration shows the TCP and UDP "pseudo-header" for IPv6: 1088 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1089 | | 1090 + + 1091 | | 1092 + Source Address + 1093 | | 1094 + + 1095 | | 1096 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1097 | | 1098 + + 1099 | | 1100 + Destination Address + 1101 | | 1102 + + 1103 | | 1104 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1105 | Upper-Layer Packet Length | 1106 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1107 | zero | Next Header | 1108 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1110 o If the IPv6 packet contains a Routing header, the Destination 1111 Address used in the pseudo-header is that of the final 1112 destination. At the originating node, that address will be in 1113 the last element of the Routing header; at the recipient(s), 1114 that address will be in the Destination Address field of the 1115 IPv6 header. 1117 o The Next Header value in the pseudo-header identifies the 1118 upper-layer protocol (e.g., 6 for TCP, or 17 for UDP). It will 1119 differ from the Next Header value in the IPv6 header if there 1120 are extension headers between the IPv6 header and the upper- 1121 layer header. 1123 o The Upper-Layer Packet Length in the pseudo-header is the 1124 length of the upper-layer header and data (e.g., TCP header 1125 plus TCP data). Some upper-layer protocols carry their own 1126 length information (e.g., the Length field in the UDP header); 1127 for such protocols, that is the length used in the pseudo- 1128 header. Other protocols (such as TCP) do not carry their own 1129 length information, in which case the length used in the 1130 pseudo-header is the Payload Length from the IPv6 header, minus 1131 the length of any extension headers present between the IPv6 1132 header and the upper-layer header. 1134 o Unlike IPv4, the default behavior when UDP packets are 1135 originated by an IPv6 node, is that the UDP checksum is not 1136 optional. That is, whenever originating a UDP packet, an IPv6 1137 node must compute a UDP checksum over the packet and the 1138 pseudo-header, and, if that computation yields a result of 1139 zero, it must be changed to hex FFFF for placement in the UDP 1140 header. IPv6 receivers must discard UDP packets containing a 1141 zero checksum, and should log the error. 1143 o As an exception to the default behaviour, protocols that use 1144 UDP as a tunnel encapsulation may enable zero-checksum mode for 1145 a specific port (or set of ports) for sending and/or receiving. 1146 Any node implementing zero-checksum mode must follow the 1147 requirements specified in "Applicability Statement for the use 1148 of IPv6 UDP Datagrams with Zero Checksums" [RFC6936]. 1150 The IPv6 version of ICMP [RFC4443] includes the above pseudo-header 1151 in its checksum computation; this is a change from the IPv4 version 1152 of ICMP, which does not include a pseudo-header in its checksum. The 1153 reason for the change is to protect ICMP from misdelivery or 1154 corruption of those fields of the IPv6 header on which it depends, 1155 which, unlike IPv4, are not covered by an internet-layer checksum. 1156 The Next Header field in the pseudo-header for ICMP contains the 1157 value 58, which identifies the IPv6 version of ICMP. 1159 8.2. Maximum Packet Lifetime 1161 Unlike IPv4, IPv6 nodes are not required to enforce maximum packet 1162 lifetime. That is the reason the IPv4 "Time to Live" field was 1163 renamed "Hop Limit" in IPv6. In practice, very few, if any, IPv4 1164 implementations conform to the requirement that they limit packet 1165 lifetime, so this is not a change in practice. Any upper-layer 1166 protocol that relies on the internet layer (whether IPv4 or IPv6) to 1167 limit packet lifetime ought to be upgraded to provide its own 1168 mechanisms for detecting and discarding obsolete packets. 1170 8.3. Maximum Upper-Layer Payload Size 1172 When computing the maximum payload size available for upper-layer 1173 data, an upper-layer protocol must take into account the larger size 1174 of the IPv6 header relative to the IPv4 header. For example, in 1175 IPv4, TCP's MSS option is computed as the maximum packet size (a 1176 default value or a value learned through Path MTU Discovery) minus 40 1177 octets (20 octets for the minimum-length IPv4 header and 20 octets 1178 for the minimum-length TCP header). When using TCP over IPv6, the 1179 MSS must be computed as the maximum packet size minus 60 octets, 1180 because the minimum-length IPv6 header (i.e., an IPv6 header with no 1181 extension headers) is 20 octets longer than a minimum-length IPv4 1182 header. 1184 8.4. Responding to Packets Carrying Routing Headers 1186 When an upper-layer protocol sends one or more packets in response to 1187 a received packet that included a Routing header, the response 1188 packet(s) must not include a Routing header that was automatically 1189 derived by "reversing" the received Routing header UNLESS the 1190 integrity and authenticity of the received Source Address and Routing 1191 header have been verified (e.g., via the use of an Authentication 1192 header in the received packet). In other words, only the following 1193 kinds of packets are permitted in response to a received packet 1194 bearing a Routing header: 1196 o Response packets that do not carry Routing headers. 1198 o Response packets that carry Routing headers that were NOT 1199 derived by reversing the Routing header of the received packet 1200 (for example, a Routing header supplied by local 1201 configuration). 1203 o Response packets that carry Routing headers that were derived 1204 by reversing the Routing header of the received packet IF AND 1205 ONLY IF the integrity and authenticity of the Source Address 1206 and Routing header from the received packet have been verified 1207 by the responder. 1209 9. IANA Considerations 1211 RFC2460 is referenced in a number of IANA registries. These include: 1213 o Internet Protocol Version 6 (IPv6) Parameters [IANA-6P] 1214 o Assigned Internet Protocol Numbers [IANA-PN] 1216 The IANA should update these references to point to this document. 1218 10. Security Considerations 1220 The security features of IPv6 are described in the Security 1221 Architecture for the Internet Protocol [RFC4301]. 1223 11. Acknowledgments 1225 The authors gratefully acknowledge the many helpful suggestions of 1226 the members of the IPng working group, the End-to-End Protocols 1227 research group, and the Internet Community At Large. 1229 The authors would also like to acknowledge the authors of the 1230 updating RFCs that were incorporated in this version of the document 1231 to move the IPv6 specification to Internet Standard. They are Joe 1232 Abley, Shane Amante, Jari Arkko, Manav Bhatia, Ronald P. Bonica, 1233 Scott Bradner, Brian Carpenter, P.F. Chimento, Marshall Eubanks, 1234 Fernando Gont, James Hoagland, Sheng Jiang, Erik Kline, Suresh 1235 Krishnan, Vishwas Manral, George Neville-Neil, Jarno Rajahalme, Pekka 1236 Savola, Magnus Westerlund, and James Woodyatt. 1238 12. References 1240 12.1. Normative References 1242 [I-D.hinden-6man-rfc4291bis] 1243 Hinden, B. and S. Deering, "IP Version 6 Addressing 1244 Architecture", draft-hinden-6man-rfc4291bis-06 (work in 1245 progress), October 2015. 1247 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 1248 10.17487/RFC0791, September 1981, 1249 . 1251 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 1252 "Definition of the Differentiated Services Field (DS 1253 Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI 1254 10.17487/RFC2474, December 1998, 1255 . 1257 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 1258 of Explicit Congestion Notification (ECN) to IP", RFC 1259 3168, DOI 10.17487/RFC3168, September 2001, 1260 . 1262 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 1263 Control Message Protocol (ICMPv6) for the Internet 1264 Protocol Version 6 (IPv6) Specification", RFC 4443, DOI 1265 10.17487/RFC4443, March 2006, 1266 . 1268 [RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme, 1269 "IPv6 Flow Label Specification", RFC 6437, DOI 10.17487/ 1270 RFC6437, November 2011, 1271 . 1273 12.2. Informative References 1275 [IANA-6P] "Internet Protocol Version 6 (IPv6) Parameters", 1276 . 1279 [IANA-PN] "Assigned Internet Protocol Numbers", 1280 . 1283 [IANA-RH] "IANA Routing Types Parameter Registry", 1284 . 1287 [RFC1661] Simpson, W., Ed., "The Point-to-Point Protocol (PPP)", STD 1288 51, RFC 1661, DOI 10.17487/RFC1661, July 1994, 1289 . 1291 [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery 1292 for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August 1293 1996, . 1295 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1296 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 1297 December 1998, . 1299 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 1300 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 1301 December 1998, . 1303 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1304 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 1305 December 2005, . 1307 [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI 1308 10.17487/RFC4302, December 2005, 1309 . 1311 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 1312 4303, DOI 10.17487/RFC4303, December 2005, 1313 . 1315 [RFC5871] Arkko, J. and S. Bradner, "IANA Allocation Guidelines for 1316 the IPv6 Routing Header", RFC 5871, DOI 10.17487/RFC5871, 1317 May 2010, . 1319 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 1320 for the Use of IPv6 UDP Datagrams with Zero Checksums", 1321 RFC 6936, DOI 10.17487/RFC6936, April 2013, 1322 . 1324 [RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing 1325 of IPv6 Extension Headers", RFC 7045, DOI 10.17487/ 1326 RFC7045, December 2013, 1327 . 1329 Appendix A. Formatting Guidelines for Options 1331 This appendix gives some advice on how to lay out the fields when 1332 designing new options to be used in the Hop-by-Hop Options header or 1333 the Destination Options header, as described in section 4.2. These 1334 guidelines are based on the following assumptions: 1336 o One desirable feature is that any multi-octet fields within the 1337 Option Data area of an option be aligned on their natural 1338 boundaries, i.e., fields of width n octets should be placed at 1339 an integer multiple of n octets from the start of the Hop-by- 1340 Hop or Destination Options header, for n = 1, 2, 4, or 8. 1342 o Another desirable feature is that the Hop-by-Hop or Destination 1343 Options header take up as little space as possible, subject to 1344 the requirement that the header be an integer multiple of 8 1345 octets long. 1347 o It may be assumed that, when either of the option-bearing 1348 headers are present, they carry a very small number of options, 1349 usually only one. 1351 These assumptions suggest the following approach to laying out the 1352 fields of an option: order the fields from smallest to largest, with 1353 no interior padding, then derive the alignment requirement for the 1354 entire option based on the alignment requirement of the largest field 1355 (up to a maximum alignment of 8 octets). This approach is 1356 illustrated in the following examples: 1358 Example 1 1360 If an option X required two data fields, one of length 8 octets and 1361 one of length 4 octets, it would be laid out as follows: 1363 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1364 | Option Type=X |Opt Data Len=12| 1365 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1366 | 4-octet field | 1367 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1368 | | 1369 + 8-octet field + 1370 | | 1371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1373 Its alignment requirement is 8n+2, to ensure that the 8-octet field 1374 starts at a multiple-of-8 offset from the start of the enclosing 1375 header. A complete Hop-by-Hop or Destination Options header 1376 containing this one option would look as follows: 1378 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1379 | Next Header | Hdr Ext Len=1 | Option Type=X |Opt Data Len=12| 1380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1381 | 4-octet field | 1382 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1383 | | 1384 + 8-octet field + 1385 | | 1386 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1388 Example 2 1390 If an option Y required three data fields, one of length 4 octets, 1391 one of length 2 octets, and one of length 1 octet, it would be laid 1392 out as follows: 1394 +-+-+-+-+-+-+-+-+ 1395 | Option Type=Y | 1396 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1397 |Opt Data Len=7 | 1-octet field | 2-octet field | 1398 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1399 | 4-octet field | 1400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1402 Its alignment requirement is 4n+3, to ensure that the 4-octet field 1403 starts at a multiple-of-4 offset from the start of the enclosing 1404 header. A complete Hop-by-Hop or Destination Options header 1405 containing this one option would look as follows: 1407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1408 | Next Header | Hdr Ext Len=1 | Pad1 Option=0 | Option Type=Y | 1409 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1410 |Opt Data Len=7 | 1-octet field | 2-octet field | 1411 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1412 | 4-octet field | 1413 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1414 | PadN Option=1 |Opt Data Len=2 | 0 | 0 | 1415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1417 Example 3 1419 A Hop-by-Hop or Destination Options header containing both options X 1420 and Y from Examples 1 and 2 would have one of the two following 1421 formats, depending on which option appeared first: 1423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1424 | Next Header | Hdr Ext Len=3 | Option Type=X |Opt Data Len=12| 1425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1426 | 4-octet field | 1427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1428 | | 1429 + 8-octet field + 1430 | | 1431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1432 | PadN Option=1 |Opt Data Len=1 | 0 | Option Type=Y | 1433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1434 |Opt Data Len=7 | 1-octet field | 2-octet field | 1435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1436 | 4-octet field | 1437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1438 | PadN Option=1 |Opt Data Len=2 | 0 | 0 | 1439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1442 | Next Header | Hdr Ext Len=3 | Pad1 Option=0 | Option Type=Y | 1443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1444 |Opt Data Len=7 | 1-octet field | 2-octet field | 1445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1446 | 4-octet field | 1447 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1448 | PadN Option=1 |Opt Data Len=4 | 0 | 0 | 1449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1450 | 0 | 0 | Option Type=X |Opt Data Len=12| 1451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1452 | 4-octet field | 1453 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1454 | | 1455 + 8-octet field + 1456 | | 1457 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1459 Appendix B. CHANGES SINCE RFC2460 1461 This memo has the following changes from RFC2460. Numbers identify 1462 the Internet-Draft version in which the change was made. 1464 Working Group Internet Drafts 1466 02) Added text to Section 4.8 "Defining New Extension Headers and 1467 Options" clarifying why no new hop by hop extension headers 1468 should be define. 1470 02) Added text to Fragment Header process on handling exact 1471 duplicate fragments. 1473 02) Editorial changes. 1475 01) Added text that Extension headers must never be inserted by 1476 any node other than the source of the packet. 1478 01) Change "must" to "should" in Section 4.3 on the Hop-by-Hop 1479 header. 1481 01) Added text that the Data Transmission Order is the same as 1482 IPv4 as defined in RFC791. 1484 01) Updated the Fragmentation header text to correct the 1485 inclusion of AH and note no next header case. 1487 01) Change terminology in Fragment header section from 1488 "Unfragmentable Headers" to "Per-Fragment Headers". 1490 01) Removed paragraph in Section 5 that required including a 1491 fragment header to outgoing packets if a ICMP Packet Too Big 1492 message reporting a Next-Hop MTU less than 1280. This is 1493 based on the update in draft-ietf-6man-deprecate-atomfrag- 1494 generation-03. 1496 01) Changed to Fragmentation Header section to clarify MTU 1497 restriction and 8-byte restrictions, and noting the 1498 restriction on headers in first fragment. 1500 01) Editorial changes. 1502 00) Add instruction to the IANA to change references to RFC2460 1503 to this document 1505 00) Add a paragraph to the acknowledgement section acknowledging 1506 the authors of the updating documents 1508 00) Remove old paragraph in Section 4 that should have been 1509 removed when incorporating the update from RFC7045. 1511 00) Editorial changes. 1513 Individual Internet Drafts 1514 07) Update references to current versions and assign references 1515 to normative and informative. 1517 07) Editorial changes. 1519 06) The purpose of this draft is to incorporate the updates 1520 dealing with Extension headers as defined in RFC6564, 1521 RFC7045, and RFC7112. The changes include: 1523 RFC6564: Added new Section 4.8 that describe 1524 recommendations for defining new Extension headers and 1525 options 1527 RFC7045: The changes were to add a reference to RFC7045, 1528 change the requirement for processing the hop-by-hop 1529 option to a should, and added a note that due to 1530 performance restrictions some nodes won't process the Hop- 1531 by-Hop Option header. 1533 RFC7112: The changes were to revise the Fragmentation 1534 Section to require that all headers through the first 1535 Upper-Layer Header are in the first fragment. This 1536 changed the text describing how packets are fragmented and 1537 reassembled and added a new error case. 1539 06) Editorial changes. 1541 05) The purpose of this draft is to incorporate the updates 1542 dealing with fragmentation as defined in RFC5722 and RFC6946. 1543 Note: The issue relating to the handling of exact duplicate 1544 fragments identified on the mailing list is left open. 1546 05) Fix text in the end of Section 4.0 to correct the number of 1547 extension headers defined in this document. 1549 05) Editorial changes. 1551 04) The purpose of this draft is to update the document to 1552 incorporate the update made by RFC6935 "UDP Checksums for 1553 Tunneled Packets". 1555 04) Remove Routing (Type 0) header from the list of required 1556 extension headers. 1558 04) Editorial changes. 1560 03) The purpose of this draft is to update the document for the 1561 deprecation of the RH0 Routing Header as specified in RFC5095 1562 and the allocations guidelines for routing headers as 1563 specified in RFC5871. Both of these RFCs updated RFC2460. 1565 02) The purpose of this version of the draft is to update the 1566 document to resolve the open Errata on RFC2460. 1568 Errata ID: 2541: This errata notes that RFC2460 didn't 1569 update RFC2205 when the length of the Flow Label was 1570 changed from 24 to 20 bits from RFC1883. This issue was 1571 resolved in RFC6437 where the Flow Label is defined. This 1572 draft now references RFC6437. No change is required. 1574 Errata ID: 4279: This errata noted that the specification 1575 doesn't handle the case of a forwarding node receiving a 1576 packet with a zero Hop Limit. This is fixed in 1577 Section 3.0 of this draft. Note: No change was made 1578 regarding host behaviour. 1580 Errata ID: 2843: This errata is marked rejected. No 1581 change is required. 1583 02) Editorial changes to the Flow Label and Traffic Class text. 1585 01) The purpose of this version of the draft is to update the 1586 document to point to the current specifications of the IPv6 1587 Flow Label field as defined in [RFC6437] and the Traffic 1588 Class as defined in [RFC2474] and [RFC3168]. 1590 00) The purpose of this version is to establish a baseline from 1591 RFC2460. The only intended changes are formatting (XML is 1592 slightly different from .nroff), differences between an RFC 1593 and Internet Draft, fixing a few ID Nits, and updates to the 1594 authors information. There should not be any content changes 1595 to the specification. 1597 Authors' Addresses 1599 Stephen E. Deering 1600 Retired 1601 Vancouver, British Columbia 1602 Canada 1604 Robert M. Hinden 1605 Check Point Software 1606 959 Skyway Road 1607 San Carlos, CA 94070 1608 USA 1610 Email: bob.hinden@gmail.com