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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group S. Deering 3 Internet-Draft Retired 4 Obsoletes: 2460 (if approved) R. Hinden 5 Intended status: Standards Track Check Point Software 6 Expires: March 17, 2017 September 13, 2016 8 Internet Protocol, Version 6 (IPv6) Specification 9 draft-ietf-6man-rfc2460bis-06 11 Abstract 13 This document specifies version 6 of the Internet Protocol (IPv6). 14 It obsoletes RFC2460 16 Status of This Memo 18 This Internet-Draft is submitted in full conformance with the 19 provisions of BCP 78 and BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF). Note that other groups may also distribute 23 working documents as Internet-Drafts. The list of current Internet- 24 Drafts is at http://datatracker.ietf.org/drafts/current/. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 This Internet-Draft will expire on March 17, 2017. 33 Copyright Notice 35 Copyright (c) 2016 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (http://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents 42 carefully, as they describe your rights and restrictions with respect 43 to this document. Code Components extracted from this document must 44 include Simplified BSD License text as described in Section 4.e of 45 the Trust Legal Provisions and are provided without warranty as 46 described in the Simplified BSD License. 48 This document may contain material from IETF Documents or IETF 49 Contributions published or made publicly available before November 50 10, 2008. The person(s) controlling the copyright in some of this 51 material may not have granted the IETF Trust the right to allow 52 modifications of such material outside the IETF Standards Process. 53 Without obtaining an adequate license from the person(s) controlling 54 the copyright in such materials, this document may not be modified 55 outside the IETF Standards Process, and derivative works of it may 56 not be created outside the IETF Standards Process, except to format 57 it for publication as an RFC or to translate it into languages other 58 than English. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 3. IPv6 Header Format . . . . . . . . . . . . . . . . . . . . . 5 65 4. IPv6 Extension Headers . . . . . . . . . . . . . . . . . . . 6 66 4.1. Extension Header Order . . . . . . . . . . . . . . . . . 9 67 4.2. Options . . . . . . . . . . . . . . . . . . . . . . . . . 10 68 4.3. Hop-by-Hop Options Header . . . . . . . . . . . . . . . . 12 69 4.4. Routing Header . . . . . . . . . . . . . . . . . . . . . 13 70 4.5. Fragment Header . . . . . . . . . . . . . . . . . . . . . 14 71 4.6. Destination Options Header . . . . . . . . . . . . . . . 21 72 4.7. No Next Header . . . . . . . . . . . . . . . . . . . . . 22 73 4.8. Defining New Extension Headers and Options . . . . . . . 22 74 5. Packet Size Issues . . . . . . . . . . . . . . . . . . . . . 23 75 6. Flow Labels . . . . . . . . . . . . . . . . . . . . . . . . . 24 76 7. Traffic Classes . . . . . . . . . . . . . . . . . . . . . . . 24 77 8. Upper-Layer Protocol Issues . . . . . . . . . . . . . . . . . 24 78 8.1. Upper-Layer Checksums . . . . . . . . . . . . . . . . . . 24 79 8.2. Maximum Packet Lifetime . . . . . . . . . . . . . . . . . 26 80 8.3. Maximum Upper-Layer Payload Size . . . . . . . . . . . . 26 81 8.4. Responding to Packets Carrying Routing Headers . . . . . 27 82 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 83 10. Security Considerations . . . . . . . . . . . . . . . . . . . 28 84 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28 85 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 86 12.1. Normative References . . . . . . . . . . . . . . . . . . 28 87 12.2. Informative References . . . . . . . . . . . . . . . . . 29 88 Appendix A. Formatting Guidelines for Options . . . . . . . . . 30 89 Appendix B. CHANGES SINCE RFC2460 . . . . . . . . . . . . . . . 33 90 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37 92 1. Introduction 94 IP version 6 (IPv6) is a new version of the Internet Protocol, 95 designed as the successor to IP version 4 (IPv4) [RFC0791]. The 96 changes from IPv4 to IPv6 fall primarily into the following 97 categories: 99 o Expanded Addressing Capabilities 101 IPv6 increases the IP address size from 32 bits to 128 bits, to 102 support more levels of addressing hierarchy, a much greater 103 number of addressable nodes, and simpler auto-configuration of 104 addresses. The scalability of multicast routing is improved by 105 adding a "scope" field to multicast addresses. And a new type 106 of address called an "anycast address" is defined, used to send 107 a packet to any one of a group of nodes. 109 o Header Format Simplification 111 Some IPv4 header fields have been dropped or made optional, to 112 reduce the common-case processing cost of packet handling and 113 to limit the bandwidth cost of the IPv6 header. 115 o Improved Support for Extensions and Options 117 Changes in the way IP header options are encoded allows for 118 more efficient forwarding, less stringent limits on the length 119 of options, and greater flexibility for introducing new options 120 in the future. 122 o Flow Labeling Capability 124 A new capability is added to enable the labeling of sequences 125 of packets that the sender requests to be treated in the 126 network as a single flow. 128 o Authentication and Privacy Capabilities 130 Extensions to support authentication, data integrity, and 131 (optional) data confidentiality are specified for IPv6. 133 This document specifies the basic IPv6 header and the initially- 134 defined IPv6 extension headers and options. It also discusses packet 135 size issues, the semantics of flow labels and traffic classes, and 136 the effects of IPv6 on upper-layer protocols. The format and 137 semantics of IPv6 addresses are specified separately in 139 [I-D.ietf-6man-rfc4291bis]. The IPv6 version of ICMP, which all IPv6 140 implementations are required to include, is specified in [RFC4443] 142 The data transmission order for IPv6 is the same as for IPv4 as 143 defined in Appendix B of [RFC0791]. 145 Note: As this document obsoletes [RFC2460], any document referenced 146 in this document that includes pointers to RFC2460, should be 147 interpreted as referencing this document. 149 2. Terminology 151 node a device that implements IPv6. 153 router a node that forwards IPv6 packets not explicitly 154 addressed to itself. [See Note below]. 156 host any node that is not a router. [See Note below]. 158 upper layer a protocol layer immediately above IPv6. Examples are 159 transport protocols such as TCP and UDP, control 160 protocols such as ICMP, routing protocols such as OSPF, 161 and internet or lower-layer protocols being "tunneled" 162 over (i.e., encapsulated in) IPv6 such as IPX, 163 AppleTalk, or IPv6 itself. 165 link a communication facility or medium over which nodes can 166 communicate at the link layer, i.e., the layer 167 immediately below IPv6. Examples are Ethernets (simple 168 or bridged); PPP links; X.25, Frame Relay, or ATM 169 networks; and internet (or higher) layer "tunnels", such 170 as tunnels over IPv4 or IPv6 itself. 172 neighbors nodes attached to the same link. 174 interface a node's attachment to a link. 176 address an IPv6-layer identifier for an interface or a set of 177 interfaces. 179 packet an IPv6 header plus payload. 181 link MTU the maximum transmission unit, i.e., maximum packet size 182 in octets, that can be conveyed over a link. 184 path MTU the minimum link MTU of all the links in a path between 185 a source node and a destination node. 187 Note: it is possible, though unusual, for a device with multiple 188 interfaces to be configured to forward non-self-destined packets 189 arriving from some set (fewer than all) of its interfaces, and to 190 discard non-self-destined packets arriving from its other interfaces. 191 Such a device must obey the protocol requirements for routers when 192 receiving packets from, and interacting with neighbors over, the 193 former (forwarding) interfaces. It must obey the protocol 194 requirements for hosts when receiving packets from, and interacting 195 with neighbors over, the latter (non-forwarding) interfaces. 197 3. IPv6 Header Format 199 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 200 |Version| Traffic Class | Flow Label | 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 202 | Payload Length | Next Header | Hop Limit | 203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 204 | | 205 + + 206 | | 207 + Source Address + 208 | | 209 + + 210 | | 211 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 212 | | 213 + + 214 | | 215 + Destination Address + 216 | | 217 + + 218 | | 219 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 221 Version 4-bit Internet Protocol version number = 6. 223 Traffic Class 8-bit traffic class field. See section 7. 225 Flow Label 20-bit flow label. See section 6. 227 Payload Length 16-bit unsigned integer. Length of the IPv6 228 payload, i.e., the rest of the packet 229 following this IPv6 header, in octets. (Note 230 that any extension headers [section 4] present 231 are considered part of the payload, i.e., 232 included in the length count.) 234 Next Header 8-bit selector. Identifies the type of header 235 immediately following the IPv6 header. Uses 236 the same values as the IPv4 Protocol field 237 [IANA-PN]. 239 Hop Limit 8-bit unsigned integer. Decremented by 1 by 240 each node that forwards the packet. When 241 forwarding, the packet is discarded if Hop 242 Limit was zero when received or is decremented 243 to zero. A node that is the destination of a 244 packet should not discard a packet with hop 245 limit equal to zero, it should process the 246 packet normally. 248 Source Address 128-bit address of the originator of the 249 packet. See [I-D.ietf-6man-rfc4291bis]. 251 Destination Address 128-bit address of the intended recipient of 252 the packet (possibly not the ultimate 253 recipient, if a Routing header is present). 254 See [I-D.ietf-6man-rfc4291bis] and section 255 4.4. 257 4. IPv6 Extension Headers 259 In IPv6, optional internet-layer information is encoded in separate 260 headers that may be placed between the IPv6 header and the upper- 261 layer header in a packet. There are a small number of such extension 262 headers, each identified by a distinct Next Header value. As 263 illustrated in these examples, an IPv6 packet may carry zero, one, or 264 more extension headers, each identified by the Next Header field of 265 the preceding header: 267 +---------------+------------------------ 268 | IPv6 header | TCP header + data 269 | | 270 | Next Header = | 271 | TCP | 272 +---------------+------------------------ 274 +---------------+----------------+------------------------ 275 | IPv6 header | Routing header | TCP header + data 276 | | | 277 | Next Header = | Next Header = | 278 | Routing | TCP | 279 +---------------+----------------+------------------------ 281 +---------------+----------------+-----------------+----------------- 282 | IPv6 header | Routing header | Fragment header | fragment of TCP 283 | | | | header + data 284 | Next Header = | Next Header = | Next Header = | 285 | Routing | Fragment | TCP | 286 +---------------+----------------+-----------------+----------------- 288 The insertion of Extension Headers by any node other than the source 289 of the packet breaks PMTU-discovery and can result in ICMP error 290 messages being sent to the source of the packet that did not insert 291 the header. 293 The current approach to allowing a header to be inserted is to 294 encapsulate the packet using another IPv6 header and including the 295 additional extension header after the first IPv6 header, for example, 296 as defined in [RFC2473]. 298 With one exception, extension headers are not processed by any node 299 along a packet's delivery path, until the packet reaches the node (or 300 each of the set of nodes, in the case of multicast) identified in the 301 Destination Address field of the IPv6 header. Note: If an 302 intermediate forwarding node examines an extension header for any 303 reason, it must do so in accordance with the provisions of [RFC7045]. 304 At the Destination node, normal demultiplexing on the Next Header 305 field of the IPv6 header invokes the module to process the first 306 extension header, or the upper-layer header if no extension header is 307 present. The contents and semantics of each extension header 308 determine whether or not to proceed to the next header. Therefore, 309 extension headers must be processed strictly in the order they appear 310 in the packet; a receiver must not, for example, scan through a 311 packet looking for a particular kind of extension header and process 312 that header prior to processing all preceding ones. 314 The exception referred to in the preceding paragraph is the Hop-by- 315 Hop Options header, which carries information that may be examined 316 and processed by every node along a packet's delivery path, including 317 the source and destination nodes. The Hop-by-Hop Options header, 318 when present, must immediately follow the IPv6 header. Its presence 319 is indicated by the value zero in the Next Header field of the IPv6 320 header. 322 NOTE: While [RFC2460] required that all nodes must examine and 323 process the Hop-by-Hop Options header, it is now expected that nodes 324 along a packet's delivery path only examine and process the Hop-by- 325 Hop Options header if explicitly configured to do so. 327 If, as a result of processing a header, a node is required to proceed 328 to the next header but the Next Header value in the current header is 329 unrecognized by the node, it should discard the packet and send an 330 ICMP Parameter Problem message to the source of the packet, with an 331 ICMP Code value of 1 ("unrecognized Next Header type encountered") 332 and the ICMP Pointer field containing the offset of the unrecognized 333 value within the original packet. The same action should be taken if 334 a node encounters a Next Header value of zero in any header other 335 than an IPv6 header. 337 Each extension header is an integer multiple of 8 octets long, in 338 order to retain 8-octet alignment for subsequent headers. Multi- 339 octet fields within each extension header are aligned on their 340 natural boundaries, i.e., fields of width n octets are placed at an 341 integer multiple of n octets from the start of the header, for n = 1, 342 2, 4, or 8. 344 A full implementation of IPv6 includes implementation of the 345 following extension headers: 347 Hop-by-Hop Options 348 Fragment 349 Destination Options 350 Routing 351 Authentication 352 Encapsulating Security Payload 354 The first four are specified in this document; the last two are 355 specified in [RFC4302] and [RFC4303], respectively. The current list 356 of IPv6 extension headers can be found at [IANA-EH]. 358 4.1. Extension Header Order 360 When more than one extension header is used in the same packet, it is 361 recommended that those headers appear in the following order: 363 IPv6 header 364 Hop-by-Hop Options header 365 Destination Options header (note 1) 366 Routing header 367 Fragment header 368 Authentication header (note 2) 369 Encapsulating Security Payload header (note 2) 370 Destination Options header (note 3) 371 upper-layer header 373 note 1: for options to be processed by the first destination that 374 appears in the IPv6 Destination Address field plus 375 subsequent destinations listed in the Routing header. 377 note 2: additional recommendations regarding the relative order of 378 the Authentication and Encapsulating Security Payload 379 headers are given in [RFC4303]. 381 note 3: for options to be processed only by the final destination 382 of the packet. 384 Each extension header should occur at most once, except for the 385 Destination Options header which should occur at most twice (once 386 before a Routing header and once before the upper-layer header). 388 If the upper-layer header is another IPv6 header (in the case of IPv6 389 being tunneled over or encapsulated in IPv6), it may be followed by 390 its own extension headers, which are separately subject to the same 391 ordering recommendations. 393 If and when other extension headers are defined, their ordering 394 constraints relative to the above listed headers must be specified. 396 IPv6 nodes must accept and attempt to process extension headers in 397 any order and occurring any number of times in the same packet, 398 except for the Hop-by-Hop Options header which is restricted to 399 appear immediately after an IPv6 header only. Nonetheless, it is 400 strongly advised that sources of IPv6 packets adhere to the above 401 recommended order until and unless subsequent specifications revise 402 that recommendation. 404 4.2. Options 406 Two of the currently-defined extension headers defined in this 407 document -- the Hop-by-Hop Options header and the Destination Options 408 header -- carry a variable number of type-length-value (TLV) encoded 409 "options", of the following format: 411 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 412 | Option Type | Opt Data Len | Option Data 413 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 415 Option Type 8-bit identifier of the type of option. 417 Opt Data Len 8-bit unsigned integer. Length of the Option 418 Data field of this option, in octets. 420 Option Data Variable-length field. Option-Type-specific 421 data. 423 The sequence of options within a header must be processed strictly in 424 the order they appear in the header; a receiver must not, for 425 example, scan through the header looking for a particular kind of 426 option and process that option prior to processing all preceding 427 ones. 429 The Option Type identifiers are internally encoded such that their 430 highest-order two bits specify the action that must be taken if the 431 processing IPv6 node does not recognize the Option Type: 433 00 - skip over this option and continue processing the header. 435 01 - discard the packet. 437 10 - discard the packet and, regardless of whether or not the 438 packet's Destination Address was a multicast address, send an 439 ICMP Parameter Problem, Code 2, message to the packet's 440 Source Address, pointing to the unrecognized Option Type. 442 11 - discard the packet and, only if the packet's Destination 443 Address was not a multicast address, send an ICMP Parameter 444 Problem, Code 2, message to the packet's Source Address, 445 pointing to the unrecognized Option Type. 447 The third-highest-order bit of the Option Type specifies whether or 448 not the Option Data of that option can change en-route to the 449 packet's final destination. When an Authentication header is present 450 in the packet, for any option whose data may change en-route, its 451 entire Option Data field must be treated as zero-valued octets when 452 computing or verifying the packet's authenticating value. 454 0 - Option Data does not change en-route 456 1 - Option Data may change en-route 458 The three high-order bits described above are to be treated as part 459 of the Option Type, not independent of the Option Type. That is, a 460 particular option is identified by a full 8-bit Option Type, not just 461 the low-order 5 bits of an Option Type. 463 The same Option Type numbering space is used for both the Hop-by-Hop 464 Options header and the Destination Options header. However, the 465 specification of a particular option may restrict its use to only one 466 of those two headers. 468 Individual options may have specific alignment requirements, to 469 ensure that multi-octet values within Option Data fields fall on 470 natural boundaries. The alignment requirement of an option is 471 specified using the notation xn+y, meaning the Option Type must 472 appear at an integer multiple of x octets from the start of the 473 header, plus y octets. For example: 475 2n means any 2-octet offset from the start of the header. 476 8n+2 means any 8-octet offset from the start of the header, plus 2 477 octets. 479 There are two padding options which are used when necessary to align 480 subsequent options and to pad out the containing header to a multiple 481 of 8 octets in length. These padding options must be recognized by 482 all IPv6 implementations: 484 Pad1 option (alignment requirement: none) 486 +-+-+-+-+-+-+-+-+ 487 | 0 | 488 +-+-+-+-+-+-+-+-+ 489 NOTE! the format of the Pad1 option is a special case -- it does 490 not have length and value fields. 492 The Pad1 option is used to insert one octet of padding into the 493 Options area of a header. If more than one octet of padding is 494 required, the PadN option, described next, should be used, rather 495 than multiple Pad1 options. 497 PadN option (alignment requirement: none) 499 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 500 | 1 | Opt Data Len | Option Data 501 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 503 The PadN option is used to insert two or more octets of padding 504 into the Options area of a header. For N octets of padding, the 505 Opt Data Len field contains the value N-2, and the Option Data 506 consists of N-2 zero-valued octets. 508 Appendix A contains formatting guidelines for designing new options. 510 4.3. Hop-by-Hop Options Header 512 The Hop-by-Hop Options header is used to carry optional information 513 that may be examined and processed by every node along a packet's 514 delivery path. The Hop-by-Hop Options header is identified by a Next 515 Header value of 0 in the IPv6 header, and has the following format: 517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 518 | Next Header | Hdr Ext Len | | 519 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 520 | | 521 . . 522 . Options . 523 . . 524 | | 525 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 527 Next Header 8-bit selector. Identifies the type of header 528 immediately following the Hop-by-Hop Options 529 header. Uses the same values as the IPv4 530 Protocol field [IANA-PN]. 532 Hdr Ext Len 8-bit unsigned integer. Length of the Hop-by- 533 Hop Options header in 8-octet units, not 534 including the first 8 octets. 536 Options Variable-length field, of length such that the 537 complete Hop-by-Hop Options header is an 538 integer multiple of 8 octets long. Contains 539 one or more TLV-encoded options, as described 540 in section 4.2. 542 The only hop-by-hop options defined in this document are the Pad1 and 543 PadN options specified in section 4.2. 545 4.4. Routing Header 547 The Routing header is used by an IPv6 source to list one or more 548 intermediate nodes to be "visited" on the way to a packet's 549 destination. This function is very similar to IPv4's Loose Source 550 and Record Route option. The Routing header is identified by a Next 551 Header value of 43 in the immediately preceding header, and has the 552 following format: 554 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 555 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 556 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 557 | | 558 . . 559 . type-specific data . 560 . . 561 | | 562 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 564 Next Header 8-bit selector. Identifies the type of header 565 immediately following the Routing header. 566 Uses the same values as the IPv4 Protocol 567 field [IANA-PN]. 569 Hdr Ext Len 8-bit unsigned integer. Length of the Routing 570 header in 8-octet units, not including the 571 first 8 octets. 573 Routing Type 8-bit identifier of a particular Routing 574 header variant. 576 Segments Left 8-bit unsigned integer. Number of route 577 segments remaining, i.e., number of explicitly 578 listed intermediate nodes still to be visited 579 before reaching the final destination. 581 type-specific data Variable-length field, of format determined by 582 the Routing Type, and of length such that the 583 complete Routing header is an integer multiple 584 of 8 octets long. 586 If, while processing a received packet, a node encounters a Routing 587 header with an unrecognized Routing Type value, the required behavior 588 of the node depends on the value of the Segments Left field, as 589 follows: 591 If Segments Left is zero, the node must ignore the Routing header 592 and proceed to process the next header in the packet, whose type 593 is identified by the Next Header field in the Routing header. 595 If Segments Left is non-zero, the node must discard the packet and 596 send an ICMP Parameter Problem, Code 0, message to the packet's 597 Source Address, pointing to the unrecognized Routing Type. 599 If, after processing a Routing header of a received packet, an 600 intermediate node determines that the packet is to be forwarded onto 601 a link whose link MTU is less than the size of the packet, the node 602 must discard the packet and send an ICMP Packet Too Big message to 603 the packet's Source Address. 605 The currently defined IPv6 Routing Headers and their status can be 606 found at [IANA-RH]. Allocation guidelines for IPv6 Routing Headers 607 can be found in [RFC5871]. 609 4.5. Fragment Header 611 The Fragment header is used by an IPv6 source to send a packet larger 612 than would fit in the path MTU to its destination. (Note: unlike 613 IPv4, fragmentation in IPv6 is performed only by source nodes, not by 614 routers along a packet's delivery path -- see section 5.) The 615 Fragment header is identified by a Next Header value of 44 in the 616 immediately preceding header, and has the following format: 618 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 619 | Next Header | Reserved | Fragment Offset |Res|M| 620 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 621 | Identification | 622 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 623 Next Header 8-bit selector. Identifies the initial header 624 type of the Fragmentable Part of the original 625 packet (defined below). Uses the same values 626 as the IPv4 Protocol field [IANA-PN]. 628 Reserved 8-bit reserved field. Initialized to zero for 629 transmission; ignored on reception. 631 Fragment Offset 13-bit unsigned integer. The offset, in 632 8-octet units, of the data following this 633 header, relative to the start of the 634 Fragmentable Part of the original packet. 636 Res 2-bit reserved field. Initialized to zero for 637 transmission; ignored on reception. 639 M flag 1 = more fragments; 0 = last fragment. 641 Identification 32 bits. See description below. 643 In order to send a packet that is too large to fit in the MTU of the 644 path to its destination, a source node may divide the packet into 645 fragments and send each fragment as a separate packet, to be 646 reassembled at the receiver. 648 For every packet that is to be fragmented, the source node generates 649 an Identification value. The Identification must be different than 650 that of any other fragmented packet sent recently* with the same 651 Source Address and Destination Address. If a Routing header is 652 present, the Destination Address of concern is that of the final 653 destination. 655 * "recently" means within the maximum likely lifetime of a 656 packet, including transit time from source to destination and 657 time spent awaiting reassembly with other fragments of the same 658 packet. However, it is not required that a source node know 659 the maximum packet lifetime. Rather, it is assumed that the 660 requirement can be met by implementing an algorithm that 661 results in a low identification reuse frequency. Examples of 662 algorithms that can meet this requirement are described in 663 [RFC7739]. 665 The initial, large, unfragmented packet is referred to as the 666 "original packet", and it is considered to consist of three parts, as 667 illustrated: 669 original packet: 671 +------------------+-------------------------+---//----------------+ 672 | Per-Fragment | Extension & Upper-Layer | Fragmentable | 673 | Headers | Headers | Part | 674 +------------------+-------------------------+---//----------------+ 676 The Per-Fragment Headers consists of the IPv6 header plus any 677 extension headers that must be processed by nodes en route to the 678 destination, that is, all headers up to and including the Routing 679 header if present, else the Hop-by-Hop Options header if present, 680 else no extension headers. 682 The Extension Headers are all other extension headers that are not 683 included in the Per-Fragment headers part of the packet. For this 684 purpose, the Encapsulating Security Payload (ESP) is not 685 considered an extension header. The Upper-Layer Header is the 686 first upper-layer header that is not an IPv6 extension header. 687 Examples of upper-layer headers include TCP, UDP, IPv4, IPv6, 688 ICMPv6, and as noted ESP. 690 The Fragmentable Part consists of the rest of the packet after the 691 upper-layer header or after any header (i.e., initial IPv6 header 692 or extension header) that contains a Next Header value of No Next 693 Header. 695 The Fragmentable Part of the original packet is divided into 696 fragments. The lengths of the fragments must be chosen such that the 697 resulting fragment packets fit within the MTU of the path to the 698 packets' destination(s). Each complete fragment, except possibly the 699 last ("rightmost") one, being an integer multiple of 8 octets long. 701 The fragments are transmitted in separate "fragment packets" as 702 illustrated: 704 original packet: 706 +-----------------+-----------------+--------+--------+-//-+--------+ 707 | Per-Fragment |Ext & Upper-Layer| first | second | | last | 708 | Headers | Headers |fragment|fragment|....|fragment| 709 +-----------------+-----------------+--------+--------+-//-+--------+ 711 fragment packets: 713 +------------------+---------+-------------------+----------+ 714 | Per-Fragment |Fragment | Ext & Upper-Layer | first | 715 | Headers | Header | Headers | fragment | 716 +------------------+---------+-------------------+----------+ 718 +------------------+--------+-------------------------------+ 719 | Per-Fragment |Fragment| second | 720 | Headers | Header | fragment | 721 +------------------+--------+-------------------------------+ 722 o 723 o 724 o 725 +------------------+--------+----------+ 726 | Per-Fragment |Fragment| last | 727 | Headers | Header | fragment | 728 +------------------+--------+----------+ 730 The first fragment packet is composed of: 732 (1) The Per-Fragment Headers of the original packet, with the 733 Payload Length of the original IPv6 header changed to contain the 734 length of this fragment packet only (excluding the length of the 735 IPv6 header itself), and the Next Header field of the last header 736 of the Per-Fragment Headers changed to 44. 738 (2) A Fragment header containing: 740 The Next Header value that identifies the first header after 741 the Per-Fragment Headers of the original packet. 743 A Fragment Offset containing the offset of the fragment, in 744 8-octet units, relative to the start of the Fragmentable Part 745 of the original packet. The Fragment Offset of the first 746 ("leftmost") fragment is 0. 748 An M flag value of 1 as this is the first fragment. 750 The Identification value generated for the original packet. 752 (3) Extension Headers, if any, and the Upper-Layer header. These 753 headers must be in the first fragment. Note: This restricts the 754 size of the headers through the Upper-Layer header to the MTU of 755 the path to the packets' destinations(s). 757 (4) The first fragment. 759 The subsequent fragment packets are composed of: 761 (1) The Per-Fragment Headers of the original packet, with the 762 Payload Length of the original IPv6 header changed to contain the 763 length of this fragment packet only (excluding the length of the 764 IPv6 header itself), and the Next Header field of the last header 765 of the Per-Fragment Headers changed to 44. 767 (2) A Fragment header containing: 769 The Next Header value that identifies the first header after 770 the Per-Fragment Headers of the original packet. 772 A Fragment Offset containing the offset of the fragment, in 773 8-octet units, relative to the start of the Fragmentable part 774 of the original packet. 776 An M flag value of 0 if the fragment is the last ("rightmost") 777 one, else an M flag value of 1. 779 The Identification value generated for the original packet. 781 (3) The fragment itself. 783 Fragments must not be created that overlap with any other fragments 784 created from the original packet. 786 At the destination, fragment packets are reassembled into their 787 original, unfragmented form, as illustrated: 789 reassembled original packet: 791 +---------------+-----------------+---------+--------+-//--+--------+ 792 | Per-Fragment |Ext & Upper-Layer| first | second | | last | 793 | Headers | Headers |frag data|fragment|.....|fragment| 794 +---------------+-----------------+---------+--------+-//--+--------+ 796 The following rules govern reassembly: 798 An original packet is reassembled only from fragment packets that 799 have the same Source Address, Destination Address, and Fragment 800 Identification. 802 The Per-Fragment Headers of the reassembled packet consists of all 803 headers up to, but not including, the Fragment header of the first 804 fragment packet (that is, the packet whose Fragment Offset is 805 zero), with the following two changes: 807 The Next Header field of the last header of the Per-Fragment 808 Headers is obtained from the Next Header field of the first 809 fragment's Fragment header. 811 The Payload Length of the reassembled packet is computed from 812 the length of the Per-Fragment Headers and the length and 813 offset of the last fragment. For example, a formula for 814 computing the Payload Length of the reassembled original packet 815 is: 817 PL.orig = PL.first - FL.first - 8 + (8 * FO.last) + FL.last 819 where 820 PL.orig = Payload Length field of reassembled packet. 821 PL.first = Payload Length field of first fragment packet. 822 FL.first = length of fragment following Fragment header of 823 first fragment packet. 824 FO.last = Fragment Offset field of Fragment header of last 825 fragment packet. 826 FL.last = length of fragment following Fragment header of 827 last fragment packet. 829 The Fragmentable Part of the reassembled packet is constructed 830 from the fragments following the Fragment headers in each of 831 the fragment packets. The length of each fragment is computed 832 by subtracting from the packet's Payload Length the length of 833 the headers between the IPv6 header and fragment itself; its 834 relative position in Fragmentable Part is computed from its 835 Fragment Offset value. 837 The Fragment header is not present in the final, reassembled 838 packet. 840 It should be noted that fragments may be duplicated in the 841 network. These exact duplicate fragments will be treated as 842 overlapping fragments and handled as described in the previous 843 paragraph. An implementation may choose to detect this case 844 and not drop the other fragments of the same packet. 846 If the fragment is a whole datagram (that is, both the Fragment 847 Offset field and the M flag are zero), then it does not need 848 any further reassembly and should be processed as a fully 849 reassembled packet (i.e., updating Next Header, adjust Payload 850 Length, removing the Fragmentation Header, etc.). Any other 851 fragments that match this packet (i.e., the same IPv6 Source 852 Address, IPv6 Destination Address, and Fragment Identification) 853 should be processed independently. 855 The following error conditions may arise when reassembling fragmented 856 packets: 858 If insufficient fragments are received to complete reassembly of a 859 packet within 60 seconds of the reception of the first-arriving 860 fragment of that packet, reassembly of that packet must be 861 abandoned and all the fragments that have been received for that 862 packet must be discarded. If the first fragment (i.e., the one 863 with a Fragment Offset of zero) has been received, an ICMP Time 864 Exceeded -- Fragment Reassembly Time Exceeded message should be 865 sent to the source of that fragment. 867 If the length of a fragment, as derived from the fragment packet's 868 Payload Length field, is not a multiple of 8 octets and the M flag 869 of that fragment is 1, then that fragment must be discarded and an 870 ICMP Parameter Problem, Code 0, message should be sent to the 871 source of the fragment, pointing to the Payload Length field of 872 the fragment packet. 874 If the length and offset of a fragment are such that the Payload 875 Length of the packet reassembled from that fragment would exceed 876 65,535 octets, then that fragment must be discarded and an ICMP 877 Parameter Problem, Code 0, message should be sent to the source of 878 the fragment, pointing to the Fragment Offset field of the 879 fragment packet. 881 If the first fragment does not include all headers through an 882 Upper-Layer header, then that fragment should be discarded and an 883 ICMP Parameter Problem, Code 3, message should be sent to the 884 source of the fragment, with the Pointer field set to zero. 886 If any of the fragments being reassembled overlaps with any other 887 fragments being reassembled for the same packet, reassembly of 888 that packet must be abandoned and all the fragments that have been 889 received for that packet must be discarded. 891 The following conditions are not expected to occur, but are not 892 considered errors if they do: 894 The number and content of the headers preceding the Fragment 895 header of different fragments of the same original packet may 896 differ. Whatever headers are present, preceding the Fragment 897 header in each fragment packet, are processed when the packets 898 arrive, prior to queueing the fragments for reassembly. Only 899 those headers in the Offset zero fragment packet are retained in 900 the reassembled packet. 902 The Next Header values in the Fragment headers of different 903 fragments of the same original packet may differ. Only the value 904 from the Offset zero fragment packet is used for reassembly. 906 4.6. Destination Options Header 908 The Destination Options header is used to carry optional information 909 that need be examined only by a packet's destination node(s). The 910 Destination Options header is identified by a Next Header value of 60 911 in the immediately preceding header, and has the following format: 913 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 914 | Next Header | Hdr Ext Len | | 915 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 916 | | 917 . . 918 . Options . 919 . . 920 | | 921 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 923 Next Header 8-bit selector. Identifies the type of header 924 immediately following the Destination Options 925 header. Uses the same values as the IPv4 926 Protocol field [IANA-PN]. 928 Hdr Ext Len 8-bit unsigned integer. Length of the 929 Destination Options header in 8-octet units, 930 not including the first 8 octets. 932 Options Variable-length field, of length such that the 933 complete Destination Options header is an 934 integer multiple of 8 octets long. Contains 935 one or more TLV-encoded options, as described 936 in section 4.2. 938 The only destination options defined in this document are the Pad1 939 and PadN options specified in section 4.2. 941 Note that there are two possible ways to encode optional destination 942 information in an IPv6 packet: either as an option in the Destination 943 Options header, or as a separate extension header. The Fragment 944 header and the Authentication header are examples of the latter 945 approach. Which approach can be used depends on what action is 946 desired of a destination node that does not understand the optional 947 information: 949 o If the desired action is for the destination node to discard 950 the packet and, only if the packet's Destination Address is not 951 a multicast address, send an ICMP Unrecognized Type message to 952 the packet's Source Address, then the information may be 953 encoded either as a separate header or as an option in the 954 Destination Options header whose Option Type has the value 11 955 in its highest-order two bits. The choice may depend on such 956 factors as which takes fewer octets, or which yields better 957 alignment or more efficient parsing. 959 o If any other action is desired, the information must be encoded 960 as an option in the Destination Options header whose Option 961 Type has the value 00, 01, or 10 in its highest-order two bits, 962 specifying the desired action (see section 4.2). 964 4.7. No Next Header 966 The value 59 in the Next Header field of an IPv6 header or any 967 extension header indicates that there is nothing following that 968 header. If the Payload Length field of the IPv6 header indicates the 969 presence of octets past the end of a header whose Next Header field 970 contains 59, those octets must be ignored, and passed on unchanged if 971 the packet is forwarded. 973 4.8. Defining New Extension Headers and Options 975 No new extension headers that require hop-by-hop behavior should be 976 defined because as specified in Section 4 of this document, the only 977 Extension Header that has hop-by-hop behavior is the Hop-by-Hop 978 Options header. 980 New hop-by-hop options are not recommended because it is expected 981 that nodes along a packet's delivery path will only examine and 982 process the hop-by-hop option header if explicitly configured to do 983 so. 985 Defining new IPv6 extension headers is not recommended. Instead of 986 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). 990 If new Extension Headers are defined, they need to use the following 991 format: 993 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 994 | Next Header | Hdr Ext Len | | 995 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 996 | | 997 . . 998 . Header Specific Data . 999 . . 1000 | | 1001 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1003 Next Header 8-bit selector. Identifies the type of 1004 header immediately following the extension 1005 header. Uses the same values as the IPv4 1006 Protocol field [IANA-PN]. 1008 Hdr Ext Len 8-bit unsigned integer. Length of the 1009 Destination Options header in 8-octet units, 1010 not including the first 8 octets. 1012 Header Specific Data Variable-length field, Fields specific to 1013 the extension header. 1015 5. Packet Size Issues 1017 IPv6 requires that every link in the internet have an MTU of 1280 1018 octets or greater. On any link that cannot convey a 1280-octet 1019 packet in one piece, link-specific fragmentation and reassembly must 1020 be provided at a layer below IPv6. 1022 Links that have a configurable MTU (for example, PPP links [RFC1661]) 1023 must be configured to have an MTU of at least 1280 octets; it is 1024 recommended that they be configured with an MTU of 1500 octets or 1025 greater, to accommodate possible encapsulations (i.e., tunneling) 1026 without incurring IPv6-layer fragmentation. 1028 From each link to which a node is directly attached, the node must be 1029 able to accept packets as large as that link's MTU. 1031 It is strongly recommended that IPv6 nodes implement Path MTU 1032 Discovery [RFC1981], in order to discover and take advantage of path 1033 MTUs greater than 1280 octets. However, a minimal IPv6 1034 implementation (e.g., in a boot ROM) may simply restrict itself to 1035 sending packets no larger than 1280 octets, and omit implementation 1036 of Path MTU Discovery. 1038 In order to send a packet larger than a path's MTU, a node may use 1039 the IPv6 Fragment header to fragment the packet at the source and 1040 have it reassembled at the destination(s). However, the use of such 1041 fragmentation is discouraged in any application that is able to 1042 adjust its packets to fit the measured path MTU (i.e., down to 1280 1043 octets). 1045 A node must be able to accept a fragmented packet that, after 1046 reassembly, is as large as 1500 octets. A node is permitted to 1047 accept fragmented packets that reassemble to more than 1500 octets. 1048 An upper-layer protocol or application that depends on IPv6 1049 fragmentation to send packets larger than the MTU of a path should 1050 not send packets larger than 1500 octets unless it has assurance that 1051 the destination is capable of reassembling packets of that larger 1052 size. 1054 6. Flow Labels 1056 The 20-bit Flow Label field in the IPv6 header is used by a source to 1057 label sequences of packets to be treated in the network as a single 1058 flow. 1060 The current definition of the IPv6 Flow Label can be found in 1061 [RFC6437]. 1063 7. Traffic Classes 1065 The 8-bit Traffic Class field in the IPv6 header is used by the 1066 network for traffic management. The value of the Traffic Class bits 1067 in a received packet might be different from the value sent by the 1068 packet's source. 1070 The current use of the Traffic Class field for Differentiated 1071 Services and Explicit Congestion Notification is specified in 1072 [RFC2474] and [RFC3168]. 1074 8. Upper-Layer Protocol Issues 1076 8.1. Upper-Layer Checksums 1078 Any transport or other upper-layer protocol that includes the 1079 addresses from the IP header in its checksum computation must be 1080 modified for use over IPv6, to include the 128-bit IPv6 addresses 1081 instead of 32-bit IPv4 addresses. In particular, the following 1082 illustration shows the TCP and UDP "pseudo-header" for IPv6: 1084 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1085 | | 1086 + + 1087 | | 1088 + Source Address + 1089 | | 1090 + + 1091 | | 1092 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1093 | | 1094 + + 1095 | | 1096 + Destination Address + 1097 | | 1098 + + 1099 | | 1100 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1101 | Upper-Layer Packet Length | 1102 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1103 | zero | Next Header | 1104 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1106 o If the IPv6 packet contains a Routing header, the Destination 1107 Address used in the pseudo-header is that of the final 1108 destination. At the originating node, that address will be in 1109 the last element of the Routing header; at the recipient(s), 1110 that address will be in the Destination Address field of the 1111 IPv6 header. 1113 o The Next Header value in the pseudo-header identifies the 1114 upper-layer protocol (e.g., 6 for TCP, or 17 for UDP). It will 1115 differ from the Next Header value in the IPv6 header if there 1116 are extension headers between the IPv6 header and the upper- 1117 layer header. 1119 o The Upper-Layer Packet Length in the pseudo-header is the 1120 length of the upper-layer header and data (e.g., TCP header 1121 plus TCP data). Some upper-layer protocols carry their own 1122 length information (e.g., the Length field in the UDP header); 1123 for such protocols, that is the length used in the pseudo- 1124 header. Other protocols (such as TCP) do not carry their own 1125 length information, in which case the length used in the 1126 pseudo-header is the Payload Length from the IPv6 header, minus 1127 the length of any extension headers present between the IPv6 1128 header and the upper-layer header. 1130 o Unlike IPv4, the default behavior when UDP packets are 1131 originated by an IPv6 node, is that the UDP checksum is not 1132 optional. That is, whenever originating a UDP packet, an IPv6 1133 node must compute a UDP checksum over the packet and the 1134 pseudo-header, and, if that computation yields a result of 1135 zero, it must be changed to hex FFFF for placement in the UDP 1136 header. IPv6 receivers must discard UDP packets containing a 1137 zero checksum, and should log the error. 1139 o As an exception to the default behaviour, protocols that use 1140 UDP as a tunnel encapsulation may enable zero-checksum mode for 1141 a specific port (or set of ports) for sending and/or receiving. 1142 Any node implementing zero-checksum mode must follow the 1143 requirements specified in "Applicability Statement for the use 1144 of IPv6 UDP Datagrams with Zero Checksums" [RFC6936]. 1146 The IPv6 version of ICMP [RFC4443] includes the above pseudo-header 1147 in its checksum computation; this is a change from the IPv4 version 1148 of ICMP, which does not include a pseudo-header in its checksum. The 1149 reason for the change is to protect ICMP from misdelivery or 1150 corruption of those fields of the IPv6 header on which it depends, 1151 which, unlike IPv4, are not covered by an internet-layer checksum. 1152 The Next Header field in the pseudo-header for ICMP contains the 1153 value 58, which identifies the IPv6 version of ICMP. 1155 8.2. Maximum Packet Lifetime 1157 Unlike IPv4, IPv6 nodes are not required to enforce maximum packet 1158 lifetime. That is the reason the IPv4 "Time to Live" field was 1159 renamed "Hop Limit" in IPv6. In practice, very few, if any, IPv4 1160 implementations conform to the requirement that they limit packet 1161 lifetime, so this is not a change in practice. Any upper-layer 1162 protocol that relies on the internet layer (whether IPv4 or IPv6) to 1163 limit packet lifetime ought to be upgraded to provide its own 1164 mechanisms for detecting and discarding obsolete packets. 1166 8.3. Maximum Upper-Layer Payload Size 1168 When computing the maximum payload size available for upper-layer 1169 data, an upper-layer protocol must take into account the larger size 1170 of the IPv6 header relative to the IPv4 header. For example, in 1171 IPv4, TCP's MSS option is computed as the maximum packet size (a 1172 default value or a value learned through Path MTU Discovery) minus 40 1173 octets (20 octets for the minimum-length IPv4 header and 20 octets 1174 for the minimum-length TCP header). When using TCP over IPv6, the 1175 MSS must be computed as the maximum packet size minus 60 octets, 1176 because the minimum-length IPv6 header (i.e., an IPv6 header with no 1177 extension headers) is 20 octets longer than a minimum-length IPv4 1178 header. 1180 8.4. Responding to Packets Carrying Routing Headers 1182 When an upper-layer protocol sends one or more packets in response to 1183 a received packet that included a Routing header, the response 1184 packet(s) must not include a Routing header that was automatically 1185 derived by "reversing" the received Routing header UNLESS the 1186 integrity and authenticity of the received Source Address and Routing 1187 header have been verified (e.g., via the use of an Authentication 1188 header in the received packet). In other words, only the following 1189 kinds of packets are permitted in response to a received packet 1190 bearing a Routing header: 1192 o Response packets that do not carry Routing headers. 1194 o Response packets that carry Routing headers that were NOT 1195 derived by reversing the Routing header of the received packet 1196 (for example, a Routing header supplied by local 1197 configuration). 1199 o Response packets that carry Routing headers that were derived 1200 by reversing the Routing header of the received packet IF AND 1201 ONLY IF the integrity and authenticity of the Source Address 1202 and Routing header from the received packet have been verified 1203 by the responder. 1205 9. IANA Considerations 1207 RFC2460 is referenced in a number of IANA registries. These include: 1209 o Internet Protocol Version 6 (IPv6) Parameters [IANA-6P] 1211 o Assigned Internet Protocol Numbers [IANA-PN] 1213 The IANA should update these references to point to this document. 1215 10. Security Considerations 1217 The security features of IPv6 are described in the Security 1218 Architecture for the Internet Protocol [RFC4301]. 1220 11. Acknowledgments 1222 The authors gratefully acknowledge the many helpful suggestions of 1223 the members of the IPng working group, the End-to-End Protocols 1224 research group, and the Internet Community At Large. 1226 The authors would also like to acknowledge the authors of the 1227 updating RFCs that were incorporated in this version of the document 1228 to move the IPv6 specification to Internet Standard. They are Joe 1229 Abley, Shane Amante, Jari Arkko, Manav Bhatia, Ronald P. Bonica, 1230 Scott Bradner, Brian Carpenter, P.F. Chimento, Marshall Eubanks, 1231 Fernando Gont, James Hoagland, Sheng Jiang, Erik Kline, Suresh 1232 Krishnan, Vishwas Manral, George Neville-Neil, Jarno Rajahalme, Pekka 1233 Savola, Magnus Westerlund, and James Woodyatt. 1235 12. References 1237 12.1. Normative References 1239 [I-D.ietf-6man-rfc4291bis] 1240 Hinden, R. and D. Deering, "IP Version 6 Addressing 1241 Architecture", draft-ietf-6man-rfc4291bis-03 (work in 1242 progress), June 2016. 1244 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 1245 10.17487/RFC0791, September 1981, 1246 . 1248 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 1249 "Definition of the Differentiated Services Field (DS 1250 Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI 1251 10.17487/RFC2474, December 1998, 1252 . 1254 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 1255 of Explicit Congestion Notification (ECN) to IP", RFC 1256 3168, DOI 10.17487/RFC3168, September 2001, 1257 . 1259 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 1260 Control Message Protocol (ICMPv6) for the Internet 1261 Protocol Version 6 (IPv6) Specification", RFC 4443, DOI 1262 10.17487/RFC4443, March 2006, 1263 . 1265 [RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme, 1266 "IPv6 Flow Label Specification", RFC 6437, DOI 10.17487/ 1267 RFC6437, November 2011, 1268 . 1270 12.2. Informative References 1272 [IANA-6P] "Internet Protocol Version 6 (IPv6) Parameters", 1273 . 1276 [IANA-EH] "IPv6 Extension Header Types", 1277 . 1280 [IANA-PN] "Assigned Internet Protocol Numbers", 1281 . 1284 [IANA-RH] "IANA Routing Types Parameter Registry", 1285 . 1288 [RFC1661] Simpson, W., Ed., "The Point-to-Point Protocol (PPP)", STD 1289 51, RFC 1661, DOI 10.17487/RFC1661, July 1994, 1290 . 1292 [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery 1293 for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August 1294 1996, . 1296 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1297 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 1298 December 1998, . 1300 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 1301 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 1302 December 1998, . 1304 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1305 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 1306 December 2005, . 1308 [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI 1309 10.17487/RFC4302, December 2005, 1310 . 1312 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 1313 4303, DOI 10.17487/RFC4303, December 2005, 1314 . 1316 [RFC5871] Arkko, J. and S. Bradner, "IANA Allocation Guidelines for 1317 the IPv6 Routing Header", RFC 5871, DOI 10.17487/RFC5871, 1318 May 2010, . 1320 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 1321 for the Use of IPv6 UDP Datagrams with Zero Checksums", 1322 RFC 6936, DOI 10.17487/RFC6936, April 2013, 1323 . 1325 [RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing 1326 of IPv6 Extension Headers", RFC 7045, DOI 10.17487/ 1327 RFC7045, December 2013, 1328 . 1330 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 1331 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 1332 February 2016, . 1334 Appendix A. Formatting Guidelines for Options 1336 This appendix gives some advice on how to lay out the fields when 1337 designing new options to be used in the Hop-by-Hop Options header or 1338 the Destination Options header, as described in section 4.2. These 1339 guidelines are based on the following assumptions: 1341 o One desirable feature is that any multi-octet fields within the 1342 Option Data area of an option be aligned on their natural 1343 boundaries, i.e., fields of width n octets should be placed at 1344 an integer multiple of n octets from the start of the Hop-by- 1345 Hop or Destination Options header, for n = 1, 2, 4, or 8. 1347 o Another desirable feature is that the Hop-by-Hop or Destination 1348 Options header take up as little space as possible, subject to 1349 the requirement that the header be an integer multiple of 8 1350 octets long. 1352 o It may be assumed that, when either of the option-bearing 1353 headers are present, they carry a very small number of options, 1354 usually only one. 1356 These assumptions suggest the following approach to laying out the 1357 fields of an option: order the fields from smallest to largest, with 1358 no interior padding, then derive the alignment requirement for the 1359 entire option based on the alignment requirement of the largest field 1360 (up to a maximum alignment of 8 octets). This approach is 1361 illustrated in the following examples: 1363 Example 1 1365 If an option X required two data fields, one of length 8 octets and 1366 one of length 4 octets, it would be laid out as follows: 1368 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1369 | Option Type=X |Opt Data Len=12| 1370 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1371 | 4-octet field | 1372 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1373 | | 1374 + 8-octet field + 1375 | | 1376 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1378 Its alignment requirement is 8n+2, to ensure that the 8-octet field 1379 starts at a multiple-of-8 offset from the start of the enclosing 1380 header. A complete Hop-by-Hop or Destination Options header 1381 containing this one option would look as follows: 1383 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1384 | Next Header | Hdr Ext Len=1 | Option Type=X |Opt Data Len=12| 1385 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1386 | 4-octet field | 1387 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1388 | | 1389 + 8-octet field + 1390 | | 1391 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1393 Example 2 1395 If an option Y required three data fields, one of length 4 octets, 1396 one of length 2 octets, and one of length 1 octet, it would be laid 1397 out as follows: 1399 +-+-+-+-+-+-+-+-+ 1400 | Option Type=Y | 1401 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1402 |Opt Data Len=7 | 1-octet field | 2-octet field | 1403 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1404 | 4-octet field | 1405 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1407 Its alignment requirement is 4n+3, to ensure that the 4-octet field 1408 starts at a multiple-of-4 offset from the start of the enclosing 1409 header. A complete Hop-by-Hop or Destination Options header 1410 containing this one option would look as follows: 1412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1413 | Next Header | Hdr Ext Len=1 | Pad1 Option=0 | Option Type=Y | 1414 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1415 |Opt Data Len=7 | 1-octet field | 2-octet field | 1416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1417 | 4-octet field | 1418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1419 | PadN Option=1 |Opt Data Len=2 | 0 | 0 | 1420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1422 Example 3 1424 A Hop-by-Hop or Destination Options header containing both options X 1425 and Y from Examples 1 and 2 would have one of the two following 1426 formats, depending on which option appeared first: 1428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1429 | Next Header | Hdr Ext Len=3 | Option Type=X |Opt Data Len=12| 1430 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1431 | 4-octet field | 1432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1433 | | 1434 + 8-octet field + 1435 | | 1436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1437 | PadN Option=1 |Opt Data Len=1 | 0 | Option Type=Y | 1438 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1439 |Opt Data Len=7 | 1-octet field | 2-octet field | 1440 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1441 | 4-octet field | 1442 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1443 | PadN Option=1 |Opt Data Len=2 | 0 | 0 | 1444 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1447 | Next Header | Hdr Ext Len=3 | Pad1 Option=0 | Option Type=Y | 1448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1449 |Opt Data Len=7 | 1-octet field | 2-octet field | 1450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1451 | 4-octet field | 1452 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1453 | PadN Option=1 |Opt Data Len=4 | 0 | 0 | 1454 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1455 | 0 | 0 | Option Type=X |Opt Data Len=12| 1456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1457 | 4-octet field | 1458 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1459 | | 1460 + 8-octet field + 1461 | | 1462 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1464 Appendix B. CHANGES SINCE RFC2460 1466 This memo has the following changes from RFC2460. Numbers identify 1467 the Internet-Draft version in which the change was made. 1469 Working Group Internet Drafts 1471 06) Added the Routing Header to the list required extension 1472 headers that a full implementation includes. 1474 06) Moved the text in Section 4.5 regarding the handling of 1475 received overlapping fragments to the list of error 1476 conditions 1478 06) Rewrote the text in Section 4.8 "Defining New Extension 1479 Headers and Options" to be clearer and remove redundant text. 1481 06) Editorial changes. 1483 05) Changed requirement for HBH header from a should to a may, 1484 and added a note to indicate what is expected. 1486 05) Corrected reference to point to draft-ietf-6man-rfc4291bis 1487 instead of draft-hinden-6man-rfc4291bis. 1489 05) Change to text regarding not inserting extension headers to 1490 cite using encapsulation as an example. 1492 04) Changed text discussing Fragment ID selection to refer to 1493 RFC7739 for example algorithms. 1495 04) Editorial changes. 1497 03) Clarified the text about decrementing the hop limit. 1499 03) Removed IP Next Generation from the Abstract. 1501 03) Add reference to the end of Section 4 to IPv6 Extension 1502 Header IANA registry. 1504 03) Editorial changes. 1506 02) Added text to Section 4.8 "Defining New Extension Headers and 1507 Options" clarifying why no new hop by hop extension headers 1508 should be defined. 1510 02) Added text to Fragment Header process on handling exact 1511 duplicate fragments. 1513 02) Editorial changes. 1515 01) Added text that Extension headers must never be inserted by 1516 any node other than the source of the packet. 1518 01) Change "must" to "should" in Section 4.3 on the Hop-by-Hop 1519 header. 1521 01) Added text that the Data Transmission Order is the same as 1522 IPv4 as defined in RFC791. 1524 01) Updated the Fragmentation header text to correct the 1525 inclusion of AH and note no next header case. 1527 01) Change terminology in Fragment header section from 1528 "Unfragmentable Headers" to "Per-Fragment Headers". 1530 01) Removed paragraph in Section 5 that required including a 1531 fragment header to outgoing packets if a ICMP Packet Too Big 1532 message reporting a Next-Hop MTU less than 1280. This is 1533 based on the update in draft-ietf-6man-deprecate-atomfrag- 1534 generation. 1536 01) Changed to Fragmentation Header section to clarify MTU 1537 restriction and 8-byte restrictions, and noting the 1538 restriction on headers in first fragment. 1540 01) Editorial changes. 1542 00) Add instruction to the IANA to change references to RFC2460 1543 to this document 1545 00) Add a paragraph to the acknowledgement section acknowledging 1546 the authors of the updating documents 1548 00) Remove old paragraph in Section 4 that should have been 1549 removed when incorporating the update from RFC7045. 1551 00) Editorial changes. 1553 Individual Internet Drafts 1555 07) Update references to current versions and assign references 1556 to normative and informative. 1558 07) Editorial changes. 1560 06) The purpose of this draft is to incorporate the updates 1561 dealing with Extension headers as defined in RFC6564, 1562 RFC7045, and RFC7112. The changes include: 1564 RFC6564: Added new Section 4.8 that describe 1565 recommendations for defining new Extension headers and 1566 options 1568 RFC7045: The changes were to add a reference to RFC7045, 1569 change the requirement for processing the hop-by-hop 1570 option to a should, and added a note that due to 1571 performance restrictions some nodes won't process the Hop- 1572 by-Hop Option header. 1574 RFC7112: The changes were to revise the Fragmentation 1575 Section to require that all headers through the first 1576 Upper-Layer Header are in the first fragment. This 1577 changed the text describing how packets are fragmented and 1578 reassembled and added a new error case. 1580 06) Editorial changes. 1582 05) The purpose of this draft is to incorporate the updates 1583 dealing with fragmentation as defined in RFC5722 and RFC6946. 1584 Note: The issue relating to the handling of exact duplicate 1585 fragments identified on the mailing list is left open. 1587 05) Fix text in the end of Section 4.0 to correct the number of 1588 extension headers defined in this document. 1590 05) Editorial changes. 1592 04) The purpose of this draft is to update the document to 1593 incorporate the update made by RFC6935 "UDP Checksums for 1594 Tunneled Packets". 1596 04) Remove Routing (Type 0) header from the list of required 1597 extension headers. 1599 04) Editorial changes. 1601 03) The purpose of this draft is to update the document for the 1602 deprecation of the RH0 Routing Header as specified in RFC5095 1603 and the allocations guidelines for routing headers as 1604 specified in RFC5871. Both of these RFCs updated RFC2460. 1606 02) The purpose of this version of the draft is to update the 1607 document to resolve the open Errata on RFC2460. 1609 Errata ID: 2541: This errata notes that RFC2460 didn't 1610 update RFC2205 when the length of the Flow Label was 1611 changed from 24 to 20 bits from RFC1883. This issue was 1612 resolved in RFC6437 where the Flow Label is defined. This 1613 draft now references RFC6437. No change is required. 1615 Errata ID: 4279: This errata noted that the specification 1616 doesn't handle the case of a forwarding node receiving a 1617 packet with a zero Hop Limit. This is fixed in 1618 Section 3.0 of this draft. Note: No change was made 1619 regarding host behaviour. 1621 Errata ID: 2843: This errata is marked rejected. No 1622 change is required. 1624 02) Editorial changes to the Flow Label and Traffic Class text. 1626 01) The purpose of this version of the draft is to update the 1627 document to point to the current specifications of the IPv6 1628 Flow Label field as defined in [RFC6437] and the Traffic 1629 Class as defined in [RFC2474] and [RFC3168]. 1631 00) The purpose of this version is to establish a baseline from 1632 RFC2460. The only intended changes are formatting (XML is 1633 slightly different from .nroff), differences between an RFC 1634 and Internet Draft, fixing a few ID Nits, and updates to the 1635 authors information. There should not be any content changes 1636 to the specification. 1638 Authors' Addresses 1640 Stephen E. Deering 1641 Retired 1642 Vancouver, British Columbia 1643 Canada 1644 Robert M. Hinden 1645 Check Point Software 1646 959 Skyway Road 1647 San Carlos, CA 94070 1648 USA 1650 Email: bob.hinden@gmail.com