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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (September 28, 2015) is 3131 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-06) exists of draft-hinden-6man-rfc4291bis-00 -- Obsolete informational reference (is this intentional?): RFC 1981 (Obsoleted by RFC 8201) -- Obsolete informational reference (is this intentional?): RFC 2460 (Obsoleted by RFC 8200) Summary: 0 errors (**), 0 flaws (~~), 6 warnings (==), 3 comments (--). 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 31, 2016 September 28, 2015 8 Internet Protocol, Version 6 (IPv6) Specification 9 draft-hinden-6man-rfc2460bis-07 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 March 31, 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 . . . . . . . . . . . . . . . . . 9 68 4.2. Options . . . . . . . . . . . . . . . . . . . . . . . . . 10 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 Extention Headers and Options . . . . . . . 22 75 5. Packet Size Issues . . . . . . . . . . . . . . . . . . . . . 23 76 6. Flow Labels . . . . . . . . . . . . . . . . . . . . . . . . . 24 77 7. Traffic Classes . . . . . . . . . . . . . . . . . . . . . . . 25 78 8. Upper-Layer Protocol Issues . . . . . . . . . . . . . . . . . 25 79 8.1. Upper-Layer Checksums . . . . . . . . . . . . . . . . . . 25 80 8.2. Maximum Packet Lifetime . . . . . . . . . . . . . . . . . 27 81 8.3. Maximum Upper-Layer Payload Size . . . . . . . . . . . . 27 82 8.4. Responding to Packets Carrying Routing Headers . . . . . 27 83 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 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 . . . . . . . . . . . . . . . . . . . . . . . 36 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 Note: As this document obsoletes [RFC2460], any document referenced 145 in this document that includes pointers to RFC2460, should be 146 interpreted as referencing this document. 148 2. Terminology 150 node a device that implements IPv6. 152 router a node that forwards IPv6 packets not explicitly 153 addressed to itself. [See Note below]. 155 host any node that is not a router. [See Note below]. 157 upper layer a protocol layer immediately above IPv6. Examples are 158 transport protocols such as TCP and UDP, control 159 protocols such as ICMP, routing protocols such as OSPF, 160 and internet or lower-layer protocols being "tunneled" 161 over (i.e., encapsulated in) IPv6 such as IPX, 162 AppleTalk, or IPv6 itself. 164 link a communication facility or medium over which nodes can 165 communicate at the link layer, i.e., the layer 166 immediately below IPv6. Examples are Ethernets (simple 167 or bridged); PPP links; X.25, Frame Relay, or ATM 168 networks; and internet (or higher) layer "tunnels", such 169 as tunnels over IPv4 or IPv6 itself. 171 neighbors nodes attached to the same link. 173 interface a node's attachment to a link. 175 address an IPv6-layer identifier for an interface or a set of 176 interfaces. 178 packet an IPv6 header plus payload. 180 link MTU the maximum transmission unit, i.e., maximum packet size 181 in octets, that can be conveyed over a link. 183 path MTU the minimum link MTU of all the links in a path between 184 a source node and a destination node. 186 Note: it is possible, though unusual, for a device with multiple 187 interfaces to be configured to forward non-self-destined packets 188 arriving from some set (fewer than all) of its interfaces, and to 189 discard non-self-destined packets arriving from its other interfaces. 190 Such a device must obey the protocol requirements for routers when 191 receiving packets from, and interacting with neighbors over, the 192 former (forwarding) interfaces. It must obey the protocol 193 requirements for hosts when receiving packets from, and interacting 194 with neighbors over, the latter (non-forwarding) interfaces. 196 3. IPv6 Header Format 198 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 199 |Version| Traffic Class | Flow Label | 200 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 201 | Payload Length | Next Header | Hop Limit | 202 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 203 | | 204 + + 205 | | 206 + Source Address + 207 | | 208 + + 209 | | 210 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 211 | | 212 + + 213 | | 214 + Destination Address + 215 | | 216 + + 217 | | 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 220 Version 4-bit Internet Protocol version number = 6. 222 Traffic Class 8-bit traffic class field. See section 7. 224 Flow Label 20-bit flow label. See section 6. 226 Payload Length 16-bit unsigned integer. Length of the IPv6 227 payload, i.e., the rest of the packet 228 following this IPv6 header, in octets. (Note 229 that any extension headers [section 4] present 230 are considered part of the payload, i.e., 231 included in the length count.) 233 Next Header 8-bit selector. Identifies the type of header 234 immediately following the IPv6 header. Uses 235 the same values as the IPv4 Protocol field 236 [IANA-PN]. 238 Hop Limit 8-bit unsigned integer. Decremented by 1 by 239 each node that forwards the packet. The 240 packet is discarded if Hop Limit is 241 decremented to zero, or is received with a 242 zero Hop Limit. 244 Source Address 128-bit address of the originator of the 245 packet. See [I-D.hinden-6man-rfc4291bis]. 247 Destination Address 128-bit address of the intended recipient of 248 the packet (possibly not the ultimate 249 recipient, if a Routing header is present). 250 See [I-D.hinden-6man-rfc4291bis] and section 251 4.4. 253 4. IPv6 Extension Headers 255 In IPv6, optional internet-layer information is encoded in separate 256 headers that may be placed between the IPv6 header and the upper- 257 layer header in a packet. There are a small number of such extension 258 headers, each identified by a distinct Next Header value. As 259 illustrated in these examples, an IPv6 packet may carry zero, one, or 260 more extension headers, each identified by the Next Header field of 261 the preceding header: 263 +---------------+------------------------ 264 | IPv6 header | TCP header + data 265 | | 266 | Next Header = | 267 | TCP | 268 +---------------+------------------------ 270 +---------------+----------------+------------------------ 271 | IPv6 header | Routing header | TCP header + data 272 | | | 273 | Next Header = | Next Header = | 274 | Routing | TCP | 275 +---------------+----------------+------------------------ 277 +---------------+----------------+-----------------+----------------- 278 | IPv6 header | Routing header | Fragment header | fragment of TCP 279 | | | | header + data 280 | Next Header = | Next Header = | Next Header = | 281 | Routing | Fragment | TCP | 282 +---------------+----------------+-----------------+----------------- 284 With one exception, extension headers are not examined or processed 285 by any node along a packet's delivery path, until the packet reaches 286 the node (or each of the set of nodes, in the case of multicast) 287 identified in the Destination Address field of the IPv6 header. 288 There, normal demultiplexing on the Next Header field of the IPv6 289 header invokes the module to process the first extension header, or 290 the upper-layer header if no extension header is present. The 291 contents and semantics of each extension header determine whether or 292 not to proceed to the next header. Therefore, extension headers must 293 be processed strictly in the order they appear in the packet; a 294 receiver must not, for example, scan through a packet looking for a 295 particular kind of extension header and process that header prior to 296 processing all preceding ones. 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 should 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 It should be noted that due to performance restrictions nodes may 323 ignore the Hop-by-Hop Option header, drop packets containing a hop- 324 by-hop option header, or assign packets containing a hop-by-hop 325 option header to a slow processing path. Designers planning to use a 326 hop-by-hop option need to be aware of this likely behaviour. 328 If, as a result of processing a header, a node is required to proceed 329 to the next header but the Next Header value in the current header is 330 unrecognized by the node, it should discard the packet and send an 331 ICMP Parameter Problem message to the source of the packet, with an 332 ICMP Code value of 1 ("unrecognized Next Header type encountered") 333 and the ICMP Pointer field containing the offset of the unrecognized 334 value within the original packet. The same action should be taken if 335 a node encounters a Next Header value of zero in any header other 336 than an IPv6 header. 338 Each extension header is an integer multiple of 8 octets long, in 339 order to retain 8-octet alignment for subsequent headers. Multi- 340 octet fields within each extension header are aligned on their 341 natural boundaries, i.e., fields of width n octets are placed at an 342 integer multiple of n octets from the start of the header, for n = 1, 343 2, 4, or 8. 345 A full implementation of IPv6 includes implementation of the 346 following extension headers: 348 Hop-by-Hop Options 349 Fragment 350 Destination Options 351 Authentication 352 Encapsulating Security Payload 354 The first three are specified in this document; the last two are 355 specified in [RFC4302] and [RFC4303], respectively. 357 4.1. Extension Header Order 359 When more than one extension header is used in the same packet, it is 360 recommended that those headers appear in the following order: 362 IPv6 header 363 Hop-by-Hop Options header 364 Destination Options header (note 1) 365 Routing header 366 Fragment header 367 Authentication header (note 2) 368 Encapsulating Security Payload header (note 2) 369 Destination Options header (note 3) 370 upper-layer header 372 note 1: for options to be processed by the first destination that 373 appears in the IPv6 Destination Address field plus 374 subsequent destinations listed in the Routing header. 376 note 2: additional recommendations regarding the relative order of 377 the Authentication and Encapsulating Security Payload 378 headers are given in [RFC4303]. 380 note 3: for options to be processed only by the final destination 381 of the packet. 383 Each extension header should occur at most once, except for the 384 Destination Options header which should occur at most twice (once 385 before a Routing header and once before the upper-layer header). 387 If the upper-layer header is another IPv6 header (in the case of IPv6 388 being tunneled over or encapsulated in IPv6), it may be followed by 389 its own extension headers, which are separately subject to the same 390 ordering recommendations. 392 If and when other extension headers are defined, their ordering 393 constraints relative to the above listed headers must be specified. 395 IPv6 nodes must accept and attempt to process extension headers in 396 any order and occurring any number of times in the same packet, 397 except for the Hop-by-Hop Options header which is restricted to 398 appear immediately after an IPv6 header only. Nonetheless, it is 399 strongly advised that sources of IPv6 packets adhere to the above 400 recommended order until and unless subsequent specifications revise 401 that recommendation. 403 4.2. Options 405 Two of the currently-defined extension headers -- the Hop-by-Hop 406 Options header and the Destination Options header -- carry a variable 407 number of type-length-value (TLV) encoded "options", of the following 408 format: 410 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 411 | Option Type | Opt Data Len | Option Data 412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 414 Option Type 8-bit identifier of the type of option. 416 Opt Data Len 8-bit unsigned integer. Length of the Option 417 Data field of this option, in octets. 419 Option Data Variable-length field. Option-Type-specific 420 data. 422 The sequence of options within a header must be processed strictly in 423 the order they appear in the header; a receiver must not, for 424 example, scan through the header looking for a particular kind of 425 option and process that option prior to processing all preceding 426 ones. 428 The Option Type identifiers are internally encoded such that their 429 highest-order two bits specify the action that must be taken if the 430 processing IPv6 node does not recognize the Option Type: 432 00 - skip over this option and continue processing the header. 434 01 - discard the packet. 436 10 - discard the packet and, regardless of whether or not the 437 packet's Destination Address was a multicast address, send an 438 ICMP Parameter Problem, Code 2, message to the packet's 439 Source Address, pointing to the unrecognized Option Type. 441 11 - discard the packet and, only if the packet's Destination 442 Address was not a multicast address, send an ICMP Parameter 443 Problem, Code 2, message to the packet's Source Address, 444 pointing to the unrecognized Option Type. 446 The third-highest-order bit of the Option Type specifies whether or 447 not the Option Data of that option can change en-route to the 448 packet's final destination. When an Authentication header is present 449 in the packet, for any option whose data may change en-route, its 450 entire Option Data field must be treated as zero-valued octets when 451 computing or verifying the packet's authenticating value. 453 0 - Option Data does not change en-route 455 1 - Option Data may change en-route 457 The three high-order bits described above are to be treated as part 458 of the Option Type, not independent of the Option Type. That is, a 459 particular option is identified by a full 8-bit Option Type, not just 460 the low-order 5 bits of an Option Type. 462 The same Option Type numbering space is used for both the Hop-by-Hop 463 Options header and the Destination Options header. However, the 464 specification of a particular option may restrict its use to only one 465 of those two headers. 467 Individual options may have specific alignment requirements, to 468 ensure that multi-octet values within Option Data fields fall on 469 natural boundaries. The alignment requirement of an option is 470 specified using the notation xn+y, meaning the Option Type must 471 appear at an integer multiple of x octets from the start of the 472 header, plus y octets. For example: 474 2n means any 2-octet offset from the start of the header. 475 8n+2 means any 8-octet offset from the start of the header, plus 2 476 octets. 478 There are two padding options which are used when necessary to align 479 subsequent options and to pad out the containing header to a multiple 480 of 8 octets in length. These padding options must be recognized by 481 all IPv6 implementations: 483 Pad1 option (alignment requirement: none) 485 +-+-+-+-+-+-+-+-+ 486 | 0 | 487 +-+-+-+-+-+-+-+-+ 488 NOTE! the format of the Pad1 option is a special case -- it does 489 not have length and value fields. 491 The Pad1 option is used to insert one octet of padding into the 492 Options area of a header. If more than one octet of padding is 493 required, the PadN option, described next, should be used, rather 494 than multiple Pad1 options. 496 PadN option (alignment requirement: none) 498 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 499 | 1 | Opt Data Len | Option Data 500 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 502 The PadN option is used to insert two or more octets of padding 503 into the Options area of a header. For N octets of padding, the 504 Opt Data Len field contains the value N-2, and the Option Data 505 consists of N-2 zero-valued octets. 507 Appendix A contains formatting guidelines for designing new options. 509 4.3. Hop-by-Hop Options Header 511 The Hop-by-Hop Options header is used to carry optional information 512 that must be examined by every node along a packet's delivery path. 513 The Hop-by-Hop Options header is identified by a Next Header value of 514 0 in the IPv6 header, and has the following format: 516 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 517 | Next Header | Hdr Ext Len | | 518 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 519 | | 520 . . 521 . Options . 522 . . 523 | | 524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 526 Next Header 8-bit selector. Identifies the type of header 527 immediately following the Hop-by-Hop Options 528 header. Uses the same values as the IPv4 529 Protocol field [IANA-PN]. 531 Hdr Ext Len 8-bit unsigned integer. Length of the Hop-by- 532 Hop Options header in 8-octet units, not 533 including the first 8 octets. 535 Options Variable-length field, of length such that the 536 complete Hop-by-Hop Options header is an 537 integer multiple of 8 octets long. Contains 538 one or more TLV-encoded options, as described 539 in section 4.2. 541 The only hop-by-hop options defined in this document are the Pad1 and 542 PadN options specified in section 4.2. 544 4.4. Routing Header 546 The Routing header is used by an IPv6 source to list one or more 547 intermediate nodes to be "visited" on the way to a packet's 548 destination. This function is very similar to IPv4's Loose Source 549 and Record Route option. The Routing header is identified by a Next 550 Header value of 43 in the immediately preceding header, and has the 551 following format: 553 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 554 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 555 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 556 | | 557 . . 558 . type-specific data . 559 . . 560 | | 561 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 563 Next Header 8-bit selector. Identifies the type of header 564 immediately following the Routing header. 565 Uses the same values as the IPv4 Protocol 566 field [IANA-PN]. 568 Hdr Ext Len 8-bit unsigned integer. Length of the Routing 569 header in 8-octet units, not including the 570 first 8 octets. 572 Routing Type 8-bit identifier of a particular Routing 573 header variant. 575 Segments Left 8-bit unsigned integer. Number of route 576 segments remaining, i.e., number of explicitly 577 listed intermediate nodes still to be visited 578 before reaching the final destination. 580 type-specific data Variable-length field, of format determined by 581 the Routing Type, and of length such that the 582 complete Routing header is an integer multiple 583 of 8 octets long. 585 If, while processing a received packet, a node encounters a Routing 586 header with an unrecognized Routing Type value, the required behavior 587 of the node depends on the value of the Segments Left field, as 588 follows: 590 If Segments Left is zero, the node must ignore the Routing header 591 and proceed to process the next header in the packet, whose type 592 is identified by the Next Header field in the Routing header. 594 If Segments Left is non-zero, the node must discard the packet and 595 send an ICMP Parameter Problem, Code 0, message to the packet's 596 Source Address, pointing to the unrecognized Routing Type. 598 If, after processing a Routing header of a received packet, an 599 intermediate node determines that the packet is to be forwarded onto 600 a link whose link MTU is less than the size of the packet, the node 601 must discard the packet and send an ICMP Packet Too Big message to 602 the packet's Source Address. 604 The currently defined IPv6 Routing Headers and their status can be 605 found at [IANA-RH]. Allocation guidelines for IPv6 Routing Headers 606 can be found in [RFC5871]. 608 4.5. Fragment Header 610 The Fragment header is used by an IPv6 source to send a packet larger 611 than would fit in the path MTU to its destination. (Note: unlike 612 IPv4, fragmentation in IPv6 is performed only by source nodes, not by 613 routers along a packet's delivery path -- see section 5.) The 614 Fragment header is identified by a Next Header value of 44 in the 615 immediately preceding header, and has the following format: 617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 618 | Next Header | Reserved | Fragment Offset |Res|M| 619 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 620 | Identification | 621 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 622 Next Header 8-bit selector. Identifies the initial header 623 type of the Fragmentable Part of the original 624 packet (defined below). Uses the same values 625 as the IPv4 Protocol field [IANA-PN]. 627 Reserved 8-bit reserved field. Initialized to zero for 628 transmission; ignored on reception. 630 Fragment Offset 13-bit unsigned integer. The offset, in 631 8-octet units, of the data following this 632 header, relative to the start of the 633 Fragmentable Part of the original packet. 635 Res 2-bit reserved field. Initialized to zero for 636 transmission; ignored on reception. 638 M flag 1 = more fragments; 0 = last fragment. 640 Identification 32 bits. See description below. 642 In order to send a packet that is too large to fit in the MTU of the 643 path to its destination, a source node may divide the packet into 644 fragments and send each fragment as a separate packet, to be 645 reassembled at the receiver. 647 For every packet that is to be fragmented, the source node generates 648 an Identification value. The Identification must be different than 649 that of any other fragmented packet sent recently* with the same 650 Source Address and Destination Address. If a Routing header is 651 present, the Destination Address of concern is that of the final 652 destination. 654 * "recently" means within the maximum likely lifetime of a 655 packet, including transit time from source to destination and 656 time spent awaiting reassembly with other fragments of the same 657 packet. However, it is not required that a source node know 658 the maximum packet lifetime. Rather, it is assumed that the 659 requirement can be met by maintaining the Identification value 660 as a simple, 32-bit, "wrap-around" counter, incremented each 661 time a packet must be fragmented. It is an implementation 662 choice whether to maintain a single counter for the node or 663 multiple counters, e.g., one for each of the node's possible 664 source addresses, or one for each active (source address, 665 destination address) combination. 667 The initial, large, unfragmented packet is referred to as the 668 "original packet", and it is considered to consist of three parts, as 669 illustrated: 671 original packet: 673 +------------------+-------------------------+---//----------------+ 674 | Unfragmentable | Extention & Upper-Layer | Fragmentable | 675 | Headers | Headers | Part | 676 +------------------+-------------------------+---//----------------+ 678 The Unfragmentable Headers consists of the IPv6 header plus any 679 extension headers that must be processed by nodes en route to the 680 destination, that is, all headers up to and including the Routing 681 header if present, else the Hop-by-Hop Options header if present, 682 else no extension headers. 684 The Ext Hdrs are all other extension headers that are not included 685 in the Unfragmentable headers part of the packet. For this 686 purpose, the IP Authentication Header (AH) and the Encapsulating 687 Security Payload (ESP) are not considered extension headers. The 688 Upper-Layer Header is the first upper-layer header that is not an 689 IPv6 extension header. Examples of upper-layer headers include 690 TCP, UDP, IPv4, IPv6, ICMPv6, and as noted AH and ESP. 692 The Fragmentable Part consists of the rest of the packet after the 693 upper-layer header. 695 The Fragmentable Part of the original packet is divided into 696 fragments, each, except possibly the last ("rightmost") one, being an 697 integer multiple of 8 octets long. The fragments are transmitted in 698 separate "fragment packets" as illustrated: 700 original packet: 702 +-----------------+-----------------+--------+--------+-//-+--------+ 703 | Unfragmentable |Ext & Upper-Layer| first | second | | last | 704 | Headers | Headers |fragment|fragment|....|fragment| 705 +-----------------+-----------------+--------+--------+-//-+--------+ 707 fragment packets: 709 +------------------+---------+-------------------+----------+ 710 | Unfragmentable |Fragment | Ext & Upper-Layer | first | 711 | Headers | Header | Headers | fragment | 712 +------------------+---------+-------------------+----------+ 714 +------------------+--------+-------------------------------+ 715 | Unfragmentable |Fragment| second | 716 | Headers | Header | fragment | 717 +------------------+--------+-------------------------------+ 718 o 719 o 720 o 721 +------------------+--------+----------+ 722 | Unfragmentable |Fragment| last | 723 | Headers | Header | fragment | 724 +------------------+--------+----------+ 726 The first fragment packet is composed of: 728 (1) The Unfragmentable 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 Unfragmentable Headers changed to 44. 734 (2) A Fragment header containing: 736 The Next Header value that identifies the first header after 737 the Unfragmentable 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. 751 (4) The first fragment. 753 The subsequent fragment packets are composed of: 755 (1) The Unfragmentable Headers of the original packet, with the 756 Payload Length of the original IPv6 header changed to contain the 757 length of this fragment packet only (excluding the length of the 758 IPv6 header itself), and the Next Header field of the last header 759 of the Unfragmentable Headers changed to 44. 761 (2) A Fragment header containing: 763 The Next Header value that identifies the first header after 764 the Unfragmentable Headers of the original packet. 766 A Fragment Offset containing the offset of the fragment, in 767 8-octet units, relative to the start of the Fragmentable part 768 of the original packet. 770 An M flag value of 0 if the fragment is the last ("rightmost") 771 one, else an M flag value of 1. 773 The Identification value generated for the original packet. 775 (3) The fragment itself. 777 The lengths of the fragments must be chosen such that the resulting 778 fragment packets fit within the MTU of the path to the packets' 779 destination(s). 781 Fragments must not be created that overlap with any other fragments 782 created from the original packet. 784 At the destination, fragment packets are reassembled into their 785 original, unfragmented form, as illustrated: 787 reassembled original packet: 789 +---------------+-----------------+---------+--------+-//--+--------+ 790 | Unfragmentable|Ext & Upper-Layer| first | second | | last | 791 | Headers | Headers |frag data|fragment|.....|fragment| 792 +---------------+-----------------+---------+--------+-//--+--------+ 794 The following rules govern reassembly: 796 An original packet is reassembled only from fragment packets that 797 have the same Source Address, Destination Address, and Fragment 798 Identification. 800 The Unfragmentable Headers of the reassembled packet consists of 801 all headers up to, but not including, the Fragment header of the 802 first fragment packet (that is, the packet whose Fragment Offset 803 is zero), with the following two changes: 805 The Next Header field of the last header of the Unfragmentable 806 Headers is obtained from the Next Header field of the first 807 fragment's Fragment header. 809 The Payload Length of the reassembled packet is computed from 810 the length of the Unfragmentable Headers and the length and 811 offset of the last fragment. For example, a formula for 812 computing the Payload Length of the reassembled original packet 813 is: 815 PL.orig = PL.first - FL.first - 8 + (8 * FO.last) + FL.last 817 where 818 PL.orig = Payload Length field of reassembled packet. 819 PL.first = Payload Length field of first fragment packet. 820 FL.first = length of fragment following Fragment header of 821 first fragment packet. 822 FO.last = Fragment Offset field of Fragment header of last 823 fragment packet. 824 FL.last = length of fragment following Fragment header of 825 last fragment packet. 827 The Fragmentable Part of the reassembled packet is constructed 828 from the fragments following the Fragment headers in each of 829 the fragment packets. The length of each fragment is computed 830 by subtracting from the packet's Payload Length the length of 831 the headers between the IPv6 header and fragment itself; its 832 relative position in Fragmentable Part is computed from its 833 Fragment Offset value. 835 The Fragment header is not present in the final, reassembled 836 packet. 838 If any of the fragments being reassembled overlaps with any 839 other fragments being reassembled for the same packet, 840 reassembly of that packet must be abandoned and all the 841 fragments that have been received for that packet must be 842 discarded. 844 If the fragment is a whole datagram (that is, both the Fragment 845 Offset field and the M flag are zero), then it does not need 846 any further reassembly and should be processed as a fully 847 reassembled packet (i.e., updating Next Header, adjust Payload 848 Length, removing the Fragmentation Header, etc.). Any other 849 fragments that match this packet (i.e., the same IPv6 Source 850 Address, IPv6 Destination Address, and Fragment Identification) 851 should be processed independently. 853 The following error conditions may arise when reassembling fragmented 854 packets: 856 If insufficient fragments are received to complete reassembly of a 857 packet within 60 seconds of the reception of the first-arriving 858 fragment of that packet, reassembly of that packet must be 859 abandoned and all the fragments that have been received for that 860 packet must be discarded. If the first fragment (i.e., the one 861 with a Fragment Offset of zero) has been received, an ICMP Time 862 Exceeded -- Fragment Reassembly Time Exceeded message should be 863 sent to the source of that fragment. 865 If the length of a fragment, as derived from the fragment packet's 866 Payload Length field, is not a multiple of 8 octets and the M flag 867 of that fragment is 1, then that fragment must be discarded and an 868 ICMP Parameter Problem, Code 0, message should be sent to the 869 source of the fragment, pointing to the Payload Length field of 870 the fragment packet. 872 If the length and offset of a fragment are such that the Payload 873 Length of the packet reassembled from that fragment would exceed 874 65,535 octets, then that fragment must be discarded and an ICMP 875 Parameter Problem, Code 0, message should be sent to the source of 876 the fragment, pointing to the Fragment Offset field of the 877 fragment packet. 879 If the first fragment does not include all headers through an 880 Upper-Layer header, then that fragment should be discarded and an 881 ICMP Parameter Problem, Code 3, message should be sent to the 882 source of the fragment, with the Pointer field set to zero. 884 The following conditions are not expected to occur, but are not 885 considered errors if they do: 887 The number and content of the headers preceding the Fragment 888 header of different fragments of the same original packet may 889 differ. Whatever headers are present, preceding the Fragment 890 header in each fragment packet, are processed when the packets 891 arrive, prior to queueing the fragments for reassembly. Only 892 those headers in the Offset zero fragment packet are retained in 893 the reassembled packet. 895 The Next Header values in the Fragment headers of different 896 fragments of the same original packet may differ. Only the value 897 from the Offset zero fragment packet is used for reassembly. 899 4.6. Destination Options Header 901 The Destination Options header is used to carry optional information 902 that need be examined only by a packet's destination node(s). The 903 Destination Options header is identified by a Next Header value of 60 904 in the immediately preceding header, and has the following format: 906 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 907 | Next Header | Hdr Ext Len | | 908 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 909 | | 910 . . 911 . Options . 912 . . 913 | | 914 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 916 Next Header 8-bit selector. Identifies the type of header 917 immediately following the Destination Options 918 header. Uses the same values as the IPv4 919 Protocol field [IANA-PN]. 921 Hdr Ext Len 8-bit unsigned integer. Length of the 922 Destination Options header in 8-octet units, 923 not including the first 8 octets. 925 Options Variable-length field, of length such that the 926 complete Destination Options header is an 927 integer multiple of 8 octets long. Contains 928 one or more TLV-encoded options, as described 929 in section 4.2. 931 The only destination options defined in this document are the Pad1 932 and PadN options specified in section 4.2. 934 Note that there are two possible ways to encode optional destination 935 information in an IPv6 packet: either as an option in the Destination 936 Options header, or as a separate extension header. The Fragment 937 header and the Authentication header are examples of the latter 938 approach. Which approach can be used depends on what action is 939 desired of a destination node that does not understand the optional 940 information: 942 o If the desired action is for the destination node to discard 943 the packet and, only if the packet's Destination Address is not 944 a multicast address, send an ICMP Unrecognized Type message to 945 the packet's Source Address, then the information may be 946 encoded either as a separate header or as an option in the 947 Destination Options header whose Option Type has the value 11 948 in its highest-order two bits. The choice may depend on such 949 factors as which takes fewer octets, or which yields better 950 alignment or more efficient parsing. 952 o If any other action is desired, the information must be encoded 953 as an option in the Destination Options header whose Option 954 Type has the value 00, 01, or 10 in its highest-order two bits, 955 specifying the desired action (see section 4.2). 957 4.7. No Next Header 959 The value 59 in the Next Header field of an IPv6 header or any 960 extension header indicates that there is nothing following that 961 header. If the Payload Length field of the IPv6 header indicates the 962 presence of octets past the end of a header whose Next Header field 963 contains 59, those octets must be ignored, and passed on unchanged if 964 the packet is forwarded. 966 4.8. Defining New Extention Headers and Options 968 No new extension headers that require hop-by-hop behavior should be 969 defined. 971 New hop-by-hop options are not recommended because, due to 972 performance restrictions, nodes may ignore the Hop-by-Hop Option 973 header, drop packets containing a hop-by-hop header, or assign 974 packets containing a hop-by-hop header to a slow processing path. 975 Designers considering defining new hop-by-hop options need to be 976 aware of this likely behaviour. There has to a very clear 977 justification why any new hop-by-hop option is needed before it is 978 standardized. 980 Instead of defining new Extension Headers, it is recommended that the 981 Destination Options header is used to carry optional information that 982 need be examined only by a packet's destination node(s), because they 983 provide better handling and backward compatibility. Defining new 984 IPv6 extension headers is not recommended. There has to a very clear 985 justification why any new extension header is needed before it is 986 standardized. 988 If new Extension Headers are defined, they need to use the following 989 format: 991 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 992 | Next Header | Hdr Ext Len | | 993 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 994 | | 995 . . 996 . Header Specific Data . 997 . . 998 | | 999 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1001 Next Header 8-bit selector. Identifies the type of 1002 header immediately following the extension 1003 header. Uses the same values as the IPv4 1004 Protocol field [IANA-PN]. 1006 Hdr Ext Len 8-bit unsigned integer. Length of the 1007 Destination Options header in 8-octet units, 1008 not including the first 8 octets. 1010 Header Specific Data Variable-length field, Fields specific to 1011 the extension header. 1013 5. Packet Size Issues 1015 IPv6 requires that every link in the internet have an MTU of 1280 1016 octets or greater. On any link that cannot convey a 1280-octet 1017 packet in one piece, link-specific fragmentation and reassembly must 1018 be provided at a layer below IPv6. 1020 Links that have a configurable MTU (for example, PPP links [RFC1661]) 1021 must be configured to have an MTU of at least 1280 octets; it is 1022 recommended that they be configured with an MTU of 1500 octets or 1023 greater, to accommodate possible encapsulations (i.e., tunneling) 1024 without incurring IPv6-layer fragmentation. 1026 From each link to which a node is directly attached, the node must be 1027 able to accept packets as large as that link's MTU. 1029 It is strongly recommended that IPv6 nodes implement Path MTU 1030 Discovery [RFC1981], in order to discover and take advantage of path 1031 MTUs greater than 1280 octets. However, a minimal IPv6 1032 implementation (e.g., in a boot ROM) may simply restrict itself to 1033 sending packets no larger than 1280 octets, and omit implementation 1034 of Path MTU Discovery. 1036 In order to send a packet larger than a path's MTU, a node may use 1037 the IPv6 Fragment header to fragment the packet at the source and 1038 have it reassembled at the destination(s). However, the use of such 1039 fragmentation is discouraged in any application that is able to 1040 adjust its packets to fit the measured path MTU (i.e., down to 1280 1041 octets). 1043 A node must be able to accept a fragmented packet that, after 1044 reassembly, is as large as 1500 octets. A node is permitted to 1045 accept fragmented packets that reassemble to more than 1500 octets. 1046 An upper-layer protocol or application that depends on IPv6 1047 fragmentation to send packets larger than the MTU of a path should 1048 not send packets larger than 1500 octets unless it has assurance that 1049 the destination is capable of reassembling packets of that larger 1050 size. 1052 In response to an IPv6 packet that is sent to an IPv4 destination 1053 (i.e., a packet that undergoes translation from IPv6 to IPv4), the 1054 originating IPv6 node may receive an ICMP Packet Too Big message 1055 reporting a Next-Hop MTU less than 1280. In that case, the IPv6 node 1056 is not required to reduce the size of subsequent packets to less than 1057 1280, but must include a Fragment header in those packets so that the 1058 IPv6-to-IPv4 translating router can obtain a suitable Identification 1059 value to use in resulting IPv4 fragments. Note that this means the 1060 payload may have to be reduced to 1232 octets (1280 minus 40 for the 1061 IPv6 header and 8 for the Fragment header), and smaller still if 1062 additional extension headers are used. 1064 6. Flow Labels 1066 The 20-bit Flow Label field in the IPv6 header is used by a source to 1067 label sequences of packets to be treated in the network as a single 1068 flow. 1070 The current definition of the IPv6 Flow Label can be found in 1071 [RFC6437]. 1073 7. Traffic Classes 1075 The 8-bit Traffic Class field in the IPv6 header is used by the 1076 network for traffic management. The value of the Traffic Class bits 1077 in a received packet might be different from the value sent by the 1078 packet's source. 1080 The current use of the Traffic Class field for Differentiated 1081 Services and Explicit Congestion Notification is specified in 1082 [RFC2474] and [RFC3168]. 1084 8. Upper-Layer Protocol Issues 1086 8.1. Upper-Layer Checksums 1088 Any transport or other upper-layer protocol that includes the 1089 addresses from the IP header in its checksum computation must be 1090 modified for use over IPv6, to include the 128-bit IPv6 addresses 1091 instead of 32-bit IPv4 addresses. In particular, the following 1092 illustration shows the TCP and UDP "pseudo-header" for IPv6: 1094 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1095 | | 1096 + + 1097 | | 1098 + Source Address + 1099 | | 1100 + + 1101 | | 1102 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1103 | | 1104 + + 1105 | | 1106 + Destination Address + 1107 | | 1108 + + 1109 | | 1110 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1111 | Upper-Layer Packet Length | 1112 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1113 | zero | Next Header | 1114 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1116 o If the IPv6 packet contains a Routing header, the Destination 1117 Address used in the pseudo-header is that of the final 1118 destination. At the originating node, that address will be in 1119 the last element of the Routing header; at the recipient(s), 1120 that address will be in the Destination Address field of the 1121 IPv6 header. 1123 o The Next Header value in the pseudo-header identifies the 1124 upper-layer protocol (e.g., 6 for TCP, or 17 for UDP). It will 1125 differ from the Next Header value in the IPv6 header if there 1126 are extension headers between the IPv6 header and the upper- 1127 layer header. 1129 o The Upper-Layer Packet Length in the pseudo-header is the 1130 length of the upper-layer header and data (e.g., TCP header 1131 plus TCP data). Some upper-layer protocols carry their own 1132 length information (e.g., the Length field in the UDP header); 1133 for such protocols, that is the length used in the pseudo- 1134 header. Other protocols (such as TCP) do not carry their own 1135 length information, in which case the length used in the 1136 pseudo-header is the Payload Length from the IPv6 header, minus 1137 the length of any extension headers present between the IPv6 1138 header and the upper-layer header. 1140 o Unlike IPv4, the default behavior when UDP packets are 1141 originated by an IPv6 node, is that the UDP checksum is not 1142 optional. That is, whenever originating a UDP packet, an IPv6 1143 node must compute a UDP checksum over the packet and the 1144 pseudo-header, and, if that computation yields a result of 1145 zero, it must be changed to hex FFFF for placement in the UDP 1146 header. IPv6 receivers must discard UDP packets containing a 1147 zero checksum, and should log the error. 1149 o As an exception to the default behaviour, protocols that use 1150 UDP as a tunnel encapsulation may enable zero-checksum mode for 1151 a specific port (or set of ports) for sending and/or receiving. 1152 Any node implementing zero-checksum mode must follow the 1153 requirements specified in "Applicability Statement for the use 1154 of IPv6 UDP Datagrams with Zero Checksums" [RFC6936]. 1156 The IPv6 version of ICMP [RFC4443] includes the above pseudo-header 1157 in its checksum computation; this is a change from the IPv4 version 1158 of ICMP, which does not include a pseudo-header in its checksum. The 1159 reason for the change is to protect ICMP from misdelivery or 1160 corruption of those fields of the IPv6 header on which it depends, 1161 which, unlike IPv4, are not covered by an internet-layer checksum. 1162 The Next Header field in the pseudo-header for ICMP contains the 1163 value 58, which identifies the IPv6 version of ICMP. 1165 8.2. Maximum Packet Lifetime 1167 Unlike IPv4, IPv6 nodes are not required to enforce maximum packet 1168 lifetime. That is the reason the IPv4 "Time to Live" field was 1169 renamed "Hop Limit" in IPv6. In practice, very few, if any, IPv4 1170 implementations conform to the requirement that they limit packet 1171 lifetime, so this is not a change in practice. Any upper-layer 1172 protocol that relies on the internet layer (whether IPv4 or IPv6) to 1173 limit packet lifetime ought to be upgraded to provide its own 1174 mechanisms for detecting and discarding obsolete packets. 1176 8.3. Maximum Upper-Layer Payload Size 1178 When computing the maximum payload size available for upper-layer 1179 data, an upper-layer protocol must take into account the larger size 1180 of the IPv6 header relative to the IPv4 header. For example, in 1181 IPv4, TCP's MSS option is computed as the maximum packet size (a 1182 default value or a value learned through Path MTU Discovery) minus 40 1183 octets (20 octets for the minimum-length IPv4 header and 20 octets 1184 for the minimum-length TCP header). When using TCP over IPv6, the 1185 MSS must be computed as the maximum packet size minus 60 octets, 1186 because the minimum-length IPv6 header (i.e., an IPv6 header with no 1187 extension headers) is 20 octets longer than a minimum-length IPv4 1188 header. 1190 8.4. Responding to Packets Carrying Routing Headers 1192 When an upper-layer protocol sends one or more packets in response to 1193 a received packet that included a Routing header, the response 1194 packet(s) must not include a Routing header that was automatically 1195 derived by "reversing" the received Routing header UNLESS the 1196 integrity and authenticity of the received Source Address and Routing 1197 header have been verified (e.g., via the use of an Authentication 1198 header in the received packet). In other words, only the following 1199 kinds of packets are permitted in response to a received packet 1200 bearing a Routing header: 1202 o Response packets that do not carry Routing headers. 1204 o Response packets that carry Routing headers that were NOT 1205 derived by reversing the Routing header of the received packet 1206 (for example, a Routing header supplied by local 1207 configuration). 1209 o Response packets that carry Routing headers that were derived 1210 by reversing the Routing header of the received packet IF AND 1211 ONLY IF the integrity and authenticity of the Source Address 1212 and Routing header from the received packet have been verified 1213 by the responder. 1215 9. IANA Considerations 1217 None. 1219 10. Security Considerations 1221 The security features of IPv6 are described in the Security 1222 Architecture for the Internet Protocol [RFC4301]. 1224 11. Acknowledgments 1226 The authors gratefully acknowledge the many helpful suggestions of 1227 the members of the IPng working group, the End-to-End Protocols 1228 research group, and the Internet Community At Large. 1230 12. References 1232 12.1. Normative References 1234 [I-D.hinden-6man-rfc4291bis] 1235 Hinden, B. and S. Deering, "IP Version 6 Addressing 1236 Architecture", draft-hinden-6man-rfc4291bis-00 (work in 1237 progress), September 2015. 1239 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 1240 "Definition of the Differentiated Services Field (DS 1241 Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI 1242 10.17487/RFC2474, December 1998, 1243 . 1245 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 1246 of Explicit Congestion Notification (ECN) to IP", RFC 1247 3168, DOI 10.17487/RFC3168, September 2001, 1248 . 1250 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 1251 Control Message Protocol (ICMPv6) for the Internet 1252 Protocol Version 6 (IPv6) Specification", RFC 4443, DOI 1253 10.17487/RFC4443, March 2006, 1254 . 1256 [RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme, 1257 "IPv6 Flow Label Specification", RFC 6437, DOI 10.17487/ 1258 RFC6437, November 2011, 1259 . 1261 12.2. Informative References 1263 [IANA-PN] "Assigned Internet Protocol Numbers", 1264 . 1267 [IANA-RH] "IANA Routing Types Parameter Registry", 1268 . 1271 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 1272 10.17487/RFC0791, September 1981, 1273 . 1275 [RFC1661] Simpson, W., Ed., "The Point-to-Point Protocol (PPP)", STD 1276 51, RFC 1661, DOI 10.17487/RFC1661, July 1994, 1277 . 1279 [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery 1280 for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August 1281 1996, . 1283 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1284 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 1285 December 1998, . 1287 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1288 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 1289 December 2005, . 1291 [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI 1292 10.17487/RFC4302, December 2005, 1293 . 1295 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 1296 4303, DOI 10.17487/RFC4303, December 2005, 1297 . 1299 [RFC5871] Arkko, J. and S. Bradner, "IANA Allocation Guidelines for 1300 the IPv6 Routing Header", RFC 5871, DOI 10.17487/RFC5871, 1301 May 2010, . 1303 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 1304 for the Use of IPv6 UDP Datagrams with Zero Checksums", 1305 RFC 6936, DOI 10.17487/RFC6936, April 2013, 1306 . 1308 [RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing 1309 of IPv6 Extension Headers", RFC 7045, DOI 10.17487/ 1310 RFC7045, December 2013, 1311 . 1313 Appendix A. Formatting Guidelines for Options 1315 This appendix gives some advice on how to lay out the fields when 1316 designing new options to be used in the Hop-by-Hop Options header or 1317 the Destination Options header, as described in section 4.2. These 1318 guidelines are based on the following assumptions: 1320 o One desirable feature is that any multi-octet fields within the 1321 Option Data area of an option be aligned on their natural 1322 boundaries, i.e., fields of width n octets should be placed at 1323 an integer multiple of n octets from the start of the Hop-by- 1324 Hop or Destination Options header, for n = 1, 2, 4, or 8. 1326 o Another desirable feature is that the Hop-by-Hop or Destination 1327 Options header take up as little space as possible, subject to 1328 the requirement that the header be an integer multiple of 8 1329 octets long. 1331 o It may be assumed that, when either of the option-bearing 1332 headers are present, they carry a very small number of options, 1333 usually only one. 1335 These assumptions suggest the following approach to laying out the 1336 fields of an option: order the fields from smallest to largest, with 1337 no interior padding, then derive the alignment requirement for the 1338 entire option based on the alignment requirement of the largest field 1339 (up to a maximum alignment of 8 octets). This approach is 1340 illustrated in the following examples: 1342 Example 1 1344 If an option X required two data fields, one of length 8 octets and 1345 one of length 4 octets, it would be laid out as follows: 1347 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1348 | Option Type=X |Opt Data Len=12| 1349 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1350 | 4-octet field | 1351 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1352 | | 1353 + 8-octet field + 1354 | | 1355 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1357 Its alignment requirement is 8n+2, to ensure that the 8-octet field 1358 starts at a multiple-of-8 offset from the start of the enclosing 1359 header. A complete Hop-by-Hop or Destination Options header 1360 containing this one option would look as follows: 1362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1363 | Next Header | Hdr Ext Len=1 | Option Type=X |Opt Data Len=12| 1364 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1365 | 4-octet field | 1366 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1367 | | 1368 + 8-octet field + 1369 | | 1370 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1372 Example 2 1374 If an option Y required three data fields, one of length 4 octets, 1375 one of length 2 octets, and one of length 1 octet, it would be laid 1376 out as follows: 1378 +-+-+-+-+-+-+-+-+ 1379 | Option Type=Y | 1380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1381 |Opt Data Len=7 | 1-octet field | 2-octet field | 1382 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1383 | 4-octet field | 1384 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1386 Its alignment requirement is 4n+3, to ensure that the 4-octet field 1387 starts at a multiple-of-4 offset from the start of the enclosing 1388 header. A complete Hop-by-Hop or Destination Options header 1389 containing this one option would look as follows: 1391 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1392 | Next Header | Hdr Ext Len=1 | Pad1 Option=0 | Option Type=Y | 1393 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1394 |Opt Data Len=7 | 1-octet field | 2-octet field | 1395 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1396 | 4-octet field | 1397 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1398 | PadN Option=1 |Opt Data Len=2 | 0 | 0 | 1399 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1401 Example 3 1403 A Hop-by-Hop or Destination Options header containing both options X 1404 and Y from Examples 1 and 2 would have one of the two following 1405 formats, depending on which option appeared first: 1407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1408 | Next Header | Hdr Ext Len=3 | Option Type=X |Opt Data Len=12| 1409 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1410 | 4-octet field | 1411 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1412 | | 1413 + 8-octet field + 1414 | | 1415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1416 | PadN Option=1 |Opt Data Len=1 | 0 | Option Type=Y | 1417 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1418 |Opt Data Len=7 | 1-octet field | 2-octet field | 1419 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1420 | 4-octet field | 1421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1422 | PadN Option=1 |Opt Data Len=2 | 0 | 0 | 1423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1426 | Next Header | Hdr Ext Len=3 | Pad1 Option=0 | Option Type=Y | 1427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1428 |Opt Data Len=7 | 1-octet field | 2-octet field | 1429 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1430 | 4-octet field | 1431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1432 | PadN Option=1 |Opt Data Len=4 | 0 | 0 | 1433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1434 | 0 | 0 | Option Type=X |Opt Data Len=12| 1435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1436 | 4-octet field | 1437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1438 | | 1439 + 8-octet field + 1440 | | 1441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1443 Appendix B. CHANGES SINCE RFC2460 1445 This memo has the following changes from RFC2460. Numbers identify 1446 the Internet-Draft version in which the change was made. 1448 07) The purpose of this draft is to update references to current 1449 versions and assign references to normative and informative. 1451 07) Editorial changes. 1453 06) The purpose of this draft is to incorporate the updates 1454 dealing with Extension headers as defined in RFC6564, 1455 RFC7045, and RFC7112. The changes include: 1457 RFC6564: Added new Section 4.8 that describe 1458 recommendations for defining new Extension headers and 1459 options 1461 RFC7045: The changes were to add a reference to RFC7045, 1462 change the requirement for processing the hop-by-hop 1463 option to a should, and added a note that due to 1464 performance restrictions some nodes won't process the Hop- 1465 by-Hop Option header. 1467 RFC7112: The changes were to revise the Fragmentation 1468 Section to require that all headers through the first 1469 Upper-Layer Header are in the first fragment. This 1470 changed the text describing how packets are fragmented and 1471 reassembled and added a new error case. 1473 06) Editorial changes. 1475 05) The purpose of this draft is to incorporate the updates 1476 dealing with fragmentation as defined in RFC5722 and RFC6946. 1477 Note: The issue relating to the handling of exact duplicate 1478 fragments identified on the mailing list is left open. 1480 05) Fix text in the end of Section 4.0 to correct the number of 1481 extension headers defined in this document. 1483 05) Editorial changes. 1485 04) The purpose of this draft is to update the document to 1486 incorporate the update made by RFC6935 "UDP Checksums for 1487 Tunneled Packets". 1489 04) Remove Routing (Type 0) header from the list of required 1490 extension headers. 1492 04) Editorial changes. 1494 03) The purpose of this draft is to update the document for the 1495 deprecation of the RH0 Routing Header as specified in RFC5095 1496 and the allocations guidelines for routing headers as 1497 specified in RFC5871. Both of these RFCs updated RFC2460. 1499 02) The purpose of this version of the draft is to update the 1500 document to resolve the open Errata on RFC2460. 1502 Errata ID: 2541: This errata notes that RFC2460 didn't 1503 update RFC2205 when the length of the Flow Label was 1504 changed from 24 to 20 bits from RFC1883. This issue was 1505 resolved in RFC6437 where the Flow Label is defined. This 1506 draft now references RFC6437. No change is required. 1508 Errata ID: 4279: This errata noted that the specification 1509 doesn't handle the case of a forwarding node receiving a 1510 packet with a zero Hop Limit. This is fixed in 1511 Section 3.0 of this draft. Note: No change was made 1512 regarding host behaviour. 1514 Errata ID: 2843: This errata is marked rejected. No 1515 change is required. 1517 02) Editorial changes to the Flow Label and Traffic Class text. 1519 01) The purpose of this version of the draft is to update the 1520 document to point to the current specifications of the IPv6 1521 Flow Label field as defined in [RFC6437] and the Traffic 1522 Class as defined in [RFC2474] and [RFC3168]. 1524 00) The purpose of this version is to establish a baseline from 1525 RFC2460. The only intended changes are formatting (XML is 1526 slightly different from .nroff), differences between an RFC 1527 and Internet Draft, fixing a few ID Nits, and updates to the 1528 authors information. There should not be any content changes 1529 to the specification. 1531 Authors' Addresses 1533 Stephen E. Deering 1534 Retired 1535 Vancouver, British Columbia 1536 Canada 1538 Robert M. Hinden 1539 Check Point Software 1540 959 Skyway Road 1541 San Carlos, CA 94070 1542 USA 1544 Email: bob.hinden@gmail.com