INTERNET DRAFT S. Deering, Xerox PARC March 17, 1995 R. Hinden, Ipsilon Obsoletes: draft-hinden-ipng-ipv6-spec-00.txt Editors Internet Protocol, Version 6 (IPv6) Specification Abstract This document specifies version 6 of the Internet Protocol, a proposed successor to IP version 4. Changes from the previous draft are listed in Appendix B. Status of this Memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). Distribution of this memo is unlimited. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 1] INTERNET DRAFT IPv6 Specification March 17, 1995 Contents Status of this Memo..............................................1 1. Introduction..................................................3 2. Terminology...................................................4 3. IPv6 Header Format............................................5 4. IPv6 Extension Headers........................................6 4.1 Extension Header Order...................................8 4.2 Options..................................................9 4.3 Hop-by-Hop Options Header...............................11 4.4 Routing Header..........................................13 4.5 Fragment Header.........................................16 4.6 Authentication Header...................................18 4.7 Destination Options Header..............................19 4.8 No Next Header..........................................20 5. Packet Size Issues...........................................21 6. Flow Labels..................................................23 7. Priority.....................................................25 8. Upper-Layer Protocol Issues..................................26 8.1 Upper-Layer Checksums...................................26 8.2 Maximum Packet Lifetime.................................27 8.3 Maximum Upper-Layer Payload Size........................27 Appendix A. Formatting Guidelines for Options...................28 Appendix B. Changes from Previous Draft.........................31 Security Considerations.........................................33 Acknowledgments.................................................33 Document Editors' Addresses.....................................33 References......................................................34 draft-ietf-ipngwg-ipv6-spec-01.txt [Page 2] INTERNET DRAFT IPv6 Specification March 17, 1995 1. Introduction IP version 6 (IPv6) is a new version of the Internet Protocol, designed as a successor to IP version 4 (IPv4) [RFC-791]. The changes from IPv4 to IPv6 fall primarily into the following categories: o Expanded Addressing Capabilities IPv6 increases the IP address size from 32 bits to 128 bits, to support more levels of addressing hierarchy, a much greater number of addressable nodes, and simpler auto-configuration of addresses. The scalability of multicast routing is improved by adding a "scope" field to multicast addresses. And a new type of address called a "region address" is defined, to identify topological regions rather than individual nodes. o Header Format Simplification Some IPv4 header fields have been dropped or made optional, to reduce the common-case processing cost of packet handling and to limit the bandwidth cost of the IPv6 header. o Improved Support for Extensions and Options Changes in the way IP header options are encoded allows for more efficient forwarding, less stringent limits on the length of options, and greater flexibility for introducing new options in the future. o Flow Labeling Capability A new capability is added to enable the labeling of packets belonging to particular traffic "flows" for which the sender requests special handling, such as non-default quality of service or "real-time" service. o Authentication and Privacy Capabilities Extensions to support authentication, data integrity, and (optional) data confidentiality are specified for IPv6. This document specifies the basic IPv6 header and the initially-defined IPv6 extension headers and options. It also discusses packet size issues, the semantics of flow labels and priority, and the effects of IPv6 on upper-layer protocols. Other aspects of IPv6 are specified in separate documents, including the following: draft-ietf-ipngwg-ipv6-spec-01.txt [Page 3] INTERNET DRAFT IPv6 Specification March 17, 1995 o IP Version 6 Addressing Architecture [IPV6-ADDR] o ICMP for the Internet Protocol Version 6 [IPV6-ICMP] o Transition Mechanisms for IPv6 Hosts and Routers[IPV6-TRAN] 2. Terminology node - a device that implements IPv6. router - a node that forwards IPv6 packets not explicitly addressed to itself. host - any node that is not a router. upper layer - a protocol layer immediately above IPv6. Examples are transport protocols such as TCP and UDP, control protocols such as ICMP, routing protocols such as OSPF, and internet or lower-layer protocols being "tunneled" over (i.e., encapsulated in) IPv6 such as IPX, AppleTalk, or IPv6 itself. link - a communication facility or medium over which nodes can communicate at the link layer, i.e., the layer immediately below IPv6. Examples are Ethernets (simple or bridged); PPP links; X.25, Frame Relay, or ATM networks; and internet (or higher) layer "tunnels", such as tunnels over IPv4 or IPv6 itself. neighbors - nodes attached to the same link. interface - a node's attachment to a link. address - an IPv6-layer identifier for an interface or a set of interfaces. packet - an IPv6 header plus payload. link MTU - the maximum transmission unit, i.e., maximum packet size in octets, that can be conveyed in one piece over a link. path MTU - the minimum link MTU of all the links in a path between a source node and a destination node. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 4] INTERNET DRAFT IPv6 Specification March 17, 1995 3. IPv6 Header Format +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| Prio. | Flow Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload Length | Next Header | Hop Limit | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Source Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Destination Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Version 4-bit Internet Protocol version number = 6. Prio. 4-bit priority value. See section 7. Flow Label 24-bit flow label. See section 6. Payload Length 16-bit unsigned integer. Length of payload, i.e., the rest of the packet following the IPv6 header, in octets. If zero, indicates that the payload length is carried in a Jumbo Payload hop-by-hop option. Next Header 8-bit selector. Identifies the type of header immediately following the IPv6 header. Uses the same values as the IPv4 Protocol field [RFC-1700]. Hop Limit 8-bit unsigned integer. Decremented by 1 by each node that forwards the packet. The packet is discarded if Hop Limit is decremented to zero. Source Address 128-bit address of the originator of the packet. See [IPV6-ADDR]. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 5] INTERNET DRAFT IPv6 Specification March 17, 1995 Destination Address 128-bit address of the intended recipient of the packet (possibly not the ultimate recipient, if a Routing header is present). See [IPV6-ADDR] and section 4.4. 4. IPv6 Extension Headers In IPv6, optional internet-layer information is encoded in separate headers that may be placed between the IPv6 header and the upper-layer header in a packet. There are a small number of such extension headers, each identified by a distinct Next Header value. As illustrated in these examples, an IPv6 packet may carry zero, one, or more extension headers, each identified by the Next Header field of the preceding header: +---------------+------------------------ | IPv6 header | TCP header + data | | | Next Header = | | TCP | +---------------+------------------------ +---------------+----------------+------------------------ | IPv6 header | Routing header | TCP header + data | | | | Next Header = | Next Header = | | Routing | TCP | +---------------+----------------+------------------------ +---------------+----------------+-----------------+----------------- | IPv6 header | Routing header | Fragment header | fragment of TCP | | | | header + data | Next Header = | Next Header = | Next Header = | | Routing | Fragment | TCP | +---------------+----------------+-----------------+----------------- With one exception, extension headers are not examined or processed by any node along a packet's delivery path, until the packet reaches the node (or each of the set of nodes, in the case of multicast) identified in the Destination Address field of the IPv6 header. There, normal demultiplexing on the Next Header field of the IPv6 header invokes the module to process the first extension header, or the upper-layer header if no extension header is present. The contents and semantics of each draft-ietf-ipngwg-ipv6-spec-01.txt [Page 6] INTERNET DRAFT IPv6 Specification March 17, 1995 header determine whether or not to proceed to the next header. The exception referred to in the preceding paragraph is the Hop-by-Hop Options header, which carries information that must be examined and processed by every node along a packet's delivery path, including the source and destination nodes. The Hop-by-Hop Options header, when present, must immediately follow the IPv6 header. Its presence is indicated by the value zero in the Next Header field of the IPv6 header. If, while processing a header, a node is required to proceed to the next header but the Next Header value in the current header is unrecognized by the node, it should discard the packet and send an ICMP Parameter Problem message to the source of the packet, with an ICMP Code value of 2 ("unrecognized Next Header type encountered") and the ICMP Pointer field containing the offset of the unrecognized value within the original packet. The same action should be taken if a node encounters a Next Header value of zero in any header other than an IPv6 header. Each extension header is an integer multiple of 8 octets long, in order to retain 8-octet alignment for subsequent headers. Multi-octet fields within each extension header are aligned on their natural boundaries, i.e., fields of width n octets are placed at an integer multiple of n octets from the start of the header, for n = 1, 2, 4, or 8. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 7] INTERNET DRAFT IPv6 Specification March 17, 1995 4.1 Extension Header Order When more than one extension header is used in the same packet, it is recommended that those headers appear in the following order: IPv6 header Hop-by-Hop Options header Destination Options header (1) Routing header Fragment header Authentication header Destination Options header (2) upper-layer header (1) for options to be processed by the first destination that appears in the IPv6 Destination Address field plus subsequent destinations listed in the Routing header. (2) for options to be processed only by the final destination of the packet. Each extension header should occur at most once, except for the Destination Options header which should occur at most twice (once before a Routing header and once before the upper-layer header). If the upper-layer header is another IPv6 header (in the case of IPv6 being tunneled over or encapsulated in IPv6), it may be followed by its own extensions headers, which are separately subject to the same ordering recommendations. If and when other extension headers are defined, their ordering constraints relative to the above listed headers must be specified. IPv6 nodes must accept and attempt to process extension headers in any order and occurring any number of times in the same packet, except for the Hop-by-Hop Options header which is restricted to appear immediately after an IPv6 header only. Nonetheless, it is strongly advised that sources of IPv6 packets adhere to the above recommended order until and unless subsequent specifications revise that recommendation. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 8] INTERNET DRAFT IPv6 Specification March 17, 1995 4.2 Options Two of the currently-defined extension headers -- the Hop-by-Hop Options header and the Destination Options header -- may carry a variable number of Type-Length-Value (TLV) encoded "options", of the following format: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - | Option Type | Opt Data Len | Option Data +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - Option Type 8-bit identifier of the type of option. Opt Data Len 8-bit unsigned integer. Length of the Option Data field of this option, in octets. Option Data Variable-length field. Option-Type-specific data. The Option Type identifiers are internally encoded such that their highest-order two bits specify the action that must be taken if the processing IPv6 node does not recognize the Option Type: 00 - skip over this option and continue processing the header. 01 - discard the packet. 10 - discard the packet and send an ICMP Parameter Problem, Code 2, message to the packet's Source Address, pointing to the unrecognized Option Type. 11 - discard the packet and, only if the packet's Destination Address is not a multicast address, send an ICMP Parameter Problem, Code 2, message to the packet's Source Address, pointing to the unrecognized Option Type. The third-highest-order bit of the Option Type specifies whether or not the Option Data of that option can change en-route to the packet's final destination. Data that can change en-route must be excluded from the integrity assurance computation performed when the Authentication header is present. 0 - Option Data does not change en-route 1 - Option Data may change en-route Individual options may have specific alignment requirements, to ensure that multi-octet values within Option Data fields fall on natural draft-ietf-ipngwg-ipv6-spec-01.txt [Page 9] INTERNET DRAFT IPv6 Specification March 17, 1995 boundaries. The alignment requirement of an option is specified using the notation xn+y, meaning the Option Type must appear at an integer multiple of x octets from the start of the header, plus y octets. For example: 2n means any 2-octet offset from the start of the header. 8n+2 means any 8-octet offset from the start of the header, plus 2 octets. There are two padding options which are used when necessary to align subsequent options and to pad out the containing header to a multiple of 8 octets in length. These padding options must be recognized by all IPv6 implementations: Pad1 option (alignment requirement: none) +-+-+-+-+-+-+-+-+ | 0 | +-+-+-+-+-+-+-+-+ NOTE! the format of the Pad1 option is a special case -- it does not have length and value fields. The Pad1 option is used to insert one octet of padding into the Options area of a header. If more than one octet of padding is required, the PadN option, described next, should be used, rather than multiple Pad1 options. PadN option (alignment requirement: none) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - | 1 | Opt Data Len | Option Data +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - The PadN option is used to insert two or more octets of padding into the Options area of a header. For N octets of padding, the Opt Data Len field contains the value N-2, and the Option Data consists of N-2 zero-valued octets. Appendix A contains formatting guidelines for designing new options. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 10] INTERNET DRAFT IPv6 Specification March 17, 1995 4.3 Hop-by-Hop Options Header The Hop-by-Hop Options header is used to carry optional information that must be examined by every node along a packet's delivery path. The Hop-by-Hop Options header is identified by a Next Header value of 0 in the IPv6 header, and has the following format: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | . . . Options . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Next Header 8-bit selector. Identifies the type of header immediately following the Hop-by-Hop Options header. Uses the same values as the IPv4 Protocol field [RFC-1700]. Hdr Ext Len 8-bit unsigned integer. Length of the Hop-by-Hop Options header in 8-octet units, not including the first 8 octets. Options Variable-length field, of length such that the complete Hop-by-Hop Options header is an integer multiple of 8 octets long. Contains one or more TLV-encoded options, as described in section 4.2. In addition to the Pad1 and PadN options specified in section 4.2, the following hop-by-hop option is defined: Jumbo Payload option (alignment requirement: 4n + 2) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 194 |Opt Data Len=4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Jumbo Payload Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Jumbo Payload option is used to send IPv6 packets with payloads longer than 65,535 octets. The Jumbo Payload Length is draft-ietf-ipngwg-ipv6-spec-01.txt [Page 11] INTERNET DRAFT IPv6 Specification March 17, 1995 the length of the packet in octets, excluding the IPv6 header. It has a maximum value of 4,294,967,295, that is, 2^32-1. It has a minimum legal value of 8, which is the length of a Hop-by-Hop Options header containing only this option, with no additional headers or data; however, use of this option for packets with payloads less than 65,535 octets is not recommended. The Payload Length field in the IPv6 header must be set to zero in every packet that carries the Jumbo Payload option. If a packet is received with a Jumbo Payload option present and a non-zero IPv6 Payload Length field, an ICMP Parameter Problem message, Code 0, should be sent to the packet's source, pointing to the Option Type field of the Jumbo Payload option. The Jumbo Payload option must not be used in a packet that carries a Fragment header. If a Fragment Header is encountered in a packet that contains a Jumbo Payload option, an ICMP Parameter Problem message, Code 0, should be sent to the packet's source, pointing to the first octet of the Fragment header. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 12] INTERNET DRAFT IPv6 Specification March 17, 1995 4.4 Routing Header The Routing header is used by an IPv6 source to list one or more intermediate nodes (or topological regions) to be "visited" on the way to a packet's destination. This function is very similar to IPv4's Source Route options. The Routing header is identified by a Next Header value of 43 in the immediately preceding header, and has the following format: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Routing Type | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | . . . type-specific data . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Next Header 8-bit selector. Identifies the type of header immediately following the Routing header. Uses the same values as the IPv4 Protocol field [RFC-1700]. Routing Type 8-bit identifier of a particular Routing header variant. type-specific data Variable-length field, of format determined by the Routing Type, and of length such that the complete Routing header is an integer multiple of 8 octets long. If the IPv6 node that is processing a Routing header does not recognize the Routing Type value, it must discard the packet and, only if the packet's Destination Address is not a multicast address, send an ICMP Parameter Problem, Code 0, message to the packet's Source Address, pointing to the unrecognized Routing Type. The Type 0 Routing header has the following format: draft-ietf-ipngwg-ipv6-spec-01.txt [Page 13] INTERNET DRAFT IPv6 Specification March 17, 1995 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header |Routing Type=0 | Num Addrs | Next Addr | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Strict/Loose Bit Mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Address[0] + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Address[1] + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . . . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Address[Num Addrs - 1] + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Next Header 8-bit selector. Identifies the type of header immediately following the Routing header. Uses the same values as the IPv4 Protocol field [RFC-1700]. Routing Type 0. Num Addrs 8-bit unsigned integer. Number of addresses in the Routing header. Maximum legal value = 24. Next Addr 8-bit unsigned integer. Index of next address to be processed; initialized to 0 by the originating node. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 14] INTERNET DRAFT IPv6 Specification March 17, 1995 Reserved 8-bit reserved field. Initialized to zero for transmission; ignored on reception. Strict/Loose Bit Mask 24-bit bit-mask, numbered 0 to 23, left-to-right. If bit n is 1, then the packet may be forwarded to Address[n] by the node that places Address[n] in the IPv6 Destination Field only if the interface identified by Address[n] is a neighbor of the forwarding node. If bit n is 0, then Address[n] need not be a neighbor of the forwarding node. A Routing header is not examined or processed until it reaches the node identified in the Destination Address field of the IPv6 header. In that node, dispatching on the Next Header field of the immediately preceding header causes the Routing module to be invoked, which, in the case of Routing Type 0, performs the following algorithm: o If Next Addr < Num Addrs, swap the IPv6 Destination Address and Address[Next Addr]. If Bit Mask[Next Addr] = 0 or if the new destination address is known to be a neighbor of this node, increment Next Addr by one and re-submit the packet to the IPv6 module for forwarding to the new destination, else send an ICMP Destination Unreachable, Not a Neighbor message to the Source Address and discard the packet. o If Next Addr = Num Addrs, dispatch to the next header processing module, as identified by the Next Header field in the Routing header. o If Next Addr > Num Addrs, send an ICMP Parameter Problem, Code 0, message to the Source Address, pointing to the Num Addrs field, and discard the packet. Multicast addresses must not appear in a Routing header of Type 0, or in the IPv6 Destination Address field of a packet carrying a Routing header of Type 0. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 15] INTERNET DRAFT IPv6 Specification March 17, 1995 4.5 Fragment Header The Fragment header is used by an IPv6 source to send payloads larger than would fit in the path MTU to their destinations. (Note: unlike IPv4, fragmentation in IPv6 is performed only by source nodes, not by routers along a packet's delivery path -- see section 5.) The Fragment header is identified by a Next Header value of 44 in the immediately preceding header, and has the following format: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Reserved | Fragment Offset |Res|M| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Identification | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Next Header 8-bit selector. Identifies the type of header immediately following the Fragment header. Uses the same values as the IPv4 Protocol field [RFC-1700]. Reserved 8-bit reserved field. Initialized to zero for transmission; ignored on reception. Fragment Offset 13-bit unsigned integer. The offset, in 8-octet units, of the following payload, relative to the start of the original, unfragmented payload. Res 2-bit reserved field. Initialized to zero for transmission; ignored on reception. M flag 1 = more fragments; 0 = last fragment. Identification 32 bits. See description below. The fragmentation algorithm is as follows: The payload (including any extension headers that need be processed only by the destination node(s)) is divided into fragments, each, except possibly the last, being an integer multiple of 8 octets long. Each fragment is prepended with a Fragment header and sent in a separate IPv6 packet. The M ("more") flag is set to 1 on all fragments of the same payload except the last. The original payload is assigned an Identification value that is different than that of any other fragmented payload sent recently* with the same IPv6 Source Address, IPv6 Destination Address, and Fragment Next Header value. (If a Routing header is present, the IPv6 Destination Address is that of the final destination.) The Identification value is carried in the Fragment header of all of the draft-ietf-ipngwg-ipv6-spec-01.txt [Page 16] INTERNET DRAFT IPv6 Specification March 17, 1995 original payload's fragments, and is used by the destination to identify all fragments belonging to the same original payload. * "recently" means within the maximum likely lifetime of a packet, including transit time from source to destination and time spent awaiting reassembly with other fragments of the same payload. However, it is not required that a source node know the maximum packet lifetime. Rather, it is assumed that the requirement can be met by maintaining the Identification value as a simple, 32-bit, "wrap-around" counter, incremented each time a payload must be fragmented. It is an implementation choice whether to maintain a single counter for the node or multiple counters, e.g., one for each of the node's possible source addresses, or one for each active (source address, destination address, next header type) combination. In a packet with a Fragment header, the Payload Length field of the IPv6 header contains the length of that packet only (excluding the IPv6 header itself), not the length of the original, unfragmented payload. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 17] INTERNET DRAFT IPv6 Specification March 17, 1995 4.6 Authentication Header The Authentication header is used to provide authentication and integrity assurance for IPv6 packets. Non-repudiation may be provided by an authentication algorithm used with the Authentication header, but it is not provided with all authentication algorithms that might be used with this header. The Authentication header is identified by a Next Header value of 51 in the immediately preceding header, and has the following format: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload Type | Auth Data Len | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Security Association ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Authentication Data . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Payload Type 8-bit selector. Identifies the type of header immediately following the Authentication header. Uses the same values as the IPv4 Protocol field [RFC-1700]. Auth Data Len 8-bit unsigned integer. Length of the Authentication Data field in 8-octet units. Reserved 8-bit reserved field. Initialized to zero for transmission; ignored on reception. Security Assoc. ID 32 bits. When combined with the IPv6 Destination Address, identifies to the receiver(s) the pre-established security association to which this packet belongs. Authentication Data Variable-length field, an integer multiple of 8 octets long. Algorithm-specific information required authenticate the source of the packet and assure its integrity, as specified for the pre-established security association. Use of the Authentication header is specified in [IPV6-AUTH]. All IPv6 nodes are required to support the keyed MD5 algorithm used with the Authentication header as described in that document. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 18] INTERNET DRAFT IPv6 Specification March 17, 1995 4.7 Destination Options Header The Destination Options header is used to carry optional information that need be examined only by a packet's destination node(s). The Destination Options header is identified by a Next Header value of TBD in the immediately preceding header, and has the following format: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | . . . Options . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Next Header 8-bit selector. Identifies the type of header immediately following the Destination Options header. Uses the same values as the IPv4 Protocol field [RFC-1700]. Hdr Ext Len 8-bit unsigned integer. Length of the Destination Options header in 8-octet units, not including the first 8 octets. Options Variable-length field, of length such that the complete Destination Options header is an integer multiple of 8 octets long. Contains one or more TLV-encoded options, as described in section 4.2. The only destination options defined in this document are the Pad1 and PadN options specified in section 4.2. Note that there are two possible ways to encode optional destination information in an IPv6 packet: either as an option in the Destination Options header, or as a separate extension header. The Fragment header and the Authentication header are examples of the latter approach. Which approach can be used depends on what action is desired of a destination node that does not understand the optional information: o if the desired action is for the destination node to discard the packet and, only if the packet's Destination Address is not a multicast address, send an ICMP Unrecognized Type message to the packet's Source Address, then the information may be encoded draft-ietf-ipngwg-ipv6-spec-01.txt [Page 19] INTERNET DRAFT IPv6 Specification March 17, 1995 either as a separate header or as an option in the Destination Options header whose Option Type has the value 11 in its highest- order two bits. The choice may depend on such factors as which takes fewer octets, or which yields better alignment or more efficient parsing. o if any other action is desired, the information must be encoded as an option in the Destination Options header whose Option Type has the value 00, 01, or 10 in its highest-order two bits, specifying the desired action (see section 4.2). 4.8 No Next Header The value 59 in the Next Header field of an IPv6 header or any extension header indicates that there is nothing following that header. If the Payload Length field of the IPv6 header indicates the presence of octets past the end of a header whose Next Header field contains 59, those octets must be ignored, and passed on unchanged if the packet is forwarded. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 20] INTERNET DRAFT IPv6 Specification March 17, 1995 5. Packet Size Issues IPv6 requires that every link in the internet have an MTU of 576 octets or greater. On any link that cannot convey a 576-octet packet in one piece, link-specific fragmentation and reassembly must be provided at a layer below IPv6. Note: this minimum link MTU is NOT the same as the one in IPv4. In IPv4, the minimum link MTU is 68 octets [RFC-791, page 25]; 576 octets is the minimum reassembly buffer size required in an IPv4 node, which has nothing to do with link MTUs. From each link to which a node is directly attached, the node must be able to accept packets as large as that link's MTU. Links that have a configurable MTU (for example, PPP links [RFC-1548]) must be configured to have an MTU of at least 576 octets; it is recommended that a larger MTU be configured, to accommodate possible encapsulations (i.e., tunneling) without incurring fragmentation. IPv6 nodes are expected to implement Path MTU Discovery [RFC-1191], in order to discover and take advantage of paths with MTU greater than 576 octets. However, a minimal IPv6 implementation (e.g., in a boot ROM) may simply restrict itself to sending packets no larger than 576 octets, and omit implementation of Path MTU Discovery. In order to send a packet larger than a path's MTU, a node may use the IPv6 Fragment header to fragment the packet at the source and have it reassembled at the destination(s). However, the use of such fragmentation is discouraged in any application that is able to adapt its packets to fit the measured path MTU (i.e., down to 576 octets). A node must not send a packet larger than the path MTU (i.e., fragments that reassemble to a size larger than the path MTU) unless it has explicit knowledge that the destination(s) can reassemble a packet of that size. In response to an IPv6 packet that is sent to an IPv4 destination (i.e., a packet that undergoes translation from IPv6 to IPv4), the originating IPv6 node may receive an ICMP Packet Too Big message reporting a Next- Hop MTU less than 576. In that case, the IPv6 node is not required to reduce the size of subsequent packets to less than 576, but must include a Fragment header in those packets so that the IPv6-to-IPv4 translating router can obtain a suitable Identification value to use in resulting IPv4 fragments. Note that this means the payload may have to be reduced to 528 octets (576 minus 40 for the IPv6 header and 8 for the Fragment header), and smaller still if additional extension headers are used. Note: Path MTU Discovery must be performed even in cases where a host "thinks" a destination is attached to the same link as itself. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 21] INTERNET DRAFT IPv6 Specification March 17, 1995 Note: Unlike IPv4, it is unnecessary in IPv6 to set a "Don't Fragment" flag in the packet header in order to perform Path MTU Discovery; that is an implicit attribute of every IPv6 packet. Also, those parts of the RFC-1191 procedures that involve use of a table of MTU "plateaus" do not apply to IPv6, because the IPv6 version of the "Datagram Too Big" message always identifies the exact MTU to be used. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 22] INTERNET DRAFT IPv6 Specification March 17, 1995 6. Flow Labels The 24-bit Flow Label field in the IPv6 header may be used by a source to label those packets for which it requests special handling by the IPv6 routers, such as non-default quality of service or "real-time" service. This aspect of IPv6 is, at the time of writing, still experimental and subject to change as the requirements for flow support in the Internet become clearer. Hosts or routers that do not support the functions of the Flow Label field are required to set the field to zero when originating a packet, pass the field on unchanged when forwarding a packet, and ignore the field when receiving a packet. A flow is a sequence of packets sent from a particular source to a particular (unicast or multicast) destination for which the source desires special handling by the intervening routers. The nature of that special handling might be conveyed to the routers by a control protocol, such as a resource reservation protocol, or by information within the flow's packets themselves, e.g., in a hop-by-hop option. The details of such control protocols or options are beyond the scope of this document. There may be multiple active flows from a source to a destination, as well as traffic that is not associated with any flow. A flow is uniquely identified by the combination of a source address and a non- zero flow label. Packets that do not belong to a flow carry a flow label of zero. A flow label is assigned to a flow by the flow's source node. New flow labels must be chosen (pseudo-)randomly and uniformly from the range 1 to FFFFFF hex. The purpose of the random allocation is to make any set of bits within the Flow Label field suitable for use as a hash key by routers, for looking up the state associated with the flow. All packets belonging to the same flow must be sent with the same source address, same destination address, and same non-zero flow label. If any of those packets includes a Hop-by-Hop Options header, then they all must be originated with the same Hop-by-Hop Options header contents (excluding the Next Header field of the Hop-by-Hop Options header). If any of those packets includes a Routing header, then they all must be originated with the same contents in all extension headers up to and including the Routing header (excluding the Next Header field in the Routing header). The routers or destinations are permitted, but not required, to verify that these conditions are satisfied. If a violation is detected, it should be reported to the source by an ICMP Parameter Problem message, Code 0, pointing to the high-order octet of the Flow Label field (i.e., offset 1 within the IPv6 packet). Routers are free to "opportunistically" set up flow-handling state for any flow, even when no explicit flow establishment information has been draft-ietf-ipngwg-ipv6-spec-01.txt [Page 23] INTERNET DRAFT IPv6 Specification March 17, 1995 provided to them via a control protocol, a hop-by-hop option, or other means. For example, upon receiving a packet from a particular source with an unknown, non-zero flow label, a router may process its IPv6 header and any necessary extension headers as if the flow label were zero. That processing would include determining the next-hop interface, and possibly other actions, such as updating a hop-by-hop option, advancing the pointer and addresses in a Routing header, or deciding on how to queue the packet based on its Priority field. The router may then choose to "remember" the results of those processing steps and cache that information, using the source address plus the flow label as the cache key. Subsequent packets with the same source address and flow label may then be handled by referring to the cached information rather than examining all those fields that, according to the requirements of the previous paragraph, can be assumed unchanged from the first packet seen in the flow. Cached flow-handling state that is set up opportunistically, as discussed in the last paragraph, must be discarded no more than 6 seconds after it is established, regardless of whether or not packets of the same flow continue to arrive. If another packet with the same source address and flow label arrives after the cached state has been discarded, the packet undergoes full, normal processing (as if its flow label were zero), which may result in the re-creation of cached flow state for that flow. The lifetime of flow-handling state that is set up explicitly, for example by a control protocol or a hop-by-hop option, must be specified as part of the specification of the explicit set-up mechanism; it may exceed 6 seconds. A source must not re-use a flow label for a new flow within the lifetime of any flow-handling state that might have been established for the prior use of that flow label. Since flow-handling state with a lifetime of 6 seconds may be established opportunistically for any flow, the minimum interval between the last packet of one flow and the first packet of a new flow using the same flow label is 6 seconds. Flow labels used for explicitly set-up flows with longer flow-state lifetimes must remain unused for those longer lifetimes before being re-used for new flows. When a node stops and restarts (e.g., as a result of a "crash"), it must be careful not to use a flow label that it might have used for an earlier flow whose lifetime may not have expired yet. This may be accomplished by recording flow label usage on stable storage so that it can be remembered across crashes, or by refraining from using any flow labels until the maximum lifetime of any possible previously established flows has expired (at least 6 seconds; more if explicit flow set-up mechanisms with longer lifetimes might have been used). If the minimum draft-ietf-ipngwg-ipv6-spec-01.txt [Page 24] INTERNET DRAFT IPv6 Specification March 17, 1995 time for rebooting the node is known (often more than 6 seconds), that time can be deducted from the necessary waiting period before starting to allocate flow labels. There is no requirement that all, or even most, packets belong to flows, i.e., carry non-zero flow labels. This observation is placed here to remind protocol designers and implementors not to assume otherwise. For example, it would be unwise to design a router whose performance would be adequate only if most packets belonged to flows, or to design a header compression scheme that only worked on packets that belonged to flows. 7. Priority The 4-bit Priority field in the IPv6 header enables a source to identify the desired delivery priority of its packets, relative to other packets from the same source. The Priority values are divided into two ranges: Values 0 through 7 are used to specify the priority of traffic for which the source is providing congestion control, i.e., traffic that "backs off" in response to congestion, such as TCP traffic. Values 8 through 15 are used to specify the priority of traffic that does not back off in response to congestion, e.g., "real-time" packets being sent at a constant rate. For congestion-controlled traffic, the following Priority values are recommended for particular application categories: 0 - uncharacterized traffic 1 - "filler" traffic (e.g., netnews) 2 - unattended data transfer (e.g., email) 3 - (reserved) 4 - attended bulk transfer (e.g., FTP, NFS) 5 - (reserved) 6 - interactive traffic (e.g., telnet, X) 7 - internet control traffic (e.g., routing protocols, SNMP) For non-congestion-controlled traffic, the lowest Priority value (8) should be used for those packets that the sender is most willing to have discarded under conditions of congestion (e.g., high-fidelity video traffic), and the highest value (15) should be used for those packets that the sender is least willing to have discarded (e.g., low-fidelity audio traffic). There is no relative ordering implied between the congestion-controlled priorities and the non-congestion-controlled priorities. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 25] INTERNET DRAFT IPv6 Specification March 17, 1995 8. Upper-Layer Protocol Issues 8.1 Upper-Layer Checksums Any transport or other upper-layer protocol that includes the addresses from the IP header in its checksum computation must be modified for use over IPv6, to include the 128-bit IPv6 addresses instead of 32-bit IPv4 addresses. In particular, the following illustration shows the TCP and UDP "pseudo-header" for IPv6: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Source Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Destination Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | zero | Next Header | Payload Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ o If the packet contains a Routing header, the Destination Address used in the pseudo-header is that of the final destination. At the originating system, that address will be in the last element of the Routing header; at the recipient(s), that address will be in the Destination Address field of the IPv6 header. o The Next Header value in the pseudo-header identifies the upper- layer protocol (e.g., 6 for TCP, or 17 for UDP). It will differ from the Next Header value in the IPv6 header if there are extension headers between the IPv6 header and the upper-layer header. o The Payload Length used in the pseudo-header is the length of the upper-layer packet, including the upper-layer header. It will be less than the Payload Length in the IPv6 header if there are extension headers between the IPv6 header and the upper-layer header. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 26] INTERNET DRAFT IPv6 Specification March 17, 1995 o Unlike IPv4, when UDP packets are originated by an IPv6 node, the UDP checksum is not optional. That is, whenever originating a UDP packet, an IPv6 node must compute a UDP checksum over the packet and the pseudo-header, and, if that computation yields a result of zero, it must be changed to hex FFFF for placement in the UDP header. IPv6 receivers must discard UDP packets containing a zero checksum, and should log the error. The IPv6 version of ICMP [IPV6-ICMP] includes the above pseudo-header in its checksum computation; this is a change from the IPv4 version of ICMP, which does not include a pseudo-header in its checksum. The reason for the change is to protect ICMP from misdelivery or corruption of those fields of the IPv6 header on which it depends, which, unlike IPv4, are not covered by an internet-layer checksum. The Next Header field in the pseudo-header for ICMP contains the value 58, which identifies the IPv6 version of ICMP. 8.2 Maximum Packet Lifetime Unlike IPv4, IPv6 nodes are not required to enforce maximum packet lifetime. That is the reason the IPv4 "Time to Live" field was renamed "Hop Limit" in IPv6. In practice, very few, if any, IPv4 implementations conform to the requirement that they limit packet lifetime, so this is not a change in practice. Any upper-layer protocol that relies on the internet layer (whether IPv4 or IPv6) to limit packet lifetime ought to be upgraded to provide its own mechanisms for detecting and discarding obsolete packets. 8.3 Maximum Upper-Layer Payload Size When computing the maximum payload size available for upper-layer data, an upper-layer protocol must take into account the larger size of the IPv6 header relative to the IPv4 header. For example, in IPv4, TCP's MSS option is computed as the maximum packet size (a default value or a value learned through Path MTU Discovery) minus 40 octets (20 octets for the minimum-length IPv4 header and 20 octets for the minimum-length TCP header). When using TCP over IPv6, the MSS must be computed as the maximum packet size minus 60 octets, because the minimum-length IPv6 header (i.e., an IPv6 header with no extension headers) is 20 octets longer than a minimum-length IPv4 header. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 27] INTERNET DRAFT IPv6 Specification March 17, 1995 Appendix A. Formatting Guidelines for Options This appendix gives some advice on how to lay out the fields in options to be used in the Hop-by-Hop Options header or the Destination Options header, as described in section 4.2. These guidelines are based on the following assumptions: o One desirable feature is that any multi-octet fields within the Option Data area of an option be aligned on their natural boundaries, i.e., fields of width n octets should be placed at an integer multiple of n octets from the start of the Hop-by-Hop or Destination Options header, for n = 1, 2, 4, or 8. o Another desirable feature is that the Hop-by-Hop or Destination Options header take up as little space as possible, subject to the requirement that the header be an integer multiple of 8 octets long. o It may be assumed that, when either of the option-bearing headers are present, they carry a very small number of options, usually only one. These assumptions suggest the following approach to laying out the fields of an option: order the fields from smallest to largest, with no interior padding, then derive the alignment requirement for the entire option based on the alignment requirement of the largest field (up to a maximum alignment of 8 octets). This approach is illustrated in the following examples: Example 1 If an option X required two data fields, one of length 8 octets and one of length 4 octets, it would be laid out as follows: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type=X |Opt Data Len=12| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4-octet field | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + 8-octet field + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Its alignment requirement is 8n+2, to ensure that the 8-octet field ends draft-ietf-ipngwg-ipv6-spec-01.txt [Page 28] INTERNET DRAFT IPv6 Specification March 17, 1995 up on a multiple-of-8 offset from the start of the enclosing header. A complete Hop-by-Hop or Destination Options header containing this one option would look as follows: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len=1 | Option Type=X |Opt Data Len=12| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4-octet field | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + 8-octet field + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Example 2 If an option Y required three data fields, one of length 4 octets, one of length 2 octets, and one of length 1 octet, it would be laid out as follows: +-+-+-+-+-+-+-+-+ | Option Type=Y | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Opt Data Len=7 | 1-octet field | 2-octet field | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4-octet field | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Its alignment requirement is 4n+3, to ensure that the 4-octet field ends up on a multiple-of-4 offset from the start of the enclosing header. A complete Hop-by-Hop or Destination Options header containing this one option would look as follows: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len=1 | Pad1 Option=0 | Option Type=Y | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Opt Data Len=7 | 1-octet field | 2-octet field | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4-octet field | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PadN Option=1 |Opt Data Len=2 | 0 | 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ draft-ietf-ipngwg-ipv6-spec-01.txt [Page 29] INTERNET DRAFT IPv6 Specification March 17, 1995 Example 3 A Hop-by-Hop or Destination Options header containing both options X and Y from Examples 1 and 2 would have one of the two following formats, depending on which option appeared first: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len=1 | Option Type=X |Opt Data Len=12| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4-octet field | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + 8-octet field + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PadN Option=1 |Opt Data Len=1 | 0 | Option Type=Y | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Opt Data Len=7 | 1-octet field | 2-octet field | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4-octet field | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PadN Option=1 |Opt Data Len=2 | 0 | 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len=1 | Pad1 Option=0 | Option Type=Y | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Opt Data Len=7 | 1-octet field | 2-octet field | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4-octet field | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PadN Option=1 |Opt Data Len=4 | 0 | 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0 | 0 | Option Type=X |Opt Data Len=12| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4-octet field | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + 8-octet field + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ draft-ietf-ipngwg-ipv6-spec-01.txt [Page 30] INTERNET DRAFT IPv6 Specification March 17, 1995 Appendix B. Changes from Previous Draft Changes from draft-hinden-ipng-ipv6-spec-00.txt, October 1994: o Changed "cluster address" to "region address". o Added definitions of "upper layer" and "packet" to Terminology section. o Changed all references of "transport layer" to "upper layer". o Changed name of "TClass" field to "Priority", changed name of "Flow ID" field to "Flow Label", and dropped the use of the name "Flow Label" to refer to the combination of those two fields. o Added note that Hop-by-Hop Options must be processed by source and destination nodes, as well as intermediate nodes along a delivery path. o Specified that unknown Next Header values, as well as a Next Value of zero in any header other than an IPv6 header, should invoke an ICMP Parameter Problem message. o Changed name of "End-to-End Options" to "Destination Options", and specified that the Destination Options header may occur twice in a packet, once before a Routing Header and once before the upper- layer header. o Changed text regarding advisability of violating recommended ordering for extension headers ("be conservative in what you send; be liberal in what you receive"). o Specified that an unrecognized option triggers an ICMP Parameter Problem, Code 2, message, not an "ICMP Unrecognized Type" message. o The third-highest-order bit of Option Type codes, which indicates whether or not an option's data can change en-route, now applies to Destination Options as well as Hop-by-Hop Options, because Destination Options can now precede a Routing header and thus may be modified en-route. o Added the Jumbo Payload hop-by-hop option. o Deleted prohibition of en-route insertion of Routing headers (though I still think it's a bad idea). o Added Strict/Loose Bit Map to the Type 0 Routing header. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 31] INTERNET DRAFT IPv6 Specification March 17, 1995 o Deleted IPv6-in-IPv6 Encapsulation section -- moved to a separate document. o Added the "no next header" Next Header type. o Added a recommendation that links with configurable MTU, such as PPP links, be configured with an MTU larger than the minimum (576) so as to accommodate encapsulations (tunneling) without incurring fragmentation. o Split the Flow Label and Priority discussion into two sections. o Changed the description of the fields that must not change within a flow to include all headers up to and including the Routing header. o Added discussion of "opportunistic" flow state set-up, and added requirement that such state must be discarded within 6 seconds of being established. Also discussed source behavior to avoid reusing an active flow label after a reboot. o Added a warning about assuming that most packets will belong to flows. o In making the distinction between the two sub-ranges of Priority values, changed the terminology from "flow-controlled" to "congestion-controlled". o Deleted statement about flow set-up mechanisms possibly redefining the semantics of the Priority (formerly TClass) field. o Rearranged some text in the Upper-Layer (formerly Transport-Layer) Checksums section, added requirement that IPv6 hosts discard UDP packets with zero checksum, and changed the ICMP pseudo-header to be the same as the TCP/UDP pseudo-header. o Added a small section about upper-layer maximum payload size. o Updated references to newer documents. o Put Deering's name back on as an editor. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 32] INTERNET DRAFT IPv6 Specification March 17, 1995 Security Considerations This document specifies the format of an Authentication header, which is part of the machinery intended to provide end-to-end authentication and integrity assurance for IPv6 packets. Non-repudiation may be provided by an authentication algorithm used with the Authentication option, but it is not provided with all authentication algorithms that might be used with this option. Usage of the option is specified in [IPV6-AUTH]. Acknowledgments The document editors gratefully acknowledge the many helpful suggestions of the members of the IPng working group, the End-to-End Protocols research group, and the Internet Community At Large. Document Editors' Addresses Stephen E. Deering Robert M. Hinden Xerox Palo Alto Research Center Ipsilon Networks, Inc. 3333 Coyote Hill Road 2465 Latham Street, Suite 100 Palo Alto, CA 94304 Mt. View, CA 94040 USA USA phone: +1 415 812 4839 phone: +1 415 528 4604 fax: +1 415 812 4471 fax: +1 415 528 4653 email: deering@parc.xerox.com email: hinden@ipsilon.com draft-ietf-ipngwg-ipv6-spec-01.txt [Page 33] INTERNET DRAFT IPv6 Specification March 17, 1995 References [IPV6-AUTH] R. Atkinson, IPv6 Authentication Header, March 1995. [IPV6-ICMP] A. Conta and S. Deering, ICMP for the Internet Protocol Version 6 (IPv6), October 1994. [IPV6-TRAN] R. Gilligan and E. Nordmark, Transition Mechanisms for IPv6 Hosts and Routers, March 1995. [IPV6-ADDR] R. Hinden, Editor, IP Version 6 Addressing Architecture, March 1995. [RFC-1191] J. Mogul and S. Deering, Path MTU Discovery, RFC-1191, November 1990. [RFC-791] J. Postel, Internet Protocol, RFC-791, September 1981. [RFC-1700] J. Reynolds and J. Postel, Assigned Numbers, RFC-1700, October 1994. [RFC-1548] W. Simpson, The Point-to-Point Protocol (PPP), RFC-1548, April 1994. draft-ietf-ipngwg-ipv6-spec-01.txt [Page 34]