Network Working Group                                         S. DeeringRequest for Comments: 2460                                         CiscoObsoletes: 1883                                                R. HindenCategory: Standards Track                                          Nokia                                                           December 1998                  Internet Protocol, Version 6 (IPv6)                             SpecificationStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (1998).  All Rights Reserved.Abstract   This document specifies version 6 of the Internet Protocol (IPv6),   also sometimes referred to as IP Next Generation or IPng.Table of Contents   1. Introduction..................................................2   2. Terminology...................................................3   3. IPv6 Header Format............................................4   4. IPv6 Extension Headers........................................6       4.1 Extension Header Order...................................7       4.2 Options..................................................9       4.3 Hop-by-Hop Options Header...............................11       4.4 Routing Header..........................................12       4.5 Fragment Header.........................................18       4.6 Destination Options Header..............................23       4.7 No Next Header..........................................24   5. Packet Size Issues...........................................24   6. Flow Labels..................................................25   7. Traffic Classes..............................................25   8. Upper-Layer Protocol Issues..................................27       8.1 Upper-Layer Checksums...................................27       8.2 Maximum Packet Lifetime.................................28       8.3 Maximum Upper-Layer Payload Size........................28       8.4 Responding to Packets Carrying Routing Headers..........29Deering & Hinden            Standards Track                     [Page 1]RFC 2460                   IPv6 Specification              December 1998   Appendix A. Semantics and Usage of the Flow Label Field.........30   Appendix B. Formatting Guidelines for Options...................32   Security Considerations.........................................35   Acknowledgments.................................................35   Authors' Addresses..............................................35   References......................................................35   Changes Since RFC-1883..........................................36   Full Copyright Statement........................................391.  Introduction   IP version 6 (IPv6) is a new version of the Internet Protocol,   designed as the 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 an "anycast address" is defined, used to send         a packet to any one of a group of 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.Deering & Hinden            Standards Track                     [Page 2]RFC 2460                   IPv6 Specification              December 1998      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 traffic classes, and   the effects of IPv6 on upper-layer protocols.  The format and   semantics of IPv6 addresses are specified separately in [ADDRARCH].   The IPv6 version of ICMP, which all IPv6 implementations are required   to include, is specified in [ICMPv6].2.  Terminology   node        - a device that implements IPv6.   router      - a node that forwards IPv6 packets not explicitly                 addressed to itself.  [See Note below].   host        - any node that is not a router.  [See Note below].   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 over a link.Deering & Hinden            Standards Track                     [Page 3]RFC 2460                   IPv6 Specification              December 1998   path MTU    - the minimum link MTU of all the links in a path between                 a source node and a destination node.   Note: it is possible, though unusual, for a device with multiple   interfaces to be configured to forward non-self-destined packets   arriving from some set (fewer than all) of its interfaces, and to   discard non-self-destined packets arriving from its other interfaces.   Such a device must obey the protocol requirements for routers when   receiving packets from, and interacting with neighbors over, the   former (forwarding) interfaces.  It must obey the protocol   requirements for hosts when receiving packets from, and interacting   with neighbors over, the latter (non-forwarding) interfaces.3.  IPv6 Header Format   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |Version| Traffic Class |           Flow Label                  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |         Payload Length        |  Next Header  |   Hop Limit   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                                                               |   +                                                               +   |                                                               |   +                         Source Address                        +   |                                                               |   +                                                               +   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                                                               |   +                                                               +   |                                                               |   +                      Destination Address                      +   |                                                               |   +                                                               +   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Version              4-bit Internet Protocol version number = 6.   Traffic Class        8-bit traffic class field.  See section 7.   Flow Label           20-bit flow label.  See section 6.   Payload Length       16-bit unsigned integer.  Length of the IPv6                        payload, i.e., the rest of the packet following                        this IPv6 header, in octets.  (Note that anyDeering & Hinden            Standards Track                     [Page 4]RFC 2460                   IPv6 Specification              December 1998                        extension headers [section 4] present are                        considered part of the payload, i.e., included                        in the length count.)   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                        et seq.].   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 [ADDRARCH].   Destination Address  128-bit address of the intended recipient of the                        packet (possibly not the ultimate recipient, if                        a Routing header is present).  See [ADDRARCH]                        and section 4.4.Deering & Hinden            Standards Track                     [Page 5]RFC 2460                   IPv6 Specification              December 19984.  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 extension header determine whether or   not to proceed to the next header.  Therefore, extension headers must   be processed strictly in the order they appear in the packet; a