rfc2460.txt

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Network Working Group                                         S. Deering
Request for Comments: 2460                                         Cisco
Obsoletes: 1883                                                R. Hinden
Category: Standards Track                                          Nokia
                                                           December 1998


                  Internet Protocol, Version 6 (IPv6)
                             Specification

Status 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..........29



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   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........................................39

1.  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.






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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.




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   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 any





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                        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.






























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RFC 2460                   IPv6 Specification              December 1998


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       |
   +---------------+----------------+-----------------+-----------------