RFC 1883                   IPv6 Specification              December 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 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.

      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.  The format and semantics
   of IPv6 addresses are specified separately in [RFC-1884].  The IPv6
   version of ICMP, which all IPv6 implementations are required to
   include, is specified in [RFC-1885].



 
RFC 1883                   IPv6 Specification              December 1995


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.