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Internet Protocol Version 6

Overview

The rapid expansion of the Internet caused the IETF to begin exploring alternatives to IPv4 addressing. Since IPv4 uses 32-bit addresses, the addition of thousands of LANs and WANs has rapidly depleted the available addresses.

In deriving IPv6, the IETF addressed not only the need for more addresses but also emerging technologies. While IPv6 protocol retains many features of the IPv4 protocol, there are some significant differences. Among these differences are :

Larger addresses
IPv6 uses a 128bit address instead of 32 bit. Provisions are made for backwards compatibility with IPv4 addressing.

New Header Format
IPv6 introduces a completely new and IPv4 incompatible header format. This requires that a router which connects to both an IPv4 network and an IPv6 network must be able to translate back and forth. Each network will, therefore, use either IPv6 or IPv4, but not both (it would be inefficient to do so).

Options
IPv6 incorporates new options in the IP datagram.

Resource allocation support
IPv6 provides support for such emerging technologies as real-time video.

Protocol extension
Unlike IPv4, IPv6 has a provision for future extensions to the protocol.


Note : For a more thorough treatment of IPv6, see RFC #1550.

Basic Address Types

IPv6 uses three basic address types.
Unicast
Identical to IPv4 in concept. A unicast address specifies a specific network interface.

Multicast
A multicast address specifies a group of network interfaces. Any communication snet to a multicast address will be delivered to all interfaces in the group. Broadcasts or packets addresses to interfaces sharing the same physical network and the same network number are a special case of multicast addressing in IPv6.

Anycast or Cluster
An anycast or cluster address also identifies a group of interfaces. The difference between anycast and multicast is that a packet addresses to an anycast address will only be delivered to the nearest member of the group.