Introduction

IPv6 Background

The Internet Protocol was introduced in the ARPANET in the mid-1970s. The version of IP in common use today is IP version 4 (IPv4), described in Request for Comments (RFC) 791 (September 1981). Although several protocol suites (including Open System Interconnection) have been proposed over the years to replace IPv4, none have succeeded because of IPv4's large, and continually growing, installed base. Nevertheless, IPv4 was never intended for the Internet that we have today, either in terms of the number of hosts, types of applications, or security concerns.

In the early 1990s, the Internet Engineering Task Force (IETF) recognized that the only way to cope with these changes was to design a new version of IP to become the successor to IPv4. The IETF formed the IP next generation (IPng) Working Group to define this transitional protocol to ensure long-term compatibility between the current and new IP versions, and support for current and emerging IP-based applications.

Work started on IPng in 1991 and several IPng proposeals were subsequently drafted. The result of this effort was IP version 6 (IPv6), described in RFCs 1883-1886; these four RFCs were officially entered into the Internet Standards Track in December 1995.

The following table shows you the history of the IPv6:

Why IPv6?

The current version of IP (IPv4) has not been substantially changed since RFC 791 was published in 1981. IPv4 has proven to be robust, easily implemented and interoperable, and has stood the test of scaling an internetwork to a global utility the size of today's Internet. This is a tribute to its initial design.

However, the initial design did not anticipate the following:

• The recent exponential growth of the Internet and the impending exhaustion of the IPv4 address space.
• The growth of the Internet and the ability of Internet backbone routers to maintain large routing tables.
• The need for simpler configuration.
• The requirement for security at the IP level.
• The need for better support for real-time delivery of data-also called quality of service (QoS).

Feature Overview

• Large Address Space
  The IP address size is increased from 32 bits to 128 bits in IPv6, supporting a much greater number of addressable nodes. Although 128 bits can express over 3.4x1038 possible combinations, the large address space of IPv6 has been designed to allow for multiple levels of subnetting and address allocation from the Internet backbone to the individual subnets within an organization. Even though only a small number of the possible addresses are currently allocated for use by hosts, there are plenty of addresses available for future use. With a much larger number of available addresses, address-conservation techniques, such as the deployment of NATs, are no longer necessary.
• Efficient and hierarchical addressing and routing infrastructure
  IPv6 supports large hierarchical addresses which will allow the Internet to continue to grow and provide new routing capabilities not built into IPv4. It has anycast addresses which can be used for policy route selection and has scoped multicast addresses which provide improved scalability over IPv4 multicast. It also has local use address mechanisms which provide the ability for "plug and play" installation.
• New Header Format
  Some IPv4 header fields have been dropped or made optional to reduce the necessary amount of packet processing and to limit the bandwidth cost of the IPv6 header.
  IPv4 headers and IPv6 headers are not interoperable. A host or router must use an implementation of both IPv4 and IPv6 in order to recognize and process both header formats. The new IPv6 header is only twice as large as the IPv4 header, even though IPv6 addresses are four times as large as IPv4 addresses.
• Improved Support for Extensions and Options
  IPv6 header options are encoded in such a way to allow for more efficient forwarding, less stringent limits on the length of options, and greater flexibility for introducing n ew options in the future. Some fields of an IPv4 header have been made optional in IPv6.
• Better support for QoS
  A new quality-of-service (QOS) capability has been added to enable the labeling of packets belonging to particular traffic "flows" for which the sender requests special handling, such as real-time service.
• Built-in security
  Extensions to support security options, such as authentication, data integrity, and data confidentiality, are built-in to IPv6.
• Stateless and stateful address configuration
  To simplify host configuration, IPv6 supports both stateful address configuration, such as address configuration in the presence of a DHCP server, and stateless address configuration (address configuration in the absence of a DHCP server). With stateless address configuration, hosts on a link automatically configure themselves with IPv6 addresses for the link (called link-local addresses) and with addresses derived from prefixes advertised by local routers. Even in the absence of a router, hosts on the same link can automatically configure themselves with link-local addresses and communicate without manual configuration.
• New protocol for neighboring node interaction
  The Neighbor Discovery protocol for IPv6 is a series of Internet Control Message Protocol for IPv6 (ICMPv6) messages that manage the interaction of neighboring nodes (nodes on the same link). Neighbor Discovery replaces the broadcast-based Address Resolution Protocol (ARP), ICMPv4 Router Discovery, and ICMPv4 Redirect messages with efficient multicast and unicast Neighbor Discovery messages.