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IPv6

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The current version of the Internet Protocol (IP) is becoming obsolete because of its limited address space, lack of needed functionality, and inadequate security features. The next generation of IP, called IPv6, has now been standardized and will carry TCP/IP networks and applications well into the next century.

Until recently, the Internet and most other TCP/IP networks have primarily provided support for rather simple distributed applications, such as file transfer, electronic mail, and remote access using TELNET; but today, the Internet is increasingly becoming a multimedia, application-rich environment, led by the huge popularity of the World Wide Web. At the same time, corporate networks have branched out from simple e-mail and file transfer applications to complex client/server environments and, most recently, intranets that mimic the applications available on the Internet.

All of these developments have outstripped the capability of IP-based networks to supply needed functions and services. An internetworked environment needs to support real-time traffic, flexible congestion control schemes, and security features. None of these requirements is easily met with the existing IP.

However, the driving force behind the development of a new IP is the stark fact that the world is running out of IP addresses for networked devices. The fixed 32-bit address length of IP is inadequate for the explosive growth of networks.

A number of new security features have been designed for use with IPv6 but can also be used with the existing IPv4; these also have been documented in requests for comments (RFCs). The driving motivation for the adoption of a new version of IP was the limitation imposed by the 32-bit address field in IPv4. But other considerations as well drove the design of IPv6. We look at these areas in this section.

Addressing

With a 32-bit address field, it is in principle possible to assign 232 different addresses, which is over 4 billion possible addresses. One might think that this number of addresses was more than adequate to meet addressing needs on the Internet. However, in the late 1980s it was perceived that there would be a problem, and this problem began to manifest itself in the early 1990s. Some of the reasons for the inadequacy of 32-bit addresses include:

  • The two-level structure of the IP address (network number, host number) is convenient but wasteful of address space. Once a network number is assigned to a network, all of the host-number addresses for that network number are assigned to that network. The address space for that network may be sparsely used, but as far as the effective IP address space is concerned, if a network number is used, all addresses within the network are.
  • It is general practice to assign a unique network number to an IP network whether or not it is actually connected to the Internet. It is possible on a private internet to reuse numbers that are in use either in the public Internet or in other private internetworks, but this is a risky and cumbersome policy.
  • Networks are proliferating rapidly. Most organizations boast multiple LANs, not just a single LAN system. Wireless networks are gradually assuming a major role. The Internet itself has been growing explosively for years.
  • Growth of TCP/IP usage in new areas will result in a rapid growth in the demand for unique IP addresses. Examples are using TCP/IP to interconnect electronic point-of-sale terminals and for cable television receivers.
  • Typically, a single IP address is assigned to each host. A more flexible arrangement is to allow multiple IP addresses per host. This, of course, increases the demand for IP addresses.

    To meet these addressing needs, IPv6 uses 128-bit addresses instead of the 32-bit addresses of IPv4. This is an increase of address space by a factor of 296! Even if addresses are very inefficiently allocated, this address space seems secure.

    Performance

    Both LANs and wide area networks (WANs) have progressed to ever-greater data rates, pushing into hundreds of megabits per second, with plans for gigabit LANs and WANs. In addition, as more services, especially graphics-based services, become available over the Internet, we can expect that the ratio of external traffic (traffic that leaves the local network) to internal traffic will rise. With these immense speeds and the increased load, it is critical that routers perform their functions as rapidly as possible. The router should be able to process and forward IP datagrams fast enough to fully utilize its high-speed links and to keep up with the traffic flow. A major factor is the hardware platform itself, but the design of the IP also plays a critical role.

    Three aspects of IPv6 design contribute to meeting performance requirements:

    • The number of fields in the IPv6 packet header are reduced from IPv4. A number of IPv6 options are placed in separate optional headers located between the IPv6 header and the transport-layer header. Most of these optional headers are not examined or processed by any router on the packet's path. This simplifies and speeds up router processing of IPv6 packets compared to IPv4 datagrams. It also makes it easier to add additional options.
    • The IPv6 packet header is fixed-length whereas the IPv4 header is variable-length. Again, the IPv6 design simplifies processing.
    • Packet fragmentation is not permitted by IPv6 routers, although it is in IPv4. In IPv6, fragmentation may only be performed by the source.

    Summary

    The Internet Protocol (IP) has been the foundation of the Internet and virtually all multivendor private internetworks. This protocol is reaching the end of its useful life and a new protocol, known as IPv6 (IP version 6), has been defined to ultimately replace IP.

    The driving motivation for the adoption of a new version of IP was the limitation imposed by the 32-bit address field in IPv4. In addition, IP is a very old protocol, and new requirements in the areas of security, routing flexibility, and traffic support have developed. To meet these needs, IPv6 has been defined, and includes functional and formatting enhancements over IPv4. In addition, a set of security specifications have been issued that can be used with both IPv4 and IPv6. With most of the technical details of these enhancements frozen, vendors may begin to move this capability into their product lines. As IPv6 is gradually deployed, the Internet and corporate networks will be rejuvenated, able to support the applications of the 21st century.


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