Understanding IPv6

The need for migrating enterprise networks from IPv4 to IPv6 is driven by a number of different technological, business, and social factors. The most important of these are:

• The exponential growth of the Internet is rapidly exhausting the existing IPv4 public address space. A temporary solution to this problem has been found in Network Address Translation (NAT), a technology that maps multiple private (intranet) addresses to a (usually) single, public (Internet) address. Unfortunately, using NAT-enabled routers can introduce additional problems, such as breaking end-to-end connectivity and security for some network applications. In addition, the rapid proliferation of mobile IP devices is accelerating the depletion of the IPv4 public address space.
• The growing use of real-time communications (RTC) on the Internet, such as Voice over IP (VoIP) telephony, instant messaging (IM), and audio/video conferencing, exposes the limited support for Quality of Service (QoS) currently provided in IPv4. These new RTC technologies need improved QoS on IP networks to ensure reliable end-to-end communications. The design of IPv4 limits possible improvements.
• The growing threats faced by hosts on IPv4 networks connected to the Internet can be mitigated considerably by deploying Internet Protocol security (IPsec), both on private intranets and on tunneled connections across the public Internet. However, IPsec was designed as an afterthought to IPv4 and is complex and difficult to implement in many scenarios.

IPv6, developed by the Internet Engineering Task Force (IETF) to solve these problems, includes the following improvements and additions:

• IPv6 increases the theoretical address space of the Internet from 4.3 x 109 addresses (based on 32-bit IPv4 addresses) to 3.4 x 1038 possible addresses (based on 128-bit IPv6 addresses), which most experts agree should be more than sufficient for the foreseeable future.
• The IPv6 address space is designed to be hierarchical rather than flat in structure, which means that routing tables for IPv6 routers can be smaller and more efficient than for IPv4 routers.
• IPv6 has enhanced support for QoS that includes a Traffic Class field in the header to specify how traffic should be handled and a new Flow Label field in the header that enables routers to identify packets that belong to a traffic flow and handle them appropriately.
• IPv6 now requires IPsec support for standards-based, end-to-end security across the Internet. The new QoS enhancements work even when IPv6 traffic is encrypted using IPsec.

Understanding how IPv6 works is essential if you plan to benefit from IPv6 by deploying it in your enterprise. The following sections provide an overview of key IPv6 concepts, features, and terminology.

Note For more detailed information on IP concepts, features, and terminology, see the white paper titled "Introduction to IP Version 6" at http://www.microsoft.com/downloads/details.aspx?FamilyID=CBC0B8A3-B6A4-4952-BB E6-D976624C257C&displaylang=en.