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IPv6 Essentials, 3rd Edition by Silvia Hagen

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Chapter 2. IPv6 Addressing

An IPv4 address has 32 bits and looks familiar. An IPv6 address has 128 bits and looks wild at first glance. Extending the address space was one of the driving reasons to develop IPv6, along with optimization of routing tables, especially on the Internet. This chapter will help you become familiar with the extended address space and will also explain how IPv6 addressing works and why it has been designed to be the way it is. There is a lot more to understand than just the 128-bit address. The address architecture has been extended and the large address space offers opportunity for new address designs. So make sure that you dive into this before you work on an IPv6 address plan. The IPv6 addressing architecture is defined in RFC 4291.

The IPv6 Address Space

The 32 bits of the IPv4 address space provide a theoretical maximum of 232 addresses, equal to approximately 4.29 billion addresses. The current world population is over 7 billion people. So even if it were possible to use 100 percent of the IPv4 address space, we would not be able to provide an IP address for everyone on the planet. As a matter of fact, only a small fraction of this address space can be used. In the early days of IP, nobody foresaw the existence of the Internet as we know it today. Therefore, large address blocks were allocated without considerations for global routing and address conservation issues. These address ranges cannot be easily reclaimed, so consequently there are many unused ...

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