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The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)                 9  Internet Protocol Version 6 (IPv6) / IP Next Generation (IPng)                      9  IPv6 Addressing

IPv6 Address Size and Address Space 1 2 3 4 IPv6 Address Space Allocation

Increasing the size of IP addresses from 32 bits to 128 bits expands the address space to a gargantuan size, ensuring that we will never again run out of IP addresses, and allowing us flexibility in how they are assigned and used. Unfortunately, there are some drawbacks to this method, and one of them is that 128-bit numbers are very large, which makes them awkward and difficult to use.

Computers work in binary, and they have no problem dealing with long strings of ones and zeroes, but humans find them confusing. Even the 32-bit addresses of IPv4 are cumbersome for us to deal with, which is why we use dotted decimal notation for them unless we need to work in binary (as with subnetting). However, IPv6 addresses are so much larger than IPv4 addresses that even using dotted decimal notation becomes problematic. To use this notation, we would split the 128 bits into 16 octets and represent each with a decimal number from 0 to 255. However, we would end up not with 4 of these numbers, but 16. A typical IPv6 address in this notation would appear as follows:

128.91.45.157.220.40.0.0.0.0.252.87.212.200.31.255

The binary and dotted decimal representations of this address are shown near the top of Figure 95. In either case, the word “elegant” doesn't exactly spring to mind.

Figure 95: Binary, Decimal and Hexadecimal Representations of IPv6 Addresses

The top two rows show binary and dotted decimal representations of an IPv6 address; neither is commonly used (other than by computers themselves!) The top row of the lower table shows the full hexadecimal representation, while the next two rows illustrate zero suppression and compression. The last row shows mixed notation, where the final 32 bits of an IPv6 address are shown in dotted decimal notation. This is most commonly used for embedded IPv4 addresses.

IPv6 Address Size and Address Space 1 2 3 4 IPv6 Address Space Allocation

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