The way that a computer or other digital device sees an IPv6 address and the way humans see an IPv6 address are different. A digital device looks at an IPv6 address as a 128-bit number. But humans have devised a way to convert this 128-bit number into something easier to look at and work with. For humans, an IPv6 address is a 128-bit number that is written as a string of hexadecimal digits. Hexadecimal is a natural fit for IPv6 addresses because any 4 bits can be represented as a single hexadecimal digit. Two hexadecimal digits represent a single byte, or octet (8 bits). The preferred form of an IPv6 address is x:x:x:x:x:x:x:x, where each x is a 16-bit section that can be represented using up to four hexadecimal digits. Each section is separated by a colon (:), as opposed to IPv4 addressing, which uses a period (.) to separate each section. The result is eight 16-bit sections (sometimes called hextets) for a total of 128 bits in the address. Figure 1 shows this format.
Figure 1 Format of an IPv6 Address
Showing all the hexadecimal digits in an IPv6 address is the longest representation of the preferred form. The next section shows you two rules for reducing the notation of an IPv6 address in the preferred format for easier use and readability.
