The double colon (::) can only be used once within an address, otherwise there would be more than one possible resulting address. The second rule reduces the notation of IPv6 addresses using a double colon (::) that can replace any single, contiguous string of one or more hextet containing all 0s. The table below shows the examples of omitting leading 0s from the IPv6 address.

This rule only omits leading 0s, not trailing 0s, otherwise, the address would be ambiguous. Following are the examples to omit any leading 0s (zeros) in any 16-bit section or hextet: Omitting leading 0 is the first rule to reduce the notation of IPv6 address. However, there are two rules we can apply to reduce the number of digits needed to represent an IPv6 address. The ideal method of representing IPv6 address is groups of eight hextet (32 hexadecimal digits). The basic relationship table of binary, decimal, and hexadecimal is following. If we convert one hextet into binary it should be 16 bits, for example, we have a hextet “0000” it is equal to 0000000000000000 (16 time 0s) and hextet “ FFFF” is equal to 1111111111111111 (16 tim1 1s). So each “x” is a single hextet, 16 bits or four hexadecimal digits. The preferred format for writing an IPv6 address is x: x: x: x: x: x: x: x, where each “x” is the group of four hexadecimal digits and each group contains 16 bits. The address can be written both lowercase or in uppercase. The length of IPv6 addresses are 128 bits and represented as eight groups of four hexadecimal digits each, each group representing 16 bits.

Ipv6 address compression rules