18.1.2 Address notation

An IPv6 address is 128 bits. The notation is as follows:

• In hexadecimal notation, an IPv6 address is written as eight 16-bit groups, each separated by a colon.

  Example: 3ffe:0501:0811:ff02:0000:08ff:fe8b:3090

• You can omit leading 0s in each of the individual blocks in hexadecimal notation.

  Example: 3ffe:501:811:ff02:0:8ff:fe8b:3090

• You can replace consecutive blocks of 0s with two colons (::). However, only one such replacement is allowed.

  Example: You can change the full IPv6 address on the left to the format on the right:

  fe80:0000:0000:0000:0000:0000:0000:3090 -> fe80::3090

  Example: Only one set of two colons is permitted.

  fe80:0000:0000:0000:0000:0000:0000:3090 -> fe80::0::3090 (incorrect)

• You can use the following formats to specify an address and the prefix length:

  • IPv6 address/prefix length

  • IPv6 address prefixlen prefix-length

  The prefix length indicates in decimal the number of bits from the leftmost end of an address that are used for the prefix.