IPv6 (IPv6 address notation)

IPv6 (IPv6 address notation)

 An IPv6 address also has 128 bits (16 bytes). Since the binary notation would be too long, it is now written in hexadecimal.

 That's still 32 digits. As will be explained later, IPv6 addresses have been devised so that they can be expressed as short as possible. Still, IPv6 addresses are getting longer.

 This is beyond the limits of human memory at a glance. This long address is difficult to manage and difficult to enter accurately.

 That said, it is very difficult to handle IPv6 addresses in 32-digit hexadecimal numbers as they are, so the abbreviated notation is at least a relief.

IPv6 notation

  • Write in hexadecimal, separating each 16 bits.
  • The delimiter is ":" (colon)
  • The first part of the IPv6 address is called the prefix, and the length is written after "/".

* "/128" (whole address) is often omitted as it is not necessary to specify it explicitly.

Classification of IPv6

An IPv6 address is divided into 8 parts by the first 3 bits (/3).

 Since 3 bits are not compatible with hexadecimal numbers and are difficult to understand, it may be easier to understand by dividing them into 16 hexadecimal digits of 4 bits.

Binary number Hexadecimal Usage
000 0 special address
001 2 Route-aggregated address
010 4 unassigned
011 6 unassigned
100 8 unassigned
101 a unassigned
110 c unassigned
111 e link-local, site-local, multicast

Shorthand notation for IPv6

The following abbreviations are available for IPv6:

  • Consecutive "0" at the beginning of each block can be omitted
  • "0000" is expressed as "0".
  • Consecutive blocks of "0" can be replaced with "::" only once

The IPv6 address notation method is as follows.


              ↓ Continuous "0" at the beginning of each block can be omitted.
                  "0000" is expressed as "0".

 2001:1000:120:0:0:0:12 34:0

              ↓ Consecutive "0" blocks can be replaced with "::" only once


 Only one location can be omitted.

 2001:1000:120::1234:: × ← cannot be written like this