IPv6 global unicast address

IPv6 global unicast addresses are similar to IPv4 public addresses. A company that needs IPv6 addresses asks for a registered IPv6 address block, which is assigned as a global routing prefix. These addresses are routable on the Internet and only that company will use them.

Global unicast addresses start with 2000::/3 (hex 2 or 3). They consists of two parts:

• subnet ID – 64 bits long. Contains the site prefix (obtained from a Regional Internet Registry) and the subnet ID (subnets within the site).
• interface ID – 64 bits long. It acts like the IPv4 host field and is typically composed of a part of the MAC address of the interface.

Here is a graphical representation of the two parts of an IPv6 global unicast address: