As we already know, IPv6 uses 128-bit addresses. Because the address format is different from the IPv4 address format that we are all accustomed to, it is often confusing at first glance. However, once understood, the logic and structure is all very simple. The 128-bit IPv6 addresses use Hexadecimal values. The Hexadecimal numbering system uses the numbers 0 through 9 and the letters A through F.  While in IPv4 the subnet mask can be represented in either CIDR notation, e.g. /16 or /32, or in dotted-decimal notation, e.g. 255.255.0.0 or 255.255.255.255, IPv6 subnet masks are represented only in CIDR notation due to the length of the IPv6 address. Global 128-bit IPv6 addresses are divided into three sections: