Windows Server® 2008 TCP/IP Protocols and Services

IPv6 Addressing

The IPv6 address is 128 bits long, creating an address space of almost inconceivable size. With 128 bits you can express more than 3.4 × 10³⁸ combinations. Unlike IPv4 unicast addresses, the structure of an IPv6 unicast address is very simple: The first 64 bits are for a subnet prefix and the last 64 bits are for an interface identifier. Although you can perform variable-length subnetting within the 64 bits of the subnet prefix, the host ID equivalent for IPv6 is always the same size. The 64 bits of subnet prefix provide enough addressing space to enumerate networks from the Internet backbone to the individual subnets within an organization’s site. The 64 bits of interface identifier can be used to map 48-bit media access control ...