IP version 6 (IPv6) serves as the protocol that will eventually replace IP version 4 (IPv4). The most obvious reason for migrating TCP/IP networks from IPv4 to IPv6 is growth. IPv4 uses a 32-bit address, which allows for a little over four billion addresses. It may seem like a pretty large number of addresses but the immense growth of networks and the Internet has almost exhausted our stock of available IPv4 addresses for new deployments. IPv6 uses 128-bit addresses and increases the number of available addresses to 2^128, a number so large that we don’t have a word for it.