IPv6 has been introduced as a replacement of IPv4, the traditional 32-bit address space used in the Internet, to solve the imminent exhaustion of available IPv4 address space. However, since IPv4 has been used by every host or device connected to the Internet, it is practically impossible to switch every one of them to IPv6 overnight. Numerous IPv4 to IPv6 transition mechanisms (e.g., dual IP stack, tunneling, proxying) have been proposed to facilitate the adoption of IPv6, and many applications are being rewritten, as we speak, to add support for IPv6.