IPv4 and IPv6 networks are not interoperable and the number of devices that use IPv4 number is still large. Some of these devices do not support IPv6 at all, so the migration process is necessary since IPv4 and IPv6 will likely coexist for some time.
Many transition mechanisms have been proposes.
1. IPv4/IPv6 Dual Stacks – each device on the network is configured with both an IPv4 and IPv6 address. When two devices want to communicate, they first agree on which IP version to use.
2. NAT64 – creates mapping between two address types. e.g. by mapping multiple IPv6 addresses to one IPv4 address.
3. Tunneling – Pv4 packets are tunneled over IPv6 infrastructure or vice versa.