The IPv6 over IPv4 tunnel technology enables communication between isolated IPv6 networks over existing IPv4 networks. IPv6 packets can be transparently transmitted over IPv4 networks after being encapsulated into IPv4 packets.
During the early transition from IPv4 to IPv6 networks, IPv4 networks have been widely deployed, whereas IPv6 networks are isolated islands scattered around the world. With the tunneling technology, IPv6 over IPv4 tunnels can be created on the IPv4 networks to connect the isolated IPv6 sites. To establish IPv6 over IPv4 tunnels, the IPv4/IPv6 dual stack must be enabled on the routers at the borders of the IPv4 and IPv6 networks.