An IPv6 over IPv4 tunnel connects isolated IPv6 sites over the IPv4 network.
During the earlier transition phase from IPv4 to IPv6, IPv4 networks have been widely deployed, and IPv6 sites are scattered across IPv4 networks. It is not economical to connect these isolated IPv6 sites with private lines. The common solution is the tunneling technology. With this technology, IPv6 over IPv4 tunnels can be created on IPv4 networks to enable communication between isolated IPv6 sites through IPv4 public networks.
Fully uses existing networks. Devices on an IPv4 backbone network do not need to upgrade to IPv6 networks.