The IPv4 over IPv6 tunneling technology enables communication between isolated IPv4 networks over existing IPv6 networks. IPv4 packets can be transparently transmitted over IPv6 networks after being encapsulated into IPv6 packets.
An IPv4 over IPv6 tunnel functions as a permanent link that connects two IPv4 domains through the IPv6 backbone network. It is a fixed channel for regular and secure communication between border devices. An IPv4 over IPv6 tunnel is a point-to-point tunnel. The source and destination IPv6 addresses of the tunnel interfaces are manually specified, and must be unique on the same device.