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.
A manual IPv6 over IPv4 tunnel is a P2P tunnel. The source address and destination address of a manual IPv6 over IPv4 tunnel are both manually assigned and must be unique on the same device. A manual IPv6 over IPv4 tunnel acts as a permanent link that connects two IPv6 networks across an IPv4 network. Border routers can communicate with each other securely and regularly through manual IPv6 over IPv4 tunnels.
A 6RD tunnel is a point-to-multipoint (P2MP) tunnel that connects IPv6 sites through a carrier's IPv4 network. 6RD tunnels have been widely deployed on carriers' networks.