4in6 | 6in4

4in6 describes the transport of IPv4 data packages within an IPv6 environment. 6in4 describes the reverse variant, in which an IPv6 data package traverses an IPv4 environment. 4in6 or also 6in4 requires a dual stack router at the end points - the start and end point of the data transfer. Dual stack means that the router supports parallel operation of both protocols. This means that at the starting point, the dual stack router, the IPv4 data package can be packed with an IPv6 envelope. Then, the data package traverses the extended address space through so-called “tunnels”. Before the package subsequently re-enters an IPv4 environment, the IPv6 envelope is removed again in a dual stack router at the end point. An IPv6 data package also goes through the same process, only in reverse, in an IPv4 environment.