Abstract: A method for supporting a 6to4 tunneling protocol across a network address translation mechanism. The method comprises the steps of receiving an outbound IPv6 packet encapsulated into an IPv4 packet, translating the private IPv4 source address in the IPv4 header of the outbound packet into a public IPv4 source address, transmitting the translated packet over the IPv4 network; and is characterized in that it further comprises the step of storing an association of the private IPv4 address and the Interface ID value of the 6to4 source address for opposite address translation of inbound packets.A corresponding device is also claimed.