6in4 ( tunneling IPv6 in IPv4 ) is an IPv6 transition mechanism for the transmission of IPv6 packets between IPv6 nodes that are connected via an IPv4 network.
In 6in4 traffic in IPv4 packets is packed, the protocol carries the decimal number 41 in the IP header. Directly to the IPv4 - IPv6 header followed by the transported data packet. The IPv4 header increases the data packet by only 20 bytes. With a maximum transmission unit (MTU) of 1500 bytes, such as for standard Ethernet connections, so IPv6 frames can be transported at 1480 bytes, without fragmentation. 6in4 tunnels are like all tunnel -type proto -41 static, ie, the endpoints are statically configured.