6 in 4

6in4 is a tunneling system that works as a transition system to IPv6 from IPv4.

Functioning 6in4 is a protocol transition mechanism from ipv4 to ipv6, which works by using a tunnel that encapsulates ipv6 packets into ipv4 as defined in RFC 4213. All ipv6 packets are sent over the internet ipv4 (within ipv4 packets) which has as the header of the protocol number 41, number created exclusively for the encapsulation of ipv6, after this header follows the rest of the packet in ipv6. This means that encapsulation overhead is simply the size of the 20-byte IPv4 header. With a 1500-byte Maximum Transmission Unit (MTU) interface, however, it can send 1480-byte IPv6 packets without fragmentation. 6in4 is also sometimes called protocol-41. There are automatic configuration methods but it is usually done manually. Using NAT

When the end of a 6in4 tunnel is behind a NAT, it is still possible in some cases to make use of the DMZ function of a NAT router. The NAT router will send all incoming protocol type 41 calls to the host configured through the tunnel. Some NAT devices even allow transparent 6in4 operations.

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