6in4 is just a basic "put the v6 packet directly into the payload of a v4 packet" tunnelling approach. It's a sensible way of tunnelling one protocol over anoth

6in4 is just a basic "put the v6 packet directly into the payload of a v4 packet" tunnelling approach. It's a sensible way of tunnelling one protocol over another (and it's the same thing as 4in6, just the other way around). HE's tunnels are 6in4, and 6to4 and 6rd are automatically-configured 6in4 tunnels.