6in4 tunnels are used to connect two hosts, routers, or to interconnect a host and router. This means that 6in4 tunnels can connect two IPv6 networks via an IPv4 network. The diagram shows a static 6in4 tunnel between the local router and a 6in4 gateway belonging to a tunnel broker.
These are dedicated services operated by a known provider. The end-points are fixed and the tunnel broker assigns a static prefix. The advantages of a 6in4 solution are that the gateways are fixed and the operator is known. The fixed prefix from the tunnel broker also determines the number of possible subnets that can be used. A 64-bit prefix (e.g. 2001:db8::/64) allows one subnet to be used. If a 48-bit prefix is used, 16 bits of the 64-bit prefix are available for use. This allows the implementation of up to 65,536 subnets.
The disadvantage of the 6in4 technology is the higher administrative effort. You must be registered with and login to the tunnel broker. In addition, the tunnel endpoints must be statically configured. Where a dynamic IPv4 address is used, the relevant data must be updated regularly. This can be automated by running a script on a router.
6in4 is a relatively secure and stable technology for providing IPv6 Internet access. This technology is thus suitable for operating web servers that are to be accessed over IPv6. The only drawback is the increased effort in administration. This technology is suitable for professional use.
