6to4 is the most common way to get your computer connected to the IPv6 Internet until your ISP provides you native IPv6 connectivity. It is a special tunnel that carries IPv6 packets between your computer and a 6to4 relay over existing IPv4 Internet. The relay router forwards your IPv6 packets to the IPv6 Internet and the replies back to your computer.
6to4 relay routers listen on address 192.88.99.1, a multicast IP address. If your public IP is 192.0.0.9, using 6to4, you can assign IPv6 address from 2002:c000:0009::/48 pool. The corresponding IPv6 address for 6to4 depends upon your public IPv4 address.
Data to the IPv6 Internet
Now when your computer sends data to IPv6 Internet, it is encapsulated within IPv4 packet and sent to the nearest 6to4 relay router. The relay router receives the packets, strips the IPv4 header and recovers the IPv6 packet. It then sends the IPv6 data to the destination.
Data from the IPv6 Internet
When an IPv6 host sends some data back to your computer, it send to the nearest 6to4 relay router. The relay extracts IPv4 address of your computer from the destination IPv6 address. It then sends the packet back to your computer using the IPv4 Internet. Once it reaches your computer, the IPv6 packet is recovered.
Ready for IPv6?
Follow the configuration example provided by 6to4.version6.net. It gives examples for
- Linux
- FreeBSD
- Windows
- MacOS X
One requirement for 6to4 is that your computer should have a valid public IPv4 address. If you are behind NAT, 6to4 won’t work, instead try Teredo.