SixXS

SixXS was an IPv6 tunnel broker service and prefix registry operated by a volunteer group, including Jeroen Massar, to assist early adopters in deploying IPv6. The project provided a practical path to reach the IPv6 Internet before widespread native deployment through a tunnel-based approach.

The core idea of SixXS was to deliver IPv6 connectivity over existing IPv4 networks using 6in4 tunnels. Users would register on the SixXS portal, request an IPv6 prefix (commonly a /48) for their site, and configure a tunnel endpoint on a router or gateway. Once the tunnel was established, the user could use IPv6 addresses within their assigned prefix and reach or be reached via the IPv6 Internet. The service included a web-based management interface and a catalog of delegated prefixes, with the community maintaining documentation and support.

SixXS played a significant role in the IPv6 ecosystem during the 2000s and early 2010s. It was widely used by academic institutions, ISPs, network operators, and enthusiasts to experiment with and learn about IPv6 deployment, routing, and address planning. The service helped demonstrate the feasibility of IPv6 adoption and contributed to best practices for prefix allocation and tunnel operation.

The SixXS project winded down as native IPv6 adoption and carrier support expanded. The service announced its retirement and gradually halted new deployments, with the site and materials later archived. Its legacy lies in the early practical experience it provided with IPv6 deployment, prefix management, and the tunnel-broker model that informed later approaches to IPv6 rollout.