Birkenwald

IPv6 is the successor of the currently common communication protocol used in the Internet, IPv4. It is currently mainly used by power users, but should gain traction among endusers pretty soon.

Most Bittorrent clients, including µTorrent, Azureus and Transmission support exchanging data with both IPv4 and IPv6 peers at the same time today. Unfortunately, to exchange data with IPv6 peers they have to find them first, which has been a problem for quite a while now.

In general BitTorrent clients have three ways to aquire lists of possible endpoints.

Clients can connect to one or more central database servers called Trackers. These systems keep track of all clients currently sharing a specific content (identified by a unique hash) and share this information with the connecting clients, allowing them to connect to other clients to pull data from.

Historically IPv6 has been supported in trackers for a long time, since the original Tracker protocol exchanged IP address information as strings and was thus agnostic of the used protocol. To reduce the overhead a compressed format for exchanging peer data has been specificed in BEP 23. IPv6-extensions to this protocol are specified in BEP 7.

While the software side was easy IPv6-support never got much traction in public trackers. Aside from projects like the SixXS IPv6 Tracker the only major tracker ever gaining IPv6 support was The Piratebay. Unfortunately they suffered from outages due to overload and network problems while being in major legal disputes at the same time. Today, TPB does not run trackers anymore.