[colinsane]

is this an issue only for magnet/DHT transfers? or does it apply to torrents that have an associated tracker too? i would have expected in the latter case that two NAT’d clients could connect to the tracker, and then the tracker could help them hole-punch a direct peer-to-peer connection.

[the8472]

Try to extrapolate. If nobody has an open port to which a connection can be established, how will the network work?

Trackers don't enable hole-punching, existing peer connections do[0]. And hole-punching is hardly a reliable measure to base your network on, if NAT or connection-tracking is implemented in an address-/port-dependent manner[1] then hole-punching becomes more complicated or fails, especially for TCP.

[0] http://bittorrent.org/beps/bep_0055.html [1] https://www.rfc-editor.org/rfc/rfc4787.html#page-6

[reisse]

It does apply to all torrents. As far as I know, by default torrent trackers provide no facilities for hole punching.

However, if you have a tracker in a sense of "community of people dedicated to file sharing", there will be guides on how to do a proper setup even behind carrier-grade NAT. For example, one of the trackers I know suggested using Teredo (IPv6-to-IPv4) tunneling to do the hole punching.

[anacrolix]

Trackers aren't used for this, but a mutually accessible peer can be used for hole punching.