Comment by 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