How does a torrent bypass NAT?

Question

Computer networks

The essence of the torrent, as far as I understand, is that the files are downloaded not from the server (well, or not only from it), but from the computers of other people who have already downloaded these same files, and this, in turn, as I understand it, means that the torrent is like -forward ports through NAT, that is, it opens ports on a gray ip.
And now the question is: how does he do it and is it possible to open a port for a server in this way, for example?

Answer 1

The torrent client can use UPnP to communicate with the router and forward ephemeral ports.

Answer 2

Whitelisted addresses, VPN/Proxy or working UPnP from other peers. Everything is clear with the first two, the third technology allows you to transparently forward the listening port for the application and is enabled by default on most home routers.

Answer 3

He doesn't drop anything. A hundred thousand times it has already been explained - any passage through NAT is done only by connecting to a previously known server (or a set of servers). Initiating a connection from inside NAT, fixing on an external server and connecting on the specified port or the default port. And that's it. And this is how all programs that "bypass" NAT work, because there is simply no other way.

Answer 4

If all distributors have gray IPs, you will not download anything. You only download from distributors with white IPs

Answer 5

UPnP

Answer 6

Your torrent client connects to the torrent tracker.
Other torrent clients connect to the torrent tracker.
The torrent tracker tells your torrent client a list of available torrent clients that are currently connected.
That is, for you, the torrent tracker acts as a server through which it connects you and provides at which port address you can exchange data directly. But this port address is already open on the client side when it connects to the torrent tracker.