Networking – Why does bittorrent not require port forwarding?


I know that usually when you set up a connection between a data source and a data receiver that you need to port forward to gain access to the data source computer so I was wondering why you don't need to port forward in bit torrent because all of the computers are sources and how they avoid the firewall of the modem?

Best Answer

If you are behind a router (more precisely, a NAT), and the other side of the connection is behind a router, you can not directly connect to each other.

This is true for BitTorrent as well, so if you are behind a router and you do not have a port forwarding configured, then you will not be able to download (or upload) from any other user who has the same configuration.

That said, many routers support the UPnP protocol, which allows an application to automatically enable port forwarding. In that case, you probably won't notice that your port has been opened.

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