title: Torrent peer-to-peer connection
body: <p>I used to think my understanding of the TCP and UDP protocols, although limited, is correct. Although recently, when I realized that peers sharing a common torrent can connect to one another through a TCP or UDP protocols without the actual need for port forwarding, I got confused. How does a router know which machine in the local network to forward packets to? Any help in clearing that up would be appreciated. The torrent protocol diagrams and articles on the Internet are greatly simplified, and hence do not contain any information that would help.</p>