aus
http://bitconjurer.org/BitTorrent/FAQ.html:
Q: I'm behind a firewall/NAT, can I use BitTorrent?
A: Yes, but you will get better performance if other peers can connect to you. By default, BitTorrent listens on port 6881, trying incrementially higher ports if it's unable to bind, and gives up after 6889 (the port range is configurable). It's up to you to figure out how to poke a hole in your firewall/NAT.