BitTorrent is a protocol designed for transferring files. It is peer-to-peer in nature, as users connect to each other directly to send and receive portions of the file. However, there is a central server (called a tracker) which coordinates the action of all such peers. The tracker only manages connections, it does not have any knowledge of the contents of the files being distributed, and therefore a large number of users can be supported with relatively limited tracker bandwidth.
A recent extension to BitTorrent is the DHT ("distributed sloppy hash table" or simply called UDP tracker) protocol. A UDP based peer to peer tracker protocol.
XXX - add a brief description of BitTorrent history
["TCP"]: Typically, BitTorrent uses ["TCP"] as its transport protocol. The well known TCP port for BitTorrent traffic is 6881-6889 (and 6969 for the tracker port). The DHT extension (peer2peer tracker) uses various UDP ports negotiated by the peers.
XXX - Add example traffic here (as plain text or Ethereal screenshot).
The BitTorrent dissector is (fully functional, partially functional, not existing, ... whatever the current state is). The DHT extension is currently not decoded.
(XXX add links to preference settings affecting how PROTO is dissected).
Example capture file
XXX - Add a simple example capture file to the SampleCaptures page and link from here (see below). Keep this file short, it's also a good idea to gzip it to make it even smaller, as Ethereal can open gzipped files automatically.
A complete list of BitTorrent display filter fields can be found in the [http://www.ethereal.com/docs/dfref/b/bittorrent.html display filter reference]
Show only the BitTorrent based traffic:
Note: implemented in Ethereal post 0.10.12!
You cannot directly filter BitTorrent protocols while capturing. However, if you know the ["TCP"] port used (see above), you can filter on that one.
Capture only the BitTorrent tracker traffic over one of the default ports (e.g. 6881):
tcp port 6881
Capture the BitTorrent tracker traffic over the range of default ports (e.g. 6881-6889):
(tcp[0:2] >= 6881 and tcp[0:2] <= 6889) or (tcp[2:2] >= 6881 and tcp[2:2] <= 6889)
(which might not work with some older versions of libpcap) or, with libpcap 0.9.1 and later,
tcp portrange 6881-6889
[http://www.bittorrent.com/] the official BitTorrent page
[http://en.wikipedia.org/wiki/Bittorrent Wikipedia Bittorrent page]
[http://userpages.umbc.edu/%7Ehamilton/btclientconfig.html How BitTorrent Works] about P2P in general, BitTorrent and firewall settings
[http://www.bittorrent.org/Draft_DHT_protocol.html distributed sloppy hash table protocol] UDP based BitTorrent extension for distributed trackers (the UDP port number is negotiated)
[http://hippie.oofle.com/tiki-index.php?page=BitTorrent Hippie protocol signature description] the TCP and UDP protocol signatures which might be used to heuristically identify the BitTorrent protocol