Doug Vitale Tech Blog

BitTorrent: How it works and how to use it

BitTorrent is not an application you install; it is a network protocol that facilitates decentralized (or distributed) file sharing over the Internet. In this way it is similar to the functionality provided by traditional peer-to-peer (P2P) applications like Napster in the 1990’s, Kazaa, and Limewire. However, BitTorrent differs fundamentally from these older P2P sharing applications because it introduces components such as BitTorrent websites, torrents, trackers, seeders, and leeches (definitions below).

BitTorrent is also unique in how it efficiently uses bandwidth to achieve high data transfer rates. If the file you want is available from multiple hosts, BitTorrent establishes connections with them and downloads chunks of the file simultaneously. Therefore you trade one large, multimegabyte or multigigabyte download for several individual downloads, each of which is handling a much smaller sized data transfer. Additionally BitTorrent allows you to share these parts of a file even if the file itself isn’t fully downloaded on your end.
Typical BitTorrent network with data flow paths shown

Image source: Threestory Studio

Going further, the BitTorrent protocol is designed to ensure that its users share (upload) as much as they take (download). This feature is known as tit-for-tat and is meant to prevent users from downloading without uploading. In fact, BitTorrent tries to reward its generous users like so: the more files you share with others, the faster your downloads are. Obviously the number of users sharing the file you want will also play a role in determining download speed.


Before continuing you should familiarize yourself with BitTorrent lingo.

  • BitTorrent client – the software which processes .torrent files, reads the information in them and begins downloading.
  • Index – a searchable list of .torrent files.
  • Leech (leecher) – a BitTorrent user who does not have a complete file but has joined the network to download it. A leecher becomes a seeder when he downloads the entire file and then shares it across the BitTorrent network.
  • Peer – any host participating in the download or upload of a torrent file.
  • Seeder – a host sharing a complete copy of a file that is being shared across a BitTorrent network.
  • Share ratio – the amount of data a user has uploaded divided by the amount of data they have downloaded for a particular torrent. The ratio can be positive (+) or negative (-).
  • Swarm – the total of all the leechers and seeders participating in the BitTorrent process.
  • Torrent (.torrent) – a “map” file that contains the information that points to the actual file and the hosts who are sharing it.
  • Tracker – a server that acts like a traffic cop directing BitTorrent data traffic between seeders and leechers.

The application that you use to transfer files with BitTorrent is called a BitTorrent client. There are several popular ones available for download. Some are compatible only with Windows and others are designed for Mac or Linux. Some popular choices are Deluge, uTorrent, Vuze (formerly known as Azureus), and KTorrent but there are dozens of others. These programs will give your computer the ability to work with files ending in the ‘.torrent’ file extension. These .torrent files are not the files themselves. In other words, if you want to download ‘cool-song-i-want.mp3′, the file ‘cool-song-i-want.torrent’ is not the MP3 file that you are after. The .torrent file only contains the data that tells your BitTorrent client where it can find peers who are also sharing and downloading that song.

While you use your BitTorrent client to initiate and handle your file transfers, you actually search for files to download using a BitTorrent website such as Torrentz, BTJunkie, KAT, or IsoHunt (update; IsoHunt offline). These websites connect to other servers known as trackers (see definition above).

If you access the Internet through a router, you will probably have to configure it to permit BitTorrent traffic to pass through. In such a case, PortForward.com is very helpful as it provides detailed instructions on a router model-by-model basis.

What about when you want to share files (i.e., lets other users download files you already have)? You can use your BitTorrent client to specify which of your files you want to publicly share. Since there are many clients available, the ways to share files will vary. LifeHacker’s How to Share Your Own Files Using BitTorrent explains this process in more detail as does BitTorrent.com’s How to Send Your Files to Friends and Family.

Further reference

The BitTorrent protocol, its functionality, and its many forms and uses are a deep subject. There are many ways it can be utilized and configured. Below you will find a collection of informative BitTorrent articles that can play a role in your use of the protocol.

Introduction to BitTorrent

Bittorrent.com, Frequently Asked Questions.
Bittorrent.com, Videos and Guides.
HowStuffWorks.com, How BitTorrent Works.
LifeHacker.com, A beginner’s guide to BitTorrent.
LifeHacker.com, BitTorrent news and reviews.
TorrentFreak.com, Top 10 Most Popular Torrent Sites of 2014.
Wikipedia.org, BitTorrent protocol.
Wired.com How-to Wiki, Use BitTorrent.

Advanced BitTorrent: Encryption and Anonymity

Arstechnica.com, Not anonymous: attack reveals BitTorrent users on Tor (also see here for reference).
Forbes.com, Post PRISM, BitTorrent’s Sync Soars To 1 Million Users.
Gigaom.com, The Next Big DDoS Attack May Come via BitTorrent.
LifeHacker.com, How to Boost Your BitTorrent Speed and Privacy.
LifeHacker.com, How to Completely Anonymize Your BitTorrent Traffic with BTGuard.
NewScientist.com, Honeytrap reveals mass monitoring of BitTorrent downloaders.
Slate.com, BitTorrent downloaders being watched.
SourceForge.net, Mute: a secure, anonymous, distributed communications framework.
TorrentFreak.com, Why Encrypting BitTorrent Traffic Is Good.
TorrentFreak.com, Truly Decentralized BitTorrent Downloading Has Finally Arrived.
TorrentFreak.com, Google Starts Censoring BitTorrent, RapidShare and More.
TorrentFreak.com, U.S. Government Targets Large BitTorrent Sites And Trackers.
Wired.com, An NSA-Proof Twitter Built With Code From Bitcoin and BitTorrent.
Wired.com How-to Wiki, Optimize BitTorrent to outwit traffic-shaping ISPs.

BitTorrent discussion forums

BitTorrent.com
DSLreports.com
FileSharingTalk.com
Slyck.com
UniteTheCows.com
ZeroPaid.com

Recommended reading

If you found the content of this article helpful and want to expand your knowledge further, please consider buying a relevant book using the links below. Thanks!

Anonymous File Sharing & Darknet on Amazon Anonymous File Sharing & Darknet Peer-to-Peer : Harnessing the Power of Disruptive Technologies on Amazon Peer-to-Peer : Power of Disruptive Tech

Complete Guide to Internet Privacy, Anonymity & Security on Amazon Internet Privacy & Anonymity  P2P Networking and Applications on Amazon P2P Networking and Applications

Peer-to-Peer Computing: Principles and Applications on Amazon Peer-to-Peer Computing  BitTorrent For Dummies on Amazon BitTorrent For Dummies

Google Hacking for Penetration Testers on Amazon Google Hacking for Pen Testers Complete Guide to Anonymous Torrent Downloading and File-sharing on Amazon Anonymous Torrent Downloading

Written by Doug Vitale

February 1, 2012 at 4:20 PM

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