What is File Sharing (BitTorrent)?

Unlike traditional file downloads, where media and software are stored in a central download server, BitTorrent users directly connects to each other from their respective locations around the world and share the work of transferring desired files using peer-to-peer (P2P) connections.

Some cloud-based file sharing solutions, such as Dropbox, seem to provide real-time computer-to-computer file transfer but these still rely on file servers operating at fixed locations. BitTorrent distributes the work of making files available among the users sharing the file, so they all contribute some of their own network bandwidth.

BitTorrent Files

To create content that can be shared over BitTorrent, that content has to initially be analyzed by BitTorrent software. The software makes a virtual “map” of the content and then breaks that map, like puzzle pieces. When a user downloads the torrent file, they get the entire map of the content. They will then have to request the matching content, piece by piece.

BitTorrent files also contain extra information (metadata) about the content being shared. The metadata typically describes the category of content (music, video, application, game, etc.), but that is something set by the creator of the torrent file and is not something the BitTorrent software can intelligently discover by itself.

Each BitTorrent file has a unique global identifier called an “info hash,” which is a hexadecimal number generated from evaluating its metadata and linked content.

When the File Sharing risk vector is assessed, it notes the info hash and associated metadata. The main BitTorrent file and its linked contents are considered as a single file. All references to file sharing and files are in this context.

Making Connections

Peers will periodically send statistics of their progress, along with their IP address, to a tracker. Files may have more than 1 tracker associated with them, for redundancy. Trackers keep a list of which peers (by IP address) are sharing files to allow new and existing peers to find each other. The entire group of peers connected to a particular torrent file is called a “swarm.”

Some torrent files do not use a tracking server. Instead, the list of active peer IP addresses for the file is obtained from a massive free-floating database of torrent info hashes and associated IP addresses. Due to the sheer size of this database, it would be impractical for every BitTorrent user to keep an entire copy of it, so it is broken up and distributed -- this forms the Distributed Hash Table (DHT) and pieces of it are passed around when requested.

The particular BitTorrent software that a file sharer uses will handle all network communications. It looks for peers for the content, which makes it easy for the average computer user to get started with sharing files.

Network Ports Used in File Sharing

BitTorrent software uses many different network ports as a normal part of operation. It’s possible for a single file sharing peer to use many different ports during the course of a day.

In summary, file sharing ports change and aren’t constrained to a particular range.