For other uses of this term, see Tracker (disambiguation).
A BitTorrent tracker is a special server that contains the information necessary for peers to connect to other peers by assisting in communication between them using the BitTorrent protocol. Trackers are the only and main meeting point that customers need to connect to in order to communicate and be able to initiate a download. Currently there is a series of alternate communications to the crawlers that allow a client to find other clients without the need to previously communicate with a crawler.
The crawlers not only coordinate the communication and distribution of data between peers who try to download the content d by torrents, but also closely monitor and keep track of statistics and verification information for each torrent. If the crawler goes down and someone tries to start a torrent download, you will not be able to connect to the swarm of users. The crawler errors are usually temporary, so it is advisable to try connecting again and again to achieve or otherwise find another source from which to download the same content.
The tracker is the only one who knows where each peer is located within a swarm, so it is indispensable to be able to communicate with the rest of the users, at least until they have connected with the swarm.
Crawlers are divided into two classes, private and public. The main difference between them is that the private ones require that the peers are registered users of a Web site, whereas in the public crawlers anyone can communicate with them. Private crawlers generally store traffic statistics for each user and use a percentage system that lets you know whether or not the user shares the data you have downloaded or downloaded. Many of these crawlers tend to expel users who have a low percentage, since they do not collaborate with the network by not sharing.
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