BEP:34
Title:DNS Tracker Preferences
Version: 6d4257025be0feed745a072cae86995e6796e3ba
Last-Modified:Fri Jul 27 15
Author: Fredrik Neij <tiamo@tfr.org>, Arvid Norberg <arvid@bittorrent.com>, Chris Brown <cbrown@bittorrent.com>
Status: Draft
Type:Standards Track
Created:26-July-2012
Post-History:

Abstract

Sometimes when users create torrents they mistakingly add website URLs as trackers. This results in those websites getting flooded with unwanted HTTP traffic.

To prevent this flooding, trackers and websites can declare via DNS TXT record which ports (if any) on which they are running trackers.

If a torrent contains a URL that according to this record does not have a tracker running on it, the client should attempt to fix the URL by trying connections on one or more of the ports in the TXT record.

This will also be helpful for example when a tracker switches from HTTP to UDP service, to prevent the tracker from being flooded with obsolete HTTP requests. This would direct the client to use UDP instead of HTTP in a old torrent where only the previous service are listed.

It's worth noting that this could potentially allow ISPs to prevent trackers from operating by injecting entries into DNS records.

Syntax

The contents of the TXT records are case-sensitive and consist of one or more words separated by spaces.

Words

  • BITTORRENT - This should always be the first word in the record. The presence of a record beginning with this word indicates that the host is only running trackers on the ports explicitly indicated in the following words.
  • UDP:X - This word indicates that there is a tracker running on UDP port X.
  • TCP:X - This word indicates that there is a tracker running on TCP port X.

The trackers should be in order of preference with preferred trackers coming first.

Unrecognized words are silently ignored for the sake of future expansion and readability (as shown below).

Examples

  • "BITTORRENT" - The host is not running any trackers.
  • "BITTORRENT DENY ALL" - Handled exactly like the previous example, but more readable. The words "DENY" and "ALL" are ignored.
  • "BITTORRENT UDP:1337 TCP:80" - The host is running two trackers, one on UDP port 1337 and one on TCP port 80. The UDP tracker is prefered.