The key thing to understand is that nobody is being forced to use Magnet links or trackerless torrents. While these long-standing technologies may prove to be the future, they will co-exist with tracker-enabled torrenting for quite some time. For now, nobody will be forced to immediately change their existing downloading habits, although it may be wise to switch to a BitTorrent client that is compatible with these technologies.

In an attempt to clear some of the mystique surrounding DHT, PEX and Magnet links we will walk through all three briefly, hoping to assure those who’ve become confused earlier this week.

DHT

Using DHT instead of trackers is one of the things The Pirate Bay is now trying to encourage, and torrent downloads that rely solely on this technology are often referred to as “trackerless torrents.” DHT is used to find the IP addresses of peers, mostly in addition to a tracker. It is enabled by default in clients such as uTorrent and Vuze and millions of people are already using it without knowing.

DHT’s function is to find peers who are downloading the same files, but without communicating with a central BitTorrent tracker such as that previously operated by The Pirate Bay.

DHT is by no means a new technology. A version debuted in the BitTorrent client Azureus in May 2005 and an alternative but incompatible version was added to Mainline BitTorrent a month later. There is, however, a plugin available for Azureus Vuze which allows it access to the Mainline DHT network used by uTorrent and other clients.

Peer Exchange (”PEX”)

Peer Exchange is yet another means of finding IP addresses. Rather than acting like a tracker, it leverages the knowledge of peers you are connected to, by asking them in turn for the addresses of peers they are connected to. Although it requires a “kick start”, PEX will often uncover more genuine peers than DHT or a tracker.

Magnet links

Traditionally, .torrent files are downloaded from torrent sites. A torrent client then calculates a torrent hash (a kind of fingerprint) based on the files it relates to, and seeks the addresses of peers from a tracker (or the DHT network) before connecting to those peers and downloading the desired content.

Sites can save on bandwidth by calculating torrent hashes themselves and allowing them to be downloaded instead of .torrent files. Given the torrent hash – passed as a parameter within a Magnet link – clients immediately seek the addresses of peers and connect to them to download first the torrent file, and then the desired content.

It is worth noting that BitTorrent can not ditch the .torrent format entirely and rely solely on Magnet links. The .torrent files hold crucial information that is needed to start the downloading process, and this information has to be available in the swarm.

Pirate Bay links cf. Mininova links: When the Magnet link specification first came out, in January last year it called for a particular format (”base32 encoded”). The links that EZTV, Mininova and ShareReactor have displayed for some time all conform to that original specification. In May of last year the specification was changed, in favor of “hex encoding”, and that is the format of the links being displayed by The Pirate Bay. Torrent clients should accept either format.

Compatible Clients

All the main torrent clients: uTorrent 1.8.5, Vuze 4.3.0.2, BitTorrent 6.3, BitComet 1.16, and Transmission 1.76 (and others) support Peer Exchange and DHT (via a plugin in the case of Vuze). Neither BitComet nor Transmission yet support Magnet links but Transmission is planning to include Magnet link support in the upcoming 1.8 release. Bearing in mind that no site, including The Pirate Bay, has yet abandoned support for traditional torrent files, there is plenty of time for support to be added.

We hope that this article has cleared some of the smoke that was generated by The Pirate Bay’s announcements earlier this week. There is no need to panic, cry or be angry, and it’s not a problem if you’re still confused after reading this article. Torrents will still be available and aside from some extra downloading options thanks to sites that add Magnet links, nothing drastic will change in the near future.

Props to ‘Adapa’ for contributing to this article.

Article from: TorrentFreak, check out our new blog at FreakBits.

The main problem is that most people just don’t understand what DHT is, what it does, and how it works. Not really a surprise since the documentation and even the Wikipedia page are filled with technical jargon, and no simple explanation.  Without that basic understanding confusion is inevitable. We did explain DHT in our jargon piece back in 2006 but after 3 years, we decide to cover it again.

The easiest way to think about DHT is to imagine it as a form of ’super tracker’, in some ways a lot like WinMX and Kazaa of old. A large ad-hoc network of peers pass on information requests about torrents without a central server, meaning no control or single point of failure. No information about the contents or even the names of torrents are passed around, making this legal and hard to shut down.

Myth: You must turn off DHT when you use private trackers.

Wrong — There is an element to a torrent that is called the ‘private flag’. It’s a small flag that marks to a client that the torrent is ‘private’ and disables any method of sharing peers (including DHT), except via the tracker. This flag also changes the hash, so peers on a non-flagged torrent could not connect to a flagged torrent in any case. Most private torrent sites check for the flag, and add it if missing when the torrent is initially uploaded to their site.

Myth: Certain clients leak DHT data and should be avoided.

Wrong (with one exception) — There are always going to be people that want control. When it comes to torrent sites (especially the private ones) they like to express their control through lists of clients you can and can’t use (a form of DRM) and sometimes give reasons to support this. An example would be this statement from a staff member at a private tracker:

Not all torrent clients respect the private flag. But if you are using a client like Vuze, uTorrent or similar if the private flag is on (set by the tracker) the DHT, peer exchange settings etc are ignored. However, if you are using something like BitComet, BitLord or their ilk they ignore the private flag so if you have DHT etc enabled it is going to be enabled no matter what.

This statement is completely false. All torrent clients that support DHT respect the flag. The flag is set by the torrent file, not the tracker (although the tracker can add the flag to the file, it’s still set by the torrent), and BitComet does NOT ignore the flag. The one exception is a single build of BitComet (0.60) that was available for 2 weeks at the end of 2005, and even then, was a fallback only if the tracker was unable to be contacted for a 30minute period. Bitlord is unable to leak to DHT, as it doesn’t use DHT at all.

If you see staff making claims like this, it’s a good indication that the staff is clueless, which might be an idea to leave that tracker. If they can’t get the basics right who knows when else is wrong. Of course, we ask those claiming other clients leak to let us know so we can test it.

Myth: You can be tracked by DHT / AntiP2P groups use DHT to find you

Unlikely — It’s much easier and simpler to use the tracker. Blocklists, used on your client and on the trackers, are generally ineffective and easily circumvented through the use of residential connections. Last year’s University of Washington study showed that they will send letters just based on tracker info.

Myth: DHT slows your system down

Generally not true — It can slow down your connection depending mainly on network hardware. The actual data used in running DHT is low, generally less than 1kilobyte a second. Some routers and modems, however, can have problems with DHT causing lockups and restarts if they run out of ram. This mostly happens with lower spec ‘home’ equipment (such as older Belkins, Netgears and D-links), or telco-provided hardware.

Myth: You need to connect to a tracker, before you can use DHT

Wrong — When DHT is enabled (certainly in uTorrent) it connects to a bootstrap node (such as router.utorrent.com or router.bittorrent.com for mainline, or dht.aelitis.com for Vuze) and uses that to enter the DHT ’swarm’. It’s handed a set of DHT nodes and uses that to build up a small group of connected nodes. Those nodes are then used to get peers. No tracker is required at any time.

Myth: When enabled, it sends usage data back to [insert company]

Wrong — This is another case of people not knowing what they’re talking about. Generally they’re misinterpreting the bootstrap node connection for their client.

When the demonoid tracker was finally resurrected last year, many of it’s torrents were still active thanks mainly to DHT. DHT with Peer Exchange (PEX) is a very powerful addition to the torrenting world, and allows torrents to stay active, irrespective of the trackers stability or even existence. Also, Azureus/Vuze users, despite having their own DHT system, can join in using a mainline DHT plugin.

Should you use DHT? Not if you only use private trackers, but if you use public ones and your network hardware can cope, then yes. It can help reduce tracker load. If you have a question about DHT not answered here, then again, let us know.

Article from: TorrentFreak, check out our new blog at FreakBits.

Torrents are deleted from trackers
Some trackers, like Demonoid.com have policies that require them to remove torrents from a tracker if they are older than a year. This way they save server resources, because a lot of the older torrents are unseeded, but still indexed by some sites, which means that the tracker is bombarded with unnecessary requests.

Trackers Die
Unfortunately BitTorrent trackers don’t live forever.

Trackers experience Downtime
A lot of BitTorrent trackers go down every now and then. Most of the time they return after a few minutes or hours, but still, the torrent won’t work when they’re down.

So, how do we solve this problem? Basically, there are two things you can do to guarantee that your torrent will stay alive. Of course these tips will only work with public trackers.

1. Use Multi-tracker Torrents
Several BitTorrent clients allow you to add multiple trackers to a torrent upon creation. So, if you add three trackers, the second one will take over if the first one fails. The multi-tracker feature was first proposed by John Hoffman, and is now supported by several clients including Azureus, BitComet, BitTornado and uTorrent.

2. Enable DHT
DHT stands for “Distributed Hash Table”. If a web based tracker goes down, the torrents stay alive because peers can act as “nodes” keeping the swarm intact, and the torrent alive. So you could say that the DHT layer serves as a peer-to-peer tracker. The DHT feature is available on Azureus, Bitcomet, uTorrent and several other BitTorrent clients.

Do these two things and your much less likely do develop a headache when you’re favourite Linux distribution stops downloading. ;-)

Article from: TorrentFreak, check out our new blog at FreakBits.