[bittorrent] What is the difference between Peer Exchange and DHT ?

Elliott Mitchell ehem at m5p.com
Tue Apr 25 22:27:39 EDT 2006


>From: Brian Dessent <brian at dessent.net>
> DHT is completely standalone and more general purpose, it allows for
> looking up peers based on info hash and requires no interaction with the
> tracker at all.  So if all you have is the info hash (and presumably the
> actual data in the 'info' key, otherwise how would you know the
> filenames and sizes?) you can query the DHT for peers based only on
> that.  It also allows data trading in a more general sense, for example
> there's an AZ plugin to do scraping over DHT too.

You have just as much of a bootstrap problem with this method as well,
the only difference is where the fixed location is. With the standard
mode the tracker is the fixed bootstrap point. With the above the
webserver with the torrent file becomes the fixed bootstrap point.

The only real difference is that with the above, you only need to
bootstrap one peer. After you've got one peer, you can use DHT to find
other peers, but you still need a centralized resource (sounds an awful
lot like "tracker") to join the swarm. While with the conventional
tracker, you need the tracker for each additional peer added. I'll admit
making things less dependant on the tracker is nice, but you've still got
the bootstrap problem.


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