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

Brian Dessent brian at dessent.net
Tue Apr 25 17:58:45 EDT 2006

FYP 2005 wrote:

> It seems that both peer exchange and DHT also get peer list from peers
> and do not need to connect to trackers.
> Then, what is the main differences between them ?

Peer exchange happens after two peers are already connected -- somewhere
in the handshake sequence they trade lists of other peers.  This is only
useful if you have already contacted the tracker at least once, or have
otherwise bootstrapped the swarm somehow.  And it is only useful to get
more peers to the current swarm from the existing ones; it cannot help
with cross-swarm situations.

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.


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