ktorrent and ARP

[T.C. Hollingsworth]

On Sat, Sep 27, 2014 at 7:27 AM, Ed Greshko <ed.greshko at greshko.com> wrote:
> It appears that ktorrent is causing ARP packets to be sent on the local network.  I don't know why, and I don't know how to prevent it.

It's DHT, which implements a distributed torrent tracker.  As part of
this, KTorrent finds other torrent clients on your local network and
the Internet, and if it finds one it can get a list of peers from it,
and maybe download a file much faster if someone on your network is
sharing it too.

As you can imagine, the local network portion of this is much more
useful on a shared network such as public wifi or a University
network, but even on a small home network it can speed up downloads a
little bit if you have more than one torrent client running on your
network by sharing certain information.

You can disable DHT in Settings > Configure KTorrent > BitTorrent, but
this disables DHT functionality everywhere and will prohibit magnet:
links from working properly.  There's no way to disable this just for
your local network, because such an option doesn't really make sense.
(Why would you not mind getting this information from random systems
on the public Internet but not want it from other local machines?)

> If I'm not running ktorrent "arp" or "ip neigh show" will only display real devices that exist on my local network.  But, a while after starting ktorrent the number of entries will increase and look like this.....

"Incomplete" ARP requests are harmless; it just means something tried
to connect to that IP but couldn't because nothing exists at it..  I'd
guess KTorrent has a local IP address cached that had DHT information
before, but DHCP assigned a different address since then, so it tries
to connect to it and fails, leaving behind the failed ARP request.

-T.C.