Accidental bittorrent on our networks

June 20, 2008

Several times now we've had cases of 'accidental BitTorrent' on our networks (and generally gotten email from the campus network people about it); people running BitTorrent clients on our networks without intending to. It turns out that this is an amusing (to me) consequence of the pervasiveness of laptops and laptop hibernation these days.

(You might reasonably ask why we 'allow' BitTorrent at all. There's at least two reasons; first, without deep packet inspection (and maybe even then) we can't tell what is and isn't BitTorrent traffic, and second, there are legitimate uses for BitTorrent, especially in a Computer Science research environment.)

What I believe generally happens is:

  • at home, the user starts their BitTorrent client on their laptop
  • the client tucks itself discreetly away somewhere in the system
  • the user hibernates or otherwise suspends their laptop, instead of shutting it down outright.
  • the user brings the laptop to here, and un-suspends it, resuming everything including the BitTorrent client (which doesn't care that it changed networks, since it's stateless overall).

It shouldn't surprise anyone that BitTorrent swarms love our network, as they love anything with a fast uplink. The resulting network utilization can be dramatic.

I don't consider this the user's fault; it is a classic case of a collection of design decisions (and human factors issues, like how people forget things in the corner) that make perfect sense in isolation but combine badly. Unfortunately all of the cures that I can think of are more complicated than the disease.

Written on 20 June 2008.
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Last modified: Fri Jun 20 03:57:01 2008
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