[metrics-team] Sudden drop in obfs3 users on 2016-09-02

Karsten Loesing karsten at torproject.org
Thu Sep 22 10:03:17 UTC 2016


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On 22/09/16 04:58, David Fifield wrote:
> In https://bugs.torproject.org/20216 we're investigating what looks
> like a recent Tor block in Iran.
> 
> The userstats-combined graph appears to show an almost complete
> collapse of obfs3 users on 2016-09-02 (which coincides with a
> decrease in direct users): 
> https://metrics.torproject.org/userstats-bridge-combined.html?start=2016-06-24&end=2016-09-22&country=ir
>
>  However, Nima noticed that the same drop in obfs3 users appeared
> in other countries on the same date: 
> https://metrics.torproject.org/userstats-bridge-combined.html?start=2016-06-24&end=2016-09-22&country=de
>
> 
https://metrics.torproject.org/userstats-bridge-combined.html?start=2016-06-24&end=2016-09-22&country=ru
> https://metrics.torproject.org/userstats-bridge-combined.html?start=2016-06-24&end=2016-09-22&country=us
>
>  I checked that the 5 current default obfs3 bridges are running,
> so that's not the problem.
> 
> Did something change recently in the way bridge users are counted, 
> perhaps?

Not sure if this explains what we're seeing here, but something that
did change on 2016-09-02 is that Tonga was shut down and Bifroest took
over.

https://metrics.torproject.org/networksize.html

The effect was that suddenly ~40% of public bridges were turned into
private bridges, in the sense that we're not learning any statistics
from them anymore.  It might be that obfs3 bridges are
disproportionately affected by that.

But this is just a first thought that coincides with the date and
needs confirmation by looking at the data.

All the best,
Karsten

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