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

[David Fifield]

On Thu, Sep 22, 2016 at 09:13:52AM -0700, David Fifield wrote:
> On Thu, Sep 22, 2016 at 12:03:17PM +0200, Karsten Loesing wrote:
> > > 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.
> 
> Thanks, I hadn't thought of that.
> 
> > > I checked that the 5 current default obfs3 bridges are running,
> > > so that's not the problem.
> 
> Hmm, 2 of the 5 bridges (1 of 4 distinct fingerprints) are not running
> this morning when I checked.
> 
> But in any case, none of the 5 default obfs3 bridges are reporting
> statistics. None of these links works:
> 
> https://atlas.torproject.org/#details/A09D536DD1752D542E1FBB3C9CE4449D51298239 (LeifEricson)
> https://atlas.torproject.org/#details/AF9F66B7B04F8FF6F32D455F05135250A16543C9 (Unnamed, formerly PacificSunset)
> https://atlas.torproject.org/#details/1E05F577A0EC0213F971D81BF4D86A9E4E8229ED (ndnop0)
> https://atlas.torproject.org/#details/4C331FA9B3D1D6D8FB0D8FBBF0C259C360D97E6A (ndnop2)
> 
> In comparison, 13/16 default obfs4 relays are findable on Atlas: all but
> LeifEricson, ndnop3, and ndnop5.
> 
> Could the tonga–bifroest migration have caused these bridges to stop
> reporting? If so, I'll make a new ticket and ask the operators to
> upgrade or whatever they need to do to start reporting again.

All the default bridges have upgraded and are once again reporting
statistics. The user numbers look to have returned to normal.

https://metrics.torproject.org/userstats-bridge-transport.html?start=2016-07-02&end=2016-09-30&transport=obfs3&transport=obfs4&transport=meek&transport=%3COR%3E

Interesting to note, the line for obfs3 goes almost all the way down to
zero. When it recovers, it returns to the previous level. From this I
infer that nearly all users who use obfs3, use the default obfs3 bridges
and not private ones.