[tor-relays] bandwidth authority algorithm is cracked

Tue Jan 21 14:01:48 UTC 2014

Hi Karsten, and thank you very much for your answer.

Few days ago I have re-started my 2 tor daemons (same identity, ArachnideFR94 and ArachnideFR94v2) on same the server on which I had these huge falling down/rising up/fall down again consensus weight problems. They started back from nearly 0 and there are currently gaining bandwith/consensus weight. I will try to analyse more precisely what will happen on the following days and weeks and keep you informed. I hope the problem will be back so I will try to understand the cause of this problem, watching everything you described to me.

I think everybody agree to say that the title of the mail has great chances to be wrong (at least, it's faaaar far far too soon to make such an affirmation !) but I anwsered to this subject since I encountered exactly the same problem described by starlight, and this problem have completely destroyed the bandwith/consensus weight of a 20MB/s server - and avoided new ones to gain more than 1 or 2 MB/s bandwith on the same machine. Everything I have seen on Tor Atlas during the problem is a consensus weight shaking like an earthquake during an entire month (december, 2013), and the real bandwith of the server followed the consensus weight with few hours late, so today I cannot explain what happened.

I will watch carefully what will happen now, and keep you informed of what I can understand if the problem is still existing (I hope so, nothing have changed into the server apart from few upgrades with apt-get). Maybe I will use a new Topic description for my next emails about this. 

Best regards !
Julien ROBIN

----- Mail original -----
De: "Karsten Loesing" <karsten at torproject.org>
À: tor-relays at lists.torproject.org
Envoyé: Mardi 21 Janvier 2014 10:59:22
Objet: Re: [tor-relays] bandwidth authority algorithm is cracked

Hi starlight, hi Julien,

the bandwidth scanner system is quite complex, so it might be the case
that part of it is broken.  But from this thread that's hard to say, and
it's impossible to know what part needs fixing.

Want to help us debug the problem(s) you observed?

Here are a few possible starting points:

 - Search your relays in Atlas at https://atlas.torproject.org/, look at
the graphs at the bottom, and tell us at what times you think the
"consensus weight fraction" plot is totally off.

 - Read Roger's blog post
https://blog.torproject.org/blog/lifecycle-of-a-new-relay and tell us
how much your findings overlap or do not overlap with the expectations
stated in that blog post.

 - More ambitiously, download the vote documents from the metrics
website at https://metrics.torproject.org/data.html, find your relay in
the votes produced by bandwidth authorities, and tell us what unexpected
things you found while doing so.

 - Even more ambitiously, read the bandwidth scanner spec at
https://gitweb.torproject.org/torflow.git/blob/HEAD:/NetworkScanners/BwAuthority/README.spec.txt
and tell us what data we could obtain from the bandwidth scanners to
further debug this problem.

Thanks!

All the best,
Karsten

On 1/10/14 9:37 AM, julien.robin28 at free.fr wrote:
> I had the same problem since begining of december on my ArachnideFR94
> server (88.191.192.25, service provider : Iliad - Online.net) :
> Consensus weight from more than 100,000 to brutally 6,000 and 20,000,
> after a few time rise up to 50,000, and brutally fall down back 3,000
> and 10,000 the following day, 30,000, 12,000, 8,000... after an
> entire month of bandwith never rising back and falling down even
> lower, after i tryed everything (create a new server identity, but
> after some weeks, same problem), seeing worst and worst, end of
> november my bandwith was about 20MB/s  (sometimes into the top 5 of
> the world biggest servers !), it was about 0,9MB/s when I decided to
> close it.
> 
> No problem of bandwith with the service provider, the bandwith graph
> were just starting to brutally go down a couple of minutes after the
> consensus weight brutally fall back. I was thinking it was because
> too many tor relays are running on this service provider (since end
> of July, 2013, Tor relays are accepted by this service provider and
> the service provider also opened to internationnal with interesting
> prices).
> 
> And I have no problem with my 2 others servers at "Digicube" service
> provider.
> 
> If it can help !
> 
> Best regards Julien ROBIN
> 
> ----- Mail original ----- De: "starlight 2014q1"
> <starlight.2014q1 at binnacle.cx> À: tor-relays at lists.torproject.org 
> Envoyé: Vendredi 10 Janvier 2014 05:49:20 Objet: [tor-relays]
> bandwidth authority algorithm is cracked
> 
> The bandwidth authorities assign all kinds of wildly incorrect
> capacities to the Tor node here.
> 
> The Tor relay software has been up for 45 days and has not been down
> for more than five minutes for three or four months.
> 
> Occasional outages from the ISP mucking with their network, but
> nothing more than ten or fifteen minutes in any week.
> 
> The local node bandwidth calculation is consistently 490-495
> Kbytes/sec.  Very stable.  Very consistent.
> 
> The Tor bandwidth authorities assign values anywhere from 100
> Kbytes/sec to almost 700 Kbytes/sec in an oscillating pattern with a
> period of about one week.
> 
> Something is seriously wrong with that.
> 
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