[tor-relays] Measuring the Accuracy of Tor Relays' Advertised Bandwidths

[teor]

Hi,

> On 26 Aug 2019, at 00:21, Felix <zwiebel at quantentunnel.de> wrote:
> 
>> I found another relay [2] where at least 4 of the 9 authorities doesn't set the "Running" flag, which is needed for "Guard", right?
>> That relay has a reasonable bw value to (23,000 , FWIW the value for [1] is about 90,000).
>> 
>> So now I do wonder why the Running flag is lost after a year.
>> 
>> [1]	https://consensus-health.torproject.org/consensus-health-2019-08-24-07-00.html#509EAB4C5D10C9A9A24B4EA0CE402C047A2D64E6
>> [3]	https://consensus-health.torproject.org/consensus-health-2019-08-24-08-00.html#0CDCFB0B6E1500E57BDD7F240543EBAEF81C11CA
> 
> I have a similar experience like Toralf. Since a week all my relays (but
> one) are middle relays. Which is fine because they push good traffic.

The Guard flags is affected by the bandwidth authority measurements.

> All are measured by maatu, gabel, moria1 and farav. But only one is
> measured by longc and bastet. [1]
> Why is that?

longclaw and bastet run sbws, the other bandwidth authorities run torflow.

There are 3 high-priority bugs that make sbws leave some useful relays out
of its bandwidth file:
https://trac.torproject.org/projects/tor/query?status=!closed&keywords=~sbws-majority-blocker

These bugs stop us deploying sbws to more than 3 authorities.

We expect to have funding to fix these bugs some time in the next month
or two.

Even after these changes, Torflow will still have more relays than sbws,
because some of the relays that Torflow reports have been down for a long
time.

> My understanding is six of nine authorities measure bandwitdh. I can
> download bandwidth files from all six from a _non_ measured server [2],
> so connection is given. But I see about 2.4MB doc size from the ones
> working for me and 4MB from the ones not working.
> Any clue what is the difference between those?
> 
> My family is [3]. The good relay is 402 and the `bad´ ones are between
> 405 and 415.
> 
> Don't get me wrong. If guard, middle or exit all relays are important.
> But it's a little strange.

I don't think the sbws bandwidth authorities are causing the issue that
you're seeing with your consensus weight or flags.

The consensus is based on majority votes, and 2/6 bandwidth authorities
or 2/9 authorities are not a majority.

T

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