[tor-relays] current HSDir flag requirements

[Scott Bennett]

Logforme <m7527 at abc.se> wrote:

>
> On 2021-05-26 08:18:32, "Scott Bennett" <bennett at sdf.org> wrote:
> >I interpret that as meaning that one
> >or more criteria being used by one or more authorities has changed,
> What I have noticed on my relay is that the "Consensus Weight" is 
> fluctuating.
> CW is too complicated for my tiny brain but I believe the measurements 
> from the Bandwidth Authorities is involved. The BWAuths are spread 
> around the world and depending on current internet conditions they get 
> different speed values to your relay. But can it cause massive swings in 
> CW?

     Yes.  My relay is on a residential service connection and its "bandwidth"
rating from the Authority relays typically oscillates between ~30 and ~120, so
proportionally the swings are often fairly wild.

> Maybe the BWAuths have changed their measurement technique during the 
> last couple of months?

     Well, I first noticed it late last year, IIRC.  The measurement technique
will, of course, often give deceptive results.  For example, if the connection
supports ~350 KB/s and the relay has little traffic at the time measurement
begins, the result should be fairly close to the true value.  OTOH, if the
relay is handling 200 KB/s of traffic for other circuits at the time measurement
begins, then the result should be at most only ~150 KB/s, which is far from the
true value.
>
> >  A further question I would like to raise is why do the Authority relays
> >use different criteria from one to another for the automatic assignment of
> >flags?  Should they not be consistent in using the same rules?
> >
> I agree that it is confusing that 2 auths don't assign the HSDir flag 
> according to the spec.
> I have no explanation apart from that AFAIK moria1 is run by Roger 
> Dingledine and I guess he runs a lot of beta and test stuff.
> moria1 publishes 2 HSDir "Flag Threshold" values (hsdir-wfu and 

     Yeah, I saw that, but don't know quite what to make of it.

> hsdir-tk) that no other auth publishes which leads me to believe moria1 
> runs another version of the auth software that handles the HSDir flag 
> differently. That don't explain bastet though.

     And it only accounts for two Authority relays, whereas you said five are
refusing to assign HSDir to my relay, which, as you pointed out, may depend
upon network conditions between those Authority relays and my relay at the time
and have nothing at all to do with my relay or how much traffic my relay could
handle or might actually be handling at the time.
>
> It's fun to speculate :)
>
     I would rather not be kept in the dark.  It should not be like trying to
get information on what the criminals who rule over us are up to.
     The problems outlined above would be mitigated somewhat if the measurements
were filtered somehow, which could be as simple a filter as a boxcar moving
average.  Yes, I know that for many purposes a rectangular window gives lousy
results, but for the purpose of understanding relays' capacities over time as
having values that usually change slowly if at all a boxcar moving average should
be plenty good enough.  An exponential moving average would probably also be
fine.  The point of using a filter for the measurements would be to minimize the
temporary interference of transient network conditions affecting the measurement
process and corrupting some of the results at some times but not at others.  Of
course, measurements outside some number of standard deviations from the mean
for a relay could be discarded, as well.  At present, it is difficult to separate
the deficiencies of the measurement method from the network realities in trying
to interpret the measurements.


                                  Scott Bennett, Comm. ASMELG, CFIAG
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