[network-health] Relays that can't extend

[Dennis Jackson]

Hi Roger,

On 31/03/2021 04:09, Roger Dingledine wrote:

> (There are some edge cases where I failed to reach the relay as the first
> hop, for example because it has gone down, or it's in the new consensus
> but my Tor client doesn't have the descriptor for it yet. I've omitted
> those edge cases from the ratio calculation, since they're not failures
> and they're not successes so they just muddy the analysis.)

Just to check I understand correctly - The attempt is considered a
failure if (and only if) you can connect to the test relay correctly,
but can't extend from the test relay to your own relay?

As many of these relays have weights, presumably they can successfully
extend to at least some relays in order to have their bandwidth
measured. I wonder how the probabilities would look if you tested with a
some other (highly weighted) relays in the 2nd-hop position?

> I'm simply making two-hop paths from my client through every relay to
> my destination relay.
>
> Here's a snapshot of some relays that fail most/all of the extend
> attempts.

Would you be comfortable sharing the unfiltered dataset? It would be
interesting to approximate the probability a client circuit is impacted
by this kind of failure.

I wrote a little python script (attached) which uses your output and
Onionoo's provided probabilities:

    python3 weights.py
    Loaded 180 relay extension failure probabilities from Roger's dataset
    Loaded 7103 relay circuit probabilities from Onionoo
    Over-estimate of probability circuit is impacted by connectivity
    issue 6.0070908572010426e-05

Best,

Dennis

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