[tor-relays] Some Dir Authorities blocked

[Roger Dingledine]

On Sat, Sep 16, 2017 at 11:44:41PM +0000, dawuud wrote:
> > Your only option would be to ask your ISP to uncensor the internet,
> > unfortunately. Tor requires that all relays are able to contact all
> > other relays, and those which cannot participate in the network.
> 
> I think you meant to say:
> "Tor requires that all relays are able to contact all directory authorities"

Actually, no, we want it to be the case that all relays can reach all
relays. The less true that becomes -- that is, the less clique-like
the network topology becomes -- the more complicated the anonymity
measurements become, and that is potentially quite bad.

> Tor certainly does NOT require all relays can contact all relays.  In
> fact, the network is *very* partitioned... but as of the past few
> months I haven't put any energy into proving this; although I do have
> some mostly finished twisted python code to make all two hop tor
> circuits and records circuit build failures and circuit build timeouts.

This is a great research area that it would be good to see some
attention for.

In particular, if there are specific relays that are doing especially
poorly for connectivity, we should work with them to try to get them to
fix it, and if it's unfixable, downgrade their weights and/or boot them
from the network.

See also
https://trac.torproject.org/projects/tor/ticket/12131
("Measure connectivity patterns between relays")
and
https://trac.torproject.org/projects/tor/ticket/19068
("Write and run a clique reachability test")

--Roger