Re: [tor-bugs] #21394 [Core Tor/Tor]: connection timeouts are affecting Tor Browser usability

["Tor Bug Tracker & Wiki" <blackhole@xxxxxxxxxxxxxx>]

#21394: connection timeouts are affecting Tor Browser usability
-------------------------------------------------+-------------------------
 Reporter:  arthuredelstein                      |          Owner:  (none)
     Type:  defect                               |         Status:  new
 Priority:  Very High                            |      Milestone:  Tor:
                                                 |  0.3.2.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  tbb-performance, tbb-usability,      |  Actual Points:
  performance, tbb-needs                         |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
-------------------------------------------------+-------------------------

Comment (by arthuredelstein):

 Replying to [comment:22 teor]:
 > Replying to [comment:20 arthuredelstein]:
 > > I did some more experiments:
 > >
 > > ...
 > > Indeed I got 9/50 timeouts for the domain with http or https, but no
 timeouts for IPv4 and only a single timeout for IPv6.
 > >
 > > Does this ring any bells for Tor core experts? What might be happening
 with DNS here?
 >
 > Some exits may be overloading their resolvers. Or our code may be buggy.
 It would be helpful to identify the particular exits that are experiencing
 these timeouts, and work out if they are in the same AS or using the same
 resolvers.

 Makes sense. If the DNS resolve fails at an exit, does the exit send an
 error message back to the client? Or does it silently fail, meaning the
 client has to wait for the full 10-second timeout?

 > I also wonder if we should ask bandwidth authorities to use DNS whenever
 possible, so they see DNS timeouts, and downgrade exits that have them.
 See #24010.

 Nice idea. Would it also be feasible to have exits periodically run
 diagnostics to see if their DNS resolution is working properly, and if
 not, report the problem to bandwidth authorities and notify their relay
 operator?

 > The only node in a tor path that uses DNS is an exit, so if DNS breaks,
 it causes issues at the exit.

 That seems sensible. I'm only a little puzzled that it seems more common
 than I would expect that I saw not a single timeout, but a double, triple
 or quadruple timeout (see instances of 2,3,4 in my raw data). Presumably
 it's switching to a new exit node after each individual timeout, so why do
 I frequently see multiple timeouts for a single connection? Maybe it's
 just bad luck, but it made me wonder if I'm seeing something that goes
 wrong for the whole connection attempt and not just individual circuits.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21394#comment:23>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online

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