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

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#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                                    |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
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Comment (by arthuredelstein):

 I did some more experiments:

 First I tried https://torpat.ch. This does not have an IPv6 address, as
 far as I can tell. I got the following result:
 {{{
 https://torpat.ch:
 00000000040000400022002100020100002100000102011100
 }}}
 where each digit represents an attempt to connect, and the number of
 timeouts before the connection succeeded. So to me it doesn't look like
 IPv6 is the (only) problem. 15/50 attempts included at least one timeout.
 About half had more than one timeout.

 So I thought I should check IPv6 as well. I found the IPv6 address for
 perdulce.torproject.org:
 {{{
 http://[2a01:4f8:172:1b46:0:abba:11:1]/ (perdulce.torproject.org ipv6):
 000000000000000000000000000000000000000000000000000000000000000
 }}}
 To my surprise, there were no timeouts at all. So I tried IPv4:
 {{{
 http://138.201.14.203/ (perdulce.torproject.org ipv4)
 000000000000000000000000000000000000000000000000000000000000000
 }}}
 Again no timeouts. Then I tried a site on perdulce:
 {{{
 https://people.torproject.org/~arthuredelstein/ :
 011000310000000111110000000010130100110122001010000
 }}}
 and the timeouts returned (20/50). That made me think this has something
 to do with the DNS resolve. To check this, I tried another site,
 example.com, including https with domain, http with domain, bare IPv4, and
 bare IPv6:
 {{{
 https://example.com
 00000010000010000000020010010210100000000000000003

 http://example.com
 00100000021000002001001001000000001000000000001000

 http://93.184.216.34/
 00000000000000000000000000000000000000000000000000

 http://[2606:2800:220:1:248:1893:25c8:1946]/
 00000000000000000000000000000000000000000000000010
 }}}
 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? Again I think the multiple timeouts are a little
 suspicious, and I don't quite understand how that jibes with it being a
 (pure) exit node problem.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21394#comment:20>
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