[tor-bugs] #30639 [Core Tor/Tor]: Tor tries so connect over IPv6 in IPv4 networks with ClientAutoIPv6ORPort set

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#30639: Tor tries so connect over IPv6 in IPv4 networks with ClientAutoIPv6ORPort
set
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 Reporter:  gk            |          Owner:  (none)
     Type:  defect        |         Status:  new
 Priority:  Medium        |      Milestone:
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:  tbb-wants     |  Actual Points:
Parent ID:                |         Points:
 Reviewer:                |        Sponsor:
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Comment (by teor):

 This bug is caused by an interaction between tor and Tor Browser:
 1. Tor speculatively tries IPv4 and IPv6
 2. Some of those connections fail
 3. Tor Browser sets DisableNetwork on any failure

 Here are some solutions that probably won't work:
 * we could try to auto-detect IPv4 or IPv6 addresses (#27492), but that's
 not reliable, because:
   * local addresses don't guarantee internet connectivity
   * some OSes and security configs don't allow tor to read local network
 information
 * we could downgrade the warning on the Tor side, but that might have
 unintended consequences for other applications that use tor
   * if fiddling with warning levels is our best option, we could defer the
 warning for 30? seconds, and cancel the pending warning if another tor
 connection succeeds

 Here's a solution that would work, but we need to schedule it in tor's
 roadmap:
 * we could implement a proper "happy eyeballs" style connection design in
 tor, where we always choose an IPv4 and IPv6 address for every connection,
 try both, and use the first one that works

 Here's a fix that Tor Browser should implement anyway:
 * stop setting DisableNetwork on tor's first connection failure, because
 tor's next connection attempt might work

 Here's a quick fix that restores the previous behaviour (and re-opens
 #29641):
 * revert the change that added ClientAutoIPv6ORPort to Tor Browser alpha

 Let me know how you'd like to move forward, and what you need the network
 team to do.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/30639#comment:3>
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