[tor-bugs] #17840 [Tor]: Add a minimal implementation of ClientUseIPv4 so IPv6-only clients can bootstrap

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#17840: Add a minimal implementation of ClientUseIPv4 so IPv6-only clients can
bootstrap
--------------------+------------------------------------
 Reporter:  teor    |          Owner:  teor
     Type:  defect  |         Status:  needs_revision
 Priority:  Medium  |      Milestone:  Tor: 0.2.8.x-final
Component:  Tor     |        Version:
 Severity:  Normal  |     Resolution:
 Keywords:  ipv6    |  Actual Points:
Parent ID:  #17811  |         Points:
  Sponsor:          |
--------------------+------------------------------------
Changes (by teor):

 * status:  needs_review => needs_revision


Comment:

 Testing on IPv6-only configs shows that we're still picking directory
 guards which only have IPv4 addresses. (Oops!)

 This issue only manifests itself the *second* time we download the
 consensus. (The first time, we download from the authorities, and that
 works, because we select authorities with IPv6 addresses. The second time,
 we use directory guards, and some of the ones we select are IPv4-only.)

 This should be easy to fix, I bet there's a fascist_firewall_* check
 missing in the directory guard selection code. (It's the weekend here now,
 and christmas next week, so it might take a little while.)

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17840#comment:3>
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