[tor-bugs] #21969 [Core Tor/Tor]: We're missing descriptors for some of our primary entry guards

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#21969: We're missing descriptors for some of our primary entry guards
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 Reporter:  asn           |          Owner:
     Type:  defect        |         Status:  new
 Priority:  High          |      Milestone:  Tor: 0.3.1.x-final
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:  tor-guard     |  Actual Points:
Parent ID:                |         Points:  1.5
 Reviewer:                |        Sponsor:  SponsorU
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Comment (by catalyst):

 I have noticed a few problems that I think are likely related.

 I attached a log of a failed bootstrap with obfs4.  (Tor Browser 7.0a3
 with defaults obfs4 bridge configuration)  It appears to have gotten stuck
 because none of the selected guards was reachable when trying to download
 the consensus.  (The guards look like they are selected prior to
 determining their reachability, which I vaguely recall is a countermeasure
 against some kinds of attacks, but is potentially a usability problem
 during bootstrap.)

 Note that two of the guards have the same fingerprint
 (`A832D176ECD5C7C6B58825AE22FC4C90FA249637`), and seem to be multiple
 ports on the same IP according to the TBB-generated torrc.  Maybe we
 should prevent this during guard selection?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21969#comment:6>
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