[tor-bugs] #21506 [Core Tor/Tor]: Client with current microdesc consensus but no descriptors chooses down fallback every time

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#21506: Client with current microdesc consensus but no descriptors chooses down
fallback every time
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     Reporter:  teor          |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: unspecified
    Component:  Core Tor/Tor  |    Version:  Tor: 0.2.8.1-alpha
     Severity:  Normal        |   Keywords:  ipv6, tor-client
Actual Points:                |  Parent ID:
       Points:  1             |   Reviewer:
      Sponsor:                |
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 Tor 0.2.9.9 doesn't have the fix for a similar issue in #20996, but
 0.3.0.2-alpha does.

 But this issue is different from that issue: the client downloads the
 consensus, then tries the same fallback (a down fallback) every time.

 This really shouldn't happen: the client should choose a different relay
 every time.

 My guess is that this relay is chosen because it's down, and all the up
 relay descriptors are unavailable. This is pathological behaviour.

 I think we fixed it in 0.3.0.2-alpha with the patch to #20996, but I'm
 logging this bug just in case.

 http://pastebin.ca/3769463

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21506>
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