[tor-bugs] #23817 [Core Tor/Tor]: Tor re-tries directory mirrors that it knows are missing microdescriptors

[Tor Bug Tracker & Wiki]

#23817: Tor re-tries directory mirrors that it knows are missing microdescriptors
------------------------------+----------------------------------------
     Reporter:  teor          |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.3.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  tor-guard, tor-hs, prop224
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
------------------------------+----------------------------------------
 When a microdescriptor for a relay changes, it takes a while to propagate
 to directory mirrors. In this time, a client can:
 1. Download a consensus that references the new microdescriptor
 2. Try a directory mirror that has an older consensus, and therefore
 doesn't have that microdescriptor
 3. Repeat 2

 This is a particular issue when:
 * the client first bootstraps, and the fallback or authority provides a
 newer consensus than any of its directory mirrors
 * the client has been asleep for a while, and its consensus has expired,
 so it fetches one straight away
 * only 1/3 of a client's directory guards has the new consensus

 We can fix this by:
 * making clients try the same directory mirror for their consensus and
 microdescriptors
 * making clients avoid directory mirrors with missing microdescriptors
 * making clients use a fallback when all of their directory mirrors don't
 have a microdescriptor

 This issue affects primary guards and v3 onion services.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23817>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online