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

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#23817: Tor re-tries directory mirrors that it knows are missing microdescriptors
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 Reporter:  teor                        |          Owner:  (none)
     Type:  defect                      |         Status:  new
 Priority:  Medium                      |      Milestone:  Tor:
                                        |  0.3.3.x-final
Component:  Core Tor/Tor                |        Version:
 Severity:  Normal                      |     Resolution:
 Keywords:  tor-guard, tor-hs, prop224  |  Actual Points:
Parent ID:  #21969                      |         Points:
 Reviewer:                              |        Sponsor:
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Comment (by asn):

 I'm inlining some logs demonstrating this issue for completeness.

 Tor failed to fetch the md with hash
 `AGkG6zefrl7Uvkqo+nfCI1fDbxjvSyzsNS5TiWa0JeU`.
 Tor's dirguards are:

  1. 79.137.112.5
  1. 54.36.38.63
  1. 86.105.212.130

 Here are some logs demonstrating the issue:

 {{{
 Oct 25 16:10:10.000 [warn] Received answer to microdescriptor request
 (status 200, body size 254796) from server '79.137.112.5:443'
 Oct 25 16:10:10.000 [warn] Initially requested 500 mds, got 495, missed 5
 Oct 25 16:10:10.000 [warn] AGkG6zefrl7Uvkqo+nfCI1fDbxjvSyzsNS5TiWa0JeU
 failed 1 time(s); I'll try again in 1 seconds.
 ...
 Oct 25 16:10:11.000 [warn] Received answer to microdescriptor request
 (status 404, body size 0) from server '79.137.112.5:443'
 Oct 25 16:10:11.000 [warn] AGkG6zefrl7Uvkqo+nfCI1fDbxjvSyzsNS5TiWa0JeU
 failed 2 time(s); I'll try again in 3 seconds.
 ...
 Oct 25 16:10:15.000 [warn] Received answer to microdescriptor request
 (status 404, body size 0) from server '79.137.112.5:443'
 Oct 25 16:10:15.000 [warn] AGkG6zefrl7Uvkqo+nfCI1fDbxjvSyzsNS5TiWa0JeU
 failed 3 time(s); I'll try again in 9 seconds.
 ...
 Oct 25 16:11:15.000 [warn] Received answer to microdescriptor request
 (status 200, body size 5182) from server '54.36.38.63:443'
 Oct 25 16:11:15.000 [warn] AGkG6zefrl7Uvkqo+nfCI1fDbxjvSyzsNS5TiWa0JeU
 failed 4 time(s); I'll try again in 15 seconds.
 ...
 Oct 25 16:12:15.000 [warn] Received answer to microdescriptor request
 (status 404, body size 0) from server '54.36.38.63:443'
 Oct 25 16:12:15.000 [warn] AGkG6zefrl7Uvkqo+nfCI1fDbxjvSyzsNS5TiWa0JeU
 failed 5 time(s); I'll try again in 38 seconds.
 ...
 Oct 25 16:13:15.000 [warn] Sent request to directory server
 '86.105.212.130:443': (purpose: 19, request size: 1123, payload size: 0)
 Oct 25 16:13:16.000 [warn] Received answer to microdescriptor request
 (status 200, body size 10713) from server '86.105.212.130:443'
 }}}


 We basically see Tor failing to fetch the same md from `79.137.112.5:443`
 three times within 2 minutes, and then it fails to fetch from
 `54.36.38.63:443` another two times within 2 minutes, until it tries
 `86.105.212.130` which succeeds (that dircache is probably more up-to-date
 than the other two).

 If a fail cache was in place, we would have gone to `86.105.212.130` on
 our third try, instead of our sixth.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23817#comment:5>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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