[tor-bugs] #11600 [Tor]: Strange nameserver fail warning in Tor log

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#11600: Strange nameserver fail warning in Tor log
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 Reporter:  s7r                 |          Owner:
     Type:  defect              |         Status:  new
 Priority:  Medium              |      Milestone:  Tor: 0.2.???
Component:  Tor                 |        Version:  Tor: 0.2.6.10
 Severity:  Normal              |     Resolution:
 Keywords:  eventdns, libevent  |  Actual Points:
Parent ID:                      |         Points:
  Sponsor:                      |
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Changes (by hdqdak8v32aor):

 * severity:   => Normal


Comment:

 Became concerned awhile back that even the brief time in state

 `All nameservers have failed`

 is harmful.  Reviewed the code and determined that when only one
 nameserver is configured nothing happens as a consequence of the state.
 Outstanding requests complete successfully and the only effect is
 `/var/log/messages` noise.

 In the case where multiple nameservers are active, outstanding resolver
 requests on the path where the `Bad response 5` appears are cancelled /
 ignored and resubmitted to a different name server.  Somewhat disruptive,
 especially when resolvers are remote instead of local.

 In the case where a local copy of `unbound` is running, stick with one
 `/etc/resolve.conf` entry as configuring a second will degrade
 performance.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/11600#comment:7>
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