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

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#11600: Strange nameserver fail warning in Tor log
--------------------+------------------------------------
 Reporter:  s7r     |          Owner:
     Type:  defect  |         Status:  new
 Priority:  normal  |      Milestone:  Tor: 0.2.4.x-final
Component:  Tor     |        Version:  Tor: 0.2.4.21
 Keywords:          |  Actual Points:
Parent ID:          |         Points:
--------------------+------------------------------------
 I am running an exit relay on Linux, my Tor version is 0.2.4.21

 I checked the log and found this strange warnings:
 Apr 24 15:14:07.000 [notice] Circuit handshake stats since last time:
 91698/91698 TAP, 15988/15988 NTor.
 Apr 24 17:40:45.000 [warn] eventdns: All nameservers have failed
 Apr 24 17:40:45.000 [notice] eventdns: Nameserver <ISP-resolver1>:53 is
 back up
 Apr 24 18:01:51.000 [warn] eventdns: All nameservers have failed
 Apr 24 18:01:51.000 [notice] eventdns: Nameserver <ISP-resolver2>:53 is
 back up
 Apr 24 18:01:52.000 [warn] eventdns: All nameservers have failed
 Apr 24 18:01:53.000 [notice] eventdns: Nameserver <ISP-resolver1>:53 is
 back up
 Apr 24 18:02:00.000 [warn] eventdns: All nameservers have failed
 Apr 24 18:02:01.000 [notice] eventdns: Nameserver <ISP-resolver1>:53 is
 back up
 Apr 24 18:02:01.000 [warn] eventdns: All nameservers have failed
 Apr 24 18:02:01.000 [notice] eventdns: Nameserver <ISP-resolver2>:53 is
 back up
 Apr 24 19:46:22.000 [warn] eventdns: All nameservers have failed
 Apr 24 19:46:22.000 [notice] eventdns: Nameserver <ISP-resolver2>:53 is
 back up
 Apr 24 20:46:25.000 [warn] eventdns: All nameservers have failed
 Apr 24 20:46:25.000 [notice] eventdns: Nameserver <ISP-resolver2>:53 is
 back up
 Apr 24 21:14:07.000 [notice] Heartbeat: Tor's uptime is 8 days 12:00
 hours, with 13940 circuits open. I've sent 549.49 GB and received 543.20
 GB.

 So I thought it's the fault of the nameservers provided by the ISP. Fair
 enough, I have configured my own resolver on localhost (where the relay is
 running) using BIND 9.10 (latest stable) with dnssec-validation and
 everything. I thought I fixed it. After some time, I checked the logs
 again and:
 Apr 24 23:26:03.000 [warn] eventdns: All nameservers have failed
 Apr 24 23:26:03.000 [notice] eventdns: Nameserver 127.0.0.1:53 is back up
 Apr 25 02:04:02.000 [warn] eventdns: All nameservers have failed
 Apr 25 02:04:02.000 [notice] eventdns: Nameserver 127.0.0.1:53 is back up
 Apr 25 02:04:03.000 [warn] eventdns: All nameservers have failed
 Apr 25 02:04:04.000 [notice] eventdns: Nameserver 127.0.0.1:53 is back up
 Apr 25 02:04:04.000 [warn] eventdns: All nameservers have failed
 Apr 25 02:04:05.000 [notice] eventdns: Nameserver 127.0.0.1:53 is back up
 Apr 25 02:04:06.000 [warn] eventdns: All nameservers have failed
 Apr 25 02:04:06.000 [notice] eventdns: Nameserver 127.0.0.1:53 is back up
 Apr 25 02:04:08.000 [warn] eventdns: All nameservers have failed
 Apr 25 02:04:08.000 [notice] eventdns: Nameserver 127.0.0.1:53 is back up

 Looks like its something Tor related. Why do I get this warning? Does this
 have any penalty on the performance or over the users who are using this
 node as an exit point? Should I just leave it alone as it works fine? From
 what I see nameservers fail and get back online immediately, fail and back
 on have same timestamp. Advices? Thanks in advance.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/11600>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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