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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Try wireshark/tcpdump to see which DNS queries goes to which server and wheter DNS server replies back .<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">You can also try dig, nslookup and couple of other cmoomd line tools form:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><a href="http://serverfault.com/questions/7056/whats-the-reverse-dns-command-line-utility/7088#7088">http://serverfault.com/questions/7056/whats-the-reverse-dns-command-line-utility/7088#7088</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Linux-il [mailto:linux-il-bounces@cs.huji.ac.il]
<b>On Behalf Of </b>Gabor Szabo<br>
<b>Sent:</b> Sunday, March 22, 2015 1:14 PM<br>
<b>To:</b> guy keren<br>
<b>Cc:</b> linux-il<br>
<b>Subject:</b> Re: Server stopped DNS name resolution<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I tried that, and although I am not sure what should I look for in there it seems to be claiming<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">rt_sigsuspend([];; connection timed out; no servers could be reached<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><o:p> </o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">I tried to telnet 72.14.179.5 53 (one of the DNS servers) and that did not got a response.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><o:p> </o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Anyway, Linode support told me to add this to the resolve.conf<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#333333;background:#F4F4FF">nameserver 8.8.8.8</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#333333;background:#F4F4FF">nameserver 8.8.4.4</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">and that seemed to do the trick.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Gabor<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Sun, Mar 22, 2015 at 1:00 PM, guy keren <<a href="mailto:guy.choo.keren@gmail.com" target="_blank">guy.choo.keren@gmail.com</a>> wrote:<o:p></o:p></p>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt">
<p class="MsoNormal"><br>
run this on the host:<br>
<br>
strace host <a href="http://www.google.com" target="_blank">www.google.com</a><br>
<br>
and scan the output.<br>
<br>
more efficient then guessing.<br>
<br>
--guy<br>
<br>
On 03/22/2015 12:50 PM, Gabor Szabo wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Hi,<br>
<br>
I run an Ubuntu based VPS on Linode.<br>
I few hours ago the machine stopped resolving hostnames.<br>
I think it was after an "aptitude safe-upgrade" and a reboot, but I am<br>
not sure. Maybe was like this earlier.<br>
<br>
It takes ages to ssh to it, once I got to the machine I can ping IP<br>
addresses from it, but I cannot ping anything with a hostname.<br>
<br>
this is what I have in resolv.conf<br>
<br>
# cat /etc/resolv.conf<br>
<br>
domain <a href="http://members.linode.com" target="_blank">members.linode.com</a> <<a href="http://members.linode.com" target="_blank">http://members.linode.com</a>><br>
<br>
search <a href="http://members.linode.com" target="_blank">members.linode.com</a> <<a href="http://members.linode.com" target="_blank">http://members.linode.com</a>><br>
<br>
nameserver 72.14.179.5<br>
<br>
nameserver 72.14.188.5<br>
<br>
options rotate<br>
<br>
<br>
I tried to replace the nameservers with others that are listed in<br>
another of my servers, but that did not make a change.<br>
<br>
How can I track down what has the server stopped resolving hostnames?<br>
<br>
Accessing the server via HTTP work as expected.<br>
<br>
Gabor<br>
<br>
<o:p></o:p></p>
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