Server stopped DNS name resolution

[Amos Shapira]

"Google unicast public DNS servers"

s/unicast/anycast/, I keep forgetting that term.

On 22 March 2015 at 22:28, Amos Shapira <amos.shapira at gmail.com> wrote:

> 1. Sounds like the ip's in your resolv.conf are wrong. Where does the
> server get them from? ip's 8.8.8.8 and 8.8.4.4 are the Google unicast
> public DNS servers. They are reliable but it's not optimal for a server to
> have to reach out to them on every query.
>
> 2. The ssh login is possibly slow because the ssh server is configured to
> try to reverse-resolve the incoming client ip address for logging. Look for
> "UseDNS" in your SERVER config (/etc/sshd_config). The default is usually
> "no" but perhaps in your case it's on.
>
> 3. Telnet is not a good indicator of reachability of DNS servers, DNS is
> UDP based and usually even the TCP port 53 is blocked because no one is
> supposed to have to access it. On the other hand, traceroute (yes, good old
> traceroute, as opposed to ping and tcptraceroute) uses UDP packets and you
> can tell it to use port 53 as destination so perhaps try that (again - pass
> "-n" flag to it to stop it from failing to reverse-resolve the ip address
> of each response).
>
> Good luck.
>
> On 22 March 2015 at 22:13, Gabor Szabo <gabor at szabgab.com> wrote:
>
>> I tried that, and although I am not sure what should I look for in there
>> it seems to be claiming
>>
>> rt_sigsuspend([];; connection timed out; no servers could be reached
>>
>>
>> I tried to telnet 72.14.179.5 53  (one of the DNS servers) and that did
>> not got a response.
>>
>>
>> Anyway, Linode support told me to add this to the resolve.conf
>>
>> nameserver 8.8.8.8
>>
>> nameserver 8.8.4.4
>>
>> and that seemed to do the trick.
>>
>> Gabor
>>
>> On Sun, Mar 22, 2015 at 1:00 PM, guy keren <guy.choo.keren at gmail.com>
>> wrote:
>>
>>>
>>> run this on the host:
>>>
>>> strace host www.google.com
>>>
>>> and scan the output.
>>>
>>> more efficient then guessing.
>>>
>>> --guy
>>>
>>> On 03/22/2015 12:50 PM, Gabor Szabo wrote:
>>>
>>>> Hi,
>>>>
>>>> I run an Ubuntu based VPS on Linode.
>>>> I few hours ago the machine stopped resolving hostnames.
>>>> I think it was after an "aptitude safe-upgrade" and a reboot, but I am
>>>> not sure. Maybe was like this earlier.
>>>>
>>>> It takes ages to ssh to it, once I got to the machine I can ping IP
>>>> addresses from it, but I cannot ping anything with a hostname.
>>>>
>>>> this is what I have in resolv.conf
>>>>
>>>> # cat /etc/resolv.conf
>>>>
>>>> domain members.linode.com <http://members.linode.com>
>>>>
>>>> search members.linode.com <http://members.linode.com>
>>>>
>>>> nameserver 72.14.179.5
>>>>
>>>> nameserver 72.14.188.5
>>>>
>>>> options rotate
>>>>
>>>>
>>>> I tried to replace the nameservers with others that are listed in
>>>> another of my servers, but that did not make a change.
>>>>
>>>> How can I track down what has the server stopped resolving hostnames?
>>>>
>>>> Accessing the server via HTTP work as expected.
>>>>
>>>> Gabor
>>>>
>>>>
>>>>
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>>
>>
>
>
> --
> <http://au.linkedin.com/in/gliderflyer>
>



-- 
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