Server stopped DNS name resolution

[Amos Shapira]

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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