[CentOS] Slow domain resolution problem
Gabriel Tabares
gabriel.tabares at roboreus.com
Mon Aug 23 15:03:01 UTC 2010
On 23/08/2010 14:48, Giles Coochey wrote:
> On Mon, August 23, 2010 15:43, Gabriel Tabares wrote:
>
>> On 23/08/2010 13:28, Joseph L. Casale wrote:
>>
>>>> Both files are the default ones from CentOS:
>>>>
>>>>
>>> So what do the host names look like that the application
>>> attempts to resolve, fully qualified or not? What does your
>>> cli based query look like?
>>>
>>>
>>>
>> My resolv.conf is:
>>
>> search mydomain.com
>> nameserver 10.3.2.2
>>
>> The hostname of the machines is set to a FQDN server.mydomain.com.
>>
>> The time it takes for the queries does not change whether we use the
>> FQDN or just the hostname.
>>
>> See below for an example (I stopped the mail server so the connection
>> was refused).
>>
>>
> The problems can sometimes be caused by not having reverse-DNS records for
> your hosts. Can you resolve to names (any name) from an IP address?
> e.g. nslookup 10.2.9.2?
>
> It doesn't matter if it doesn't resolve to the rigt name, just that it
> resolves to something (and avoids the timeout)...
>
>
They don't resolve to anything:
Server: 10.2.2.254
Address: 10.2.2.254#53
Non-authoritative answer:
*** Can't find 2.9.2.10.in-addr.arpa.: No answer
Authoritative answers can be found from:
>> #time telnet md-mail02.mydomain.com 25
>> (long wait)
>> Trying 10.2.9.2...
>> telnet: connect to address 10.2.9.2: Connection refused
>> telnet: Unable to connect to remote host: Connection refused
>>
>> real 0m20.005s
>> user 0m0.000s
>> sys 0m0.005s
>>
>> #time telnet md-mail02 25
>> (long wait)
>> Trying 10.2.9.2...
>> telnet: connect to address 10.2.9.2: Connection refused
>> telnet: Unable to connect to remote host: Connection refused
>>
>> real 0m10.004s
>> user 0m0.001s
>> sys 0m0.002s
>>
>> #time telnet 10.2.9.2 25
>> (no wait)
>> Trying 10.2.9.2...
>> telnet: connect to address 10.2.9.2: Connection refused
>> telnet: Unable to connect to remote host: Connection refused
>>
>> real 0m0.005s
>> user 0m0.001s
>> sys 0m0.002s
>>
>> Nslookup responds immediately:
>>
>> #time nslookup my-mail02.mydomain.com
>> Server: 10.2.2.254
>> Address: 10.2.2.254#53
>>
>> Non-authoritative answer:
>> Name: my-mail02.mydomain.com
>> Address: 10.2.9.2
>>
>>
>> real 0m0.006s
>> user 0m0.003s
>> sys 0m0.003s
>>
>> #time nslookup my-mail02
>> Server: 10.2.2.254
>> Address: 10.2.2.254#53
>>
>> Non-authoritative answer:
>> Name: my-mail02.mydomain.com
>> Address: 10.2.9.2
>>
>>
>>
>
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