[CentOS] Slow domain resolution problem

[Gabriel Tabares]

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).

#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


real    0m0.005s
user    0m0.001s
sys     0m0.004s