[CentOS] DNS lookup delay with centos & postfix

[Les Mikesell]

On Wed, Jul 25, 2012 at 4:25 PM, Dennis Jacobfeuerborn
<dennisml at conversis.de> wrote:
> On 07/25/2012 10:57 PM, Steve Lindemann wrote:
>> I'm a bit baffled by this and I'm looking for ideas...
>>
>> background:
>> two DNS servers (ns1 & ns2)(64bit CentOS 5.8)
>> one email server (64bit CentOS 5.8 & postfix 2.3.3)
>> one nagios server (64bit CentOS 5.8 & nagios 3.3.1)
>>
>> situation:
>> - all servers configured to use both DNS servers for lookups
>> - ns1 server down for hardware problem
>> - nagios alerts that smtp on email server taking longer than 2 seconds
>> to respond
>> - nagios alert for smtp on email server clears when ns1 returns to service
>>
>> - when I use dig from the email server command line there is no problem
>> or delay when ns1 is offline.  It worked without a hitch using ns2.
>>
>> Anyone have any ideas for why nagios would have trouble testing smtp on
>> the email server when the primary dns goes offline?  I'm not even sure
>> where to look or who else would make sense to ask the question of on
>> this one.  I'd appreciate any insight anyone out there has on this.
>>
>
> The default timeout for a DNS lookup is usually 5 seconds so the system
> will try ns1, time out after 5 seconds and then use ns2.
>

Yes, a delay is normal when the 1st dns server is down.   You might
want to run a caching nameserver on your email server (and perhaps
others) so you don't wait for cached addresses.  The caching servers
can use the main ones as forwarders if necessary.

-- 
   Les Mikesell
     lesmikesell at gmail.com