[CentOS] DNS lookup delay with centos & postfix

Wed Jul 25 21:25:05 UTC 2012
Dennis Jacobfeuerborn <dennisml at conversis.de>

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.