[CentOS] DNS lookup delay with centos & postfix

Wed Jul 25 21:31:26 UTC 2012
Les Mikesell <lesmikesell at gmail.com>

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