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. -- Steve
Does dig use libresolv or read directly from resolv.conf? Also do you have a timeout configured in resolv.conf or are you relying on the os default? On 25 Jul 2012, at 21:57, Steve Lindemann <steve at marmot.org> 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. > -- > Steve > _______________________________________________ > CentOS mailing list > CentOS at centos.org > http://lists.centos.org/mailman/listinfo/centos
Dennis Jacobfeuerborn
2012-Jul-25 21:25 UTC
[CentOS] DNS lookup delay with centos & postfix
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. Regards, Dennis
On 07/25/12 1:57 PM, Steve Lindemann wrote:> 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.DNS lookups default to using 53/udp, and only use 53/tcp for zone transfers. could it be 53/udp is being lost/blocked between this host and your ns1 ? -- john r pierce N 37, W 122 santa cruz ca mid-left coast