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