Ref: http://www.nagiosexchange.org/cgi-bin/page.cgi?g=Detailed%2F1948.html;d=1

NOTE: May require installation of additional perl modules.

I renamed the check to "check_ns_servers" on my install to be a little more obvious as to its function.  After several DNS hosting provider outages which would manifest a wide array of errors over odd periods of time thanks to DNS caching, I wanted a Nagios plugin to check to make sure our DNS was working correctly.  Sure there is "check_dns" which I also use to check the resolution of a name to correct IP, but I wanted something a bit more powerful.

"check_dns_secondary" will query for the name servers of the provided domain.  Each NS server is queried individually for the SOA record of the domain.  An error is generated if any server is not functioning, or not authoritative.  A warning is generated if any server lags the others in serial-number.