Following is a general definition of the technology that lays behind DNSMonitor.
There are a handful of important fields:
Following is the documentation from the nagios version of the same implementation, which Zennos’s is based off of. Very similar functionality and provides some more detailed descriptions.
$ $ZENHOME/libexec/check_dns --help check_dns (nagios-plugins 1.4.5) 1.54 This plugin uses the nslookup program to obtain the IP address for the given host/domain query. An optional DNS server to use may be specified. If no DNS server is specified, the default server(s) specified in /etc/resolv.conf will be used. Usage:check_dns -H host [-s server] [-a expected-address] [-A] [-t timeout] [-w warn] [-c crit] Options: -h, --help Print detailed help screen -V, --version Print version information -H, --hostname=HOST The name or address you want to query -s, --server=HOST Optional DNS server you want to use for the lookup -a, --expected-address=IP-ADDRESS|HOST Optional IP-ADDRESS you expect the DNS server to return. HOST must end with . -A, --expect-authority Optionally expect the DNS server to be authoritative for the lookup -w, --warning=seconds Return warning if elapsed time exceeds value. Default off -c, --critical=seconds Return critical if elapsed time exceeds value. Default off -t, --timeout=INTEGER Seconds before connection times out (default: 10)