Following is a general definition of the technology that lays behind DNSMonitor.

• DNSMonitor users the nslookup command
  • nslookup sends queries to Internet domain name servers. It is used to display the name and requested information for a host or domain.

There are a handful of important fields:

• hostname
  • The domain name or url you want to query
• dnsServer
  • DNS server you want to use for the lookup
• expectedIPAddress
  • the IP you expect the hostname to resolve to
• severity
  • the severity of an event, if thrown
• cycle time
  • how often the domain is checked

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)