Create custom Discovery rule check

[silvan78]

While Discovery allows me to find out machines with certain ports open (or responding to ping), it fails to detect entirely firewalled hosts. For this occasion would like to use arp pinging, preferably using nmap:

nmap -sn -n -PR {$IP}

While it's relatively easy to do for a defined host, adding a custom check to network discovery rule eludes me. There are only predefined check types deeply embeded in Zabbix code (0 - SSH; 1 - LDAP; 2 - SMTP; 3 - FTP; 4 - HTTP; 5 - POP; etc..), but no clear method to add a new one.

Where should i start?