monitor pfSense with nagios

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http://serverfault.com – I have pFsense machine and one nagios(NagiosXI) installed machine. On pfSense machine DHCP server is running. i want to monitor pfSense i.e DHCP status, interface through nagios using SNMP. I have add pfSense in Nagios and it is showing CPU usage,swap,memory etc. i want to know who do i monitor interface, what is the status of DHCP and also i have written rules what request is coming from outside..? (HowTos)