FreeBSD: How to consider the traffic by means of IPFW?

[AlexWhite]

In agentd.conf I have added a line

UserParameter=inet.in,/sbin/ipfw show 150|awk '{print $3}'

After reboot agentd and run command

zabbix_get -s ip-addres -k "inet.in"

has received error

ipfw: socket: Operation not permitted

What to do?

[Klug]

Why not using SNMP ?

[AlexWhite]

To start one more service? Though can and it is necessary to start net-snmp.
But if it is started fierwall why to not use it.