Да сложим firewall на FreeBSD-то

# sysinstall

Configure > Distributions > src > base + sys

# cd /usr/src/sys/i386/conf
# cp GENERIC MYKERNEL

Добавете в MYKERNEL:

options IPFIREWALL
options IPFIREWALL_VERBOSE

След това:

# cd /usr/src
# make buildkernel KERNCONF=MYKERNEL
# make installkernel KERNCONF=MYKERNEL

Добавете в /etc/rc.conf

firewall_enable="YES"
firewall_type="OPEN"

Рестарт!