# default policy to drop
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP

 # allow loopback
iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -o lo -j ACCEPT

 # allow SSH from internal network
iptables -A INPUT -p tcp -s 192.168.0.0/24 --destination-port 22 -j ACCEPT

 # drop traffic, for sure
iptables -A INPUT -j DROP
iptables -A OUTPUT -j DROP