こんな感じ

gistfile1.txt

iptables -F
iptables -X
iptables -Z

iptables -P INPUT   DROP   # 受信はすべて破棄
iptables -P OUTPUT  ACCEPT # 送信はすべて許可
iptables -P FORWARD DROP   # 通過はすべて破棄

iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT

iptables -A INPUT -p tcp -m conntrack --ctstate NEW --dport 80 -j ACCEPT  # http
iptables -A INPUT -p tcp -m conntrack --ctstate NEW --dport 22 -j ACCEPT  # ssh