iptables

iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD ACCEPT

# drop과 whitelist의 순서를 바꿔야지 네트웍에서 안 끊어진다.

# init
iptables -F
iptables -X
iptables -Z

# allow whitelist
iptables -A INPUT -i eth0 -p tcp -m tcp --dport 22 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp -m tcp --sport 22 -j ACCEPT

iptables -A INPUT -i lo -j ACCEPT 

iptables -A OUTPUT -o lo -j ACCEPT

#all drop
iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP

service iptables save
service iptables restart