主要的命令行如下：
Allowing Loopback Connections
sudo iptables -A INPUT -i lo -j ACCEPT
sudo iptables -A OUTPUT -o lo -j ACCEPT
Allowing Established and Related Incoming Connections
sudo iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
Allowing Established Outgoing Connections
sudo iptables -A OUTPUT -m conntrack --ctstate ESTABLISHED -j ACCEPT
Dropping Invalid Packets
sudo iptables -A INPUT -m conntrack --ctstate INVALID -j DROP
Allowing All Incoming SSH
sudo iptables -A INPUT -p tcp --dport 22 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
sudo iptables -A OUTPUT -p tcp --sport 22 -m conntrack --ctstate ESTABLISHED -j ACCEPT
Allowing Outgoing SSH
sudo iptables -A OUTPUT -p tcp --dport 22 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
sudo iptables -A INPUT -p tcp --sport 22 -m conntrack --ctstate ESTABLISHED -j ACCEPT
Allowing All Incoming HTTP
sudo iptables -A INPUT -p tcp --dport 80 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
sudo iptables -A OUTPUT -p tcp --sport 80 -m conntrack --ctstate ESTABLISHED -j ACCEPT
Allowing All Incoming HTTPS
sudo iptables -A INPUT -p tcp --dport 443 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
sudo iptables -A OUTPUT -p tcp --sport 443 -m conntrack --ctstate ESTABLISHED -j ACCEPT
Dropping Unwanted Traffic
sudo iptables -A INPUT -j DROP
