How to configure Iptables firewall in linux - mode basic

The followed config is basic, allow all traffic outgoing and block all traffic incoming what not be local.

 
Create file with extension .sh or anyone.

# touch /root/firewall.sh

Required grants permission the executed with.

# chmod +x /root/firewall.sh


Append the next contend  the file /root/firewall.sh.

# nano /root/firewall.sh

"""

#!/bin/bash

#Reset policy all rules.
iptables -F
iptables -X
iptables -Z
iptables -t nat -F

# Set policy default, allow all traffic.
iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -t nat -P PREROUTING ACCEPT
iptables -t nat -P POSTROUTING ACCEPT

#Set allow full access to LOCAL HOST
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

# Set allow input response de input Related or Established.
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

# Drop all port listen
iptables -A INPUT -j DROP

"""

Save file with Control + O. 

The followed config allow traffic incoming to ssh, mysql and nginx.


"""

#!/bin/bash

#Reset policy all rules.
iptables -F
iptables -X
iptables -Z
iptables -t nat -F

# Set policy default, allow all.
iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -t nat -P PREROUTING ACCEPT
iptables -t nat -P POSTROUTING ACCEPT

#Set allow full access to LOCAL HOST
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

# Set allow input response de input Related or Established.
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

# Set allow full access to one ip for traffic incoming.
iptables -A INPUT -s 8.8.8.8/32 -j ACCEPT

# Set open port incoming only  for SSH.
iptables -A INPUT -p tcp --dport 22 -j ACCEPT

# Set open port for traffic incoming in one line, allow http, https, mysql.

iptables -A INPUT -p tcp -m tcp -m multiport --dports 80,443,3306 -j ACCEPT


# Drop all port listen
iptables -A INPUT -j DROP

"""


For activate rules we must  run the next command.

# sh /root/firewall.sh

Check rules with.

# iptables -L