Configure firewall

Updated on: 5.Dec.2020

To speed up the firewall setup, best is to rely on ufw (uncomplicated firewall) which is a program that will handle the low level configuration in iptables for you.

With UFW

• To install,   
  

  sudo apt install ufw

• To check daemon status

  sudo systemctl status ufw

• To view the rules

  sudo ufw status

 

OR with the rule number:

 

  sudo ufw status numbered

• Update the firewall policies,

 sudo ufw allow ssh

 sudo ufw allow http

 sudo ufw allow https

• Finally, to enable the ufw 

  sudo ufw enable

• There is a convenient way to add the ports by adding the app   
  

  sudo ufw app list

Then, 

  sudo ufw allow 'Nginx Full'
  sudo ufw allow 'OpenSSH'

With iptables

If you want to handle the low level configuration, you will have to use iptables.

       To view the rules in the firewall (where ‘-L’ is list all and ‘-n’ is skip checking with DNS server):

                   sudo iptables -L -n

       To block ip address from accessing the server, add a rule to the firewall:

                   sudo iptables -A INPUT -j DROP -s 192.168.1.200

       To remove the rule

                   sudo iptables -D INPUT -j DROP -s 192.168.1.200

      NOTE: don’t forget to call “sudo iptables-persistent save” to save the changes.

Reference
http://www.cyberciti.biz/faq/how-do-i-block-an-ip-on-my-linux-server/
https://help.ubuntu.com/community/IptablesHowTo

To save the firewall rules (prevent the rules lost after server restart), run the following commands. If you are using fail2ban program, try not to install this.

       Use the addon => iptables-persistent

                   sudo apt-get install iptables-persistent

       To save the rules:

                   sudo /etc/init.d/iptables-persistent save

       To reload the rules:

                   sudo /etc/init.d/iptables-persistent reload

       The rules are stored in :

                   /etc/iptables/rules.v4

Reference:
http://askubuntu.com/questions/119393/how-to-save-rules-of-the-iptables