Firewall:

Firewall is a network security system that monitors and controls the incoming and outgoing network traffic based on predefined rules. It typically establishes a barrier between a trusted network and an untrusted network. A firewall can be a software firewall, hardware firewall, or both.

Firewalls in Linux:

The famous firewalls in linux are:

• Iptables

• Uncomplicated Firewall (UFW)

UFW:

UFW stands for Uncomplicated Firewall. It is a front-end-framework that provides a simple interface for using iptables utility to manage netfilter. UFW uses a command-line interface with a small number of simple commands.

• Install UFW:

  To install UFW sudo apt install ufw is used.

• Check Status:

  To check the status of UFW sudo ufw status is used.

• Enable UFW:

  To enable UFW, sudo ufw enable is used.

• Disable UFW:

  To disable UFW, sudo ufw disable is used.

• Check UFW Configuration File:

  To check the configuration file of UFW, sudo nano /etc/default/ufw is used.

• Allow Incoming Traffic:

  By default UFW is configured to deny all incoming traffic. To allow incoming traffic sudo ufw default allow incoming is used.

• Deny Incoming Traffic:

  To deny incoming traffic sudo ufw default deny incoming is used.

• Deny Outgoing Traffic:

  By default UFW is configured to allow all outgoing traffic. To deny outgoing traffic sudo ufw default deny outgoing is used.

• Allow Outgoing Traffic:

  To allow outgoing traffic sudo ufw default allow outgoing is used.

• Allow SSH Connections:

1. By Service:

   To allow incoming SSH connections by service sudo ufw allow ssh is used.

1. By Port Number:

   To allow incoming SSH connections by port number sudo ufw allow 22 is used.

   

• Deny SSH Connections:

1. By Service:

   To deny incoming SSH connections by service sudo ufw deny ssh is used.

1. By Port Number:

   To deny incoming SSH connections by port number sudo ufw deny 22 is used.

   

• View the Application List:

  To view the application list sudo ufw app list is used.

• View the Added Rules:

  To view the added rules sudo ufw show added is used.

  

• Allow HTTP Connections:

1. By Service:

   To enable HTTP traffic by service sudo ufw allow http is used.

1. By Port Number:

   To enable HTTP traffic by port number sudo ufw allow 80 is used.

   

• Deny HTTP Connections:

1. By Service:

   To disable HTTP traffic by service sudo ufw deny http is used.

1. By Port Number:

   To disable HTTP traffic by port number sudo ufw deny 80 is used.

   

• Allow HTTPS Connections:

1. By Service:

   To enable HTTPS traffic by service sudo ufw allow https is used.

1. By Port Number:

   To enable HTTPS traffic by port number sudo ufw allow 443 is used.

   

• Deny HTTPS Connections:

1. By Service:

   To disable HTTPS traffic by service sudo ufw deny https is used.

1. By Port Number:

   To disable HTTPS traffic by port number sudo ufw deny 443 is used.

   

• Allow Port Ranges:

  To allow port ranges sudo ufw allow [start-port]:[end-port]/[ptotocol] is used.

• Deny Port Ranges:

  To deny port ranges sudo ufw deny [start-port]:[end-port]/[protocol] is used.

• Allow IP Address:

  To allow IP address sudo ufw allow from [IP-address] is used.

• Deny IP Address:

  To deny IP address sudo ufw deny from [IP-address] is used.

• Delete UFW Firewall Rules:

1. Delete by Number:

   To delete a UFW rule by number, first check a numbered list of UFW rules using sudo ufw status numbered .

   

   Then delete the rule number using sudo ufw delete [rule-number] .

1. Delete by Rule Name:

   To delete a UFW rule by rule name, first list the UFW rules by using sudo ufw show added .

   

   Then delete the rule name using sudo ufw delete [rule-name] .