🔥 Firewall Configuration and Traffic Filtering

🎯 Objective

To configure and test basic firewall rules to allow or block network traffic and understand how firewall rules control network access.

🛠️ Tools Used

• UFW (Uncomplicated Firewall) – Firewall management tool on Linux
• Ubuntu 22.04 – Operating system
• Terminal – Used to execute firewall commands

📋 Task Overview

The goal of this task was to configure and test firewall rules on a Linux system using UFW.

The practical focused on:

• Checking the firewall status
• Enabling UFW
• Listing existing firewall rules
• Blocking inbound traffic on a specific port
• Testing the firewall rule
• Allowing SSH traffic
• Removing the test block rule
• Documenting the firewall commands and results

🔧 Step-by-Step Execution

1. Check Firewall Status

The UFW firewall status was checked using:

sudo ufw status

UFW was initially disabled, so it was enabled using:

sudo ufw enable

2. List Current Firewall Rules

The current firewall configuration was checked using:

sudo ufw status

The output initially showed no specific rules for ports 23 or 22.

3. Block Inbound Traffic on Port 23

Port 23, commonly associated with Telnet, was blocked using:

sudo ufw deny 23/tcp

The rule was verified using:

sudo ufw status

Example output:

To                         Action      From
--                         ------      ----
23/tcp                     DENY        Anywhere
23/tcp (v6)                DENY        Anywhere (v6)

4. Test the Firewall Rule

A Telnet connection to port 23 was attempted from another machine:

telnet <linux-machine-ip> 23

The connection was refused, confirming that the configured firewall rule blocked the traffic.

5. Allow SSH Traffic on Port 22

SSH traffic was allowed using:

sudo ufw allow 22/tcp

The firewall configuration was then verified using:

sudo ufw status

Example output:

To                         Action      From
--                         ------      ----
23/tcp                     DENY        Anywhere
22/tcp                     ALLOW       Anywhere
23/tcp (v6)                DENY        Anywhere (v6)
22/tcp (v6)                ALLOW       Anywhere (v6)

6. Remove the Test Block Rule

After completing the test, the temporary Telnet block rule was removed using:

sudo ufw delete deny 23/tcp

The firewall status was checked again:

sudo ufw status

The final configuration retained the SSH rule.

💻 Commands Used

sudo ufw enable
sudo ufw status
sudo ufw deny 23/tcp
sudo ufw allow 22/tcp
sudo ufw delete deny 23/tcp

🧠 How a Firewall Filters Traffic

A firewall filters network traffic by evaluating incoming and outgoing connections against predefined rules.

In this practical:

• The deny 23/tcp rule blocked inbound TCP traffic on port 23.
• The allow 22/tcp rule permitted inbound TCP traffic on port 22.
• UFW provided a simplified interface for managing Linux firewall rules.

📚 Key Concepts Demonstrated

• Firewall configuration
• Network traffic filtering
• Inbound traffic control
• Port-based firewall rules
• UFW
• Linux security
• Telnet and SSH ports
• Firewall rule testing
• Security configuration

📌 Outcome

This practical demonstrated how to configure and test firewall rules on a Linux system using UFW.

The exercise provided hands-on experience with blocking and allowing specific network traffic, testing firewall behavior, and restoring the firewall configuration after testing.

⚠️ Ethical Use

This practical is intended for educational and cybersecurity learning purposes.

Firewall configuration and security testing should only be performed on systems and networks where you have appropriate authorization.

👩‍💻 Author

Jahnavi Pokala

• GitHub: jahnavi9905
• LinkedIn: Jahnavi Pokala