How to Configure Ubuntu Firewall with UFW

Introduction

A firewall is a security system for networks that monitors all incoming and outgoing traffic. It permits or blocks data packets based on predefined security rules.

If you are running a production system, it is vital for you to understand how to configure a firewall. Firewall-protected systems are less likely to get infected by harmful information because they are less exposed to the Internet, as incoming and outgoing traffic is strictly filtered according to the security rules.

What is UFW?

UFW, also called the Uncomplicated Firewall, is a front-end framework that provides a simple interface for using the iptables utility to manage netfilter – a default Linux kernel packet filtering system. It is a built-in firewall system for Ubuntu 20.04 that simplifies complicated iptables commands and allows you to create basic firewall configurations more easily.

UFW uses a command-line interface with a small number of simple commands. It supports all the basic firewall rules, various network protocols, logging, and many more features. You may check an extensive list of features in the official UFW documentation.

How to Configure Ubuntu Firewall with UFW – step sy step

Prerequisites

To configure UFW, you need to have the following:

• Ubuntu 20.04 system with root privileges
• Basic knowledge of the command-line interface (CLI)

Note: This tutorial is applicable to Ubuntu 20.04 and other LTS versions. Early versions of UFW have been available since Ubuntu 12.04.

Install UFW Firewall

UFW comes pre-installed with the Ubuntu operating system. However, you can make sure that you have the latest version by running:

sudo apt install ufw

After installation, check the status of UFW with:

ufw status

By default, UFW is inactive. We will enable it after making some important changes.

UFW Default Firewall Policies

When starting with UFW, it’s a good idea to double-check the default firewall policies. View the default configuration file of UFW:

sudo nano /etc/default/ufw

By default, UFW is configured to deny all incoming traffic and allow all outgoing traffic. This means no one can reach your system, but your system can make outgoing requests. Change the default UFW policies with:

ufw default <policy> <chain>

For example, to allow all incoming traffic:

ufw default allow incoming

To deny all outgoing traffic:

ufw default deny outgoing

Allow SSH Connections

By default, UFW blocks all incoming traffic, including SSH. If you enable UFW without setting an SSH exception, you’ll be locked out. To allow SSH connections:

ufw allow ssh

If SSH uses another port (e.g., 4422), allow it with:

ufw allow 4422/tcp

Enable UFW Firewall

To enable UFW, run:

ufw enable

This will immediately start UFW and enable it on system startup. Confirm it’s running with:

systemctl status ufw

Add UFW Firewall Rules

UFW supports various rules:

• allow: allow traffic
• deny: silently discard traffic
• reject: reject traffic and send an error packet
• limit: limit connections from a specific IP after multiple attempts

To apply a rule:

ufw [rule] [target]

For incoming or outgoing traffic specifically:

ufw [rule] in [target]
ufw [rule] out [target]

Target Application Profiles

Applications that rely on the network often register their profile with UFW. Check registered applications with:

ufw app list

Allow an application’s access:

ufw allow [App name]

For instance, allow OpenSSH:

ufw allow OpenSSH

For added security, use the limit rule for OpenSSH:

ufw limit OpenSSH

Target IP Addresses

To allow or deny a specific IP address:

ufw [rule] from [ip_address]

For example, block IP 192.168.100.20:

ufw deny from 192.168.100.20

If needed, use prepend to prioritize specific rules:

ufw prepend deny from 192.168.100.20

Target Ports

To allow connections to port 8080:

ufw allow 8080

For a specific protocol:

ufw allow 8080/tcp

To allow a range of ports:

ufw allow 8080:9090/tcp

Target Network Interfaces

To target a specific network interface, first list them:

ip addr

Allow traffic only on interface eth0 from 192.168.100.255:

ufw allow in on eth0 from 192.168.100.255

Check UFW Firewall Rules

View active rules:

ufw status

For a more detailed view:

ufw status verbose

Delete UFW Firewall Rules

To delete a rule by number:

ufw status numbered
ufw delete [number]

To delete a rule by name:

ufw delete deny from 192.168.100.20

Manage UFW Logs

Check logging status:

ufw status verbose

Set UFW Logging Level

UFW logging levels:

• off – disables logging
• low – logs blocked packets
• medium – logs more data
• high and full – logs all data

Change logging level:

ufw logging [level]

Understand UFW Logs

UFW logs are stored in /var/log/. View them with:

less /var/log/ufw.log

Reset UFW Configuration

To reset UFW configuration:

ufw reset

Conclusion

Now you know how to set up and manage UFW on Ubuntu 20.04. For more details, refer to the official Ubuntu documentation.