Learning Objectives

By the end of this chapter, you should be able to:

• Explain what a firewall is and why it is essential.
• Understand how firewalls inspect and control network traffic.
• Differentiate between stateful and stateless firewalls.
• Distinguish between network firewalls and host-based firewalls.
• Understand packet filtering and firewall rules.
• Compare Linux firewalls (iptables, nftables, ufw, and firewalld).
• Explain AWS Security Groups and Network ACLs.
• Troubleshoot common firewall-related connectivity problems.

Introduction

Imagine an office building with valuable company information.

At the entrance is a professional security guard.

Every person who wants to enter or leave the building must pass through the guard.

The guard checks:

• Who the visitor is.
• Where they are going.
• Whether they have permission.
• Whether they are carrying anything suspicious.