Firewalls and Penetration Testing

Firewalls and penetration testing are two essential components of network security. Firewalls act as a barrier between trusted and untrusted networks, while penetration testing proactively identifies vulnerabilities before attackers can exploit them. This lesson covers both topics in the depth required for GCSE Computer Science.

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What Is a Firewall?

A firewall is a security device (hardware, software or both) that monitors and controls incoming and outgoing network traffic based on a set of predetermined security rules. It acts as a barrier between a trusted internal network and untrusted external networks (such as the internet).

How a Firewall Works

1. Every piece of data travelling across a network is broken into packets
2. Each packet has a header containing information such as the source IP address, destination IP address, port number and protocol
3. The firewall examines each packet against its rule set
4. Packets that match an allow rule are permitted through
5. Packets that match a deny rule are blocked (dropped)
6. Packets that match no rule are handled by the default policy (usually deny)

Firewall Rules Example