AQA 8525 · Section 3.5 · Networks

Network
Security

Firewalls · Encryption · Authentication · MAC Filtering

CSZoneAQA GCSE Computer Science 8525

Network Threats

What Networks Need to Defend Against

Unauthorised access — hackers gaining entry to the network or systems

Interception — data captured while in transit (man-in-the-middle attack)

DoS/DDoS — flooding a server with requests to make it unavailable

Malware — viruses, worms, trojans spread across networks

Security Measures

How Networks Are Protected

Firewall — monitors all incoming and outgoing network traffic; blocks unauthorised packets based on rules

Encryption — scrambles data so it cannot be read if intercepted (e.g. WPA2 for Wi-Fi, TLS for web)

User authentication — usernames/passwords, two-factor authentication

MAC address filtering — only devices with approved MAC addresses can join the network

WPA2/WPA3 — encryption standard for Wi-Fi. Requires a password to join the wireless network

Firewalls in Detail

Packet Filtering and Proxy Firewalls

Packet filtering firewall — examines each packet's source/destination IP and port number. Blocks packets that don't match the allow rules. Fast but basic.

Stateful inspection — tracks the state of active connections. More sophisticated — knows which packets belong to established sessions.

Note:Firewalls can be hardware (physical device) or software (installed on the OS, like Windows Firewall).

Exam Practice

Have a go at this question

AQA-style question

Describe how a firewall helps to protect a network.

2 marks

A firewall monitors all data packets entering and leaving the network [1] and blocks any packets that do not meet the configured security rules, preventing unauthorised access [1].

Key Takeaways

What to Remember

Firewall — monitors and filters network traffic using rules

Encryption — scrambles data so interceptors can't read it

Authentication — verifies identity (password, 2FA)

MAC filtering — only approved hardware addresses can connect to the network