A2.4 Network security: notes and practice

What you need to know

Our summary of the topic in our own words, not the IB guide. Points marked HL are for Higher Level only.

• Explain what a firewall does and where it sits in a network
• Evaluate how effective a firewall is, including what it cannot protect against
• Describe common network attacks including DoS and DDoS, man in the middle, phishing, malware, SQL injection and cross-site scriptingHL
• Describe vulnerabilities that arise from weak authentication, unpatched software and insecure protocolsHL
• Identify which vulnerability a described incident exploitedHL
• Describe technical countermeasures including encrypted protocols, input validation, multi-factor authentication, VPNs, intrusion detection and prevention systems, and patchingHL
• Describe procedural countermeasures including password policy, staff training and security testingHL
• Recommend a layered set of countermeasures for a described threat and justify each layerHL
• Explain what encryption does and distinguish plaintext from ciphertext
• Compare symmetric and asymmetric encryption, including the key distribution problem
• Explain what a digital certificate is and how it establishes identity in an HTTPS connection

Practice questions

Original questions written for the 2027 course, marked as you go. Easiest first.

• What a firewall can and cannot stopWritten · Stretch
• Symmetric and asymmetric encryption comparedWritten · Stretch
• Phishing attack and layered defencesWritten · Stretch

Exam tips for A2.4

• Say what a firewall cannot stop as well as what it can. Evaluation questions reward both sides.
• For symmetric and asymmetric encryption, explain the key distribution problem in one or two sentences.
• Match each countermeasure to a specific threat instead of listing defences in general.