Quick Answer
The correct answer is encrypting data at rest, as it represents a critical layer of defense that protects sensitive information even if an attacker bypasses network or system controls. Encryption renders data unreadable without the proper decryption key, ensuring that a breach of physical storage or a compromised server does not automatically expose the underlying data. On the ISC2 Certified in Cybersecurity CC exam, this concept tests your understanding that defense in depth relies on overlapping, independent controls—not just a single solution. A common trap is assuming only perimeter tools like firewalls count, but true layered security includes administrative, physical, and technical controls across all stages. Remember the mnemonic “PIE” for Physical, Infrastructure, and Endpoint controls to recall that encryption at rest falls under endpoint and data security layers.
This CC practice question tests your understanding of security principles. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which THREE of the following are examples of implementing defense in depth? (Select THREE.)
Enabling single sign-on for all applications
Why wrong: SSO reduces authentication layers.
Using a firewall to filter traffic
Correct. Firewall is a layer.
Allowing all traffic by default
Why wrong: Default allow removes a layer.
Implementing access control lists
Correct. ACLs provide granular control.
Encrypting data at rest
Correct. Encryption adds a layer.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Using a firewall to filter traffic
Option B is correct because a firewall is a fundamental component of defense in depth, providing network-level traffic filtering based on rules. It acts as a first line of defense by blocking unauthorized access and malicious traffic, thereby reducing the attack surface. This layered security approach ensures that even if other controls fail, the firewall can still prevent or mitigate threats.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Enabling single sign-on for all applications
Why it's wrong here
SSO reduces authentication layers.
Using a firewall to filter traffic
Why this is correct
Correct. Firewall is a layer.
Related concept
Read the scenario before looking for a memorised answer.
Allowing all traffic by default
Why it's wrong here
Default allow removes a layer.
Implementing access control lists
Why this is correct
Correct. ACLs provide granular control.
Related concept
Read the scenario before looking for a memorised answer.
Encrypting data at rest
Why this is correct
Correct. Encryption adds a layer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
ISC2 often tests the concept that defense in depth requires multiple independent layers of security, so candidates mistakenly select options that improve convenience (like SSO) or violate security principles (like allowing all traffic) instead of recognizing that each correct option adds a distinct security control at a different layer.
Detailed technical explanation
Defense in depth relies on multiple, overlapping security controls at different layers (network, host, application, data). For example, a firewall (Layer 3/4) filters traffic, while access control lists (ACLs) on routers or switches provide additional packet filtering based on source/destination IP and port. Encrypting data at rest (e.g., using AES-256 for storage) ensures that even if an attacker bypasses network and host controls, the data remains unreadable. In a real-world scenario, a web application might use a WAF (Layer 7), a network firewall (Layer 3/4), and database encryption (data layer) to protect against SQL injection and data breaches.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
What to study next
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FAQ
Security Principles — This question tests Security Principles — Read the scenario before looking for a memorised answer..
The correct answer is: Using a firewall to filter traffic — Option B is correct because a firewall is a fundamental component of defense in depth, providing network-level traffic filtering based on rules. It acts as a first line of defense by blocking unauthorized access and malicious traffic, thereby reducing the attack surface. This layered security approach ensures that even if other controls fail, the firewall can still prevent or mitigate threats.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This CC practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CC exam.
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