Which combination exemplifies a defense-in-depth approach?

• A. Firewall + intrusion detection + endpoint protection + access control
• B. Firewall alone
• C. Antivirus alone
• D. User education only

Answer: (A)

Defense in depth means using multiple security controls across different layers so that if one layer fails or is bypassed, others still provide protection. The combination of a firewall, intrusion detection capability, endpoint protection, and access control covers different parts of the system and different kinds of threats. The firewall helps block unauthorized network access at the perimeter. An intrusion detection system adds monitoring to catch suspicious activity that slips through or originates inside the network. Endpoint protection guards individual devices from malware and exploits, even if traffic gets past the network boundary. Access control enforces who can do what, reducing the risk of misuse or unauthorized actions.

Together, these layers create redundancy and complementary protection. If the firewall misses something, the IDS can flag it; if something reaches a device, endpoint protection can stop it; and strict access control limits what infected or compromised accounts can do. Relying on a single control—like just a firewall or just antivirus—leaves gaps that attackers can exploit, whereas education alone addresses behavior but not technical breaches. This multi-layer approach is the essence of defense in depth.