🔍 What Is Defense in Depth?

Defense in Depth is a cybersecurity strategy that uses multiple layers of protection to safeguard systems, data, and networks. Instead of relying on a single security measure, it combines technical, physical, and administrative controls to reduce risk and delay or prevent attacks.

🧠 Think of it like a medieval castle: moats, walls, guards, and towers — each layer adds resilience.

🧱 Core Layers of Defense

Layer	Description
🔐 Perimeter Security	Firewalls, intrusion detection/prevention systems (IDS/IPS)
🧬 Network Segmentation	Isolating sensitive systems to limit lateral movement
🧑‍💻 Access Controls	Role-based access, MFA, least privilege
🧼 Endpoint Protection	Antivirus, EDR, patch management
📦 Application Security	Secure coding, input validation, WAFs
🗄️ Data Protection	Encryption, backups, DLP
📜 Policies & Training	Security awareness, incident response plans

🔄 Why Layers Matter

Why not just one layer?

• Attackers often bypass single defenses.
• Layers slow down intrusions, giving defenders time to respond.
• Each layer compensates for weaknesses in others.

🧰 Real-World Example

🧠 A phishing email bypasses spam filters and reaches an employee. They click the link — but endpoint protection blocks the malware. Even if it didn’t, network segmentation would prevent it from reaching critical systems.

📌 Best Practices

• ✅ Implement MFA across all access points
• ✅ Regularly patch and update systems
• ✅ Train staff on phishing and social engineering
• ✅ Monitor logs and set up alerts
• ✅ Test incident response plans