Network & Systems Security

Defense in Depth · Firewalls · VPNs · IDS/IPS · Zero Trust

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How to defend machines and networks in depth — firewalls, segmentation, VPNs, IDS/IPS, and the zero-trust model that replaces blind perimeter trust.

By the end, you can

Explain defense in depth and name the five layers in order from perimeter to logging.
Distinguish stateless packet filter, stateful firewall, and NGFW by what each inspects.
Describe what a DMZ is and why it limits the blast radius of a compromised public server.
Explain how a VPN tunnel protects traffic in transit and contrast site-to-site with remote-access VPN.
Contrast IDS and IPS by their placement and what action each can take on malicious traffic.
Compare signature-based and anomaly-based detection, including each method's key weakness.
Describe how ARP poisoning and DNS spoofing create a man-in-the-middle, and name the defenses.
Explain how a scrubbing center mitigates a DDoS flood.
Articulate why castle-and-moat fails against insider threats and lateral movement.
State the zero-trust principle and identify least privilege, microsegmentation, and SIEM as its pillars.

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