Most attacks travel across networks, so controlling that traffic is fundamental. This reuses your Networking Fundamentals knowledge.
How a Firewall Evaluates Traffic
Ordered rules, first match wins, everything else denied.
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Src/dst IP, port, protocol.
Every packet arriving at the firewall carries a source and destination IP, a port and a protocol. The firewall checks it against an ordered rule list to decide allow or deny.
Check your understanding
1. How are firewall rules evaluated?
2. What does a default-deny policy do?
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Core controls
- Firewalls enforce a default-deny policy — only explicitly permitted traffic passes.
- Segmentation divides the network into zones so a breach in one area can't reach everything (a zero-trust idea in practice).
Why Networks Are Segmented
From one flat network to isolated zones with controlled crossings.
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One big zone.
In a flat network every device sits in one broadcast domain. It's simple, but a single compromised device can reach everything — one breach spreads freely.
Check your understanding
1. What is the main security benefit of segmentation?
2. How is traffic between segments controlled?
Keep learning
- VPNs protect data in transit for remote access; IDS/IPS detect and block malicious patterns.
Secure design combines these into defence in depth, feeding the Security Engineer role and Security+.