Firewalls act as barriers between trusted internal networks and untrusted external networks, filtering traffic to prevent unauthorized access and attacks.
Types of firewalls
- Packet-filtering: Inspects packets against basic rules (IP, port, protocol).
- Stateful inspection: Tracks connection states for context-aware filtering.
- Application-layer: Deep packet inspection at the application level (Layer 7).
- Next-generation (NGFW): Combines traditional filtering with IPS, malware detection, and application awareness.
- Web application firewall (WAF): Protects web apps from HTTP-based attacks.
Why it matters
- First line of defense against network-based attacks and unauthorized access.
- Reduces attack surface by blocking unused ports and services.
- Provides segmentation between network zones (DMZ, internal, external).
- Required for compliance with PCI DSS, HIPAA, and other frameworks.
Implementation best practices
- Deploy in layers: perimeter firewalls, internal segmentation, host-based firewalls.
- Follow least-privilege principles: deny by default, allow only necessary traffic.
- Regularly review and audit firewall rules to remove outdated entries.
- Enable logging and monitoring for security event correlation.
- Keep firmware updated and test rule changes in staging environments.
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