Firewall
A firewall filters traffic between networks based on rules and inspection.
Updated: 2026-03-05
Definition
A firewall is a security device or software that enforces rules about what network traffic is allowed between zones.
Firewalls can be stateful, perform deep packet inspection, and enforce application-level policies.
Key points
- Rule-based filtering between zones
- Stateful inspection tracks connections
- NGFW adds application awareness and IPS features
Common mistakes
- Using overly broad rules (any/any).
- No logging/alerting on critical denies/allows.
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