A firewall enforces the oldest question in security—who do you trust?—at network speed, examining millions of packets per second against the rules you've written.
A firewall processes rules from top to bottom and stops at the first match. That single principle—first match wins—explains nearly everything about how firewalls make split-second security decisions.
Every packet faces a gauntlet of questions. The order you ask them—and the default answer when none match—determines whether your network stays secure or silently fails open.
A stateless firewall checks every packet but remembers nothing—it can't tell a legitimate reply from an attack. Stateful firewalls changed everything by remembering which conversations you started.
Default allow protects you from threats you know about. Default deny protects you from threats you don't. This choice determines whether your firewall is a security tool or a false sense of security.
Firewalls don't just guard a single door—they manage territories with different trust levels, deciding what can cross each boundary and why.
Hardware and software firewalls aren't different things—they're the same protection deployed at different vantage points. Understanding where each sits and what it can see is the key to layered security.
Firewalls make thousands of decisions per second. Their logs tell the story of every attack attempt, every blocked threat, every suspicious pattern. Learn to read what your firewall is trying to tell you.
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