Firewalls
Definition
A firewall is a security control that inspects network traffic and enforces policy to allow or block connections between networks or hosts.
Examples
- A home router blocks unsolicited inbound traffic from the internet while allowing devices inside the house to browse the web.
- An enterprise perimeter firewall only permits HTTPS and DNS from staff networks to the internet and blocks remote desktop ports.
Overview
Firewalls act as traffic gatekeepers. They sit at boundaries between networks or security zones and decide which packets may pass based on defined rules. Early firewalls focused on IP addresses, ports, and protocols; modern platforms add deep inspection, application and user awareness, and security services such as intrusion prevention and anti-malware. Deployed correctly, firewalls reduce attack surface, enforce least privilege for network access, and contain incidents by preventing lateral movement.
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