A firewall is a network security system that filters incoming and outgoing traffic. It sits between your network and the internet, deciding what to let through and what to block. Think of it as a security guard at a building entrance. It checks IDs. It keeps a list. It turns away anyone not on it.

Firewalls can be hardware, software, or both. A home router usually has a basic firewall. Enterprises use advanced firewalls that inspect packets, detect intrusions, and manage thousands of rules. Cloud firewalls protect virtual networks and workloads.

Types of firewalls

• Packet filtering: checks headers against rules
• Stateful inspection: tracks active connections
• Proxy: mediates traffic between networks
• Next-generation: adds deep packet inspection and threat intelligence

Firewalls are necessary but not sufficient. They do not stop phishing emails or stolen passwords. They do not protect against insider threats. Security requires layers. A firewall is one layer among many.