A network security device that monitors incoming and outgoing network traffic and determine whether to allow or block that traffic.
It can be implemented in software, hardware or a combination.
Types
Packet filtering firewall
Operates at Layer 3 (Network) and Layer 4 (Transport) of the The OSI Model and filters Packets based on their:
- source/destination IP Address
- source/destination Port
- Protocol
Stateful inspection firewall
Tracks the state of network connections and filter packets based on context, e.g. only allow inbound data from already established outbound requests.
Application layer (proxy) firewall
Operates at level 7 (application layer) of the The OSI Model to inspect content of traffic and block content that looks malicious.
Next-generation firewall
Combines stateful inspection with advanced features like deep packet inspection, intrusion detection/prevention, and application control.