A firewall is a security device or software application that acts as a barrier between a private network and external networks, such as the internet, to control and monitor the incoming and outgoing network traffic. Its primary purpose is to enforce a set of rules or policies to allow or block specific data packets based on predetermined criteria.
The main functions of a firewall include:
Packet filtering: Examining individual data packets and determining whether to permit or block them based on predefined rules. These rules can be based on criteria like source and destination IP addresses, port numbers, protocol types, and more.
Stateful inspection: Tracking the state of active connections and allowing only legitimate traffic that matches established connections while blocking unauthorized or potentially malicious connection attempts.
Application-level filtering: Analyzing the data within the packets at the application layer (Layer 7 of the OSI model) to filter specific types of traffic or to enforce more sophisticated security policies.
Proxy service: Acting as an intermediary between the internal network and the external network, forwarding requests from internal clients and then forwarding the external responses back to the clients. This helps to hide the internal network’s details and enhances security.
Firewalls are an essential component of network security, as they help protect the internal network from unauthorized access, data breaches, and various cyber threats, such as hacking attempts, malware, and denial-of-service (DoS) attacks. They are widely used in both home networks and large enterprise environments to create a secure perimeter and regulate network traffic according to security policies set by network administrators.