Firewall definition in Cybersecurity

A firewall is a network security device that monitors incoming and outgoing network traffic and permits or blocks data packets based on a set of security rules. Its purpose is to establish a barrier between your internal network and incoming traffic from external sources (such as the internet) to block malicious traffic like viruses and hackers.

Open source solutions:

1. pfSense: A free, open source firewall and router platform that also includes features like VPN and content filtering.
2. iptables: A flexible firewall utility built for Linux operating systems.

Paying solutions

1. Cisco ASA: Offers a comprehensive suite of network security features, from basic firewall capabilities to advanced VPN services.
2. Palo Alto Networks: Provides a range of firewall solutions that include advanced threat protection, URL filtering, and application firewall services.