The main purpose of a firewall in a computer network is to act as a barrier that monitors and controls incoming and outgoing network traffic based on predetermined security rules. By allowing or blocking data packets, a firewall helps prevent unauthorized access to the network and protects sensitive information from cyber threats. Firewalls can be hardware-based, software-based, or a combination of both, and they play a crucial role in establishing a layered security approach. Their effective implementation is vital for maintaining the integrity and confidentiality of organizational data.