The purpose of a firewall in a computer network is to protect systems from unauthorized access and cyber threats. Acting as a barrier between trusted internal networks and untrusted external networks, firewalls monitor and control incoming and outgoing traffic. They use predefined security rules to allow or block data packets based on various criteria, such as IP addresses, ports, and protocols. Firewalls can be hardware-based, software-based, or a combination of both. By preventing unauthorized access and filtering harmful traffic, firewalls are essential for maintaining network security and safeguarding sensitive information.