The primary purpose of a firewall in networking is to protect a network from unauthorized access and potential threats. Firewalls act as a security barrier between trusted internal networks and untrusted external networks, controlling incoming and outgoing traffic based on predetermined security rules. They can be hardware or software-based, providing features such as traffic filtering, intrusion detection, and VPN support. By monitoring and regulating network traffic, firewalls help to prevent cyberattacks, data breaches, and other security incidents, thus ensuring the integrity and confidentiality of sensitive information.