Which of the following mechanisms helps prevent unauthorized access to a network?

Firewalls play a critical role in network security by acting as a barrier between a trusted internal network and untrusted external networks. Their primary function is to monitor and control incoming and outgoing network traffic based on predetermined security rules. By doing so, firewalls can block unauthorized access to the network while allowing legitimate traffic to pass through, thereby safeguarding sensitive data and preventing malicious attacks.

Moreover, firewalls can provide features such as packet filtering, stateful inspection, and proxy services, which enhance their ability to prevent unauthorized access. They can be hardware-based or software-based and can be configured to limit access to specific ports or protocols, making them essential for maintaining network integrity.

While data encryption, cloud storage solutions, and backup systems are important for protecting data, managing storage, and ensuring data recovery in case of loss, they do not serve the specific purpose of controlling unauthorized access to a network like firewalls do. These other mechanisms complement network security but primarily focus on protecting data rather than restricting access at the network perimeter.