Which device is designed to block unauthorized network access?

A firewall is a security device specifically designed to monitor and control incoming and outgoing network traffic based on predetermined security rules. Its primary function is to create a barrier between a trusted internal network and untrusted external networks, such as the Internet. By doing so, it helps to prevent unauthorized access and cyber threats, while still allowing legitimate traffic to flow through.

Firewalls can operate in both hardware and software forms and can include features such as packet filtering, stateful inspection, and proxy services. They are essential components in network security architecture and provide organizations with the ability to protect sensitive data and maintain the integrity of their networks.

In contrast, a router primarily directs data between different networks and does not inherently block unauthorized access without additional configurations or security features. A switch, on the other hand, connects devices within the same network and efficiently manages the data flow, but it does not provide security functions like a firewall. A modem serves as a bridge between the Internet and a home or office network, translating digital data from a computer into the analog signal needed to transmit over telephone lines or cable systems; it does not provide access control features.