Which device is commonly used to prevent unauthorized access to a network?

A firewall is specifically designed to protect a network by controlling incoming and outgoing traffic based on predetermined security rules. It acts as a barrier between a trusted network and untrusted networks, such as the internet. By inspecting the data packets that attempt to enter or leave the network, a firewall can block or allow traffic based on the established security policies, thereby preventing unauthorized access.

Firewalls can be hardware-based, software-based, or a combination of both, and they are essential for protecting sensitive information from attackers or unauthorized users. This capability to enforce security policies is what makes firewalls a crucial component in network security architecture.

In contrast, devices like modems facilitate internet connections, switches manage data traffic within a local network by connecting devices, and routers direct data packets between different networks but do not inherently provide the same level of access control that firewalls do.