The firewall has as its primary responsibility the regulation of network traffic flow based on different trust levels for different computers or networks. In the network diagram shown in the exhibit, a firewall protects the network from unauthorized access attempts. A firewall can be implemented in hardware or software. Firewalls permit, deny, or filter data packets coming into and going out of the network. This helps prevent unauthorized access attempts from outside the network.

The primary function of a router is to perform routing between two subnets or between dissimilar network technologies. Routers can provide limited firewall functionality, but a firewall is a dedicated hardware or software solution with the primary responsibility of securing the network. A router does not have as its primary responsibility the regulation of network traffic flow based on different trust levels.

Switches work at Layer 2 in the Open System Interconnection (OSI) model and perform the function of separating collision domains. A switch does not have as its primary responsibility the regulation of network traffic flow based on different trust levels.

A hub is a device that provides a common connection point for network devices. The primary responsibility of a hub is not to regulate network traffic flow based on different trust levels.