Which device is essential for connecting multiple computers within a local network?

A switch is essential for connecting multiple computers within a local network because it operates at the data link layer of the OSI model, managing data traffic effectively between devices on the same local area network (LAN). The primary function of a switch is to receive incoming data packets and redirect them to their destination on the network, allowing multiple devices to communicate with each other. This facilitates data sharing, resource access, and collaboration among the connected computers.

In contrast, a router connects different networks, directing data packets between them and allowing access to external networks, such as the internet. A firewall serves to protect the network by filtering traffic based on predetermined security rules; it does not connect devices within a local network. A modem modulates and demodulates signals for internet access but is not directly involved in connecting computers within a local network.

Thus, in a typical local network setup, the switch plays a crucial role in enabling communication amongst devices, making it the key component for this specific function.