Which device is primarily used to connect multiple devices within the same network?

The primary function of a switch is to connect multiple devices within the same local area network (LAN). It operates at the data link layer (Layer 2) of the OSI model, using MAC addresses to forward data to the correct device on the network. This allows for efficient communication among connected devices, such as computers, printers, and servers, facilitating data transfer without unnecessary broadcasting.

In contrast, a router connects different networks and directs data between them, often providing features like NAT and DHCP. A modem is responsible for converting digital signals to analog for transmission over telephone lines or cable systems and vice versa, allowing internet connectivity rather than local device communication. A firewall provides security by monitoring and controlling incoming and outgoing network traffic based on predetermined security rules, thus playing a different role in network management and safety.

The switch's specific purpose of creating a network infrastructure that enables multiple devices to communicate is what makes it the correct answer in this scenario.