A router is a network device that forwards data between different networks by examining packet headers, specifically the IP address information contained in Layer 3 (Network Layer) of the OSI model. According to the CompTIA A+ Core 1 (220-1201) networking objectives, routers use routing tables and packet header analysis to determine the best path for data to travel from a source network to a destination network. When a packet arrives at a router interface, the router reads the destination IP address in the packet header, compares it against its routing table, and then forwards the packet to the appropriate next hop or network interface. This function allows routers to connect multiple networks such as LANs, WANs, and the internet.

The other options do not perform this function. A hub operates at Layer 1 (Physical Layer) and simply broadcasts incoming signals to all connected ports without inspecting any packet information. A repeater also operates at the physical layer and is used only to regenerate or amplify signals to extend network distance. An unmanaged switch operates mainly at Layer 2 (Data Link Layer) and forwards frames based on MAC addresses, not IP packet headers. Because only routers analyze packet headers and forward traffic between different networks, Router is the correct answer.