When a network device sends data to a physical hub, the hub broadcasts the data out of all its ports except the one it received the data on. This is because a hub is a simple device that operates at the OSI Layer 1 (Physical Layer) and does not perform any filtering or addressing. Contrastingly, a network switch, which operates at OSI Layer 2 (Data Link Layer), forwards data only to the specific destination port after examining the data's MAC address. A router, on the other hand, operates at OSI Layer 3 (Network Layer) and routes data based on IP addresses.