Which device operates at layer 2 and makes forwarding decisions based on MAC addresses?

• A. Switch
• B. Router
• C. Hub
• D. Bridge

Answer: (A)

In the data link layer, forwarding decisions are based on MAC addresses. A switch is the device built for this purpose: it learns which MAC addresses can be reached through which ports by inspecting the source MAC of frames as they arrive. It stores this in a MAC address table and uses it to forward frames only to the port where the destination device is reachable, flooding only if the destination is unknown. This per-port forwarding provides efficient, scalable traffic isolation for Ethernet networks.

A router operates at the network layer and makes decisions using IP addresses, not MACs. A hub operates at the physical layer and simply repeats signals to all ports, spreading traffic everywhere. A bridge also works at layer 2, but switches are the more common, higher-port-count, higher-performance devices used today for MAC-based forwarding, which is why the switch is the best fit for this function.