Which Layer 2 device forwards Ethernet frames using MAC addresses and builds a MAC address table by listening to traffic?

Which Layer 2 device forwards Ethernet frames using MAC addresses and builds a MAC address table by listening to traffic?

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

Answer: (A)

Layer 2 forwarding uses MAC addresses to decide where frames go, and the device learns where those MACs live by listening to traffic. A switch does this best: as frames arrive on a port, it notes the source MAC and the port in a MAC address table, so when a frame with a known destination MAC comes in, the switch can send it only to the correct port. If the destination isn’t in the table yet, it floods the frame to all ports in the same collision domain, then as replies come back, it learns the mapping. This dynamic learning and selective forwarding is what makes a switch efficient at Layer 2. A hub, by contrast, just repeats every signal to all ports without learning anything, so it can’t build a MAC table. A router operates at Layer 3 and forwards based on IP addresses, not MACs. A bridge also uses MAC addresses and learns a MAC table, but a switch is essentially a many-port bridge with higher performance and scale, which is why the described behavior points to the switch.

Layer 2 forwarding uses MAC addresses to decide where frames go, and the device learns where those MACs live by listening to traffic. A switch does this best: as frames arrive on a port, it notes the source MAC and the port in a MAC address table, so when a frame with a known destination MAC comes in, the switch can send it only to the correct port. If the destination isn’t in the table yet, it floods the frame to all ports in the same collision domain, then as replies come back, it learns the mapping. This dynamic learning and selective forwarding is what makes a switch efficient at Layer 2.

A hub, by contrast, just repeats every signal to all ports without learning anything, so it can’t build a MAC table. A router operates at Layer 3 and forwards based on IP addresses, not MACs. A bridge also uses MAC addresses and learns a MAC table, but a switch is essentially a many-port bridge with higher performance and scale, which is why the described behavior points to the switch.