Which device primarily forwards frames within a LAN using MAC addresses?

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

Answer: (D)

Frames are forwarded inside a LAN by using MAC addresses at the local switching layer. A switch learns which MAC addresses are reachable on which ports by inspecting the source MAC of every frame it receives. It then builds a MAC address table mapping each device’s MAC to the port where that device is connected. When a frame needs to be sent, the switch looks up the destination MAC in this table and forwards the frame only to the port that leads to that device. If the destination MAC isn’t known yet, the switch floods the frame to all ports except the one it came from, until it learns the correct path.

This behavior makes switching efficient for intra-LAN communication, reducing unnecessary traffic and collisions. A hub simply repeats every frame to all ports, causing lots of wasted bandwidth. A bridge also uses MAC addresses but is typically used to connect two segments and doesn’t scale as well as a multiport switch. A router moves data between networks using IP addresses, not for forwarding frames within a single LAN.