How does MAC learning work on a switch?

MAC learning is a fundamental function of a switch. When a switch receives a frame, it examines the source MAC address. If this MAC address is not already in its MAC address table, the switch adds it along with the port number on which the frame was received. This process allows the switch to build a table of MAC addresses and their corresponding ports, enabling efficient forwarding of future frames directly to the intended destination port. "Protects against denial-of-service attacks" is incorrect; while security features exist, MAC learning's primary role isn't DoS protection. "Sends frames with unknown destinations to a multicast group" is incorrect; frames with unknown destination MACs are flooded out all ports except the ingress port, not sent to a multicast group. "Sends a retransmission request when a new frame is received" is incorrect; retransmission is typically handled at higher layers (e.g., TCP) or by the sending device if an acknowledgment is not received, not by the switch upon receiving a new frame.