Learning by ListeningA Great Life Lesson

When Fred sends a frame, the frame contains Fred's MAC address (0200.1111.1111) in the source address field of the Ethernet header. The switch knows that the MAC address of whoever sent the frame should be in the source address field. So, the switch believes MAC address 0200.1111.1111 is connected to the port in which the switch received the frameport E0 in this case. The switch simply adds 0200.1111.1111 to the MAC address table, and it associates port E0 with that MAC address.

When Barney sends a frame, the switch learns Barney's MAC address (0200.2222.2222) by looking at the source address of the frame that Barney sent. The switch associates that MAC address with port E1 because that's the port in which the frame was received.