A switch floods ports if it does not know where to send a packet.

• A. True
• B. False
• C. It drops the packet
• D. It sends to a random port

Answer: (A)

When a switch handles a frame, it builds a MAC address table by recording the source MAC address and the port it came from. If the destination MAC isn’t yet in that table, the switch can’t know which single port leads to the target host. To make sure the frame still reaches its destination, it floods the frame out all ports in the same VLAN except the incoming port. This guarantees delivery to the unknown host, and once the destination responds, the switch learns which port that host is on for future frames, so they can be sent directly. Dropping the frame or sending it to a random port would fail to reach the destination, so flooding is the correct behavior.