Why does a switch flood a frame to all ports?
A. The frame has zero destination MAC addresses.
B. The destination MAC address of the frame is unknown.
C. The source MAC address of the frame is unknown
D. The source and destination MAC addresses of the frame are the same.
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Highlighted answer is incorrect
C is incorrect. Switches “learn” based on the Source Mac Address but make forwarding decisions based on the destination Mac Address (discovered during the learning process). When the switch receives a frame dedicated for a particular destination but that destination does not have an entry in the MAC Address Table, the switch has no choice but to flood the frame. The goal of this flood is that the device using the MAC address in the destination of the frame will receive the flood and respond to the message.
B is the correct answer.