When a switch does not know the destination port for a frame, what action is typically taken?

• A. Floods all ports
• B. Drops the frame
• C. Sends to the uplink port only
• D. Sends to a single random port

Answer: (A)

Switches forward frames using a MAC address table that maps devices to their ports. When a frame arrives, the switch notes the source MAC and the port it came from. If the destination MAC is already in the table, the switch sends the frame only to the specific port connected to that device. If the destination MAC isn’t yet known, the switch can’t pick one port, so it floods the frame out all active ports in the same VLAN (except the incoming port). This guarantees delivery and also helps the switch learn the correct port for that destination when the host replies. Flooding stays within the VLAN and won’t cross into other segments unless routing is involved. It’s not dropped, and it isn’t limited to just the uplink or a random port.