When a switch receives a frame with an unknown source MAC, what action does it take?

When a switch receives a frame, it examines the source MAC address. If this MAC address is not already present in its MAC address table (also known as the CAM table), the switch learns it. It associates the source MAC address with the specific port (ingress port) on which the frame was received and adds this entry to its MAC address table. This process is fundamental to how switches build their forwarding tables and efficiently direct future traffic. Incorrect options: Flooding the frame out all interfaces (including the ingress port) is what a switch does when it receives a frame with an unknown destination MAC address, not an unknown source MAC. Sending the frame to ports identified with an unknown source MAC in the CAM table is not a standard switch operation; the switch learns new source MACs rather than forwarding based on an "unknown source" entry. Switches do not send frames back to the source to verify MAC addresses; they passively learn them from incoming traffic.