When a switch receives a frame from an unknown source MAC address, which action does the switch take with the frame?

The CAM table does not identify ports with 'unknown' source MAC addresses; instead, it stores known MAC-to-port mappings, and if a MAC is unknown, it's learned, not simply identified as unknown in the table for forwarding.

Flooding occurs when a switch receives a frame destined for an unknown MAC address, not typically for learning an unknown source MAC address, though it might flood if the *destination* is unknown after learning the source.

Switches use MAC address learning to build their Content Addressable Memory (CAM) table; upon receiving a frame, the switch extracts the source MAC address and binds it to the incoming physical port, storing this mapping in the CAM table for future forwarding decisions.

A switch does not attempt to send a frame back to the source to verify its MAC address; it passively learns the source MAC from incoming frames.