What happens when a switch receives a frame with a destination MAC address that it does not recognize?

When a switch receives a frame with a destination MAC address that it does not recognize, it will flood the frame out all switch ports except the port on which it received the frame. This is done in order to locate the device associated with that unknown MAC address. The switch maintains a MAC address table that maps MAC addresses to specific ports based on the frames it has previously processed. If the switch has not yet learned the destination MAC address, flooding helps ensure that the frame can reach its intended destination if that device is connected to one of the other switch ports.

This behavior is essential for switching functionality, as it allows for dynamic learning of devices on the network. Once the unknown device responds or sends a frame back, the switch will learn its MAC address and update its MAC address table accordingly. This enables the switch to send future frames destined for that MAC address directly to the correct port, optimizing network performance.