What action does a switch take when it encounters a frame with an unknown destination MAC address?

When a switch encounters a frame with an unknown destination MAC address, it floods the frame to all ports in the same VLAN except for the port on which the frame was received. This flooding occurs because the switch does not have the destination MAC address in its MAC address table, which is essential for making forwarding decisions. By sending the frame out to all ports, the switch allows devices on the network to respond, and in the process, it may learn the MAC address of the destination device if it is present on the network. Once the destination device responds, the switch can update its MAC address table with the new address and the corresponding port, allowing for more efficient forwarding of future frames addressed to that MAC address. This behavior is fundamental to how switches build their MAC address tables and manage communication on a local area network.