What happens to all frames received through a switch port when there are no learned unicast entries in the bridge table?

When a switch port receives frames and there are no learned unicast entries in the bridge table, the switch does not know the specific destination for those frames. In this scenario, the appropriate action taken by the switch is to flood the frames out of all other switch ports that belong to the same VLAN. This behavior is essential for ensuring that the frames can reach their intended destination, especially when the destination MAC address is unknown.

Flooding allows the switch to deliver the frames to all devices within the same VLAN, increasing the chance that the intended recipient will receive the frame. As devices respond and the switch learns their MAC addresses, these entries will be added to the bridge table for future reference, allowing for more efficient unicast transmission rather than flooding. This mechanism is fundamental to the operation of Ethernet switches, facilitating communication on a local area network when the destination is initially unknown.