Cisco Certified Network Associate (CCNA) Practice Exam

What happens when a switch does not recognize a MAC address?

1. Flood all ports with the unknown MAC address

2. Block all traffic until it verifies the address

3. Send an ARP request for the MAC address

4. Log an error and drop the packet

The correct answer is: Flood all ports with the unknown MAC address

When a switch encounters a MAC address that it does not recognize, it will flood all the ports in the same VLAN with the frame that contains the unknown MAC address. This flooding is necessary because the switch needs to ensure that the frame can reach its intended destination, even if it does not have the destination MAC address in its MAC address table. By flooding, the switch allows the device with the unknown MAC address to respond, which enables the switch to learn and record this new MAC address for future communication. This behavior is crucial for the operation of local area networks (LANs), as it ensures that devices can communicate with each other even when they are not yet recognized by the switch. Once the switch receives a response from the device with the unknown MAC address, it can update its MAC address table to include the new entry and subsequent communications to that MAC address will no longer require flooding. The other choices involve operations that do not align with a switch's functioning with unknown MAC addresses. Blocking traffic is not a typical action for a switch; it aims to facilitate communication. Sending an ARP request is specific to IP address resolution, not directly connected to MAC address learning processes. Logging an error and dropping a packet would not help in communication, as the switch is