Cisco Certified Network Associate (CCNA) Practice Exam

How do switches determine where MAC addresses are located within a LAN?

1. Associate the destination port and MAC address upon frame reception

2. Flood all ports if a MAC address is not known

3. Map source MAC addresses using a signaling protocol

4. Look at the source MAC address and the port number used

The correct answer is: Look at the source MAC address and the port number used

Switches determine the location of MAC addresses within a Local Area Network (LAN) by examining the source MAC address and the associated port number when they receive frames. When a frame arrives at a switch, it includes a source MAC address that identifies the device sending the frame. The switch records this MAC address in its MAC address table along with the port through which the frame was received. This mapping process enables the switch to learn which devices are reachable through which ports. As the switch builds this MAC address table over time, it can efficiently forward frames to the correct destination port rather than broadcasting the traffic to all ports, which would increase network congestion. This process effectively enhances the efficiency of the network's operation by ensuring that data frames reach their intended destinations without unnecessary flooding. In contrast, flooding occurs when the switch does not yet have an entry for a particular MAC address in its table, resulting in sending the frame out of all ports. However, this is a backup mechanism rather than the primary method of determining where MAC addresses are located. Other options involve signaling protocols or methods that are not typically used by switches to map MAC addresses. Thus, the approach of looking at the source MAC address along with the port used is fundamental to how switches manage MAC addresses in a