What change is made to the MAC table aging time when a configuration BPDU is received with the Topology Change flag set?

When a configuration Bridge Protocol Data Unit (BPDU) is received with the Topology Change flag set, the MAC table aging time is decreased to 15 seconds. This adjustment is a part of the Spanning Tree Protocol (STP) designed to improve the responsiveness of the network to changes.

When a topology change occurs, the switch needs to ensure that any MAC address entries that may become stale or invalid are removed quickly. By lowering the aging time to 15 seconds, switches can rapidly clear out any MAC addresses that are no longer reachable due to the changes in the network topology. This helps to avoid forwarding frames to ports that no longer lead to the intended destinations, thereby maintaining network efficiency and reducing potential loops or conflicts caused by outdated MAC address entries.

The prompt response to topology changes minimizes the risk of sending data to the wrong ports and ensures the integrity of the switch's MAC address table reflects the current network layout. Hence, the decision to set the MAC address aging time to 15 seconds during a topology change is crucial for maintaining optimal network performance and stability.