Cisco Certified Network Associate (CCNA) Practice Exam

What are the symptoms of a spanning-tree failure?

1. Traffic remains constant across the network

2. Switches experience frequent MAC address table changes

3. Routers fail to connect to the VLAN

4. No configuration changes are seen in devices

The correct answer is: Switches experience frequent MAC address table changes

When spanning-tree fails, one significant symptom is that switches experience frequent MAC address table changes. This occurs because, with a malfunctioning spanning-tree protocol, there may be topological loops in the network. In a bridged Ethernet network, such loops can cause frames to circulate indefinitely. As a result, switches continuously see packets from devices, which leads them to update their MAC address tables frequently, thinking devices are moving or connecting/disconnecting. This constant fluctuation can cause network congestion and unpredictable performance. The other symptoms listed do not directly indicate a spanning-tree failure. For instance, constant traffic across the network, while a potential issue in terms of performance, does not specifically diagnose spanning-tree problems. Routers failing to connect to a VLAN could be caused by various factors, not just spanning-tree issues. Lastly, a lack of configuration changes in devices is not typically associated with spanning-tree failures, as a malfunction might not prevent configuration changes but rather affect how the network behaves.