Cisco Certified Network Associate (CCNA) Practice Exam

What are common symptoms of spanning-tree failure?

1. Frequent firmware updates

2. Increased network security alerts

3. Frequent MAC address table changes

4. Unresponsive router interfaces

The correct answer is: Frequent MAC address table changes

Frequent MAC address table changes are a common symptom of spanning-tree failure. When spanning tree protocol (STP) is operating correctly, it is responsible for preventing loops in a network topology, thus creating a stable path for data to travel. If STP fails, it can lead to network loops, causing switches to continuously receive and send broadcast frames. This results in switches updating their MAC address tables frequently as they learn new source MAC addresses from the incoming frames. The instability of the MAC address table can create significant performance issues, including slow network performance and increased CPU load on switches. While other symptoms might indicate various network problems, they are not directly related to spanning-tree failures. For instance, frequent firmware updates may suggest the need for patches or upgrades to address other issues within the network but do not indicate spanning-tree issues. Increased network security alerts may hint at other vulnerabilities or malicious activities but are not a direct consequence of spanning-tree failure. Unresponsive router interfaces could result from many factors, such as hardware failure or misconfiguration, rather than specifically indicating a spanning-tree problem.