Cisco Certified Network Associate (CCNA) Practice Exam

How long does it take for an STP-enabled switch network to converge?

1. 30 seconds

2. 50 seconds

3. 70 seconds

4. 90 seconds

The correct answer is: 50 seconds

In a Spanning Tree Protocol (STP)-enabled switch network, convergence refers to the time it takes for the network to stabilize after a topology change, such as a switch or link failure. STP is designed to prevent loops in Layer 2 networks by placing ports in various states (blocking, listening, learning, or forwarding) based on the topology. When a change occurs, STP goes through several stages. Initially, all ports that are not part of the active path may enter a blocking state. Following this, the remaining ports transition through the listening state where they stop forwarding frames to gather information about the network topology. They then move into the learning state to build a MAC address table, where the switch learns the destination addresses of incoming frames. Finally, ports can transition to the forwarding state, enabling packet transmission. The standard convergence time for STP, according to the original specifications, can take up to 50 seconds. This consists of a default listening period of 15 seconds and a learning period of another 15 seconds before ports can enter the forwarding state, in addition to the time taken for the protocol to detect a topology change and converge. While enhancements like Rapid Spanning Tree Protocol (RSTP) significantly reduce convergence times to a