CompTIA Network+ Practice Test

In STP, what is the port state that prevents data forwarding to avoid loops?

1. Listening

2. Disabled

3. Blocking

4. Learning

The correct answer is: Blocking

In Spanning Tree Protocol (STP), the port state that prevents data forwarding to avoid loops is known as the blocking state. When a port is in the blocking state, it does not send or receive any data frames. This is crucial in a switched network where loops can create broadcast storms, leading to network congestion and failure. By blocking certain ports, STP ensures that only one active path exists in the logical topology, thereby preventing loops. The other states, while important in the STP process, serve different functions. The listening state allows the port to listen to BPDUs (Bridge Protocol Data Units) without forwarding frames, while the learning state allows the switch to identify MAC addresses by learning which devices are connected to which ports. The disabled state indicates that a port is administratively turned off, which also halts any data transmission but doesn't serve the purpose of preventing loops within the context of STP’s operational flow. Thus, the blocking state is specifically designed to manage and prevent potential looping issues in the network.