STP and Forwarding Loops

D.

The correct answer is D. Port blocking.

The Spanning Tree Protocol (STP) is a protocol used in computer networking to prevent forwarding loops at OSI Layer 2 (Data Link Layer) by blocking certain ports on switches in a redundant network topology.

A forwarding loop occurs when there are multiple paths between two switches, and each switch forwards the same packet out of multiple ports, causing the packet to loop endlessly between the switches. This can result in network congestion and even network failure.

To prevent forwarding loops, STP uses a distributed algorithm to select a single active path in a redundant network topology and blocks the other redundant paths. STP builds a logical tree structure that spans all switches in the network and uses a root bridge as a central point for all traffic.

When a switch is first connected to the network, it sends out Bridge Protocol Data Units (BPDUs) to discover other switches and to determine the location of the root bridge. Each switch then selects a designated port that provides the best path to the root bridge, and all other ports on the switch are placed in a blocking state to prevent forwarding loops.

If the active path fails or becomes congested, STP recalculates the best path to the root bridge and activates the blocked ports on the alternative path, ensuring that network traffic can continue to flow without creating forwarding loops.

Therefore, STP prevents forwarding loops by dynamically blocking redundant paths in a network topology, allowing network traffic to flow efficiently and without interruption.