What is the primary purpose of a BPDU Guard?

The primary purpose of BPDU Guard is to enhance the stability and security of a network by preventing potential loops in the Spanning Tree Protocol (STP). When BPDU Guard is enabled on an interface, it actively monitors for Bridge Protocol Data Units (BPDUs). If any BPDUs are received on an interface that has BPDU Guard activated—typically an edge port configured with PortFast—the interface will be disabled immediately to prevent any risk of a loop forming.

This feature is particularly useful in scenarios where an end host or device, which should not participate in STP, is inadvertently connected to a port that is configured to monitor for BPDUs. By disabling the interface upon detection of these packets, BPDU Guard helps to maintain the integrity of the network topology and ensures that the STP process remains effective in preventing loops.

The other options, such as ignoring all BPDUs, enabling PortFast on trunk links, or globally enabling STP on all interfaces, do not accurately capture the essential function of BPDU Guard, which focuses specifically on reacting to the presence of BPDUs to secure the network.