Which of the following is not a feature of Spanning Tree Protocol (STP)?

The option identified as the correct answer, which states "Shared Bandwidth," is not a feature of Spanning Tree Protocol (STP) because STP primarily focuses on preventing network loops in Ethernet networks rather than managing bandwidth.

STP operates by placing certain ports into a blocking state based on the topology of the network, ensuring that there is only one active path between any two network devices to prevent loops. Features like Loop Guard and Root Guard enhance STP's ability to maintain a loop-free topology. Loop Guard prevents the formation of loops in specific scenarios where a network segment might become unblocked incorrectly, while Root Guard protects the Root Bridge by preventing BPDU (Bridge Protocol Data Unit) packets from non-root switches that could alter the topology.

Portfast is another important feature that allows ports connected to end devices to bypass the usual STP states and enter the forwarding state immediately. This is useful for reducing the time a device takes to connect to the network without waiting for STP to converge.

On the other hand, "Shared Bandwidth" does not pertain to the functionality of STP, as STP is primarily concerned with loop prevention and topology management, rather than the distribution or sharing of bandwidth among devices.