Which Spanning-Tree Protocol rides on top of another?

Explanation

The correct answer is A. MSTP (Multiple Spanning Tree Protocol) which rides on top of the original Spanning Tree Protocol (STP).

Spanning Tree Protocol is a Layer 2 protocol that helps prevent loops in redundant network topologies by disabling some links to create a loop-free tree. STP uses a root bridge election process and port costs to calculate the best path from the root bridge to each network segment.

MSTP is an extension of STP that allows for the creation of multiple spanning trees on a single physical network. It maps multiple VLANs to a single spanning tree instance, thereby reducing the number of spanning tree instances required for a large network with multiple VLANs.

MSTP rides on top of the original STP by providing a separate instance of STP for each VLAN. MSTP ensures that a change in one VLAN will not affect the other VLANs in the network. This is accomplished by mapping each VLAN to a unique instance of STP.

RSTP (Rapid Spanning Tree Protocol) is an improvement over STP that provides faster convergence times and better support for VLANs. However, RSTP does not ride on top of STP.

PVST+ (Per VLAN Spanning Tree Plus) is a Cisco proprietary protocol that provides a separate instance of STP for each VLAN in a network. PVST+ is similar to MSTP in that it allows for the creation of multiple spanning trees on a single physical network. However, PVST+ is not an extension of STP and does not ride on top of it.

Mono Spanning Tree A is not a recognized protocol and is an incorrect option.

In summary, MSTP is the protocol that rides on top of the original STP to provide multiple spanning trees on a single physical network.