Final answer:
The term that describes the reference point for all path calculations in STP is the 'root bridge.' It is selected based on the lowest bridge ID, and all other network decisions are made in relation to this bridge. The root bridge is the central point of a spanning tree topology in a computer network. The correct answer is option 2) root port
Step-by-step explanation:
The student's question pertains to the Spanning Tree Protocol (STP), which is used in computer networks to prevent loop occurrences. The reference point for all path calculations in STP is known as the root bridge. This critical component is elected based on the lowest bridge ID, and all other decisions within the network topology, such as which ports will be blocked or forwarded, are made concerning this bridge. Being the focal point, the root bridge serves as the logical center of the spanning tree topology.
Importance of the Root Bridge
In STP, each switch in the network believes it might be the root bridge until it hears from a switch with a lower bridge ID. All the switches exchange Bridge Protocol Data Units (BPDUs) to decide which switch has the lowest identifier and should be the root. The switch with the lowest bridge ID becomes the root bridge. The paths from all switches toward the root bridge are then calculated to ensure that there is a single active path between any two network devices.
Path Selection in STP
Once a root bridge has been elected, each non-root switch determines its root port, which is the port with the least cost path to the root bridge. The designated ports are then determined for every network segment; these are the ports that are chosen to forward traffic towards the root bridge. Ports that do not get elected as either root or designated become alternate ports and are put into a blocking state to avoid loops. The STP algorithm ensures there is only one active path between two endpoints, preventing broadcast storms and network outages caused by loops.