What criteria is used first during the root port selection process?
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A. B. C. D.B.
In the Spanning Tree Protocol (STP), the root port is the port on a non-root bridge that provides the least-cost path to the root bridge. When multiple ports on a non-root bridge can reach the root bridge with the same cost, the bridge selects a single root port based on a set of criteria.
The first criteria used in the root port selection process is the lowest path cost to the root bridge. The path cost is calculated based on the bandwidth of the link between the bridges, with higher bandwidth links having a lower path cost. The path cost is then added up as packets travel from the non-root bridge to the root bridge. The bridge with the lowest accumulated path cost to the root bridge will have its port selected as the root port.
If there are multiple ports with the same lowest path cost to the root bridge, the second criteria is used, which is the lowest neighbor's bridge ID. Each bridge has a unique bridge ID, which consists of a priority value and a MAC address. The bridge with the lowest bridge ID will have its port selected as the root port.
If multiple ports have the same lowest neighbor's bridge ID, the third criteria used is the lowest neighbor's port ID. Each port on a bridge is identified by a port ID, which consists of a port priority value and a port number. The port with the lowest port ID will be selected as the root port.
Finally, if there are still multiple ports with the same lowest path cost, neighbor's bridge ID, and neighbor's port ID, the STP algorithm will put one of the ports into a blocking state, effectively removing it from the active topology.
So, the correct answer to the question is B. The lowest path cost to the root bridge is the first criteria used during the root port selection process.