Designated Ports Election
Once the Root Path Cost values have been computed, the Root Ports have been identified; however, all other links are still connected and could be active, leaving bridging loops. To remove the bridging loops, STP makes a final computation to identify one Designated Port on each network segment which would forward traffic to and from that segment. Switches choose a Designated Port based on the lowest cumulative Root Path Cost to the Root Bridge. All ports are still active and bridging loops are still possible. STP has a set of progressive states that each port must go through, regardless of the type or identification. These states will actively prevent loops from forming.