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When a superior Bridge Protocol Data Unit (BPDU) is received while Root Guard is enabled, the port enters the Root-inconsistent state. This state occurs because Root Guard is designed to ensure that only designated ports can become root ports. When a port that is configured with Root Guard receives a BPDU indicating that a superior root bridge has been detected, it prevents the port from participating in the Spanning Tree Protocol (STP) active topology.

By entering the Root-inconsistent state, the port effectively blocks any traffic from passing through it to maintain the network's stability. This is a protective measure to avoid potential loops or inconsistencies that could be caused by a new or different root bridge being introduced into the topology. The port will remain in this state until the condition for Root Guard is cleared, ensuring that the port does not inadvertently become a root port in a topology that could lead to issues.

Overall, the Root-inconsistent state is a critical feature in maintaining the integrity of the spanning tree, particularly in complex network environments where changes may occur frequently.