Cisco Certified Network Professional 2026 – 400 Free Practice Questions to Pass the Exam

In the context of the Spanning Tree Protocol (STP), an "inferior BPDU" refers to a Bridge Protocol Data Unit that has a lower Bridge ID or priority than the one currently accepted by a switch on a blocking port. When a switch receives an inferior BPDU on a blocking port, it indicates that the information being received is not sufficient to influence a change in the port's state.

As a result, nothing occurs; the port remains in its blocked state. This reinforces the idea that blocking ports are designed to prevent loops in the network while still maintaining the topology. The switch does not transition to forwarding mode, as it only processes superior BPDUs that convey more advantageous information about the network topology.

This behavior is essential for the stability and reliability of the network, ensuring that changes in the network structure are managed properly and that the risk of loops is minimized. Other scenarios or states, such as immediate forwarding or trying to transition the port, do not apply when dealing with inferior BPDUs on blocking ports.