What is the protocol version identifier used in a Rapid Spanning Tree Protocol (RSTP) BPDU?

The Rapid Spanning Tree Protocol (RSTP), defined in IEEE 802.1w, uses a specific protocol version identifier in its Bridge Protocol Data Units (BPDUs) to differentiate between different versions of the spanning tree protocol. The version identifier in RSTP BPDUs is set to 2. This allows network devices to recognize that the BPDU being processed is using RSTP rather than the original Spanning Tree Protocol (STP), which uses a version identifier of 0.

By using this version identifier, RSTP can efficiently manage changes in the network topology, providing a much quicker convergence time than its predecessor. This distinction is crucial for devices operating in a mixed environment where both STP and RSTP might co-exist, ensuring they can properly interpret the BPDUs they receive based on the protocol version being utilized.