Rapid Spanning Tree (IEEE 802.1w)

The IEEE has improved the 802.1d protocol, which defines STP, with the definition of Rapid Spanning Tree Protocol (RSTP), as defined in standard 802.1w. RSTP is similar to STP in that it elects the root switch using the same parameters and tiebreakers; elects the root port on nonroot switches with the same rules; elects designated ports on each LAN segment with the same rules; and places each port in either a forwarding state or a blocking state, with the latter being called the discarding state instead of the blocking state.

RSTP can be deployed alongside traditional STP bridges and switches, with RSTP features working in switches that support it, and STP features working in the switches that support only STP. The advantage RSTP has over STP is improved network convergence when network topology changes occur. STP convergence has essentially wait periods: a switch must first cease to receive root BPDUs for MaxAge seconds before it can begin to transition any interfaces from blocking to forwarding. For any interfaces that need to transition from blocking to forwarding, the interface must endure Forward Delay seconds in listening state and Forward Delay more seconds in learning state before being placed in forwarding state. By default, these three wait periods of are 20, 15, and 15 seconds.

RSTP convergence times typically take less than 10 seconds. In some cases, they can be as low as 1 to 2 seconds.