Rapid Spanning Tree Protocol (RSTP)


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Industrial Communications Handbook

By Mick Crabtree

Chapter 9: Rapid Spanning Tree Protocol (RSTP)




In practice, Spanning Tree Protocol (STP) can actually take anything from 10 to 50 s to reconverge following a topology change. In order to provide a faster recovery, the IEEE introduced Rapid Spanning Tree Protocol (RSTP) (IEEE 802.1w) – having backwards compatibility with STP.

Probably the most important feature introduced by 802.1w is rapid transition. RSTP provides significantly faster spanning tree convergence – responding to a topology change within 3XHello times (3 x 2 s default) or a few milliseconds of a physical link failure.

While the legacy STP waited passively for the network to converge before it turned a port into the forwarding state, RSTP is able to actively confirm that a port can safely transition to the forwarding state without having to rely on any timer configuration.

As opposed to STP, RSTP clearly distinguishes between the state of a port and the role of a port.