RSTP
acronymStands for: Rapid Spanning Tree Protocol (IEEE 802.1w)
The rapid version of spanning tree, IEEE 802.1w, which converges in moments by handshake instead of waiting out timers.
Incorporated into 802.1D-2004, which obsoleted the original protocol. Cisco's Rapid PVST+ runs one RSTP instance per VLAN.
Classic spanning tree waits: a port moves through listening and learning on 15-second forward delays, and an indirect failure can take 50 seconds with default timers. RSTP replaces most of the waiting with an exchange between neighbours: a switch 'sets the proposal bit on the BPDUs it sends out', and once the other end answers with an agreement the port can move to forwarding at once, which Cisco puts 'sometimes in the order of a few hundred milliseconds'.
The handshake only works where two switches face each other, so RSTP moves quickly on point-to-point links and on edge ports, the ports facing hosts, which go straight to forwarding and lose that status the moment a BPDU arrives. It also renames the roles: the old blocking port becomes an alternate (a backup path to the root through another switch) or a backup (a second link to the same segment), and the disabled, blocking and listening states merge into one, discarding.
Also known as: rapid spanning tree, rapid spanning tree protocol, 802.1w, rapid pvst+