The answer to yesterday’s question (If a switch running MST stops receiving BPDUs on its root port, how long will it take for the convergence process to start?) is about 6 seconds. With rapid STP (as used in MST and RPVST+), convergence begins after 3 missed BPDUs. By default, BPDUs are sent every 2 seconds.
This is in contrast with traditional STP (802.1D), where spanning tree waits until the hold time (20 seconds by default) expires. If the link had actually gone down (rather than BPDUs just stopping), convergence would start immediately.
