Validate STP hello, max-age and forward-delay timers against the IEEE inequalities and get the convergence time.
Classic STP is timer-driven: a bridge waits max age to notice the root is gone, then 15 seconds each in listening and learning, giving the familiar 50-second outage. RSTP replaces the wait with an explicit handshake on point-to-point links, so hello timers only matter for detecting a dead neighbour. Tuning timers down to speed up convergence is how people accidentally build an unstable domain — below the IEEE minimums a BPDU can expire in transit and the topology never settles.
BPDU Timer
IEEE 802.1D requires max age ≥ 2 × (hello + 1) and forward delay ≥ (max age ÷ 2) + 1; classic convergence = max age + 2 × forward delay.
802.1w convergence
Rapid STP converges in roughly 3 × hello, because it uses proposal/agreement instead of timers.
IEEE 802.1D requires max age ≥ 2 × (hello + 1) and forward delay ≥ (max age ÷ 2) + 1; classic convergence = max age + 2 × forward delay. Classic STP is timer-driven: a bridge waits max age to notice the root is gone, then 15 seconds each in listening and learning, giving the familiar 50-second outage. RSTP replaces the wait with an explicit handshake on point-to-point links, so hello timers only matter for detecting a dead neighbour.
Tuning timers down to speed up convergence is how people accidentally build an unstable domain — below the IEEE minimums a BPDU can expire in transit and the topology never settles.
This calculator takes 4 inputs: Hello time, Max age, Forward delay, Spanning-tree version. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
No — move to RSTP or MSTP instead. Timer tuning trades stability for speed and only pays off in a small, well-understood diameter; RSTP gets you sub-second convergence without breaking the inequalities.