What are the three STP (Spanning Tree Protocol) convergence timers, and what are their default values?

Question

Accepted Answer

Hello Timer (2s), Forward Delay Timer (15s), and Max Age Timer (20s).

Timer
Default
Range
Purpose

Hello Timer
2 seconds
1–10s
Interval between BPDU (Bridge Protocol Data Unit) transmissions

Forward Delay
15 seconds
4–30s
Time spent in each of the listening and learning states

Max Age
20 seconds
6–40s
How long a switch waits without receiving a BPDU before attempting topology change

How they work together:

Root bridge sends BPDUs every 2 seconds (hello)
If a switch doesn't receive a BPDU for 20 seconds (max age), it assumes the topology has changed
When transitioning from blocking to forwarding, a port spends 15s listening + 15s learning = 30 seconds total before forwarding

Important: These timers can only be changed on the root bridge, which then dictates the values for the entire STP domain.
Tip: The classic STP convergence time is roughly 30–50 seconds (max age + 2× forward delay). This is one of the main reasons RSTP (Rapid Spanning Tree Protocol) was developed.
Go deeper:

Spanning Tree Protocol — timers (Wikipedia) — hello (2s), forward delay (15s), max age (20s) and how they yield ~30–50s convergence.

Timer	Default	Range	Purpose
Hello Timer	2 seconds	1–10s	Interval between BPDU (Bridge Protocol Data Unit) transmissions
Forward Delay	15 seconds	4–30s	Time spent in each of the listening and learning states
Max Age	20 seconds	6–40s	How long a switch waits without receiving a BPDU before attempting topology change