3com MSR 20-20 참조 매뉴얼

forwarding state, and must wait a certain period of time before it transitions from 
one state to another to keep synchronized with the remote device during state 
transition. The forward delay timer set on the root bridge determines the time 
interval of state transition.

If the current device is the root bridge, the state transition interval of the device 
depends on the set forward delay value; for a secondary root bridge, its state 
transition interval is determined by the forward delay timer set on the root bridge.

The setting of the hello time, forward delay and max age timers must meet the 
following formulae.

■

2 

× (forward delay - 1 second) ƒ max age

■

Max age ƒ 2 

× (hello Time + 1 second)

MSTP can work effectively on the entire network only when the above-mentioned 
conditions are met; otherwise, network instability will frequently occur. We 
recommend that you specify the network diameter of the switched network in the 
stp bridge-diameter bridge-number command and let MSTP automatically 
calculate an optimal setting of these three timers.

stp timer hello, stp timer max-age, and stp bridge-diameter.

# Set the forward delay timer of the device to 2,000 centiseconds.

<Sysname> system-view

[Sysname] stp timer forward-delay 2000 

stp timer hello centi-seconds

System view

centi-seconds: Hello time, in the range 100 to 1,000 (in centiseconds). This 
argument must be a multiple of 100.

Use the stp timer hello command to set the hello time of the device.

Use the undo stp timer hello command to restore the hello time of the device 
to the default setting.

By default, the hello time is set to 200 centiseconds.

Hello time is the time interval at which MSTP-compliant devices send configuration 
BPDUs to maintain spanning tree stability. If a device fails to receive configuration 
BPDUs within the set period of time, a new spanning tree computing process will 
be triggered due to timeout. The root bridge sends configuration BPDUs at the