Configuration Guide     234
Configuring Spanning Tree MSTP Configurations
Step 3 spanning-tree timer {[ forward-time 
forward-time
 ] [ hello-time 
hello-time
 ] [ max-age 
max-age
 ]}
(Optional) Configure the Forward Delay, Hello Time and Max Age.
forward-time: 
Specify the value of Forward Delay. The valid values are from 4 to 30 in seconds, 
and the default value is 15. Forward Delay is the time for the port to transit its state after the 
network topology is changed.
hello-time: 
Specify the value of Hello Time. The valid values are from 1 to 10 in seconds, and 
the default value is 2. The root bridge sends configuration BPDUs at an interval of Hello Time to 
check whether the links are failed.
max-age: 
Specify the value of Max Age. The valid values are from 6 to 40 in seconds, and the 
default value is 20. Max Age is the maximum time the switch can wait without receiving a BPDU 
before attempting to regenerate a spanning tree.
Step 4 spanning-tree hold-count 
value
(Optional) Configure the maximum number of BPDU packets transmitted per Hello Time interval.
value: 
Specify the maximum number of BPDU packets transmitted per Hello Time interval. The 
valid values are from 1 to 20 pps, and the default value is 5.
Step 5 spanning-tree max-hops 
value
(Optional) Configure the maximum number of hops that occur in a specific region before the 
BPDU is discarded.
value: 
Specify the maximum number of hops that occur in a specific region before the BPDU is 
discarded. The valid values are from 1 to 40 in hop, and the default value is 20.
Step 6 show spanning-tree bridge
(Optional) View the global parameters of the switch.
Step 7 end
Return to privileged EXEC mode. 
Step 8 copy running-config startup-config
Save the settings in the configuration file.
Note:
To prevent frequent network flapping, make sure that Hello Time, Forward Delay, and Max Age 
conform to the following formulas:
• 
2*(Hello Time + 1) <= Max Age
• 
2*(Forward Delay - 1) >= Max Age
This example shows how to configure the CIST priority as 36864, the Forward Delay as 12 
seconds, the Hold Count as 8 and the Max Hop as 25:
Switch#configure
Switch(config)#spanning-tree priority 36864
Switch(config-if)#spanning-tree timer forward-time 12