1-18 
Item  Description 
Bridge Diameter 
Any two stations in a switched network are interconnected through a 
specific path composed of a series of devices. The bridge diameter (or the 
network diameter) is the number of devices on the path composed of the 
most devices.  
After you set the network diameter, you cannot set the timers. Instead, the 
device automatically calculates the forward delay, hello time, and max age. 
 
z  The configured network diameter is effective for CIST only, not for 
MSTIs. 
z  The bridge diameter cannot be configured together with the timers.  
Forward 
Delay
 
Set the delay for the root and designated 
ports to transit to the forwarding state. 
 
Hello 
Time
 
Set the interval at which the device 
sends hello packets to the surrounding 
devices to ensure that the paths are 
fault-free. 
 
Timers
 
Max Age 
Set the maximum length of time a 
configuration BPDU can be held by the 
device. 
 
 
z  The settings of hello time, 
forward delay and max age 
must meet a certain formula. 
Otherwise, the network 
topology will not be stable. 
You are recommended to set 
the network diameter and 
then have the device 
automatically calculate the 
forward delay, hello time, 
and max age. 
z  The bridge diameter cannot 
be configured together with 
the timers. 
Instance 
ID
 
Root Type
 
Instance 
Bridge 
Priority
 
Set the role of the device in the MSTI or the bridge priority of the device, 
which is one of the factors deciding whether the device can be elected as 
the root bridge. 
Role of the device in the MSTI: 
z  Not Set: Not set (you can set the bridge priority of the device when 
selecting this role) 
z  Primary: Configure the device as the root bridge (you cannot set the 
bridge priority of the device when selecting this role) 
z  Secondary: Configure the device as a secondary root bridge (you cannot 
set the bridge priority of the device when selecting this role).  
tc-protection 
Select whether to enable TC-BPDU guard.  
When receiving topology change (TC) BPDUs, the device flushes its 
forwarding address entries. If someone forges TC-BPDUs to attack the 
device, the device will receive a large number of TC-BPDUs within a short 
time and frequently flushes its forwarding address entries. This affects 
network stability. 
With the TC-BPDU guard function, you can prevent frequent flushing of 
forwarding address entries. 
 
You are recommended not to disable this function.  
tc-protection 
threshold 
Set the maximum number of immediate forwarding address entry flushes 
the device can perform within a certain period of time after receiving the first 
TC-BPDU. 
 
 
Return to 
MSTP configuration task list.