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Huawei Router: Setting RSTP Parameters That Affect RSTP Convergence

Huawei Router such as AR28-11: Setting RSTP Parameters That Affect RSTP Convergence

RSTP implements rapid convergence by configuring the link type of a port and fast transition
mechanism.
 
1 Setting the RSTP Network Diameter
Context
On a switched network, any two terminals on the switching network are connected through a specific path along which multiple devices reside. The network diameter is the maximum number of devices between any two terminals. A larger network diameter indicates a larger network scale.
An improper network diameter may cause slow network convergence and affects
communication. Run the stp bridge-diameter command to set a network diameter based on the network scale, which helps speed up convergence.
It is recommended that all devices use the same network diameter.
Procedure
Step 1 Run:
system-view
The system view is displayed.
 
Step 2 Run:
stp bridge-diameter diameter
The network diameter is configured.
By default, the network diameter is 7.
 
NOTE
l RSTP uses a single spanning tree instance on the entire network. As a result, performance deterioration cannot be prevented when the network scale grows. Therefore, the network diameter cannot be larger than 7.
l It is recommended that you run the stp bridge-diameter diameter command to set the network diameter. Then, the switching device calculates the optimal Forward Delay period, Hello timer value, and Max Age timer value based on the set network diameter.
----End
 
2 Setting RSTP Timers
 
Context
The following parameters are used in spanning tree calculation:
l Forward Delay: determines the interval for port status transition. To prevent temporary
loops, an interface first enters the Learning state when transiting from Discarding to
Forwarding. The status transition lasts for the time specified by Forward Delay so that the
local device can synchronize the status with the remote switch.
l Hello Time: is the interval at which hello packets are sent. The switching device sends
configuration BPDUs at an interval of Hello Time to check whether links are faulty. If the
switching device does not receive any BPDU at an interval of Hello Time, the switching
device recalculates the spanning tree due to BPDU timeout.
l Max Age: determines whether BPDUs expire. The switching device determines whether
the received BPDU expires based on this value. If the received BPDU expires, the spanning tree needs to be recalculated.
Devices on a ring network must use the same values of Forward Delay, Hello Time, and Max Age.
Generally, you are not advised to directly adjust the preceding three parameters. This is because the three parameters are relevant to the network scale. It is recommended that the network diameter be adjusted so that the spanning tree protocol automatically adjusts the three parameters. When the default network diameter is used, the default values of the three parameters are used.
 
CAUTION
To prevent frequent network flapping, make sure that Hello Time, Forward Delay, and Max Age conform to the following formulas:
l 2 x (Forward Delay - 1.0 second) >= Max Age
l Max Age >= 2 x (Hello Time + 1.0 second)
 
Procedure, use the Huawei AR19 for the example
Step 1 Run:
system-view
The system view is displayed.
 
Step 2 Set Forward Delay, Hello Time, and Max Age.
1. Run:
stp timer forward-delay forward-delay
The value of Forward Delay of the switching device is set.
By default, the value of Forward Delay of the switching device is 1500 centiseconds.
2. Run:
stp timer hello hello-time
The value of Hello Time of the switching device is set.
By default, the value of Hello Time of the switching device is 200 centiseconds.
3. Run:
stp timer max-age max-age
The value of Max Age of the switching device is set.
By default, the value of Max Age of the switching device is 2000 centiseconds.
----End
 
Checking the Configuration
Run the display stp [ interface interface-type interface-number ] [ brief ] command to
view the spanning-tree status and statistics.
----End



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