Procedure
Step 1 Run:
system-view
The system view is displayed.
Step 2 Run:
stp [ instance instance-id ] priority priority
A priority is set for the switching device in an MSTI.
The default priority value of the switching device is 32768.
If the instance is not designated, a priority is set for the switching device in MSTI0.
NOTE
l To configure a switching device as the primary root bridge, run the stp [ instance instance-id ] root
primary command directly. The priority value of this switching device is 0.
l To configure a switching device as the secondary root bridge, run the stp [ instance instance-id ] root
secondary command. The priority value of this switching device is 4096.
In an MSTI, a switching device cannot act as the primary root bridge and secondary root bridge at the
same time.
l To change the priority of a switching device after you run the stp root primary command or the stp
[ instance instance-id ] root secondary command to configure the switching device as a primary root
bridge or a secondary root bridge, disable the root bridge function or secondary root bridge function
and then run the stp [ instance instance-id ] priority priority command to re-set a priority.
----End
8.3.5 (Optional) Configuring a Path Cost of a Port in an MSTI
The MSTP path cost determines root port selection in an MSTI. The port with the lowest path
cost to the root bridge is selected as the root port.
Context
A path cost is port-specific and is used by MSTP to select a link.
Path costs of ports are an important basis for calculating spanning trees. If you set different path
costs for a port in different MSTIs, VLAN traffic can be transmitted along different physical
links for load balancing.
In the Huawei proprietary calculation method for example, the link rate determines the
recommended value for the path cost. The following table lists the recommended path costs for
ports with different link rates.
Table 8-6 Mappings between link rates and path cost values
Link Rate
Recommended
Path Cost
Recommended
Path Cost Range
Path Cost Range
10 Mbit/s 2000 200 to 20000 1 to 200000
100 Mbit/s 200 20 to 2000 1 to 200000
1 Gbit/s 20 2 to 200 1 to 200000
Huawei AR3200 Series Enterprise Routers
Configuration Guide - LAN 8 MSTP Configuration
Issue 02 (2012-03-30) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
235
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