User's Manual
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MSTP can set the switch to the network root through configuration. You can run the command Spanning-tree
mstp instance-id root to modifythe priority value of the switch in a spanning tree instance from the default value
(32768) to a sufficiently small value, ensuring the switch turns to be the root in the spanning tree instance.
In general, after the command to set the primary root is executed, the protocol automatically check the bridge
ID of the current network’s root and then sets the priority of the bridge ID to 24576, which guarantees that the
current switch serves as the root of the STP instance.
If the priority value of the network root is less than 24576, the protocol will automatically set the STP priority of
the current bridge to a value which is 4096 smaller than the priority of the root. It deserves attention that 4096
is the step of the priority value of the bridge.
When setting the root, you can run the diameter subcommand to the network diameter of the spanning tree
network. The keyword is effective only when the spanning tree instance ID is 0. After the network diameter is
set, MSTP automatically calculates proper STP time parameters to ensure the stability of network convergence.
Time parameters include Forward Delay and Maximum Age. The subcommandHello-time can be used to set
a new hello time to replace the default settings.
Run the following command to set the switch to the network root:
Command Purpose
spanning-tree mstp
instance-id
root primary
[
diameter
net-diameter [
hello-time
seconds ] ]
Sets the switch to the root in the designated
spanning treeinstance.
instance-id represents the number of the
spanning treeinstance, ranging from 0 to 15.
net-diameter represents the network diameter,
which is anoptional parameter. It is effective when
instance-id is 0. It ranges from 2 to 7.
seconds represents the unit of the hello time,
ranging from1 to 10.
no spanning-tree mstp
instance-id
root
Cancels the root configuration of the switch in the
spanning tree.
instance-id represents the number of the
spanning treeinstance, ranging from 0 to 15.
Run the following command to check the MSTP message:
Command Purpose
show spanning-tree mstp
[
instance
instance-id ]
Checks the MSTP message.
36.3.5 Configuring secondary root
After the network root is configured, you can run spanning-tree mstp instance-id root secondary to set one or
multiple switches to the secondary roots or the backuproots. If the root does not function for certain reasons,
the secondary roots will become the network root.
Different from primary root configuration, after the command to set the secondary root is executed, the protocol
directly set the STP priority of the switch to 28672. In case that the priority value of other switches in the
network is 32768 by default, the current switch serves as the secondary root.
When configuring the secondary root, you can run the subcommands diameter and hello-time to update the