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RSTP Configuration 549
Set Priority of a
Specified Bridge
Whether a bridge can be selected as the “root” of the spanning tree depends on its
priority. By assigning a lower priority, a bridge can be artificially specified as the root
of the spanning tree.
You can use the following command to configure the priority of a specified bridge.
Perform the following configurations in System View.
Table 600 Set Priority of a Specified Bridge
Note that if the priorities of all the bridges in the Switching network are the same, the
bridge with the smallest MAC address will be selected as the “root”. When RSTP is
enabled, an assignment of a priority to the bridge will lead to recalculation of the
spanning tree.
By default, the priority of the bridge is 32768.
Specify the Switch as
Primary or Secondary
Root Bridge
RSTP can determine the spanning tree root through calculation. You can also specify
the current Switch as the root using this command.
You can use the following commands to specify the current Switch as the primary or
secondary root of the spanning tree.
Perform the following configuration in System View.
Table 601 Specify the Switch as Primary or Secondary Root Bridge
After a Switch is configured as primary root bridge or secondary root bridge, you
cannot modify the bridge priority of the Switch.
A Switch can either be a primary or secondary root bridge, but not both of them.
If the primary root of a spanning tree instance is down or powered off, the secondary
root will take its place, unless you configure a new primary root. Of two or more
configured secondary root bridges, RSTP selects the one with the smallest MAC
address to take the place of the failed primary root.
To configure a Switch as the root of the spanning tree instance, you can specify its
priority as 0 or simply set it as the root, using the command.
It is not necessary to specify two or more roots for an STI—do not specify the root for
an STI on two or more Switches.
You can configure more than one secondary root for a spanning tree through
specifying the secondary STI root on two or more Switches.
Generally, you are recommended to designate one primary root and more than one
secondary roots for a spanning tree.
Operation Command
Set priority of a specified bridge stp priority bridge_priority
Restore the default priority of specified bridge undo stp priority
Operation Command
Specify the current Switch as the primary root bridge of the
spanning tree.
stp root primary
Specify the current Switch as the secondary root bridge of the
spanning tree.
stp root secondary
Disqualify the current Switch as the primary or secondary root. undo stp root