stp priority
Function
The stp priority command sets the priority of the switching device in a spanning tree.
The undo stp priority command restores the default priority.
By default, the priority of the switching device in a spanning tree is 32768.
Format
STP/RSTP/MSTP: stp [ instance instance-id ] priority priority
STP/RSTP/MSTP: undo stp [ instance instance-id ] priority
VBST: stp [ vlan { vlan-id1 [ to vlan-id2 ] } &<1-10> ] priority priority
VBST: undo stp [ vlan { vlan-id1 [ to vlan-id2 ] } &<1-10> ] priority
Parameters
| Parameter | Description | Value |
|---|---|---|
instance instance-id |
Specifies the ID of a spanning tree instance. If the parameter instance instance-id is not specified, the configuration takes effect on a CIST instance. |
The value is an integer ranging from 0 to 4094. Value 0 refers to CIST. instance-id ranges from 0 to 4094. Each process supports a maximum of 65 instances. |
priority |
Specifies the priority of the switching device in a spanning tree. The smaller the value is, the higher the switch priority is. |
The priority ranks from 0 to 61440. The value is an integer multiple of 4096, such as 0, 4096 and 8192. The default is 32768. |
vlan vlan-id1 [ to vlan-id2 ] |
Specifies one or more VLANs in which the switch priority is configured.
In the stp priority command, you can specify a maximum of 10 VLAN ranges. NOTE:
VLANs can be specified only when VBST is running. |
The value is an integer that ranges from 1 to 4094. |
Views
System view or MSTP process view
VBST does not support processes. When VBST is running, you cannot run the stp priority command in the MSTP process view.
Usage Guidelines
Usage Scenario
Priorities of switching devices are an important factor to calculate a spanning tree and determine the selection of the root bridge.
On an STP/RSTP/MSTP/VBST network, each spanning tree has only one root bridge, which is responsible for sending BPDUs. Owning to the importance of the root bridge, the switching device with high performance and network hierarchy is generally chosen as the root bridge. The priority of such a switching device, however, may not be that high. Therefore, setting a high priority for the switching device is necessary so that the device can function as a root bridge.
Other devices with low performance and network hierarchy are not fit to be a root bridge. Therefore, set low priorities for these devices.
On an MSTP network, each switching device can be set with a distinct priority in each spanning tree instance. On a VBST network, each switch can be set with a priority for the spanning tree in each VLAN.
Precautions
The smaller the priority value of a switching device is, the higher the possibility that the switching device is selected as the root bridge.
If a switching device has been configured as the primary or secondary root bridge, before changing the priority of the switching device, run the undo stp [ instance instance-id ] root command to disable the root bridge or secondary root bridge function.
If the stp root primary command is run to set a switching device as the primary root bridge, the priority value of the switching device is 0.
If the stp root secondary command is run to set a switching device as the secondary root bridge, the priority value of the switching device is 4096.
Enabling MSTP on a ring network immediately triggers spanning tree calculation. If basic configurations are not performed on switches and interfaces before MSTP is enabled, network flapping may occur upon changes to parameters such as device priority and interface priority.