H3C Technologies H3C SecPath F1000-E - Manual (Page 112)

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Configuring the root bridge or a secondary root bridge
The root bridge of a spanning tree is determined through spanning tree calculation. Alternatively, you
can specify the current device as the root bridge or a secondary root bridge.
A device has independent roles in different spanning trees. It can act as the root bridge in one spanning
tree and as a secondary root bridge in another. However, a device cannot be the root bridge and a
secondary root bridge in the same spanning tree.
A spanning tree can have one root bridge only. If two or more devices are selected as the root bridge in
a spanning tree at the same time, the device with the lowest MAC address wins out.
When the root bridge of an instance fails or is shut down, the secondary root bridge (if you have
specified one) can take over the role of the primary root bridge. However, if you specify a new primary
root bridge for the instance then, the secondary root bridge will not become the root bridge. If you have
specified multiple secondary root bridges for an instance, when the root bridge fails, the secondary root
bridge with the lowest MAC address is selected as the new root bridge.
Configuring the current device as the root bridge of a specific spanning tree
Step Command Remarks
1. Enter system view. system-view N/A
2. Configure the device as the
root bridge.
• In STP/RSTP mode:
stp root primary
• In MSTP mode:
stp [ instance instance-id ] root
primary
Use either command.
By default, a device does not
function as the root bridge.
Configuring the current device as a secondary root bridge of a specific spanning tree
Step Command Remarks
1. Enter system view. system-view N/A
2. Configure the device as the
secondary root bridge.
• In STP/RSTP mode:
stp root secondary
• In MSTP mode:
stp [ instance instance-id ] root
secondary
Use either command.
By default, a device does not
function as a secondary root
bridge.
NOTE:
•
You can specify one root bridge for each spanning tree, regardless of the device priority settings. Once
you specify a device as the root bridge or a secondary root bridge, you cannot change its priority.
• You can configure the current device as the root bridge by setting the device priority to 0. For the device
priority configuration, see "
Configuring the device priority ."
Configuring the device priority
Device priority is a factor in spanning tree calculation. The priority of a device determines whether the
device can be elected as the root bridge of a spanning tree. A lower value indicates a higher priority.