H3C Technologies H3C S12500-X Series Switches - Manual (Page 89)

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Configuring the root bridge or a secondary root
bridge
You can have the spanning tree protocol determine the root bridge of a spanning tree through MSTP
calculation, or you can specify the current device as the root bridge or as 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, one device cannot be the root bridge and a
secondary root bridge in the same spanning tree.
A spanning tree can have only one root bridge. 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 is chosen.
When the root bridge of an instance fails or is shut down, the secondary root bridge (if you have
specified one) becomes the root bridge if you have not specified a new root bridge. If you specify
multiple secondary root bridges for an instance, the secondary root bridge with the lowest MAC address
is given priority.
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 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 current
device as the root
bridge.
• In STP/RSTP mode:
stp root primary
• In MSTP mode:
stp [ instance instance-list ] root primary
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 current
device as a secondary root
bridge.
• In STP/RSTP mode:
stp root secondary
• In MSTP mode:
stp [ instance instance-list ] root
secondary
By default, a device does not
function as a secondary root
bridge.