H3C Technologies H3C WX5500E Series Access Controllers User Manual

Page 84

Configuring the root bridge or a secondary root

bridge

You can have MSTP 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 at

the same time, the device with the lowest MAC address wins.
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 one that you specify, rather than the secondary root bridge, will

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.
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

Enter system view.

system-view

N/A

Configure the current

device as the root
bridge.

•

In STP/RSTP mode:
stp root primary

•

In PVST mode:

stp vlan vlan-list root primary

•

In MSTP mode:

stp [ instance instance-id ] root primary

Use one of the commands.
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

Enter system view.

system-view

N/A