HP VPN Firewall Appliances Network Management Configuration Guide

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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 one root bridge only. 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, the one that you specify, and not 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
Ste
p
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-id ]
root primary
Use one of the commands.
By default, a device is not a root bridge.
For information about the value range for
the instance-id argument, see Network
Management Command Reference.
Configuring the current device as a secondary root bridge of a specific spanning tree
Ste
p
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-id ]
root secondary
Use one of the commands.
By default, a device is not a secondary root
bridge.
For information about the value range for
the instance-id argument, see Network
Management Command Reference.
Configuring the device priority
Priority is a factor in spanning tree calculations. The priority of a device determines whether the device
can be elected as the root bridge of a spanning tree. A lower numeric value indicates a higher priority.
You can set the priority of a device to a low value to specify the device as the root bridge of the spanning
tree. A spanning tree device can have different priorities in different MSTIs.
You cannot change the priority of a device after it is configured as the root bridge or as a secondary root
bridge.
During root bridge selection, if all devices in a spanning tree have the same priority, the one with the
lowest MAC address will be selected as the root bridge of the spanning tree.