98
•
MST region revision level.
•
VLAN-to-instance mapping entries in the MST region.
The configuration of MST region-related parameters (especially the VLAN-to-instance mapping table)
might cause MSTP to begin a new spanning tree calculation. To reduce the possibility of topology
instability, the MST region configuration takes effect only after you activate it by doing one of the
following:
•
Use the
active region-configuration
command.
•
Enable a spanning tree protocol by using the
stp global enable
command if the spanning tree
protocol is disabled.
In STP, RSTP, or PVST mode, MST region configurations do not take effect.
To configure an MST region:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter MST region view.
stp region-configuration
N/A
3.
Configure the MST region
name.
region-name
name
The default setting is the MAC
address.
4.
Configure the
VLAN-to-instance mapping
table.
•
instance
instance-id
vlan
vlan-id-list
•
vlan-mapping modulo
modulo
Use one of the commands.
By default, all VLANs in an MST
region are mapped to the CIST (or
MSTI 0).
5.
Configure the MSTP revision
level of the MST region.
revision-level
level
The default setting is 0.
6.
(Optional.) Display the MST
region configurations that are
not activated yet.
check region-configuration
N/A
7.
Manually activate MST region
configuration.
active region-configuration
N/A
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
calculation. You can also specify a 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 multiple devices can be selected as the root bridge in
a spanning tree, the device with the lowest MAC address is selected.
When the root bridge of an instance fails or is shut down and no new root bridge is specified:
•
If you specify only one secondary root bridge, it becomes the root bridge.