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19 Spanning Tree Protocol
Enables Multiple Spanning Tree and starts CIST operation.
Notes
When the
operating mode settings for Multiple Spanning Tree, the default operating mode of
pvst
(2) Setting regions and instances
Points to note
MST regions require that all switches belonging to the same region have the same
region name, revision number, and MST instance settings.
The instance number of an MST instance and the VLAN to which the instance
belongs are set at the same time. To make the regions match, the Switch allows
unset VLAN IDs to be set for the belonging instance. VLANs for which no belonging
instance is specified automatically belong to the CIST (instance 0).
As many as 16 MST instances can be set, including the CIST (instance 0).
Command examples
1.
(config)# spanning-tree mst configuration
(config-mst)# name "REGION TOKYO"
(config-mst)# revision 1
Switches to the Multiple Spanning Tree configuration mode, and sets
name) and
2.
(config-mst)# instance 10 vlans 100-150
(config-mst)# instance 20 vlans 200-250
(config-mst)# instance 30 vlans 300-350
(config-mst)# exit
Sets instances 10, 20, and 30, and sets the VLANs belonging to each instance.
VLANs 100 to 150 are set for instance 10, VLANs 200 to 250 are set for instance 20,
and VLANs 300 to 350 are set for instance 30. Other VLANs that are not specified
belong to the CIST (instance 0).
19.10.3 Configuring topologies for Multiple Spanning Tree
(1) Setting bridge priority for each instance
The bridge priority is a parameter for determining the root bridge. When a topology is
designed, the highest priority is set for the switch to be used for the root bridge, and the
second highest priority is set for the switch to be used next for the root bridge in case a fault
occurs on the root bridge.
Points to note
For bridge priorities, a lower value indicates a higher priority, and the switch with the
lowest set value is the root bridge. Because the root bridge is decided by a bridge ID
consisting of the bridge priority and switch MAC address, if this parameter is not set,
the switch with the lowest MAC address becomes the root bridge.
The bridge priority for Multiple Spanning Tree is set for each instance. When values
are changed for each instance, load balancing (building different topologies) can be
performed per instance.
332
no spanning-tree mode
is used. In this case, PVST+ operation starts automatically on the port VLAN.
revision
(revision number).
configuration command is used to delete
name
(region
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