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Chapter 7
Configuring Spanning Tree
Unmapping VLANs from an MISTP Instance
The keyword none is used to unmap the specified VLANs from the MISTP instances to which they are
currently mapped. When you unmap a VLAN from an MISTP instance, the resulting state of all the ports
of the VLAN (if the VLAN exists) is blocking.
To unmap a VLAN or all VLANs from an MISTP instance, perform this task in privileged mode:
Task
Unmap a VLAN from an MISTP instance.
This example shows how to unmap a VLAN from an MISTP instance:
Console> (enable) set vlan 6 mistp none
Vlan 6 configuration successful
Disabling MISTP-PVST+ or MISTP
When the switch is in MISTP mode, you disable spanning tree on an instance, not for the whole switch.
When you disable spanning tree on an MISTP instance, the instance still exists on the switch, all of the
VLANs mapped to it have all of their ports forwarding, and the instance BPDUs are flooded.
To disable an MISTP instance, perform this task in privileged mode:
Task
Disable an MISTP instance.
This example shows how to disable an MISTP instance:
Console> (enable) set spantree disable mistp-instance 2
MI-STP instance 2 disabled.
Configuring a Root Switch
This section explains how to configure a primary root switch and a secondary root switch, and how to
prevent a switch from becoming a root switch using the root guard feature.
Configuring a Primary Root Switch
You can set a root switch on a VLAN when the switch is in PVST+ mode or on an MISTP instance when
the switch is in MISTP mode. Enter the set spantree root command to lower the bridge priority (the
value that is associated with the switch) below the default (32,768); the switch can then become the root
switch.
78-15486-01
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide
Command
set vlan vlan mistp-instance none
Command
set spantree disable mistp-instance instance [all]
Configuring a Root Switch
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Release 8.1
7-39
- Quick Links:
- Configuration Guide
- Catalyst 2980G Switch
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