Disabling Spanning Tree; Configuring The Root Switch - Cisco Catalyst 3750 Software Configuration Manual

Configuring Spanning-Tree Features
Command
Step 7 show spanning-tree summary
and
show spanning-tree interface
interface-id
Step 8
copy running-config startup-config
To return to the default setting, use the no spanning-tree mode global configuration command. To return
the port to its default setting, use the no spanning-tree link-type interface configuration command.

Disabling Spanning Tree

Spanning tree is enabled by default on VLAN 1 and on all newly created VLANs up to the spanning-tree
limit specified in the
only if you are sure there are no loops in the network topology.
Caution When spanning tree is disabled and loops are present in the topology, excessive traffic and indefinite
packet duplication can drastically reduce network performance.
Beginning in privileged EXEC mode, follow these steps to disable spanning-tree on a per-VLAN basis.
This procedure is optional.
Command
Step 1 configure terminal
Step 2
no spanning-tree vlan vlan-id
Step 3
end
Step 4 show spanning-tree vlan vlan-id
Step 5
copy running-config startup-config
To re-enable spanning-tree, use the spanning-tree vlan vlan-id global configuration command.

Configuring the Root Switch

The switch maintains a separate spanning-tree instance for each active VLAN configured on it. A bridge
ID, consisting of the switch priority and the switch MAC address, is associated with each instance. For
each VLAN, the switch with the lowest bridge ID becomes the root switch for that VLAN.
To configure a switch to become the root for the specified VLAN, use the spanning-tree vlan vlan-id
root global configuration command to modify the switch priority from the default value (32768) to a
significantly lower value. When you enter this command, the software checks the switch priority of the
root switches for each VLAN. Because of the extended system ID support, the switch sets its own
priority for the specified VLAN to 24576 if this value will cause this switch to become the root for the
specified VLAN.
Catalyst 3750 Metro Switch Software Configuration Guide
14-14
Purpose
Verify your entries.
(Optional) Save your entries in the configuration file.
"Supported Spanning-Tree Instances" section on page
Purpose
Enter global configuration mode.
For vlan-id, the range is 1 to 4094.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Chapter 14 Configuring STP
14-10. Disable spanning tree
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