If a Switch has multiple paths to reach the Root Bridge (Switch), it must select one path and the associated port as theRoot Port. Following are the different steps for selecting the Root Bridge (Switch).

• If there are two or more paths to reach the Root Bridge (Switch) select the path with the lowest accumulated path cost.
• Select the neighboring switch with the lowest Switch ID value to reach the Root Bridge (Switch).
• Select the port with the lowest Port Priority value, if you have multiple paths to reach the Root Bridge (Switch) via same neighbor switch.
• If all the ports are configured with same priority number (32 by default), select the lowest port number on the switch.

• Blocking
• listening
• learning
• Forwarding
• disabled.

Spanning Tree Protocol (STP) is enabled by default on modern switches. It is possible to disable or enable theSpanning Tree Protocol (STP) when required.

To enable Spanning Tree Protocol (STP) on an IOS based switch, use the "spanning-tree vlan vlan_number" command from global configuration mode as shown below.

switch01>
switch01>enable
switch01#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
switch01(config)#spanning-tree vlan 1
switch01(config)#exit
switch01#

To disable Spanning Tree Protocol (STP) on an IOS based switch use "no spanning-tree vlan vlan_number" commandfrom global configuration mode as shown below.

switch01>enable
switch01#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
switch01(config)#no spanning-tree vlan 1
switch01(config)#exit
switch01#