How to Configure Cisco Switch as Root Bridge in Cisco Packet Tracer

The Spanning Tree protocol handles BID values ​​to determine port states on Cisco Switches automatically.

How to Configure Root Bridge

The Spanning Tree handles the BID values ​​of the Switches and evaluates the Priority and MAC Addresses. In short, the Root is selected using the Priority + MAC Address = BID formula.

After you have added three Switches to the workspace in the Cisco Packet Tracer, the Spanning Tree Protocol will automatically identify a Switch’s interface as Blocked when you connect all of these Switches with a cross cable. If the STP does not block a port, a Loop will occur on the network.

A Switch on the network communicates with other Switches with BPDU packets, so Priority values ​​are crucial. If a Switch has a low Priority value, it will be the Root Bridge in the network.

If the Priority values ​​of all Switches in the network are equal, the Switch with the lowest MAC address will be selected as ROOT. However, when designing an enterprise network, manually configuring the Root Bridge on the end switches in the distribution layer creates a better network design.

Select Root Bridge Manually

Before proceeding to configure a Switch on the network as Root, review the topology below.

In the above network design, the Priority values of all Switches are equal, and therefore, the Switch with the smallest MAC address will be configured as Root.

In SW2 privileged mode, you can use the show spanning-tree command to find the Switch, the Root Bridge.

SW2#show spanning-tree
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0003.E44B.4AC0
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0003.E44B.4AC0
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20

Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --
Gi0/1 Desg FWD 4 128.25 P2p
Gi0/2 Desg FWD 4 128.26 P2p

SW2#
Copy

When you check the above output, you can see that SW2 is Root. If you want to configure the SW1 on the network as Root, you can use the spanning-tree vlan 1 priority command in configuration mode.

SW1(config)#spanning-tree vlan 1 priority ?
bridge priority in increments of 4096
SW1(config)#spanning-tree vlan 1 priority 4096
Copy

From the above image, you can now see that SW1 is Root. You can use the show spanning-tree command to verify.

   Video

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Conclusion

In this article, we have manually configured a Switch between three Switches on the Packet Tracer as Root. Thanks for following us!