How to Set Root Bridge on Cisco Switch in GNS3?

How to Set Root Bridge on Cisco Switch in GNS3? – On Cisco Switches, the Root Bridge is automatically selected by the Spanning Tree Protocol. When the Root Bridge select, the lowest MAC address, Priority values, and Cost values evaluate.
How to Set Root Bridge on Cisco Switch in GNS3?

How to Set Root Bridge on Cisco Switch in GNS3?

We can manually configure the Cisco Switch as the Root Bridge on topology we designed. We can easily do this by changing the priority values of Cisco switches. Priority values increase from 0 to multiples of 4096.

In our previous article, we have explained how does Cisco Switch select as Root Bridge in the article called Examining Spanning Tree Protocol in GNS3. We have also talked about port states (Root, Designated, Blocked) of Cisco switches.

In this article, we will explain the steps to set Root Bridge on Cisco Switch using the GNS3 program.

Manual Root Bridge Configuration

Manual configuration of Root Bridge in GNS3 is quite simple. At the Switch CLI command prompt that we want to set as the Root Bridge, we set the Priority value for the existing VLAN. Then, the BPDU packets are sent between the Switches and then changed Switch as the root bridge.

In GNS3, follow the steps of configuring the Root Bridge in order.

   Step 1

To set Cisco Switch as Root Bridge in GNS3, open the GNS3 program and create a new project.

How to Set Root Bridge on Cisco Switch in GNS3?

   Step 2

In the GNS3 program, create a network topology as shown in the following figure. Add three Layer 2 Switches to GNS3 workspace and cable all Switches.

How to Set Root Bridge on Cisco Switch in GNS3?

   Step 3

Up to now, no action has been taken on Layer 2 Switches. Note the MAC addresses and Priority values of all Switches as shown in the following image. You can find the MAC address and priority of the Cisco Switches by using the show spanning-tree command.

After you apply the show spanning-tree command at the L2-SW-2 CLI command prompt, you can see that L2-SW-2 is the Root Bridge.

How to Set Root Bridge on Cisco Switch in GNS3?

   Step 4

Since we will manually configure the Root Bridge in this article, we must not specify the Root Bridge Switch. If you want to configure L2-SW-1 in this topology as Root Bridge, open the CLI command prompt and change the priority value.

[code]
SW1# conf t
SW1(config)# spanning-tree vlan 1 priority 4096
[/code]

How to Set Root Bridge on Cisco Switch in GNS3?

   Step 5

After changing the priority value on the L2-SW-2 Switch, the Switches will communicate with the BPDU packets on the network and will be Root Bridge L2-SW-1.

After you apply the show spanning-tree command on the Cisco Switch, you can see that the Switch is the Root Bridge. Also, the port status of switches in the network changes.

How to Set Root Bridge on Cisco Switch in GNS3?

   Step 6

After setting Root Bridge on Cisco Switch in GNS3 has changed the ports state of the Switch. The new state of the ports will be as follows.

How to Set Root Bridge on Cisco Switch in GNS3?

   Step 7

You can check the L2-SW-2 port status from the following image.

How to Set Root Bridge on Cisco Switch in GNS3?

   Step 8

Likewise, you can check the port status of L2-SW-3 from the following image.

How to Set Root Bridge on Cisco Switch in GNS3?

   Step 9

Finally, you can see that Switch L2-SW-1 is the Root Bridge and GigabitEthernet0/0 and GigabitEthernet0/1 interfaces set to Designated Port.

How to Set Root Bridge on Cisco Switch in GNS3?

Show Commands Related to How to Set Root Bridge on Cisco Switch in GNS3

[su_tabs active=”1″]
[su_tab title=”SW1#show spanning-tree”]
SW1#show spanning-tree

VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 0062.dee0.5a00
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 4097 (priority 4096 sys-id-ext 1)
Address 0062.dee0.5a00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 15 sec

Interface Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
Gi0/0 Desg FWD 4 128.1 Shr
Gi0/1 Desg FWD 4 128.2 Shr
Gi0/2 Desg FWD 4 128.3 Shr
Gi0/3 Desg FWD 4 128.4 Shr

SW1#
[/su_tab]
[su_tab title=”SW2#show spanning-tree”]
SW2#show spanning-tree

VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 0062.dee0.5a00
Cost 4
Port 1 (GigabitEthernet0/0)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0062.de7b.5600
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
Gi0/0 Root FWD 4 128.1 Shr
Gi0/1 Desg FWD 4 128.2 Shr
Gi0/2 Desg FWD 4 128.3 Shr
Gi0/3 Desg FWD 4 128.4 Shr

SW2#
[/su_tab]
[su_tab title=”SW3#show spanning-tree”]
SW3#show spanning-tree

VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 0062.dee0.5a00
Cost 4
Port 3 (GigabitEthernet0/2)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0062.deb5.a800
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
Gi0/0 Desg FWD 4 128.1 Shr
Gi0/1 Altn BLK 4 128.2 Shr
Gi0/2 Root FWD 4 128.3 Shr
Gi0/3 Desg FWD 4 128.4 Shr

SW3#
[/su_tab]
[su_tab title=”SW1#show spanning-tree detail”]
SW1#show spanning-tree detail

VLAN0001 is executing the ieee compatible Spanning Tree protocol
Bridge Identifier has priority 4096, sysid 1, address 0062.dee0.5a00
Configured hello time 2, max age 20, forward delay 15
We are the root of the spanning tree
Topology change flag not set, detected flag not set
Number of topology changes 2 last change occurred 00:03:16 ago
Times: hold 1, topology change 35, notification 2
hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0, aging 300

Port 1 (GigabitEthernet0/0) of VLAN0001 is designated forwarding
Port path cost 4, Port priority 128, Port Identifier 128.1.
Designated root has priority 4097, address 0062.dee0.5a00
Designated bridge has priority 4097, address 0062.dee0.5a00
Designated port id is 128.1, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is shared by default
BPDU: sent 99, received 81

Port 2 (GigabitEthernet0/1) of VLAN0001 is designated forwarding
Port path cost 4, Port priority 128, Port Identifier 128.2.
Designated root has priority 4097, address 0062.dee0.5a00
Designated bridge has priority 4097, address 0062.dee0.5a00
Designated port id is 128.2, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is shared by default
BPDU: sent 179, received 0

Port 3 (GigabitEthernet0/2) of VLAN0001 is designated forwarding
Port path cost 4, Port priority 128, Port Identifier 128.3.
Designated root has priority 4097, address 0062.dee0.5a00
Designated bridge has priority 4097, address 0062.dee0.5a00
Designated port id is 128.3, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is shared by default
BPDU: sent 100, received 83

Port 4 (GigabitEthernet0/3) of VLAN0001 is designated forwarding
Port path cost 4, Port priority 128, Port Identifier 128.4.
Designated root has priority 4097, address 0062.dee0.5a00
Designated bridge has priority 4097, address 0062.dee0.5a00
Designated port id is 128.4, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is shared by default
BPDU: sent 179, received 0

SW1#
[/su_tab]
[su_tab title=”SW1#show spanning-tree bridge”]
SW1#show spanning-tree bridge

Hello Max Fwd
Vlan Bridge ID Time Age Dly Protocol
—————- ——————————— —– — — ——–
VLAN0001 4097 ( 4096, 1) 0062.dee0.5a00 2 20 15 ieee
SW1#
[/su_tab]
[su_tab title=”SW1#show spanning-tree ?”]
SW1#show spanning-tree ?
WORD bridge group list, example 1,3-5,7,9
active Report on active interfaces only
backbonefast Show spanning tree backbonefast status
blockedports Show blocked ports
bridge Status and configuration of this bridge
detail Detailed information
inconsistentports Show inconsistent ports
interface Spanning Tree interface status and configuration
mst Multiple spanning trees
pathcost Show Spanning pathcost options
root Status and configuration of the root bridge
summary Summary of port states
uplinkfast Show spanning tree uplinkfast status
vlan VLAN Switch Spanning Trees
| Output modifiers

SW1#
[/su_tab]
[/su_tabs]

How to Set Root Bridge on Cisco Switch in GNS3? ⇒ Video

You can watch how to set Root Bridge on Cisco Switch in GNS3 and you can also subscribe to our YouTube channel…

  Final Word

How to Set Root Bridge on Cisco Switch in GNS3? – In this article, we manually identified the Root Bridge on a small topology and configured it by changing the Priority value.

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