Lab 67: Configuring Spanning Tree Protocol Root Bridges Manually

Lab Objective:

The objective of this lab exercise is for you to learn and understand how to manually configure a switch to become the root bridge for a particular VLAN. By default, all VLANs have a priority of 32,768 (plus the VLAN number), which are used to determine the Spanning Tree root bridge.

Lab Purpose:

STP root bridge configuration is a fundamental skill. It is always recommended that the root bridge be manually configured to ensure that the Layer 2 network is deterministic. As a Cisco engineer, as well as in the Cisco CCNA exam, you will be expected to know how to configure a switch as a root bridge.

Certification Level:

This lab is suitable for ICND2 and CCNA certification exam preparation.

Lab Difficulty:

This lab has a difficulty rating of 6/10.

Readiness Assessment:

When you are ready for your certification exam, you should complete this lab in no more than 15 minutes.

Lab Topology:

Please use the following topology to complete this lab exercise:

Lab 67: Configuring Spanning Tree Protocol Root Bridges Manually 1

Task 1:

Based on the topology above, configure a hostname on Sw1 and Sw2 and configure the VLANs listed.

Task 2:

Configure the switches to support the VLANs listed in the topology. Configure the VLANs and check that they are visible on both switches. Manually set the interface to trunk on one side.

Task 3:

Configure Sw1 as the root bridge for VLANs 2010 and 2030.  Configure Sw2 as the root bridge for VLANS 2020 and 2040. Use the second non-zero priority value for root bridges.

Task 4:

Verify your configuration with the appropriate show commands.

Configuration and Verification

Task 1:

For reference information on configuring hostnames, please refer to earlier labs.

Task 2:

NOTE: By default, Cisco switches are VTP servers. However, to configure the extended range of VLANs (i.e., VLANs 1006 and above), you need to configure the switch as a VTP Transparent switch. For reference information on Transparent mode and extended VLANs, please refer to earlier labs.

Task 3:

NOTE: Spanning Tree priority values increment in amounts of 4096. The allowed values are illustrated on the switch if you issue an illegal value:

Sw1(config)#spanning-tree vlan2010 priority 4192 
% Bridge Priority must be in increments of 4096. 
% Allowed values are: 
 0     4096  8192  12288 16384 20480 24576 28672 
 32768 36864 40960 45056 49152 53248 57344 61440 

Sw1(config)#spanning-tree vlan2010 priority 8192 
Sw1(config)#spanning-tree vlan2030 priority 8192 

Sw2(config)#spanning-tree vlan2020 priority 8192 
Sw2(config)#spanning-tree vlan2040 priority 8192

Task 4:

NOTE: Verify the same for VLAN2030 on Sw1, as well as for VLANs 2020 and 2040 on Sw2. In addition, you can also issue the show spanning-tree root command (it won’t work on Packet Tracer) to view the Spanning Tree root bridge for all VLANs in the domain. This is illustrated below:

Sw1#show spanning-tree root 

Root Hello Max Fwd 
Vlan                   Root ID          Cost  Time Age Dly  Root Port 
---------------- -------------------- ----- ----- --- ---  ---------- 
VLAN2010         10202 000d.bd06.4100      0    2   20  15 

Sw1#show spanning-tree vlan2010 

Spanning tree enabled protocol ieee 
Root ID    Priority    10202 
           Address     000d.bd06.4100              
           This bridge is the root 
           Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec   

Bridge ID  Priority    10202  (priority 8192 sys-id-ext 2010) 
           Address     000d.bd06.4100 
           Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec 
           Aging Time 15 

Interface        Role Sts Cost      Prio.Nbr Type 
---------------- ---- --- --------- -------- ------------------------- 
Fa0/1            Desg FWD 100       128.2    Shr


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