mediumMultiple Choice
CCNP Practice Question: Runs the following command on Switch SW1: SW1#…
A network engineer runs the following command on Switch SW1:
SW1# show spanning-tree vlan 10
VLAN0010 Spanning tree enabled protocol ieee Root ID Priority 32778 Address 0011.2233.4455 Cost 19 Port 1 (GigabitEthernet0/1) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32778 (priority 32768 sys-id-ext 10) Address 0011.2233.4466 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- -------------------------------- Gi0/1 Root FWD 19 128.1 P2p Gi0/2 Altn BLK 19 128.2 P2p
Based on this output, what can be concluded?
⚠ Common exam trap
Cisco often tests the distinction between the Root ID and Bridge ID in 'show spanning-tree' output, where candidates mistakenly assume the local switch is the root if they see a priority value without checking the MAC address.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The local switch is not the root bridge for VLAN 10
The output shows that the local switch (Bridge ID 0011.2233.4466) has a Root ID of 0011.2233.4455, which is different from its own Bridge ID. Additionally, the Root Cost is 19, and the Root Port is Gi0/1. This confirms that the local switch is not the root bridge for VLAN 10; it is a non-root switch with a root port in the forwarding state.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The local switch is the root bridge for VLAN 10
Why it's wrong here
The output clearly distinguishes the Root ID from the local switch's Bridge ID. The Root ID lists the MAC address 0011.2233.4455, while the Bridge ID for the local switch is 0011.2233.4466, which is a higher MAC address. Since STP elects the root bridge by the lowest bridge ID, a different MAC address confirms the local switch is not that root.
- ✓
The local switch is not the root bridge for VLAN 10
Why this is correct
This is the correct inference from the spanning-tree output. The Root ID field shows a MAC address of 0011.2233.4455, whereas the local switch's Bridge ID uses 0011.2233.4466, so they are different. In STP, a switch knows it is not the root when its own bridge ID does not match the Root ID. Therefore, the local switch must be a non-root switch, and it will have a root port selected toward the root bridge.
- ✗
Interface Gi0/2 is in a forwarding state
Why it's wrong here
The interface status in the show spanning-tree output lists Gi0/2 as BLK, which stands for blocking. A blocking port does not forward user traffic; it only listens for BPDUs and is prevented from causing loops. This is distinct from the forwarding state, where the port sends and receives frames. Thus, claiming Gi0/2 is in a forwarding state directly contradicts the output.
- ✗
The spanning-tree mode is Rapid PVST+
Why it's wrong here
The command output displays 'protocol ieee', which denotes the original IEEE 802.1D STP, not Rapid PVST+. Rapid PVST+ would still show 'protocol ieee' but with additional RSTP-specific port roles such as Alternate and Backup, and it might include timing characteristics like Uptime and Port State based on RSTP. In this output, the only states shown are BLK and FWD, which match 802.1D STP, not the RSTP-based states or roles. Therefore, the spanning-tree mode cannot be Rapid PVST+.
Visual reference
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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