The answer is that SW1 is the root bridge for VLAN 10, and all its interfaces are in the Designated role. This is correct because the output explicitly states “This bridge is the root,” and every interface—Gi0/1, Gi0/2, and Gi0/3—shows a role of Desg (Designated) with a state of FWD (Forwarding). In a stable Spanning Tree Protocol topology, only the root bridge can have all its active ports as Designated; any non-root bridge must have at least one Root port. On the ENCOR 350-401 exam, interpreting show spanning-tree output to identify root bridge and port roles is a frequent troubleshooting task, often hiding traps like a non-root bridge with a lower bridge ID or a blocked alternate port. A common memory tip is: “Root has all Desg—no Root port needed.”
350-401 Spanning Tree Protocol Practice Question
This 350-401 practice question tests your understanding of spanning tree protocol. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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 24586
Address aabb.cc00.0100
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24586 (priority 24576 sys-id-ext 10)
Address aabb.cc00.0100
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
SW1 is the root bridge for VLAN 10, and all its interfaces are in the Designated role.
The output explicitly states 'This bridge is the root' and shows all three interfaces (Gi0/1, Gi0/2, Gi0/3) in the Designated (Desg) role with a Forwarding (FWD) state. In a stable STP topology, only the root bridge has all its active ports as Designated; non-root bridges will have at least one Root port. Therefore, SW1 is the root bridge for VLAN 10, and all its interfaces are in the Designated role.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
SW1 is the root bridge for VLAN 10, and all its interfaces are in the Designated role.
Why this is correct
Correct. The output explicitly states 'This bridge is the root' and all interfaces are Desg FWD.
Related concept
Read the scenario before looking for a memorised answer.
✗
SW1 is not the root bridge; the root bridge has MAC address aabb.cc00.0100 but is a different switch.
Why it's wrong here
Incorrect. The output says 'This bridge is the root', so SW1 is the root bridge.
✗
SW1 has a port in the Blocking state, preventing loops.
Why it's wrong here
Incorrect. All ports are FWD (Forwarding), none are blocking.
✗
The root bridge priority for VLAN 10 is 24576 without the system ID extension.
Why it's wrong here
Incorrect. The priority shown is 24586, which includes the system ID extension of 10 (24576 + 10 = 24586). The base priority is 24576.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between the configured bridge priority (without the system ID extension) and the effective priority displayed in the 'show spanning-tree' output, leading candidates to mistakenly think the root priority is 24576 when it is actually 24586.
Trap categories for this question
Command / output trap
Incorrect. The output says 'This bridge is the root', so SW1 is the root bridge.
Detailed technical explanation
How to think about this question
The system ID extension (also called VLAN ID extension) is part of the 16-bit bridge priority field as defined in IEEE 802.1t. The priority value displayed (24586) is the sum of the configurable priority (24576, which is a multiple of 4096) and the VLAN ID (10). This allows per-VLAN STP instances to have unique bridge IDs without manual configuration. In a real-world scenario, if a network engineer misinterprets the priority as 24576 instead of 24586, they might incorrectly assume the root bridge selection is different, leading to troubleshooting errors in a multi-VLAN STP environment.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
Spanning Tree Protocol — This question tests Spanning Tree Protocol — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: SW1 is the root bridge for VLAN 10, and all its interfaces are in the Designated role. — The output explicitly states 'This bridge is the root' and shows all three interfaces (Gi0/1, Gi0/2, Gi0/3) in the Designated (Desg) role with a Forwarding (FWD) state. In a stable STP topology, only the root bridge has all its active ports as Designated; non-root bridges will have at least one Root port. Therefore, SW1 is the root bridge for VLAN 10, and all its interfaces are in the Designated role.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network engineer runs the following command on Switch SW8:
SW8# show spanning-tree vlan 80
VLAN0080
Spanning tree enabled protocol ieee
Root ID Priority 24656
Address aabb.cc00.0e00
Cost 12
Port 1 (GigabitEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32768 (priority 32768 sys-id-ext 80)
Address aabb.cc00.0f00
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 12 128.1 P2p
Gi0/2 Desg FWD 4 128.2 P2p
Gi0/3 Desg FWD 4 128.3 P2p
Gi0/4 Altn BLK 4 128.4 P2p
Based on this output, what is the cost of the root port?
easy
A.4
B.8
✓ C.12
D.16
Why C: The root port is Gi0/1, and its cost is shown as 12 in the interface table.
Variation 2. A network engineer runs the following command on Switch SW9:
SW9# show spanning-tree vlan 90
VLAN0090
Spanning tree enabled protocol ieee
Root ID Priority 24666
Address aabb.cc00.1000
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24666 (priority 24576 sys-id-ext 90)
Address aabb.cc00.1000
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 Desg FWD 4 128.1 P2p
Gi0/2 Desg FWD 4 128.2 P2p
Gi0/3 Desg FWD 4 128.3 P2p
Gi0/4 Desg FWD 4 128.4 P2p
Based on this output, what is the base priority of the root bridge?
hard
✓ A.24576
B.24666
C.32768
D.32858
Why A: The root bridge priority is 24666, which includes the system ID extension of 90. The base priority is 24666 - 90 = 24576.
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Question Discussion
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