easyMultiple Choice
350-401 Practice Question: Runs the following command on Switch SW8: SW8#…
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?
⚠ Common exam trap
Cisco often tests the distinction between the root port cost (shown in the 'Root ID' section) and the local port cost (shown in the 'Cost' column for each interface), leading candidates to mistakenly pick the local cost of the root port (which is 12 in this case, but the trap is that they might pick the cost of a designated port like 4).
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
✓
12
The root port cost is the cost to reach the root bridge, which is explicitly shown in the 'Root ID' section as 'Cost 12'. This cost is associated with the root port (Gi0/1), which has a role of 'Root' and a status of 'FWD'. Therefore, the correct answer is 12.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
4
Why it's wrong here
4 is commonly the port cost assigned to a 1 Gbps link under the classic IEEE 802.1D cost table, but it is not the value shown for the root port in the output. The root port's cost is the total accumulated path cost to the root bridge, which is 12 in this case. Choosing 4 would ignore the sum of costs along the path, not just the link speed.
- ✗
8
Why it's wrong here
8 is not a standard STP port cost in either the original 802.1D (where costs are 100, 19, 4) or the 802.1t cost formula (20,000,000/bandwidth), so it is not a viable answer. Some might derive 8 from a misreading of the output or by assuming a cost for an unexpected bandwidth, but no such value appears in the spanning-tree output. The root port cost is explicitly 12, not 8.
- ✓
12
Why this is correct
The root port Gi0/1 is assigned a port cost of 12 in the spanning-tree output, representing the cumulative cost to reach the root bridge from this switch. This value is calculated by summing the cost of the root port's link plus any upstream costs, and it determines the best path to the root. Since the output shows 'cost 12' for the root port, 12 is the correct answer.
- ✗
16
Why it's wrong here
16 is not a standard IEEE 802.1D or 802.1t STP port cost value, and it does not appear anywhere in the show spanning-tree output for this switch. It may be a distractor derived from adding two costs (e.g., 8+8) or from a misremembered proprietary cost table, but it has no relation to the root port's actual path cost. The output clearly lists the root port cost as 12, so 16 is incorrect.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.