The answer is that the port cost for VLAN 20 is set to 100, making it more likely to be selected as the root port if lower than other paths. This configuration overrides the default STP port cost on the interface, which for a GigabitEthernet link is typically 4 under the short path cost method (IEEE 802.1D) or 20,000 under the long cost method (IEEE 802.1t). By manually setting a lower cost of 100, the switch artificially improves the desirability of this path for VLAN 20 traffic, influencing the root port election in favor of this interface. On the ENCOR 350-401 exam, this tests your understanding of per-VLAN Spanning Tree (PVST+) and the ability to manipulate path selection without altering the physical link speed. A common trap is confusing port cost with port priority—cost affects root port selection, while priority affects designated port selection. Remember the mnemonic: "Lower cost wins the root, lower priority wins the designated."
CCNP Spanning Tree Protocol Practice Question
This 350-401 practice question tests your understanding of spanning tree protocol. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The port cost for VLAN 20 is set to 100, making it more likely to be selected as root port if lower than other paths.
This sets the STP path cost for VLAN 20 on this interface to 100, influencing the root port selection.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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 port cost for VLAN 20 is set to 100, making it more likely to be selected as root port if lower than other paths.
Why this is correct
Lower cost is preferred; 100 is lower than default for GigabitEthernet (4).
Related concept
Access ports place end devices into a single VLAN.
✗
The port cost for all VLANs is set to 100.
Why it's wrong here
The command is VLAN-specific; only VLAN 20 is affected.
✗
The port will become a designated port for VLAN 20.
Why it's wrong here
Cost influences root port selection, not designated port role directly.
✗
The port will have a higher priority in the spanning-tree algorithm.
Why it's wrong here
Cost is separate from priority; lower cost means better path.
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Trap categories for this question
Command / output trap
The command is VLAN-specific; only VLAN 20 is affected.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
→Use show vlan brief to verify access VLANs.
→Use show interfaces trunk to verify trunk state and allowed VLANs.
→Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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.
What to study next
Got this wrong? Here's your next step.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 350-401 questions on switching, trunking, and access-port configuration.
Spanning Tree Protocol — This question tests Spanning Tree Protocol — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The port cost for VLAN 20 is set to 100, making it more likely to be selected as root port if lower than other paths. — This sets the STP path cost for VLAN 20 on this interface to 100, influencing the root port selection.
What should I do if I get this 350-401 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 350-401 questions on switching, trunking, and access-port configuration.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
About these practice questions
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Variation 1. What is the default STP port cost for a 10 Gigabit Ethernet interface?
easy
A.1
✓ B.2
C.4
D.19
Why B: Using the short path cost method (default), the cost for 10 Gbps is 2.
Last reviewed: Jun 18, 2026
Question Discussion
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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.
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