CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: a VLAN must be locally defined and active on a switch for traffic to pass, even if it is allowed on the trunk link.. 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 switch trunk is carrying several VLANs, but VLAN 99 traffic is failing. The trunk allowed list includes VLAN 99 on both sides. Which statement best explains why a VLAN can still fail even when it is allowed?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Because the VLAN may still be absent, inactive, or otherwise not operational locally even if it is allowed on the trunk
A VLAN can still fail across a trunk even when it is allowed because the allowed list is only one part of the overall design. In plain language, a switch may permit the VLAN on the link, but if the VLAN does not actually exist locally, is not active, or if some other trunk characteristic is inconsistent, traffic can still fail. This is an important CCNA troubleshooting principle: one correct line of configuration does not guarantee the full end-to-end condition is correct.
Candidates often stop at the allowed VLAN list because it is visible in common show commands. However, VLAN presence, local status, and other trunk parameters still matter. The best answer is the one recognizing that permission on the trunk does not automatically prove the entire VLAN path is healthy.
Key principle: A VLAN must be locally defined and active on a switch for traffic to pass, even if it is allowed on the trunk link.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Because the VLAN may still be absent, inactive, or otherwise not operational locally even if it is allowed on the trunk
Why this is correct
This is correct because an allowed-list entry alone does not guarantee that the VLAN exists and operates correctly end to end.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
A VLAN must be locally defined and active on a switch for traffic to pass, even if it is allowed on the trunk link.
✗
Because allowing a VLAN on a trunk automatically disables it
Why it's wrong here
This is wrong because allowing a VLAN does not disable it.
When this WOULD be correct
In a different scenario, if a question stated that enabling a VLAN on a trunk link would automatically disable it due to a misconfiguration or a specific switch model behavior, then this option could be correct. For example, a question could involve a legacy switch that has a unique feature where enabling VLANs on a trunk link disables them until explicitly activated.
✗
Because VLANs can cross trunks only when PAT is enabled
Why it's wrong here
This is wrong because PAT is unrelated to VLAN carriage on trunks.
When this WOULD be correct
In a scenario where the question asks about the conditions under which VLANs can only communicate across trunks if Port Address Translation (PAT) is enabled, this option would be correct. For example, if the exam focused on specific configurations that require PAT for inter-VLAN routing, then this statement would apply.
✗
Because VLAN 99 must always be the native VLAN
Why it's wrong here
This is wrong because a VLAN does not have to be the native VLAN in order to work across a trunk.
When this WOULD be correct
In a different question, if it were stated that VLAN 99 must be the native VLAN for traffic to be allowed on the trunk, then this option would be correct. For example, if the question specified that any VLAN must be configured as the native VLAN to pass traffic, then this statement would apply.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Because the VLAN may still be absent, inactive, or otherwise not operational locally even if it is allowed on the trunkCorrect answer▾
Why this is correct
This is correct because an allowed-list entry alone does not guarantee that the VLAN exists and operates correctly end to end.
✗Because allowing a VLAN on a trunk automatically disables itWrong answer — click to see why▾
Why this is wrong here
This option is incorrect because allowing a VLAN on a trunk does not disable it; rather, it simply permits traffic for that VLAN to traverse the trunk link. VLANs can be allowed on a trunk while still being operational if configured correctly.
★ When this WOULD be the correct answer
In a different scenario, if a question stated that enabling a VLAN on a trunk link would automatically disable it due to a misconfiguration or a specific switch model behavior, then this option could be correct. For example, a question could involve a legacy switch that has a unique feature where enabling VLANs on a trunk link disables them until explicitly activated.
Why candidates choose this
Candidates may find this option tempting because it suggests a direct relationship between VLAN configuration and operational status, which aligns with common misconceptions about VLAN management and trunking behavior.
✗Because VLANs can cross trunks only when PAT is enabledWrong answer — click to see why▾
Why this is wrong here
This option is incorrect because allowing a VLAN on a trunk does not disable it; rather, it simply permits the VLAN's traffic to traverse the trunk link. VLANs can still function normally if they are allowed on the trunk, regardless of the trunk's configuration.
★ When this WOULD be the correct answer
In a scenario where the question asks about the conditions under which VLANs can only communicate across trunks if Port Address Translation (PAT) is enabled, this option would be correct. For example, if the exam focused on specific configurations that require PAT for inter-VLAN routing, then this statement would apply.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of VLAN configurations and trunking principles, mistakenly believing that enabling a VLAN on a trunk link could somehow interfere with its functionality.
✗Because VLAN 99 must always be the native VLANWrong answer — click to see why▾
Why this is wrong here
This option is wrong because VLAN 99 can be operational and still not be the native VLAN; being the native VLAN is not a requirement for VLAN traffic to traverse a trunk link.
★ When this WOULD be the correct answer
In a different question, if it were stated that VLAN 99 must be the native VLAN for traffic to be allowed on the trunk, then this option would be correct. For example, if the question specified that any VLAN must be configured as the native VLAN to pass traffic, then this statement would apply.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of native VLANs and trunk configurations, believing that a VLAN must be the native VLAN to function properly on a trunk link.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common exam trap is assuming that simply including VLAN 99 in the trunk allowed list guarantees that VLAN 99 traffic will pass. Many candidates stop troubleshooting once they see the VLAN is allowed on the trunk, neglecting to verify if VLAN 99 is actually created and active on each switch. This mistake leads to incorrect conclusions, as the allowed list only controls trunk forwarding permissions, not VLAN existence or operational status. The exam tests your understanding that VLAN configuration and status are equally critical for successful VLAN traffic flow.
Detailed technical explanation
How to think about this question
A VLAN (Virtual Local Area Network) logically segments a switched network into separate broadcast domains, allowing devices to communicate as if they were on distinct physical networks. Switch trunks carry traffic for multiple VLANs simultaneously by tagging frames with VLAN identifiers, typically using the IEEE 802.1Q standard. The trunk allowed VLAN list controls which VLANs are permitted to traverse the trunk link, but this list only governs frame forwarding on the trunk interface itself.
Even if VLAN 99 is included in the trunk allowed list on both ends, the VLAN must also be defined and active locally on each switch. This means the VLAN must exist in the VLAN database, be operational (not shutdown), and have associated Layer 2 interfaces or ports assigned to it. If VLAN 99 is missing, inactive, or misconfigured on either switch, traffic for that VLAN will fail despite being allowed on the trunk. Thus, the allowed VLAN list is necessary but not sufficient for VLAN traffic to pass.
A common exam trap is assuming that allowing a VLAN on a trunk automatically guarantees connectivity for that VLAN. Candidates often overlook the local VLAN configuration status and operational state. In practice, VLANs must be consistently configured and active on all switches in the path. Failure to verify VLAN presence and status can lead to troubleshooting delays and incorrect conclusions about trunk or VLAN issues.
KKey Concepts to Remember
A VLAN must be locally defined and active on a switch for traffic to pass, even if it is allowed on the trunk link.
The trunk allowed VLAN list controls which VLANs can traverse the trunk but does not create or activate VLANs on the switch.
Switch trunks use 802.1Q tagging to carry multiple VLANs, requiring consistent VLAN configuration on both ends.
Traffic for a VLAN fails if the VLAN is absent or inactive locally, regardless of trunk allowed VLAN settings.
The native VLAN setting does not affect whether a VLAN is allowed or operational on a trunk.
Allowing a VLAN on a trunk does not disable it; VLANs must be explicitly configured and active to forward traffic.
Troubleshooting VLAN issues requires verifying VLAN presence, status, and trunk configuration on all involved switches.
Exam candidates often mistake allowed VLAN lists as a complete solution, ignoring local VLAN operational state.
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
A VLAN must be locally defined and active on a switch for traffic to pass, even if it is allowed on the trunk link.
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 200-301 question in full detail.
Review a VLAN must be locally defined and active on a switch for traffic to pass, even if it is allowed on the trunk link., then practise related 200-301 questions on the same topic to reinforce the concept.
Switching and Network Access — This question tests Switching and Network Access — A VLAN must be locally defined and active on a switch for traffic to pass, even if it is allowed on the trunk link..
What is the correct answer to this question?
The correct answer is: Because the VLAN may still be absent, inactive, or otherwise not operational locally even if it is allowed on the trunk — A VLAN can still fail across a trunk even when it is allowed because the allowed list is only one part of the overall design. In plain language, a switch may permit the VLAN on the link, but if the VLAN does not actually exist locally, is not active, or if some other trunk characteristic is inconsistent, traffic can still fail. This is an important CCNA troubleshooting principle: one correct line of configuration does not guarantee the full end-to-end condition is correct.
Candidates often stop at the allowed VLAN list because it is visible in common show commands. However, VLAN presence, local status, and other trunk parameters still matter. The best answer is the one recognizing that permission on the trunk does not automatically prove the entire VLAN path is healthy.
What should I do if I get this 200-301 question wrong?
Review a VLAN must be locally defined and active on a switch for traffic to pass, even if it is allowed on the trunk link., then practise related 200-301 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
A VLAN must be locally defined and active on a switch for traffic to pass, even if it is allowed on the trunk link.
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