CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: a Cisco switch trunk interface uses 802.1Q tagging to carry traffic from multiple VLANs over a single physical 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 interface connected to another switch must carry VLANs 10, 20, and 30 only. Which command best enforces that requirement on the trunk?
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.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
switchport trunk allowed vlan 10,20,30
The correct command is the one that explicitly sets the allowed VLAN list on the trunk. In plain language, the administrator wants the inter-switch link to carry only the named VLANs instead of every VLAN by default. Cisco trunks can transport multiple VLANs, but that does not mean every VLAN should always be permitted. Restricting the allowed list supports cleaner design and helps reduce unnecessary VLAN transport.
This is a common CCNA switching task because it distinguishes between creating a trunk and controlling what the trunk actually carries. Simply enabling trunking is not enough when the requirement names exact VLANs. The answer must directly restrict the allowed list rather than change the native VLAN or apply an unrelated access-port command.
Key principle: A Cisco switch trunk interface uses 802.1Q tagging to carry traffic from multiple VLANs over a single physical 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.
✓
switchport trunk allowed vlan 10,20,30
Why this is correct
This is correct because it explicitly restricts the trunk to VLANs 10, 20, and 30.
Clue confirmation
The clue words "best", "which command" in the question point toward this answer.
Related concept
A Cisco switch trunk interface uses 802.1Q tagging to carry traffic from multiple VLANs over a single physical link.
✗
switchport access vlan 10,20,30
Why it's wrong here
This is wrong because an access port belongs to one VLAN, and this is not valid multi-VLAN trunk syntax.
When this WOULD be correct
In a different scenario where the question asks for the configuration of a switch port that should only allow traffic from a single VLAN, such as 'Which command sets the access VLAN for a port to VLAN 10?' this option would be correct, as it would specify the single VLAN for that access port.
✗
switchport mode dynamic auto
Why it's wrong here
This is wrong because it affects negotiation behavior, not the allowed VLAN list directly.
When this WOULD be correct
In a scenario where the question asks for configuring a switch port to automatically negotiate trunking without specifying VLAN restrictions, 'switchport mode dynamic auto' would be the correct answer. For example, if the question required enabling trunking without VLAN filtering, this command would be appropriate.
✗
switchport trunk native vlan 10,20,30
Why it's wrong here
This is wrong because the native VLAN command identifies one native VLAN, not a list of allowed VLANs.
When this WOULD be correct
In a different scenario where the question asks for configuring the native VLAN for untagged traffic on a trunk link, and it specifies that VLAN 10 should be the native VLAN while VLANs 20 and 30 are allowed, then 'switchport trunk native vlan 10' would be the correct command.
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.
This is correct because it explicitly restricts the trunk to VLANs 10, 20, and 30.
✗switchport access vlan 10,20,30Wrong answer — click to see why▾
Why this is wrong here
The 'switchport access vlan' command is used on access ports to assign a single VLAN, not on trunk ports. It cannot specify multiple VLANs, and using it on a trunk would misconfigure the port, potentially causing connectivity issues.
★ When this WOULD be the correct answer
In a different scenario where the question asks for the configuration of a switch port that should only allow traffic from a single VLAN, such as 'Which command sets the access VLAN for a port to VLAN 10?' this option would be correct, as it would specify the single VLAN for that access port.
Why candidates choose this
Students might confuse 'access vlan' with 'trunk allowed vlan' because both involve VLAN configuration. The word 'access' might be misinterpreted as allowing access to multiple VLANs, but it is strictly for a single VLAN on an access port.
✗switchport mode dynamic autoWrong answer — click to see why▾
Why this is wrong here
The 'switchport mode dynamic auto' command sets the port to negotiate trunking using DTP, but it does not restrict which VLANs are allowed. The port may become a trunk or access port depending on the neighbor, and even if it becomes a trunk, all VLANs are allowed by default.
★ When this WOULD be the correct answer
In a scenario where the question asks for configuring a switch port to automatically negotiate trunking without specifying VLAN restrictions, 'switchport mode dynamic auto' would be the correct answer. For example, if the question required enabling trunking without VLAN filtering, this command would be appropriate.
Why candidates choose this
Students may think 'dynamic auto' automatically handles VLANs or that it implies trunking with specific VLANs. However, it only controls trunk negotiation, not the allowed VLAN list.
✗switchport trunk native vlan 10,20,30Wrong answer — click to see why▾
Why this is wrong here
The 'switchport trunk native vlan' command specifies the native VLAN for untagged traffic on a trunk, and it accepts only a single VLAN ID, not a list. Using it with multiple VLANs is syntactically invalid and would be rejected by the switch.
★ When this WOULD be the correct answer
In a different scenario where the question asks for configuring the native VLAN for untagged traffic on a trunk link, and it specifies that VLAN 10 should be the native VLAN while VLANs 20 and 30 are allowed, then 'switchport trunk native vlan 10' would be the correct command.
Why candidates choose this
Students might confuse 'native vlan' with 'allowed vlan' because both are trunk-related commands. The word 'native' might be misread as 'allowed', leading to the incorrect assumption that it can specify multiple VLANs.
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 selecting commands that do not correctly restrict VLANs on a trunk. For example, using 'switchport access vlan 10,20,30' is invalid because access ports support only one VLAN. Another trap is confusing the native VLAN setting with allowed VLANs; 'switchport trunk native vlan' only defines the untagged VLAN and does not filter VLANs. Also, relying on dynamic trunk negotiation commands like 'switchport mode dynamic auto' does not restrict VLANs and can lead to trunks carrying all VLANs by default. These mistakes cause VLAN traffic to flow where it shouldn’t, violating design requirements.
Trap categories for this question
Command / output trap
This is wrong because the native VLAN command identifies one native VLAN, not a list of allowed VLANs.
Detailed technical explanation
How to think about this question
In Cisco switching, VLAN trunks are essential for carrying multiple VLANs across a single physical link between switches. A trunk interface uses IEEE 802.1Q encapsulation to tag frames with VLAN identifiers, allowing traffic from multiple VLANs to traverse the link simultaneously. By default, a trunk carries all VLANs allowed on the switch, which can lead to unnecessary VLAN traffic on links where only specific VLANs are needed.
To control which VLANs a trunk carries, the command 'switchport trunk allowed vlan' is used. This command explicitly restricts the VLANs permitted on the trunk link, ensuring that only the specified VLANs (in this case, VLANs 10, 20, and 30) are forwarded. This selective VLAN filtering improves network security and efficiency by preventing unwanted VLAN traffic from traversing the trunk.
A common exam trap is confusing the 'switchport trunk allowed vlan' command with other trunk or access port commands. For example, 'switchport access vlan' applies only to access ports and cannot specify multiple VLANs. Similarly, 'switchport trunk native vlan' sets a single native VLAN for untagged traffic but does not restrict allowed VLANs. Understanding these distinctions is critical for correctly configuring VLAN trunks and avoiding misconfigurations that could disrupt VLAN segmentation or cause traffic leakage.
KKey Concepts to Remember
A Cisco switch trunk interface uses 802.1Q tagging to carry traffic from multiple VLANs over a single physical link.
The 'switchport trunk allowed vlan' command explicitly restricts which VLANs are permitted to traverse a trunk link.
By default, trunks allow all VLANs, so restricting allowed VLANs improves security and reduces unnecessary VLAN traffic.
The 'switchport access vlan' command applies only to access ports and cannot specify multiple VLANs on a trunk.
The 'switchport trunk native vlan' command sets a single native VLAN for untagged frames but does not limit allowed VLANs.
Dynamic trunking protocols like 'switchport mode dynamic auto' affect trunk negotiation but do not control VLAN filtering.
Proper VLAN filtering on trunks prevents VLAN leakage and enforces network segmentation policies.
Misconfiguring trunk VLANs can cause connectivity issues or unintended VLAN access across switches.
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 Cisco switch trunk interface uses 802.1Q tagging to carry traffic from multiple VLANs over a single physical 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 Cisco switch trunk interface uses 802.1Q tagging to carry traffic from multiple VLANs over a single physical 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 Cisco switch trunk interface uses 802.1Q tagging to carry traffic from multiple VLANs over a single physical link..
What is the correct answer to this question?
The correct answer is: switchport trunk allowed vlan 10,20,30 — The correct command is the one that explicitly sets the allowed VLAN list on the trunk. In plain language, the administrator wants the inter-switch link to carry only the named VLANs instead of every VLAN by default. Cisco trunks can transport multiple VLANs, but that does not mean every VLAN should always be permitted. Restricting the allowed list supports cleaner design and helps reduce unnecessary VLAN transport.
This is a common CCNA switching task because it distinguishes between creating a trunk and controlling what the trunk actually carries. Simply enabling trunking is not enough when the requirement names exact VLANs. The answer must directly restrict the allowed list rather than change the native VLAN or apply an unrelated access-port command.
What should I do if I get this 200-301 question wrong?
Review a Cisco switch trunk interface uses 802.1Q tagging to carry traffic from multiple VLANs over a single physical 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", "which command". 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 Cisco switch trunk interface uses 802.1Q tagging to carry traffic from multiple VLANs over a single physical link.
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