Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
A switch interface connected to another switch must carry VLANs 10, 20, and 30 only. Which command best enforces that requirement on the trunk?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
switchport trunk allowed vlan 10,20,30
This is correct because it explicitly restricts the trunk to VLANs 10, 20, and 30.
B
Distractor review
switchport access vlan 10,20,30
This is wrong because an access port belongs to one VLAN, and this is not valid multi-VLAN trunk syntax.
C
Distractor review
switchport mode dynamic auto
This is wrong because it affects negotiation behavior, not the allowed VLAN list directly.
D
Distractor review
switchport trunk native vlan 10,20,30
This is wrong because the native VLAN command identifies one native VLAN, not a list of allowed VLANs.
Common exam trap
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.
Technical deep dive
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.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
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Question 2
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Question 3
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Question 4
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Question 5
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Question 6
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FAQ
Questions learners often ask
What does this 200-301 question test?
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?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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