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Open the full VLAN trunking answer →Question 1,057 of 1,819
Quick Answer
The correct answer is that the 'switchport trunk allowed vlan' command restricts which VLANs are permitted on a trunk, as it prunes unnecessary VLAN traffic to optimize bandwidth and security. This works because a trunk link, by default, carries all active VLANs, but the allowed VLAN list explicitly filters which VLAN frames can traverse the link, preventing unauthorized or unwanted VLANs from crossing. On the CCNA 200-301 v2 exam, this concept tests your understanding of VLAN trunking and native VLAN configuration, often appearing in multiple-choice questions where a common trap is confusing the allowed VLAN list with the native VLAN—remember, the native VLAN carries untagged traffic and must match on both ends to avoid spanning-tree issues or VLAN hopping. Another frequent pitfall is assuming an access port can carry multiple VLANs, but it is strictly single-VLAN, unlike a trunk. Memory tip: think of the trunk as a highway with toll booths—'allowed vlan' is the list of cars permitted, while the native VLAN is the unmarked car that always gets through without a ticket.
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. 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.
Which of the following statements about VLAN configuration and trunking on a Cisco switch are correct? (Choose all that apply.)
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
✓
The native VLAN on a trunk link is used for untagged traffic and should match on both ends of the link.
The native VLAN on a trunk carries untagged traffic, and mismatched native VLANs can cause spanning-tree issues, VLAN hopping, and misdirected control traffic, so both ends must match. VLAN 1 is a system-defined VLAN that cannot be deleted or shut down, making it always available. Dynamic Trunking Protocol (DTP) is a Cisco proprietary protocol that can automatically negotiate trunk links when interfaces are set to desirable or auto. The 'switchport trunk allowed vlan' command prunes VLANs on a trunk, restricting which VLANs are permitted. A trunk link forwards traffic only for VLANs that exist in the local VLAN database, so the statement that it can only carry globally created VLANs is correct. The incorrect option is that an access port can carry multiple VLANs; in reality, an access port is assigned to a single VLAN and cannot carry traffic for multiple VLANs like a trunk.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common mistake is thinking an access port can carry multiple VLANs like a trunk, or that a trunk automatically forwards all VLANs without requiring them to be locally defined.
Detailed technical explanation
How to think about this question
The native VLAN concept is defined in IEEE 802.1Q, which specifies that frames on the native VLAN are sent untagged to maintain backward compatibility with devices that do not understand VLAN tagging. When configuring a trunk, the 'switchport trunk native vlan' command changes the native VLAN, and mismatched native VLANs can lead to a VLAN hopping attack if an attacker can inject frames on the native VLAN. Additionally, the 'switchport trunk allowed vlan' command uses a VLAN list that can be specified as 'add', 'remove', or 'except' to control which VLANs traverse the trunk, and this list is independent of whether the VLANs are globally created on the switch.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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
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FAQ
Questions learners often ask
What does this 200-301 question test?
Switching and Network Access — This question tests Switching and Network Access — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The native VLAN on a trunk link is used for untagged traffic and should match on both ends of the link. — The native VLAN on a trunk carries untagged traffic, and mismatched native VLANs can cause spanning-tree issues, VLAN hopping, and misdirected control traffic, so both ends must match. VLAN 1 is a system-defined VLAN that cannot be deleted or shut down, making it always available. Dynamic Trunking Protocol (DTP) is a Cisco proprietary protocol that can automatically negotiate trunk links when interfaces are set to desirable or auto. The 'switchport trunk allowed vlan' command prunes VLANs on a trunk, restricting which VLANs are permitted. A trunk link forwards traffic only for VLANs that exist in the local VLAN database, so the statement that it can only carry globally created VLANs is correct. The incorrect option is that an access port can carry multiple VLANs; in reality, an access port is assigned to a single VLAN and cannot carry traffic for multiple VLANs like a trunk.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Same concept, more angles
1 more ways this is tested on 200-301
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which TWO statements about 802.1Q trunking, native VLANs, and inter-VLAN routing are correct? (Choose two.)
medium- A.802.1Q trunking is a Cisco-proprietary protocol that uses a 4-byte tag to identify VLAN membership.
- ✓ B.By default, frames belonging to the native VLAN are sent untagged across an 802.1Q trunk.
- C.Inter-VLAN routing can be accomplished using a Layer 2 switch configured with VLAN access maps.
- ✓ D.The native VLAN must be identical on both ends of an 802.1Q trunk to avoid native VLAN mismatch errors.
- E.Switches strip the 802.1Q tag from all frames before forwarding them out of a trunk port.
Why B: Option B is correct because, by default, 802.1Q trunking treats the native VLAN (typically VLAN 1) as untagged. Frames in the native VLAN are sent without an 802.1Q tag, allowing interoperability with devices that do not understand trunking. This behavior is defined in IEEE 802.1Q and is essential for backward compatibility.
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Last reviewed: Jun 11, 2026
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