CCNA Switching and Network Access Practice Question
A trunk link between two switches is operational, but one side shows a native VLAN mismatch warning. What is the main concern with that condition?
⚠ Common exam trap
Be careful not to confuse native VLAN mismatches with general trunk failures or issues affecting tagged traffic.
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
✓
Untagged traffic may be associated with different VLANs on each end of the trunk
A native VLAN mismatch can cause untagged traffic to be interpreted as belonging to different VLANs on each end of the trunk. In plain language, the two switches disagree about where untagged frames belong. That can lead to confusing traffic behavior, reachability problems for certain flows, and operational warnings. It is not always a total outage, but it is a design inconsistency that should be corrected. This matters because trunks carry multiple VLANs, and the native VLAN defines how untagged traffic is handled. If both ends do not agree, the logical treatment of those frames becomes inconsistent. The correct answer is the one that focuses on misclassification of untagged traffic, not on unrelated routing behavior.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Untagged traffic may be associated with different VLANs on each end of the trunk
Why this is correct
On an IEEE 802.1Q trunk, the native VLAN is the only VLAN whose frames are sent untagged. If the two switches have different native VLANs configured, untagged frames arriving on the trunk are placed into the receiving switch's configured native VLAN, which may be a different VLAN than the one used by the sending switch. This causes the untagged traffic to be silently associated with the wrong VLAN, breaking Layer 2 segmentation and potentially creating a security or bridging loop, while tagged VLAN traffic still works normally.
- ✗
All tagged VLAN traffic is automatically converted to routed traffic
Why it's wrong here
A native VLAN mismatch does not alter the fundamental operation of a trunk link, which remains a Layer 2 forwarding path. The 802.1Q tag is still applied to frames from all non-native VLANs, and those frames are switched based on MAC addresses exactly as they would be with a correctly configured trunk. There is no mechanism that converts tagged VLAN traffic into routed traffic; routing would only occur if the frames are sent to a Layer 3 interface, which is a separate configuration unrelated to trunk native VLAN settings.
When this WOULD be correct
In a question focused on VLAN configuration and routing protocols, where the context involves a scenario of VLAN tagging and routing behavior, this option could be correct if it specifically states that tagged traffic is being routed due to a misconfiguration, leading to confusion in the network.
- ✗
The mismatch forces OSPF adjacency reset on all routers
Why it's wrong here
A native VLAN mismatch is a Layer 2 trunking misconfiguration; it directly affects only how untagged frames are interpreted on the trunk. OSPF adjacency is a Layer 3 routing process that relies on IP reachability and multicast hello packets, not on the native VLAN assignment of a trunk. While an IP connectivity issue could indirectly cause OSPF neighbors to go down, the mismatch itself does not force an OSPF adjacency reset on any router, and OSPF has no mechanism that reacts specifically to trunk native VLAN mismatches.
When this WOULD be correct
If the question were about the impact of VLAN mismatches on OSPF routing protocols, specifically asking how such mismatches can disrupt OSPF neighbor relationships, this option could be correct. For example, if the question stated that a native VLAN mismatch could lead to OSPF adjacency issues due to improper handling of untagged traffic, then this option would apply.
- ✗
The trunk can carry only one VLAN until the mismatch is cleared
Why it's wrong here
An 802.1Q trunk is designed to carry multiple VLANs simultaneously by adding a 4-byte tag to frames from all VLANs except the native VLAN. When a native VLAN mismatch exists, the untagged frames on the native VLAN are mishandled, but frames from other VLANs remain correctly tagged and continue to traverse the trunk normally. Therefore the trunk does not become limited to a single VLAN; it continues to transport all configured tagged VLANs, and only the untagged native VLAN traffic is subject to misassociation.
When this WOULD be correct
In a different scenario, if the question specified that the trunk link was configured to allow only a single VLAN due to a specific policy or configuration, then this option could be correct. For example, if the question stated that the trunk was intended to support only a management VLAN, the mismatch could lead to confusion about which VLAN is being carried.
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.
✓Untagged traffic may be associated with different VLANs on each end of the trunkCorrect answer▾
Why this is correct
On an IEEE 802.1Q trunk, the native VLAN is the only VLAN whose frames are sent untagged. If the two switches have different native VLANs configured, untagged frames arriving on the trunk are placed into the receiving switch's configured native VLAN, which may be a different VLAN than the one used by the sending switch. This causes the untagged traffic to be silently associated with the wrong VLAN, breaking Layer 2 segmentation and potentially creating a security or bridging loop, while tagged VLAN traffic still works normally.
✗All tagged VLAN traffic is automatically converted to routed trafficWrong answer — click to see why▾
Why this is wrong here
A native VLAN mismatch does not convert tagged traffic into routed traffic. Tagged frames continue to be switched based on their VLAN tags, and the trunk remains a Layer 2 link. The mismatch only affects untagged frames on the native VLAN.
★ When this WOULD be the correct answer
In a question focused on VLAN configuration and routing protocols, where the context involves a scenario of VLAN tagging and routing behavior, this option could be correct if it specifically states that tagged traffic is being routed due to a misconfiguration, leading to confusion in the network.
Why candidates choose this
Students might confuse the native VLAN mismatch with a scenario where the trunk is misconfigured as a routed port, or they may think that the mismatch causes the trunk to behave like a Layer 3 link. However, trunk ports remain Layer 2 regardless of native VLAN issues.
✗The mismatch forces OSPF adjacency reset on all routersWrong answer — click to see why▾
Why this is wrong here
A native VLAN mismatch is a Layer 2 trunking issue and does not directly affect OSPF or any routing protocol. OSPF adjacency is a Layer 3 process and would only be impacted if the mismatch caused connectivity loss for the router interfaces, but the mismatch itself does not force OSPF adjacency resets.
★ When this WOULD be the correct answer
If the question were about the impact of VLAN mismatches on OSPF routing protocols, specifically asking how such mismatches can disrupt OSPF neighbor relationships, this option could be correct. For example, if the question stated that a native VLAN mismatch could lead to OSPF adjacency issues due to improper handling of untagged traffic, then this option would apply.
Why candidates choose this
Students might associate any VLAN mismatch with routing protocol issues because they have seen scenarios where VLAN misconfigurations lead to routing problems. However, the native VLAN mismatch specifically does not trigger OSPF events.
✗The trunk can carry only one VLAN until the mismatch is clearedWrong answer — click to see why▾
Why this is wrong here
A native VLAN mismatch does not prevent the trunk from carrying other tagged VLANs. Tagged frames for other VLANs are still forwarded correctly because they are not affected by the native VLAN configuration. The trunk can carry multiple VLANs, but the native VLAN traffic is misdirected.
★ When this WOULD be the correct answer
In a different scenario, if the question specified that the trunk link was configured to allow only a single VLAN due to a specific policy or configuration, then this option could be correct. For example, if the question stated that the trunk was intended to support only a management VLAN, the mismatch could lead to confusion about which VLAN is being carried.
Why candidates choose this
Students might think that any mismatch on a trunk would cause the entire trunk to fail or limit its functionality. However, the native VLAN mismatch only affects untagged traffic, not the entire trunk.
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?”
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
Go deeper
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Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
CAN
A CAN (Controller Area Network) is a robust vehicle bus standard designed to allow microcontrollers and devices to communicate with each other without a host computer.
Key term
VLAN mismatch
A VLAN mismatch occurs when two connected network devices are configured with different VLAN assignments on the same link, causing traffic to be dropped or misrouted.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 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 200-301 exam.