Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
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?
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
Untagged traffic may be associated with different VLANs on each end of the trunk
This is correct because that is the direct risk of a native VLAN mismatch.
B
Distractor review
All tagged VLAN traffic is automatically converted to routed traffic
This is wrong because a native VLAN mismatch does not convert the trunk into a Layer 3 routed link.
C
Distractor review
The mismatch forces OSPF adjacency reset on all routers
This is wrong because the condition described is a trunking issue, not an OSPF-specific mechanism.
D
Distractor review
The trunk can carry only one VLAN until the mismatch is cleared
This is wrong because other tagged VLANs may still pass even though the native mismatch is a problem.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is to assume that a native VLAN mismatch affects all VLAN traffic or converts the trunk into a routed link. Some candidates mistakenly believe that routing protocols like OSPF will reset adjacency due to this mismatch. However, the native VLAN mismatch only impacts untagged traffic classification at Layer 2. Tagged VLAN traffic continues to flow normally, and routing protocols operate independently of VLAN tagging mismatches. Misunderstanding this leads to incorrect answers that confuse Layer 2 VLAN behavior with Layer 3 routing functions.
Technical deep dive
How to think about this question
A trunk link in Cisco networking carries traffic for multiple VLANs between switches, using tagging to differentiate VLAN frames. The native VLAN is a special VLAN on a trunk port where untagged frames are assigned. By default, Cisco switches use VLAN 1 as the native VLAN, but this can be changed for security or design reasons. When a native VLAN mismatch occurs, one switch associates untagged frames with one VLAN, while the other switch associates them with a different VLAN, causing inconsistent frame handling. The native VLAN mismatch warning indicates that the native VLAN IDs configured on each end of the trunk do not match. This mismatch causes untagged traffic to be misclassified, potentially leading to traffic leaks, broadcast storms, or security vulnerabilities. The trunk still carries tagged VLAN traffic correctly, but untagged frames are at risk of being sent to the wrong VLAN, disrupting communication and network segmentation. Cisco switches generate syslog warnings to alert administrators to this condition. In practice, the native VLAN mismatch does not convert the trunk into a routed link nor does it directly affect routing protocols like OSPF. The main operational impact is on Layer 2 VLAN tagging consistency. The exam trap is to confuse native VLAN mismatch effects with routing or protocol adjacency issues. Understanding that the mismatch affects only untagged traffic classification helps avoid this mistake and ensures proper trunk configuration and VLAN isolation in Cisco environments.
KKey Concepts to Remember
- A trunk link carries multiple VLANs between switches by tagging frames except for the native VLAN, which sends untagged frames.
- The native VLAN defines how untagged frames are handled on a trunk port and must match on both ends to avoid traffic misclassification.
- A native VLAN mismatch causes untagged traffic to be assigned to different VLANs on each switch, leading to inconsistent Layer 2 forwarding.
- Cisco switches generate native VLAN mismatch warnings in syslog to alert administrators of potential VLAN tagging issues on trunks.
- Tagged VLAN traffic continues to pass normally despite a native VLAN mismatch, but untagged traffic may be misrouted or lost.
- Native VLAN mismatches do not convert trunk links into Layer 3 routed links and do not directly impact routing protocols like OSPF.
- Proper trunk configuration requires matching native VLAN IDs on both ends to maintain VLAN segmentation and prevent security risks.
- Ignoring native VLAN mismatches can cause broadcast storms, VLAN leaks, and unpredictable network behavior in Cisco switched networks.
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.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
A trunk link carries multiple VLANs between switches by tagging frames except for the native VLAN, which sends untagged frames.
What is the correct answer to this question?
The correct answer is: 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 or DHCP behavior.
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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