Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A trunk link has a native VLAN mismatch between two switches. What is the most likely result?
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
Distractor review
All VLANs except the native VLAN stop forwarding immediately.
A native VLAN mismatch does not automatically shut down all other VLANs.
B
Best answer
Untagged frames can be interpreted as belonging to different VLANs on each switch.
Correct. That is the classic native VLAN mismatch issue.
C
Distractor review
The trunk automatically converts to an access port.
Trunks do not auto-convert because of a native VLAN mismatch.
D
Distractor review
STP is disabled on the trunk until the mismatch is corrected.
STP continues to run.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is to assume that a native VLAN mismatch causes the trunk link to shut down or convert to an access port automatically. Cisco switches do not disable trunks or change port modes due to native VLAN mismatches. Instead, the mismatch causes untagged frames to be misclassified into different VLANs on each switch, leading to traffic leakage or connectivity problems. Candidates might also incorrectly believe that all VLANs stop forwarding or that STP is disabled, but these are false. Understanding that the native VLAN mismatch affects only untagged frame classification helps avoid this trap.
Technical deep dive
How to think about this question
A trunk link in Cisco networking carries traffic for multiple VLANs between switches by tagging frames with VLAN identifiers. The native VLAN is a special VLAN on a trunk port where untagged frames are placed. By default, the native VLAN is VLAN 1, but it can be changed. When two switches have a trunk link, they must agree on the native VLAN to correctly interpret untagged traffic. If there is a native VLAN mismatch, untagged frames sent from one switch are assigned to a different VLAN on the receiving switch, causing VLAN leakage and connectivity issues. The native VLAN mismatch problem arises because untagged frames are assumed to belong to the native VLAN on each side of the trunk. If Switch A uses VLAN 10 as native and Switch B uses VLAN 20, untagged frames sent by Switch A are placed into VLAN 10, but Switch B treats those same frames as VLAN 20 traffic. This mismatch leads to frames being misclassified, which can cause traffic to be forwarded incorrectly or dropped, and can also introduce security risks by leaking traffic between VLANs. In practical Cisco environments, a native VLAN mismatch does not disable the trunk or shut down VLANs; instead, it causes subtle and hard-to-diagnose connectivity problems. The Spanning Tree Protocol (STP) continues to operate normally despite the mismatch. Network engineers must verify and align native VLAN settings on both ends of a trunk to prevent these issues. The exam trap is assuming that a native VLAN mismatch causes trunks to fail or convert to access ports, which does not happen in Cisco switches.
KKey Concepts to Remember
- A trunk link carries traffic for multiple VLANs by tagging frames with VLAN identifiers except for untagged frames assigned to the native VLAN.
- The native VLAN on a trunk port determines how untagged frames are classified and forwarded between switches.
- A native VLAN mismatch occurs when two switches on a trunk link have different native VLAN configurations, causing untagged frames to be misclassified.
- Untagged frames sent on a trunk are assigned to the native VLAN configured on the receiving switch, which can differ if there is a mismatch.
- A native VLAN mismatch does not cause the trunk to shut down or convert to an access port automatically on Cisco switches.
- Spanning Tree Protocol (STP) continues to operate normally on trunks even if there is a native VLAN mismatch.
- Traffic leakage or connectivity problems occur because untagged frames are interpreted as belonging to different VLANs on each side of the trunk.
- Network engineers must ensure native VLAN consistency on both ends of a trunk to maintain proper VLAN segregation and traffic forwarding.
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 traffic for multiple VLANs by tagging frames with VLAN identifiers except for untagged frames assigned to the native VLAN.
What is the correct answer to this question?
The correct answer is: Untagged frames can be interpreted as belonging to different VLANs on each switch. — Untagged traffic may be placed into different VLANs on each side of the trunk, causing traffic leakage or connectivity problems.
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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