Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
Two switches are connected by an 802.1Q trunk. CDP reports a native VLAN mismatch. Which issue is most likely to appear because of this?
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 placed into different VLANs on each switch.
That is the classic symptom of a native VLAN mismatch.
B
Distractor review
All tagged traffic on the trunk is dropped immediately.
Tagged traffic can still pass normally if allowed VLANs match.
C
Distractor review
STP is disabled on the trunk link.
A native VLAN mismatch does not disable STP.
D
Distractor review
The trunk automatically converts to an access port.
That is not normal switch behavior.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is to believe that a native VLAN mismatch causes the trunk link to shut down or block all traffic. In reality, only untagged traffic is affected, and tagged VLAN traffic continues to pass normally if allowed VLANs match. Another mistake is thinking the trunk automatically converts to an access port, which Cisco switches do not do. Candidates may also overlook that STP remains enabled and functional despite the mismatch. Focusing only on trunk status without considering untagged traffic behavior leads to incorrect answers.
Technical deep dive
How to think about this question
802.1Q trunking allows switches to carry traffic for multiple VLANs over a single physical link by tagging frames with VLAN identifiers. The native VLAN is a special VLAN on a trunk port where frames are sent untagged. By default, VLAN 1 is the native VLAN on Cisco switches, but this can be changed. When two switches connect via an 802.1Q trunk, they must agree on the native VLAN to ensure untagged traffic is handled consistently. If the native VLAN is mismatched between the two switches, untagged frames sent by one switch are assigned to the native VLAN configured on the receiving switch, which may be different. This causes untagged traffic to be placed into different VLANs on each side, leading to connectivity problems and VLAN leakage. CDP can detect this mismatch and alert administrators, but the trunk link remains operational for tagged VLAN traffic. STP continues to function normally, and the trunk does not revert to an access port automatically. The exam trap is to assume that a native VLAN mismatch disables the trunk or blocks all traffic, but only untagged traffic is affected. Tagged VLAN traffic passes normally if allowed VLANs match. Another common mistake is to overlook the security implications of native VLAN mismatches, as untagged traffic could cross VLAN boundaries unintentionally. In practical networks, it is best practice to change the native VLAN to an unused VLAN and ensure both ends match to avoid these issues.
KKey Concepts to Remember
- An 802.1Q trunk link carries multiple VLANs by tagging frames except for the native VLAN, which is sent untagged by default.
- A native VLAN mismatch occurs when the native VLAN configured on one switch does not match the native VLAN on the connected switch’s trunk port.
- When a native VLAN mismatch exists, untagged frames sent from one switch are assigned to a different VLAN on the receiving switch, causing connectivity issues.
- Cisco Discovery Protocol (CDP) can detect and report native VLAN mismatches between connected switches to help identify configuration errors.
- Tagged traffic on a trunk is not affected by a native VLAN mismatch as long as allowed VLANs and tagging are consistent on both ends.
- A native VLAN mismatch does not disable Spanning Tree Protocol (STP) or cause the trunk to convert to an access port automatically.
- Native VLAN mismatches can create security risks by allowing untagged traffic to be misclassified and potentially leak between VLANs.
- Properly matching native VLANs on both ends of a trunk is essential to maintain VLAN separation and prevent untagged traffic misrouting.
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?
An 802.1Q trunk link carries multiple VLANs by tagging frames except for the native VLAN, which is sent untagged by default.
What is the correct answer to this question?
The correct answer is: Untagged traffic may be placed into different VLANs on each switch. — A native VLAN mismatch can cause untagged traffic sent on one side to be placed into a different VLAN on the other side. That leads to confusing connectivity issues and can also create security concerns. It does not automatically disable the trunk.
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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