This 200-901 practice question tests your understanding of network fundamentals. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 TWO of the following are common causes of VLAN connectivity issues?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
VLAN not created on all switches
Option A is correct because VLANs must exist in the VLAN database of every switch that needs to forward traffic for that VLAN. If a VLAN is not created on a switch, interfaces assigned to that VLAN will be in an inactive or error-disabled state, and the switch will not forward frames for that VLAN across trunk links. This is a common misconfiguration when adding a new VLAN to a network without propagating it to all switches.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
VLAN not created on all switches
Why this is correct
If a VLAN is missing on a switch, ports assigned to that VLAN will be down.
Related concept
Read the scenario before looking for a memorised answer.
Default gateway is used for routing between subnets, not for VLAN connectivity.
✓
Mismatched VLAN IDs on trunk ports
Why this is correct
If trunk ports have different allowed VLANs or native VLAN mismatch, traffic may be dropped.
Related concept
Read the scenario before looking for a memorised answer.
✗
STP blocking port
Why it's wrong here
STP blocking is a loop prevention mechanism and is not specifically a VLAN issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between Layer 2 and Layer 3 issues, so candidates mistakenly select subnet mask or default gateway problems as VLAN connectivity issues when those are actually routing or host configuration problems.
Detailed technical explanation
How to think about this question
VLANs are identified by a 12-bit VLAN ID (1-4094) in the IEEE 802.1Q tag. When a trunk port is configured, both ends must agree on the allowed VLANs and the native VLAN; mismatched VLAN IDs cause frames to be dropped or misdelivered. In a real-world scenario, a common mistake is forgetting to create a VLAN on a downstream switch, causing all access ports in that VLAN to be non-operational until the VLAN is added to the switch's database.
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Fundamentals — This question tests Network Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: VLAN not created on all switches — Option A is correct because VLANs must exist in the VLAN database of every switch that needs to forward traffic for that VLAN. If a VLAN is not created on a switch, interfaces assigned to that VLAN will be in an inactive or error-disabled state, and the switch will not forward frames for that VLAN across trunk links. This is a common misconfiguration when adding a new VLAN to a network without propagating it to all switches.
What should I do if I get this 200-901 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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Question Discussion
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