The answer is to verify that the SVI for VLAN 30 has an IP address configured. Since hosts in VLAN 10 can already reach VLAN 20, the Layer 3 switch is performing inter-VLAN routing correctly for those subnets, which means the routing engine and VLAN interfaces are operational. The specific failure to reach VLAN 30 points directly to a missing SVI IP—without an IP address assigned to that VLAN’s switch virtual interface, the switch has no local gateway to route traffic into that subnet. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding that SVIs must have an IP in the corresponding VLAN’s subnet to enable inter-VLAN routing; a common trap is to immediately suspect a VLAN mismatch or trunk issue when the real problem is a missing SVI address. Remember the mnemonic “No IP, no trip”—if an SVI lacks an IP, traffic cannot enter that VLAN.
N10-009 Network Troubleshooting Practice Question
This N10-009 practice question tests your understanding of network troubleshooting. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
A network technician is troubleshooting inter-VLAN routing. Hosts in VLAN 10 can communicate with hosts in VLAN 20, but cannot communicate with hosts in VLAN 30. All VLANs are configured on the same Layer 3 switch with SVIs. Which of the following should the technician verify FIRST?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The SVI for VLAN 30 is missing an IP address.
Since all VLANs are configured on the same Layer 3 switch with SVIs, inter-VLAN routing occurs internally. Hosts in VLAN 10 can reach VLAN 20, proving the Layer 3 switch is routing correctly for those VLANs. The failure to reach VLAN 30 most likely indicates that the SVI for VLAN 30 is missing an IP address, which prevents the switch from having a local interface to route traffic to that subnet.
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 30 is not allowed on the trunk port to the switch.
Why it's wrong here
Trunk ports are used for inter-switch links; since all VLANs are on the same switch, this is not relevant.
✓
The SVI for VLAN 30 is missing an IP address.
Why this is correct
An SVI without an IP address cannot route traffic, which would prevent inter-VLAN communication for that VLAN.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The default gateway on hosts in VLAN 10 is incorrect.
Why it's wrong here
If the default gateway were incorrect, hosts in VLAN 10 would likely fail to reach both VLAN 20 and VLAN 30.
✗
The routing table does not have a route to VLAN 30.
Why it's wrong here
A missing route could be caused by an unconfigured SVI; verifying the SVI first is more direct.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a missing VLAN on a trunk is the cause of inter-VLAN routing failure, but when all VLANs reside on the same Layer 3 switch, the SVI configuration is the first thing to verify.
Detailed technical explanation
How to think about this question
An SVI (Switch Virtual Interface) is a Layer 3 interface that represents a VLAN; it must have an IP address in the corresponding subnet to act as the gateway for that VLAN. Without an IP address on the SVI for VLAN 30, the switch cannot route packets to or from that VLAN, even though the VLAN itself exists and hosts may be connected. In a real-world scenario, this often happens after adding a new VLAN and forgetting to assign the SVI IP, which can be verified with 'show ip interface brief' or 'show running-config interface vlan 30'.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Network Troubleshooting — This question tests Network Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The SVI for VLAN 30 is missing an IP address. — Since all VLANs are configured on the same Layer 3 switch with SVIs, inter-VLAN routing occurs internally. Hosts in VLAN 10 can reach VLAN 20, proving the Layer 3 switch is routing correctly for those VLANs. The failure to reach VLAN 30 most likely indicates that the SVI for VLAN 30 is missing an IP address, which prevents the switch from having a local interface to route traffic to that subnet.
What should I do if I get this N10-009 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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