- A
Spanning Tree Protocol (STP) is blocking the link between the HR and IT switches.
Why wrong: STP prevents loops but does not block all traffic between VLANs; if it blocked the link, there would be no connectivity at all, not just cross-VLAN.
- B
The HR workstation has an incorrect subnet mask.
Why wrong: An incorrect subnet mask would prevent the workstation from determining which destinations are local vs. remote, but the scenario states correct IP and subnet masks.
- C
The HR VLAN switch port is incorrectly configured with the wrong VLAN ID.
Why wrong: A VLAN mismatch on the access port would prevent the HR workstation from communicating within its own VLAN, but it would not affect routing to other VLANs if the port is correctly configured for HR.
- D
No routing is configured between the HR and IT VLANs.
VLANs are separate broadcast domains; inter-VLAN communication requires a router or Layer 3 switch with routing enabled.
Quick Answer
The answer is that no routing is configured between the HR and IT VLANs. VLANs function as separate Layer 2 broadcast domains, so traffic cannot cross between them without a Layer 3 routing process. Even though the file server’s default gateway points to the IT VLAN interface, the HR workstation’s packets have no path to reach that interface because the router or Layer 3 switch has not been configured with an interface or static route for the HR VLAN. On the CISSP exam, this scenario tests your understanding of network segmentation and the fundamental role of routing in inter-VLAN communication—a common trap is assuming that correct IP addressing or a default gateway alone enables cross-VLAN traffic. Remember the key principle: VLANs isolate by design; routing is the bridge. A quick memory tip: “VLANs block, routing unlocks.”
CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. 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 company uses VLANs to separate traffic between the IT, HR, and Finance departments. A user in the HR VLAN reports that she cannot access a file server located in the IT VLAN. The file server's default gateway is correctly set to the IT VLAN interface. All workstations have correct IP addresses and subnet masks. What is the most likely cause of this issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
No routing is configured between the HR and IT VLANs.
VLANs create separate broadcast domains, so traffic between different VLANs must be routed. Since the HR workstation is in a different VLAN than the file server, and no routing is configured between the HR and IT VLANs, the HR workstation cannot reach the file server even though the server's default gateway is correctly set. This is the most likely cause because all other network settings (IP addresses, subnet masks, switch port configurations) are described as correct.
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.
- ✗
Spanning Tree Protocol (STP) is blocking the link between the HR and IT switches.
- ✗
The HR workstation has an incorrect subnet mask.
Why it's wrong here
An incorrect subnet mask would prevent the workstation from determining which destinations are local vs. remote, but the scenario states correct IP and subnet masks.
- ✗
The HR VLAN switch port is incorrectly configured with the wrong VLAN ID.
Why it's wrong here
A VLAN mismatch on the access port would prevent the HR workstation from communicating within its own VLAN, but it would not affect routing to other VLANs if the port is correctly configured for HR.
- ✓
No routing is configured between the HR and IT VLANs.
Why this is correct
VLANs are separate broadcast domains; inter-VLAN communication requires a router or Layer 3 switch with routing enabled.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume VLANs inherently block all cross-VLAN traffic, but the real issue is the absence of a Layer 3 routing mechanism; VLANs only separate broadcast domains, not routed traffic.
Trap categories for this question
Scenario analysis trap
An incorrect subnet mask would prevent the workstation from determining which destinations are local vs. remote, but the scenario states correct IP and subnet masks.
Detailed technical explanation
How to think about this question
Inter-VLAN routing requires a Layer 3 device (router or Layer 3 switch) with an interface in each VLAN or a router-on-a-stick configuration using 802.1Q trunking. Without a configured routing protocol or static routes between VLANs, packets from the HR VLAN are dropped at the default gateway because the gateway has no route to the IT VLAN subnet. In real-world scenarios, misconfigured access control lists (ACLs) on the Layer 3 device can also block inter-VLAN traffic even when routing is enabled.
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 security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
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.
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FAQ
Questions learners often ask
What does this CISSP question test?
Communication and Network Security — This question tests Communication and Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: No routing is configured between the HR and IT VLANs. — VLANs create separate broadcast domains, so traffic between different VLANs must be routed. Since the HR workstation is in a different VLAN than the file server, and no routing is configured between the HR and IT VLANs, the HR workstation cannot reach the file server even though the server's default gateway is correctly set. This is the most likely cause because all other network settings (IP addresses, subnet masks, switch port configurations) are described as correct.
What should I do if I get this CISSP 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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 24, 2026
This CISSP practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CISSP exam.
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