SSCP Network and Communications Security Practice Question
This SSCP practice question tests your understanding of network and communications security. 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.
A company has segmented its network into VLANs for different departments: HR, Finance, and IT. The router interconnecting the VLANs has ACLs configured to block traffic from HR to Finance. However, IT has noticed that traffic from HR VLAN is reaching the Finance VLAN. The network uses managed switches with 802.1Q trunking. All access ports are configured as untagged members of their respective VLANs. What is the most likely cause of this unauthorized traffic flow?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
VLAN hopping attack via double tagging
The most likely cause is a VLAN hopping attack via double tagging. In this attack, an attacker on the HR VLAN sends a frame with two 802.1Q tags: the outer tag matches the native VLAN of the trunk (often VLAN 1), and the inner tag is the target VLAN (Finance). When the switch receives the frame on an access port, it strips the outer tag (as it is the native VLAN) and forwards the frame with the inner tag over the trunk, allowing the traffic to bypass the ACLs and reach the Finance VLAN.
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.
✗
DHCP snooping disabled
Why it's wrong here
DHCP snooping prevents rogue DHCP servers, but does not enforce VLAN segmentation.
✓
VLAN hopping attack via double tagging
Why this is correct
Double tagging can allow an attacker to send frames to a VLAN other than the source VLAN, potentially bypassing ACLs.
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.
✗
Default gateway misconfiguration
Why it's wrong here
A misconfigured default gateway would affect connectivity to other networks, but would not allow traffic to bypass router ACLs.
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the distinction between VLAN hopping via double tagging versus switch spoofing; the trap here is that candidates may confuse this with a simple ACL misconfiguration or assume the router is the only point of control, overlooking that the attack occurs at Layer 2 before the router even sees the traffic.
Detailed technical explanation
How to think about this question
Double tagging exploits the behavior of 802.1Q trunking where the native VLAN (typically VLAN 1) is not tagged. An attacker on an access port can craft a frame with two VLAN tags; the first switch strips the outer tag (native VLAN) and forwards the frame with the second tag over the trunk, allowing the frame to reach a different VLAN. This attack is unidirectional and requires the attacker to know the native VLAN of the trunk; mitigation includes changing the native VLAN to an unused VLAN and explicitly tagging it on all trunk ports.
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.
Network and Communications Security — This question tests Network and Communications Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: VLAN hopping attack via double tagging — The most likely cause is a VLAN hopping attack via double tagging. In this attack, an attacker on the HR VLAN sends a frame with two 802.1Q tags: the outer tag matches the native VLAN of the trunk (often VLAN 1), and the inner tag is the target VLAN (Finance). When the switch receives the frame on an access port, it strips the outer tag (as it is the native VLAN) and forwards the frame with the inner tag over the trunk, allowing the traffic to bypass the ACLs and reach the Finance VLAN.
What should I do if I get this SSCP 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.
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Question Discussion
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