- A
Use VLAN access control lists (VACLs) only
Why wrong: VACLs can filter traffic but may not prevent the double-tagging technique itself.
- B
Implement port security with sticky MAC
Why wrong: Port security limits MAC addresses, but does not prevent VLAN hopping.
- C
Disable the native VLAN and explicitly tag all VLANs
By not using a native VLAN (i.e., tagging all traffic including the default), double-tagging attacks fail because the switch strips the outer tag and expects no tag for native VLAN.
- D
Enable Dynamic Trunking Protocol (DTP) on all ports
Why wrong: DTP can actually increase risk by allowing trunk negotiation; best practice is to disable DTP.
Question 698 of 1,000
CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
During a penetration test, the tester successfully performs a VLAN hopping attack by sending packets with a specific tag. Which mitigation technique is most effective at preventing double-tagging VLAN hopping?
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
✓
Disable the native VLAN and explicitly tag all VLANs
Option C is correct because double-tagging VLAN hopping exploits the native VLAN (typically VLAN 1) on a trunk link. By disabling the native VLAN and explicitly tagging all VLANs, including the native VLAN, the switch will not forward untagged frames or frames with a single 802.1Q tag that can be misinterpreted by the next switch, thus preventing the attacker from injecting frames into a different 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.
- ✗
Use VLAN access control lists (VACLs) only
Why it's wrong here
VACLs can filter traffic but may not prevent the double-tagging technique itself.
- ✗
Implement port security with sticky MAC
Why it's wrong here
Port security limits MAC addresses, but does not prevent VLAN hopping.
- ✓
Disable the native VLAN and explicitly tag all VLANs
Why this is correct
By not using a native VLAN (i.e., tagging all traffic including the default), double-tagging attacks fail because the switch strips the outer tag and expects no tag for native VLAN.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Enable Dynamic Trunking Protocol (DTP) on all ports
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse VLAN hopping with MAC flooding or ARP spoofing, or they assume that VACLs or port security can stop Layer 2 tagging attacks, when in fact the root cause is the untagged native VLAN behavior on trunk ports.
Detailed technical explanation
How to think about this question
Double-tagging VLAN hopping works by sending a frame with two 802.1Q tags: the outer tag matches the native VLAN of the trunk, and the inner tag specifies the target VLAN. The first switch strips the outer tag (since native VLAN frames are sent untagged) and forwards the frame with the inner tag intact, causing the second switch to interpret the inner tag as the actual VLAN assignment. This attack is mitigated by explicitly tagging the native VLAN (e.g., using 'switchport trunk native vlan <tag>' or setting the native VLAN to an unused VLAN and tagging all traffic), which prevents the switch from stripping the outer tag.
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 team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.
Visual reference
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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Communication and Network Security — study guide chapter
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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: Disable the native VLAN and explicitly tag all VLANs — Option C is correct because double-tagging VLAN hopping exploits the native VLAN (typically VLAN 1) on a trunk link. By disabling the native VLAN and explicitly tagging all VLANs, including the native VLAN, the switch will not forward untagged frames or frames with a single 802.1Q tag that can be misinterpreted by the next switch, thus preventing the attacker from injecting frames into a different VLAN.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 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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