The answer is that Dynamic Trunking Protocol (DTP) enabled on access ports is the misconfiguration allowing VLAN hopping attacks. This works because DTP negotiates trunk links automatically; an attacker can spoof DTP messages from a host in VLAN 10 to trick the switch port into forming an 802.1Q trunk, thereby gaining access to traffic from other VLANs like VLAN 20. On the CISSP exam, this question tests your understanding of Layer 2 security controls and the risks of default switch configurations. A common trap is confusing VLAN hopping with double-tagging attacks—DTP exploitation relies on trunk negotiation, not frame manipulation. Remember that DTP should be disabled on all access ports using the command "switchport nonegotiate" to prevent unauthorized trunking. For a quick memory tip: think "DTP = Don’t Trunk Ports" on access interfaces.
CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network 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.
During a security assessment, a penetration tester successfully performed a VLAN hopping attack from a host in VLAN 10 to a host in VLAN 20. The switches are configured with IEEE 802.1Q trunking. Which misconfiguration likely allowed this attack?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Dynamic Trunking Protocol (DTP) is enabled on access ports
D is correct because VLAN hopping attacks exploit Dynamic Trunking Protocol (DTP) to negotiate a trunk link between an attacker's host and a switch port. If DTP is enabled on an access port, the attacker can spoof DTP messages to form a trunk, gaining access to traffic from multiple VLANs, including VLAN 20 from VLAN 10.
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.
✗
The native VLAN is not used on any trunk ports
Why it's wrong here
Not using a native VLAN actually reduces risk of double tagging; it would not enable a VLAN hopping attack.
✗
Spanning Tree Protocol is disabled
Why it's wrong here
STP prevents loops; its disablement does not directly enable VLAN hopping.
✗
Port security is disabled on all ports
Why it's wrong here
Port security limits MAC addresses but does not prevent VLAN hopping via DTP or double tagging.
✓
Dynamic Trunking Protocol (DTP) is enabled on access ports
Why this is correct
With DTP enabled on an access port, an attacker can send DTP frames to negotiate a trunk, then tag frames to hop VLANs.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the distinction between the two types of VLAN hopping (switch spoofing vs. double-tagging), and the trap here is that candidates confuse disabling STP or port security as relevant mitigations, when the core issue is DTP-enabled access ports allowing trunk negotiation.
Detailed technical explanation
How to think about this question
VLAN hopping via switch spoofing works by an attacker sending DTP frames to negotiate a trunk, often using tools like Yersinia or Scapy. Once the port becomes a trunk, the attacker can send frames with any VLAN tag, bypassing VLAN segmentation. Cisco switches with DTP enabled in 'dynamic desirable' or 'dynamic auto' mode on access ports are vulnerable, and the fix is to set switchport mode access and disable DTP with 'switchport nonegotiate'.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
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: Dynamic Trunking Protocol (DTP) is enabled on access ports — D is correct because VLAN hopping attacks exploit Dynamic Trunking Protocol (DTP) to negotiate a trunk link between an attacker's host and a switch port. If DTP is enabled on an access port, the attacker can spoof DTP messages to form a trunk, gaining access to traffic from multiple VLANs, including VLAN 20 from VLAN 10.
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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Question Discussion
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