The answer is that Dynamic Trunking Protocol (DTP) enabled on access ports is the configuration flaw allowing VLAN hopping. This is correct because a VLAN hopping attack exploits DTP’s default ability to negotiate a trunk link; when an attacker’s workstation sends crafted DTP frames to a switch port configured as an access port but with DTP still active, the switch mistakenly establishes a trunk, letting the attacker tag frames from VLAN 10 and forward them to VLAN 20. On the ISC2 Certified in Cybersecurity CC exam, this question tests your understanding of Layer 2 security weaknesses and common switch misconfigurations—a frequent trap is assuming VLAN hopping requires a double-tagging attack, but the DTP flaw is simpler and more common. Remember the memory tip: “DTP on access ports is a trunking invitation,” so always disable it with the ‘switchport nonegotiate’ command to close this exploit.
ISC2 CC Network Security Practice Question
This CC practice question tests your understanding of 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.
A security auditor discovers that during a VLAN hopping attack, a threat actor was able to send frames from a workstation on VLAN 10 to a target on VLAN 20. Which configuration flaw is most likely responsible?
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
✓
Dynamic Trunking Protocol (DTP) is enabled on access ports
Option A is correct because a VLAN hopping attack exploits the Dynamic Trunking Protocol (DTP) to negotiate a trunk link between the attacker's workstation and the switch. If DTP is enabled on an access port, the attacker can send DTP frames to form a trunk, allowing frames from VLAN 10 to be tagged and forwarded to VLAN 20. Disabling DTP on all access ports with the 'switchport nonegotiate' command prevents this attack.
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.
✓
Dynamic Trunking Protocol (DTP) is enabled on access ports
Why this is correct
DTP allows an attacker to negotiate a trunk and access other VLANs.
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.
✗
The trunk port is set to native VLAN 1
Why it's wrong here
Native VLAN misuse is used for double-tagging attacks, but not the most common for this scenario.
✗
The switch is using default VLAN 1 for management
Why it's wrong here
VLAN 1 is a security concern but not directly related to VLAN hopping.
✗
Port security is not configured
Why it's wrong here
Port security limits MAC addresses but does not prevent VLAN hopping.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the distinction between VLAN hopping via DTP (trunk negotiation) and double-tagging attacks (native VLAN manipulation), so candidates may confuse the two and incorrectly choose the native VLAN option.
Trap categories for this question
Scenario analysis trap
Native VLAN misuse is used for double-tagging attacks, but not the most common for this scenario.
Detailed technical explanation
How to think about this question
DTP uses Cisco proprietary messages (802.1Q trunking) to negotiate trunk links; when an access port has DTP enabled (default on many Cisco switches), it can enter 'dynamic desirable' or 'dynamic auto' mode, allowing an attacker to send DTP frames and establish a trunk. Once the trunk is up, the attacker can use 802.1Q tagging to send frames to any VLAN, bypassing VLAN segmentation. In real-world scenarios, misconfigured 'switchport mode dynamic desirable' on a port connected to a user workstation is a common oversight that leads to this vulnerability.
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 CC question in full detail.
Network Security — This question tests 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 — Option A is correct because a VLAN hopping attack exploits the Dynamic Trunking Protocol (DTP) to negotiate a trunk link between the attacker's workstation and the switch. If DTP is enabled on an access port, the attacker can send DTP frames to form a trunk, allowing frames from VLAN 10 to be tagged and forwarded to VLAN 20. Disabling DTP on all access ports with the 'switchport nonegotiate' command prevents this attack.
What should I do if I get this CC 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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