The answer is to disable Dynamic Trunking Protocol (DTP) and set access ports as static VLANs. These two techniques work together because VLAN hopping attacks exploit the automatic trunk negotiation enabled by DTP; an attacker can spoof DTP messages to trick a switch port into forming a trunk, thereby gaining access to traffic from multiple VLANs. By disabling DTP with the command 'switchport nonegotiate' and configuring ports as 'switchport mode access', you prevent any interface from dynamically becoming a trunk, closing the primary vector for hopping. On the CISSP exam, this concept tests your understanding of Layer 2 security controls within the Communication and Network Security domain, often appearing in scenario-based questions where an attacker uses a rogue switch to gain unauthorized VLAN access. A common trap is assuming that simply using VLANs is sufficient, but the real defense lies in disabling trunk negotiation. Remember the mnemonic: "DTP is a Trap" — if you don't need a trunk, shut DTP down.
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.
Which TWO are common techniques to defend against VLAN hopping attacks? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Disable DTP
Disabling Dynamic Trunking Protocol (DTP) on all switch ports prevents interfaces from automatically negotiating trunk links, which is the primary vector for VLAN hopping attacks. By setting ports to 'switchport mode access' and disabling DTP with 'switchport nonegotiate', an attacker cannot trick the switch into forming a trunk and gain access to traffic from multiple VLANs.
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.
✓
Disable DTP
Why this is correct
DTP can be exploited to negotiate a trunk, enabling hopping.
Related concept
Read the scenario before looking for a memorised answer.
Private VLANs limit traffic within a broadcast domain but don't prevent trunk attacks.
✗
Enable Port Security
Why it's wrong here
Port security limits MAC addresses but does not prevent VLAN hopping.
✓
Set access ports as static VLAN
Why this is correct
Static access ports do not negotiate trunks, reducing hopping risk.
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 DTP-related defenses (disabling DTP, setting static access) and other Layer 2 security features like BPDU Guard or Port Security, leading candidates to confuse STP or MAC-based protections with VLAN hopping countermeasures.
Detailed technical explanation
How to think about this question
VLAN hopping exploits either DTP negotiation (attacker sends DTP frames to become a trunk) or double-tagging (attacker crafts frames with two 802.1Q tags, where the outer tag is stripped by the first switch and the inner tag is forwarded to a different VLAN). Disabling DTP and setting ports to static access mode stops the first attack; for double-tagging, the best defense is to use a native VLAN that is not used for any user traffic and to explicitly tag the native VLAN on 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.
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: Disable DTP — Disabling Dynamic Trunking Protocol (DTP) on all switch ports prevents interfaces from automatically negotiating trunk links, which is the primary vector for VLAN hopping attacks. By setting ports to 'switchport mode access' and disabling DTP with 'switchport nonegotiate', an attacker cannot trick the switch into forming a trunk and gain access to traffic from multiple VLANs.
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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