Introduction

The world of network security is constantly evolving as attackers seek new methods to exploit system vulnerabilities. As enterprises increasingly rely on Virtual Local Area Networks (VLANs) to segment and manage network traffic efficiently, it becomes critically important to understand the threats that accompany such architectures. One such threat is VLAN-hopping, a malicious technique that allows attackers to access VLANs they are not authorized to interact with. Among the various methods of VLAN-hopping, one particular variant can be mitigated effectively by implementing a specific configuration: assigning an unused VLAN as the native VLAN. In this comprehensive blog by DumpsQueen, we’ll dive into the intricacies of VLAN-hopping, how the native VLAN contributes to this attack vector, and ultimately, in which type of VLAN-hopping attack may be prevented by designating an unused VLAN as the native VLAN. By the end, you'll gain a deeper technical understanding along with sample questions to reinforce your learning.

What is VLAN-Hopping?

VLAN-hopping is a type of network attack where an unauthorized device gains access to traffic on VLANs to which it does not belong. This unauthorized access compromises the security model designed by VLAN segmentation. The attacker takes advantage of switch behavior and misconfigurations to inject packets into other VLANs, essentially “hopping” from one VLAN to another. Typically, VLAN-hopping is carried out through two main types of techniques: switch spoofing and double-tagging. Each uses different mechanics but ultimately aims to bypass normal access controls to reach restricted network zones.

The Role of Native VLAN in Switch Communication

Before we understand how VLAN-hopping can be prevented, it’s important to revisit the concept of a native VLAN. In Ethernet networks that use IEEE 802.1Q tagging, the native VLAN is the VLAN that carries untagged traffic. When two switches are connected, trunk ports are often configured to allow multiple VLANs to pass traffic. If a frame is sent without a VLAN tag, it is assumed to belong to the native VLAN. This behavior creates a vulnerability in certain configurations. Attackers can exploit the fact that untagged traffic is accepted on a trunk port and may use it as an entry point into other VLANs.

Double-Tagging VLAN-Hopping Attack Explained

Of the two main VLAN-hopping techniques, double-tagging is the one that specifically exploits the native VLAN configuration. Here's how it works: In a double-tagging attack, the malicious host sends a specially crafted frame with two VLAN tags. The outer tag corresponds to the attacker's VLAN, which the switch processes and strips off. The inner tag is left intact and forwarded to the target VLAN as the frame traverses the network. If the native VLAN is misconfigured or if it matches the attacker’s VLAN, the inner tag is accepted by the target VLAN without further verification. This technique is particularly dangerous because it does not require the attacker to negotiate a trunking protocol, making it harder to detect.

The Importance of Using an Unused VLAN as the Native VLAN

This brings us to the core of the discussion in which type of VLAN-hopping attack may be prevented by designating an unused VLAN as the native VLAN? The answer is: double-tagging attacks. By setting the native VLAN to a VLAN ID that is not used for any real traffic essentially an unused VLAN administrators can ensure that untagged traffic (which might contain malicious frames) is dropped or isolated, and not forwarded to any production VLANs. This configuration thwarts the double-tagging strategy since the inner tag won’t be forwarded through the trunk, making it ineffective. It also breaks the assumption attackers rely on: that the native VLAN will carry or bridge their traffic to the intended target.

Implementation Considerations

When implementing this defensive configuration, network engineers need to do more than simply assign an unused VLAN as the native VLAN. Other best practices that reinforce this strategy include:

Ensuring all access ports are explicitly configured and do not negotiate trunking dynamically.
Avoiding use of VLAN 1 as the default or native VLAN.
Disabling auto-trunking protocols like Dynamic Trunking Protocol (DTP) where not necessary.
Consistently applying the unused VLAN configuration across all trunk ports.

While these additional steps are not required to answer the specific keyword query, they form a holistic approach to securing VLAN environments.

Why DumpsQueen Recommends Understanding VLAN Security

At DumpsQueen, we specialize in offering expertly prepared exam resources that not only help you pass certifications but also deepen your practical understanding. Network certifications such as Cisco CCNA, CompTIA Network+, and CEH (Certified Ethical Hacker) include VLAN-related questions that test your ability to recognize attack vectors like double-tagging. By understanding concepts like native VLAN configuration and VLAN-hopping techniques, candidates not only pass their exams with confidence but also carry forward real-world skills applicable in enterprise-grade network environments.

Real-World Example of a Double-Tagging Attack

Imagine a data center network where VLAN 10 is used for users, and VLAN 20 is reserved for financial systems. The native VLAN on the trunk ports is VLAN 10 the same VLAN the attacker is on. The attacker sends a frame with an outer VLAN tag of 10 (which the switch strips) and an inner tag of 20. The switch receives the untagged frame (after stripping the outer tag), interprets it as native VLAN traffic, and forwards it through the trunk. Since the second switch does not check for inner tags, it forwards the frame to VLAN 20. If the native VLAN had instead been an unused VLAN (e.g., VLAN 99), the frame would not have been processed as intended, and the attack would have failed.

VLAN-Hopping and Certification Exams

Understanding VLAN-hopping attacks is not just a theoretical exercise; it’s a highly tested topic in various certifications. Exams will often present a scenario describing network traffic misbehaviors or configurations and ask the candidate to determine the cause or prevention method. In such cases, knowing in which type of VLAN-hopping attack may be prevented by designating an unused VLAN as the native VLAN gives a clear, confident answer: double-tagging. Whether you're preparing for Cisco CCNA, CompTIA Security+, or EC-Council CEH, DumpsQueen provides curated exam content with updated practice tests and explanations aligned to the latest syllabus.

Free Sample Questions

1. In which type of VLAN-hopping attack may designating an unused VLAN as the native VLAN help in mitigation?
A. MAC flooding
B. Double-tagging
C. Switch spoofing
D. ARP poisoning
Correct Answer: B. Double-tagging

2. What is the main purpose of assigning an unused VLAN as the native VLAN on a trunk port?
A. To increase VLAN capacity
B. To enable inter-VLAN routing
C. To block untagged frames from reaching production VLANs
D. To simplify VLAN management
Correct Answer: C. To block untagged frames from reaching production VLANs

3. Which of the following is a valid technique to prevent double-tagging VLAN-hopping attacks?
A. Enable DTP on all switch ports
B. Use VLAN 1 as the native VLAN
C. Assign an unused VLAN as the native VLAN
D. Allow all VLANs on trunk ports
Correct Answer: C. Assign an unused VLAN as the native VLAN

4. What behavior allows double-tagging VLAN-hopping attacks to succeed?
A. Incorrect VLAN tagging on access ports
B. Acceptance of tagged frames on access ports
C. The stripping of the outer tag on a trunk port
D. Use of encrypted management protocols
Correct Answer: C. The stripping of the outer tag on a trunk port

Conclusion

Securing VLANs requires a deep understanding of how traffic moves across trunk links and how attackers might exploit these mechanisms. One of the most effective yet often overlooked defenses is the configuration of an unused VLAN as the native VLAN. This strategy directly addresses the risk posed by double-tagging VLAN-hopping attacks, which rely on the switch’s handling of native VLAN traffic to succeed. For aspiring IT professionals and network engineers, this is not just another exam topic it’s a real-world tactic that strengthens network security posture. At DumpsQueen, our mission is to equip candidates with both the knowledge and the tools to pass their certifications and succeed in their careers. We offer updated exam dumps, practice tests, and full study guides for CCNA, CEH, and more all crafted to include key topics like VLAN security, attack vectors, and mitigation strategies. Understanding in which type of VLAN-hopping attack may be prevented by designating an unused VLAN as the native VLAN is just one example of how DumpsQueen helps you master certification objectives with clarity and confidence.