VLAN Hopping Attack Explained | Techniques, Real-World Risks, and Prevention 2025

Table of Contents

•  What Is VLAN Hopping?
• Why VLAN Hopping Is a Threat in 2025
• How VLAN Hopping Works
• Real-World Attack Flow Example
• Common Misconfigurations That Enable VLAN Hopping
• Detection and Prevention Techniques
• VLAN Hopping in Modern Networks (Cloud and SDN)
• Case Study: Internal Pentest VLAN Bypass)
•  Key Takeaways
• Tools for VLAN Hopping Simulation (For Ethical Use)
• Conclusion
•  Frequently Asked Questions (FAQs)

What Is VLAN Hopping?

VLAN Hopping is a network-based attack technique where an attacker exploits misconfigured switch ports or VLAN tagging mechanisms to gain unauthorized access to network segments (VLANs) that they shouldn’t have access to.

In essence, the attacker manipulates VLAN tagging or switch behaviors to "hop" from their assigned VLAN to another, bypassing routers or firewalls that normally isolate network segments.

Why VLAN Hopping Is a Threat in 2025

Despite improved switch security, VLAN hopping remains a real concern in many enterprise networks due to:

• Legacy switches with insecure default settings

• Dynamic trunking configurations left exposed

• Incorrect native VLAN settings

• Unmonitored or misconfigured ports

If successful, VLAN hopping allows attackers to eavesdrop, sniff traffic, inject packets, or even perform lateral movement toward critical systems.

How VLAN Hopping Works

There are two main VLAN hopping techniques:

1. Switch Spoofing

• The attacker tricks a switch into thinking their port is a trunk port.

• Using Dynamic Trunking Protocol (DTP), they negotiate a trunk.

• Once a trunk is established, the attacker can send traffic to multiple VLANs by adding 802.1Q tags.

2. Double Tagging Attack

• The attacker sends a specially crafted Ethernet frame with two VLAN tags:

  • Outer tag: native VLAN (which gets stripped)

  • Inner tag: target VLAN

• The first switch removes the native VLAN tag, forwarding the packet.

• The second switch reads the inner tag and forwards the traffic to the target VLAN.

 Double tagging is usually unidirectional, allowing the attacker to send packets but not receive responses.

Real-World Attack Flow Example

Let’s say an attacker is on VLAN 10 and wants to access VLAN 20.

Switch Spoofing Steps:

1. NIC config to send DTP packets

2. Victim switch sets port to trunk mode

3. Attacker tags traffic for VLAN 20

4. Attacker gains access to VLAN 20 traffic

Double Tagging Steps:

1. Craft frame with VLAN 10 (outer) + VLAN 20 (inner)

2. First switch strips outer tag (native VLAN 10)

3. Second switch sees VLAN 20 tag

4. Packet is delivered to VLAN 20

Common Misconfigurations That Enable VLAN Hopping

Detection and Prevention Techniques

✅ Disable DTP on all access ports

switchport mode access
switchport nonegotiate

✅ Set a dedicated, unused native VLAN on all trunk links

switchport trunk native vlan 999

Use a VLAN that has no hosts or routing assigned to it.

✅ Use Port Security

Limit the number of MAC addresses allowed per port. Shut down if exceeded.

✅ Monitor with IDS/IPS

Configure your IDS to detect:

• DTP negotiation packets

• Unexpected VLAN tags

• Native VLAN traffic anomalies

✅ Use 802.1X and NAC (Network Access Control)

Enforce device authentication before granting network access.

VLAN Hopping in Modern Networks (Cloud and SDN)

Even in cloud and software-defined networks, similar issues arise when:

• Segmentation is not enforced properly

• Overlay networks (e.g., VXLAN) have misconfigured tenant isolation

• Lack of micro-segmentation allows horizontal access

Security teams must combine logical isolation with policy enforcement, whether on-prem or in the cloud.

Case Study: Internal Pentest VLAN Bypass

During a red team exercise, a consultant discovered a switch port set to dynamic mode. Using the tool yersinia, they negotiated trunking and injected packets into the finance VLAN, which should have been isolated.

The lack of ACLs, dynamic VLAN assignment, and shared native VLANs allowed full visibility into sensitive data streams.

 Key Takeaways

• VLANs are not security boundaries unless configured properly.

• VLAN hopping exploits:

  • Switch spoofing via DTP

  • Double tagging when native VLANs are misused

• Strong prevention requires:

  • Disabling trunk negotiation

  • Using unused native VLANs

  • Enforcing authentication

  • Monitoring for anomalous traffic

Tools for VLAN Hopping Simulation (For Ethical Use)

Conclusion

As attackers become more advanced, lateral movement techniques like VLAN hopping remain effective in environments with poor segmentation hygiene.

Security teams must treat switch configuration audits as seriously as patching and endpoint security.

“Your VLAN setup should be your network’s first checkpoint—not its weakest link.”

If you’d like a full VLAN configuration audit checklist or training on network hardening, let us know—we’d be happy to help secure your infrastructure.

 FAQs

What is VLAN hopping?

VLAN hopping is a network attack where an attacker bypasses VLAN isolation to access other VLANs through switch spoofing or double tagging.

How does VLAN hopping work?

It works by exploiting switch configurations. The attacker either tricks the switch into trunking (switch spoofing) or crafts double-tagged packets to access another VLAN.

What is switch spoofing in VLAN attacks?

Switch spoofing is when an attacker makes their port act like a trunk port to access multiple VLANs.

What is double tagging in VLAN hopping?

Double tagging is the use of two VLAN tags in a packet to sneak past the first switch and be delivered to a second VLAN.

Is VLAN hopping still a threat in 2025?

Yes. Despite improvements, misconfigurations and legacy setups still make VLAN hopping a relevant security risk.

How can I detect VLAN hopping attacks?

Use IDS/IPS systems, monitor VLAN tagging in network traffic, and regularly audit switch configurations.

Can VLAN hopping be used for lateral movement?

Absolutely. Attackers use it to move laterally across segmented networks, bypassing traditional defenses.

What role does native VLAN play in VLAN hopping?

If native VLANs are not changed from default, they allow double-tagged packets to pass through unfiltered.

How to prevent VLAN hopping via switch spoofing?

Set all access ports to switchport mode access and disable DTP with switchport nonegotiate.

How to prevent VLAN hopping via double tagging?

Use a dedicated, unused native VLAN (e.g., VLAN 999) that has no assigned hosts.

Which tools simulate VLAN hopping attacks?

Yersinia, Scapy, and Ettercap are common tools used in ethical hacking to test VLAN security.

What is DTP and how does it relate to VLAN hopping?

DTP (Dynamic Trunking Protocol) auto-negotiates trunk links. Attackers abuse it to spoof trunk ports.

What is the CVSS rating for VLAN hopping?

There’s no fixed CVSS score—it depends on the vulnerability exploited. However, it is considered a high-risk threat.

Can VLAN hopping happen over Wi-Fi?

Indirectly. If the wireless access point is misconfigured as part of a VLAN, the risk increases.

Does enabling 802.1X prevent VLAN hopping?

802.1X helps by enforcing user/device authentication before VLAN access is granted, reducing attack surface.

What operating systems are affected by VLAN hopping?

It’s not OS-specific—it targets the network infrastructure, particularly Layer 2 switches.

Can VLAN hopping be done remotely?

No, it typically requires local network access or physical access to an internal network port.

Are cloud VLANs vulnerable to hopping?

While cloud networks abstract VLANs, misconfigurations in software-defined networks (SDN) can mimic similar risks.

Does microsegmentation help stop VLAN hopping?

Yes. Microsegmentation ensures stricter security boundaries even within the same VLAN.

What are common signs of VLAN hopping attacks?

Unusual VLAN-tagged traffic, unexpected trunk port behavior, or data leakage across segments.

Is using VLANs alone enough for network security?

No. VLANs help with segmentation but are not a replacement for firewalls or access controls.

Should VLAN IDs be randomized for security?

It helps slightly, but proper configuration is more important than ID randomness.

What’s the difference between VLAN hopping and ARP spoofing?

VLAN hopping targets switch behavior; ARP spoofing targets host communications and ARP tables.

How often should I audit VLAN settings?

Quarterly or after major infrastructure changes, including new devices or access points.

Can firewall rules prevent VLAN hopping?

No. VLAN hopping happens at Layer 2, below most firewall layers.

Does disabling trunk ports prevent hopping?

Yes, disabling unnecessary trunk ports and using static access mode mitigates switch spoofing.

What is the best VLAN security checklist?

• Disable DTP

• Set unused native VLAN

• Use port security

• Monitor trunk ports

• Enforce 802.1X

How does VLAN hopping affect compliance (e.g., PCI-DSS)?

It can violate segmentation requirements, leading to compliance failures or audit flags.

Is VLAN hopping part of penetration testing?

Yes, it's a standard part of Layer 2 network security tests in red teaming and audits.

What training or certification covers VLAN hopping?

Courses like CEH, OSCP, and CompTIA Security+ often include VLAN attack techniques and mitigation.