Is VLAN Hopping in Modern Networks Still a Thing?

If you’ve spent any time in the networking or cybersecurity space, you’ve probably heard the term “VLAN hopping.” It refers to an attacker’s ability to break out of a designated VLAN (Virtual Local Area Network) and move into another, potentially more sensitive, VLAN within the same network environment. As more organizations invest in managed switches, firewall segmentation, and other network defense mechanisms, one might wonder if VLAN hopping is still something to worry about.

Unfortunately, like many lingering security issues, VLAN hopping remains a concern if the right precautions aren’t taken. Below, we’ll walk through what VLAN hopping actually is, how attackers traditionally try to pull it off, why it continues to be relevant today, and what steps you can take to defend your network from this sneaky attack method.

Understanding VLAN Hopping

VLANs are a way to segment a network logically—essentially, to divide a larger, flat network into separate, contained areas. This helps with both organizational structure and security. For instance, an enterprise might keep its HR department’s resources on one VLAN and its finance infrastructure on another to keep sensitive information separate. By default, traffic on one VLAN isn’t meant to be accessible to someone on another VLAN unless specific routing rules allow it.

The trouble lies in network misconfigurations or inherent vulnerabilities that, when exploited, let an attacker “hop” from one VLAN to another. Once inside a more privileged or sensitive segment, the attacker can attempt to execute lateral movement and compromise more critical systems or data. Even in modern networks, where security best practices are at the forefront, misconfigurations or overlooked details can still leave an open door.

Classic Attack Techniques

There are two primary methods attackers use for VLAN hopping, and both hinge on a misuse or misconfiguration of VLAN tagging. Although these techniques have been around for years, they can remain effective if organizations fail to lock down their switches properly.

Switch Spoofing

In switch spoofing, the attacker’s system is configured to pretend it’s a trunk port. A trunk port is a switch port configured to carry traffic for multiple VLANs. Under normal circumstances, trunk ports only exist between switches or between a switch and a router to handle inter-VLAN traffic. But if an attacker can trick the switch into thinking their host is a legitimate trunk port, the switch might send along traffic from several VLANs.

This scenario can happen if a switch port is set to “dynamic desirable” or “dynamic auto,” which historically allowed switches to negotiate trunk ports automatically. If an attacker plugs into such a port, they can coax the switch into trunking and effectively open the gate to traffic from the trunked VLANs. It was once considered more common in older Cisco-based environments, but even modern networks can become vulnerable if legacy configurations remain.

Double Tagging

Double tagging relies on the idea that a VLAN tag might get stripped off in a particular way by the first switch, leaving a second tag intact for an attacker to exploit. Essentially, the attacker’s packet carries two VLAN tags. The first tag is recognized and stripped by the switch, revealing a “hidden” second tag that the next switch in the path honors. This can allow a packet to slip into an unauthorized VLAN.

While this technique often has more limitations—like requiring the attacker to be on a native VLAN—it can still cause trouble if not properly mitigated. That said, double tagging is more likely to be successful if the network hasn’t enforced protective measures such as tagging all VLANs separately or ensuring the native VLAN is not used for sensitive traffic.

Why VLAN Hopping Still Matters

Considering the maturity of network technology, you might assume vendors have patched out the vulnerabilities. In many cases, they have implemented preventative defaults. But human factors remain the wildcard. Misconfigurations, outdated hardware in smaller offices, or a lack of attention to legacy settings all create openings. Organizations are also embracing more complex network infrastructures—software-defined networking (SDN), hybrid cloud setups, and container-based deployments.

Complexity can breed misconfigurations. A single oversight on a switch port in a remote office or a test environment can leave a window open for an attacker. Furthermore, the stakes are higher than ever: once inside a VLAN that houses sensitive systems, attackers can exfiltrate valuable data, disrupt operations, or pivot deeper into the enterprise.

Best Practices to Mitigate VLAN Hopping

Lock Down Trunk Ports

Restrict trunk ports to those that truly need to carry multiple VLANs. Manually configure trunks rather than relying on dynamic negotiation protocols. This alone can eliminate many potential attacks tied to switch spoofing.

Configure the Native VLAN

Some experts advise avoiding the use of VLAN 1 (the default native VLAN) for actual user traffic, preferring to handle all user data on explicitly configured VLANs. Properly configuring the native VLAN can limit the success of double-tagging attacks.

Use VLAN Access Control Lists (VACLs)

Many enterprise-grade switches let you apply ACLs directly at the VLAN level. A well-thought-out ACL strategy can prevent unauthorized or unexpected traffic from traversing VLAN boundaries, even in the face of a successful hop attempt.

Implement Port Security

Port security can prevent unrecognized MAC addresses from sending or receiving traffic on a particular port. Although this won’t solve every VLAN hopping scenario, it helps ensure that only legitimate devices can connect to your network.

Monitor Network Traffic

As soon as you see unusual traffic patterns or indications that VLANs are carrying data they shouldn’t investigate. Proactive monitoring and intrusion detection can help you spot strange events before they snowball into full-on compromises.

Regular Audits and Testing

Conduct periodic network audits to catch misconfigurations early. Include VLAN hopping scenarios in your penetration tests to see if any overlooked weaknesses remain. The quicker you catch an “almost old-school” vulnerability, the less likely it is to be weaponized against you.

Stay Current on Firmware and Best Practices

Switch vendors often update firmware patches that enhance security, close known vulnerabilities, and provide better default configurations. By staying up to date, you’ll help ensure that your network infrastructure isn’t left open to known exploits.

Conclusion

Yes, VLAN hopping is “still a thing,” but it largely remains effective only when administrators or engineers haven’t hardened their networks to modern security standards. Like many security threats, it thrives where misconfigurations and complacency intersect. A bit of consistent diligence—especially around ensuring trunk ports are explicitly configured, controlling the native VLAN, and staying current with vendor updates—goes a long way toward keeping attackers locked out.