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In the world of IT, there is one expression that lowers defenses more effectively than any zero-day exploit: “Don’t worry, they’re on different VLANs.”
It is a reassuring phrase, usually spoken in good faith, but it masks a massive cultural blind spot. The moment you assign “strong” security value to a VLAN, you are already building a vulnerability. It’s silent, orderly, and clean-exactly the way attackers like it.
VLANs were never created for security; they were created for organization. Treating them as an impenetrable wall is one of the most common-and longest-standing-mistakes in enterprise networking.
A VLAN’s job is to divide broadcast domains, tidy up traffic, and make the network manageable. These are legitimate, useful goals.
But separation does not equal protection.
The problem arises when this logical separation is mistaken for a defensive barrier. We see it constantly: user VLANs over here, servers over there, and management “somewhere else.” On paper, it looks beautiful. In a diagram, even better. In reality, it takes very little for that separation to become purely cosmetic.
And no, you don’t need a sophisticated attack. More often than not, a “convenient” configuration is all it takes.
It’s true: many classic VLAN hopping techniques have been known for decades.
And that is precisely the point.
If they still work, it’s not because the attacker is a genius; it’s because the network has been left behind. Native VLANs still in use, trunks left open “just in case,” access ports using dynamic negotiation-these are things that shouldn’t exist in 2026, yet there they are.
However, focusing solely on VLAN hopping is almost misleading, because in most real-world incidents, you don’t even need to “hop.”
In daily practice, the scenario looks like this:
An attacker gains entry through a low-impact VLAN, perhaps a user workstation or a marginal IoT device. From there, they discover that inter-VLAN routing is broad and permissive-designed more to “make things work” than to actually limit access.
At that point, the VLAN stops being an obstacle and becomes a fast lane. Servers, backups, management systems, and dev environments: everything is reachable because it’s “internal,” because it’s “trusted,” because “it’s on another VLAN anyway.”
This is where security truly breaks.
Many network architectures still carry the weight of a twenty-year-old idea: Inside the network, we can trust each other.
In this model, the VLAN is just there to provide order. But order is not security-and it certainly isn’t Zero Trust. If your defense relies on the concept that “whoever is on that VLAN is trustworthy,” then you aren’t segmenting; you are distributing trust in bulk. And in cybersecurity, trust is always the first asset to be betrayed.
Some think this is only a “traditional” networking problem. It isn’t.
In virtualized datacenters and cloud environments, segmentation is even more abstract. VLANs, VXLANs, overlays, vSwitches-it’s all very elegant and powerful. It is also extremely fragile if misconfigured.
A slip-up in a virtual switch, an overly broad policy, or a poorly copy-pasted rule, and lateral movement becomes invisible, rapid, and incredibly difficult to intercept. The segmentation exists, but only in theory.
A VLAN only begins to make sense from a security perspective when it is treated for what it is: a brick, not a wall.
You need more. You need control. You need friction. You need a point where traffic is actually inspected, filtered, and authorized. This means inter-VLAN firewalls, sensible ACLs, access authentication, and continuous monitoring.
Above all, it requires a shift in mindset: A VLAN is not a security perimeter. It is just a line on a map.
If there is one thing that should be erased from the corporate IT vocabulary, it’s this: “It can’t happen; they’re on different VLANs.”
Because in most cases, when it does happen, they were indeed on different VLANs. It’s just that nobody realized that wasn’t enough.
VLANs organize. Security is built.
Confusing the two is exactly why we continue to see “well-segmented” networks fall without making a sound.
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