I Spent Half a Day Fixing an Internet Outage -Network Loop

The Cause Was One Cable. Nobody Admits Who Put It There.

I was in the middle of a product label design.

Photoshop open. Layers organized. The artwork was going well. Then someone from another department approach me. His computer had no internet.

I saved my file, closed my layers panel, and went to check.

The Standard Troubleshooting Run

When a single computer loses internet while the rest of the network is fine, the diagnostic path is fairly predictable. You check the basics first.

IP address — is it valid or has it defaulted to a self-assigned 192.168.x.x address? DNS settings — are the correct servers configured? Physical connection — is the cable seated properly, is the port active on the switch? Network adapter — is it enabled, are the drivers current?

I ran through all of it. Everything looked correct on paper.

IP address — fine. DNS — fine. Cable — connected. Adapter — enabled. Network status showing connected. But no internet.

I tried the usual fixes. Release and renew the IP. Flush the DNS cache. Disable and re-enable the adapter. Restart the machine.

(flushdns command in command prompt. search cmd, run as admin.see image below)

Still nothing.

Then I Noticed Something

While I was still troubleshooting that one unit, I started asking around the department casually.

"Is anyone else having issues?"

Silence. Then one person quietly mentioned that actually — yes. Her computer also had no internet. Then another. Then another.

The entire department had lost internet access. Not just one unit.

This changes everything. A single computer losing internet is a local problem — driver, configuration, bad cable, faulty port. An entire department losing internet simultaneously is a network problem. Specifically, it is a problem somewhere between their switch and the rest of the building.

I went to check the switch.

The Network Loop

I looked at the switch. I checked every port — what was plugged in, where each cable was going, whether anything looked out of place.

And there it was.

One extra UTP cable. Plugged into two ports on the same switch.

A network loop.

For non-IT readers — here is what a network loop does. Ethernet switches work by forwarding data packets to their destination. When a cable connects two ports on the same switch, it creates a closed circle. A packet enters, gets forwarded, comes back, gets forwarded again, comes back again — indefinitely. The switch begins drowning in its own traffic. Network performance collapses. Internet access disappears. And the switch itself, depending on the model, may not have Spanning Tree Protocol configured to catch and break the loop automatically.

The result looks like an internet outage. But it is not the internet. It is the switch suffocating under a loop it cannot escape from.

I unplugged the extra cable.

Internet came back immediately. All units. Entire department. One cable removed.

The Part Nobody Will Admit

Here is the thing about that extra UTP cable.

It did not plug itself in

(To my work-mates, if you're reading this, sorry! 😂)

Someone in that department, at some point before I was called, decided to do some self-diagnosis. Maybe a cable looked loose. Maybe they thought connecting something would help. Maybe they just wanted to try something — the way non-IT people try things on computers when they are frustrated, with complete confidence and zero information.

And they created a network loop.

When I asked — gently, professionally, with my best neutral IT face — nobody knew anything about the cable. Nobody saw anything. Nobody touched anything. The cable had apparently materialized in the switch port through some process that did not involve any human hands in that department.

I nodded. I said okay. I packed up my tools.

But I know. They know I know. We all know. 😄

This is one of the unwritten rules of IT support: sometimes the problem is not technical. It is social. And the correct professional response is to fix the cable, restore the internet, and let everyone quietly return to pretending the incident never happened.

What a Network Loop Is and How to Spot It

For anyone managing a small office network — here are the signs that you might have a loop:

Sudden complete loss of network access across multiple devices simultaneously, with no changes made to the main router or internet connection.

Switch indicator lights flashing rapidly and continuously across multiple ports — more activity than normal traffic would generate.

The internet was working fine, then suddenly was not — with no storm, no power outage, no ISP notification.

Basic troubleshooting on individual computers finds nothing wrong — because nothing is wrong with the computers. The problem is at the switch level.

The fix, in a small unmanaged switch environment, is straightforward: identify and remove the cable creating the loop. If your switch supports it, enabling Spanning Tree Protocol (STP) provides automatic loop detection and prevention — so future loops are handled by the switch itself before they take down the network.

In a larger managed network environment, loop protection features can be configured per-port. But for a small government office with an unmanaged switch and a department full of people who occasionally try to help — the most practical protection is a label on the switch that says: "Do not plug cables here without calling IT first."

Before I Close This Tab

Whole afternoon. That is what a single misplaced cable cost.

Half a day of troubleshooting, diagnosing, running through configurations that were all correct, checking ports, tracing cables, and finally finding the one physical thing that should not have been there.

The product label I was working on waited patiently in Photoshop. The layers were still organized when I got back. The design picked up where it left off.

The internet in that department was restored. Nobody admitted anything. Life continued.

This is IT support in a government office. It is not always glamorous. It is not always logical. Sometimes the problem is one cable and half a day. Sometimes the mystery is solved and the culprit is never named.

But the switch is clean now. The network is loop-free. And somewhere in that department, one person is very quietly relieved that the internet works again. 

P.S. — If you work in an office and you ever feel the urge to "just try something" with a cable or a network port without calling IT first: please do not. Call IT first. We will come. We do not judge. We just need you to not create a network loop while we are in the middle of a label design. Thank you. 😄

-Mavs