For a few weeks now, I’ve been puzzling over a frustrating problem. My laptop sits on a 2.5Gb wired link, and I have a 1Gb internet connection. Yet every time I ran a speed test, I was getting around 200Mb. Not terrible, but nowhere near what I was paying for.
The strange part? Other devices on my network were getting the full gigabit. Just not this laptop.
So I did what any of us would do: I started swapping hardware. I replaced the cable to the laptop. I replaced the switch. I even replaced the 2.5Gb USB dongle. Nothing changed. Still stuck at roughly 200Mb.
Then one of our engineers made a suggestion I hadn’t considered: could it be the antivirus?
It turns out that was exactly the problem. When I access resources on my local network, the antivirus treats that traffic as trusted and doesn’t bother with deep packet inspection. But when I run a speed test out to the internet, the antivirus inspects every incoming packet. That’s a CPU-intensive job, and at gigabit speeds it becomes the bottleneck. My network was fine all along. My laptop simply couldn’t inspect packets fast enough to keep up.
The moral of the story: if your speed test results aren’t what you expect, try temporarily disabling your antivirus before you start replacing hardware. It might save you a few weeks of head-scratching (and a few cables, switches, and dongles). Just remember to turn it back on afterwards!
