Network performance weirdness (SOLVED: caused by LastPass extension)

Hi guys!

I have a weird issue. I’m on a fiber connection with a 100/100 Mbit connection. Using our local testing tools for bandwidth testing, my iMac reports download speeds of around 120 down, but I generally get only 25 to 30 up. This iMac is on Ethernet with a router between my switch and the ISP’s endpoint.

I did the same test using a Lenovo laptop hooked directly into the ISP box too, with very similar results.

So, I used the same test tool on my iPad Pro over WiFi. Imagine my surprise when I suddenly get upload speeds reported as 125 Mbit. This goes through an access point connected to the same switch and router as before. Weird, right?

Not really sure where to continue with troubleshooting here, so wondering if anyone here can explain this behavior? My only idea is messing with the “Hardware” settings on my Ethernet port, but I’m not too keen on this. (Current settings are “Automatic” which translates to 1000baseT, full-duplex, MTU standard (1500) and a tick box enabling AVB/EAV mode, whatever that is…

Thanks for any insights into this mystery!

EDIT: When using the iMac over WiFi, I get very similar results as when using Ethernet.

Could this be a case of your ISP sensing that you are running a speed test and adapting your connection to appear faster?
I can’t find a ref, but have heard of this happening.
This would mean adapting to different clients, which might be far-fetched.

Thought: do you have anything running that might be changing your throughput (firewall, little snitch, etc.)? Maybe try a clean account on each device?

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I would begin by running traffic tests between machines on your own network connected to the switch via ethernet and with their WiFi radios turned off.

Edit: It’s probably best to leave the switchport hardware settings as they are.

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Thanks John!

  1. I very much doubt the ISP is dynamically shaping the bandwidth, as I was on the phone with their tech and re-running the measurement in order to determine if his applied changes was working or not.

I have considered that the Mac/Windows clients are somewhat differently written or use a different method to saturate the upload pipe.

  1. In my iMac, I don’t have a lot of software running that should affect network performance. The Lenovo has a bit more, but reported results were comparable.
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SOLVED: So, it turns out the culprit was a browser extension. The LastPass extension was for some reason either slowing the upload test or messing with the calculations used by the speed test software.

Now I need to figure out if my upload speed is indeed lowered. If it truly affects performance this much, I may need to consider moving to 1Password. In any case, it should only be affecting uploads done through a web browser, but still.

Weird indeed…

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