Ethernet suddenly running at 100Mbps instead of 1000Mbps

Rydberg95 · 20 Jan 2021

Hi,

So, a few weeks ago I had some problems with getting 1000Mbps running (it ran at 100Mbps) on the motherboards ethernet port. It ended in me buying a PCI-E express card, and the connection started running at 1000Mbps.

The PCI-e card is of model TP-Link TG-3468.
The router is of model ASUS RT-AX82U.
My Windows Version is "Version 20H2 (OS Build 19042.746)"

Fast forward to yesterday, when I (unrelatedly) installed a switch between the router and a couple of other connected devices. I noticed that my desktop computer started running at 100Mbps again, and I can't get it to run at 1000Mbps. I'm not sure that it's related to me installing the switch (it shouldn't be).

Some things I've tried/other info:

The desktop computer not getting gigabit speed is not connected to the switch - it's connected directly to the router.
I tried connecting a Raspberry Pi 4 with the same cable that the desktop computer is using, and it gets 1000Mbps speed. So - the cable doesn't seem to be the problem.
I tried switching the PCI-E slot that the gigabit card is installed into, and it doesn't make a difference-.
I tried installing the latest drivers (both from TP-Link:s website, and Windows Update). No difference.
I tried forcing gigabit speed in the settings of the adapter, but it still connects with 100Mbps.
I tried connecting the desktop computer with a brand new cat 6 cable, and it still connects at 100Mbps.
I think some Windows Updates was installed a few days ago. Don't know if it could be related.

Does anyone have any suggestions in getting my connection to run at 1000Mbps again?

RickC · 20 Jan 2021

The first thing I would try is another ethernet cable as a substitution test.

(I realise you did a check already using a Raspberry Pi and the cable appeared OK.)

Hope this helps...

Rydberg95 · 20 Jan 2021

RickC said:

The first thing I would try is another ethernet cable as a substitution test.

Hope this helps...

The same cable works with gigabit speed when connecting a Raspberry Pi 4 with it.

I also tried a brand new cat 6 cable, and it makes no difference. I'll update the initial post with this.

zebal · 20 Jan 2021

Rydberg95 said:

Fast forward to yesterday, when I (unrelatedly) installed a switch between the router and a couple of other connected devices. I noticed that my desktop computer started running at 100Mbps again, and I can't get it to run at 1000Mbps.

Network can't be faster than slowest hardware device on network link.
That means even if your NIC is 1000 Mbps it won't run higher than 100 Mbps if at least one link node run at 100 Mbps.

it looks like your switch can't work at 1000 Mbps, or there is some other device that limits you to 100 Mmbps.

Rydberg95 · 20 Jan 2021

Well, then I don't understand how it is explained that I get gigabit speed when I connect the Raspberry Pi 4 using the same cable? And I get true gigabit speed - I checked using iPerf.

I do however have a Raspberry Pi 3, which is limited to 100Mbps, but I don't see how it's related?

zebal · 20 Jan 2021

You need to investigate which device (network card, cable, switch, laptop, PC, phone etc..) anything attached to network, is working at 100 Mbps.

then to confirm remove it from network to verify.
Just one node that is capped at 100 Mbps will make whole network work at 100 Mbps.

Once you identify problem node, you can investigate whether it supports 1000 Mbps.

Rydberg95 · 20 Jan 2021

Well, no, the whole network is not running at 100Mbps. The two Raspberry Pi 4:s i have connected are running at 1000Mbps.

NavyLCDR · 20 Jan 2021

Connect the Raspberry Pi4 directly to the desktop computer and see if they establish a gigabit link between them.

Rydberg95 · 20 Jan 2021

Tried that now, and it connects at 100Mbps... I'm starting to think that the ethernet card has gone defective for 1000Mbps speed or something. It just feels like it shouldn't have, since it's brand new.

NavyLCDR · 20 Jan 2021

Rydberg95 said:

Tried that now, and it connects at 100Mbps... I'm starting to think that the ethernet card has gone defective for 1000Mbps speed or something. It just feels like it shouldn't have, since it's brand new.

Yes, you have now isolated it to the computer rather than the network. You might want to try making a linux live USB, boot the computer into Linux and see if you can get gigabit. If you do, then you have isolated it to a software problem rather than a hardware problem. You could also retest the motherboard's onboard network adapter with Linux as well.