"Browsing from a Ubuntu Live CD - All fine here."
In this case I'd be blaming the OS. how and why I don't know though. maybe something is still pointing to your old router or trying to find something on your old network?
Fingers crossed the new NIC gets around whatever the issue is

ipconfig /flushdns
would be a good one then to get rid of old entries.

What for category ethernet cables have you tried?

evasive wrote on 2021-03-24, 11:18:

ipconfig /flushdns
would be a good one then to get rid of old entries.

I've tried that once and while it seemed to have fixed it for a while, the network connection reverted back to its unstable state on the next day. I've ran it again just now, so we'll see if that fixes it.

SpectriaForce wrote on 2021-03-24, 15:31:

What for category ethernet cables have you tried?

I'm using CAT5E Ethernet cables.

"Both computers are plugged in directly to my Xfinity modem via Ethernet."
AFAIK, xifnity doesn't support multiple IP addresses for consumer plans. Did you try putting a router behind the modem and plug computers to the router instead ?

^ "Modem" in this case probably refers to the wifi-router-modem combo unit they give you by default to rent from them.

Completely reset the TCP/IP config on the problem computer.

In an admin command prompt run:

netsh int ip reset

Then reboot and try again.

cyclone3d wrote on 2021-03-26, 02:15:

Completely reset the TCP/IP config on the problem computer. […]
Show full quote

Completely reset the TCP/IP config on the problem computer.

In an admin command prompt run:

netsh int ip reset

Then reboot and try again.

Tried that. While it seemed to have worked after the first reboot, it became slow and unstable again on the next day. I'm wondering if my integrated Intel NIC is borked or something.

Is this https://downloadcenter.intel.com/download/187 … 7-Final-Release the driver you're using ? if not... why don't ya give it a try.

weedeewee wrote on 2021-03-28, 14:44:

Is this https://downloadcenter.intel.com/download/187 … 7-Final-Release the driver you're using ? if not... why don't ya give it a try.

Tried that, didn't change a thing. Now I think I'll try uninstalling and reinstalling my Ethernet drivers to see if that fixes anything.

EDIT: Reinstalling the drivers didn't fix it. The internet connection is still unstable. While restarting the computer does fix it, it tends to be an annoying task to have to restart the computer shortly after turning it on every time just to fix the internet connection. If I leave the computer turned off for 30 seconds then turn it back on, the connection becomes unstable again. I've tried unplugging it for 30 seconds to see if it's a dead CMOS battery that's causing it, definitely not the case as the BIOS settings remained intact.

I guess it would be worth a shot to wait until my TP-Link NIC arrives so I can try that just to see if it is a faulty NIC that's causing this issue.

Given that you already covered many of the basics I will go for some odd possibilities :

¿Did yo try manually setting DNS servers of fast providers, i.e. Google's DNS? (8.8.8.8 / 8.8.4.4)

¿Have you checked your router's config to confirm there is no binding of you PC's MAC address to an IP address other than the one it is currently using?

HTH

Random question have you tried swapping the Ethernet port for the slow computer on the router it could be that port on the router is flaky/ going bad. I had a very similar issue with a switch at work swapped the port and it's been fine since.

I ran into this once and I had to mess with TCP auto-tuning settings in Windows via command line. Absolutely can't remember what I changed it's been so long, but worth a search/try.

Reduce the network speed , from 1Gb to 100Mb

I'd be switching OSs

I know I'm necroposting on a 6-month old thread, but I've managed to fix this issue not long after my last reply. I was able to fix it by following this suggestion:

dataino.it wrote on 2021-04-16, 16:20:

Reduce the network speed , from 1Gb to 100Mb

This miraculously fixed the issue for me, everything's all good now. Thanks.

---

Caluser2000 wrote on 2021-04-16, 16:32:

I'd be switching OSs

Unfortunately, that is easier said than done for me as I despise Windows 10 (and 11) with a burning passion. I've already used my only Windows 8.1 Pro license on another computer (the one that was working the whole time). I can't use Linux because there are certain Windows-only applications that I rely on (e.g. Paint.NET, which doesn't seem to work properly on WINE) and my printer's manufacturer (Canon) is notorious for having bad Linux support (just going by what some people have reported, I haven't actually tested my printer with a Linux computer so IDK if it'll work or not). However, I was pretty close to giving it a try since I've tried posting this topic on a couple other forums with no replies at all (and was about to post it on more forums, if not for me managing to fix the issue).

Have you tried changing the flow control setting in the nic driver ?

KCompRoom2000 wrote on 2021-09-15, 00:57:

Unfortunately, that is easier said than done for me as I despise Windows 10 (and 11) with a burning passion.

You and me both. Haven’t tried 11 yet.