Question Getting much slower internet speeds with Comcast than what I'm paying for

Mervil

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I have noticed that my zoom call quality has been subpar lately. In troubleshooting this, I did a speedtest, and found that I am getting 250-300 mbps on my main device, rather than the 800mbps that I pay for with Comcast Xfinity.
I called Comcast and they reported to me that everything seemed to be fine on their end, and blamed my modem. At that time (which was just 4-5 days ago), I was using a TP-Link TC-7620 (DOCSIS 3.0) modem, with a TP-Link AC1900 wifi router. I was previously getting good speeds on the modem, so I didn't think it was the modem. But the phone tech, as well as the in-person tech said it was the modem, and that replacing it would fix the issue.

I have now purchased a Netgear Nighthawk CM-1200 (DOCSIS 3.1) modem. And wouldn't you know it? It DIDN'T fix the issue! (still using the TP-Link router)

Spent a lot of time with customer service, and a second technician just left my home. Issue still persists.
The technician WAS very helpful. He had me tweak some ethernet controller settings (in particular I changed my "Speed & Duplex" from "Auto Negotiate" to "1.0 Gbps Full Duplex"). This did improve my download speeds a small amount.
When he connected his tester to my router, he showed he was able to pull in a full 950-980 Mbps through the router. So the technician concluded that it must be my device's fault.
However, ALL of my devices have the same issue: Whenever I run a speedtest with ANY of my devices (connected directly into the modem, or the router's LAN port, or via the router's wifi) with either Ookla or Xfinity speed tests, the speed starts FAST initially, showing 750-920 mbps (which is what I expect), but after 2-3 seconds, the speed begins to taper down and completes at 250-300 mbps. Sometimes lower, sometimes higher (like I just did it and got 500, but then tested again and got 220).

My PC is using a wired connection with a CAT6 cable to the router, which in turn is connected to the modem with a CAT6 cable. But even when I am hardlined into the modem with my PC, it doesn't change anything (getting the same speedtest results). Even if I have no other devices connected to the router (via wifi) the issue persists (this is ensured by turning the wifi radio off). At any one time I could have about 12 devices connected to the wifi, but only about 6-8 of those are using internet. When all the kids are home, this can increase to about 16-20 devices on the network, with tablets and smart TVs being on (and accessing internet, all via wifi). Will note here that there is only one device that uses ethernet instead of wifi and that is my main PC. However, ALL of my devices that access the internet and can run speedtest are showing the same results.


My Network:
Netgear Nighthawk CM-1200 cable modem with 4 ports (only 1 being used)
TP-Link ArcherC9 AC1900 wifi router with 4 LAN ports (only 1 being used currently during testing)
[[Disney's MyCircle ver.2 connected to the router via stock CAT cable, and wifi when fully setup (but disabled for this testing)]]
[[TP-Link AV600 Powerline Adapter (TL-PA-4010) connected via CAT6 cable to the router (but unplugged for testing)]]
[[Netgear WiFi Mesh Range Extender EX-7000 plugged into the other end of the powerline adapter (but unplugged for testing)]]


My PC:
MoBo: ASUS ROG Strix B550-F gaming
CPU: AMD Ryzen 5 5600x (no overclocking) with stock cooler
RAM: brand new G.Skill Trident Z RGB DDR4-3200 8GBx2
SSD: SK Hynix Gold P31 1TB (M.2-2280 NVME) with about 350GB of space left
(there is another SATA III SSD and two HDD in my rig, but are used for storage, and no OS services)
GPU: Gigabyte Radeon RX 5700XT 8GB Gaming OC
PSU: Enermax Revolution D.F. 850W 80+ Gold cert

WOA. Update.
I actually just discovered that my laptop has an ethernet port (it was a very narrow ethernet port, but the bottom edge of the port can spring down to fit the CAT cable...).
When I tested my laptop via WiFi right next to the router, it was pulling down 260Mbps. However! when I connected the cable, I am pulling 940-960Mbps consistently.
So...IS it my PC? How would I fix this!?

Thank you very much!
 
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Mervil

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what kind of cable your PC is using?
All my cables are CAT6 (including the one to the PC), except for the one connected to the Disney Circle ver2, i have no idea what kind of cable that is. It has ethernet connectors, but the cable is gray and flat, with no labeling. However, I'm not using that one currently anyway.
 
All my cables are CAT6 (including the one to the PC), except for the one connected to the Disney Circle ver2, i have no idea what kind of cable that is. It has ethernet connectors, but the cable is gray and flat, with no labeling. However, I'm not using that one currently anyway.
hmm something unlabeled, that could be anything like aluminium coated with copper

you tryied multiple cables on your PC?

do a small test, copy some big file from your laptop to your PC over local ethernet
you will need to setup windows file sharing, once done, than you can see how bandwith goes
 

Mervil

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hmm something unlabeled, that could be anything like aluminium coated with copper

you tryied multiple cables on your PC?

do a small test, copy some big file from your laptop to your PC over local ethernet
you will need to setup windows file sharing, once done, than you can see how bandwith goes
Ok. What exactly am I looking for when I do this? What should I take note of?
 
You can also use a very old program called IPERF to test between machines in your house. This is a line mode program that is not affected by things web browsers or cpu or even memory. It is a very simple test that pretty much checks the hardware and the drivers.
You really want all the devices on ethernet since wifi will bottleneck the connection.

I am surprised if wifi speedtest are anywhere close to your cabled PC. It is kinda expected that you will not get much over 300-400mbps on most wifi.

There are a couple of common things that cause this. First try to disable IPv6 on your pc or even on your router. IPv6 pretty much just causes issues and provide very little benefit. Next check that you do not have any form of QoS or so called "gamer" software installed. This would be anything that claims to prioritize traffic.
This software tends to be bundled with the bloatware you find in some motherboards and video cards. It tends to install when you load drivers unless you happen to see the option to not install it. These too provide no benefit and cause all kinds of issues for people with faster connections.

I would be suspect of any cables that do not have clear markings on them. You should find markings and most times the letter EIA/TIA. The key ones to look for is the wire size normally you see something like 23 AWG. This number needs to be 22-24. You also might find the letter CU which indicates the wire is pure copper but if you find the marking CCA that is copper clad aluminum which is not a valid material to make ethernet cables from. Any cable that is flat likely have extremely small wire...most times 30 or even 33 (bigger number is thinner). None of these meet the standard for ethernet cable.

A bad ethernet cable will many time appear just as you describe. It will start fast but as it takes more and more errors speedtest will drop the speed trying to prevent the errors. That is actually how speedtest figures out the speed. It will send data until it exceeds the internet connection which will cause the ISP to drop the data.
When you have something else causing the loss like a bad cable the speedtest numbers will be lower than they should be.
 
So i went and looked up your motherboard. Like many of the new asus things it does have that stupid "gamerfirst" software. If you have that installed uninstall it.

The other thing I noticed is it has a 2.5g ethernet port. These have a history of strange issues. Intel shipped a bunch of chipsets a couple years back that they could not fully fix with just drivers. But both realtek and intel have had a long list of bugs that they fix and break something else.
It has been so long you would have though it would be fixed. I would verify you have the newest driver directly from intel. Windows tends to be "helpful?" sometimes and loads default drivers.
 

Mervil

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So i went and looked up your motherboard. Like many of the new asus things it does have that stupid "gamerfirst" software. If you have that installed uninstall it.

The other thing I noticed is it has a 2.5g ethernet port. These have a history of strange issues. Intel shipped a bunch of chipsets a couple years back that they could not fully fix with just drivers. But both realtek and intel have had a long list of bugs that they fix and break something else.
It has been so long you would have though it would be fixed. I would verify you have the newest driver directly from intel. Windows tends to be "helpful?" sometimes and loads default drivers.
Thank you for looking into this! I do have ASUS Armoury Crate installed, but it looks like GameFirst VI is not installed (i never installed it, and when I look at the list of Utilities that are installable in ASUS Armoury Crate, it seems to indicate it has not yet been installed). But there IS something called "GameSDK Service" installed. I have no idea what that is, or how to remove it...yet.
I actually do have the most recent version of the driver from Intel (intel driver 27.2 for Ethernet Controller I225-V).

The cable that isn't labeled is not being used currently. It only links my router to the Disney MyCircle device, which is currently disabled, and the cable is unplugged from my router. The cable that runs between my router and my PC is a clearly labeled CAT6 cable.
That same CAT6 cable, when plugged into my laptop pulls a nice 940Mbps, and that is with IPv6 turned on.

Now, here is something I find very strange:
I was thinking it could be a driver issue, so I uninstalled the drivers for my ethernet controller. I then went and downloaded the original drivers from the ASUS website for my motherboard. After this, I found that the speed test WAS giving me full speed of 940Mbps consistently on my main PC!
But then I went and broke it again--I installed the most recent drivers over those original drivers, and it stopped working (I did this to test what would happen).
Well, I figured I would just uninstall the drivers and re-install the original drivers. Well, now it is NOT working. So, I am getting crap speeds on my PC even with the original drivers installed now.
I just don't get it.
 
The cheapest thing and one of the simplest is to try a new cable just to be sure. Cables are really strange when they fail they can work randomly and they can work on some machines and not others. All it takes is a wire internal to one of the ends to be just slighltly loose and it can cause errors and it may change a bit as the end of the cable changes in temperature.

You could try a USB linux boot image. These run completely from the USB stick. It would let you test the hardware is ok. Unfortunately if it tests good you are back to what garbage is hiding some place in windows either software or some magic setting someplace.

I would not worry a lot about the gamesdk thing. It is bloatware but all it does is let games run the fancy leds on video cards or even the backlight on asus monitors.
 

Mervil

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So I tried a different CAT6 cable (the one that I had running to a powerline adapter), and I'm still having the same issue.
However, operating off of the possible driver issue or possible bloatware slowing me down, I just reformatted my PC and re-installed Windows with no extra software, and only minimal drivers at this time.
I am currently getting good speeds. So, my guess is some driver issue or bloatware. I'm going to install everything piecemeal and see if anything causes the slow down as I go.
 

Mervil

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So I tried a different CAT6 cable (the one that I had running to a powerline adapter), and I'm still having the same issue.
However, operating off of the possible driver issue or possible bloatware slowing me down, I just reformatted my PC and re-installed Windows with no extra software, and only minimal drivers at this time.
I am currently getting good speeds. So, my guess is some driver issue or bloatware. I'm going to install everything piecemeal and see if anything causes the slow down as I go.
Wanted to let you all know, that I think I have pinpointed the cause of my issue:
After formatting and re-installing everything piecemeal, after I installed "ASUS Armoury Crate" with "AURA Sync", my internet speeds dropped from 940 to 250. I uninstalled every component of that, and speeds are back up. I have this software installed so that I can control the RGB of my pc. but for now, I guess I'll leave it off.
 

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