Question Not Getting Gigabit Speeds with Two AsRock B450M Steel Legend and Windows May Updates.

Aug 25, 2019
I just had Comcast install a Gigabit service to my home. I have 2 AsRock B450M Steel Legend builds. Both have a HP NC364T NICs and the onboard Realtek Gigabit LAN.

I am unable to get more than 490Mbps ( 112Mbps on on any port using multiple Cat6 cables (varies manufactures) even if it is the only device plug directly into the Gigabit Modem.

I have an HP Omen 15, Dell Latitude E7270, and a MacBook Air, that all, when wired, get the Gigabit Speeds 880-1280Mbps on both and Also have an iPhone 10Xs that gets into the 600-700Mbps on the wireless network. So, it being a configuration issue on Comcast's side is pretty unlikely at this point. But to confirm this I had Comcast do further diagnostics and everything seems to be running very well on their end.

In my testing –

I have disabled all Ports and attempted to use one port at a time while connected straight to the Modem using different Cat6 cables. Same results on each.

I have reset the Network through Windows 10 Settings and have only reconnected the onboard LAN using DHCP straight to the Modem and than Static. Same results.

I have removed one of the HP NC364T (didn’t have it configured correctly for Link Aggregation anyway) from one desktop thinking it might be the problem. Reset the Network again, and I get the same results. I have also tried it plugged into the Gigabit Switch or to the modem directly, didn’t matter, same results.

I have upgraded the onboard Realtek Gigabit LAN drivers, first from AsRock, and then straight from Realtek. Same results.

Thinking it was a Service issue – Though one machine is Windows 10 machine and the other is Windows Server 2016 (running only Hyper-V) – I have attempted to boot into Safe Mode with Networking. Same results directly plugged into the modem using cables that tested at 1 Gig on the three laptops.

I have attempted to use different DNS servers, very little difference in any.

I have ran Ubuntu Live on the same PC and get 1.1Gbps downloads and the same 40-50Mbps upload speeds. (Suggests a Window's Issue)

I have installed an Ubuntu Desktop on the other machine as a VM and get 1.2Gbps on that. (Suggest a Window's OS Throttling issue) But I also have installed Windows 10 Pro on a VM and get the similar results as the Ubuntu.

Testing further through all my VMs, the Windows Server 2019 VMs have the same results as the host, limited speeds to 400-500Mbps.

The biggest difference I can tell in the host and VM’s compared to the Window 10 Pro OS VM in testing the is that this version of windows is the 1809 while the rest have been updated to the 1903 base version, or whatever the Server Versions equivale to.

So, the issue is ether Windows settings or with the Windows Drivers and MOBO combination with the May Updates conflicts is my thinking. I might be way off on this thought process though.

Any help or suggestion are welcome. Brainstorming and troubleshooting this issue is starting to burn me out.
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Try a program like iperf to test between machines in your house. I would use the laptop that you say works fine as one end. Most people get over 900mbps in both directions when things are running properly.

It is a very simplistic program not affected by things like cpu,memory or disk. It should isolate your issue to the network drivers or ports or eliminate them as the cause.

The other very common cause of issues like this are any so called "gaming" network accelerators. Make sure you have nothing like that installed.