X8 Modem compatibility with different NIC's (Ethernet connection): Speed Issues

[fixplease]

I have four computers with 2.5 GB NIC's.  The Killer E3100G (2 systems) and Intel I226 T1 (2 systems).  My Rogers connection has a download speed of around 2.5 Gbps.  I use port 4 on the modem and I get proper speeds (approx 2.3 Gbps) when using the Killer NIC's but when I use the Intel I226 I only get around 1.1 Gbps.  Both NICs are 2.5 Gbps compatible.  I also did a iperf test between the two different NIC's and the speeds were close to 2.5 Gbps.  So why is the Killer able to handle WAN traffic well but the I226 has issues???  I have tried many different setting within the Intel I226 ethernet adapter but nothing seems to work.  Cables are all fine as well.  Is there any known issues with the X8 Modem and that specific NIC (Intel I226 T1)??

*Added Labels*

[-G-]

My router/firewall runs on an Intel box with i225 NICs and I have no issues.  However, I'm a primarily a Mac/Unix/Linux guy, and my Windows system has a Realtek NIC, so I can't help you too much with this hardware.

That said, a lot of Windows users have issues with the i225/i226 hardware, and it can vary depending on the hardware revision of the NIC in your system and the drivers that you are running.

There was an issue where older drivers used a bad IPG setting and this caused performance to plummet under certain circumstances.

Enabling full hardware offloading at high speeds limits available buffers and causes throughput to drop when they fill

TCP autotuning can cause problems.  The weird thing is that for some, disabling autotuning fixes problems; for others, setting it to "normal" improves throughput.

Hopefully, you can find the help you need here:

https://learn.microsoft.com/en-us/windows-server/networking/technologies/network-subsystem/net-sub-p...

https://www.intel.com/content/www/us/en/support/articles/000005811/ethernet-products.html

The OPNsense community is also tracking issues with the i225/i226 hardware:

https://forum.opnsense.org/index.php?topic=38055.0

It's not directly applicable to Windows but has some useful links.

[fixplease · Accepted solution]

turns out the issue was clearly with the NIC's (Intel i226).  Complete garbage as the latest Intel driver (2.1.3.15) was . .  They have a new one coming in Feb 2025 that is suppose to fix this.  Instead I went out and purchased reliable ones and they work great.