Poor network performance with ethernet interface intel i219-v

Help
1

Hi everyone ; I have an important performance issue on a wired gigabit network interface under nixos 26.05 : The bandwidth is arround 3MB/s, and very erratic.

With ubuntu 26.04 the performance is nominal (arround 300MB/s from the same internet speed test used under nixos)

Any idea to troubleshoot this ?

Thanks in advance

2

I had similar problem but with docker networks.

I had to disable the firewall networking.firewall.enable = false;. In the configuration I didn’t have anything special other than networking.firewall.enable = true.

I have the firewall disabled for now as I didn’t have time to debug what causes the issue.

3

Thanks ; I’ve tested it has no effect for me

4

I’d consider testing a different kernel e.g. boot.kernelPackages = pkgs.linuxPackages_latest;and a different method of testing, e.g. iperf to a local machine. After that, i’d start looking into NIC offloading features, packet fragmentation issues, etc.

5

Besides, what you’re looking at is more like 300 Mb/s (Megabits/MegaBytes), considering it’s a gigabit NIC. At first it thought i219-v was some kind of 2.5 Gb NIC.

6

Thanks ; I’ll try this

7

300Mbps is the max I can expect from that network/Internet link

I discovered the issue in the first place by doing a rsync between two laptops and having sub 1MBps of bandwidth during the transfer ; (using an usbc ethernet adapter on the computer which has the intel i219-v gives a Gigabit bandwidth as expected)