25Gbe Server Interface Negotiation and Speed Capping Issue

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P10i

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May 20, 2025
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Hi,

I have a Dell PowerEdge R640 Host on which I have installed Proxmox. It has 25GBPS Link on Mellanox Card and it is hosted on Redswitches.

I have only 2 vms on it, one is ubuntu and one is windows 2022. On Proxmox host I am getting full 25GBPS Speed, On Ubuntu VM I am getting full 25GBPS but on windows 2022 VM I am getting only 3GBPS.

Windows
[SUM] 0.00-9.72 sec 4.22 GBytes 3.73 Gbits/sec

Ubuntu VM
[SUM] 3.00-3.46 sec 1.25 GBytes 23.5 Gbits/sec 1089

I also noticed for virtio adapter the negotiated speed in windows vm is 10GBPS and on ubuntu its not a problem on same host.

1747820230247.png

I followed related articles and guides, I have disabled ASPM and saerver is on performance mode and the speed is not affected on VM in any way.
M

Post in thread '25GbE network capped at 10GbE'

cheiss said:
Hi,


how exactly are you running iperf3? Are you using the -P, e.g. iperf3 -P8 ...
This enables parallel stream, as your machine might be just capped by the CPU in this regard.
Click to expand...

yes exactly, I also had this idea.
However, I tested iperf with all variants:

iperf3 (with no options)
iperf3 -P 4
iperf3 -P 8
iperf3 -P16

however, the difference between all the variants was nonexistent to negligible.

I have my Proxmox connected to a bridge, and the bridge is connected to a bond, and the bond contains the 25G interface, as well as an 1G "emergency failover" interface, in...
B

Thread 'I AM GOING CRAZY 2GBIT 10G WHY.....'

First off i live in Communist Australia, we have an NTU "network termination unit" aka bridge media converter, i have a nic in passthrough that is assigned to a vm with opnsense the lan has a virtio nic that does show up as 10G, i have a fileserver vM with virtio nic 10G plus the proxmox bridge has two 10G fibre Intel 520 googus.

speed test using iperf3 on all vm's 25G wow ok..... with the exception of opnsense if i perf that 2Gb i am talking about the LAN IP.

the 10G 520 has a direct connection to my workstation which is running Windows 10 64bit PRO. same card but cisco OEM.

Using AOC...

I also upgraded network drivers from latest virtio iso. I am not getting even full 10gbps on windows and on ubuntu I am getting full speed, so opening a ticket to them is useless as this is clearly something from proxmox side not their side.

What is wrong here? Any help on this problem will be appreciated.

Thank you
 
LnxBil said:
Can you share the configuration of your VM?
Click to expand...
Hello @LnxBil ,

Below is the configuration of VM

q35, 8GB Ram, 50G Drive, Virtio Interface, OVMF (uefi bios) - WIndows Server 2022 DC Core, Machine OS Type selected windows 11/2022/2025.

vm ram and cpu doesn't go beyond 30 percent while doing speedtest. 3.7 to 4gbps is the max I am getting
 
Last edited:
LnxBil said:
Does it show higher speed in Linux? AFAIK not.
Click to expand...
yes on ubuntu it shows below speeds
[ 5] 3.00-3.46 sec 88.6 MBytes 1.62 Gbits/sec 45 1.35 MBytes
[ 7] 3.00-3.46 sec 99.1 MBytes 1.81 Gbits/sec 45 1.56 MBytes
[ 9] 3.00-3.46 sec 117 MBytes 2.13 Gbits/sec 90 1.88 MBytes
[ 11] 3.00-3.46 sec 72.8 MBytes 1.33 Gbits/sec 45 1.07 MBytes
[ 13] 3.00-3.46 sec 118 MBytes 2.17 Gbits/sec 170 1.87 MBytes
[ 15] 3.00-3.46 sec 84.9 MBytes 1.55 Gbits/sec 45 1.32 MBytes
[ 17] 3.00-3.46 sec 181 MBytes 3.31 Gbits/sec 63 2.97 MBytes
[ 19] 3.00-3.46 sec 102 MBytes 1.86 Gbits/sec 45 1.60 MBytes
[ 21] 3.00-3.46 sec 231 MBytes 4.22 Gbits/sec 540 3.93 MBytes
[ 23] 3.00-3.46 sec 191 MBytes 3.49 Gbits/sec 1 3.16 MBytes
[SUM] 3.00-3.46 sec 1.25 GBytes 23.5 Gbits/sec 1089


I ran 10 parallel streams and even though eth tool shows Duplex as unknown it gives speed near to 25gbps.

root@inv:~# ethtool ens18
Settings for ens18:
Supported ports: [ ]
Supported link modes: Not reported
Supported pause frame use: No
Supports auto-negotiation: No
Supported FEC modes: Not reported
Advertised link modes: Not reported
Advertised pause frame use: No
Advertised auto-negotiation: No
Advertised FEC modes: Not reported
Speed: Unknown!
Duplex: Unknown! (255)
Auto-negotiation: off
Port: Other
PHYAD: 0
Transceiver: internal
Link detected: yes
 
Last edited:
Just FYI I purchased additional public ips for those vms so they are not communicating on bridge or private network, and I am doing speed test using another provider iperf .

Just in case if you think that test traffic is flowing between vms and getting divided. On Proxmox host itself I am getting full speeds.
 
Boot 2 pc with live iso or a win10 and link local the 2x 25g card together. normal iperf3 will give a full 25gbps. Even an old hp microserver8 do give a full speed without parallel load.
getting unknow is many time the sfp or cable. confirm that , then a fresh install of prox without vlan crap and that can give good test results.
 
So I got it to work. I don't know how but, I reinstalled windows, Selected secondary drivers from virtio iso.

The negotiated speed still shows 10G but the speed reaches upto 18Gigs.

So in conclusion even if the interface shows 10G you can get full speed

Hope this helps somebody.

Thank You
 
LnxBil said:
I was refering to this ... the shown speed, not the measured speed. It's in Linux also not present, so the same is true for windows.
Click to expand...
Thank You for your reply.

You are referring to interface negotiation speed and Duplex.

Yes. But as I mentioned in previous speed that even if negotiation is unknown but I was getting full speed in ubuntu VM, same thing was not happening in Windows. Both negotiation and Speedtest results were not trustworthy.

I pointed it out as I thought maybe it will help somebody recalling any solution. Both things were my concern

In the end, everything is working good now.

Thank You
 
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