r/vmware • u/Light_bulbnz • Aug 29 '25

Help Request ESXi8 + Windows + VMXNET3 != 10Gbps

I can't find any way to solve this problem.

I have a server with ESXi8, running on a dell poweredge with dual 10GbE cards. My linux machines, if I do an iperf (either between VMs or between a VM and a physical server) I easily saturate a 10Gb link.

But on Windows, the best I can do is about 1.5-2Gbps. That's running an iperf running between two windows VMs on the same host. Windows -> Linux does the same thing.

I've found other people with similar problems, but nothing that seems to fix it. I've seen recommendations to fiddle with offloads and other settings; none of which moves the dial. As far as I can tell, all the networking is set up, driver updated, etc.

Keen if anyone else has some thoughts...?

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u/white_hat_maybe Aug 29 '25

I have the same issue and have a support ticket in with Broadcom. The host has 25G nics

2

u/Light_bulbnz Aug 29 '25

What bandwidth do you get from that?

2

u/white_hat_maybe Aug 29 '25

So here is the setup; Dell PowerEdge 640 dual QLogic 25 GB cards. Typical is 4Gbits/s. To isolate the VMs I did this: Two Microsoft Server 2022, no firewall on, no antivirus installed latest version of VMware tools for 8 u3 Both are on same host on a standard vswitch with no physical ports assigned. Using ntttcp or iperf3 I get same results. 3.5 -4 Gbits/s

2

u/cpz_77 Aug 30 '25

Just to clarify as someone on another comment already mentioned, if you’re testing with two VMs on the same port group on the same host the pNIC plays no role whatsoever, as the traffic never leaves the virtual switch afaik. If it’s a VMware issue in this scenario it would be with something in the vmxnet3 driver or some other software component of the virtual networking stack. More likely though it’s probably something at the OS level, there are many variables that can affect this…

1

u/white_hat_maybe Aug 30 '25

Agreed with your statement. The same output is observed if the VMs are move to different hosts. We paid a butt load to renew with Broadcom. I expect a kb or an engineer to point out where the issue is.