🚀 Supercharge Your VMXNET3 Link Speed in VMware vSphere

by · 19/06/2025

By default, VMware’s VMXNET3 virtual NIC reports a 10 Gbps link inside the guest OS—even when your physical network can handle more. This discrepancy can impact diagnostics, in-guest backup, and performance tools that rely on reported link speed. Fortunately, vSphere 8.0.2 and above allows you to manually adjust this speed up to 65 Gbps.

Here’s how to manually increase that virtual NIC speed—up to 65 Gbps—to align with your physical network and satisfy high-performance application demands.

🔧 How to Change VMXNET3 Link Speed

There are two methods—vSphere Client and CLI—both of which achieve identical results.

Method 1: vSphere Client (Recommended)

  1. Browse to the virtual machine in the vSphere Client.
  2. To find a virtual machine, select a data center, folder, cluster, resource pool, or host.
  3. Shut down the VM.
  4. Once powered off, right-click the virtual machine and select Edit Settings.
  5. Move to the Advanced Parameters tab.
  6. Under Advanced Parameters, use the Attribute and Value text boxes.
  7. Click Add in the resulting dialog box to add a new parameter and its value.
    • Attribute: ethernetX.linkspeed, where X is the virtual device whose link speed we want to change.
    • Value: This will be the link speed value we wish to set in Mbps. This should be any value between 10000 and 65000. e.g., ethernet0.linkspeed 65000
  8. Click OK and save changes
  9. Power On the virtual machine
  10. Once you check the network speed from inside of the OS, you should be able to see something like the screenshot below.

Method 2: CLI / .vmx Edit

  1. Alternatively, you can modify the VM’s configuration file (.vmx) from the command line:
  2. From the vSphere Client, shut down the virtual machine.
  3. Open an SSH session to the ESXi host where the VM is registered.
  4. Navigate to the datastore where the VM is located, e.g., cd /vmfs/volumes/<DATASTORE>.
  5. Change to the VM’s folder, e.g., cd <VM_folder>.
  6. Open the virtual machine’s configuration file (.vmx) in a text editor such as vi, e.g., vi <VM-name>.vmx
  7. Add the following line: Set ethernetX.linkspeed to “Y”, where X represents the virtual device number and Y indicates the desired link speed value in Mbps. Y should be any value between 10000 and 65000. e.g., ethernet0.linkspeed = “65000”
  8. Please save the changes and exit the text editor.

⚠️ Important Notes:

  • Link speeds below 10000 Mbps or above 65000 Mbps default back to 10000 Mbps.
  • This tweak only alters the reported speed; actual throughput depends on your physical NICs, switches, cables, and host hardware.
  • If you are changing the speed because of packet loss or traffic bursts, also check the VMXNET3 buffer settings. Adjust receive buffers in the guest OS for optimal reliability.
  • You can find the official KB link below

📌 Conclusion

By tweaking the VMXNET3 advanced setting, you align your VM’s reported link speed with actual physical capabilities. It’s a simple yet powerful way to improve transparency in network diagnostics and licensing—without impacting real-world throughput.

Tags:

You may also like...