How to change the vmxnet3 link speed of a VM

Products

• VMware vSphere ESXi 8.0

Issue/Introduction

The default link speed of a vmxnet3 adapter is 10Gbps. This article provides steps to change the vmxnet3 link speed of a VM.

Environment

VMware vSphere 8.0.2 and later versions

Resolution

Configuration change from the vSphere Client:

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. Shutdown the VM.
4. Once powered off, right-click the virtual machine and select Edit Settings.
5. Click VM Options.
6. Expand Advanced.
7. Under Configuration Parameters, click the Edit Configuration button.
8. In the dialog box that appears, click Add Row to enter a new parameter and its value.
   New Parameter - 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
9. Click OK.

Alternatively the configuration change can be made by editing the VM's configuration file (.vmx) from command line:

1. From the vSphere Client, shut down the virtual machine.
2. Open an ssh session to the ESXi host where the VM is registered.
3. Navigate to the datastore where the VM is located e.g.
   cd /vmfs/volumes/<DATASTORE>
4. Change to the VM's folder e.g.
   cd <VM_folder>
5. Open the virtual machine's configuration file (.vmx) in a text editor such as vi e.g.
   vi <VM-name>.vmx
6. Add the following line
   ethernetX.linkspeed = "Y"
   where, X is the virtual device number and Y is the link speed value we want in Mbps.
   Y should be any value between 10000 and 65000.
   e.g. ethernet0.linkspeed = "65000"
7. Save the changes and exit the text editor.
   
   Here is a KB with further information about using the vi editor in ESXi: Editing files on an ESXi host using vi

Notes:

• On vSphere 8.0.2 and later vmxnet3 link speed supports speeds between 10Gbps and 65Gbps.
• The default link speed value is 10Gbps.
• If the link speed value is set to a value less than 10000, the link speed value will default to 10Gbps.
• If the link speed value is set to a value greater than 65000, the link speed will default to 10Gbps.

Additional Information

It is also important to note that this change is specific to a VM's in-guest virtual networking adapter, and that the actual network speed of the VM will still be limited by the physical hardware (host CPU, physical NICs, etc.). This change is designed to overcome OS or application-level limitations that may exist based on the default detected 10Gb speed of the vmxnet3 adapter.