High-Speed Networking for VMs: VMXNET3 Now Supports Up to 65 Gbps

The VMXNET3 adapter is VMware's high-performance virtual network adapter, designed for optimized performance in vSphere environments. It is the default and recommended adapter for most modern workloads on ESXi, delivering high throughput, low latency, and support for advanced networking features.

With the release of vSphere ESXi 8.0 Update 2, VMXNET3 introduces new capabilities that significantly enhance virtual network performance.

What’s New in ESXi 8.0 Update 2 for VMXNET3?

Traditionally, VMXNET3 reports a default link speed of 10 Gbps to the guest operating system. However, the actual achievable throughput often exceeds this value—thanks to technologies such as multi-queue support, Receive Side Scaling (RSS), and Large Packet Offload.

Starting with ESXi 8.0 Update 2, this limitation can now be overridden, and VMXNET3 can be configured to support custom link speeds of up to 65 Gbps. This enhancement enables improved flexibility and throughput for high-performance workloads.

NSX Integration and Edge Node Optimization

In NSX environments, this update provides a strategic benefit: it allows Bare Metal Edge-level performance using VM-based Edge Nodes, eliminating the need for dedicated hardware in certain use cases. With vSphere 8.0.2 and above, virtual NICs configured with VMXNET3 can operate between 10 Gbps and 65 Gbps, offering a significant boost in data plane performance.

How to Configure VMXNET3 for 65 Gbps

You can configure the custom link speed using either the vSphere Client UI or by directly editing the VM configuration (.vmx) file.

Option 1: Configuration via vSphere Client

1. Navigate to the virtual machine in the vSphere Client.

2. Shut down the VM.

3. Right-click the VM and select Edit Settings.

4. Go to the VM Options tab.

5. Expand Advanced > Configuration Parameters, and click Edit Configuration.

6. Click Add Row and input the following:

   • Name: ethernetX.linkspeed (Replace X with the NIC number, e.g., ethernet0)

   • Value: Desired link speed in Mbps (between 10000 and 65000)

     • Example: ethernet0.linkspeed = 65000

7. Click OK to save the changes.

Option 2: Configuration via CLI (.vmx File Edit)

1. Shut down the VM.

2. SSH into the ESXi host where the VM resides.

3. Navigate to the VM's folder:

   bash
   
   cd /vmfs/volumes/<DATASTORE>/<VM_NAME>
   

4. Open the .vmx file in a text editor (e.g., vi):

   bash
   
   vi <VM_NAME>.vmx
   

5. Add the following line:

   bash
   
   ethernetX.linkspeed = "65000"
   

   Replace X with the appropriate NIC number.

6. Save and close the file.

7. Power on the VM to apply the changes.

Important Notes

• The linkspeed parameter is cosmetic—it changes what the guest OS perceives as the NIC speed but does not inherently guarantee line-rate throughput unless the VM and host are optimized.

• Ensure that VMware Tools are installed and up to date for optimal driver compatibility.

• Verify that the guest OS supports higher speeds and can take advantage of multi-queue NICs and large packet optimizations.

This configuration is particularly impactful for high-performance network functions virtualization (NFV), data-intensive workloads, and virtualized edge appliances in modern vSphere and NSX environments.

Infographic Summary – VMXNET3 Speed Enhancement (ESXi 8.0 U2)

PowerCLI Script:  

Set VMXNET3 Link Speed to 65 Gbps

# PowerCLI Script to Set VMXNET3 Link Speed to 65000 Mbps

$vmName = "YourVMName"

$nicNumber = 0  # Use 0 for ethernet0, 1 for ethernet1, etc.

$desiredSpeed = 65000

# Get the VM object

$vm = Get-VM -Name $vmName

# Power off the VM

Stop-VM -VM $vm -Confirm:$false

# Construct the parameter key

$paramKey = "ethernet$nicNumber.linkspeed"

# Update configuration parameter

$vm | New-AdvancedSetting -Name $paramKey -Value $desiredSpeed -Force

# Power on the VM

Start-VM -VM $vm

Write-Host "Link speed for ethernet$nicNumber set to $desiredSpeed Mbps on $vmName"

Reference

• Broadcom KB Article 368812