Network connectivity loss on virtual machines with Windows Guest OS configured with VMXNET3 nic after VMware Tools (11.3.5 or later) downgrade

Products

• VMware
• VMware vSphere ESXi

Issue/Introduction

Symptoms:

There can be different symptoms such as described below:

• After vmxnet3 driver or VMTools downgrade, there is no network connectivity
• Below logs are present in vmware.log

ethernet0.exposeLargeBAR = "TRUE"

OR
Below log is visible in the logs of previous virtual machine boot i.e. vmware-1.log

Expose large BAR for the device in the next vmx boot

OR
UPT was requested for the vnic but guest is running vmxnet3 driver which does not support UPT

The issue is specifically seen on Windows Virtual Machines.

Environment

VMware vSphere ESXi 7.0.3

Cause

This is due to introduction of LargeBAR setting for vmxnet3 in VMTools 11.3.5. When new driver is loaded in the virtual machine, this setting gets configured and gets effective in next and subsequent vmx boot.
So, things work fine for the first time, but after next power on of the virtual machine if driver is downgraded to older version, then network connectivity is not present.
 
The issue can happen in below cases:
After running with newer VMTools (11.3.5 or later) for one or more times, the tools and in particular vmxnet3 Windows driver is downgraded to an older version or booted with an older version of VMTools or vmxnet3 Windows driver (older than version 1.8.17.0).

When the Virtual Machine is using mixed version of VMTools. For example, Windows Virtual Machine boots with VMTools 11.3.5 but later pxe boots with WinPE image which uses older VMTools.

Resolution

The issue is resolved in ESXi 7.0.3 release.

Workaround:

To workaround the issue you can follow one of the options listed below:

• Ensure that VMTools 11.3.5 or later is being used, and all components (like WinPE image) are also using 11.3.5 or later version.
  OR

• The issue can be avoided by applying below configuration in advanced setting for the Virtual Machine:

1. Right-click the virtual machine and click Edit Settings.

2. Click the VM Options tab.

3. Select Advanced.

4. Click the Edit Configuration button.

5. From the Configuration Parameters window, click Add Configuration Parameters
   vmxnet3.disableLargeBAR = "TRUE" in attribute and value respectively.