Link speed of VMXNET3 may be reported incorrectly by guest operating system

Products

• VMware vSphere ESXi

Issue/Introduction

The VMXNET3 virtual network interface identifies itself to the guest operating system inside a VM and exposes a sequence of configuration bits to report a link speed to the OS. This configuration is changeable for user convenience and defaults to 10Gb/s on current versions.

The operating system may correctly not report the link speed offered by the VMXNET3 driver. For example, the operating system may report a link speed 10Mb/s (megabits per second) instead of 10Gb/s (gigabits per second).

The reported link speed does not have any bearing on the actual data transmission rate allowed by the virtual network interface or virtual switch.

Resolution

The incorrect network adapter description is possibly due to an error in how the operating system reports the VMXNET3 driver data. 

You can try to change the reported link speed using the steps in this KB article:

How to change the vmxnet3 link speed of a VM

These steps may or not be successful. However, VMXNET3 is not limited by the reported media link speed and will transmit as fast as possible subject to the host's CPU resources, virtual switch traffic shaping policies, available uplink speed and other resource factors.