VMXNET3 Guest OS Link Speed Resets and Does Not Enforce Bandwidth Limits

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

• Virtual machines utilizing VMXNET3 adapters show network link speeds intermittently resetting to default values (e.g., 2 Gbps or 10 Gbps) within the guest OS after being manually modified.
• Manually modifying the link speed within the guest OS network adapter properties to 100 Mbps or 1 Gbps fails to accurately restrict or rate-limit the actual network throughput for the virtual machine.

Environment

• Vmware vCenter Server
• VMware vSphere ESXi 

Cause

Modifying the negotiated link speed of a paravirtualized VMXNET3 adapter from within the guest OS is purely cosmetic. The guest OS link speed does not dictate actual hypervisor-level throughput capabilities and will dynamically reset during standard operations.

Resolution

To throttle or rate-limit virtual machine network traffic, the vSphere Distributed Switch (vDS) Traffic Shaping feature should be used:

1. Revert any manual link speed or duplex changes on the guest OS VMXNET3 adapter back to "Auto Negotiation" or default settings.
2. Configure Traffic Shaping on the virtual switch by following the official documentation: Traffic Shaping Policy

Additional Information

Link speed of vmxnet3 may be reported incorrectly in the Guest OS
How to change the vmxnet3 link speed of a VM