Understanding VMXNET3 Ring Buffer Persistency and Counter Resets

Products

• VMware vSphere ESXi

Issue/Introduction

When troubleshooting packet loss at the Guest OS level using the VMXNET3 adapter, administrators may observe that networking statistics (counters) reset following specific lifecycle events.
This KB clarifies the behavior of configuration settings versus performance counters during vMotion, reboots, and power cycles.

Environment

• vSphere ESXi
• vCenter Server

Resolution

• Distinction Between Configuration Settings and vsish Counters
  There is a critical distinction between the Configuration Parameters (Settings) and the Performance Statistics (Counters):
  
  
• Counters (Statistics): When using the vsish command (e.g., get /net/portsets/vSwitch0/ports/ID/vmxnet3/rxSummary) to monitor drops, the values are volatile. These  readings reset to zero upon a vMotion or Power Cycle.
  
  
• Settings (Configuration): The manual adjustments made to buffer sizes (e.g., increasing Rx Ring #1 from 512 to 4096) are persistent. These values are stored in the Virtual Machine configuration/registry and are not reset when the counters clear.
  
  
• Solution Status: Permanent Optimization vs. Workaround
  Adjusting VMXNET3 ring buffers is considered a Permanent Configuration Optimization rather than a temporary workaround.
  
  
• While administrators should first verify that physical NIC firmware and drivers are up to date, increasing guest-level buffers is the standard procedure for handling high-traffic bursts that exceed default driver capacities.
  
  
• These settings remain permanent until manually reverted by an administrator.
• Persistence in Windows Guest Operating Systems.
  Settings modified within the Windows Device Manager (e.g., Small Rx Buffers or Rx Ring #1 Size) are written directly to the Windows Registry.
  
  
• Reboots: The VMXNET3 driver loads the Registry-defined values during the boot sequence.
  
  
• Migrations (vMotion): Since vMotion preserves the entire state of the Guest OS memory and Registry, the VM continues to operate with the optimized buffer sizes on the destination host.

Additional Information

Large packet loss (dropped packets in VM) in the guest OS using VMXNET3 in ESXi

https://knowledge.broadcom.com/external/article?legacyId=2039495