Enabling Promiscuous Mode on a vSwitch Used for NFS Connectivity May Cause VM Freeze or NFS Datastore Unresponsiveness

Products

• VMware vSphere ESXi

Issue/Introduction

When enabling Promiscuous Mode on a port group that resides on the same vSwitch used for NFS datastore connectivity, you may experience the following symptoms:

• VMs may freeze when adding a vNIC to a port group with Promiscuous Mode = Accept.

• All VMs running on the NFS datastore may become unresponsive or freeze.

• ESXi hosts may temporarily lose connectivity to the NFS datastore.

Environment

VMware vSphere ESXi

Cause

When Promiscuous Mode is enabled on a port group residing on the same vSwitch as NFS traffic, the following occurs:

• Every read/write operation to the NFS datastore generates corresponding network packets.

• With Promiscuous Mode enabled, the vSwitch creates multiple mirrored packets for all traffic, including high-volume NFS operations.

• This results in a massive increase in traffic load on the vSwitch.

• The excessive mirrored traffic creates network congestion, leading to:

  • Loss of NFS connectivity

  • Increased latency

  • VM freezes or unresponsiveness

When multiple traffic types (NFS, vMotion, Production VM traffic, and mirrored traffic) share the same vSwitch, congestion becomes severe enough to disrupt normal operations.

Resolution

To avoid network congestion and NFS datastore connectivity loss:

• Do NOT enable Promiscuous Mode on the same vSwitch used for NFS datastore connectivity.

• Use a separate vSwitch for NFS traffic to ensure isolation from monitoring, mirrored, or diagnostic traffic.

• If Promiscuous Mode is required (e.g., packet capture, monitoring tools), configure it on a dedicated vSwitch.

Additional Information

This KB is informational only