Broadcom BCM5720 (ntg3 Driver) NIC Reports False Link-Up Status to ESXi

Products

• VMware vSphere ESXi

Issue/Introduction

• An ESXi host reports the link status for one or more  BCM5720 NIC ports (vmnic0, vmnic1, etc.) as UP, even though the physical network cable is disconnected, and the corresponding switch port shows a DOWN state.
• vmkwarning.log repeatedly shows PHY read timeouts: WARNING: ntg3: Ntg3PhyRead:371: vmnicX:PHY reg (25) read timeout
• vobd.log subsequently logs a link-up event: [vob.net.vmnic.linkstate.up] vmnic vmnicX linkstate up
• From iDRAC for Esxi host, it shows down
   

• However ESXi still thinks it is UP
  
  

Environment

VMware vSphere ESXi 8.x

Cause

The underlying cause is a miscommunication or an error within the Broadcom NIC's firmware or its interaction with the ESXi ntg3 driver. 

When the ESXi host's driver attempts to poll the hardware for link status (potentially during a timeout event), the NIC firmware incorrectly signals a "link up" event to the hypervisor kernel, even if the physical link is down. The ESXi host, trusting the hardware's signal, proceeds to bring the virtual link online and reports an UP status.

This incorrect signal is the source of the false positive link state on the ESXi host.

Resolution

This issue needs to be addressed at the hardware/firmware level, which typically falls under the server or NIC vendor’s scope. Please engage the respective vendor for further assistance.