Micro link flaps on ESX physical NIC

Products

• VMware vSphere ESXi

Issue/Introduction

• A physical NIC on an ESX is flapping up/down frequently.
• ESX logs shows the flapping.
  
  /var/log/vmkernel.log
2025-11-06T08:32:49.618 In(182) vmkernel: cpu12:2098268)bnxtnet: bnxtnet_display_link:2955: [vmnicX : 0x45210fe2c000] NIC Link is down
2025-11-06T08:32:50.733 In(182) vmkernel: cpu12:2098268)bnxtnet: bnxtnet_display_link:2951: [vmnicX : 0x45210fe2c000] NIC Link is Up, 10000 Mbps (NRZ) full duplex, Flow control: none
  
  
• The flap lasts a few seconds so it's possible no functional impact is observed.
• Running the following command doesn't show any drops on the NIC.
  
  esxcli network nic stats get -n vmnic<X>
  
  
• From within an ESX log bundle the private NIC stats shows Frame Check Sequence errors.
  
  egrep "NIC:|fcs_err_frames" <esx-log-bundle>/commands/nicinfo.sh.txt
NIC:  vmnic1
      rx_fcs_err_frames: 0
      tx_fcs_err_frames: 0
NIC:  vmnic2
      rx_fcs_err_frames: 0
      tx_fcs_err_frames: 0
NIC:  vmnic3
      rx_fcs_err_frames: 0
      tx_fcs_err_frames: 0
NIC:  vmnic4
      rx_fcs_err_frames: 10000
      tx_fcs_err_frames: 0

Environment

VMware ESX

Cause

Frame Check Sequence errors indicate a cable or hardware issue.

Resolution

Check cable and hardware.