A physical NIC may be brought down due to frequent link status flapping

Products

• VMware vSphere ESXi

Issue/Introduction

• When a physical NIC experiences frequent link status flapping, ESXi may turn off the physical NIC to avoid unnecessary link failover and network instability.
• For example, a physical NIC driver may reset the physical NIC when it detects "tx Hang". A reset causes a link down/up event to be generated. If the physical NIC is itself bad, this causes periodic reset and link status flapping. The vmkernel.log log file on the ESXi host will show that one or more network cards and repeated state change between "Up" and "Down".
• During link status flapping, traffic may migrate between different physical NICs. If the flapping is too frequent, you experience network issues, such as bandwidth reduction or an unstable network.
  
  Similar logs can be noticed in vobd.log
  
  In(14) vobd[2098027]:  [netCorrelator] 764747381136us: [esx.problem.net.vmnic.linkstate.flapping] Taking down physical NIC vmnic5 because the link is flapping.
  In(14) vobd[2098027]:  [netCorrelator] 764820363271us: [esx.problem.net.vmnic.linkstate.flapping] Taking down physical NIC vmnic5 because the link is flapping.
  
  hostd.log reports below events
  
  In(166) Hostd[2103930]: [Originator@6876 sub=Vimsvc.ha-eventmgr] Event 132032 : Taking down physical NIC vmnic5 because the link is unstable.
  In(166) Hostd[2103925]: [Originator@6876 sub=Vimsvc.ha-eventmgr] Event 132175 : Taking down physical NIC vmnic5 because the link is unstable.

Resolution

ESXi automatically alerts you to the bad hardware and disables the device to avoid the link flapping state. Work with hardware vendor or physical network team to validate the link/switchport to isolate and fix the flapping issue.