ESXi host reports repeated vmnic linkstate down/up events for a physical uplink

Products

• VMware vSphere ESXi

Issue/Introduction

An ESXi host reports repeated link down/up events for a physical NIC (for example, vmnicX, where X represents the actual NIC number).

Messages similar to the following may appear in /var/run/log/vobd.log,

[vob.net.dvport.uplink.transition.down] Uplink: vmnicX is down. Affected dvPort: ...
[vob.net.vmnic.linkstate.down] vmnic vmnicX linkstate down
[vob.net.vmnic.linkstate.up] vmnic vmnicX linkstate up
[vob.net.dvport.uplink.transition.up] Uplink: vmnicX is up. Affected dvPort: ...

The issue may cause transient network disconnections or redundancy loss alarms on the Distributed Switch.

This behavior indicates that the physical link associated with the NIC is intermittently going down and coming back up.

Environment

VMware vSphere ESXi 8.0

VMware vSphere ESXi 9.0

Cause

This issue occurs due to physical layer link instability, commonly caused by one of the following:

• Faulty or loose network cable

• Faulty switch port or SFP/GBIC module

• Hardware issue on the physical NIC

Resolution

Follow the steps below to isolate and resolve the issue:

1. Verify NIC status
   

   Run the following commands to list NICs and check link status:

   esxcfg-nics -l

   If a specific NIC (for example, vmnicX) shows repeated “Down/Up” transitions, test by manually bringing it down and back up:

   esxcli network nic down -n vmnicX
   esxcli network nic up -n vmnicX

   Observe whether the link remains stable.

2. Physical layer verification

   Since the linkstate transitions are physical-layer events, perform the following checks:

   • Replace the network cable with a known-good one.
   • Move the cable to a different switch port that is known to be stable.
   • Replace the SFP/GBIC transceiver if used
   • If link stability does not improve, contact the hardware vendor to investigate potential issues with the NIC or server motherboard.

    

3. Monitor after changes

   After performing the hardware or cable swap, monitor the NIC link state using:

    

   tail -f /var/log/vobd.log | grep -i vmnicX

   If no further link flapping is observed, the issue is resolved.

Additional Information

Avoid performing nic down/up operations on NICs used for Management Network unless console access is available.