Intermittent "Network Connectivity Loss" Alarm on ESXi hosts in vCenter UI

Products

• VMware vSphere ESXi

Issue/Introduction

• An ESXi host may generate repeated Network Connectivity Lost alerts in vCenter when a physical uplink (vmnic) experiences intermittent link flapping.
  
  
• The host's /var/log/vobd.log may show the uplink transitioning between link up and link down states frequently, with Failed criteria: 128 events recorded. 
  
  

2025-##-##T13:35:59.####: [netCorrelator] ####722####29us: [vob.net.pg.uplink.transition.down] Uplink: vmnic# is down. Affected portgroup: #####. 0 uplinks up. Failed criteria: 128 
2025-##-##T13:35:59.0122: [netCorrelator] ####722####13us: [vob.net.vmnic.linkstate.down] vmnic vmnic# linkstate down 
2025-##-##T13:36:01.0022: [netCorrelator] ####693####06us: [esx.problem.net.connectivity.lost] Lost network connectivity on virtual switch "#####". Physical NIC vmnic# is down. Affected port groups: "######" 
2025-##-##T13:36:01.6162: [netCorrelator] ####725####96us: [vob.net.vmnic.linkstate.up] vmnic vmnic# linkstate up 
2025-##-##T13:36:01.7172: [netCorrelator] ####725####12us: [vob.net.pg.uplink.transition.up] Uplink:vmnic# is up. Affected portgroup: #####. 1 uplinks up 
2025-##-##T13:36:03.0022: [netCorrelator] ####695####72us: [esx.clear.net.connectivity.restored] Network connectivity restored on virtual switch "#####", portgroups: "#####". Physical NIC vmnic# is up 
2025-##-##T13:36:03.9152: [netCorrelator] ####727####55us: [vob.net.pg.uplink.transition.down] Uplink: vmnic# is down. Affected portgroup: #####. 0 uplinks up. Failed criteria: 128 
2025-##-##T13:36:03.9162: [netCorrelator] ####727####62us: [vob.net.vmnic.linkstate.down] vmnic vmnic# linkstate down 
2025-##-##T13:36:05.0022: [netCorrelator] ####697####66us: [esx.problem.net.connectivity.lost] Lost network connectivity on virtual switch "#####". Physical NIC vmnic# is down. Affected port groups: "#####" 
2025-##-##T13:36:06.295Z: [netCorrelator] ####730####82us: [vob.net.vmnic.linkstate.up] vmnic vmnic# linkstate up 
2025-##-##T13:36:06.3972: [netCorrelator] ####730####89us: [vob.net.pg.uplink.transition.up] Uplink:vmnic# is up. Affected portgroup: ####. 1 uplinks up 
2025-##-##T13:36:08.0022: [netCorrelator] ####700####66us: [esx.clear.net.connectivity.restored] Network connectivity restored on virtual switch "####", portgroups: "####". Physical NIC vmnic# is up

• vmnic statistics (esxcli network nic stats get -n vmnicX) show no drops or errors.

Environment

VMware ESXi 8.x

Resolution

1. Verify the physical connections for the affected vmnic:
   
   
   • Reseat both ends of the cable.
     
     
   • Confirm proper lock-in of SFP/SFP+ modules.
     
     
2. Monitor vmnic link state after reseating the cable:
   
   
   • If the flapping stops, the cause was physical-layer instability.
     
     
   • If the issue persists, refer to the article “Network adapter (vmnic) is down or fails with a Failed Criteria Code” for additional symptoms and guidance related to Failed criteria 128.

Additional Information

Network Connectivity Lost Due to Physical Link Down