vSAN Network Partition and Host Not Responding After Reboot Due to Physical Network Connectivity Issue.

Products

• VMware vSAN

Issue/Introduction

Symptoms:

• Following a host reboot, the ESXi host appears as Not Responding in vCenter Server.
• vSAN Health reports a Network Partition, causing the cluster to become unhealthy.
• Multiple vSAN objects enter a non-compliant or reduced availability state.
• The affected host is unable to ping other hosts in the vSAN cluster despite the unicast agent table being correctly populated.
• Restarting management agents and recreating the vSAN VMkernel interface (vmk), fails to restore connectivity.

Environment

VMware vSAN 8.x

Cause

• The issue is caused by a malfunctioning physical uplink (vmnic). Although the vmnic status remains "Active" or "Up" in the ESXi stack, it is experiencing a total failure in packet transmission (100% packet loss). This "silent" failure prevents both Management and vSAN traffic from reaching the rest of the cluster, resulting in host isolation and a network partition.
• Multiple link down events appear in logs .

• Diagnostic Logs

  Look for vob.net.vmnic.linkstate.down or LACP transition warnings in /var/run/log/vobd.log: [vob.net.vmnic.linkstate.down] vmnic vmnic0 linkstate down [1].

       /var/run/log/vobd..log :

    2026-01-12T02:30:51.298Z In(14) vobd[2097812]:  [netCorrelator] 354098842283us: [vob.net.vmnic.linkstate.down] vmnic vmnic0 linkstate down
    2026-01-12T02:30:51.527Z In(14) vobd[2097812]:  [netCorrelator] 354099070966us: [vob.net.lacp.uplink.transition.down] LACP warning: Uplink vmnic0 on VDS DvsPortset-0 moved out of the link aggregation group.
    2026-01-12T02:30:51.527Z In(14) vobd[2097812]:  [netCorrelator] 354099024161us: [esx.problem.net.lacp.uplink.transition.down] uplink vmnic0 on VDS DvsPortset-0 is moved out of link aggregation group.
    2026-01-12T02:30:51.527Z In(14) vobd[2097812]:  The event ([esx.problem.net.lacp.uplink.transition.down] uplink vmnic0 on VDS DvsPortset-0 is moved out of link aggregation group.) was sent immediately to hostd;
    2026-01-12T02:30:52.002Z In(14) vobd[2097812]:  [netCorrelator] 354099498857us: [esx.problem.net.vmnic.linkstate.down] Physical NIC vmnic0 linkstate is down
    2026-01-12T02:30:52.002Z In(14) vobd[2097812]:  The event ([esx.problem.net.vmnic.linkstate.down] Physical NIC vmnic0 linkstate is down) was sent immediately to hostd;
    2026-01-12T02:35:37.701Z In(14) vobd[2097812]:  [netCorrelator] 354385245465us: [vob.net.vmnic.linkstate.down] vmnic vmnic1 linkstate down 

• Packet loss may appear while performing the ping connectivity test between hosts .

     ESX:~] vmkping -I vmk2 10.###.###.## -d -s 1472
     --- 10.###.###.## ping statistics ---
     3 packets transmitted, 0 packets received, 100% packet loss
     round-trip min/avg/max = 0.092/0.098/0.102 ms

Resolution

To restore services, you must bypass the faulty physical path to allow traffic to failover:

1. Isolate the faulty uplink: Manually take down the suspect vmnic using the ESXi command line or vSphere Client.
2. Verify recovery: Confirm the host returns to a Responding state in vCenter and vSAN Health returns to Healthy.
3. Hardware Inspection: Contact your network or hardware vendor to inspect:
   • Physical switch port configurations.
   • Cabling and SFP/transceiver integrity.
   • NIC firmware and hardware health.
4. Remediation: Replace faulty hardware or clear port errors before re-enabling the vmnic in ESXi [1].