Duplicate vSAN IP address causes vSAN hosts to become network partitioned

Products

VMware vSAN

Issue/Introduction

This article provides guidance on identifying and resolving vSAN network partitioning caused by duplicate IP addresses. This issue may be observed in VCF Management Domains where VMs may appear in an inconsistent power state across different ESXi hosts.

vSAN host frequently becomes network partitioned, then after some time the host joins back without any intervention.
Skyline Health reports "vSAN cluster partition" or "vSAN health degraded".
Running esxcli vsan debug object health summary may show that some vSAN objects are inaccessible.
Some VMs may become Invalid or Inaccessible.

ESXi vsansystem.log, located: /var/run/log/vsansystem.logs will report the change in membership count:

YYYY-MM-DDTHH:MM:SS.###Z cpux: 2098825)CMMDS: CMMDSUtil_PrintArenaEntry:100: ########-####-####-####-######### : [60579888]:Adding a new Membership entry (########-####-####-####-##########) with 5 members:
YYYY-MM-DDTHH:MM:SS.###Z cpux: 2098825)CMMDS: CMMDSUtil_PrintArenaEntry:100: ########-####-####-####-######### : [60644183]:Adding a new Membership entry (########-####-####-####-##########) with 1 members:
YYYY-MM-DDTHH:MM:SS.###Z cpux: 2098825)CMMDS: CMMDSUtil_PrintArenaEntry:100: ########-####-####-####-######### : [60697647]:Adding a new Membership entry (########-####-####-####-##########) with 5 members:

ESXi vmkernel.log, located: /var/run/log/vmkernel.log reports ARP conflicts:

Tcpip_Vmk: 124: arp: ##:##:##:##:##:## is using my IP address ###.###.##.## on vmkX!

ESXi vobd.log, located: /var/run/log/vobd.log will detect duplicate IPs:

2026-07-02T05:11:18.0032 In (14) vobd[#######] : [netCorrelator] 7977550671us: [esx. problem.net . vmknic. ip.duplicate] Duplicate IP address detected for ####::##:###:###:### on interface vmkl, current owner being <unknown>
2026-07-02T05:11:18.376Z In (14) vobd [#######] : [vSANCorrelator] 7977953713us: [vob. vsan.net. noip] vmknic vmkl was designated for use by vSAN but has not received an IP address yet.
2026-07-02T05:11:18.376Z In (14) vobd[#######] : [vSANCorrelator] 7977923843us: [esx.problem. vsan.net. not. ready] vmknic vmkl that is currently configured to be used with vSAN doesn't have an IP address yet. There are no other active network configuration and therefore the vSAN node does't have network connectivity.

Environment

VMware vSAN 7.x
VMware vSAN 8.x
VMware Cloud Foundation (VCF) 4.x / 5.x

Cause

This issue occurs when another device on the physical or logical network is configured with the same IP address as a VMkernel adapter (vmknic) tagged for vSAN traffic. This addressing conflict disrupts unicast communication, leading to host isolation and cluster partitioning.

Resolution

Identify the VMkernel adapter used for vSAN traffic:
```
esxcli vsan network list
```
Review the ESXi host logs (/var/run/log/vobd.log or vmkernel.log) to find the MAC address of the conflicting device reported in the duplicate IP error.
Engage the network administration team to trace the conflicting MAC address on the physical switch fabric.
Change the IP address of the conflicting device or the vSAN VMkernel interface to resolve the overlap.
Verify the hosts with duplicate IP issues in vSAN Skyline Health displays a green status.
Run this command on the ESXi hosts to ensure that all nodes are residing in a single cluster partition:
```
 esxcli vsan cluster get
```

Additional Information

Troubleshoot duplicate IP without shutting down known device