Duplicate IP address on ESXi vmknic interface (VMware vSphere ESXi)
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Duplicate IP address on ESXi vmknic interface (VMware vSphere ESXi)

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Article ID: 317922

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Updated On:

Products

VMware vCenter Server VMware vSphere ESXi

Issue/Introduction

Introduction

Network connectivity failures, including vMotion errors and iSCSI instability, occur when a duplicate IP address is assigned to an ESXi vmkernel (vmknic) interface. This conflict prevents the host from maintaining consistent communication with the vCenter Server and external storage. 

Symptoms

  • ESXi host appears as Not Responding in vCenter Server.
  • vSphere Client reports an alarm: Host IP Address Conflict Detected.
  • vMotion operations fail with generic network connectivity errors.
  • Network connectivity tests (using vmkping) to the vMotion or Management interface show random packet loss.
  • iSCSI storage paths experience frequent instability or path thrashing.
  • NFS datastores disconnect or fail to mount after a host reboot.
  • NSX-T or VCF environments report Geneve tunnels as Down or Unknown.

 

Example

If ####.####.####.####  is the IP address used by the remote interface with mac address   ##:##:##:##:##:##, the following event will be seen when the same IP address is being assigned to the local vmknic interface vmk#. A duplicate IP address was detected for ####.####.####.####  on interface vmk#, the current owner being    ##:##:##:##:##:##

 

/var/log/vobd.log:

[YYYY-MM-DDTHH:MM:SS]: [netCorrelator] #############us: [esx.problem.net.vmknic.ip.duplicate] Duplicate IP address detected for ####.####.####.#### on interface vmk#, current owner being ##:##:##:##:##:##
[YYYY-MM-DDTHH:MM:SS]: InetCorrelator1 #############us: [vob.net.vmknic.ip.duplicate] A duplicate IP address was detected for ####.####.####.#### on interface vmk#. The current owner is ##:##:##:##:##:##

 

Impact

Network connectivity failures, including vMotion errors and iSCSI instability, occur when a duplicate IP address is assigned to an ESXi vmkernel (vmknic) interface. This conflict prevents the host from maintaining consistent communication with the vCenter Server and external storage.  

  • Any services that rely on the misconfigured interface might be affected by IP network connectivity issues. For example, if the interface on which the duplicate IP address is detected is on the vMotion NIC, then vMotion might fail.
  • If the interface on which the duplicate IP address is detected is on the VSAN NIC, then the VMs might have connectivity issues and restart as a result.
  • If vmk#'s IP is in conflict, user can lose access to the ESXi host for management tasks. This can lead to disconnection from vCenter and inability to perform essential management tasks like restarting services, configuring settings, or applying patches.
  • The presence of a duplicate IP address causes immediate iSCSI session termination, resulting in the inaccessibility of storage volumes and potential VM outages.
  • If the vmk10 and vmk11 are in conflict, the Geneve tunnels will go down, resulting in overlay traffic failure.

 

Environment

  • Product: VMware vSphere ESXi 7.x, 8.x
  • Components: VMware vCenter Server, VMware Cloud Foundation (VCF), NSX-T/NSX
  • Networking: Static IP configurations, DHCP-managed subnets

Cause

This connectivity failure is caused by a duplicate IP address in the network environment. Common causes include:

  • Another ESXi host or physical device using the identical IP address.
  • A DHCP server assigning a previously used static IP to a new device.
  • Manual misconfiguration of a vmkernel port during deployment.

 

 

Resolution

Step 1: Identify the Duplicate IP and MAC Address

Review the host logs to identify the IP in conflict and the MAC address of the device claiming it.

  1. Log in to the ESXi shell or SSH as root.
  2. Search /var/log/vobd.log for duplicate IP events:
    [YYYY-MM-DDTHH:MM:SS]: [netCorrelator] ####us: [esx.problem.net.vmknic.ip.duplicate] Duplicate IP address detected for ####.####.####.#### on interface vmk#, current owner being ##:##:##:##:##:##
  3. Search /var/log/vmkernel.log for ARP warnings:
    YYYY-MM-DDTHH:MM:SS.###Z cpu##:####)Tcpip_Vmk: ####: arp: ##:##:##:##:##:## is using my IP address ####.####.####.#### on vmk#!

Step 2: Locate the Conflicting Device

  1. Check the physical switch MAC address table to locate the port where MAC ##:##:##:##:##:## is learned.
  2. If the MAC belongs to a VMware OUI (starts with 00:50:56), check other ESXi hosts or vCenter for a VM or vmknic with that MAC.
  3. Perform an nslookup on the host FQDN to ensure it does not return multiple IP addresses. Remove any stale records from the DNS server.

Step 3: Correct the Configuration

  1. Reconfigure the conflicting device with a unique IP address.
  2. If the ESXi host must be changed, use the following commands to update the vmknic:
    • To list current interfaces: esxcli network ip interface ipv4 get
    • To set a new static IP: esxcli network ip interface ipv4 set -i vmk# -I ####.####.####.#### -N ####.####.####.#### -t static
  3. Restart the management network via the DCUI if connectivity is not immediately restored.

Note: For additional information on changing management IPs, see Changing the ESXi server management IP address.

 

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