Duplicate IP Address Conflict Detected on ESXi vmknic Interface

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

Network connectivity failures may occur depending on which vmk interface (and enabled services on that vmk) has a duplicate IP address. A duplicate IP address on the management vmk will impact ESX host connectivity. VMware vSphere ESXi host may show as Not Responding or Disconnected in vCenter. The vSphere Client may report the following error: "Host IP Address Conflict Detected". If the management vmk interface IP address is in conflict, access to the ESXi host for management tasks is lost. Connectivity tests may fail such as pinging the gateway from the impacted ESX host or being unable to ping the management interface of the impacted ESX host from external devices/VMs.

A duplicate IP address on other vmks may impact respective services (vMotion, vSAN, NSX, etc.). Errors with vMotion and iSCSI instability may 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. NSX TEP tunnels with the host may be down with IP address conflicts on NSX vmk interfaces (usually vmk10, vmk11, etc).

 

Log entries in /var/run/log/vobd.log indicate duplicate IP assignments:

/var/run/log/vobd.log:
YYYY-MM-DDTHH:MM:SS.SSSIn(14) vobd[2098164]:  [netCorrelator] ###########us: [vob.net.vmknic.ip.duplicate] A duplicate IP address was detected for ###.##.###.## on interface vmk0. The current owner is ##:##:##:##:##:##.
YYYY-MM-DDTHH:MM:SS.SSSIn(14) vobd[2098164]:  [netCorrelator] ###########us: [esx.problem.net.vmknic.ip.duplicate] Duplicate IP address detected for ###.##.###.## on interface vmk0, current owner being  ##:##:##:##:##:##.
YYYY-MM-DDTHH:MM:SS.SSSIn(14) vobd[2098164]:  The event ([esx.problem.net.vmknic.ip.duplicate] Duplicate IP address detected for ###.##.###.## on interface vmk0, current owner being ##:##:##:##:##:##.)

 

Environment

VMware vSphere ESXi 7.x, 8.x, 9.x

VMware Cloud Foundation 5.x

Cause

A duplicate IP address has been assigned to the ESXi vmkernel interface by another physical device, a manual deployment misconfiguration, or a DHCP server allocating a previously used static IP.

Resolution

1. Log in to the ESXi shell or SSH as root to identify the conflicting IP and MAC address.

2. Search /var/log/vobd.log for duplicate IP events:

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

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#!

      

4. Check the physical switch MAC address table to locate the port where the conflicting MAC address <##:##:##:##:##:##> is learned. If the MAC belongs to a VMware OUI (starts with 00:50:56), check other ESXi hosts or vCenter for a virtual machine or vmknic with that MAC.

5. Perform an nslookup on the host FQDN to ensure it does not return multiple IP addresses. Remove any stale records from the DNS server.

6. Reconfigure the conflicting device with a unique IP address.

7. If the ESXi host must be changed instead, list the current interfaces using the command:

   • esxcli network ip interface ipv4 get

8. Set a new static IP for the ESXi host using the command:

   • esxcli network ip interface ipv4 set -i vmk# -I ####.####.####.#### -N ####.####.####.#### -t static

      

9. 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.