Duplicate IP address detected

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

• You have issues completing a vMotion process successfuly from and to a specific host.
• Whilst doing a vmkping to the vmknic configured for vMotion, you find that it loses ping randomly before or during initiation of a vMotion process from the host.
• A duplicate IP address is detected for a vmknic interface configuration. This can impact IPv4 and IPv6.

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 vmk2.

A duplicate IP address was detected for ###.###.##.## on interface vmk2, the current owner being  ##:##:##:##:##:##

vobd.log:

[YYYY-MM-DDTHH:MM:SS]: [netCorrelator] #############us: [esx.problem.net.vmknic.ip.duplicate] Duplicate IP address detected for ###.###.##.## on interface vmk0, current owner being ##:##:##:##:##:##
[YYYY-MM-DDTHH:MM:SS]: InetCorrelator1 #############us: [vob.net.vmknic.ip.duplicate] A duplicate IP address was detected for ###.###.##.## on interface vmk0. The current owner is ##:##:##:##:##:##

Impact

• 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 vmk0'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.

Environment

VMware vSphere 7.x
VMware vSphere 8.x
VMware vSphere ESXi 7.x
VMware vSphere ESXi 8.x

Cause

This IP address conflict can occur due to:

• Another ESXi host or physical device using the same IP address.
• A DHCP server mistakenly assigning the same IP address to multiple devices (if static IP addresses are used incorrectly in a DHCP-managed network).
• Manual IP address misconfiguration or a network management error.

Resolution

• Correctly set the IP address with the esxcfg-vmknic command or set it to DHCP mode.
• Perform a network scan or use network management tools to find which device is associated with the MAC address.
• Use network switches to check the MAC address table and verify if the MAC address is being learned by the switch port where the ESXi host is connected.
• If there is a managed switch, query the MAC address table to see where this MAC address is located and identify any misconfigured ports.