Duplicate IP address detected

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

 

• vMotion operations fail to complete successfully when migrating virtual machines to or from a specific ESXi host.
• Network connectivity tests (using vmkping) to the vMotion interface show random packet loss either before or during the migration attempts.
• The system detects a duplicate IP address on the vmknic interface, which may affect both IPv4 and IPv6 configurations.
• iSCSI storage paths experience frequent instability, intermittent disconnects, or path thrashing.

 

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

• 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.

Environment

VMware vSphere ESXi

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

This connectivity failure is caused by a duplicate IP address in the environment. To resolve this, review the following suggestions to identify the conflicting device and correct its network configuration: 

1. 1. Correctly set the IP address with the esxcfg-vmknic command or set it to DHCP mode.
   2. Perform a network scan or use network management tools to find which device is associated with the MAC address.
   3. 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.
   4. If there is a managed switch, query the MAC address table to see where this MAC address is located and identify any misconfigured ports.