Intermittent vCenter connectivity loss due to duplicate IP address in the environment

Products

• VMware vSphere ESXi
• VMware vCenter Server

Issue/Introduction

• You may experience intermittent connectivity loss to the vCenter Server Appliance (VCSA) while other virtual machines residing on the same ESXi host continue to function normally.
• Pings between virtual machines on the same host work consistently.
• However external connectivity to the vCenter becomes unstable.

Environment

VMware vSphere ESXi

VMware vCenter Server

Cause

The issue is caused by an IP address conflict. Another device or virtual machine on the network is configured with the same IP address as the vCenter Server. This creates a duplicate entry for the MAC address in the ARP table, causing network traffic to be misrouted intermittently.

 

 

Resolution

• Verify the Uplink: Log in to the ESXi host via SSH and run esxtop. Press n to view networking and verify that the vCenter VM and a known working VM are using the same physical uplink.
• Check ARP Entries:
  1.       From a working VM on the same network, run arp -a to view the ARP table.
  2.       From the ESXi host where vCenter resides, run the following command to check the neighbor list: esxcli network ip neighbor list

 

• Identify the Conflict: Look for duplicate MAC address entries or unexpected MAC addresses associated with the vCenter IP address.
• Locate the Conflicting VM: Search your inventory for other virtual machines that may be statically configured with the vCenter's IP address.
• Reconfigure: Change the IP address of the conflicting VM (e.g., App-Server) to a unique, available IP address.
• Validate: Perform a continuous ping to the vCenter Server to ensure connectivity is stable and the ARP entries have updated correctly.