vCenter and ESXi Host Sync Issues caused by IP Conflict

Products

• VMware vSphere ESXi

Issue/Introduction

• The old vCenter instance VM, with the same IP address, was powered on, resulting in communication disruptions.

• ESXi hosts or virtual machines become unmanageable via the vSphere Client or appear as “Not Responding” or Disconnected in vCenter.

• Intermittent communication failures occur between the vCenter Server and one or more ESXi hosts.

• During the same period, the VPXD service on the active vCenter crashed, which coincided with the power-on attempt of the vCLS VM. Log entries  /var/log/vMonCoredumper.log confirm this, showing core dumps generated by the vpxd-worker process, indicating a service crash at that time.

Notify vMon about vpxd-worker dumping core. Pid : 6354
Successfully generated core file /var/core/core.vpxd-worker.6354
Notify vMon about vpxd-worker dumping core. Pid : 36989
Successfully generated core file /var/core/core.vpxd-worker.36989

Cause

The issue was triggered by an IP conflict between the active production vCenter Server and an outdated vCenter Server instance that was accidentally powered on. Both instances shared the same IP address, leading to conflicting authentication attempts and communication failures.

Resolution

Step 1: Identify and Remove IP Conflict

• Locate and power off the duplicate vCenter instance using the same IP address as the production system.

• Verify that only one vCenter Server is active with the intended IP.

Step 2: Reconnect ESXi Hosts

1. In the vCenter UI:

   • Right-click each affected ESXi host → Connection → Connect

   • Provide the root credentials to reauthenticate and resync vpxuser.

2. If the above fails:

   • SSH into each affected ESXi host and restart the management agents:

     /etc/init.d/hostd restart /etc/init.d/vpxa restart