VMs disconnect from network after vMotion due to IP conflict

Products

• VMware vCenter Server

Issue/Introduction

Following a vMotion migration, VMs report a disconnected network adapter state or loss of connectivity.

Symptoms:

• VM network adapter shows "Disconnected" in vCenter.
• Connectivity is restored only after manually checking the "Connected" box in VM settings.
• Logs in /var/log/vobd.log may show: [vob.net.ip.duplicate] A duplicate IP address was detected.

Environment

VMware ESXi

Cause

A duplicate IP address assignment between two VMs. The conflict is surfaced during vMotion when the destination host broadcasts a Gratuitous ARP to update the physical network fabric.

Resolution

1. Check the guest OS configuration for VM1 and VM2 to identify overlapping static IP assignments.
2. Modify the network configuration within the OS VM to ensure each VM has a unique IP address.
3. Reset vNIC::
   1. Right-click the affected VM > Edit Settings.
   2. Disconnect the Network Adapter by unchecking Connected.
   3. Click OK.
   4. Re-open Edit Settings and check Connected.
4. If connectivity does not return immediately, clear the ARP cache on the upstream physical switch for the affected IP/VLAN.