ESXi hosts show Not Responding in vCenter due to duplicate MAC address on vmk0

Products

• VMware vSphere ESXi

Issue/Introduction

 

• Hosts frequently disconnect and reconnect within the vCenter inventory.

• High packet loss (up to 100%) when attempting to ping the host management IP addresses from the same subnet.

• No specific warnings regarding duplicate IPs are present in the vobd logs.

 

Environment

VMware vSphere ESXi

Cause

The issue is caused by a duplicate MAC address assigned to the vmk0 management interface.

Investigation reveals that the MAC address on the virtual interface vmk0 of one host matches the physical MAC address of both vmnic0 and virtual interface vmk0 of a different host. This conflict typically arises when hardware configurations are updated but the ESXi operating system is not reinstalled, causing the network stack to retain legacy or mismatched MAC information.

Resolution

To resolve this conflict, you can rebuild the affected ESXi host to recreate the networking stack.

1. Verify the MAC mismatch: Log in to the ESXi shell or SSH and run the following commands to compare the physical and virtual MAC addresses:

   esxcfg-vmknic -l
   esxcli network nic list
   

2. Reinstall ESXi: Perform a fresh installation of ESXi on the affected host.

Additional Information

If reinstalling ESXi is not feasible in your environment, refer to vmk0 management network MAC address is not updated after a NIC replacement or a MAC address change for alternative steps to change the vmk0 MAC address of a host.

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