Intermittent RDP and Ping Drops Due to Cloned Virtual Machine MAC Address Conflict

Products

• VMware vSphere ESXi
• VMware vCenter Server

Issue/Introduction

• A virtual machine experiences intermittent Remote Desktop Protocol (RDP) disconnects and ICMP ping drops.
  
  
• The issue persists regardless of the ESXi host where the virtual machine resides and follows the virtual machine during migrations.
  
  
• Other virtual machines on the same subnet do not experience this issue.
  
  
• Packet captures confirm that packets are not taking the incorrect route during transmission and reception across ESXi host uplinks.
  
  
• Packet capture at the active uplink confirms that for every ICMP request received, the reply is sent back to the physical network.

Environment

VMware vSphere ESXi

VMware vCenter Server

Cause

The intermittent network drops are caused by a duplicate MAC address conflict on the physical network fabric. A virtual machine was cloned from the existing virtual machine and inherited the exact same manual MAC address . This duplicate assignment causes MAC flapping on the upstream physical switches, resulting in packets being routed to the incorrect destination physical switch port.

Resolution

 

• Identify the cloned virtual machine that shares the duplicate MAC address.

  •  Here are the PowerCLI instructions for listing all MAC addresses in a cluster. .

# 1. Connect to vCenter Server
Connect-VIServer -Server "your-vcenter-server" -User "username" -Password "password"

# 2. Define the Cluster
$clusterName = "YourClusterName"

# 3. Retrieve VM Name, Network Adapter, and MAC Address
Get-Cluster -Name $clusterName | Get-VM | Get-NetworkAdapter | Select-Object @{N="VMName";E={$_.Parent.Name}}, Name, MacAddress | Sort-Object VMName

# 4. Disconnect from vCenter
Disconnect-VIServer -Server * -Confirm:$false

• Disconnect the virtual network interface card (vNIC) of the cloned virtual machine from the network to immediately stabilize the physical switch MAC tables.

• Edit the hardware settings of the cloned virtual machine (VM must be in powered off state).

• Change the vNIC MAC address assignment from "Manual" to "Automatic" to allow vCenter Server to generate a unique MAC address from its pool, or assign a valid, unique manual MAC address.

• Reconnect the vNIC to the network.

• Verify that RDP and ICMP connectivity to the production virtual machine is stable and packet drops have ceased.

 

Additional Information

Intermittent connectivity between VMs on different ESXi hosts due to duplicate MAC addresses

Virtual machine MAC address conflicts

Packet capture on ESXi using the pktcap-uw tool