Users may experience a loss of network connectivity to a Virtual Machine (VM) immediately following a vMotion migration to a different host.

Products

• VMware vSphere ESX 8.x

Issue/Introduction

• Continuous ping to the VM IP address fails as soon as the migration completes.
• Connectivity is eventually restored after manually disconnecting and reconnecting the VM’s virtual network adapter multiple times.
• Captures on the host uplink confirm that the Reverse ARP (RARP) packet is successfully sent out by the host after migration. Additionally, the VM switchport shows the VM sending multiple ARP packets to resolve its default gateway IP address.
  
  
• The "Notify Switch" option is correctly enabled on the Distributed Switch (vDS).

Environment

VMware vSphere ESXi

Cause

When a VM moves to a new host, the physical switch port connected to the destination host must learn the VM's MAC address to update its forwarding table (MAC table). This is typically triggered by a Reverse ARP (RARP) packet sent by the ESXi host on behalf of the VM.

The connectivity failure occurs when:

1. The RARP packet or subsequent ARP requests from the VM are disregarded or dropped by the physical network infrastructure.

2. There is a delayed MAC table update on the physical switches.

Resolution

Since packet captures confirm that the ESXi host is correctly egressing the RARP and ARP packets, the issue resides within the physical network fabric.

This needs to be further investigated by the physical networking team to check on delayed MAC learning.

Refer to KB to know more about IP to MAC mapping, GARP, RARP and Notify Switch setting for Virtual Machine Connectivity

 

Additional Information

For related information, check below KBs:

Troubleshooting when a virtual machine loses network connection after vMotion

VMs intermittently lose network connections after vMotion