Virtual Machines Sporadically Lose Network Connectivity on a Particular ESXi Host

Products

• VMware vSphere ESXi

Issue/Introduction

• Virtual Machines become unreachable sporadically on specific ESXi hosts after a vMotion.
• Only specific VLANs are affected, while others remain functional.
• Packet captures on the physical NICs (vmnics) of the affected host show zero incoming traffic for the impacted VLANs.

Environment

VMware vSphere ESXi

Cause

This behavior indicates a missing VLAN from the trunk configuration on the upstream physical switch ports connected to the newly provisioned or affected ESXi hosts.

Resolution

Engage the internal network team to add the affected VLANs to the trunk configuration on the relevant physical switch ports.

To identify the relevant ports on the upstream physical switch:

1. In vSphere, select the affected host.
2. Navigate to Configure > Networking > Physical Adapters.
3. Select the active vmnic.
4. Review the CDP or LLDP tab to identify the neighboring switch device and port ID.

Additional Information

For further guidance on VLAN configuration, see VLAN configuration on virtual switches, physical switches, and virtual machines.