ESXI host was not reachable to the default Gateway and went into not responding state on the Vcenter

Products

• VMware vSphere ESX 8.x

Issue/Introduction

• An ESXi host becomes unreachable via its Management IP address.

• Pings to the Default Gateway from the ESXi console (DCUI) fail.
  

• The host shows as "Disconnected" or "Not Responding" in vCenter Server.

Environment

VMware vSphere ESXi

Cause

The issue is caused by a VLAN ID mismatch between the Virtual Management Kernel (vmk0) and the physical switch infrastructure.

1. The vmk0 adapter was residing on a Standard Switch (VSS) with no VLAN ID defined (VLAN 0/Untagged).

2. The physical switch ports were configured as Trunk Ports, expecting tagged traffic for Management (VLAN X).

3. Because the Standard Switch was sending untagged frames into a port expecting tagged frames, the physical switch dropped the management traffic, severing the connection.

Resolution

Step 1: Assign VLAN to the Standard Switch.

If the host is managed via a Standard Switch and is currently disconnected:

1. Log in to the Direct Console User Interface (DCUI).

2. Navigate to Configure Management Network > VLAN (optional).

3. Enter the correct Management VLAN ID (e.g., x).

4. Ensure the physical team has configured the correct VLAN on the physical switch uplink connecting to the ESXI host.

5. Verify that all required Workload VLANs are "allowed" on the trunk ports.

6. Apply the changes and connectivity to the Gateway should be restored.

Step 2: Migrate to Distributed Virtual Switch (Best Practice)

Once the host is reachable in vCenter:

1. Navigate to the Networking tab in vSphere Client.

2. Right-click the Distributed Switch and select Add and Manage Hosts.

3. Select the affected host and assign the physical uplinks.

4. Migrate the Management Network (vmk0) from the Standard Switch to the designated DVS Port Group.

5. Ensure the DVS Port Group is explicitly configured with VLAN X.

 

Additional Information

• Incorrect VLAN tagging on a Management Kernel will result in an immediate loss of network access to the host
• Please refer to the kb Configuring Standard vSwitch (vSS) or virtual Distributed Switch (vDS) from the command line in ESXi to configure the VLAN using the CLI.