Cloned vSphere VM automatically connects to network after power-on

Products

• VMware vSphere ESXi

Issue/Introduction

Users in a vSphere 8.0U3g environment report that virtual machines (VMs) created via cloning exhibit unexpected networking behavior during the initial power-on sequence.

1. A VM is cloned from a source template or existing VM.
2. In the "Edit Hardware" section of the cloning wizard, the Connect at Power On option for the Network Interface Card (NIC) is explicitly unckecked.
3. Upon powering on the cloned VM, the NIC initially appears disconnected (both "Connected" and "Connect at Power On" are unchecked).
4. Approximately 30 seconds after the guest OS begins booting, the VM automatically toggles the NIC state to Connected, potentially causing IP conflicts or unauthorized network access.

Environment

VMware vSphere ESXi

VMware vCenter Server

Cause

This behavior often occurs when the guest operating system's networking stack or a Guest Customization task overrides the hardware configuration during the initial boot phase. If the underlying .vmx file or the Customization Specification triggers a re-read of the hardware state, the NIC may be "hot-added" or re-enabled by the VMware Tools service to complete customization tasks.

Resolution

To ensure a cloned VM remains isolated from the network until manually configured, use one of the following validated methods.

Method 1: Hardware Customization (Manual Clone)

1. This is the most straightforward method for one-off cloning operations.
2. Initiate the Clone Virtual Machine wizard.
3. Select the destination VM name, folder, and compute resource.
4. Specify the target storage.
5. On the Customize hardware page, expand the Network Adapter section.
6. Uncheck the "Connect At Power On" option.
7. Complete the wizard. The VM will remain disconnected upon power-on, allowing you to manually verify IP settings before toggling the "Connected" state.

Method 2: VM Customization Specifications (Recommended for Automation)

For a robust, repeatable process that prevents IP conflicts and SID issues in Windows, use a Customization Specification.

1. Navigate to Menu > Policies and Profiles > VM Customization Specifications.
2. Create or Edit a specification.
3. Go to the Network settings tab.
4. Select Manually select network settings.
5. Do not configure IP, Gateway, or DNS settings if you want the interface to remain dormant.
6. Apply this specification during the "Customize Guest OS" phase of the cloning wizard. This ensures that even if VMware Tools initializes the NIC, it will not have a valid configuration to communicate on the network.

Method 3: Direct .vmx Modification (Advanced)

If the GUI settings are being bypassed, you can hard-code the state into the VM configuration file.

1. Clone the VM but do not power it on.
2. Locate the VM folder in the Datastore Browser and download the .vmx file.
3. Open the file in a text editor and locate the ethernet entries.
4. Ensure the following parameter is set to FALSE: ethernet0.startConnected = "FALSE"
5. Upload the file back to the datastore.
6. Right-click the VM in vCenter and select Reload from Disk (or unregister/re-register) to apply changes.

Additional Information

Clone an Existing Virtual Machine