A systems administrator needs to apply a custom ESXi image to a host using VMware...

This is because VIA service uses PXE boot to install ESXi on the servers, and it requires onboard NICs to be enabled and connected to an untagged VLAN/Network1.

According to VMware documentation on VMware Imaging Appliance, when preparing a host for imaging using VIA, it is recommended to enable the onboard NICs on the server. This enables the network adapter to participate in the boot sequence of the host to retrieve the image from the Imaging Appliance.

Here is the relevant quote from the documentation:

"To prepare the host, ensure that the onboard NICs are enabled on the server. During boot up, the server firmware detects the network adapter and adds it to the boot sequence list so that it can participate in network boot."

https://docs.vmware.com/en/VMware-Cloud-Foundation/4.5/vcf-deploy/GUID-735928E5-1DD7-44E5-BE32-E598230326AD.html