In VMware ESX, you can configure a guest operating system to have its network adapter disconnected at power on. This is critically important for a phase of a physical to virtual (P2V) migration where the system is migrated yet there are some offline tasks to be done. This can also be during a build before you go live. This configuration will present the virtual hardware inventory to the guest operating system – but it will appear as if the cable were unplugged. In this situation, you can configure all of your IP addressing (though you could not test it), DNS information, and other environment factors entirely offline of your network. Should you need some files or other access, a CD-ROM image would be a good way to prep up the system. I use the term “Stage Configure” for a virtual machine that is being prepped for prime time, and when I am complete with the configuration the option is reverted back to connect at power on (the default). This would include computer names, network configuration, services management for Windows systems, some benchmarks on performance, as well as any other local configuration elements.
To configure a virtual machine to not have its network connected at power-on, edit the settings of a virtual machine and deselect the option as shown in the figure below:
Once you are done with your staging configuration, power off the virtual machine and change the option back to connecting at power on.
Extra Step in Protection
With VMware ESX, it is simply too easy to accidentally cause conflicts that may arise from having a candidate virtual machine on the network too early and performing its intended tasks. Errors can be a duplicate IP address, the application on the virtual machine picking up data simultaneously as the live system, formatting issues from a newer version of a business system feeding results to another system, and many other situations.