I wasn't talking about an office environment. I'm talking server-to-server communication. Like all the internal infrastructure to support a web application. Maybe I should have been more explicit about that.

How a new device bootstraps on the network without DNS? Depends, on the device, but a physical server doesn't need DNS, only PXE boot / TFTP / HTTP as usual and maybe a proxy to access an update server if you don't run one yourself.