Enroll Android devices without Internet access

Enroll Android devices without Internet access

I am working with devices connected to a network that does not have any access to the Internet. It was my understanding that the MDM on-premise server is able to manage the devices on a network directly, have I just missed some configuration or is Internet access required to enroll devices?
If the answer to the previous question is yes, then assuming I enroll the devices while connected to a different network that does have access to Internet, will the server be able to manage them properly if I disconnect them and connect them back to the isolated network once enrolled?
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