Windows CAL licence

Question

Hi, I would like to ask whether I need a Windows CAL (Client Access License) for a server running Windows that is used as a control server, especially if that server is joined to a domain controlled by a domain controller.

Specifically, for the communication between the control server and the domain controller, is a Windows CAL required?

I have already accounted for the licenses for the workstations accessing the domain controller (for example, 15 workstations accessing the domain controller and other Windows servers would require 15 Windows CALs — is that correct?).

Many thanks in advance!