For those who are looking for knowing what protocol each test on DCDIAG command uses, this post shows all ports and protocols.
This is useful when you need to make sure the firewall rules are allowing communication between Domain Controllers when you execute the command dcdiag /e for example, to check all DCs in the enterprise, or dcdiag /a to check all DCs in the same Site.
For any doubts or suggestions, please leave a comment below.