When installing (promoting) your Domain Controller, you can get this error:
Verification of prerequisites for Domain Controller promotion failed. The TCP ports required by Active Directory Domain Services are already in use on this computer. You must remove or reconfigure the services that are currently using these ports (88, 389, 636, 3268, 3269).
To find out what ports are already being used that cause the TCP ports required by Active Directory Domain Services are already in use on this computer error, run this command in the command prompt:
netstat