You can enable Windows Firewall on your domain controllers for enhanced security, but you need to do it right, otherwise problems can arise such as not being able to join client machines to your domain. Here's how you need to configure Windows Firewall on a domain controller: Enable the File And Print Sharing exception. Enable program exceptions for lsass.exe and ntfrs.exe.exe which are found under %windir%\system32. Enable port exceptions for ports 53 (TCP and UDP), 88 (TCP and UDP), 123 (UDP), 135 (TCP), 137 (TCP), 389 (UDP), 464 (TCP and UDP) and 636 (TCP).