Joining a Windows Domain Controller as an Additional DC in a Domain
Once you have a Samba domain controller set up, you can choose to join additional domain controllers to the domain, whether they be additional Samba domain controllers, or additional Windows domain controllers.
If you wish to join an additional Samba domain controller to a domain, then please see the Joining a domain as a DC page. The instructions on that page are the same for joining Samba to a Windows domain as they are for joining Samba to an existing Samba domain.
If you wish to join a new Windows domain controller to a Samba domain, then you should use the 'dcpromo' tool on the Windows machine. Please see the normal instructions for installing dcpromo on Windows, with the exception that you should not check the 'DNS server' option box when it is offered. Right now you should either use Windows for DNS, or use Samba and bind9 for DNS. Mixing the two can work, but it is an advanced topic that is beyond the scope of this howto.