The answer to your question is not related to DNS.
When you create an Active Directory domain, amongst other things, you need to specify the domain name and the domain NetBIOS name. The domain name is the FQDN of your domain (
acme.local). The domain NetBIOS name is by default (and usually never changed) the first part of your FQDN (
acme) and also referred to as the pre-2000 domain name or legacy domain name.
When you log on to a machine with a domain user account, you can either
- user the User Principal Name (UPN): email@example.com,
- the down-level logon name: ACME\user
- just the user name (SAM Account Name): user
Regardless of what method you chose for authentication, the computer is always sending the username to the domain controller of the currently joined domain (which is resolved by DNS). From comments: If you pull down the drop down for the local computer you do not authenticate against the domain.
The down-level logon name is derived from the NetBIOS name. If you chose
acme, the downlevel logon name is
ACME (which in reality is case-insensitive).
If you omit the down-level logon name, Windows always authenticated towards a domain controller of the currently joined domain.
(For the record: You can add multiple UPN suffixes per domain.)
You can use
nbtstat -n to find the NetBIOS domain name of the currently joined domain.
I found some sources: