OK, thank you for clarifying that for me.
Now, with that in mind, why will the QNAP try to connect to the domain controller as: nsdc-dc.nsdc-dc.ad.mydomain.local?
Also, as I wrote in the beginning, in QNAP I have the error message:
[Security mode] Failed to join domain. Cannot resolve domain. Check DNS server, AD servewr name and Domain.
Cannot resolve Domain
What name should I put in the DNS?
The QNAP is configured to use the NS DNS:
the IP of 192.168.10.1 is the internet connection gateway