Security settings failed to apply [Error in joining domain]

Ixa wrote:
Check this link and hope it helps as reference guide: https://drive.google.com/file/d/0B4PuVEYxkQ5oTFFrb3lWeHcwZm8/view?usp=sharing

Thanks Ixa.

I was inclined to think the problem was the hostname, because - contrary to the picture in the link - there is no way to set the FQDN hostname in 6.2.4.
The "hostname" field can only be changed from the System ➼ Overview page but it accepts only 15 chars and no "•".
Maybe the setup pages changed since December.
It happens that during the "join" operation, the RN edits the /etc/hosts file to force the FQDN hostname!

The problem, just identified, was the hosts allow directive in the smb.conf file of the AD server which - while allowing all LAN networks (even 127.0.0.0/8) - caused some trouble during the last steps of the "join", for some reasons (maybe the weird Netbios protocol?).
Removing the directive (and setting "bind interfaces only") fixed the problem.

The RN (new) 6.2.4 setup pages look maybe simpler - but for IT pros used to refine settings it's hard to focus on the right area when the necessary setting doesn't seem to be available.
At least the picture you provided helped to figure out what could be missing, and check from a ssh.