nameservers setup in hosting server control panel and registrar
 

i have an email from my registrar as below:

You must use the same set of nameservers for your domain name. For example, you can use NS1.DOMAINCONTROL.COM and NS2.DOMAINCONTROL.COM, or you could use ISPCONFIG.yourdomain.INFO and create another nameserver of ISPCONFIG2.yourdomain.INFO. Although the nameservers may point to different IP addresses (or servers), you cannot use our nameservers in conjunction with third party nameservers. I apologize for any inconvenience this may cause.

in this case, in the same ispconfig 3 (or 2) hosting server and control panel, is it ok to create both ISPCONFIG.yourdomain.INFO and ISPCONFIG2.yourdomain.INFO as nameservers and set them up in my registrar system, even though they both point to the same IP/server (even though in concept, they should point to different IP/server )?

You can try that - some registrars accept this, and some not. That depends on the registrar.

in ispconfig 3 control panel, how to create a master database user account for all the databases for all the mutisites?

Databases are not connected to the dns records in ispconfig.

hello till, i mean to create only one set of database username and password across all the databases for all the websites, for the users' convenience. i don't understand the relationship between your answer and my previous post.

The Topic of this thread is "nameservers setup in hosting server control panel and registrar". So every answer in this thread is related to this topic. I explained you in my answer that databases are not connected to DNS in ispconfig, so creating dns records does not influence the creation of databases and vice versa.

If you have other questions that are not related to a thread topic, then please make a new thread.

If thats a intranet server without connection to the internet, then you can do something like that. On internet servers, thats far too insecure as it would mean that a single hacked website can bring all websites down.

In ISPConfig, every client database has its own user and password for that reason. If you want to create a user that can access more databases, then you can do that in phpmyadmin. But its highly recommended to not do that.