Apex domains cannot have CNAME records.
Question and response
Question
dig int-tech.de. NS
Answer
int-tech.de. 3 NS ns2.inttech.de.
int-tech.de. 3 NS ns.inttech.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0