Apex domains cannot have CNAME records.
Question and response
Question
dig int-dyn.de. NS
Answer
int-dyn.de. 5 NS ns.inttech.de.
int-dyn.de. 5 NS ns2.inttech.de.
Authority
The response has no authority records.
Additional
ns.inttech.de. 5 A 188.65.145.250
ns2.inttech.de. 5 A 185.183.158.44
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0