Apex domains cannot have CNAME records.
Question and response
Question
dig domain24.com. NS
Answer
domain24.com. 5 NS dns.dns2.de.
domain24.com. 5 NS dns.dns1.de.
domain24.com. 5 NS dns.dns3.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0