Apex domains cannot have CNAME records.
Question and response
Question
dig medianet-world.de. NS
Answer
medianet-world.de. 5 NS a.ns.medianet-world.de.
medianet-world.de. 5 NS b.ns.medianet-world.de.
Authority
The response has no authority records.
Additional
a.ns.medianet-world.de. 5 A 213.157.0.194
b.ns.medianet-world.de. 5 A 212.19.34.52
a.ns.medianet-world.de. 5 AAAA 2a02:b98:0:2001:0:0:0:53
b.ns.medianet-world.de. 5 AAAA 2a02:2e0:3ef:0:0:0:0:52
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0