Apex domains cannot have CNAME records.
Question and response
Question
dig cronon.de. NS
Answer
cronon.de. 5 NS dns-b2.cronon.de.
cronon.de. 5 NS dns-b1.cronon.de.
cronon.de. 5 NS dns-hh1.cronon.de.
Authority
The response has no authority records.
Additional
dns-b1.cronon.de. 5 A 192.166.192.224
dns-b2.cronon.de. 5 A 192.166.196.224
dns-hh1.cronon.de. 5 A 81.169.191.16
dns-b1.cronon.de. 5 AAAA 2a01:238:e100:f003:0:0:0:110
dns-b2.cronon.de. 5 AAAA 2a01:238:e100:f303:0:0:0:120
dns-hh1.cronon.de. 5 AAAA 2a01:238:cca:101:0:0:0:16
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0