Apex domains cannot have CNAME records.
Question and response
Question
dig odn.de. NS
Answer
odn.de. 5 NS dns2.odn.de.
odn.de. 5 NS dns3.odn.de.
odn.de. 5 NS dns1.odn.de.
Authority
The response has no authority records.
Additional
dns1.odn.de. 5 A 212.34.160.53
dns2.odn.de. 5 A 212.34.164.234
dns3.odn.de. 5 A 212.34.166.20
dns1.odn.de. 5 AAAA 2a01:120:0:101:0:0:0:d1
dns2.odn.de. 5 AAAA 2a01:120:0:102:0:0:0:d2
dns3.odn.de. 5 AAAA 2a01:120:0:103:0:0:0:d3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0