Apex domains cannot have CNAME records.
Question and response
Question
dig nroute.de. NS
Answer
nroute.de. 5 NS dns02.nroute.de.
nroute.de. 5 NS dns01.nroute.de.
Authority
The response has no authority records.
Additional
dns01.nroute.de. 5 A 185.30.156.233
dns02.nroute.de. 5 A 51.195.45.27
dns01.nroute.de. 5 AAAA 2a04:4b07:21dc:8:100:0:0:1
dns02.nroute.de. 5 AAAA 2001:41d0:701:1100:0:0:0:44f7
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0