Apex domains cannot have CNAME records.
Question and response
Question
dig bmsdns.de. NS
Answer
bmsdns.de. 5 NS ns2.virtualhosts.de.
bmsdns.de. 5 NS ns3.virtualhosts.eu.
bmsdns.de. 5 NS ns1.virtualhosts.de.
Authority
The response has no authority records.
Additional
ns1.virtualhosts.de. 5 A 195.128.160.129
ns2.virtualhosts.de. 5 A 195.68.246.129
ns3.virtualhosts.eu. 5 A 80.83.124.49
ns1.virtualhosts.de. 5 AAAA 2a02:e00:fff0:ba:0:0:0:1
ns2.virtualhosts.de. 5 AAAA 2a02:e00:ffed:90:0:0:0:1
ns3.virtualhosts.eu. 5 AAAA 2a02:e00:ffec:d8:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0