Apex domains cannot have CNAME records.
Question and response
Question
dig dsinet.de. NS
Answer
dsinet.de. 5 NS ns2.dsinet.de.
dsinet.de. 5 NS ns.dsinet.de.
dsinet.de. 5 NS ns.dsinet.eu.
Authority
The response has no authority records.
Additional
ns.dsinet.de. 5 A 217.18.176.246
ns.dsinet.eu. 5 A 217.18.184.246
ns2.dsinet.de. 5 A 178.249.27.6
ns.dsinet.eu. 5 AAAA 2a00:8180:1001:1:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0