Apex domains cannot have CNAME records.
Question and response
Question
dig minuskel.de. NS
Answer
minuskel.de. 5 NS ns3.routing.net.
minuskel.de. 5 NS nsh.ipn.de.
minuskel.de. 5 NS ns1.routing.net.
minuskel.de. 5 NS ns2.routing.net.
Authority
The response has no authority records.
Additional
ns1.routing.net. 5 A 134.0.30.178
ns2.routing.net. 5 A 194.50.113.2
ns3.routing.net. 5 A 194.126.196.2
nsh.ipn.de. 5 A 157.90.122.239
ns1.routing.net. 5 AAAA 2a03:2900:3:1:0:0:0:2
ns2.routing.net. 5 AAAA 2001:4d8f:2:0:0:0:0:2
ns3.routing.net. 5 AAAA 2a03:2902:3:1:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0