Apex domains cannot have CNAME records.
Question and response
Question
dig mcs.de. NS
Answer
mcs.de. 5 NS ns3.mcs.de.
mcs.de. 5 NS ns2.mcs.de.
mcs.de. 5 NS ns1.mcs.de.
Authority
The response has no authority records.
Additional
ns1.mcs.de. 5 A 147.78.89.212
ns2.mcs.de. 5 A 147.78.89.220
ns3.mcs.de. 5 A 194.13.83.222
ns1.mcs.de. 5 AAAA 2a09:2040:0:16:0:0:0:10
ns2.mcs.de. 5 AAAA 2a09:2040:0:17:0:0:0:10
ns3.mcs.de. 5 AAAA 2a03:4000:43:502:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0