Apex domains cannot have CNAME records.
Question and response
Question
dig inxserver.de. NS
Answer
inxserver.de. 5 NS ns2.bringe.net.
inxserver.de. 5 NS ns1.bringe.net.
Authority
The response has no authority records.
Additional
ns1.bringe.net. 5 A 93.191.165.4
ns2.bringe.net. 5 A 213.144.3.30
ns1.bringe.net. 5 AAAA 2a06:5d00:0:1005:0:0:0:53
ns2.bringe.net. 5 AAAA 2a02:788:10c:200:0:0:0:42
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0