Apex domains cannot have CNAME records.
Question and response
Question
dig ddnss.de. NS
Answer
ddnss.de. 5 NS ns2.ddnss.de.
ddnss.de. 5 NS ns3.ddnss.de.
ddnss.de. 5 NS ns1.ddnss.de.
Authority
The response has no authority records.
Additional
ns1.ddnss.de. 5 A 85.114.136.161
ns3.ddnss.de. 5 A 78.31.65.41
ns1.ddnss.de. 5 AAAA 2001:4ba0:ffe6:1f:0:0:0:1
ns3.ddnss.de. 5 AAAA 2001:4ba0:cafe:15a2:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0