Apex domains cannot have CNAME records.
Question and response
Question
dig link-m.de. NS
Answer
link-m.de. 3 NS ns.link-m.de.
link-m.de. 3 NS ns.ipn.de.
link-m.de. 3 NS ns2.link-m.de.
Authority
The response has no authority records.
Additional
ns.ipn.de. 4 A 193.96.188.100
ns.link-m.de. 3 A 82.135.8.2
ns2.link-m.de. 3 A 194.39.121.2
ns.link-m.de. 3 AAAA 2001:a60:901e:0:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0