Apex domains cannot have CNAME records.
Question and response
Question
dig cgrx.de. NS
Answer
cgrx.de. 5 NS ns2.asok.de.
cgrx.de. 5 NS ns3.asok.de.
cgrx.de. 5 NS ns1.asok.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0