Apex domains cannot have CNAME records.
Question and response
Question
dig ispgateway.de. NS
Answer
ispgateway.de. 5 NS ns2.namespace4you.de.
ispgateway.de. 5 NS ns.namespace4you.de.
Authority
The response has no authority records.
Additional
ns.namespace4you.de. 5 A 80.67.16.124
ns2.namespace4you.de. 5 A 193.223.77.3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0