Apex domains cannot have CNAME records.
Question and response
Question
dig hostonserver.de. NS
Answer
hostonserver.de. 5 NS delta.host-on.net.
hostonserver.de. 5 NS beta.host-on.net.
hostonserver.de. 5 NS alpha.host-on.net.
hostonserver.de. 5 NS gamma.host-on.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0