Apex domains cannot have CNAME records.
Question and response
Question
dig muerznet.at. NS
Answer
muerznet.at. 5 NS dns2.muerznet.at.
muerznet.at. 5 NS dns1.muerznet.at.
Authority
The response has no authority records.
Additional
dns1.muerznet.at. 5 A 81.21.112.130
dns2.muerznet.at. 5 A 81.21.113.130
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0