Apex domains cannot have CNAME records.
Question and response
Question
dig brunner.at. NS
Answer
brunner.at. 5 NS ns2.brunner.at.
brunner.at. 5 NS ns1.brunner.at.
Authority
The response has no authority records.
Additional
ns1.brunner.at. 5 A 192.174.68.100
ns2.brunner.at. 5 A 176.97.158.100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0