Apex domains cannot have CNAME records.
Question and response
Question
dig trexler.at. NS
Answer
trexler.at. 5 NS ns2.domaindiscount24.net.
trexler.at. 5 NS ns.trexler.at.
trexler.at. 5 NS ns1.domaindiscount24.net.
Authority
The response has no authority records.
Additional
ns.trexler.at. 5 A 91.98.23.146
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0