Apex domains cannot have CNAME records.
Question and response
Question
dig apa.at. NS
Answer
apa.at. 4 NS ns4.apa.net.
apa.at. 4 NS ns3.apa.at.
Authority
The response has no authority records.
Additional
ns3.apa.at. 4 A 192.174.68.100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0