Apex domains cannot have CNAME records.
Question and response
Question
dig cna.at. NS
Answer
cna.at. 5 NS cna-gdwi-0.cna.at.
cna.at. 5 NS sec1.rcode0.net.
cna.at. 5 NS cna-gdwi-2.cna.at.
cna.at. 5 NS sec2.rcode0.net.
cna.at. 5 NS cna-gdwi-1.cna.at.
Authority
The response has no authority records.
Additional
sec1.rcode0.net. 5 A 192.174.68.100
sec2.rcode0.net. 5 A 176.97.158.100
cna-gdwi-0.cna.at. 5 A 85.158.228.100
cna-gdwi-1.cna.at. 5 A 85.158.228.102
cna-gdwi-2.cna.at. 5 A 95.131.192.101
sec1.rcode0.net. 5 AAAA 2001:67c:1bc:0:0:0:0:100
sec2.rcode0.net. 5 AAAA 2001:67c:10b8:0:0:0:0:100
cna-gdwi-0.cna.at. 5 AAAA 2a00:4400:f:7110:0:0:0:10
cna-gdwi-1.cna.at. 5 AAAA 2a00:4400:f:7110:0:0:0:12
cna-gdwi-2.cna.at. 5 AAAA 2a00:4400:f:7111:0:0:0:11
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0