Apex domains cannot have CNAME records.
Question and response
Question
dig nic.at. NS
Answer
nic.at. 5 NS ns5.univie.ac.at.
nic.at. 5 NS ns1.nic.at.
nic.at. 5 NS ns5.nic.at.
nic.at. 5 NS ns2.nic.at.
nic.at. 5 NS ns10.univie.ac.at.
Authority
The response has no authority records.
Additional
ns1.nic.at. 5 A 192.174.68.98
ns2.nic.at. 5 A 176.97.158.98
ns5.nic.at. 5 A 194.58.198.32
ns5.univie.ac.at. 5 A 193.171.255.77
ns10.univie.ac.at. 5 A 192.76.243.2
ns1.nic.at. 5 AAAA 2001:67c:1bc:0:0:0:0:98
ns2.nic.at. 5 AAAA 2001:67c:10b8:0:0:0:0:98
ns5.nic.at. 5 AAAA 2a01:3f1:3032:0:0:0:0:53
ns5.univie.ac.at. 5 AAAA 2001:628:453:4305:0:0:0:53
ns10.univie.ac.at. 5 AAAA 2001:67c:133c:0:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0