Apex domains cannot have CNAME records.
Question and response
Question
dig nameservice.at. NS
Answer
nameservice.at. 5 NS ns2.nameservice.at.
nameservice.at. 5 NS ns1.nameservice.at.
Authority
The response has no authority records.
Additional
ns1.nameservice.at. 5 A 46.125.235.217
ns2.nameservice.at. 5 A 84.115.254.100
ns1.nameservice.at. 5 AAAA 2001:4bc8:2000:702:0:0:0:1
ns2.nameservice.at. 5 AAAA 2a02:8383:d:200a:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0