Apex domains cannot have CNAME records.
Question and response
Question
dig citynet.at. NS
Answer
citynet.at. 5 NS ns1.cnh.at.
citynet.at. 5 NS ns2.cnh.at.
citynet.at. 5 NS ns3.cnh.at.
Authority
The response has no authority records.
Additional
ns1.cnh.at. 1 A 195.149.216.2
ns2.cnh.at. 1 A 185.164.5.43
ns3.cnh.at. 1 A 80.92.113.13
ns1.cnh.at. 2 AAAA 2a02:28e8:3:2:0:0:0:2
ns3.cnh.at. 2 AAAA 2a02:28e8:4:2:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0