Apex domains cannot have CNAME records.
Question and response
Question
dig hostingnetwork.at. NS
Answer
hostingnetwork.at. 5 NS ns3.internex.at.
hostingnetwork.at. 5 NS ns4.internex.at.
hostingnetwork.at. 5 NS ns1.internex.at.
hostingnetwork.at. 5 NS ns2.internex.at.
Authority
The response has no authority records.
Additional
ns1.internex.at. 5 A 217.160.80.161
ns2.internex.at. 5 A 217.160.81.161
ns3.internex.at. 5 A 185.132.35.161
ns4.internex.at. 5 A 185.132.34.161
ns1.internex.at. 5 AAAA 2001:8d8:fe:53:217:160:80:161
ns2.internex.at. 5 AAAA 2001:8d8:fe:53:217:160:81:161
ns3.internex.at. 5 AAAA 2607:f1c0:fe:53:185:132:35:161
ns4.internex.at. 5 AAAA 2607:f1c0:fe:53:185:132:34:161
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0