Apex domains cannot have CNAME records.
Question and response
Question
dig iinet.net.au. NS
Answer
iinet.net.au. 3 NS ns1.iinet.net.au.
iinet.net.au. 3 NS ns3.iinet.net.au.
iinet.net.au. 3 NS ns2.iinet.net.au.
Authority
The response has no authority records.
Additional
ns1.iinet.net.au. 3 A 203.14.168.3
ns2.iinet.net.au. 3 A 203.59.24.3
ns3.iinet.net.au. 3 A 203.14.169.3
ns1.iinet.net.au. 3 AAAA 2001:4478:ff00:0:203:14:168:3
ns2.iinet.net.au. 3 AAAA 2001:4478:ff01:0:203:59:24:3
ns3.iinet.net.au. 3 AAAA 2001:4478:ff02:0:203:14:169:3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0