Apex domains cannot have CNAME records.
Question and response
Question
dig VOCUS.net.au. NS
Answer
VOCUS.net.au. 5 NS ns02.VOCUS.net.au.
VOCUS.net.au. 5 NS ns01.VOCUS.net.au.
VOCUS.net.au. 5 NS ns03.VOCUS.net.au.
Authority
The response has no authority records.
Additional
ns01.vocus.net.au. 5 A 208.79.89.218
ns02.vocus.net.au. 5 A 208.79.89.218
ns03.vocus.net.au. 5 A 175.45.91.235
ns02.vocus.net.au. 5 AAAA 2607:f2f8:2000:0:0:0:0:2
ns03.vocus.net.au. 5 AAAA 2402:7800:fe01:1:0:0:0:235
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0