Apex domains cannot have CNAME records.
Question and response
Question
dig oz.au. NS
Answer
OZ.AU. 3 NS rip.psg.COM.
OZ.AU. 3 NS ns.sw.OZ.AU.
OZ.AU. 3 NS munnari.OZ.AU.
Authority
The response has no authority records.
Additional
ns.sw.oz.au. 3 A 203.31.96.3
rip.psg.com. 3 A 147.28.0.39
munnari.oz.au. 3 A 202.29.151.3
rip.psg.com. 3 AAAA 2001:418:1:0:0:0:0:39
munnari.oz.au. 3 AAAA 2001:3c8:9007:1:0:0:0:21
munnari.oz.au. 3 AAAA 2001:3c8:9009:181:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0