Apex domains cannot have CNAME records.
Question and response
Question
dig bigair.com.au. NS
Answer
bigair.com.au. 5 NS ns1.bigair.com.au.
bigair.com.au. 5 NS ns2.bigair.com.au.
bigair.com.au. 5 NS ns2.bigair.net.au.
Authority
The response has no authority records.
Additional
ns1.bigair.com.au. 5 A 125.253.59.210
ns2.bigair.com.au. 5 A 125.253.59.220
ns2.bigair.net.au. 5 A 125.253.59.220
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0