Apex domains cannot have CNAME records.
Question and response
Question
dig a7b3b2.bne.nbn.aussiebb.net. NS
Answer
a7b3b2.bne.nbn.aussiebb.net. 3 NS ns2.wide.net.au.
a7b3b2.bne.nbn.aussiebb.net. 3 NS ns1.wide.net.au.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0