Apex domains cannot have CNAME records.
Question and response
Question
dig 79c80b.mel.nbn.aussiebb.net. NS
Answer
79c80b.mel.nbn.aussiebb.net. 5 NS ns1.wide.net.au.
79c80b.mel.nbn.aussiebb.net. 5 NS ns2.wide.net.au.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0