Apex domains cannot have CNAME records.
Question and response
Question
dig bigpond.net.au. NS
Answer
bigpond.net.au. 2 NS adns03.bigpond.com.
bigpond.net.au. 2 NS adns04.bigpond.com.
bigpond.net.au. 2 NS adns01.bigpond.com.
bigpond.net.au. 2 NS adns02.bigpond.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0