Apex domains cannot have CNAME records.
Question and response
Question
dig renet.net.au. NS
Answer
renet.net.au. 5 NS ns.renet.net.au.
renet.net.au. 5 NS ns.renet.co.nz.
renet.net.au. 5 NS ns.renet.io.
renet.net.au. 5 NS ns.renet.com.au.
Authority
The response has no authority records.
Additional
ns.renet.net.au. 5 A 205.251.195.82
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0