Apex domains cannot have CNAME records.
Question and response
Question
dig static.exetel.com.au. NS
Answer
static.exetel.com.au. 4 NS ns1.exetel.com.au.
static.exetel.com.au. 4 NS ns3.exetel.com.au.
static.exetel.com.au. 4 NS ns2.exetel.com.au.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0