Apex domains cannot have CNAME records.
Question and response
Question
dig ess.au.barracudanetworks.com. NS
Answer
ess.au.barracudanetworks.com. 5 NS ns-371.awsdns-46.com.
ess.au.barracudanetworks.com. 5 NS ns-1170.awsdns-18.org.
ess.au.barracudanetworks.com. 5 NS ns-982.awsdns-58.net.
ess.au.barracudanetworks.com. 5 NS ns-1970.awsdns-54.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0