Apex domains cannot have CNAME records.
Question and response
Question
dig ess.uk.barracudanetworks.com. NS
Answer
ess.uk.barracudanetworks.com. 5 NS ns-1302.awsdns-34.org.
ess.uk.barracudanetworks.com. 5 NS ns-145.awsdns-18.com.
ess.uk.barracudanetworks.com. 5 NS ns-877.awsdns-45.net.
ess.uk.barracudanetworks.com. 5 NS ns-1769.awsdns-29.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0