Apex domains cannot have CNAME records.
Question and response
Question
dig ess.barracudanetworks.com. NS
Answer
ess.barracudanetworks.com. 5 NS ns-599.awsdns-10.net.
ess.barracudanetworks.com. 5 NS ns-1883.awsdns-43.co.uk.
ess.barracudanetworks.com. 5 NS ns-457.awsdns-57.com.
ess.barracudanetworks.com. 5 NS ns-1380.awsdns-44.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0