Apex domains cannot have CNAME records.
Question and response
Question
dig ista-na.com. NS
Answer
ista-na.com. 5 NS ns-641.awsdns-16.net.
ista-na.com. 5 NS ns-1760.awsdns-28.co.uk.
ista-na.com. 5 NS ns-310.awsdns-38.com.
ista-na.com. 5 NS ns-1396.awsdns-46.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0