Apex domains cannot have CNAME records.
Question and response
Question
dig zdsys.com. NS
Answer
zdsys.com. 5 NS ns-968.awsdns-57.net.
zdsys.com. 5 NS ns-1588.awsdns-06.co.uk.
zdsys.com. 5 NS ns-429.awsdns-53.com.
zdsys.com. 5 NS ns-1254.awsdns-28.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0