Apex domains cannot have CNAME records.
Question and response
Question
dig sys.silversky.com. NS
Answer
sys.silversky.com. 5 NS ns-224.awsdns-28.com.
sys.silversky.com. 5 NS ns-1447.awsdns-52.org.
sys.silversky.com. 5 NS ns-579.awsdns-08.net.
sys.silversky.com. 5 NS ns-1695.awsdns-19.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0