Apex domains cannot have CNAME records.
Question and response
Question
dig vip2.coolcom.com. NS
Answer
vip2.coolcom.com. 2 NS ns7.coolcom.com.
vip2.coolcom.com. 2 NS ns777.coolcom.com.
vip2.coolcom.com. 2 NS ns77.coolcom.com.
Authority
The response has no authority records.
Additional
ns7.coolcom.com. 2 A 72.249.68.145
ns77.coolcom.com. 2 A 209.142.64.139
ns777.coolcom.com. 2 A 165.140.159.117
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0