Apex domains cannot have CNAME records.
Question and response
Question
dig cdn77.com. NS
Answer
cdn77.com. 5 NS ns2.cdn77.com.
cdn77.com. 5 NS ns1.cdn77.com.
Authority
The response has no authority records.
Additional
ns1.cdn77.com. 5 A 185.102.216.100
ns2.cdn77.com. 5 A 185.102.216.200
ns1.cdn77.com. 5 AAAA 2a02:6ea0:babe:0:0:0:0:1
ns2.cdn77.com. 5 AAAA 2a02:6ea0:babe:0:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0