Apex domains cannot have CNAME records.
Question and response
Question
dig sentris.com. NS
Answer
sentris.com. 4 NS ns100.sentris.com.
sentris.com. 4 NS ns200.sentris.com.
Authority
The response has no authority records.
Additional
ns100.sentris.com. 4 A 63.223.114.3
ns200.sentris.com. 4 A 107.155.198.79
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0