Apex domains cannot have CNAME records.
Question and response
Question
dig sms.edu.do. NS
Answer
sms.edu.do. 5 NS ns1.alante.net.
sms.edu.do. 5 NS ns2.collisioncode.com.
sms.edu.do. 5 NS ns2.alante.net.
sms.edu.do. 5 NS ns1.collisioncode.com.
Authority
The response has no authority records.
Additional
ns1.collisioncode.com. 5 A 209.133.201.10
ns2.collisioncode.com. 5 A 209.133.201.10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0