Apex domains cannot have CNAME records.
Question and response
Question
dig entornodns.com. NS
Answer
entornodns.com. 3 NS ns3.entorno.com.
entornodns.com. 3 NS ns2.entorno.com.
entornodns.com. 3 NS ns1.entorno.com.
entornodns.com. 3 NS ns4.entorno.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0