Apex domains cannot have CNAME records.
Question and response
Question
dig brasildigital.net.br. NS
Answer
brasildigital.net.br. 2 NS ns1.brasildigital.net.br.
brasildigital.net.br. 2 NS ns3.brasildigital.net.br.
brasildigital.net.br. 2 NS ns2.brasildigital.net.br.
Authority
The response has no authority records.
Additional
ns2.brasildigital.net.br. 2 A 177.221.56.35
ns3.brasildigital.net.br. 2 A 177.221.56.36
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0